Archives of Biochemistry and Biophysics 444 (2005) 139–158
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Cold, salinity and drought stresses: An overview
Shilpi Mahajan, Narendra Tuteja ¤
Plant Molecular Biology, International Centre for Genetic Engineering and Biotechnology, Aruna Asaf Ali Marg, New Delhi 110067, India
Received 31 August 2005, and in revised form 14 October 2005
Available online 9 November 2005
Abstract
World population is increasing at an alarming rate and is expected to reach about six billion by the end of year 2050. On the other
hand food productivity is decreasing due to the eVect of various abiotic stresses; therefore minimizing these losses is a major area of concern for all nations to cope with the increasing food requirements. Cold, salinity and drought are among the major stresses, which
adversely aVect plants growth and productivity; hence it is important to develop stress tolerant crops. In general, low temperature mainly
results in mechanical constraint, whereas salinity and drought exerts its malicious eVect mainly by disrupting the ionic and osmotic equilibrium of the cell. It is now well known that the stress signal is Wrst perceived at the membrane level by the receptors and then transduced
in the cell to switch on the stress responsive genes for mediating stress tolerance. Understanding the mechanism of stress tolerance along
with a plethora of genes involved in stress signaling network is important for crop improvement. Recently, some genes of calcium-signaling and nucleic acid pathways have been reported to be up-regulated in response to both cold and salinity stresses indicating the presence
of cross talk between these pathways. In this review we have emphasized on various aspects of cold, salinity and drought stresses. Various
factors pertaining to cold acclimation, promoter elements, and role of transcription factors in stress signaling pathway have been
described. The role of calcium as an important signaling molecule in response to various stress signals has also been covered. In each of
these stresses we have tried to address the issues, which signiWcantly aVect the gene expression in relation to plant physiology.
 2005 Elsevier Inc. All rights reserved.
Keywords: Calcium; CBL; CIPK; Cold; Drought; Helicase; Plants; Salt; SOS pathway; Stress
Plant growth and productivity is adversely aVected by
nature’s wrath in the form of various abiotic and biotic
stress factors. Plants are frequently exposed to a plethora of
stress conditions such as low temperature, salt, drought,
Xooding, heat, oxidative stress and heavy metal toxicity.
Various anthropogenic activities have accentuated the
existing stress factors. Heavy metals and salinity have
begun to accumulate in the soil and water tables and may
soon reach toxic levels. Plants also face challenges from
pathogens including bacteria, fungi, and viruses as well as
from herbivores. All these stress factors are a menace for
plants and prevent them from reaching their full genetic
potential and limit the crop productivity worldwide. Abiotic stress in fact is the principal cause of crop failure world
wide, dipping average yields for most major crops by more
*
Corresponding author. Fax: +91 11 26162316.
E-mail address: narendra@icgeb.res.in (N. Tuteja).
0003-9861/$ - see front matter  2005 Elsevier Inc. All rights reserved.
doi:10.1016/j.abb.2005.10.018
than 50% [1]. Abiotic stresses cause losses worth hundreds
of million dollars each year due to reduction in crop productivity and crop failure. In fact these stresses, threaten
the sustainability of agricultural industry.
In response to these stress factors various genes are upregulated, which can mitigate the eVect of stress and lead to
adjustment of the cellular milieu and plant tolerance. In
nature stress does not generally come in isolation and many
stresses act hand in hand with each other. In response to
these stress signals that cross talk with each other, nature
has developed diverse pathways for combating and tolerating them. These pathways act in cooperation to alleviate
stress.
In this review we have Wrst emphasized cold stress
followed by salt and drought stresses and the reason for
these stresses being injurious for plants. Various genes
involved in cold acclimation and their role towards membrane stabilization have been discussed. The physiological
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S. Mahajan, N. Tuteja / Archives of Biochemistry and Biophysics 444 (2005) 139–158
parameters pertaining to each stress, various promoter elements, transcription factors, negative regulators and the
role of calcium in relation to cold and salinity stress have
also been covered. Furthermore, the role of SOS pathway
in imparting salt tolerance to plants and the role of glycine
betaine as a major osmolyte in response to salt stress and
Wnally the role of abscisic acid (ABA)1 in stress have also
been discussed.
What is stress?
Stress in physical terms is deWned as mechanical force
per unit area applied to an object. In response to the
applied stress, an object undergoes a change in the dimension, which is also known as strain. As plants are sessile, it is
tough to measure the exact force exerted by stresses and
therefore in biological terms it is diYcult to deWne stress. A
biological condition, which may be stress for one plant may
be optimum for another plant. The most practical deWnition of a biological stress is an adverse force or a condition,
which inhibits the normal functioning and well being of a
biological system such as plants [2].
Various stress elicitors
A cell is separated from its surrounding environment by
a physical barrier, which is the plasma membrane. This
membrane is permeable to only some small lipid molecules
such as steroid hormones, which can diVuse through the
membrane into the cytoplasm and is impermeable to the
water-soluble material including ions, proteins and other
macromolecules. The cellular responses are initiated primarily by interaction of the extracellular material with a
plasma membrane protein. This extracellular molecule is
called a ligand (or an elicitor) and the plasma membrane
protein, which binds and interacts with this molecule, is
called a receptor. Various stress signals both abiotic as well
as biotic serve as elicitors for the plant cell (see Table 1).
Stress signaling pathways an overview
The stress is Wrst perceived by the receptors present on
the membrane of the plant cells (Fig. 1A), the signal is then
transduced downstream and this results in the generation
of second messengers including calcium, reactive oxygen
species (ROS) and inositol phosphates. These second mes1
Abbreviations used: ABA, abscisic acid; ROS, reactive oxygen species;
LEA, late embryogenesis abundant; MAP, mitogen-activated protein;
DRE, dehydration responsive elements; ABRE, ABA-responsive element;
ICE1, inducer of CBF expression 1; CDPKs, calcium-dependent protein
kinases; GA, gibberellin; SOS, salt overly sensitive; SNF, sucrose non-fermenting kinases; PS II, photosystem II; PQ, plastoquinone; GR, glutathione reductase; APX, ascorbate peroxidase; P5CS, pyrroline-5-carboxylate
synthase; HSPs, heat shock proteins; smHS, small HS; DAG, diacylglycerol; PA, phosphatidic acid; PLC, phospholipase C; PLD, phospholipase D;
CaM, calmodulin; CBL, calcineurin B-like; CIPK, CBL-interacting protein kinase.
Table 1
Various abiotic as well as biotic stress signals for plants
Abiotic stresses
1. Cold (chilling and frost)
2. Heat (high temperature)
3. Salinity (salt)
4. Drought (water deWcit condition)
5. Excess water (Xooding)
6. Radiations (high intensity of ultra-violet and visible light)
7. Chemicals and pollutants (heavy metals, pesticides, and aerosols)
8. Oxidative stress (reactive oxygen species, ozone)
9. Wind (sand and dust particles in wind)
10. Nutrient deprivation in soil
Biotic stresses
1. Pathogens (viruses, bacteria, and fungi)
2. Insects
3. Herbivores
4. Rodents
sengers, such as inositol phosphates, further modulate the
intracellular calcium level. This perturbation in cytosolic
Ca2+ level is sensed by calcium binding proteins, also
known as Ca2+ sensors. These sensors apparently lack any
enzymatic activity and change their conformation in a calcium dependent manner. These sensory proteins then interact with their respective interacting partners often initiating
a phosphorylation cascade and target the major stress
responsive genes or the transcription factors controlling
these genes. The products of these stress genes ultimately
lead to plant adaptation and help the plant to survive and
surpass the unfavorable conditions. Thus, plant responds to
stresses as individual cells and synergistically as a whole
organism. Stress induced changes in gene expression in turn
may participate in the generation of hormones like ABA,
salicylic acid and ethylene. These molecules may amplify
the initial signal and initiate a second round of signaling
that may follow the same pathway or use altogether diVerent components of signaling pathway. Certain molecules
also known as accessory molecules may not directly participate in signaling but participate in the modiWcation or
assembly of signaling components. These proteins include
the protein modiWers, which may be added cotranslationally to the signaling proteins like enzymes for myristoylation, glycosylation, methylation and ubiquitination.
The various stress responsive genes can be broadly categorized as early and late induced genes (Fig. 1B). Early
genes are induced within minutes of stress signal perception
and often express transiently. Various transcription factors
are included in the list of early genes as the induction of
these genes does not require synthesis of new proteins and
signaling components are already primed. In contrast, most
of the other genes, which are activated by stress more
slowly, i.e. after hours of stress perception are included in
the late induced category. The expression of these genes is
often sustained. These genes include the major stress
responsive genes such as RD (responsive to dehydration)/
KIN (cold induced)/COR (cold responsive), which encodes
and modulate the proteins needed for synthesis, for
S. Mahajan, N. Tuteja / Archives of Biochemistry and Biophysics 444 (2005) 139–158
A
Stress
[Ca2 +]ext
PLC
IP3 + DAG
Ca2 +
and other
second messengers
(InsP, ROS)
Ca2+ Sensors
(CBLs/CaM…)
Kinases/Phosphatases
~PO4/de~PO4
CIPKs/SOS2, CDPKs,
MAPKs and various
protein phosphatases
Transcription factors
Major stress responsive genes
Physiological response
B
Stress Responsive Genes
EARLY GENES
DELAYED GENES
(RD/KIN/COR/RAB18/RAB29B)
MODULATE
Encode proteins like
transcription factors/
calcium sensors.
example LEA-like proteins (late embryogenesis abundant),
antioxidants, membrane stabilizing proteins and synthesis
of osmolytes.
Cold stress
Receptors
PIP2
141
ACTIVATE
STRESS TOLERANCE EFFECTORS
e.g. LEA like proteins, antioxidants
osmolyte synthesiszing enzymes
Fig. 1. (A and B) Generic signal transduction pathway as well as the expression of early and late genes in response to abiotic stress signaling. (A) Represents the overview of signaling pathway under stress condition. Stress signal is
Wrst perceived by the membrane receptor, which activates PLC and hydrolyses
PIP2 to generate IP3 as well as DAG. Following stress, cytoplasmic calcium
levels are up-regulated via movements of Ca2+ ions from apoplast or from its
release from intracellular sources mediated by IP3. This change in cytoplasmic
Ca2+ level is sensed by calcium sensors which interact with their down stream
signaling components which may be kinases and/or phosphatases. These proteins aVect the expression of major stress responsive genes leading to physiological responses. (B) Early and delayed gene expression in response to abiotic
stress signaling. Various genes are triggered in response to stress and can be
grouped under early and late responsive genes. Early genes are induced within
minutes of stress perception and often express transiently. In contrast, various
stress genes are activated slowly, within hours of stress expression and often
exhibit a sustained expression level. Early genes encode for the transcription
factors that activate the major stress responsive genes (delayed genes). The
expression of major stress genes like RD/KIN/COR/RAB18/RAB29B result
in the production of various osmolytes, antioxidants, molecular chaperones
and LEA-like proteins, which function in stress tolerance.
In this section, we have emphasized on various aspects
of cold stress, which includes aVect of cold on plants physiology, cold acclimation and its role in providing freeze-tolerance, function of cold-regulated genes in cold
acclimation, negative regulation of cold stress and the role
of calcium in relation to cold stress. All these topics would
help in our better understanding of cold induced cellular
changes and its aVect on gene expression.
AVect of cold on plants physiology
Each plant has its unique set of temperature requirements, which are optimum for its proper growth and development. A set of temperature conditions, which are
optimum for one plant may be stressful for another plant.
Many plants, especially those, which are native to warm
habitat, exhibit symptoms of injury when exposed to low
non-freezing temperatures [3]. These plants including maize
(Zea mays), soybean (Glycine max), cotton (Gossypium
hirsutum), tomato (Lycopersicon esculentum) and banana
(Musa sp.) are in particular sensitive to temperatures below
10–15 °C and exhibit signs of injury see [3–5]. The symptoms of stress induced injury in these plants appear from 48
to 72 h, however, this duration varies from plant to plant
and also depend upon the sensitivity of a plant to cold
stress. Various phenotypic symptoms in response to chilling
stress include reduced leaf expansion, wilting, chlorosis
(yellowing of leaves) and may lead to necrosis (death of tissue). Chilling also severely hampers the reproductive development of plants for example exposure of rice plants to
chilling temperature at the time of anthesis (Xoral opening)
leads to sterility in Xowers [6].
The major malicious eVect of freezing is that it induces
severe membrane damage [7,8]. This damage is largely due
to the acute dehydration associated with freezing. Membrane lipids are primarily composed of two kinds of fatty
acids unsaturated as well as saturated fatty acids. Unsaturated fatty acids have one or more double bonds between
two carbon atoms (ACHBCHA) whereas saturated fatty
acids are fully saturated with hydrogen atoms
(ACH2ACH2A). It is a well-known fact that lipids containing saturated fatty acids solidify at temperatures higher
than those containing unsaturated fatty acids. Therefore,
the relative proportion of unsaturated fatty acids in the
membrane strongly inXuences the Xuidity of the membrane
[8]. The temperature at which a membrane changes from
semi Xuid state to a semi crystalline state is known as the
transition temperature. Chilling sensitive plants usually
have a higher proportion of saturated fatty acids and,
therefore, a higher transition temperature. Chilling resistant
species on the other hand are marked by higher proportion
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S. Mahajan, N. Tuteja / Archives of Biochemistry and Biophysics 444 (2005) 139–158
of unsaturated fatty acids and correspondingly a lower
transition temperature.
The success of many crops rests on their ability to withstand the freezing temperature of late spring or early
autumn frost. Therefore tolerance to freezing temperatures
is in particular important for the sustainability of agricultural crops. As understanding the basics of a disease is
essential for its cure, in the same way understanding of how
freezing induces its injurious eVects on plants is essential for
the development of frost tolerant crops. The real cause of
freeze-induced injury to plants is the ice formation rather
than low temperatures. It is noteworthy to mention here
that dehydrated tissues such as seeds and fungal spores can
survive at very low temperatures without any symptoms of
injury. Even cryopreservation is a common method for
storage of seeds and other biological materials, which is
based on the fact that water essentially solidiWes without
the formation of ice crystals.
Ice formation in plants, begins in the apoplastic space as
it has relatively lower solute concentration. As the vapor
pressure of ice is much lower than water at any given temperature, ice formation in the apoplast establishes a vapor
pressure gradient between the apoplast and surrounding
cells. The unfrozen cytoplasmic water migrates down the
gradient from the cell cytosol to the apoplast, which contributes to the enlargement of existing ice crystals and
causes a mechanical strain on the cell wall and plasma
membrane leading to cell rupture [9,10]. Freeze induced cellular dehydration results in multiple forms of membrane
damage including expansion-induced-cell lyses and fracture
lesions [8,11] and lamellar-to-hexagonal-II phase transition.
Although freeze exerts its eVect largely by membrane damage due to severe cellular dehydration, certain additional
factors may also contribute to damage induced by freeze.
ROS produced in response to freeze stress contributes to
membrane damage. Chilling sensitive plants characteristically exhibits structural injuries and may suVer from metabolic dysfunction when chilled [12]. Overall, chilling
ultimately results in loss in membrane integrity, which leads
to solute leakage. The integrity of intracellular organelles is
also disrupted leading to the loss of compartmentalization,
reduction and impairing of photosynthesis, protein assembly and general metabolic processes. The primary environmental factors responsible for triggering increased
tolerance against freezing, is the phenomenon known as
‘cold acclimation.’ It is the process where certain plants
increase their freezing tolerance upon prior exposure to low
non-freezing temperatures.
Cold acclimation and its role in providing freeze-tolerance
The primary function of cold acclimation is to stabilize
the membranes against freeze injury. Acclimation results in
increase in proportion of unsaturated fatty acids and
thereby a drop in transition temperature [13,14]. It functions to prevent the expansion-induced lyses and formation
of hexagonal II phase lipids in rye and other plants [8,11].
Cold acclimation results in physical and biochemical
restructuring of cell membranes through changes in the
lipid composition and induction of other non-enzymatic
proteins that alter the freezing point of water. Addition of
solutes decreases the freezing point of water to a more negative value, thus preventing ice formation.
Low temperatures induce a number of alterations in cellular components, including the extent of unsaturated fatty
acids [15], the composition of glycerolipids [16], changes in
protein and carbohydrate composition and the activation
of ion channels [17]. Accumulation of sucrose and other
simple sugars that occurs with cold acclimation also contributes to the stabilization of membrane as these molecules
can protect membranes against freeze-damage. Freezing
tolerance is a multigenic trait. Low temperatures activate a
number of cold-inducible genes [18], such as those that
encode dehydrins, lipid transfer proteins, translation elongation factors and the late-embryogenesis-abundant proteins [19]. Moreover, intercellular ice formation can cause a
mechanical strain on cell wall and membrane leading to cell
rupture [9,10]. There is also substantiation that protein
denaturation occurs in plants at low temperature which
could also result in cellular damage [20].
Overall, cold acclimation results in protection and stabilization of the integrity of cellular membranes, enhancement
of the antioxidative mechanisms, increased intercellular
sugar levels as well as accumulation of other cryoprotectants including polyamines that protect the intracellular
proteins by inducing the genes encoding molecular chaperones [21]. All these modiWcations help the plant to withstand and surpass the severe dehydration associated with
freezing stress.
Function of cold-regulated genes in cold acclimation
Considerable eVorts have been directed towards determining the nature of cold-inducible genes and establishing
their role in freezing tolerance. The Arabidopsis FAD8 gene
[22] encodes a fatty acid desaturase that contributes to
freezing tolerance by altering the lipid composition.
Cold-responsive genes encoding molecular chaperones
including a spinach hsp70 gene [23], and a Brassica napus
hsp90 gene [24], contribute to freezing tolerance by stabilizing proteins against freeze-induced denaturation. Many
cold-responsive genes encoding various signal transduction
and regulatory proteins have been identiWed and this list
includes the mitogen-activated protein (MAP) kinase [25],
MAP kinase, kinase, kinase (MAPKKK) [26] and the calmodulin-related proteins [27]. These proteins might contribute to freezing tolerance as well as tolerance to other
stresses by controlling or regulating the expression and
activity of the major stress genes as well their proteins.
The largest class of cold induced genes encodes polypeptides that are homologs of LEA proteins and the polypeptides that are synthesized during the late embryogenesis
phase, just prior to seed desiccation and also in the seedlings in response to dehydration stress [28–30]. These LEA
S. Mahajan, N. Tuteja / Archives of Biochemistry and Biophysics 444 (2005) 139–158
like proteins are mainly hydrophilic, many have relatively
simple amino-acid composition, and are composed largely
of a few amino acids with repeated amino acid sequence
motifs. Many of these proteins are predicted to contain
regions capable of forming amphipathic helices. The
examples of cold responsive genes include: COR15a, [31],
alfalfa Cas15 [32], and wheat WCS120 [33]. The expression
of COR genes has been shown to be critical for both chilling tolerance and cold acclimation in plants [34]. Arabidopsis COR genes include: COR78/RD29, COR47, COR15a,
COR6.6 and encode LEA like proteins [34]. These genes are
induced by cold, dehydration or ABA. COR15A polypeptide is targeted to the chloroplast. Formation of hexagonal
II phase lipids is a major cause of membrane damage in
non-acclimated plants. COR15a expression decreases the
propensity of the membranes to form hexagonal II phase
lipids in response to freezing [8,11].
The analysis of the promoter elements of COR genes
revealed that they contain DRE (dehydration responsive
elements) or CRT (C-repeats) and some of them contain
ABRE (ABA-responsive element) as well [35,36]. Induction
of the COR genes was accomplished by over-expression of
transcription factor CBF (CRT/DRE binding factor) [36].
CBF binds to the CRT/DRE elements present in the promoter of the COR genes and other cold-regulated genes.
The over-expression of these regulatory elements not only
resulted in increased freezing tolerance but also an increase
to drought tolerance [37]. This Wnding provides strong support that a fundamental role of cold-inducible genes is to
protect the plant cells against cellular dehydration. Lee
et al. [38] genetically analyzed HOS1 (high expression of
osmotically responsive genes) locus of Arabidopsis. The
hos1 mutation resulted in sustained and super induction of
CBF2, CBF3 and their target regulatory genes during cold
stress. Therefore, HOS1 was identiWed as a negative regulator of COR genes by modulating the expression level of
CBFs. [39]. HOS1 gene encodes a ring Wnger protein and is
constitutively expressed but gets drastically down-regulated
within 10 min of cold stress. Genetic analysis led to the
identiWcation of ICE1 (inducer of CBF expression 1) as an
activator of CBF3 [39]. ICE1 encoded a transcription factor
that speciWcally recognized MYC sequence on the CBF3
promoter. Transgenic lines overexpressing ICE1 did not
express CBF3 at warm temperature but showed a higher
level of expression for CBF3 as well as RD29 and COR15a
at low temperatures. This study suggests that cold induced
modiWcation of ICE1 is necessary for it to act as an activator of CBF3 in planta.
Recently two CBF1-like cDNAs CaCBFIA and CaCBFIB have been cloned and characterized [40] from hot pepper. These were induced in response to low temperature
stress (4 °C) and not in response to wounding or ABA.
Two-hybrid screening led to the isolation of a homeodomain leucine zipper (4D-Zip) protein that interacts with
CaCBFIB. The expression of 4D-Zip was elevated by low
temperature and drought [40]. Calcium-dependent protein
kinases (CDPKs) play an important role in the signal trans-
143
duction and recently the function of OsCDPK13 (Oryza
sativa CDPK 13) has been characterized [41]. The gene
expression as well as protein accumulation of OsCDPK13
were up-regulated in response to cold and gibberellin (GA)
but suppressed under salt and drought stress and also in
response to ABA. The overexpressing transgenic lines of
OsCDPK13 had higher recovery rates following cold stress
in comparison with the vector control rice. Cold-tolerant
rice varieties exhibited higher expression of OsCDPK13
than the cold sensitive ones. Antisense OsCDPK13 transgenic lines were shorter in comparison with the vector control lines. Moreover, dwarf mutants of rice also had lower
level of OsCDPK13 than in wild type [41]. However, there
has been no mention of the sensitivity of OsCDPK13 antisense lines in response to cold stress [41]. We however
expect that these antisense lines should be hypersensitive to
cold stress as the gene has been shown to play an important
role in mediating tolerance in response to cold stress which
is evident due to higher recovery rates following cold stress
than the vector control lines.
Negative regulation of cold stress
Mutagenesis study resulted in the identiWcation of a
gene, eskimo l (esk1), which has a major eVect on freezing
tolerance. These plants were more freeze tolerant than the
wild type plants without cold acclimation. The concentration of free proline [42] in the esk1 mutant was found to be
30-fold higher than in the wild-type plants. Proline has been
shown to be an eVective cryoprotectant and this is also one
of the major factors imparting freezing tolerance. In addition to the total sugars, which were elevated, the expression
of RAB18 cold-responsive LEA II gene was also found to
be elevated three fold. This suggests that ESK1 may act as a
negative regulator. SigniWcantly, the esk 1 mutation did not
appear to aVect the expression of COR genes. This suggests
that multiple signaling pathways are involved in response
to cold stress and they may cross talk with each other as
well as with genes involved in other stresses.
Role of calcium in relation to cold stress
Calcium is an important messenger in a low temperature
signal transduction pathway. The change in cytosolic calcium levels is a necessary Wrst step in a temperature sensing
mechanism, which enables the plant to withstand future
cold stress in a better way. In both Arabidopsis [17,27] and
alfalfa [43] cytoplasmic calcium levels increase rapidly in
response to low temperature, largely due to an inXux of calcium from extracellular stores. Through the use of pharmacological and chemical reagents, it has been demonstrated
that calcium is required for the full expression of some of
the cold induced genes including the CRT/DRE controlled
COR6 and KIN1 genes of Arabidopsis [17,32,43]. For example, Ca2+ chelators such as BAPTA and Ca2+ channel
blockers such as La3+ inhibited the cold-induced inXux of
calcium and resulted in the decreased expression of the cold
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S. Mahajan, N. Tuteja / Archives of Biochemistry and Biophysics 444 (2005) 139–158
inducible Cas15 gene and blocked the ability of alfalfa to
acclimate in cold. In addition Cas15 expression can be
induced at a much higher temperature, i.e., 25 °C by treating
the cells with A23187, a Ca2+ ionophore that causes a rapid
inXux of calcium [43].
Salinity stress
Salinity is a major environmental stress and is a substantial constraint to crop production. Increased salinization of
arable land is expected to have devastating global eVects,
resulting in 30% land loss within next 25 years and up to
50% by the middle of 21st century [44]. High salinity causes
both hyperionic and hyperosmotic stress and can lead to
plant demise. Sea water contains approximately 3% of
NaCl and in terms of molarity of diVerent ions, Na+ is
about 460 mM, Mg2+ is 50 mM and Cl¡ around 540 mM
along with smaller quantities of other ions. Salinity in a
given land area depends upon various factors like amount
of evaporation (leading to increase in salt concentration),
or the amount of precipitation (leading to decrease in salt
concentration). Weathering of rocks also aVects salt concentration. Inland deserts are marked by high salinity as the
rate of evaporation far exceeds the rate of precipitation.
Agricultural lands that have been heavily irrigated are
highly saline. As drier areas in particular need intense irrigation, there is extensive water loss through a combination
of both evaporation as well as transpiration. This process is
known as evapotranspiration and as a result, the salt
delivered along with the irrigation water gets concentrated,
year-by-year in the soil. This leads to huge losses in terms of
arable land and productivity as most of the economically
important crop species are very sensitive to soil salinity.
These salt sensitive plants, also known as glycophytes
include rice (Oryza sativa), maize (Zea mays), soybean (Glycine max) and beans (Phaseolus vulgaris). High salt concentration (Na+) in particular which deposit in the soil can
alter the basic texture of the soil resulting in decreased soil
porosity and consequently reduced soil aeration and water
conductance. The basic physiology of high salt stress and
drought stress overlaps with each other. High salt depositions in the soil generate a low water potential zone in the
soil making it increasingly diYcult for the plant to acquire
both water as well as nutrients. Therefore, salt stress essentially results in a water deWcit condition in the plant and
takes the form of a physiological drought. The major ions
involved in salt stress signaling, include Na+, K+, H+ and
Ca2+. It is the interplay of these ions, which brings homeostasis in the cell.
In this section, we have emphasized on various aspects
of salinity stress, which includes the reasons why salinity
stress is injurious to plant cells, generic function of K+, role
of Ca2+ and SOS pathway in relation to imparting salt
stress tolerance, loss of water due to salinity stress and the
role of glycine betaine as a major osmolyte. Moreover, the
role of DNA unwinding enzymes, i.e., helicases, imparting
salinity stress tolerance have also been discussed.
Maladies caused by salt stress on plant cells arise from the
following
(1) Disruption of ionic equilibrium: InXux of Na+ dissipates the membrane potential and facilitates the
uptake of Cl¡ down the chemical gradient.
(2) Na+ is toxic to cell metabolism and has deleterious
eVect on the functioning of some of the enzymes [45].
(3) High concentrations of Na+ causes osmotic imbalance, membrane disorganization, reduction in
growth, inhibition of cell division and expansion.
(4) High Na+ levels also lead to reduction in photosynthesis and production of reactive oxygen species [46–
48].
Where sodium (Na+) is deleterious for plant growth, K+
is one of the essential elements and is required by the plant
in large quantities.
Generic functions of K+
(1) K+ is required for maintaining the osmotic balance.
(2) K+ has a role in opening and closing of stomata.
(3) K+ is an essential co-factor for many enzymes like the
pyruvate kinase, whereas Na+ is not.
Movement of salt into roots and to shoots is a product
of the transpirational Xux required to maintain the water
status of the plant [48,49]. As common proteins transport
Na+ and K+, Na+ competes with K+ for intracellular inXux
[45,50,51]. Many K+ transport systems have some aYnity
for Na+, i.e., Na+/K+ symporters. Thus external Na+ negatively impacts intracellular K+ inXux. Most cells maintain
relatively high K+ and low concentrations of Na+ in the
cytosol. This is achieved through a coordinated regulation
of transporters for H+, K+, Ca2+ and Na+.
The plasma membrane H+-ATPases serves as the primary pump that generates a proton motive force driving
the transport of other solutes including Na+ and K+.
Increased ATPase-mediated H+ translocation across the
plasma membrane is a component of the plant cell response
to salt imposition [52,53]. K+ and Na+ inXux can be diVerentiated physiologically into two categories, one with high
aYnity for K+ over Na+ and the other for which there is
lower K+/Na+ selectivity. The Na+/K+ transporter and K+
transporters with dual high and low aYnity may contribute
substantially to Na+ inXux.
Role of Ca2+ in relation to salt stress
For decades it has been shown that another ion, Ca2+
has role in providing salt tolerance to plant. Externally
supplied Ca2+ reduces the toxic eVects of NaCl, presumably by facilitating higher K+/Na+ selectivity [54–56].
High salinity results in increased cytosolic Ca2+ that is
transported from the apoplast as well as the intracellular
compartments [57]. This transient increase in cytosolic
S. Mahajan, N. Tuteja / Archives of Biochemistry and Biophysics 444 (2005) 139–158
Ca2+ initiates the stress signal transduction leading to salt
adaptation.
The search to identify genes involved in providing salt
tolerance commenced in 1998, by Liu and Zhu [56] where
several mutants were screened and SOS (salt overly sensitive) genes were identiWed through positional cloning.
BrieXy, SOS pathway results in the exclusion of excess Na+
ions out of the cell via the plasma membrane Na+/H+ antiporter and helps in reinstating cellular ion homeostasis. The
discovery of SOS genes paved the way for elucidation of a
novel pathway linking the Ca2+ signaling in response to a
salt stress [58,59].
SOS3 gene encodes a Ca2+ binding protein with 4 EF
hand Ca2+ binding motifs and a myristoylation sequence
(MGXXXST/K) at the N-terminus of the protein. In
response to Ca2+ perturbation SOS3 changes its conformation and transduces the signal downstream by interacting
with an eVector kinase. Mutation in SOS3 (sos 3-1), which
results in the reduction of its Ca2+ binding ability also
impairs the cellular ionic equilibrium and renders the plant
hypersensitive to salt stress [60]. This defect can be partially
rescued by addition of high levels of Ca2+ in the growth
medium [56]. Ca2+ sensors diVer in their aYnity with which
they bind Ca2+ and this diVerence is an important parameter in distinguishing and decoding various Ca2+ sensors. In
comparison with Ca2+ sensors like calmodulin and caltractin, SOS3 binds Ca2+ with a relatively low aYnity.
SOS2 gene was isolated through the genetic screening
of mutants oversensitive to salt stress in Arabidopsis. The
mRNA level of SOS2 was shown to be up-regulated in
response to salt stress in the roots [61]. SOS2/CIPK24
encodes a novel serine/threonine protein kinase with an
N terminal catalytic and C terminal regulatory domain.
Whereas the N terminal domain shares sequence homology with sucrose non-fermenting kinases (SNF), the C
terminal domain is unique to this class of kinases and
harbors a 21 amino acid FISL/NAF motif [62]. FISL
motif acts as an autoinhibitory domain and interacts
with the catalytic domain thereby keeping the enzyme in
an OFF state under normal conditions. SOS3 interacts
with SOS2 via FISL motif and relieves the protein from
autoinhibition thereby making the kinase active. SOS3
activates SOS2 protein kinase activity in a calciumdependent manner [63]. SOS2 could be constitutively
activated by the deletion of FISL motif [64] and this deletion resulted in SOS2 acting independent of SOS3. Arabidopsis plants with double mutant genotype (sos3/sos2)
showed no additive eVects towards salt sensitivity, this
indicates that SOS3 and SOS2 function in the same pathway [63]. Constitutively over-expressed SOS2 under the
control of CaMV35S promoter could rescue the salt
hypersensitive phenotype of both sos3 and sos2 mutants,
thereby further supporting the functioning of SOS3 and
SOS2 in the same Ca2+ mediated pathway during salt
stress [59,65].
SOS1 gene was identiWed as the target of SOS3–SOS2
pathway by genetic analysis of sos1 mutants of Arabidopsis.
145
Osmotic as well as ionic balance was impaired in sos1
mutants and they exhibited hypersensitivity towards salt
stress. SOS genes (SOS1, SOS2 and SOS3) were genetically
conWrmed to function in a common pathway of salt tolerance [58]. SOS1 gene was cloned and predicted to encode a
127-kDa protein with a N terminal region composed of 12
trans-membrane domains and a C terminal region with a
long hydrophilic cytoplasmic tail [66]. The trans-membrane
region of SOS1 shared substantial sequence homology to
the plasma membrane Na+/H+ antiporter isolated from
bacteria and fungi [66].
The SOS pathway is depicted in Fig. 2. The perception of
salt stress by an unknown hypothetical plasma membrane
sensor elicits cytoplasmic Ca2+ perturbations. This perturbation in the cytosolic Ca2+ levels is sensed by SOS3, which
transduces the signal to the down stream components. The
myristoylation motif of SOS3 results in the recruitment of
SOS3–SOS2 complex to the plasma membrane, where
SOS2 phosphorylates and activates SOS1 (a plasma membrane Na+/H+ antiporter) [67]. The excess Na+ ions are
expelled out of the cell and cellular ion homeostasis is
restored. SOS pathway regulates Na+ ion homeostasis by
interacting with other regulatory proteins and seems to
have additional branches. AtHKT1 is a low aYnity Na+
transporter and seems to mediate Na+ entry into the root
cells of Arabidopsis during a salt stress [68]. Remarkably,
mutation in Athkt1 also suppresses the sos3 mutation [69]
suggesting that SOS3–SOS2 complex functions to down
regulate HKT1 gene expression or inactivate the HKT1
protein during salt stress, thereby preventing the Na+ entry
and its build up in the cell [59]. SOS3 and SOS2 seem to
negatively regulate the activity of AtHKT1 under salt
stress.
In addition to controlling SOS1 activity resulting in
eZux of excess Na+ ions, SOS3–SOS2 complex also seems
to function in sequestration of excess Na+ ions in the intracellular compartments. SOS2 is shown to interact with vacuolar Na+/H+ antiporter and inXuence the Na+/H+
exchange activity signiWcantly [70]. Recently, further cross
talk in the SOS pathway was explored and it was shown
that SOS2 interacted with the N terminus of CAX1 (H+/
Ca2+) antiporter and regulated its activity [65]. This activation of CAX1 via SOS2 was however independent of SOS3
and resulted in maintenance of Ca2+ homeostasis. SOS
pathway may also inXuence the functioning of other membrane proteins in sequestration of excess Na+ ions in other
sub-cellular compartments.
Overall, osmotic homeostasis after salt stress is mediated
by Na+ eZux across the plasma membrane and/or by its
compartmentalization into the vacuoles. The energy for
these reactions is provided by H+-ATPases that serve as
primary pumps. Plant cDNAs encoding NHE (Na+/H+
exchanger)-like proteins similar to mammalian sodium/
proton exchangers were isolated and can functionally complement a yeast mutant deWcient for the endomembrane
Na+/H+ transporter, NHX1 [71,72]. The AtNHX1 gene
encodes a tonoplast Na+/H+ antiporter and functions in
146
S. Mahajan, N. Tuteja / Archives of Biochemistry and Biophysics 444 (2005) 139–158
The ionic aspect of salt stress signaled via SOS pathway
SALT STRESS
(excess Na+)
Salt Sensor?
Ca2+ Increase
?
Motor proteins?
SOS3 (CBL)
(Ca2+ Sensor)
SOS2 (CIPK)
Ca2+ homeostasis
SOS3 + SOS2
TRANSPORTERS
?
NHX
(V-Na+/H+ exchanger)
Na+ in vacuoles
CAX1
(V-Ca2+/H+ antiporter)
HKT
SOS1
(Low affinity Na+ transporter) (PM-Na+/H+ anti-porter)
Na+ entry blocked
Na+ efflux-PM
LOW CYTOPLASMIC Na+
SALINITY
TOLERANCE
Fig. 2. Regulation of ion homeostasis by SOS and related pathways in relation to salt stress adaptation. Salt stress is perceived by an unknown receptor (?)
present at the plasma membrane (PM) of the cell. This induces a cytosolic calcium perturbation, which is sensed by SOS3 and accordingly changes its conformation in a Ca2+-dependent manner and interacts with SOS2. This interaction relieves SOS2 of its auto-inhibition and results in activation of the
enzyme. Activated SOS2, in complex with SOS3 phosphorylates SOS1, a Na+/H+ antiporter resulting in eZux of excess Na+ ions. SOS3–SOS2 complex
interacts with and inXuences other salt mediated pathways resulting in ionic homeostasis. This complex inhibits HKT1 activity (a low aYnity Na+ transporter) thus restricting Na+ entry into the cytosol. SOS2 also interacts and activates NHX (vacuolar Na+/H+ exchanger) resulting in sequestration of
excess Na+ ions, further contributing to Na+ ion homeostasis. CAX1 (H+/Ca+ antiporter) has been identiWed as an additional target for SOS2 activity reinstating cytosolic Ca2+ homeostasis.
compartmentalizing excess Na+ into the vacuole [72]. Overexpression of AtNHX1 antiporter substantially enhanced
salt tolerance of Arabidopsis [71].
Loss of water due to salinity stress
A major consequence of NaCl stress is the loss of intracellular water. To prevent this water loss from the cell and
protect the cellular proteins, plants accumulate many
metabolites that are also known as “compatible solutes.”
These solutes do not inhibit the normal metabolic reactions
[73,74]. Frequently observed metabolites with an osmolyte
function are sugars, mainly fructose and sucrose, sugar
alcohols and complex sugars like trehalose and fructans. In
addition charged metabolites like glycine betaine proline
and ectoine are also accumulated. The accumulation of
these osmolytes, facilitate the osmotic adjustment [75–77].
Water moves from high water potential to low water potential and accumulation of these osmolytes make the water
potential low inside the cell and prevent the intracellular
water loss.
Role of glycine-betaine
Glycine betaine (N,N,N-trimethylglycine-betaine) is a
major osmolyte [78,79] and is synthesized by many plants
in response to abiotic stresses. Biosynthetic pathway of
betaine is a two-step oxidation of choline. Recently, a biosynthetic pathway of betaine from glycine, catalyzed by
two N-methyl transferase enzymes, was found [80]. The
potential role of N-methyl transferase gene for betaine
synthesis has been examined in Synechococcus sp. a fresh
water cyanobacteria, and in Arabidopsis. It has been
found that the co-expression of N-methyl transferase gene
in cyanobacteria caused accumulation of betaine in signiWcant amounts and conferred salt tolerance to a fresh
water cyanobacterium suYcient for it to become capable
of growth in seawater [80]. Arabidopsis plants expressing
N-methyltransferase gene also accumulated betaine to
high levels and improved seed yield under stress conditions [80].
On the whole, plants possess speciWc mechanisms to
overcome the hypersaline environment and thrive in such
S. Mahajan, N. Tuteja / Archives of Biochemistry and Biophysics 444 (2005) 139–158
conditions by adjusting their internal osmotic status. These
mechanisms have already been discussed brieXy and
include: exclusion of Na+ from cell by plasma membrane
Na+/H+ antiporter, sequestration of excess Na+ in vacuoles
by tonoplast Na+/H+ antiporters and accumulation of
organic, compatible solutes such as sugars, certain amino
acids and glycine betaine.
Role of helicases in imparting salinity stress tolerance
Abiotic stress condition often aVects the cellular geneexpression machinery. Therefore, the molecules that are
involved in the processing of nucleic acids including helicases are also likely to be aVected. Multiple DNA helicases are present in the cell and are involved in gene
regulation at various developmental stages as well as in
stress conditions. These DNA unwinding enzymes may
have diVerent substrates as well as structural requirements [81,82]. Though a number of diVerent helicases
have been reported from E. coli, bacteriophages, viruses,
yeast, calf thymus and humans the biological role of only
a few DNA helicases have been explored [83–85]. Moreover, our knowledge about plant DNA helicases has also
been limited with only 6 helicase proteins having been
puriWed [82]. The role of helicases and the underlying
molecular mechanisms is only beginning to be understood.
Recently the potential role of PDH45 (pea DNA helicase 45) in overcoming salinity stress was explored [86]. The
authors have proved that PDH45 overexpressing transgenic lines showed high salinity tolerance and the T1 transgenic plants were able to grow to maturity and set normal
viable seeds under continuous salinity stress without any
reduction in plant yield in terms of seed weight. The
authors have proposed a dual mode of action for PDH45.
(i) PDH45 may act at the translation level to stabilize or
enhance protein synthesis. As a support to this hypothesis it
was earlier proved that antibodies against PDH45 inhibited
the protein synthesis in vitro, suggesting its role in translation [87]. mRNA and protein synthesis machinery are sensitive to stress and may be potential targets to salt toxicity in
plants. (ii) PDH45 may associate with DNA multi-subunit
protein complexes to alter gene expression. This hypothesis
was supported by the demonstration of the interaction of
PDH45 with topoisomerase I. This interaction was proposed to play an important role at the level of transcriptional regulation by the authors.
Recently, a novel DNA helicase gene PDH47 (pea
DNA helicase 47) was isolated and shown to be induced
under cold as well as salinity stress [88]. The enzyme contained a bi-directional DNA helicase activity (both 3⬘–5⬘
and 5⬘–3⬘) and was involved in translation initiation of
the proteins. This enzyme showed a dual localization in
nucleus as well as in the cytoplasm. Another report
proved that a DEAD box RNA helicase, LOS4, is essential for mRNA export and is important for development
and stress response in Arabidopsis [89].
147
Drought stress
Water stress may arise as a result of two conditions,
either due to excess of water or water deWcit. Flooding is an
example of excess of water, which primarily results in
reduced oxygen supply to the roots. Reduced O2 results in
the malfunctioning of critical root functions including limited nutrient uptake and respiration. The more common
water stress encountered is the water deWcit stress known as
the drought stress. Removal of water from the membrane
disrupts the normal bilayer structure and results in the
membrane becoming exceptionally porous when desiccated. Stress within the lipid bilayer may also result in displacement of membrane proteins and this contributes to
loss of membrane integrity, selectivity, disruption of cellular compartmentalization and a loss of activity of enzymes,
which are primarily membrane based. In addition to membrane damage, cytosolic and organelle protein may exhibit
reduced activity or may even undergo complete denaturation when dehydrated. The high concentration of cellular
electrolytes due to the dehydration of protoplasm may also
cause disruption of cellular metabolism.
The components of drought and salt stress cross talk
with each other as both these stresses ultimately result in
dehydration of the cell and osmotic imbalance. Virtually
every aspect of plants physiology as well cellular metabolism is aVected by salt and drought stress. Drought and salt
signaling encompasses three important parameters [56].
(1) Reinstating osmotic as well as ionic equilibrium of
the cell to maintain cellular homeostasis under the
condition of stress.
(2) Control as well as repair of stress damage by detoxiWcation signaling.
(3) Signaling to coordinate cell division to meet the
requirements of the plant under stress.
As a consequence of drought stress many changes occur
in the cell and these include change in the expression level
of LEA/dehydrin-type genes, synthesis of molecular chaperones, which help in protecting the partner protein from
degradation and proteinases that function to remove denatured and damaged proteins. This stress also leads to activation of enzymes involved in the production and removal
of ROS [59,90]. The over-expression of barley group 3 LEA
gene HVA1 in leaves and roots of rice and wheat lead to
improved tolerance against osmotic stress as well as
improved recovery after drought and salinity stress [91].
Dehydrins, also known as group 2 LEA proteins accumulate in response to both dehydration as well as low temperature [28].
Other physiological eVects of drought on plants are the
reduction in vegetative growth, in particular shoot growth.
Reduced cyclin-dependent kinase activity results in slower
cell division as well as inhibition of growth under water
deWcit condition [92]. Leaf growth is generally more sensitive than the root growth. Reduced leaf expansion is
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beneWcial to plants under water deWcit condition, as less
leaf area is exposed resulting in reduced transpiration. In
accordance, many mature plants, for example cotton subjected to drought respond by accelerating senescence and
abscission of the older leaves. This process is also known as
leaf area adjustment. Regarding root, the relative root
growth may undergo enhancement, which facilitates the
capacity of the root system to extract more water from
deeper soil layers.
Under drought stress, we have focused on various
aspects, which include response of stomata to drought condition, eVect of drought on photosynthetic machinery, role
of sugars and other osmolytes, and the role of MAP
Kinases in mediating osmotic stress tolerance. Moreover,
the role of phospholipids signaling under an osmotic stress
condition and a generic pathway in response to salt,
drought and cold stress is also described in this section.
sensitivity of stomata towards ABA see [95]. It has been
proposed by Sharp [98] that the concentration of various
hormones may govern their mode of action. For instance,
as ethylene inhibits growth, an insuYcient amount of
ABA accumulation in the shoot would result in ethylene
mediated growth inhibition, whereas, higher accumulation of ABA in the root would prevent the ethylene mediated growth inhibition.
ABA promotes the eZux of K+ ions from the guard
cells, which results in the loss of turgor pressure leading to
stomata closure. Stomata closure does not always depend
upon the perception of water deWcit signals arising from
leaves. In fact, stomata closure also responds directly to the
soil desiccation even before there is any signiWcant reduction in leaf mesophyll turgor pressure. The fact that ABA
can act as a long distance communication signal between
water deWcit roots and leafs, inducing the closure of stomata is about two decades old [99].
Response of stomata to drought condition
AVect of drought on photosynthetic machinery
Increase in temperature or a rapid drop in humidity
often results in acute water deWcit condition in plants.
Moreover, dry air mass, which moves into the environment,
can also add to rapid and acute water losses from plants.
Such atmospheric changes result in a dramatic increase in
the vapor pressure gradient between leaf and the ambient
air. This results in increased rate of transpiration. Moreover, increase in vapor pressure gradient enhances water
loss from the soil.
The Wrst response of virtually all the plants to acute
water deWcit is the closure of their stomata to prevent the
transpirational water loss [93]. Closure of stomata may
result from direct evaporation of water from the guard cells
with no metabolic involvement. This process of stomatal
closure is referred to as hydropassive closure. Stomatal closure may also be metabolically dependent and involve processes that result in reversal of the ion Xuxes that cause
stomatal opening. This process of stomatal closure, which
requires ions and metabolites, is known as hydroactive closure. This process seems to be ABA regulated.
Plant growth and response to a stress condition is
largely under the control of hormones. Hormones, in particular ABA along with cytokinins and ethylene, have
been implicated in the root–shoot signaling. This long distance signaling may be mediated particularly via ABA as
well as ROS [94]. Recent studies have implicated that the
transport of ABA into root xylem is modulated by environmental factors such as xylem pH and the duration of
the day see [95]. Under the water deWcit condition the pH
of xylem sap increases therefore promoting the loading of
ABA into the root xylem and its transport to the shoot
[96]. Environmental conditions that increase the rate of
transpiration also result in an increase in the pH of leaf
sap, which can promote ABA accumulation and lead to
reduction in stomatal conductance [95,97]. Increased cytokinin concentration in the xylem sap was shown to promote stomatal opening directly as well as decrease the
As stresses co-exist in nature with each other, a crop
therefore may have to survive a stress episode of drought
accompanied by high temperature. Plants respond quickly
to prevent the photosynthetic machinery from suVering
from irreversible damages. Stomatal closure in response to
a water deWcit stress primarily results in decline in the rate
of photosynthesis. Very severe drought conditions results in
limited photosynthesis due to decline in Rubisco activity
[100]. The activity of photosynthetic electron chain is Wnely
tuned to the availability of CO2 in the plant and photosystem II (PS II) often declines in parallel under drought conditions [101]. It has been shown that the decline in the rate
of photosynthesis in drought stress is primarily due to CO2
deWciency, as the photochemical eYciency could be brought
back to normal after a fast transition of leaves to an environment enriched in CO2 [102]. Decline in intracellular CO2
levels results in the over-reduction of components within
the electron transport chain and the electrons get transferred to oxygen at photosystem I (PS I). This generates
ROS including superoxide, hydrogen peroxide (H2O2) and
hydroxyl radicals. These ROS need to be scavenged by the
plant as they may lead to photo-oxidation. Redox signals
are like a forewarning for the plant, controlling the energy
balance of the leaves. Some of the key electron carriers such
as plastoquinone (PQ), or the electron acceptors such as
ferredoxin/thioredoxin system as well as ROS are included
in the redox signaling molecules. Whereas a reduced PQ
pool activates the transcription of PS I reaction centre, the
oxidized pool activates the transcription of PS II reaction
centre [103]. Plant detoxifying systems, which include ascorbate and glutathione pools control the intracellular concentration of ROS. These ROS acts as second messengers in
redox signal transduction and are implicated in hormonal
mediated events [104]. H2O2 acts as a signal for the closure
of leaf stomata, acclimation of leaf to high irradiation and
the induction of heat shock proteins [105]. In Arabidopsis
S. Mahajan, N. Tuteja / Archives of Biochemistry and Biophysics 444 (2005) 139–158
application of ABA to guard cells was shown to induce a
burst of H2O2 that resulted in stomatal closure [106].
In a situation where water deWcit becomes too intense
or prolonged, plants can wilt, cells can undergo shrinkage
and this may lead to mechanical constraint on cellular
membranes. The strain on membrane is one of the severe
eVects of drought implicated on a plants’ physiology. This
in particular impairs the functioning of ions and transporters as well as membrane associated enzymes. Chloroplast membranes are in particular sensitive to oxidation
stress damage caused by the generation of excessive
amount of ROS in these membranes. ROS can cause
extensive peroxidation and de-esteriWcation of membrane
lipids, as well as lead to protein denaturation and mutation of nucleic acids [107]. Dehydration results in cell
shrinkage and consequently a decline in cellular volume.
This results in cellular content becoming viscous, therefore increasing the probability of protein–protein interaction leading to their aggregation and denaturation [108].
Increased concentration of solutes may also exceed toxic
levels, which may be deleterious for the functioning of
some of the enzymes including the enzymes required for
photosynthetic machinery [108]. The transcript of some of
the antioxidant genes such as glutathione reductase (GR)
or the ascorbate peroxidase (APX) is higher during the
recovery of water deWcit period and may play a role in the
protection of cellular machinery against photo-oxidation
by ROS [109].
Role of sugars and other osmolytes in response to drought
stress
Plants tend to cope with water deWcit stress by a process
known as osmotic adjustment. In this process, plants
decrease their cellular osmotic potential by the accumulation of solutes. Certain metabolic processes are triggered in
response to stress, which increase the net solute concentration in the cell, thereby helping the movement of water into
the leaf resulting in increase in leaf turgor. Large numbers
of compounds are synthesized, which play a key role in
maintaining the osmotic equilibrium and in the protection
of membranes as well as macromolecules. These compounds include proline, glutamate, glycine-betaine, carnitine, mannitol, sorbitol, fructans, polyols, trehalose,
sucrose, oligosaccharides and inorganic ions like K+. These
compounds help the cells to maintain their hydrated state
and therefore function to provide resistance against
drought and cellular dehydration [108,110]. The hydroxyl
group of sugar alcohols substitutes the OH group of water
to maintain the hydrophilic interactions with the membrane lipids and proteins. Thus, these molecules help to
maintain the structural integrity of the membranes. The
most striking property of these stress-accumulated solutes
is that they do not intervene with cells normal metabolic
processes. The species, which synthesize large quantities of
solutes, are known as osmotic adjusters for example Vigna
unguiculata.
149
In response to a stress, the carbohydrate status of a leaf
gets altered and this might serve as a metabolic signal in
response to stress [111,112]. Whereas the starch synthesis is
normally under strong inhibition even under moderate
water deWcit condition [113], the concentration of soluble
sugars in general increases or at least remains constant
under a stress condition [114]. Recent studies report the
accumulation of simple sugars such as glucose and fructose
following an increase in the invertase activity in the leaves
of the drought challenged plants [114,115].
There was a direct correlation between the activities of
acid vacuolar invertase with the concentration of ABA in
the xylem sap [115]. ABA has been implicated in enhancing
the activity and expression of vacuolar invertase [115].
There may also be a direct control of ABA biosynthesis by
glucose as the transcript of several genes responsible for
ABA synthesis was increased by glucose in Arabidopsis
seedlings [116]. A signaling pathway, which is initiated by
diVerent elicitors such as light, water and CO2 may converge down stream and be integrated as sugar signals
[117,118]. Whereas, a decline in the sugar level triggers an
increase in the plants photosynthetic activity due to a derepression of sugar control on transcription, the accumulation of sugar due to its low utilization have opposite eVect
on photosynthetic activity [117].
There may exist cross talk between the sugars and plant
hormones such as ABA and ethylene. Glucose and ABA
signaling act in coordination regulating plants growth and
development. Whereas high concentration of ABA and
sugars act to inhibit growth in a severe drought stress, low
concentration can promote growth. The inhibitory inXuence of glucose on growth could be overcome by ethylene
[119]. These interactions appear to be dependent on the
concentration as well as tissue speciWc localization of these
hormones.
Osmolytes in low accumulation function in protecting
macromolecules either by stabilizing the tertiary structure
of protein or by scavenging ROS produced in response to
drought [120]. However, higher accumulation of osmolytes
in transgenic plants can cause impaired growth in the
absence of any stress probably due to plants adaptation
strategy to conserve water in acute stress [121,122]. Therefore, controlled synthesis of osmolytes is the main concern
in designing transgenic strategies for crop improvement.
Oligosaccharides such as raYnose and galactinol are
among the sugars synthesized in response to drought. These
compounds seem to function as osmoprotectants rather
than providing osmotic adjustment [123]. Mannitol is one
of the most widely distributed sugar alcohol in nature and
functions to scavenge the ROS, hydroxyl radicals and it
also stabilizes the macro molecular structure of enzymes
[124,125]. These osmolytes form hydrogen bonds with macromolecules under water deWcit condition and prevent the
formation of intramolecular hydrogen bonds, which could
irreversibly damage the 3-dimensional structure of protein.
Trehalose is a non-reducing disaccharide of glucose and
has been shown to exert its positive inXuence during
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drought by stabilizing membranes and macromolecules.
Trehalose over-expression helps in the maintenance of an
elevated capacity for photosynthesis primarily due to
increased protection of PS II against photooxidation [126].
Some of the compatible solutes such as betaines, ectoine
and proline accumulate in plants in response to various
environmental stresses [127,128]. Proline is one of the
amino acids, which appear most commonly in response to
stress. Plants synthesize proline from glutamine in their
leaves. Some of the crop plants for instance wheat is
marked by low level of these compounds and correspondingly the accumulation and mobilization of proline was
found to increase tolerance towards water deWcit stress
[129]. The over-expression of P5CS (pyrroline-5-carboxylate synthase) gene from Vigna aconitifolia in tobacco, lead
to increased levels of proline and consequently improved
growth under drought stress [130].
The maintenance of membrane Xuidity is an important
parameter against stress injury. Rehydration, after a long
period of dehydration can also cause disruption of membrane integrity and leakage of solutes. During rehydration,
water replaces sugar at the membrane surface leading to a
transient membrane leakage [108]. Heat shock proteins
(HSPs) are synthesized in response to cold as well as dehydration. These HSPs act as molecular chaperones and protect the associated protein both during dehydration as well
as rehydration process. These HSPs help the protein to
maintain its tertiary structure and minimize the aggregation and degradation of proteins [131]. The small HS
(smHS) for instance the over-expression of AtHSP17.6A
class from Arabidopsis could increase salt and drought
stress due to its chaperone-like activity [132].
Role of MAP kinases in osmotic stress
In plants several MAPKs (mitogen activated protein
kinase) are activated in response to hyperosmotic stress. In
alfalfa, a 46 kDa MAP kinase named SIMK (salt stress
inducible MAPK) became activated in response to moderate hyperosmotic stress [133]. In tobacco cells, a SIMK-like
MAP kinase named SIPK (salicylic acid-induced protein
kinase) was activated by hyperosmotic stress [134]. Transcript level for a number of protein kinases including a twocomponent histidine kinase MAPKKK, MAPKK and
MAPK increases in response to osmotic stress [134]. This
ultimately results in the accumulation of osmolytes that
helps reestablish the osmotic balance, protection from
stress damage or repair mechanisms by induction of LEA/
dehydrin-type stress genes.
Osmotic stress activates phospholipids signaling
Membrane phospholipids constitute a dynamic system
that generates a multitude of signaling molecules like inositol
1,4,5-triphosphate (IP3), diacylglycerol (DAG), phosphatidic
acid (PA), etc. [59]. Phospholipase C (PLC) catalyzes the
hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2)
into IP3 and DAG, which acts as second messengers. IP3
releases Ca2+ from internal stores. Several studies have
shown that in various plants systems IP3 levels rapidly
increase in response to hyperosmotic stress [135–137]. IP3 levels also increased upon treatment with exogenous ABA in
Vicia faba guard cell protoplast [138] and in Arabidopsis
seedlings [139]. An Arabidopsis PLC gene, AtPLC, is also
induced by salt and drought stress [140]. In guard cells, IP3
induced Ca2+ increase in the cytoplasm lead to stomatal closure and thus retention of water in the cells [141]. Microinjection as well as pharmacological experiments suggested that
increase in the cytoplasmic Ca2+ could lead to the expression
of osmotic stress responsive genes [142].
Osmotic stress activates Phospholipase D (PLD) activity
in the suspension cells of Chlamydomonas, tomato, and
alfalfa [143]. PLD cleaves membrane phospholipids to produce PA and free head groups. PLD was rapidly activated
in response to drought stress in two plant species, i.e., Craterostigma plantagineum and Arabidopsis [144,145]. When
drought stress-induced PLD activity was compared
between drought-resistant and sensitive cultivars of cowpea, it was found that activity was higher in the droughtsensitive cultivars [146]. Consistent with this observation,
blocking PLD activity resulted in reduced stress injury and
improved freezing tolerance. This suggests that PLD activation results in lipolitic membrane disintegration during
stress injuries. Interestingly, the PLD product, PA has
emerged as a molecule to mitigate the eVect of stress injury.
The application of PA mimics the eVect of ABA in inducing
the closure of stomata [147].
A generic pathway in response to salt, drought and cold
stress is described in Fig. 3. Salt and drought exert their inXuence on a cell by disrupting the ionic and osmotic equilibrium
resulting in a stress condition. Thus excess of Na+ ions and
osmotic changes in the form of turgor pressure are the initial
triggers of this pathway. This leads to a cascade of events,
which can be grouped under ionic and osmotic signaling
pathway, the out come of which is ionic and osmotic homeostasis, leading to stress tolerance. These stresses are marked by
symptoms of stress injury including chlorosis and necrosis
and may also exert its negative inXuence on cell division
resulting in growth retardation of plant. Reduction in shoot
growth, especially, leaves is beneWcial for plant as it reduces
the surface area exposed for transpiration hence minimizing
water loss. Plants may also sacriWce or shed their older leaves,
which is another adaptation in response to drought. Stress
injury may occur through denaturation of cellular proteins/
enzymes or through the production of ROS, Na+ toxicity and
disruption of membrane integrity. In response to a stress
injury plants trigger a detoxiWcation process, which may
include change in the expression of LEA/dehydrin type gene
synthesis of molecular chaperones, proteinases, enzymes for
scavenging ROS and other detoxiWcation proteins. This process functions in the control and repair of stress induced damage and results in stress tolerance. Cold stress mainly results in
disruption of membrane integrity leading to severe cellular
dehydration and osmotic imbalance. Cold acclimation results
S. Mahajan, N. Tuteja / Archives of Biochemistry and Biophysics 444 (2005) 139–158
Ion
ic s
tres
s
SALT
O
sm
ic
ot
Activation of
Stress genes
DROUGHT
ss
re
st
(1) ABA causes seed dormancy and delays its germination.
(2) ABA promotes stomatal closure.
COLD
Disruption of membrane
integrity, dehydration,
solute leakage and
metabolic dysfunction
Stress
induced injury
Activation of
Stress genes
Detoxification
signaling
Ionic and osmotic
Regulation of cell
homeostasis via SOS
division and
pathway or related pathways
expansion
Damage control
and repair
Growth inhibition
151
Restructuring of cell
membrane and
synthesis of osmolytes
STRESS TOLERANCE
Fig. 3. A generic pathway under salt, drought and cold stress. Salt and
drought disrupt the ionic and osmotic equilibrium of the cell resulting in a
stress condition. This triggers the process, which functions to reinstate
ionic and osmotic homeostasis leading to stress tolerance. Stress imposes
injury on cellular physiology and result in metabolic dysfunction. This
injury imposes a negative inXuence on cell division and growth of a plant.
This is an indirect advantage to the plant as reduction of leaf expansion
reduces the surface area of leaves exposed for transpiration and thereby
reducing water loss. Stress injury and ROS generated in response to stress
also triggers a detoxiWcation signaling by activating genes responsible for
damage control and repair mechanism therefore leading to stress tolerance. Cold stress mainly exerts its malicious eVect by disruption of membrane integrity and solute leakage. Moreover, other physiological factors
such as rate of photosynthesis, protein assembly and general metabolic
processes are severely hampered. Cold acclimation results in the restructuring of cellular membranes and synthesis of various osmolytes, which
function towards reinstating the normal cellular metabolism and stress
tolerance.
in the triggering of various genes, which result in restructuring
of the cellular membranes by change in the lipid composition
and generation of osmolytes, which prevent cellular dehydration therefore leading to stress tolerance.
ABA and abiotic stress signaling
ABA is an important phytohormone and plays a critical
role in response to various stress signals. The application of
ABA to plant mimics the eVect of a stress condition. As
many abiotic stresses ultimately results in desiccation of the
cell and osmotic imbalance, there is an overlap in the
expression pattern of stress genes after cold, drought, high
salt or ABA application. This suggests that various stress
signals and ABA share common elements in their signaling
pathways and these common elements cross talk with each
other, to maintain cellular homeostasis [34,148–150]. Functions of ABA include:
ABA levels are induced in response to various stress signals. ABA actually helps the seeds to surpass the stress conditions and germinate only when the conditions are
conducive for seed germination and growth. ABA also prevents the precocious germination of premature embryos.
Stomatal closure under drought conditions prevents the
intracellular water loss and thus ABA is aptly called as a
stress hormone.
The main function of ABA seems to be the regulation of
plant water balance and osmotic stress tolerance. Several
ABA deWcient mutants namely aba1, aba2 and aba3 have
been reported for Arabidopsis [151]. ABA deWcient mutants
for tobacco, tomato and maize have also been reported
[152]. Without any stress treatment the growth of these
mutants is comparable to wild type plants. Under drought
stress, ABA deWcient mutants readily wilt and die if the
stress persists. Under salt stress also ABA deWcient mutants
show poor growth [139]. In addition, ABA is required for
freezing tolerance, which also involves the induction of
genes in response to dehydration stress [139,153].
Processes that trigger activation of ABA synthesis and
inhibition of its degradation result in ABA accumulation.
Several ABA biosynthesis genes have been cloned which
includes zeathanxin epoxidase (known as ABA1 in Arabidopsis), [154], 9-cis-epoxycarotenoid dioxygenase (NCED)
[155], ABA aldehyde oxidase and ABA3 also known as
LOS5 [139].
Studies suggest that osmotic stress imposed by high salt
or drought is transmitted through at least two pathways;
one is ABA-dependent and the other ABA independent.
Cold exerts its eVects on gene expression largely through an
ABA-independent pathway [150]. ABA induced expression
often relies on the presence of cis acting element called
ABRE [34,149,150,156]. Genetic analysis indicates that
there is no clear line of demarcation between ABA-dependent and ABA-independent pathways and the components
involved may often cross talk or even converge in the signaling pathway [157,158]. Calcium, which serves as a second messenger for various stresses, represents a strong
candidate, which can mediate such cross talk. Several studies have demonstrated that ABA, drought, cold and high
salt result in rapid increase in calcium levels in plant cells
[141,159,160]. The signaling pathway results in the activation of various genes, which play signiWcant role towards
the maintenance of cellular homeostasis.
Role of transcription factors in the activation of stress
responsive genes
The promoters of stress responsive genes have typical
cis-regulatory elements like DRE/CRT, ABRE, MYCRS/
MYBRS and are regulated by various upstream transcriptional factors (Fig. 4). These transcription factors fall in the
152
S. Mahajan, N. Tuteja / Archives of Biochemistry and Biophysics 444 (2005) 139–158
Drought
Drought
Cold
Cold
Salt
Salt
Ca2+
ICE
inactive
MYB
HOS1
ICE active
TATA
MYC G BOX
CBF1,2,3/
DREB1B,
1C,1A
ABA
SCOF
SCOF
ABA
AB
ABA
activates
A
DREB2A,
DREB2A, 2B
2B
bZIP
SOS pathway
SOS3/SOS2
~ PO4
SOS1
MYC/MYB
SGBF
SGBF
DRE/CRT
ABRE
MYCRS/
MYBRS
mRNA
Fig. 4. Involvement of diVerent transcription factors in response to cold, salinity and drought pathways in the induction of stress genes. Various transcription factors such as CBF1, 2 and 3 are triggered in response to cold stress and mediate their inXuence on stress genes mainly via ABA-independent pathway. Transcription factors such as SCOF-1 and SGBF-1 seem to follow ABA dependent pathway for expression of genes involved in imparting cold
tolerance. Osmotic stress signaling generated via salinity and drought stress seems to be mediated by transcription factors such as DREB2A, DREB2B,
bZip and MYC and MYB transcription activators, which interacts with CRT/DRE, ABRE or MYCRE/MYBRE elements in the promoter of stress
genes. Salinity mainly works through SOS pathway reinstating cellular ionic equilibrium.
category of early genes and are induced within minutes of
stress. The transcriptional activation of some of the genes
including RD29A has been well worked out. The promoter
of this gene family contains both ABRE as well as DRE/
CRT elements [36]. Transcription factors, which can bind
to these elements were isolated and were found to belong to
AP2/EREBP family and were designated as CBF1/
DREB1B,
CBF2/DREB1C,
and
CBF3/DREB1A
[36,161,162]. These transcription factors (CBF1, 2 and 3)
are cold responsive and in turn bind CRT/DRE elements
and activate the transcription of various stress responsive
genes. A novel transcription factor responsive to cold as
well as ABA was isolated from soybean and termed as
SCOF-1 (soybean zinc Wnger protein). This transcription
factor, however, was not responsive to drought or salinity
stress [163]. SCOF1 was a zinc Wnger nuclear localized protein but failed to bind directly to either CRT/DRE or
ABRE elements. Yeast 2-hybrid study revealed that SCOF1 interacted strongly with SGBF-1 (Soybean G-box binding bZip transcription factor) and in vitro DNA binding
activity of SGBF-1 to ABRE elements was greatly
improved by the presence of SCOF-1. This study supported
that protein–protein interaction is essential for the activation of ABRE-mediated cold responsive genes [163]. Transcription factors like DREB2A and DREB2B gets
activated in response to dehydration and confer tolerance
by induction of genes involved in maintaining the osmotic
equilibrium of the cell [37]. Several basic leucine zipper
(bZip) transcription factors (namely ABF/AREB) have
been isolated which can speciWcally bind to ABRE element
and activate the expression of stress genes [156,164]. These
AREB genes (AREB1 and AREB2) are ABA responsive
and need ABA for their full activation. These transcription
factors exhibited reduced activity in the ABA-deWcient
mutant aba2 as well as in ABA insensitive mutant aba1-1.
Some of the stress responsive genes for example RD22 lack
the typical CRT/DRE elements in their promoter indicating their regulation by other mechanisms. Transcription
factor RD22BP1 (a MYC transcription factor) and
AtMYB2 (a MYB transcription factor) could bind
MYCRS (MYC recognition sequence) and MYBRS (MYB
recognition sequence) elements, respectively, and could
cooperatively activate the expression of RD22 gene [165].
As cold, salinity and drought stress ultimately impair the
osmotic equilibrium of the cell it is likely that these transcription factors as well as the major stress genes may cross
talk with each other for their maximal response and help in
reinstating the normal physiology of the plant.
Role of CBL and CIPK genes in response to abiotic stresses
in plants
Signaling pathway is complex as it involves the coordinated action of various genes in a single pathway or diverse
pathways. Calcium is a prime candidate, which functions as
a central node in mediating the coordination and synchronization of diverse stimuli into speciWc cellular responses.
Thus, the proteins, which sense cytoplasmic Ca2+ perturbations and relay this information to downstream molecules,
serve as an important component of signaling. In plant cell
many calcium sensors have been recognized which include
calmodulin (CaM) and calmodulin-related proteins
S. Mahajan, N. Tuteja / Archives of Biochemistry and Biophysics 444 (2005) 139–158
153
Table 2
Expression of CBL and CIPK genes in response to abiotic stresses
CBL and CIPK genes
Responsive to stress/hormones/sugars
Species
Reference
CBL1
CBL2
CBL3
Salt, drought and cold. Negative regulator of cold signaling
Light and G.A
Late induced under cold, salt, S.A and proposed to be involved
in maintenance of stress response
Salt stress
ABA
Negative regulator of ABA signaling and promotes seed germination.
Expression induced strongly in response to cold followed by
drought salinity, wounding and ABA signaling. May act as a cross
talk node between ABA-dependent and independent signaling
Transgenic plants overexpressing CIPK8 were resistant to high level
of glucose indicating its role in sugar signaling
mRNA level was up-regulated in response to sugars such as sucrose,
glucose and fructose
Arabidopsis
Arabidopsis & Oryza sativa
Pisum sativum
[172,174]
[175,176]
(Unpublished data)
Arabidopsis
Arabidopsis
Arabidopsis
Arabidopsis
[56,61,70,177,178]
[64]
[173]
[171]
Arabidopsis
[179]
Arabidopsis
[180]
CBL4/SOS3
CBL5
CBL9
CIPK3
CIPK8/PKS11
CIPK14
[166,167], Ca2+-dependent protein kinases (CDPKs)
[159,168,169] and the relatively recently discovered sensor
CBL (calcineurin B-like) protein [56]. CBLs are characterized by 4 helix-loop-helix calcium binding domains termed
as EF hands. Currently, 10 isoforms of CBL have been discovered in Arabidopsis and named as CBL due to their signiWcant sequence similarity to animal calcineurin B. Despite
this sequence similarity, Arabidopsis lacks calcineurin in its
data bank [170]. Various isoforms of CBL are up-regulated
in stress condition (refer Table 2). CBLs speciWcally interact
with a class of kinases known as CBL-interacting protein
kinase (CIPKs) to transduce the signal via phosphorylation
of downstream signaling components.
Presently the direction of research is more towards isolation of master switches, which can control these stress
genes. As cytosolic calcium upregulation is more or less a
universal phenomenon associated with stress signaling, thus
the calcium sensors, which decode these Ca2+ signatures
and relay the information down stream, may act as master
switches in controlling various stress genes. Moreover,
mutations in these calcium sensors like AtCBL1 and their
interacting protein kinases have been shown to cause aberrations in the expression of some of the major stress
responsive genes like RD29A, KINI, KIN2 and RD22 indicating their immense signiWcance in stress signaling [171–
173].
Conclusion and future prospects
Abiotic stress signaling is an important area with respect
to increase in plant productivity. Therefore, the basic
understanding of the mechanisms underlying the functioning of stress genes is important for the development of
transgenic plants. Each stress is a multigenic trait and
therefore their manipulation may result in alteration of a
large number of genes as well as their products. A deeper
understanding of the transcription factors regulating these
genes, the products of the major stress responsive genes and
cross talk between diVerent signaling components should
remain an area of intense research activity in future.
The knowledge generated through these studies should
be utilized in making transgenic plants that would be able
to tolerate stress condition without showing any growth
and yield penalty. In the improvement of crops it is very
important to perturb the natural machinery as minimum as
possible and activate the stress genes at a correct time.
Therefore, it is desirable that appropriate stress inducible
promoters should drive the stress genes as well as transcription factors, which will minimize their expression under a
non-stressed condition thereby reducing yield penalty. The
product of these genes should also be targeted to the
desired tissue as well as cellular location to control the timing as well as intensity of expression.
Attempts should be made to design suitable vectors for
stacking relevant genes of one pathway or complementary
pathways to develop durable tolerance. These genes should
preferably be driven by a stress inducible promoter to have
maximal beneWcial eVects. Additionally, due importance
should be laid on the physiological parameters such as the
relative content of diVerent ions present in the soil as well as
the water status of the crop in designing transgenic plants
for the future.
Acknowledgments
We thank Dr. Renu Tuteja for critically reading the
manuscript and the Department of Biotechnology, Government of India grant for partial support and Council of ScientiWc and Industrial Research, New Delhi for fellowship to
S.M. We apologize if some references could not been cited
due to space constraint.
References
[1] E.A. Bray, J. Bailey-Serres, E. Weretilnyk, Responses to abiotic
stresses, in: W. Gruissem, B. Buchannan, R. Jones (Eds.), Biochemistry and Molecular Biology of Plants, American Society of Plant Biologists, Rockville, MD, 2000, pp. 158–1249.
[2] H.G. Jones, M.B. Jones, Introduction: some terminology and common
mechanisms, in: H.G. Jones, T.J. Flowers, M.B. Jones (Eds.), Plants
Under Stress, Cambridge university Press, Cambridge, 1989, pp. 1–10.
154
S. Mahajan, N. Tuteja / Archives of Biochemistry and Biophysics 444 (2005) 139–158
[3] D.V. Lynch, Chilling injury in plants: the relevance of membrane lipids, in: F. Katterman (Ed.), Environmental Injury to Plants, Academic
press, New York, 1990, pp. 17–34.
[4] .L. Guy, cold acclimation and freezing stress tolerance: role of protein
metabolism, Annu. Rev. Plant. Physiol. 41 (1990) 187–223.
[5] W.G. Hopkins, The physiology of plants under stress, in: Introduction
to Plant Physiology, second ed., Wiley, New York, 1999, pp. 451–475.
[6] Q.W Jiang, O. Kiyoharu, I. Ryozo, Two novel mitogen-activated protein signaling components, OsMEK1 and OsMAP1, are involved in a
moderate low-temperature signaling pathway in Rice1, Plant Physiol.
129 (2002) 1880–1891.
[7] P.L. Steponkus, Role of the plasma membrane in freezing injury and
cold acclimation, Annu. Rev. Plant. Physiol. 35 (1984) 543–584.
[8] P.L. Steponkus, M. Uemura, M.S. Webb, A contrast of the cryostability of the plasma membrane of winter rye and spring oat-two species
that widely diVer in their freezing tolerance and plasma membrane
lipid composition, in: P.L. Steponkus (Ed.), Advances in Low-Temperature Biology, vol. 2, JAI Press, London, 1993, pp. 211–312.
[9] B.D. McKersie, S.R. Bowley, Active Oxygen and Freezing Tolerance
in Transgenic Plants, Plant Cold Hardiness, Molecular Biology, Biochemistry and Physiology, Plenum, New York, 1997, pp. 203–214.
[10] C.R. Olien, M.N. Smith, Ice adhesions in relation to freeze stress,
Plant Physiol. 60 (1997) 499–503.
[11] M. Uemura, P.L. Steponkus, EVect of Cold Acclimation on Membrane Lipid Composition and Freeze Induced Membrane Destabilization, Plant Cold Hardiness. Molecular Biology, Biochemistry and
Physiology, Plenum, New York, 1997, pp. 171–79.
[12] A. Kacperska, Metabolic consequences of low temperature stress in
chilling-insensitive plants, in: P.H. Li (Ed.), Low Temperature
Stress Physiology in Crops, CRC Press, Boca Raton, FL, 1989, pp.
27–40.
[13] J.K. Raison, G.R. Orr, Phase transition in liposomes formed from
polar lipids of mitochondria from chilling sensitive plants, Plant
Physiol. 81 (1986) 807–811.
[14] J.P. Williams, M.U. Kahn, K. Mitchell, G. Johnson, The eVect of temperature on the level and biosynthesis of unsaturated fatty acids in
diaglycerols of Brassica napus leaves, Plant Physiol. 87 (1988) 904–
910.
[15] A.R. Cossins, Homeoviscous adaptation of biological membranes and
its functional signiWcance, in: A.R. Cossins (Ed.), temperature Adaptation of Biological membranes, Portland Press, London, 1994, pp.
63–76.
[16] D.V. Lynch, G.A. Thompson Jr., Low temperature-induced alterations in the chloroplast and microsomal membrane of Dunaliella
salina, Plant Physiol. 69 (1982) 1369–1375.
[17] H. Knight, A.J. Trewavas, M.R. Knight, Cold calcium signaling in
Arabidopsis involves two cellular pools and a change in calcium signature after acclimation, Plant Cell 8 (1996) 489–503.
[18] P.G. Jones, M. Inouye, The cold shock response—a hot topic, Mol.
Microbiol. 11 (1994) 811–818.
[19] I. Nishida, N. Murata, Chilling sensitivity in plants and Cyanobacteria: the crucial contribution of membrane lipid, Annu. Rev. Plant
Physiol. Plant Mol. Biol. 47 (1996) 541–568.
[20] C. Guy, D. Haskell, Q.B. Li, Association of proteins with the stress 70
molecular chaperones at low temperature evidence for the existence
of cold labile proteins in spinach, Cryobiology 36 (1998) 301–314.
[21] C.L. Guy, Q.B. Li, The organization and evolution of the spinach stress
70 molecular chaperone gene family, Plant Cell 10 (1998) 539–556.
[22] S. Gibson, V. Arondel, K. Iba, C. Somerville, Cloning of a temperature-regulated gene encoding a chloroplast Omega-3 desaturase from
Arabidopsis thaliana, Plant Physiol. 106 (1994) 1615–1621.
[23] Anderson, Q.B. Li, D.W. Haskell, C.L. Guy, Structural organization
of the spinach endoplasmic reticulum-luninal 70-kilodalton heatshock cognate gene and expression of 70-kilodalton heat shock genes
during cold acclimation, Plant Physiol. 104 (1994) 1359–1370.
[24] P. Krishna, M. Sacco, J.F. Cherutti, S. Hill, Cold-induced accumulation of hsp 90 transcripts in Brasscia napus, Plant Physiol. 107 (1995)
915–923.
[25] T. Mizoguchi, N. Hayashida, K. Yamaguchi-Schinozaki, H. Kamada,
K. Shinozaki, AtMPKs: a gene family of plant MAP Kinases in Arabidopsis thaliana, FEBS Lett. 336 (1993) 440–444.
[26] T. Mizoguchi, K. Irie, T. Hirayama, N. Hayashida, K. YamaguchiShinozaki, et al., A gene encoding a mitogen activated protein kinase
kinase kinase is induced simultaneously with genes for a mitogen-activated protein kinase and an S6 ribosomal protein kinase by touch,
cold and water stress in Arabidopsis thaliana, Proc. Natl. Acad. Sci.
USA 93 (1996) 765–769.
[27] D.H. Polisensky, J. Braam, Cold shock regulation of the Arabidopsis
TCH genes and the eVects of modulating intracellular calcium levels,
Plant Physiol. 111 (1996) 1271–1279.
[28] TJ. Close, Dehydrins: a commonality in the response of plants to
dehydration and low temperature, Physiologia Plantarum 100 (1997)
291–296.
[29] L. Dure III, A repeating 11-mer amino acid motif and plant desiccation, Plant J. 3 (1993) 363–369.
[30] J. Ingram, D. Bartels, The molecular basis of dehydration tolerance in
plants, Annu. Rev. Plant Physiol. Plant Mol. Biol. 47 (1996) 377–403.
[31] N.N. Artus, M. Uemura, P.L. Steponkus, S.J. Gilmour, C.T. Lin, M.F.
Thomashow, Constitutive expression of the cold regulated Arabidopsis thaliana COR 15a gene aVects both chloroplast and protoplast
freezing tolerance, Proc. Natl. Acad. Sci. USA 93 (1996) 13404–13409.
[32] A.F. Monroy, Y. Castonguay, S. Laberge, F. Sarhan, L.P. Vezina, R.S.
Dhindsa, A new cold-induced alfalfa gene is associated with enhanced
hardening at sub zero temperature, Plant Physiol. 102 (1993) 873–879.
[33] M. Houde, R.S. Dhindsa, F. Sarhan, A molecular marker to select for
freezing tolerance in Gramineae, Mol. Gen. Genet. 234 (1992) 43–48.
[34] M.F. Thomashow, Plant cold acclimation: freezing tolerance genes
and regulatory mechanism, Annu. Rev. Plant Physiol. Plant Mol. Biol.
50 (1999) 571–599.
[35] K. Yamaguchi-Shinozaki, K. Shinozaki, A novel cis-acting element in
an Arabidopsis gene is involved in responsiveness to drought, lowtemperature, or high-salt stress, Plant Cell 6 (1994) 251–264.
[36] E.J. Stockinger, S.J. Gilmour, M.F. Thomashow, Arabidopsis thaliana
CBF1 encodes an AP2 domain-containing transcription activator
that binds to the C-repeat/DRE, a cis-acting DNA regulatory element
that stimulates transcription in response to low temperature and
water deWcit, Proc. Natl. Acad. Sci. USA 94 (1997) 1035–1040.
[37] Q. Liu, M. Kasuga, Y. Sakuma, H. Abe, S. Miura, et al., Two transcription factors, DREBI and DREB2, with an EREBP/AP2 DNA
binding domain separate two cellular signal transduction pathways in
drought and low temperature responsive gene expression respectively,
in Arabidopsis, Plant Cell 10 (1998) 1391–1406.
[38] H. Lee, L. Xiong, Z. Gong, M. Ishitani, B. Stevenson, J.K. Zhu, The
Arabidopsis HOS1 gene negatively regulates cold signal transduction and encodes a RING Wnger protein that displays cold-regulated nucleo-cytoplasmic partitioning, Genes Dev. 15 (2001) 912–
924.
[39] V. Chinnusamy, M. Ohta, S. Kanrar, B.H. Lee, X. Hong, M. Agarwal,
J.K. Zhu, ICE1: a regulator of cold-induced transcriptome and freezing tolerance in Arabidopsis, Genes Dev. 17 (2003) 1043–1054.
[40] S. Kim, C.S. An, Y.N. Hong, K.W. Lee, Cold-inducible transcription
factor, CaCBF, is associated with a homeodomain Leucine Zipper
protein in hot pepper, Mol. Cells 18 (2004) 300–30836.
[41] F. Abbasi, H. Onodera, S. Toki, H. Tanaka, S. Komatsu, OsCDPK 13,
a calcium-dependent protein kinase gene from rice, is induced by cold
and gibberellin in rice leaf sheath, Plant Mol. Biol. 55 (2004) 541–552.
[42] Z. Xin, J. Browse, Eskimo1 mutants of Arabidopsis are constitutively
freezing tolerant, Proc. Natl. Acad. Sci. USA 95 (1998) 7799–7804.
[43] A.F. Monroy, R.S. Dhindsa, Low temperature signal transduction:
induction of cold acclimation-speciWc genes of alfalfa by calcium at
25 °C, Plant Cell 7 (1995) 321–331.
[44] W. Wang, B. Vinocur, A. Altman, Plant responses to drought, salinity
and extreme temperatures: towards genetic engineering for stress tolerance, Planta 218 (2003) 1–14.
[45] X. Niu, R.A. Bressan, P.M. Hasegawa, J.M. Pardo, Ion homeostasis in
NaCl stress environments, Plant Physiol. 109 (1995) 735–742.
S. Mahajan, N. Tuteja / Archives of Biochemistry and Biophysics 444 (2005) 139–158
[46] T.J. Flowers, P.F. Troke, A.R. Yeo, The mechanisms of salt tolerance
in halophytes, Annu. Rev. Plant Physiol. 28 (1977) 89–121.
[47] H. Greenway, R. Munns, Mehcnaisms of salt tolerance in non halphytes, Annu. Rev. Plant Physiol. 31 (1980) 149–190.
[48] A.R. Yeo, Molecular biology of salt tolerance in the context of wholeplant physiology, J. Exp. Bot. 49 (1998) 915–929.
[49] T.J. Flowers, A.R. Yeo, Solute Transport in plants, Glasgow, Scotland, Blackie, vol. 176, 1992, pp. 45.
[50] A. Amtmann, D. Sanders, Mechanism of Na+ uptake by plant cells,
Adv. Bot. Res. 29 (1999) 75–112.
[51] E. Blumwald, G.S. Aharaon, M.P. Apse, Sodium transport in plant
cells, Biochem. Biophys. Acta (2000).
[52] Y. Braun, M. Hassidim, H.R. Lerner, L. Reinhold, Studies on H+translocating ATPase in plants of varying resistance to salinity. I.
Salinity during growth modulates the proton pump in the halophyte
Atriplex nummularia, Plant physiol. 81 (1986) 1050–1056.
[53] A.A. Watad, M. Reuveni, R.A. Bressan, P.M. Hasegawa, Enhanced
net K+ uptake capacity of NaCl-adapted cells, Plant Phyisol. 95
(1991) 1265–1269.
[54] G.R. Cramer, J. Lynch, A. Lauchli, E. Epstein, InXux of Na +, K+, and
Ca2+ into roots of salt-stressed cotton seedlings, Plant Physiol. 83
(1987) 510–516.
[55] A. Lauchli, S. Schubert, The role of calcium in the regulation of membrane and cellular growth processes under salt stress, NATO ASI Ser.
G. 19 (1989) 131–137.
[56] J. Liu, J.K. Zhu, A calcium sensor homolog required for plant salt tolerance, Science 280 (1998) 1943–1945.
[57] H. Knight, A.J. Trewavas, M.R. Knight, Calcium signalling in Arabidopsis thaliana responding to drought and salinity, Plant J. 12 (1997)
1067–1078.
[58] J.K. Zhu, J. Liu, L. Xiong, Genetic analysis of salt tolerance in Arabidopsis. Evidence for a critical role of potassium nutrition, Plant Cell 10
(1998) 1181–1191.
[59] J.K. Zhu, Salt and drought stress signal transduction in plants, Annu.
Rev. Plant Physiol. Plant Mol. Biol. 53 (2002) 247–273.
[60] M. Ishitani, J. Liu, U. Halfter, C.S. Kim, W. Shi, J.K. Zhu, SOS3 function in plant salt tolerance requires N-myristoylation and calcium
binding, Plant Cell 12 (2000) 1667–1677.
[61] J. Liu, M. Ishitani, U. Halfter, C.S. Kim, J.K. Zhu, The Arabidopsis
thaliana SOS2 gene encodes a protein kinase that is required for salt
tolerance, Proc. Natl. Acad. Sci. USA 97 (2000) 3730–3734.
[62] V. Albrecht, O. Ritz, S. Linder, K. Harter, J. Kudla, The NAF domain
deWnes a novel protein–protein interaction module conserved in Ca2+regulated kinases, EMBO J. 20 (2001) 1051–1063.
[63] U. Halfter, M. Ishitani, J.K. Zhu, The Arabidopsis SOS2 protein
kinase physically interacts with and is activated by the calcium-binding protein SOS3, Proc. Natl. Acad. Sci. USA 97 (2000) 3735–3740.
[64] Y. Guo, L. Xiong, C.P. Song, D. Gong, U. Halfter, J.K. Zhu, A calcium sensor and its interacting protein kinase are global regulators of
abscisic acid signaling in Arabidopsis, Dev. Cell 3 (2002) 233–244.
[65] N.H. Cheng, J.K. Pittman, J.K. Zhu, K.D. Hirschi, The protein kinase
SOS2 activates the Arabidopsis H+/Ca+ antiporter CAX1 to integrate
Ca transport and salt tolerance, J. Biol. Chem. 279 (2004) 2922–2926.
[66] H. Shi, M. Ishitani, C. Kim, J.-K. Zhu, The Arabidopsis thaliana salt
tolerance gene SOS1 encodes a putative Na+/H+ antiporter, Proc.
Natl. Acad. Sci. USA 97 (2000) 6896–6901.
[67] F.J. Quintero, M. Ohta, H. Shi, J.K. Zhu, J.M. Pardo, Reconstitution
in yeast of the Arabidopsis SOS signaling pathway for Na+ homeostasis, Proc. Natl. Acad. Sci. USA 99 (2002) 9061–9066.
[68] N. Uozumi, E.J. Kim, F. Rubio, T. Yamaguchi, S. Muto, et al., The
Arabidopsis HKT1 gene homolog mediates inward Na currents in
Xenopus laevis oocytes and Na uptake in Saccharomyces cerevisiae,
Plant Physiol. 122 (2000) 1249–1260.
[69] A. Rus, S. Yokoi, A. Sharkhuu, M. Reddy, B.H. Lee, et al., AtHKT1 is
a salt tolerance determinant that controls Na entry into plant roots,
Proc. Natl. Acad. Sci. USA 98 (2001) 14150–14155.
[70] Q.S. Qiu, Y. Guo, M. Dietrich, K.S. Schumaker, J.K. Zhu, Regulation
of SOS1, a plasma membrane Na/H exchanger in Arabidopsis thali-
155
ana, by SOS2 and SOS3, Proc. Natl. Acad. Sci. USA 99 (2002) 8436–
8441.
[71] M.P. Apse, G.S. Aharon, W.A. Snedden, E. Blumwald, Salt tolerance
conferred by over expression of a vacuolar Na+/H+ antiport in Arabidopsis, Science 285 (1999) 1256–1258.
[72] R.A. Gaxiola, R. Rao, A. Sherman, P. GrisaW, S. Alper, G.R. Fink,
The Arabidopsis thaliana proton transporters AtNhx1 and Avp1, can
function in cation detoxiWcation in yeast, Proc. Natl. Acad. Sci. USA
96 (1999) 1480–1485.
[73] C.W. Ford, Accumulation of low molecular weight solutes in water
stress tropical legumes, Phytochemistry 22 (1984) 875–884.
[74] R.A. Breesan, P.M. Hasegawa, J.M. Pardo, Plants use calcium to
resolve salt stress, Trends Plant Sci. 3 (1998) 411–412.
[75] A.J. Delauney, D.P.S. Verma, Proline biosynthesis and osmoregulation in plants, Plant J. 4 (1993) 215–223.
[76] P. Louis, E.A. Galinski, Characterization of genes for the biosynthesis
of the compatible solute ectoine from Marinococcus halophilus and
osmoregulated expression in E. coli, Microbiology 143 (1997) 1141–
1149.
[77] K.F. McCue, A.D. Hanson, Drought and salt tolerance: towards
understanding and application, Biotechnology 8 (1990) 358–362.
[78] D. Rhodes, A.D. Hanson, Quaternary ammonium and tertiary sulphonium compounds in higher plants, Annu. Rev. Plant Physiol. Mol.
Biol. 44 (1993) 357–384.
[79] A.D. Hanson, B. Rathinasabapathi, J. Rivoal, M. Burnet, M.O. Dillon, D.A. Gage, Osmoprotective compound in the Plumbaginaceae: a
natural experiment in metabolic engineering of stress tolerance, Proc.
Natl. Acad. Sci. USA 91 (1994) 306–310.
[80] R. Waditee, N.H. Bhuiyan, V. Rai, K. Aoki, Y. Tanaka, T. Hibino, S.
Suzuki, J. Takano, A.T. Jagendorf, T. Takabe, T. Takabe, Genes for
direct methylation of glycine provide high levels of glycine betaine
and abiotic-stress tolerance in Synechococcus and Arabidopsis, Proc.
Natl. Acad. Sci. USA 102 (2005) 1318–1323.
[81] S.W. Matson, D. Bean, J.W. George, DNA helicases; enzymes with
essential roles in all aspects of DNA metabolism, BioEssays 16 (1994)
13–21.
[82] N. Tuteja, R. Tuteja, DNA helicases: the long unwinding road, Nat.
Genet. 13 (1996) 11–12.
[83] T.M. Lohman, K.P. Bjornson, Mechanism of helicase-catalyzed DNA
unwinding, Ann. Rev. Biochem. 65 (1996) 169–214.
[84] N. Tuteja, R. Tuteja, Prokaryotic and eukaryotic DNA helicases.
Essential molecular motor proteins for cellular machinery, Eur. J.
Biochem. 271 (2004) 1835–1848.
[85] N. Tuteja, R. Tuteja, Unraveling DNA helicases. Motif, structure,
mechanism and function, Eur. J. Biochem. 271 (2004) 1849–1863.
[86] N. Sanan-Mishra, X.H. Phan, S.K. Sopory, N. Tuteja, Pea DNA helicase 45 overexpression in tobacco confers high salinity tolerance without aVecting yield, Proc. Natl. Acad. Sci. USA 102 (2005) 509–514.
[87] X.H. Pham, M.K. Reddy, N.Z. Ehtesham, B. Matta, N. Tuteja, A DNA
helicase from Pisum sativum is homologous to translation initiation factor and stimulates topoisomerase I activity, Plant J. 24 (2000) 219–229.
[88]A.A. Vashisht, A. Pradhan, R. Tuteja, N. Tuteja, Cold and salinity
stress-induced bipolar pea DNA helicase 47 is involved in protein
synthesis and stimulated by phosphorylation with protein kinase C,
Plant J. 44 (2005) 76–87.
[89] Z. Gong, C.H. Dong, H. Lee, J. Zhu, L. Xiong, D. Gong, B. Stevenson,
J.K. Zhu, A DEAD BOX RNA helicase is essential for mRNA export
and important for development and stress responses in Arabidopsis,
Plant Cell 17 (2005) 256–267.
[90] J.C. Cushman, H.J. Bohnert, Genomic approaches to plant stress tolerance, Curr. Opin. Plant Biol. 3 (2000) 117–124.
[91] E. Sivamani, A. Bahieldin, J.M. Wraith, T. Al-Niemi, W.E. Dyer,
T.H.D. Ho, R. Qu, Improved biomass productivity and water use
eYciency under water deWcit conditions in transgenic wheat constitutively expressing the barley HVA1 gene, Plant Sci. 155 (2000) 1–9.
[92] U. Schuppler, P.H. He, P.C.L. John, R. Munns, EVects of water stress
on cell division and cell-division-cycle-2-like cell-cycle kinase activity
in wheat leaves, Plant Physiol. 117 (1998) 667–678.
156
S. Mahajan, N. Tuteja / Archives of Biochemistry and Biophysics 444 (2005) 139–158
[93] T.J. MansWeld, C.J. Atkinson, Stomatal behaviour in water stressed
plants, in: R.G. Alscher, J.R. Cumming (Eds.), Stress Responses in
Plants: Adaptation and Acclimation Mechanisms, Wiley-Liss, New
York, 1990, pp. 241–264.
[94] J.A. Lake, F.I. Woodward, W.P. Quick, Long-distance CO2 signalling
in plants, J. Exp. Bot. 53 (2002) 183–193.
[95] S. Wilkinson, W.J. Davies, ABA-based chemical signalling: the coordination of responses to stress in plants, Plant Cell Environ. 25
(2002) 195–210.
[96] W. Hartung, A. Sauter, E. Hose, Abscisic acid in the xylem: where
does it come from, where does it go to? J. Exp. Bot. 53 (2002) 27–37.
[97] W.J. Davies, S. Wilkinson, B. Loveys, Stomatal control by chemical
signalling and the exploitation of this mechanism to increase water
use eYciency in agriculture, The New Phytol. 153 (2002) 449–460.
[98] R.E. Sharp, Interaction with ethylene: changing views on the role of
abscisic acid in root and shoot growth responses to water stress, Plant
Cell Environ. 25 (2002) 211–222.
[99] P.G. Blackman, W.J. Davies, Root-to-shoot communication in maize
plants of the eVects of soil drying, J. Exp. Bot. 36 (1985) 39–48.
[100] J. Bota, J. Flexas, H. Medrano, Is photosynthesis limited by
decreased Rubisco activity and RuBP content under progressive
water stress? New Phytol. 162 (2004) 671–681.
[101] F. Loreto, D. Tricoli, G. Di Marco, On the relationship between electron transport rate and photosynthesis in leaves of the C4 plant Sorghum bicolor exposed to water stress, temperature changes and
carbon metabolism inhibition, Aust. J. Plant Physiol. 22 (1995) 885–
892.
[102] S. Meyer, B. Genty, Mapping intercellular CO2 mole fraction (Ci) in
Rosa rubiginosa leaves fed with abscisic acid by using chlorophyll
Xuorescence imaging: signiWcance of Ci estimated from leaf gas
exchange, Plant Physiol. 116 (1998) 947–957.
[103] H. Li, L.A. Sherman, A redox-responsive regulator of photosynthesis
gene expression in the cyanobacterium Synechocystis sp. strain PCC
6803, J. Bacteriol. 182 (2000) 4268–4277.
[104] C.H. Foyer, G. Noctor, Redox sensing and signalling associated with
reactive oxygen in chloroplasts, peroxisomes and mitochondria,
Physiol. Plantarum 119 (2003) 355–364.
[105] B. Karpinska, G. Wingsle, S. Karpinski, Antagonistic eVects of
hydrogen peroxide and glutathione on acclimation to excess excitation energy in Arabidopsis, IUBMB Life 50 (2000) 21–26.
[106] R. Desikan, M.K. Cheung, J. Bright, D. Henson, J. Hancock, S. Neill,
ABA, hydrogen peroxide and nitric oxide signaling in stomatal
guard cells, J. Exp. Bot. 55 (2004) 205–212.
[107] C. Bowler, M.V. Montagu, D. Inze, Superoxide dismutase and stress
tolerance, Ann. Rev. Plant Physiol. Plant Mol. Biol. 43 (1992) 83–
116.
[108] F.A. Hoekstra, E.A. Golovina, J. Buitink, Mechanisms of plant desiccation tolerance, Trends Plant Sci. 6 (2001) 431–438.
[109] H.H. Ratnayaka, W.T. Molin, T.M. Sterling, Physiological and antioxidant responses of cotton and spurred anoda under interference
and mild drought, J. Exp. Bot. 54 (2003) 2293–2305.
[110] S. Ramanjulu, D. Bartels, Drought- and desiccation-induced modulation of gene expression in plants, Plant Cell Environ. 25 (2002)
141–151.
[111] J.C. Jang, J. Sheen, Sugar sensing in higher plants, Trends Plant Sci. 2
(1997) 208–214.
[112] M.M. Chaves, J.P. Maroco, J.S. Pereira, Understanding plant
response to drought: from genes to the whole plant, Funct. Plant
Biol. 30 (2003) 239–264.
[113] M.M. Chaves, EVects of water deWcits on carbon assimilation, J. Exp.
Bot. 42 (1991) 1–16.
[114] C. Pinheiro, M.M. Chaves, C.P. Ricardo, Alterations in carbon and
nitrogen metabolism induced by water deWcit in the stems and leaves
of Lupinus albus L., J. Exp. Bot. 52 (2001) 1063–1070.
[115] J. Trouverie, C. The’venot, J.P. Rocher, B. Sotta, J.L. Prioul, The
role of abscisic acid in the response of a speciWc vacuolar invertase
to water stress in the adult maize leaf, J. Exp. Bot. 54 (2003) 2177–
2186.
[116] W.H. Cheng, A. Endo, L. Zhou, et al., A unique short-chain dehydro-genase/reductase in Arabidopsis glucose signaling and abscisic
acid biosynthesis and functions, The Plant Cell 14 (2002) 2732–2743.
[117] J.V. Pego, A.J. Kortstee, C. Huijser, S.C.M. Smeekens, Photosynthesis, sugars and the regulation of gene expression, J. Exp. Bot. 51
(2000) 407–416.
[118] S.L. Ho, Y.C. Chao, W.F. Tong, S.M. Yu, Sugar co-ordinately and
diVerentially regulates growth- and stress-related gene expression via
a complex signal transduction network and multiple control mechanisms, Plant Physiol. 125 (2001) 877–890.
[119] P. Leon, J. Sheen, Sugar and hormone connections, Trends Plant Sci.
8 (2003) 110–116.
[120] J.K. Zhu, Plant salt tolerance, Trends Plant Sci. 6 (2001) 66–71.
[121] A. Maggio, S. Miyazaki, P. Veronese, T. Fujita, J.I. Ibeas, B. Damsz,
M.L. Narasimhan, P.M. Hasegawa, R.J. Joly, R.A. Bressan, Does
proline accumulation play an active role in stress-induced growth
reduction? Plant J. 31 (2002) 699–712.
[122] T. Abebe, A.C. Guenzi, B. Martin, J.C. Chushman, Tolerance of
mannitol-accumulating transgenic wheat to water stress and salinity,
Plant Physiol. 131 (2003) 1748–1755.
[123] T. Taji, C. Ohsumi, S. Iuchi, M. Seki, M. Kasuga, M. Kobayashi, K.
Yamaguchi-Shinozaki, K. Shinozaki, Important roles of droughtand cold-inducible genes for galactinol synthase in stress tolerance in
Arabidopsis thaliana, Plant J. 29 (2002) 417–426.
[124] B. Shen, R.G. Jensen, H.J. Bohnert, Increased resistance to oxidative
stress in transgenic plants by targeting mannitol biosynthesis to
chloroplasts, Plant Physiol. 113 (1997) 1177–1183.
[125] B. Shen, R.G. Jensen, H.J. Bohnert, Mannitol protects against oxidation by hydroxyl radicals, Plant Physiol. 115 (1997) 527–532.
[126] A.K. Garg, J.K. Kim, T.G. Owens, A.P. Ranwala, Y.D. Choi, L.V.
Kochian, R.J. Wu, Trehalose accumulation in rice plants confers
high tolerance levels to diVerent abiotic stresses, Proc. Natl. Acad.
Sci. USA 99 (2002) 15898–15903.
[127] T.H.H. Chen, N. Murata, Enhancement of tolerance of abiotic stress
by metabolic engineering of betaines and other compatible solutes,
Curr. Opin. Plant Biol. 5 (2002) 250–257.
[128] D. Rontein, G. Basset, A. Hanson, Metabolic engineering of osmoprotectant accumulation in plants, Metab. Eng. 4 (2002) 49–56.
[129] H. Nayyar, D.P. Walia, Water stress induced proline accumulation
in contrasting wheat genotypes as aVected by calcium and abscisic
acid, Biol. Plantarum 46 (2003) 275–279.
[130] P.B. Kavi Kishor, Z. Hong, G.H. Miao, C.A.A. Hu, D.P.S. Verma,
Overexpression of D1-pyrroline-5-carboxylate synthetase increases
proline production and confers osmotolerance in transgenic plants,
Plant Physiol. 108 (1995) 1387–1394.
[131] M.E. Feder, G.E. Hofmann, Heat-shock proteins, molecular chaperones, and the stress response: evolutionary and ecological physiology, Ann. Rev. Physiol. 61 (1999) 243–282.
[132] W. Sun, C. Bernard, B.V.D. Cotte, M.V. Montagu, N. Verbruggen,
At-HSP17.6A, encoding a small heat-shock protein in Arabidopsis,
can enhance osmotolerance upon overexpression, Plant J. 27 (2001)
407–415.
[133] T. Munnik, W. Ligterink, I. Meskiene, O. Calderini, J. Beyerly, et al.,
Distinct osmosensing protein kinase pathways are involved in signaling moderate and severe hyperosmotic stress, Plant J. 20 (1999)
381–388.
[134] M. Mikolajczyk, S.A. Olubunmi, G. Muszynska, D.F. Klessig, G.
Dobrowolska, Osmotic stress induces rapid activation of a salicylic
acid-induced protein kinase and a homolog of protein kinase ASK1
in tobacco cells, Plant Cell 12 (2000) 165–178.
[135] D.B. DeWald, J. Torabinejad, C.A. Jones, J.C. Shope, A.R. Cangelosi, et al., Rapid accumulation of phosphatidylinositol 4,5-bisphosphate and inositol 1,4,5-trisphosphate correlates with calcium
mobilization in salt-stressed Arabidopsis, Plant Physiol. 126 (2001)
759–769.
[136] I. Heilmann, I.Y. Perera, W. Gross, W.F. Boss, Change in phosphoinositide metabolism with days in culture aVect signal transduction pathways in Galdieria suphuraria, Plant Physiol. 119 (1999) 1331–1339.
S. Mahajan, N. Tuteja / Archives of Biochemistry and Biophysics 444 (2005) 139–158
[137] S. Takahashi, T. Katagiri, T. Hirayama, K. Yamaguchi-Shinozaki,
K. Shinozaki, Hyperosmotic stress induced a rapid and transient
increase in inositol 1,4,5-trisphosphate independent of abscisic acid
in Arabidopsis cell culture, Plant Cell Physiol. 42 (2001) 214–222.
[138] Y. Lee, Y.B. Choi, J. Suh, J. Lee, S.M. Assmann, et al., Abscisic acidinduced phosphoinositide turnover in guard cell protoplasts of Vicia
faba, Plant Physiol. 110 (1996) 987–996.
[139] L. Xiong, M. Ishitani, H. Lee, J.K. Zhu, The Arabidopsis LOS5/
ABA3 locus encodes a molybdenum cofactor sulfurase and modulates cold stress- and osmotic stress-responsive gene expression,
Plant Cell 13 (2001) 2063–2083.
[140] T. Hirayama, C. Ohto, T. Mizoguchi, K. Shinozaki, A gene encoding
a phosphatidylinositol-speciWc phospholipase C is induced by dehydration and salt stress in Arabidopsis thaliana, Proc. Natl Acad. Sci.
USA 92 (1995) 3903–3907.
[141] D. Sanders, C. Brownlee, J.F. Harper, Communicating with calcium,
Plant Cell 11 (1999) 691–706.
[142] Y. Wu, J. Kuzma, E. Marechal, R. GraeV, H.C. Lee, et al., Abscisic
acid signaling through cyclic ADP-ribose in plants, Science 278
(1997) 2126–2130.
[143] T. Munnik, H.J.G. Meijer, B. ter Riet, W. Frank, D. Bartels, A. Musgrave, Hyperosmotic stress stimulates phospholipae D activity and
elevates the levels of phosphatidic acid and diacylglycerol pyrophosphate, Plant J. 22 (2000) 147–154.
[144] W. Frank, T. Munnik, K. Kerkmann, F. Salamini, D. Bartels, Water
deWcit triggers phospholipase D activity in the resurrection plant
Craterostigma plantagineum, Plant Cell 12 (2000) 111–123.
[145] T. Katagiri, S. Takahashi, K. Shinozaki, Involvement of a novel Arabidopsis phospholipase D, AtPLD delta, in dehydration-inducible
accumulation of phosphatidic acid in stress signaling, Plant J. 26
(2001) 595–605.
[146] H. El Maarouf, Y. Zuily-Fodil, M. Gareil, A. d’Arcy-Lameta, A.T.
Pham-Thi, Enzymatic activity and gene expression under water
stress of phospholipase D in two culitivars of Vigna unguiculata L.
Walp. DiVering in drought tolerance, Plant Mol. Biol. 39 (1999)
1257–1265.
[147] T. Jacob, S. Ritchie, S.M. Assmann, S. Gilroy, Abscisic acid signal
transduction in guard cells is mediated by phospholipase D activity,
Proc. Natl. Acad. Sci. USA 96 (1999) 12192–12197.
[148] J. Leung, J. Giraudat, Abscisic acid signal transduction, Annu. Rev.
Plant Physiol. Plant Mol. Biol. 49 (1998) 199–222.
[149] K. Shinozaki, K. Yamaguchi-Shinozaki, Molecular responses to
dehydration and low temperature: diVerences and cross-talk
between two stress signaling pathways, Curr. Opin. Plant Biol. 3
(2000) 217–223.
[150] R.R. Finkelstein, S.S.L. Gampala, C.D. Rock, Abscisic acid signaling
in seeds and seedlings, Plant Cell 14 (suppl.) (2002) S15–S45.
[151] M. Koornneef, K.M. Leon-Kloosterziel, S.H. Schwartz, J.A.D.
Zeevaart, The genetic and molecular dissection of abscisic acid biosynthesis and signal transduction in Arabidopsis, Plant Physiol. Biochem. 36 (1998) 83–89.
[152] S. Liotenberg, H. North, A. Marion-Poll, Molecular biology and regulation of abscisic acid biosynthesis in plants, Plant Physiol. Biochem. 37 (1999) 341–350.
[153] F. Llorente, J.C. Oliveros, J.M. Martinez-Zapater, J. Salinas, A freezing-sensitive mutant of Arabidopsis, frs1, is a new aba3 allele, Planta
211 (2000) 648–655.
[154] E. Marin, L. Nussaume, A. Quesada, M. Gonneau, B. Sotta, et al.,
Molecular identiWcation of zeaxanthin expoxidase of Nicotiana
plumbaginifolia, a gene involved in abscisic acid biosynthesis and
corresponding to the ABA locus of Arabidopsis thalian, EMBO J. 15
(1996) 2331–2342.
[155] B.C. Tan, S.H. Schwartz, J.A.D. Zeevaart, D.R. Mc-Carty, Genetic
control of abscisic acid biosynthesis in maize, Proc. Natl. Acad. Sci.
USA 94 (1997) 12235–12240.
[156] Y. Uno, T. Furihata, H. Abe, R. Yoshida, K. Shinozaki, K. Yamaguchi Shinozaki, Arabidopsis basic leucine zipper transcription factors
involved in an abscisic acid-dependent signal transduction pathway
[157]
[158]
[159]
[160]
[161]
[162]
[163]
[164]
[165]
[166]
[167]
[168]
[169]
[170]
[171]
[172]
[173]
[174]
[175]
[176]
157
under drought and high-salinity conditions, Proc. Natl. Acad. Sci.
USA 97 (2000) 11632–11637.
H. Knight, M.R. Knight, Abiotic stress signaling pathways: speciWcity and cross talk, Trends Plant Sci. 6 (2001) 262–267.
L. Xiong, J.K. Zhu, Abiotic stress signal transduction in plants: molecular and genetic perspectives, Physiol. Plant 112 (2001) 152–166.
D. Sanders, J. Pelloux, C. Brownlee, J.F. Harper, Calcium at the
crossroads of signaling, Plant Cell 14 (suppl.) (2002) S401–S417.
H. Knight, M.R. Knight, Imaging spatial and cellular characteristics
of low temperature calcium signature after cold acclimation in Arabidopsis, J. Exp. Bot. 51 (2000) 1679–1686.
S.J. Gilmour, D.G. Zarka, E.J. Stockinger, M.P. Salazar, J.M. Houghton, M.F. Thomashow, Low temperature regulation of the Arabidopsis
CBF family of AP2 transcriptional activators as an early step in coldinduced COR gene expression, Plant J. 16 (1998) 433–443.
J. Medina, M. Bargues, J. Terol, M. Perez-Alonso, J. Salinas, The
Arabidopsis CBF family is composed of three genes encoding AP2
domain containing proteins whose expression is regulated by low
temperature but not by abscisic acid or dehydration, Plant Physiol.
119 (1999) 463–470.
J.C. Kim, S.H. Lee, Y.H. Cheng, et al., A novel cold-inducible zinc
Wnger protein from soybean, SCOF-1, enhances cold tolerance in
transgenic plants, Plant J. 25 (2001) 247–259.
H.I. Choi, J.H. Hong, J.O. Ha, J.Y. Kang, S.Y. Kim, ABFs a family
of ABA-responsive element binding factors, J. Biol. Chem. 275
(2000) 1723–1730.
H. Abe, K. Yamaguchi-Shinozaki, T. Urao, T. Iwasaki, D. Hosakawa, K. Shinozaki, Role of Arabidopsis MYC and MYB homologs
in drought- and abscisic acid regulated gene expression, Plant Cell 9
(1997) 1859–1868.
R.E. Zielinski, Calmodulin and calmodulin-binding proteins in
plants, Ann. Rev. Plant Physiol. Plant Mol. Biol. 49 (1998) 697–725.
S. Luan, J. Kudla, M. Rodríguez-Concepción, S. Yalovsky, W. Gruissem, Calmodulins and calcineurin B-like proteins: calcium sensors
for speciWc signal response coupling in plants, Plant Cell 14 (2002)
S389–S400.
S.K. Sopory, M. Munchi, Protein kinases and phosphatases and
their role in cellular signaling in plants, Crit. Rev. Plant Sci. 17
(1998) 245–318.
S. Pandey, S.B. Tiwari, K.C. Upadhyaya, S.K. Sopory, Calcium signaling: linking environmental signals to cellular functions, Crit. Rev.
Plant Sci. 19 (2000) 219–318.
D. Gong, Y. Guo, K.S. Schumaker, J.K. Zhu, The SOS3 family of
calcium sensors and SOS2 family of protein kinases in Arabidopsis,
Plant Physiol. 134 (2004) 919–926.
K.N. Kim, Y.H. Cheong, J.J. Grant, G.K. Pandey, S. Luan, CIPK3, a
calcium sensor-associated protein kinase that regulates abscisic acid
and cold signal transduction in Arabidopsis, Plant Cell 15 (2003)
411–423.
Y.H. Cheong, K.N. Kim, G.K. Pandey, R. Gupta, J.J. Grant, S. Luan,
CBL1, a calcium sensor that diVerentially regulates salt, drought,
and cold responses in Arabidopsis, Plant Cell 15 (2003) 1833–1845.
G.K. Pandey, Y.H. Cheong, K.N. Kim, J.J. Grant, L. Li, W. Hung, C.
D‘Angelo, S. Weinl, J. Kudla, S. Luan, The calcium sensor calcineurin B-Like 9 modulates ABA sensitivity and biosynthesis in Arabidopsis, Plant Cell 16 (2004) 1912–1924.
V. Albrecht, S. Weinl, D. Blazevic, C. D’Angelo, O. Batistic, U.
Kolukisaoglu, R. Bock, B. Schulz, K. Harter, J. Kudla, The calcium
sensor CBL1 integrates plant responses to abiotic stresses, Plant J. 36
(2003) 457–470.
A. Nozawa, N. Koizumi, H. Sano, An Arabidopsis SNF1-related
protein kinase, AtSR1, interacts with a calcium-binding protein,
AtCBL2, of which transcripts respond to light, Plant Cell Physiol. 42
(2001) 976–981.
Y.S. Hwang, P.C. Bethke, Y.H. Cheong, H.S. Chang, T. Zhu, R.L.
Jones, A gibberellin-regulated calcineurin B in rice localizes to the
tonoplast and is implicated in vacuole function, Plant J. 138 (2005)
1347–1358.
158
S. Mahajan, N. Tuteja / Archives of Biochemistry and Biophysics 444 (2005) 139–158
[177] S.J. Wu, D. Lee, J.K. Zhu, SOS1, a genetic locus essential for
salt tolerance and potassium acquisition, Plant Cell 8 (1996)
617–627.
[178] M.J. Sanchez-Barrena, M. Martinez-Ripoll, J.K. Zhu, A. Albert, The
structure of the Arabidopsis thaliana SOS3: molecular mechanism of
sensing calcium for salt stress response, J. Mol. Biol. 345 (2005)
1253–1264.
[179] D. Gong, Z. Gong, Y. Guo, X. Chen, J.K. Zhu, Biochemical and
functional characterization of PKS11, a novel Arabidopsis protein
kinase, J. Biol. Chem. 277 (2002) 28340–28350.
[180] E.J. Lee, Hiromichi, H. Sano, N. Koizumi, Sugar responsible and tissue speciWc expression of a gene encoding AtCIPK14, an Arabidopsis CBL-interacting protein kinase, Biosci. Biotechnol. Biochem. 69
(2005) 242–245.