Inorganic Nutrients and Nutrient
uptake
Fig.
1
2
Table.
1
2
3
3
4
4
5
6
7
Plant and Inorganic Nutrients
• The acquisition of inorganic nutrients
(minerals) is part of the plant nutrition.
• Plant nutrition can be viewed as two parts:
organic nutrition, which is mainly dealing
with photosynthesis; and inorganic nutrition.
• Organic nutrition (photosynthesis) and
inorganic nutrition are highly
interdependent.
Chapter Outline
• Mineral nutrition
• The metabolic roles of
study methods
the 14 essential
mineral elements
• Essential and benefical
elements
• The concept of critical
and deficient
• Macronutrients and
concentration
micronutrients
• Deficiency symptoms
• Micronutrient toxicity
N.T. de Saussure found some elements might be
indispensable (essential) in plants.
C.S. Sprengel hypothesized that soils might be
unproductive even if only one necessary element is
deficient.
J.-B. Boussingault found quantitative relationships
between the effect of fertilizer and nutrient uptake on
crop yields. He also found legumes can assimilate
atmospheric nitrogen.
In 1860, Julius Sachs set up solution culture
(hydroponics), demonstrating plants could be grown to
maturity in defined nutrient solutions.
Table 12.1
Sach’s system contained nine mineral nutrient plus carbon,
hydrogen, and oxygen in the form of carbon dioxide and
water.
Table 12.2
Most modern formulations are based on a solution originally
developed by D.R. Hoagland, called modified Hoagland’s
solution.
Table 12.3
Figure 12.1
Solution culture
(hydroponics)
Solution must be
replenished
regularly or the
growth of plants
will be stopped.
Aeration to keep
plants from anoxia
Container painted
black or wrapped to
keep out light so the
growth of algae will
be reduced.
Because in solution culture the replenishment of
nutrient solution is a disadvantage, other methods
were developed.
In these methods, plants were grown in nonnutritive
medium (perlite 珍珠石 or vermiculite 蛭石) and
fresh nutrient solution was applied from the top (slop
culture) or slowly dripping from a reservoir (drip
culture).
perlite 珍珠石
vermiculite蛭石
Or subirrigation….
Figure 12.2
Nutrient film technique
(subirrigation)
Essential nutrient elements
There are 17 essential elements in plants.
Absence of any one of the element could prevent
plants from completing its normal life cycle or some
essential plant constituent or metabolite will not be
manufactured.
According to the relative concentrations found in
tissue (or the relative concentrations required in
nutrient solution), these 17 elements are classified as
macronutrients and micronutrients (trace elements).
Macronutrients are more than 10 mmole per kilogram
of dry weight, micronutrient are less than 10 mmole
per kilogram of dry weight.
Table 12.4
Beneficial elements
Sodium, Silicon, Cobalt, and Selenium are required
for some plants. Because they are not required for all
plants, they are called beneficial elements instead of
essential elements.
Beneficial elements - Sodium
Sodium is required for plants that have C4
photosynthetic pathway (ex. bladder salt bush). For
these, when sodium is deficient, they will exhibit
symptoms like
- reduced growth
- chlorosis (yellowing
due to loss of chlorophyll)
- necrosis (dead tissue)
of the leaves
Beneficial elements – Silicon
Silicon is particularly beneficial for grasses. It
accumulates in the cell walls to prevent lodging (stems
bent over by heavy winds or rain). It also has roles in
fending off fungal infections.
Beneficial elements - Cobalt
Cobalt is required for nitrogen fixing bacteria. So it
was found to be a requirement for legumes. However,
if fixed nitrogen is provided to legumes the need of
cobalt cannot be demonstrated.
Beneficial elements - Selenium
Selenium are probably not required for plants.
Although selenium is toxic to most plants and animals,
Astragalus spp. are known to accumulate selenium.
Eating Astragalus spp. causes alkali poisoning or
blind-staggers in grazing animals. They are called
“loco weeds”.
Nutrient roles and deficiency
symptoms
It is difficult to categorize the nutrient element
according to their functions because one
nutrient element could have several different
functions.
Figure 12.3
Growth falls
off sharply in
this range
At this range additional
increments in nutrient
content will have no
beneficial effect on
growth.
The concentration of that nutrient, measured in the
tissue, just below the level that gives maximum growth.
Some symptoms could tell us more
about this particular nutrient
Chlorosis (yellowing)
deficiency of this nutrient element
causes plant unable to synthesize chlorophyll
Symptoms first appear at older tissue
this nutrient element is probably mobile
Symptoms first appear at younger tissue
this nutrient element is probably
immobile
Nitrogen
3(NO ,
4+
NH )
-N
Most of the time, nitrogen is the limiting factor for
crop growth.
Nitrogen deficiency symptoms include:
slow, stunted growth
general chlorosis of leaves (starting with older
leaves)
accumulation of anthocyanin
early flowering
Excess: abundant growth of the shoot system,
delayed flowering
Phosphorus(PO4
-P
3-)
pH
0
6.8
H2PO4orthophosphate anion
7.2
HPO42less readily
absorbed
PO43not available for plants
In soil, phosphorus has two forms: organic and
inorganic. Plant cannot utilize organic form.
Inorganic phosphorus
When soil pH is above 6.8, the phosphorus will
form complex with aluminum, iron, calcium, or
magnesium.
When phosphorus forms complexes with calcium or
magnesium in alkaline soil and this complex will
precipitate. The precipitated complex cannot be
absorbed.
In natural ecosystems, phosphorus deficiency is the
most frequent reason why plant growth is limited.
Phosphorus deficiency symptoms
intense green coloration of the leaves
malformed leaves and necrotic spots
(anthocyanin accumulation)
rapid senescence and death of the older
leaves
shortened and slender stems
reduced yield of fruits and seeds
Excess
abundant growth of the roots
Potassium,
+
K
Potassium deficiency symptoms
mottling or chlorosis of older leaves
necrotic lesions at leaf margins
stems are shortened and weakened
 easily lodged
increased susceptibility to rootrotting fungi
Sulfur (SO4
2-)
Sulfur deficiency symptoms
generalized chlorosis of the leaf because
reduced protein synthesis
symptoms first appear at younger leaves
2+
Calcium(Ca )
2+
-Ca
Calcium deficiency symptoms
symptoms appears at meristematic
region
young leaves deformed and necrotic
death of the meristem
roots discolored and slippery
Magnesium
2+
(Mg )
Magnesium deficiency
symptoms
usually happens in strongly acid,
sandy soils
chlorosis in the interveinal region
symptoms first appears at older
leaves
Iron
3+
(Fe ,
2+
Fe )
-Fe
Iron deficiency symptoms
loss of chlorophyll and degeneration
of chloroplast structure
chlorosis in the interveinal region of
younger leaves  chlorosis progress to
the vein  leaves turn white
Because iron is easily precipitated in neutral
or alkaline soil but it is readily dissolved in
acidic soil, iron in fertilizers is usually
supplied with chelating agent like EDTA.
Because iron is very important for the
growth and development of plants,
plants devise several strategies to
acquire iron when it is under iron stress.
(1) form specilized transfer cells in
root epidermis
(2)enhanced proton secretion into the
soil
(3) Release strong ligands (chelating
agents) to bind iron (e.g. caffeic acid)
(4) Synthesize phytosiderophores (lowmolecular weight, iron-binding ligands)
Figure 12.6
Release strong ligands to bind iron
Acidification of the
rhizosphere encourages
chelation of the Fe3+ with
caffeic acid (or other phenolic
acids, Ch). Then Ch-Fe3+
complex will move to the root
surface where iron is reduced
by FeIII reductase (expression
of this enzyme is induced
under iron stress). The
reduction of Fe3+ cause the
ligand (Ch) to release the iron
then plant will absorb it
before it forms insoluble
precipitates.
Figure 12.6
Synthesis of phytosiderophores
Phytosiderophores have
been found only in the
family Gramineae (禾本科).
It is only synthesized and
released when plants are
under iron stress. It has a
very high affinity for Fe3+.
After it absorb FeIII, it will
be reabsorbed by the root
entirely.
Phytosiderophores
Boron (BO3
3-)
Boron deficiency symptoms
marked structural abnormalities
inhibition of cell division and root
elongation (stubby, bushy roots)
necrosis of meristem
Copper
2+
(Cu )
Copper deficiency symptoms
stunted growth
distortion of young leaves
summer dieback of citrus trees
Zinc
2+
(Zn )
Zinc deficiency symptoms
shortened internode
smaller leaves
Maganese
2+
(Mn )
Manganese deficiency
symptoms
grey speck of cereal grains
greenish grey, oval-shaped
spots on the basal regions of young
leaves
interveinal chlorosis, discoloration
and defromities in legume seeds
Molybdenum (MoO4
2-)
Molybdenum deficiency
symptoms
whip-tail (twisted and deformed
young leaves)
interveinal chlorosis
necrosis along the veins of older
leaves
Chlorine
(Cl )
Chlorine deficiency
symptoms
reduced growth
wilting of the leaf tips
general chlorosis
Nickel
2+
(Ni )
Nickel deficiency symptoms
low germination rate
depressed seedling vigor
chlorosis
necrotic lesions in the leaves
Critical toxicity levels
the tissue concentration that gives
a 10 percent reduction in dry matter
Toxicity in micronutrients
inhibit root growth
Colloids
Colloids are particles small
enough to remain in suspension
but too large to go into true
solution.
Colloids provide (1) large
specific surface area (2) binding
surface for cations
Colloids provide large specific surface area
• Particles of
colloidal dimension
have a high surface
area per unit mass,
or specific surface
area.
Colloids provide binding surface for
cations.
Whether it’s colloidal clay
(Al2Si2O5·(OH)4) or colloidal carbonaceous
residue (humus), the surfaces are all negatively
charged. This will make colloids capable of
binding cations and this will also make colloids
easily hydrated.
Because the ability of exchange cations of
colloidal surfaces, the colloidal fraction of
soil is the principal nutrient reservoir for the
soil.
Protons (hydrogen ion)
can replace most of
the cations easily.
Therefore, plant roots
also secrete protons to
make cations available
for absorption. Acid
rain will wash out the
cations of soil
solutions and colloidal
surfaces by the same
mechanism of cation
exchange.
Because soil is predominately negative charged,
the anions tend to leach out of the soil. This is
the reason of eutrophication.
Due to the inability of soil to hold anion, farmers
usually apply at least twice the amount of
nitrogen (NO3-) required on the crops. However,
most of the nitrogen is leaching into the ground
water, contaminating streams and lakes. High
nitrogen content in the water bodies stimulate
the growth of algae, resulting eutrophication.
Fig. 13.3
Facilitated diffusion
Simple diffusion
For a membrane-bound cell,
Fick’s first law may be restated as:
flux
permeability
areas of cell membrane
coefficient (cm/s)
Facilitated diffusion
The solutes are
transported by transport
proteins (channels and
carriers). The direction
of transport is still
determined by the
concentration gradient.
Active transport
- leads to accumulation of
solute
- requires energy
- unidirectional
- pumps
Selectively uptake of ion
Although [K+] is
higher inside than
outside, due to the
[cation] of the cell
wall space is higher
than cytosol, so
K+ will still move
into the cell until the
membrane potentials
on the both sides
reaches equilibrium.
Donnan equilibrium and Donnan
potential
• Donnan potential is referring to the potential that
is generated by such a combination of
nondiffusible anions and mobile cations.
• Because there are large number of fixed or
nondiffusible charges (-COO- and –NH4+) in
cytosol, the equilibrium of cations such as K+ will
be achieved when the membrane potential
differences reaches a value such that the force of
the concentration gradient pulling K+ out of the
cell is balanced by the force of the electrical
gradient pulling K+ back into the cell. This type of
equilibrium is called Donnan equilibrium.
The effect of Donnan equilibrium
• Anion is also influenced by this
phenomenon, but in opposite direction.
• All of these results in membrane potential
as we use microelectrode to determine the
difference between plasma membrane.
-100~-130 mV for
young roots and
stems
Figure 13.5 (p.264)
Transmembrane
potential can be
measured with a
microelectrode made
from finely drawn-out
glass tubing. With the
aid of a microscope,
the electrode is
inserted into the
vacuole of a cell. A
reference electrode is
placed in the medium
surrounding the cell.
Figure 13.6 Patch-clamp technique can
measure current flow through individual
channels by taking a small piece of
membrane containing a single channel.
antiport
symport
Uncharged
solute (ex.
sugars)
ATPase-proton pumps
are the major factor in
the membrane potential
of most plant cells
plasma
membrane-type protonpumping ATPase (Ptype ATPase)
tonoplast-type
proton-pumping ATPase
(V-type ATPase
ATPase-proton pump
• The activity of ATPase-proton pump results
in 1.5 to 2 pH units differences between
plasma membrane.
• Since one pH unit difference at 25°C
contributes 59 mV to the potential, the
activity of ATPase-proton pump can account
for approximately 90 to 120 mV of the total
membrane potential.
Structures of proton-pumping
ATPase
P-type ATPase and V-type ATPase are
structurally different.
Plasma membrane type protonpumping ATPase
(P-type ATPase)
• The ATP-binding site of
P-type ATPase is an
aspartic acid residue (D).
• Hydrolysis of ATP at the
binding site is thought to
change the conformation
of the enzyme, thereby
exposing the H+-binding
site to the outside of the
membrane where the H+ is
released.
Plasma membrane-type protonpumping ATPase
(P-type ATPase)
Plasma membrane-type proton-pumping ATPase (Ptype ATPase) is inhibited by VO3-, stimulated by
K+, insensitive to NO3-.VO3- is competing with
phosphate for phosphate binding site, so there is
phosphoryl transfer between ATP and P-type
ATPase.
It pumps protons out of the cell, keeps cytosol more
negative than cell wall space so cations can enter
the cell .
Tonoplast-type proton-pumping
ATPase (V-type ATPase)
Tonoplast-type proton-pumping ATPase (V-type
ATPase) is structurally more similar to F-type
ATPases (chloroplast and mitochondria type).
However, although it can be inhibited by NO3-, it
is insensitive to VO3-, oligomycin, azide.
It pumps protons into the vacuole, keeps vacuole
more positive than the cytosol so anions (Cl-) can
enter the vacuole.
The insensitivity of vanadate (VO3-) indicate that it
does not form complex with phosphate.
V-type ATPase
F-type ATPase
Methods to study membrane
ATPases
• Studies on membrane
ATPase has been
conducted with small,
spherical vesicles obtained
from isolated cellular
membranes. The
preparation of vesicles
must avoid contamination
of chloroplast and
mitochondrial ATPases.
Methods to study membrane
ATPases
• To avoid contamination of
chloroplast ATPase, darkgrown, etiolated tissue
was used.
• To avoid mitochondrial
ATPase contamination,
differential centrifugation
is used.
• However it is still difficult
to isolate ONLY vacuolar
membrane (although
density gradient can fulfill
part of the requirement).
2+
Ca -ATPases
• Plasma membranes, chloroplast envelope, ER, and vacuolar membrane
also contain calcium-pumping ATPases (Ca2+-ATPase).
• Ca2+-ATPase couple the hydrolysis of ATP with the translocation of
Ca2+ across the membrane.
• In the case of plasma membrane, the calcium is pumped out of the
cytosol to keep [Ca2+] low so phosphate won’t precipitate and the
Ca2+-dependent signaling pathways operating properly.
Uptake of
+
K
into cells
• Using 86Rb (radioactive K+ analog) found K+
absorption is biphasic, i.e. there are two types of
K+ transport systems.
(1) high affinity uptake system. This system is
active at low [K+] (≦200m). It is probably a H+ATPase-linked K+-H+ symporter.
(2) low affinity uptake system. This system is
bidirectional.
Study of
+
K
transporter
• Using yeast mutant
lacking K+ transporter,
a high affinity K+
transporter was
isolated from
Arabidopsis thaliana
(AKT1). It is a high
affinity K+ transporter
from the roots and
hydathodes.
Hydathode
High affinity
+
K
transporter
• Another high affinity
K+ transporter, KAT1,
is found expressed
selectively in guard
cells.
Aquaporins
All aquaporins have highly
conserved NPA residues present
in both the N- and C-terminal
halves of the protein.
• Water entering plant cells is not
done by simple diffusion. It is
aided by channel-forming
proteins called aquaporins. The
direction of water movement
through aquaporins are
determined by the difference in
water potential.
• In plants aquaporins are
classified as TIP (tonoplast
intrinsic protein) and PIP
(plasma membrane intrinsic
protein) families.
Ion uptake by roots
• The most popular
organ for study of ion
uptake is excised roots.
• So called “low-salt
roots” are grown
under conditions (see
fig. 13.11 for the
legend) that encourage
depletion of nutrient
elements.
Figure 13.12
Apparent free space (AFS)
Cations in
AFS is lost
Simple diffusion
is occuring in
AFS
=
Ca2+ is being
exchanged by Mg2+
Ions lost in the AFS is a two-step
process
• Because cell wall component (galacturonic
acid residues of pectic acid), which is the
main constituent of AFS, is negatively
charged, cations will not be readily lost
once they have been absorbed. However, it
can be exchanged.
Apparent free space (AFS) is the cell wall and intercellular
spaces of the epidermis and cortex of the roots (regions of
the root that can be entered without crossing a membrane;
apoplast space of the root epidermal and cortical cells).
AFS occupied about 10%~25% of root volume.
AFS includes space accessible to free diffusion and ions
restrained electrostatically due to charges that line the
space.
Figure 5.11
Root epidermis
Endodermis + suberized Vascular tissues: vessel
(rhizodermis), cortical cells
Casparian band
elements, parenchyma cells
Ion
Symplast
Apoplast
Symplast
Apoplast
The other function of Casparian band
Because the ion concentration of stelar
apoplast is much higher than in the
surrounding coretx, the other function of
Casparian band could be to prevent loss of
ions from the stele by diffusion.
Inhibitors of ion transport such as
cycloheximide suggests that ion release into
the vessels is a different kind of process than
ion uptake by the roots.
Ion passing endodermis must take the
symplastic pathway. However, passage cells
(unsuberized endodermal cells) and lateral
roots provide routes for ion passing
endodermis via apoplastic pathway.
The uptake of ions is not uniform along the
length of the root.
What takes up in the tip remains in the root.
Root-microbe interactions
Bacteria
mucilages (mucigels)
proteoid roots
Mycorrhiza
ectomycorrhizae
endomycorrhizae
VAM (vasicular-arbuscular
mycorrhiza)
Because bacteria can
enhance nutrient
uptake of roots, the
Golgi apparatus of root
cells (root cap cells,
young epidermis cells,
and root hairs) secrete
polysaccharide-based
mucilages to attract
bacteria.
Mucilages
Bacteria
Colloidal soil particles
Ectomycorrhizae
-this family of
mycorrhizae is
restricted to temperate
trees and shrubs such
as pines and beech.
-they are short, highly
branched, and
ensheathed by a
tightly interwoven
mantle of fungal
hyphae.
-it also penetrates the
intercellular of
apoplastic spaces of
the root cortex,
forming a intercellular
network
Endomycorrhizae
-it is found in some species
of virtually every
angiosperm family and most
gymnosperms.
-it is developed extensively
within cortical cells of the
host roots.
-VAM (vesicular-arbuscular
mycorrhiza) is the most
common type of
endomycorrhiza.
-VAM forms arbuscule with
host cells without
penetrating protoplasm of its
host. Arbuscules increase
contact surface area by two
or three times.
Maize seedlings that
is not colonized by
myccorrhiza.
Figure 13.15
Nutrient depletion zone defines
the limits of the soil from which
the root is able to readily extract
nutrient elements.
Mycorrhiza can extend the
nutrient depletion zone for a
plant.
Figure 13.16