TRANSPIRATION
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Science online by Heba Soffar is licensed under a Creative Commons
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TRANSPIRATION
• Process where water moves in liquid form in plants, and
released in vapor form through aerial parts, but mostly in
leaves, to the atmosphere
• Energy dependent process
• The transformation of liquid to gas phase involves use of
energy
• 97-99.5% of water taken up is lost in transpiration
H2O(liquid)
540 cal g-1
H2O(gas)
Importance of Transpiration
1. Keeps cells hydrated
2. Maintains favorable turgor pressure for the transport of nutrients
absorbed by the roots from the soil
3. Cools the plant
–
–
heat load is dissipated in the process due to the high heat of vaporization of water
If transpiration is extremely high dehydration and desiccation death
*** daily water loss
–
–
–
large, well-aerated, tropical plant: 500 L
corn plant : 3-4 L day-1 (99% of the water absorbed by a corn plant) during its
growing season is lost in transpiration)
tree-size desert cactus loses less than 25 mL day-1
Types of Transpiration
Based on the avenue of exit of water vapor
❑Cuticular transpiration
❑ Loss of water through cuticle
❑5-10% of the water loss
❑Lenticular transpiration
❑Lenticels - pores in the outer layer of a woody plant stem
❑In deciduous species (trees which sheds off leaves) and in some fruits, water
loss through lenticels may be quite substantial.
❑Stomatal transpiration
❑Through the stomata
❑As much as 90% of the water lost from plants.
What affects diffusion of water from leaf to
atmosphere?
❖ Relative
humidity (RH) (%)
❖ actual water vapor in the air: water vapor pressure in leaf
❖ In leaves 100% RH; in atmosphere, RH
rarely exceeds 90%
❖ water diffuses out from the plants to the atmosphere
❖ Vapor
pressure deficit (VPD) (pascal (Pa))
❖ Actual water vapor pressure - water vapor pressure
at saturation at the
same temperature
❖ when VPD is 0 Pa (i.e. when RH of the atmosphere is 100%), there is no net
movement of water
❖ when the RH of the atmosphere is low, the VPD is high, and the rate of
transpiration is faster
Soil-Plant-Air Continuum of Water
1.
Movement of water from the soil to the root xylem
a. Extracellular or apoplastic route - water moves through non-living parts,
e.g. capillary spaces of the cell walls and intercellular spaces
b. Intracellular route
1) symplastic pathway - plasmodesmata
2) transmembrane or transcellular pathway - vacuolar membrane (tonoplast)
and the plasma membranes
2 . Movement of water from root xylem to leaf xylem
– transpiration-cohesion-adhesion theory
3. Movement of water from leaf xylem to the air
– influenced by RH and VPD
– Towards lower water potential (Ψ; expressed in megaPascal, MPa)
Movement of water from root xylem to
leaf xylem
The transpiration cohesionadhesion theory
1. water vapor leaves the air
spaces of the plant via the
stomates
2. this water is replaced by
evaporation of the thin layer of
water that clings to the
mesophyll cells
3. tension (pulling) on the water in
the xylem gently pulls the water
toward the direction of water
loss
4. the cohesion of water is strong
enough to transmit this pulling
force all the way down to the
roots
5. adhesion of water to the cell
wall also aids in resisting gravity
FeltyRacketeer6 2019. .https://upload.wikimedia.org/wikipedia/commons/8/85/Transpiration_of_Water_in_Xylem.svg
Factors that Affect Transpiration
I. Plant Factors
1.
2.
3.
4.
5.
Efficiency of evaporative surface
Efficiency of water absorption.
Other surface/stomatal modifications
Phytohormones
Canopy structure.
1.
2.
Edaphic (soil) factors
Atmospheric factors
II. Environmental Factors
•
•
•
•
•
Light
Relative humidity
Temperature
Wind velocity
Oxygen and carbon dioxide concentrations
How Plant and Environmental Factors Affect
Transpiration
• Leaf number: more leaves, more transpiration
• Number, size, position of stomata: more and large, more
transpiration, under leaf, less transpiration
• Cuticle: waxy cuticle, less evaporation from leaf surface
• Light: more gas exchange as stomata are open
• Temperature: high temperature, more evaporation, more diffusion
• Humidity: high humidity, less transpiration
• Wind: more wind, more transpiration
• Water availability: less water in soil, less transpiration (e.g. in winter,
plants lose leaves)
TRANSLOCATION
• If
TRANSPIRATION is the transport of
water and nutrients from soil thru roots and xylem,
then
TRANSLOCATION is the
movement of assimilates (sugars and other
chemicals) from the leaf through the phloem to other
areas for storage, utilization and consumption by the
plant
Why need a
transport system
in plants?
• so that cells deep within
the plant tissues can
receive the nutrients they
need for cell processes
• In fact:
• roots can obtain water,
but not sugar,
• leaves can produce sugar,
but can’t get water from the
air
CNX OpenStax / CC BY
http://cnx.org/contents/GFy_h8cu@10.53:rZu
dN6XP@2/Introduction
https://commons.wikimedia.org/wiki/File:Figure_
30_05_07.jpg
The vascular tissues: xylem and phloem
• Sugars required for metabolism
– all the time, in all tissues
• Sugars produced only
– by source tissues
– in light period
• Translocation occurs
– source to sink over short term
– from storage tissues to young
tissues over long term
Kyla Andrea Mendoza. 2020.
Created with BioRender.com
Sucrose
• is principal photosynthetic
product
Photosynthetic cell
– accounts for most of CO2 absorbed
– Glucose, as initial product of photosynthesis, is
converted to sucrose which is the major form for
transport or translocation
• important storage sugar
– tap root of carrots and sugar beet (up to 20% dry weight)
– and in leaves, eg 25% leaf dry weight in ivy
• major form for translocation of
carbon
– from photosynthetic leaves (source leaves)
– in germinating seedlings after starch or lipid breakdown
CO2
RuBP
Starch
PGA
Chloroplast
1,3 bisPGA
Triose P
Sucrose
Kyla Andrea Mendoza. 2020.
Created with BioRender.com
Other compounds are also translocated:
Direction of translocation:
• From Source: a part of the
plant that releases sucrose to
the phloem e.g. leaf
• To Sink: a part of the plant
that removes sucrose from the
phloem e.g. root
• A plant part can act as source or sink
depending on its developmental stage:
for example- young leaves act as sink,
but later their predominant role would
be as source, once they are active in
photosynthesis
Kyla Andrea Mendoza. 2020.
Created with BioRender.com
ALLOCATION
• The channelling of fixed carbon into various metabolic
pathways within an organ or tissue
• In a source organ:
– Metabolic utilization within the chloroplast
– Synthesiszof starch within the chloroplasts
– Synthesis of sucrose for export to sink
• In a sink organ
– Metabolic utilization and growth processes
– Storage
PARTITIONING
• DISTRIBUTION of assimilates to competing sinks
– Lower mature leaves feed mainly the roots
– Higher mature leaves feed mainly the young leaves and
shoot apex
• SOURCE LEAVES
– Preferentially supply sink organs with which they have
vascular connection
• Flower or fruit nearest to them (directly above or below them
– Basis for flower and fruit thinning
Mechanism of translocation of
photosynthates
1. Mass or bulk flow (Münch pressure flow hypothesis)
2. Diffusion- slow
3. Cytoplasmic streaming- within the cytoplasm through
plasmodesmatal connections between cells
4. Others
1. Facilitated diffusion
2. Active transport across membranes
Phloem Cells
Kelvinsong / CC BY-SA
https://commons.wikimedia.org/wiki/File:Phloem_cells.svg
CNX OpenStax / CC BY
http://cnx.org/contents/GFy_h8cu@10.53:rZudN6XP@2/Intro
duction
https://commons.wikimedia.org/wiki/File:Figure_30_05_06.jpg
Mechanism of assimilate translocation:
The Münch pressure flow hypothesis of assimilate transport from source to sink
Alyssa Pham / CC BY-SA
https://commons.wikimedia.org/wiki/File:Translocation_
from_the_source_to_the_sink_within_the_phloem.svg
APOPLAST PATHWAY
•
sucrose is loaded into the phloem with the help of
active transport. A sucrose transporter protein is
used to co-transport H+ and sucrose across the cell
membrane.
•
the apoplast path utilizes ATP to pump H+ against
the concentration gradient.
•
ATP is reduced to ADP+Pi which expels energy that
enable H+ to be pushed against the gradient.
•
The H+ proton that is pumped against the gradient
is then used by the sucrose transporter protein to
move sucrose through the membrane.
•
The sucrose accumulated in the companion cell is
able to flow down its concentration gradient via the
plasmodesmata and into the phloem.
Picture cropped and text retyped from work by Emily Xie / CC BY-SA
https://commons.wikimedia.org/wiki/File:An_Annotated_Diagram_of_the_Vertical_CrossSections_for_Apoplast_and_Symplast_Pathways_Involved_in_Phloem_Loading.svg
SYMPLAST PATHWAY
•
•
sucrose travels in the
plasmodesmata which are
connections between cells.
Therefore, the sucrose is able to
flow down the sucrose
concentration gradient into the
phloem which has a lot of
concentration of sucrose.
Picture cropped and text retyped from work by Emily Xie / CC BY-SA
https://commons.wikimedia.org/wiki/File:An_Annotated_Diagram_of_the_
Vertical_CrossSections_for_Apoplast_and_Symplast_Pathways_Involved_in_Phloem_Loa
ding.svg
Study questions
I. Identify if source or sink
1. Fully expanded mature leaf
2. Unripe fruit
3. Young leaf
4. Flowers
II. True or False. If false, give the reason why
1. Transpiration is driven or directed by the amount of
water in the soil
2. Water leaves the plants/leaves as water vapor
3. Sugars are the major form of compounds that are
translocated
4. When there is RH is 100%, there is 100% transpiration
also
MINERAL NUTRITION
Mineral Nutrition in plants
Plants are:
Capable of making all necessary organic
compounds from inorganic compounds and
elements in the environment (autotrophic)
Supplied with all the carbon, hydrogen, and
oxygen they could ever need (CO2, H2O)
Required to obtain all other elements from
the soil so in a sense plants act as soil
miners.
Kyla Andrea Mendoza 2020.
Created with BioRender.com
Nutrient
• any substance that can be metabolized by an
organism to give energy and build tissue
• growth and development
• source of nourishment, especially a nourishing
ingredient in a food
• providing nourishment
Categories of Plant Nutrients
•
•
•
Based on Function
❖ Essential
❖ Beneficial
Based on amount required by crop
❖ Macroelements
❖ Microelements
Based on capability to move from one part of the plant to
another
❖ Mobile
❖ Immobile
CRITERIA OF ESSENTIALITY
1. If the nutrient is absent, then the plant is unable to
complete its life cycle
2. The function of the nutrient must not be replaceable by
another element
3. The nutrient must act directly in the metabolism of the
plant
Functions of the Essential Elements
▪ Structural
▪
important components of biomolecules (e.g. N, P, Ca, Mg, S)
▪ Catalytic
▪
as co-factor of enzymes (e.g. most micronutrients)
▪ Osmotic
▪
regulation of cellular hydration (e.g. K)
The Essential Nutrients
▪ Macronutrients:
▪ Nitrogen, phosphorus, potassium, calcium, sulfur,
magnesium, oxygen, carbon,hydrogen
▪ Micronutrients:
▪ Iron, boron, copper, zinc, manganese, molybdenum,
chloride
Macroelements/
Macronutrients
Microelements/
Micronutrients
Required in relatively large
Required in minute quantities
quantities like one to 10 milligram like 0.1 mg per gram of dry
per gram of dry
matter
matter
Carbon, Hydrogen, Oxygen
Phosphorous, Potassium,
Calcium and
Nitrogen, Sulphur
Manganese, Boron, Copper,
Molybdenum, Iron, Zinc and
and Chloride
The essential nutrients- plants take up only
INORGANIC nutrients
Macronutrient
Inorganic Form
Micronutrient
Inorganic Form
Nitrogen (N)
NH4+ , NO3-
Iron (Fe)
Fe+2, Fe+3
Phosphorus (P)
H2PO4-, HPO4-2, PO4- Boron (B)
BO-3
Potassium (K)
K+
Manganese (Mn)
Mn+2
Calcium (Ca)
Ca+2
Zinc (Zn)
Zn+2
Magnesium (Mg)
Mg+2
Copper (Cu)
Cu+2
Molybdenum (Mo)
MoO5-
Sulfur (S)
SO4-2
Chlorine (Cl)
Cl-1
3
Carbon (C)
Hydrogen (H)
Oxygen (O)
Nitrogen (N)
Phosphorus (P)
Constituent of all organic molecules
Component of proteins, enzymes, and nucleic acids
In nucleic acids, phytin, coenzymes, adenylases; regulatory function
Potassium (K)
Osmoregulation; enzyme activator, and protein component
Calcium (Ca)
Magnesium (Mg)
In pectates, and regulatory protein ; regulation of enzyme
Integral component of chlorophyll, Mg-ATP; activator of phosphorylation, RuBP carboxylase
Sulfur (S)
Constituent of several coenzymes, vitamins and amino acids
Iron (Fe)
Copper (Cu)
Zinc (Zn)
Components of Fe- and Fe-S proteins, cytochromes, and ferredoxins
Activator of several oxidases and lignin synthesis
Activator of enzymes
Manganese (Mn)
Enzyme activator and photosynthetic evolution of oxygen (Hill reaction)
Molybdenum (Mo)
Enzyme component essential for nitrogenase in bacteria for N2-fixation
Boron (B)
Complex with protein
Chlorine (Cl)
Activator of photosystem II;
Nickel (Ni)
Integral component of urease enzyme
Beneficial Elements
o Elements which promote plant growth in many plant species but
are not absolutely necessary for completion of the plant life cycle
o Silicon, sodium, cobalt, and selenium
Plant nutrient
Source
Air
Carbon
X
Oxygen
X
Water
Soil
X
Hydrogen
X
Macronutrients
Nitrogen
X
Phosphorus
X
Potassium
X
Calcium
X
Magnesium
X
Sulfur
X
Micronutrients
Boron
X
Chlorine
X
Copper
X
Iron
X
Manganese
X
Molybdenum
X
Nickel
X
Zinc
X
Decline in Soil Fertility
▪ Soil erosion
▪ physical loss and displacement of the fertile topsoil
▪
Geological erosion
▪
Wind erosion
▪
Water-borne erosion
▪
Accelerated erosion due to human activity
▪ Crop removal
▪ Conversion of nutrients to unavailable forms
▪ Formation of insoluble forms
▪ Microbial mediated transformations
▪ Volatilization (especially nitrogen)
▪ Leaching
pH affects the growth of
plant roots and soil
microbes
Root growth favors a pH
of 5.5 to 6.5
CoolKoon / CC BY
https://commons.wikimedia.org/wiki/File:Soil_pH_effect_on_nutrient_availability.svg
NUTRIENT DEFICIENCIES
• Mineral nutrient deficiencies occur when the concentration
of a nutrient decreases below its typical range
• Deficiencies of specific nutrients lead to specific visual, often
characteristic, symptoms reflective of the role of that
nutrient in plant metabolism
NUTRIENT DEFICIENCY SYMPTOMS
❑ Chlorosis (uniform or interveinal) or yellowing of the leaves due to
chlorophyll degradation
❑ Necrosis (tip, marginal, or interveinal) or death of leaf tissue
❑ Lack of new growth, which may result in death of terminal or
axillary buds and leaves, dieback, or resetting
❑ Accumulation of anthocyanin resulting in reddish coloration of leaf
tissues
❑ Stunted leaf growth with green, off-green, or yellow color
NUTRIENT DEFICIENCY
SYMPTOMS
P deficient
K deficient
N deficient
N surplus Farnaz Khakpoor / CC BY-SA
C deficient
https://commons.wikimedia.org/wiki/File:%D9%86%DB%8C%DA%A9%
D9%84.jpg
‘Apple Nutrition’ (1941) by Davis, Malcolm B, Hill H, Canada Dept. of Agriculture
Retrieved from
https://commons.wikimedia.org/wiki/File:Apple_nutrition_(1941)_(19124665773).jpg
Patterns of deficiency
▪ Patterns of deficiency are
important in identifying which
nutrient is deficient or lacking
▪ The location where a deficiency
reflects the mobility of a nutrient
▪ Nutrients are redistributed via
movement through the phloem
▪ If the deficiency is seen in old
leaves = nutrient is mobile
▪ If the deficiency is seen in young
leaves =nutrient is fixed or
immobile
How to address nutrient deficiency?
1. Establish an attainable yield level – the crop’s total needs
2. Calculate the nutrient requirement of the crop
3. Effectively use existing nutrients
a. organic fertilizers
i. manure
ii. plant biomass
iii. vermicompost
iv. fermented plant juice
b. nutrients from irrigation water
c. indigenous soil nutrients
4. For deficiencies, top up with or add inorganic fertilizers
Plant Growth and
Development
Development
The attainment of size by virtue of growth and
architectural style by morphogenesis
(differentiation of cells into tissues, organs and
organisms)
Aspects
1. Growth
2. Differentiation
3. Organization
Growth
the irreversible increase of cell number, and
essentially its dry mass or weight
increase in size does not mean an increase in growth.
Growth curve
• Cells/organs show a
definite pattern of growth
Differentiation
• Reflects the orderly processes by which genetically identical
cells become different, forming specialized tissues and
organs
• The reflection of change in the cell’s biochemical program,
controlled by developmental genes
Dedifferentiation
-the reversal of the cell specialization
Important in the repair of injury, where cell near damaged
sites become totipotent and reprogram their development
Organization
• – orientation and integration of differentiated cells in
space together with regulated growth whole plant
Morphogenesis
• the orientation and integration of differentiated cells in
space together with regulated growth, and the consequent
attainment of form and structure of the complete organism.
growth
differentiation
development
• Plants, develop according to a predetermined genetic
blueprint
• Expression is greatly influenced by signals received
from the external environment
• Plants are always undergoing development.
pattern formation
morphogenesis
Localization of Growth
Essential characteristics of organisms
- take up relatively simple substances from environment and
synthesize these to complex substances
At cellular level
- increase in living material leads to increase in cell size and
ultimately cell division complex process in multicellular
organisms
Localization of Growth
• Growth is restricted to certain embryonic regions called the
meristems
Meristems
♣ Where plant growth occurs
♣ Site of repeated cell division of unspecialised cells
♣ Cells differentiate, and become specialised in relation to
the function they will perform
Basic Structures involved in Plant Growth
and Development
Embryo
Cotyledons, shoots and root apical meristems
Meristems
- Shoot
- Axillary root (apical and lateral)
- Floral
- Cambiums (cork, vascular)
Types of Meristems
Apical
♥ tips of roots and shoot
♥ site of primary growth in a plant
Lateral
♥ side portions, arising from the cambium (base of nodes and
stems),
responsible for secondary thickening of the stem and roots
Intercalary
♥ inserted between regions of differentiated tissues
Types of Growth
1. Indeterminate (ricebean, winged bean)
- apical meristems of the roots and stems remain permanently
embryonic over long periods
2. Determinate (corn, rice, mungbean)
- other plant parts (leaves, flowers, fruits) are embryonic for limited
period before the plant reaches maturity, have precise morphology and
definite number of parts
Internal Growth Mechanisms
Correlation Effect
The regulatory effects exerted by one part of the plant on the
growth or development in another part
Internal Growth Mechanisms
Organ Differentiation
♥ As shoot increases in bulk, the size of the root system becomes
proportionately larger
♥ Reduction in vegetative growth when the plant is fruiting
♥ Stimulation of fruit growth by hormones produced in the developing
seeds
♥ Stimulating effects of buds/leaves on the rooting of stem cuttings