Agriculture crop physiology and biochemistry

1. Dr Saboohi Raza
Associate Professor

2. Mechanism of absorption and
translocation of water

3. Importance of water
 Morphology and anatomy of plant
 Good solvent
 Component of protoplasm
 Absorbance and translocation mineral, salts and
dissolve substances
 Photosynthesis
 Seed germination, respiration transpiration,
activation of enzymes, hydrolysis of ATP
 Maintain temperature
 Turgidity of plant body

4. Soil water
 Gravitational water
 Capillary water
 Hygroscopic water
 Crystalline water
 Running water
Water holding capacity=capillary +hygroscopic
+crystalline water

5. Water absorbing parts of the plants
ROOTS

6. Regions of Roots
 Root Cap region
 Meristematic region
 Region for elongation
 Region for root hair
 Mature region

7. Internal structure of root

8. Some term involved in water
absorption and translocation
 Osmosis
 Active transport
 Passive transport
 ATP
 Hypertonic solution
 Hypotonic solution
 Isotonic solution

9. Water potential (Ψ)
 is a measurement that combines the effects of solute
concentration and pressure
 determines the direction of movement of water
 Water flows from regions of higher water potential to regions
of lower water potential (osmosis)
 MPa = unit of measurement (megapascal)
• Ψ = 0 MPa for pure water at sea level and room temperature
• Both pressure and solute concentration affect water potential
• solute potential (ΨS) is proportional to the number of
dissolved molecules also called osmotic potential

10.  Pressure potential (ΨP) is the physical pressure on a
solution
 Ψ = Ψs + Ψp

11. Measuring Water Potential
• Consider a U-shaped tube where the two arms
are separated by a membrane permeable only to
water
• Water moves in the direction from higher water
potential to lower water potential

12. ψ = −0.23 MPa
0.1 M
solution
Pure
water
H2O
ψP = 0
ψS = 0
ψP = 0
ψS = −0.23
ψ = 0 MPa
If no pressure is applied:
The addition of solutes reduces water
potential

13. Positive
pressure
H2O
ψP = 0.23
ψS = −0.23
ψP = 0
ψS = 0
ψ = 0 MPa ψ = 0 MPa
Physical pressure increases water potential

14. ψP = 0.30
ψS = −0.23
Increased
positive
pressure
H2O
ψ = 0.07 MPa
ψP = 0
ψS = 0
ψ = 0 MPa
Increased positive pressure on the right
causes the water to move to the left

15. Negative
pressure
(tension)
H2O
ψP = −0.30
ψS = 0
ψP = 0
ψS = −0.23
ψ = −0.30 MPa ψ = −0.23 MPa
Negative pressure decreases water
potential

16. (a) Initial conditions: cellular ψ > environmental ψ
ψP = 0
ψS = −0.9
ψP = 0
ψS = −0.9
ψP = 0
ψS = −0.7
ψ = −0.9 MPa
ψ = −0.9 MPa
ψ = −0.7 MPa0.4 M sucrose solution:
Plasmolyzed cell
Initial flaccid
cell:
60% H2O
A cell placed in a high solute concentration it will lose
water, plasmolyzing
Turgor loss in plants causes wilting, which can be
reversed when the plant is watered

17. ψP = 0
ψS = −0.7
Initial flaccid
cell:
Pure water:
ψP = 0
ψS = 0
ψ = 0 MPa
ψ = −0.7 MPa
ψP = 0.7
ψS = −0.7
ψ = 0 MPa
Turgid cell
(b) Initial conditions: cellular ψ < environmental ψ
100% H20
If the same flaccid cell is placed in a solution with a lower solute
concentration, the cell will gain water and become turgid

18. Mechanism of water absorption

19. Path for translocation of water
Root Hairs Epidermal cell Cortex Cell
Endoderma
l cells
Cells of
PericycleXylem cells
Xylem Duct
Upward

20. Non osmotic Active absorption
 Sometime water absorbance takes place against the
osmotic gradient
 Require ATP produced during respiration
 It requires oxygen
 Create root pressure

21. Passive absorption
 According to osmotic gradient
 Does not require energy
 Does not require oxygen
 Root pressure not created

22. Factors affecting on the rate of
water absorption
 Available Soil water
 Soil aeration : oxygen required
 Concentration of soil solution
 Soil temperature :20-30˚C
 Root system: hairy and well developed root system

23. Ascent of Sap
The water and soluble minerals salts absorbed by the
roots reached to the leaves through roots, stem and
branches of plant. The phenomenon of ascending of
absorbed water against gravitation through vessels and
tracheids of xylem is called ascent of sap

24. Theories of
ascent of sap
Vital
theories
Root
pressure
theory
Godlewski
theory
Vital force
theory
Physical
theories
Imbibitions
theory
Capillary
force theory
Cohesion
theory

25. Cohesion Theory
 By Dixon and Jolly (1894)
 The water molecule remain attracted
by a force called cohesive force
 This force maintain the continuity of
water column in the xylem vessels.
 Water evaporates from the leave due
to transpiration that creates a
transpiration pull.
 Ascent of sap and water is directly
proportional to the rate of
transpiration

26. Transpiration
The loss of excess water in form of vapours from
various aerial parts of plants is called transpiration
Only 5% absorbed water is retained in plant body
Remaining 95% lost through aerial parts

27. Difference between transpiration
and evaporation
Transpiration Evaporation
Transpiration is biological
phenomenon
Evaporation is simple physical
phenomenon
It is control by guard cells It is control by guard cells
It take place through the surface of
leaves
It take place through the surface of
various open water bodies
It take place due to osmotic pressure
and suction pressure
no suction and osmotic pressure is
involved
It take place in living cells No required living cells
The temperature of the plant is
maintained due to transpiration
Not any relation with plant cell

28. Kinds of transpiration
 Cuticle transpiration: from aerial parts of plants 5-
15% water loss
 Lenticular Transpiration: small pores presents
below the bark of trees
 Stomatal Transpiration:
Through stomata of leaves
80-90 % water loss

29. STOMATA

30. Cuticle
Cuticle
Mesophyll
Stomata Guard cells
Prevents water
loss
Site of
photosynthesis
Openings allow gases
and water to move in
and out of leaf
Open and close
the stomata
Stomatal transpiration

31. Stomata movement
 Sun rises- stomata start opening
 Light intensity increases- more opening of stomata
 High rate of transpiration decreases the turgidity of
leave cells- water deficit-partial closing of stomata
 More water absorption due to difference in water
potential guard cells become turgid- stomata reopen-
start transpiration
 As light intensity decreased transpiration rate
decreased
 At sunset stomata become closed

32. 32
Regulating Stomatal Opening:-the
potassium ion pump hypothesis
Guard cells flaccid
Stoma closed
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+ ions have the same concentration in
guard cells and epidermal cells
Light activates K+ pumps which
actively transport K+ from the
epidermal cells into the guard cells

33. 33
Regulating Stomatal Opening:-the
potassium ion pump hypothesis
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
Increased concentration of K+
in guard cells
Lowers the  in the guard cells
Water moves in by osmosis, down
 gradient
H2O
H2O
H2O
H2O
H2O

34. 34
Stoma open
Guard cells turgid
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
Increased concentration of K+
in guard cells
Lowers the  in the guard cells
Water moves in by osmosis, down
 gradient
H2O
H2O
H2O
H2O
H2O
H2O

35. 35
Adaptations to Reduce Water Loss in
Xerophytes
 Thick waxy cuticle to reduce evaporation
 Reduced leaf area e.g.needles
 Hairy leaves:- the hairs trap a layer of saturated air
 Sunken stomata:- the pits above the stomata become saturated
 Rolled leaves:- this reduces the area exposed to the air and keeps the
stomata on the inside so increasing the water vapour inside the roll
Increasing the water vapour around the stomata reduces the water
potential gradient so slows water loss

36. Factors affecting Transpiration
External or environmental Factors
 Humidity in air
 Temperature
 Light
 Wind velocity
 Water content in soil

37. Factors affecting Transpiration
Internal Factors for reduce transpiration
 Morphological feature
 Anatomical features
 Physiological features

38. Morphological features
 Presence of dry, hard and cylindrical stem
 Presence of bark on stem
 Reduction in number of branches
 Presences of fleshy roots for storage of water
 Presences of scaly and reduced leaves
 Presence of thick leaves covered by thick waxy layer or
cuticle

39. Anatomical Features
 Presence of multilayered epidermis
 Presence of sunken and less number of stomata
 Presence of excessive amount of Sclerenchyma

40. Physiological features
 Presence of high OP in cell-sap of leaves
 Excessive growth in roots due to which they become
quite long and reach at the greater depth to absorb
water
 Closing stomata during adverse conditions of
environment

41. Importance of transpiration
 The water and minerals absorbed by the roots from the
soil reached continuously in different parts of the
plants through transpiration
 Transpiration maintains the concentration of mineral
salts
 Maintain the temperature of plants