This document discusses plant water relations and transport. It covers how water is absorbed by roots, transported through the xylem, and moves upwards through the plant. It describes several theories for water transport, including root pressure theory, capillary theory, and cohesion theory. It also discusses transpiration, opening and closing of stomata, mineral nutrition, and classification of essential nutrients. The key points covered are the role of water in plants, absorption and transport pathways, factors affecting absorption, and mechanisms regulating transpiration and water movement.

1. Plant Water
Relations

2. • It plays the role of solvent.
• Water – Liquid of Life.
• 90 to 95 % of protoplasm is water
• Water is absorbed by roots and further transported by Xylem (Water
conducting tissue of Vascular Bundles)
Introduction
• It also acts as an essential medium for transport and
• Medium for chemical reactions.
• It maintains turgidity of the cell which is required for normal growth
and development.
Role of Water

3. Ideal Properties of Water
• It has high melting and boiling point.
• It has highest specific heat capacity (except liquid
NH4 slow to heat and cool).
• Greater adhesive force which helps in ascent of sap
(transportation).
• Capillaries fill easily because of High Surface Tension
(except Mercury).
• It is in liquid state at room temperature

4. • Strong Cohesive Force provides greater Tensile
Strength.
• Works as a very good solvent.
• Absorbs light hence submerged plants can
photosynthesize.
• It also acts as a good insulator (protection from
excessive heat).
Ideal Properties of Water contd…..

5. Hygroscopic water
The water which is held very tightly around soil particles by adhesive
forces is called as hygroscopic water.
Not available to plants
Combined water
Water present in the hydrated oxides of Aluminium, Silicon is called as
combined water. Not available to plants
Gravitational water
Water which goes down through large pores and reaches the water
table is called as gravitational water. Not available to plants
Capillary water
Water held in the small spaces between small, non colloidal soil
particles is called capillary water.
Only available to plants.
Water and its forms
Hygroscopic water& combined water is also called as Bound water.

6. Imbibition: The process by which the colloidal substance adsorb water
from their surroundings and swells. (Hydrophillic colloids like Cellulose,
proteins and pectic substances in cellwall imbibe water)
Diffusion: Movement of ions, atoms, molecules of solutes from region
of higher concentration to region of lower concentration till equilibrium
is called as Diffusion.
Selective transport of large molecules across cell membrane is facilitated
diffusion (energy less, occurs through porins– special proteins)
Water soluble substances are transported by 8 aqua porins
Osmosis: It is a special type of diffusion, it is defined as migration of
solvent molecules from a solution of lower concentration to a solution
of higher concentration through a semi-permeable membrane.
Physical Processes
Transport of 2 molecules in same direction is called symport, whereas in
opposite direction it is called as antiport. If movement is independent it
is said to be uniport.

7. Water
Absorbing
Machinery

8. Root and Root Hair
Section of Root
Entire Root

9. Route of
Water
Transport
(From
Root tip
to Leaf)

10. Route of Water Transport
Soil Solution (Water)
Outer wall (Pectin)
Inner wall (cellulose)
Plasma membrane
Tonoplast (vacuolar membrane)
Neck cell (cortex)
Endodermal Passage cell (special endodermal cells)
Protoxylem
Metaxylem

11. Diagram of Pathways

12. Pathways of Water Transport
According to Munch, there are three pathways of water passage
from root hairs to xylem namely,
1. Symplast pathway
2. Apoplast pathway
3. Vacuolar pathway
Cont…..

13. Pathways of Water Transport
1. Symplast Pathway: In symplast pathway cells are interconnected
by the plasmodesmata in the plasma membrane and the transfer
takes from root to cortex, the endodermis and finally the
protoxylem of the vascular bundle.
2. Apoplast Pathway: In Apoplast pathway the water molecules travel
through the membrane and intercellular spaces till the endodermal
lining, further it has to follow the symplast pathway, as the
casparian strips in the endoderm block the apoplast pathway.

14. Mechanism of Absorption
1. Active absorption (Root cells take active part)
Active osmotic absorption
No ATP required
Water is absorbed across a concentration gradient
Soil solution is at low concentration than the cell sap hence
transport of water takes place from soil solution to cell sap.
Active non osmotic absorption
ATP is employed as it states that the absorption takes place against
potential gradient.
2. Passive absorption(shoot cells take active part and root cells just
act like a passage)
This concept is based on the suction force developed by the
process of transpiration

15. Factors affecting absorption
• Available soil water – if soil water decreases till the permanent
wilting percentage then there is considerable decrease in absorption.
• Concentration of Soil Solution – More concentration i.e. more
Osmotic pressure less is the absorption. In other words Osmotic
pressure is inversely proportional to absorption.
• Soil Aeration – Low oxygen and more carbon dioxide content
decreases absorption, Water logging also decreases absorption.
Cont…..

16. Factors affecting absorption
• Soil Temperature – Ideal temperature for absorption is 20 to 30oC, if
it fluctuates beyond these limits absorption decreases.
The decreases is because of the following reasons
a. Slower rate of root elongation.
b. Reduced diffusion
c. Reduction in permeability
d. Increased viscosity of water, protoplasm etc.
e. Reduction in metabolic activity.
f. Root anatomy – less root hairs, thick walled cortical cells,
casparian strips (endodermal tissue reduces absorption)
• Transpiration

17. Terms
• Hypertonic solution: A solution is said to be hypertonic when the
concentration of the solution is more than the surrounding medium
• Hypotonic solution: A solution is said to be hypotonic when its
concentration is less than the surrounding medium
• Isotonic solution: A solution is said to be isotonic when its
concentration is equal to that of the surrounding medium.
• Endosmosis: When water enters a cell the process is called
endosmosis
• Exosmosis: When water moves out of the cell the process is called
exosmosis.
• Osmotic pressure: The pressure needed to prevent the passage of
pure water into it through a semi-permeable membrane.

18. Terms
• Turgor pressure: Hydrostatic pressure developed on the walls of the
cells due to endosmosis.
• Diffusion Pressure: it is the potential ability of the solid, liquid, gas to
diffuse from an area of its higher concentration to an area of lesser
concentration
• Diffusion Pressure deficit: The difference between the diffusion
pressures of two different solution is termed as DPD (diff in DP of
pure water and another solution is DPD)
Diffusion Pressure of any pure solvent is always maximum. If solute is
dissolved Diffusion Pressure decreases (OP increases due to increase in
concentration of solvent, endosmosis takes place thereby decreases DP)
If the above mentioned solutions are subjected to same pressure the
difference in Diffusion Pressure is exactly equal to Osmotic Pressure of
the solution therefore DPD = OP-TP

19. Concept of Water potential
The kinetic/free energy possessed by molecules is called as chemical
potential. The chemical potential of water is called as Water potential. It
is 0 at normal pressure, temperature. When solutes are added the value
decreases.
It is represented by psi Ψ. it is measured in Pascal (Pa). Water potential
is equal to DPD in magnitude but has negative value.
Water moves from less negative water potential to more negative water
potential. Some solutes when dissolved reduce water potential, the
magnitude of this lowering is called as solute potential Ψs. It is always
negative.

20. Theories of Water Transport
Water translocated from root is not only water but a dilute solution of
mineral ions from soil, such a solution is called as sap and its
translocation is called as ascent of sap.
After absorption of water by root, it needs to be translocated to various
aerial parts of the plant.
In plants of the group Thallophyta there is no problem for translocation
of water as the distance between the absorbing end and the receiving
end is very less but in plants with the height of about 317 metres there
has to be a definite mechanism for its transportation.
ASCENT OF SAP: Water present in the plant body in a form of
weak solution of minerals & salts is called as SAP.

21. Theories of Water Transport
Some theories have been put forth to explain the phenomenon of
upward movement of water.
1. Root Pressure theory
2. Capillary theory
3. Cohesion theory

22. Root Pressure Theory
• OP of root hair is higher than soil solution.
• Water osmoses into root hair and enters root system.
• If transpiration is low accumulation of water takes place.
• Accumulation creates hydrostatic pressure called as root pressure.
• If stem is cut near soil surface xylem sap exudes (1 to 6 atm)

23. OBJECTIONS
• Magnitude of root pressure is very low (required 13 atm.)
Root pressure formation is not universal.
• During Summer root pressure is very high (not possible because of
higher transpiration – no accumulation) and winter very low (not
possible because of lower transpiration – accumulation takes place).

24. Capillary Theory
• Xylem elements are made up of number of capillaries
• Water rises due to adhesion between water molecules and walls.
• Adhesion forms meniscus and water tends to climb.
• Smaller the diameter greater is the lifting force.

25. Objections
• Water cannot be raised to a height of 400 ft.
• Considering the diameter water will not be raised even to a height of
1mt.

26. Cohesion theory of Dixon
This theory is based on following points
• Strong cohesive force of water molecules
• Adhesive forces between water column and cell wall.
• Transpirational Pull.
A continuous water column is formed in Xylem because of
adhesive and cohesive forces.
Cont…..

27. Cohesion theory of Dixon
When water is lost due to transpiration the concentration of the
protoplasm of the Mesophyll cells increases, resulting in
absorption of water from the adjacent cell, thereby this absorption
finally leads to the absorption from the xylem tissue
The continuity of the water column is maintained by the cohesive
force which is so great that it can withstand a pressure of about
300 atm.
Finally it tends to pull the water column to satisfy the need of the
adjoining tissues.

28. Objections
• Spontaneous bubble formation takes place in xylem which may
break the continuity of the column but the known ability of the
water molecules to stick together and the cell walls makes the
probability of breaking the water column very less.
• The conducting elements also form an anastomosing network hence
if any part gets air plugged there is always a bypass to maintain the
continuity

29. Transpiration
• The process by which excess water is lost in the form of vapours
through the aerial parts of the plant is called transpiration.
It is of the following three types Cuticular, Lenticular, and Stomatal
• Cuticular transpiration is negligible, Lenticular transpiration is carried
out by Lenticels which are small openings in the cork of woody
stems, twigs and fruits.

30. Stomatal Transpiration
• Most of the Mesophyll cells
release water in the form of
vapours in the intercellular spaces.
• Intercellular spaces are
interconnected to the sub-
stomatal chambers & finally
stomata.
• Stomatal transpiration is controlled
by Guard cells.
• Each stoma has 2 kidney shaped
guard cells, full of chloroplast, with
thick and non elastic inner walls
and thin elastic outer walls.

31. Diagram of stomata

32. In presence of light CO2 is consumed, increasing the
pH hence Starch  Sugar resulting in increase in
osmotic concentration of Guard cells leading to
endosmosis and thus stomata opens.
In the absence of light, CO2 is accumulated which
reduces pH hence Sugar  Starch hence osmotic
concentration of guard cells decreases leading to
exosmosis and results in closing the stomata.
Mechanism of Opening and Closing of Stomata
Stomata are generally open during day and closed during night.
Following are the theories which explain the opening and closing
of stomata

33. Mechanism of Opening and Closing of Stomata
Stomata are generally open during day and closed during night.
Following are the theories which explain the opening and closing
of stomata
Starch Sugar Hypothesis -- According to Llyod (LIGHT)
In presence of light starch  Sugar hence osmotic concentration of
Guard cells increases leading to endosmosis and thus stomata opens.
In the absence of light sugar  starch hence osmotic concentration of
guard cells decrease leading to exosmosis and results in closing the
stomata.
During night CO2 is accumulated in Guard cells which reduces pH,
converting sugar to starch, resulting in exosmosis and stomata closes
During day CO2 is consumed, increases the pH thereby converting starch
into sugar which results in endosmosis and stomata opens.

34. Steward’s pH theory
During night CO2 is accumulated in Guard cells which reduces pH,
converting sugar to starch, resulting in exosmosis and stomata closes
During day CO2 is consumed, increases the pH thereby converting starch
into sugar which results in endosmosis and stomata opens.
Active K+ transport or Potassium pump theory
Accumulation of potassium ions in guard cells is also responsible for the
opening and closing of stomata.
During day the stomata open due to increase in the pH, increase in pH is
due to transport of K+ ions from adjacent cells to Guard cells which
results in endosmosis and stomata opens
During night the stomata are closed because of loss of K+ ions from the
Guard cells which results in exosmosis and thus stomata are closed.
ATP energy is required in the process of transport of K+ ions. Organic
acids, especially Abscisic acid controls the entry and exit of K+ ions
(changes the permeability of the membrane).

35. Monocot Stomata

36. Significance
Ascent of sap
removal of excess water
cooling effect
development of mechanical tissues
opening and closing of stomata
a necessary evil

37. Translocation of Food
Carbohydrates are mainly formed in leaves. The storage organs, leaves
are called as supply points / Supply ends whereas growing regions are
termed as consumption points / sink ends.
Transport of organic substances from Supply ends to Sink ends is called
as translocation of organic food.
Plants have all the forms of food namely, Carbohydrates, Proteins, fats
& oils but transported as soluble sugars through phloem.
Course (direction) of Translocation
Course of translocation varies depending on the developing stages .
In young seedling it is upwards from cotyledons to plumule, new buds.
From leaves the course changes, now it is in downward direction for
storage. During development of flowers & fruits, food migrates
upwards or laterally. Radial direction is in cells of pith to cortex.

38. Path / Mechanism of Translocation of Food
Organic substances are translocated by Phloem. According to Munch
hypothesis a turgor pressure gradient exists between the supply end
& sink end. (Higher conc. to lower conc.).

39. Mineral
Nutrition

40. Various types of inorganic elements obtained from soil constitute
mineral nutrients.
Carbon, Hydrogen, Oxygen are obtained from air & water & termed as
non mineral nutrients.
About 30 to 40 different nutrients have been identified in the plants.
They are categorized as Essential (required for normal growth &
development) & Non essential nutrients.
Utilization of various kinds of absorbed minerals by plants is called as
mineral nutrition.
Essential Nutrients C, H, O, N, P, K, Ca, S, Mg, Fe, Mn, Zn, B, Cu, Mo, Cl.
NPK are critical elements.
Al, Si, Na, Co, Ga (Gallium) are necessary for some plants.
Hydroponics is the technique of growing plants in soil less aqueous
medium, useful to study deficiency symptoms.

41. Classification of Essential Nutrients
Major/Macroelements/Macronutrients/Meganutrients
They are C, H, O, N, P, K, Ca, S, Mg, Fe.
They are permanent constituents & required in large quantities as they
are the components of large biomolecules.
Minor/Trace elements/Micronutrients
They are Mn, Zn, B, Cu, Mo, Cl.
They are required in traces, act as co factors or activators for various
enzymes.

42. Sr.No Nutrient Component Deficiency disease
1 Nitrogen Nucleic acids, Proteins, Vitamins, alkaloids,
Porphyrins, Coenzymes, Cytochromes
Chlorosis (yellowing) of leaves, Petioles & veins
become purple (Anthocyanin) Flowering delayed or
suppressed completely.
2 Sulphur Methionine, Cystine, Biotin, Thiamin,
Coenzyme
Chlorosis, Inward rolling of leaf margins & tips.
3 Phosphorus Phospholipids, Nucleic acids, Coenzymes(NAD,
NADP & ATP)
Premature leaf fall & formation of necrotic areas on
leaves &fruits. Stunted growth.
4 Calcium Middle lamella, chromosome Malformation of younger leaves & chlorosis around
margins
5 Magesium Chlorophyll, Activator, Binding agent in
Ribosome
Extensive Chlorosis, Older leaves affected first,
develop necrotic spots
6 Potassium Activator, Protein synthesis. Leaf tips & margins show chlorosis, Shortening of
internodes, stunted growth.
7 Iron Chlorophyll, Ferredoxin, Flavoprotein, Iron-
porphyrin, Cytochromes
Chlorosis
8 Manganese Activator Chlorosis, develop necrotic spots
9 Boron Translocation of sugars Death of shoot & root tips, Stunted growth, Flowers
are not formed
10 Copper Redox reactions Dieback in citrus, reclamation disease of cereals &
legumes
11 Zinc Activator, Forms hormones (IAA) Chlorosis of older leaves, Mottle leaf disease in
Apple, Citrus.
12 Molybdenum Activator Whiptail in Cauliflower (flower formation inhibited)
13 Chlorine Transfer of electrons in phosphorylation Poor growth

43. Mineral
Toxicity

44. Moderate increase of micronutrients causes toxicity.
Narrow range of concentration is optimum, varies in different
plants
The reduction in dry weight of tissues by 10% by any mineral
is termed as toxicity.
Many times excess of some elements inhibits the uptake of
another element.
Appearance of brown spots surrounded by chlorotic veins is a
prominent symptom of Manganese toxicity.
Manganese competes with Iron & Magnesium for uptake, also
inhibits calcium translocation in shoot apex hence the
symptoms for Mn, toxicity, are same as that for deficiency of
Mg, Fe, Ca.

45. Nitrogen
Metabolism

46. Biological nitrogen fixation is reduction of N2to ammonia
It takes place due to Nitrogenase, present only in Prokaryotes
& Cyanobacteria.
Clostridium, Azotobacter free living, Rhizobia – symbiotic
bacteria.
Nostoc, Aulosira -- free living, Anabaena azollae -- symbiotic
cyanobacteria
Rhizobia are aerobic N2 fixers, nodules develop in legumes,
Leghaemoglobin is jointly synthesized by both, which does
not allow the deposition of free O2 as nitrogenase requires
anaerobic conditions.
In Cyanobacteria few thick walled, colourless slightly enlarged
cells called Heterocysts are the sites of N2 fixation.

47. Nitrogen
Cycle

48. N2 is inert due to triple bond N atoms, hence it is converted
into Ammonium (NH4 +), Nitrate (NO3-), organic nitrogen
(Urea – ((NH2)2CO)
Movement of Nitrogen between atmosphere, biosphere &
geosphere in different forms is called nitrogen cycle.
Following are the five main processes that cycle nitrogen
Nitrogen Fixation, Nitrogen Uptake & Formation of Biomass,
Ammonification, Nitrification & Denitrification.
Nitrifying bacteria – Nitrosomonas, Nitrococcus & Nitrobacter
Denitrifying bacteria – Psuedomonas denitrificans.