PHYSIOLOGY OF PLANTS

PLANT WATER RELATION

MAIN POINT

· Plant physiology-study of life process in plants
Eg: - Transpiration, Photosynthesis, Respiration etc.
· Stephan Hales- father of plant physiology

· Plant cell

Cytoplasm+ Nucleus → Protoplasm
Protoplasm+ plasmalemma →Protoplast
Protoplast + cell wall → Pant cell
· Mature plant cell consist of three compartments.

Cell wall + Protoplasm+ Vacuole
- cell wall and protoplasm separated by plasmalemma
- protoplasm and vacuole separated by Tonoplast
- Fluid filled inside vacuole –cell sap

· Plasma membrane and tonoplast serlectively permeable
· Cytoplasm of neighboring cells are connected by cytoplasmic stands called plasmo clesmata passing through pits o cell walls.
· The net work of cytoplasm of all cells inter connected by plasmodesmata is called symplast
· The network of the cell walls of all cells inter connected to from Apoplast.
Physical phenomina involved in plant water relations

(1) Imbibition
The phenomenon of absorption of water by hydrophilic colloidal substances (eg:- cellulose, pectin etc)
· The pressure developed inside the imbibant due to imbibition – Imbibition pressure or matric potential(ψm)
· Imbibition has important role in absorption of water and germination of seeds.
· First step in absorption of water by plant roots

(2) Diffuson
Random movement of individual molecules (ions of particles) from a region of their higher concentration to a region of their lower concentration down concentration down concentration gradient is called diffusion,
· The potential ability of substance to diffuse is called diffusion pressure (DP)
· Diffusion takes place from higher DP to lower DP.
· Gaseous exchange and transpiration in plants occurs by diffusion

(3) Osmosis
Diffusion of solvent molecules (water molecules) through a semi permeable membrane is called Osmosis
· Water molecules always move from a region of their higher concentration(i.e. Dilute the solution) to a region of their lower concentration
· The pressure needed to prevent to prevent the osmotic entry of water into an aquous solution through a semi permeable membrane is called osmotic pressure. (OP of II)
· The more concentrated a solution the more will be its OP.
· The negative osmotic pressure is called osmotic potential designated as ψs ie, ψ3 = -OP or –π
- The movement of water onto a cell is called Endosmosis and moving out of water from a cell is called Exosmosis. The moving out of water from a solution by applying pressure is called Reverse osmosis
- Endosmosis and Exosmosis occurs according to the external osmotic environment (Tonicity) of a cell.
- Based of tonicity three typed of solution .
1. Hypotonic solution-Solution whose solute concentration is lower than cell sap
2. Hypertonic solution –solution having solute concentration higher than cell sap
3. Isotonic solution – Solution having solute concentration equal to cell sap.
- A plant cell if placed in a hypotonic of in pure water will become turgid due to endosmosis. eg :Swelling of raisins.
- A plant cell if placed in a hypertonic solution will become flaccid due to Exosmosis
- Shrinkage of group when they one placed in concentrated sugar solution.
- The shrinkage of protoplast of a cell due to ex osmosis called plasmolysis
- Plasmolysis x De plasmolysis
- Turgid x flaccid
- Endosmosis x Ex osmosis
· In plant plasmolysis causes wilting and drooping of leaves
· The pressure developed inside the cell due toe the entry of water by endosmosis is called Turgor pressure (TP). It is exerted against cell wall.
Diffusion pressure Deficit (DPD or SP)
· The decrease in diffusion pressure of a solution due to dissolved solutes in it is called DPD of succession pressure.
· When DPD increases the ability to absorb water increases. (because the concentration of solute is more in a solution with high DPD).


· Water moves from a region of lower DPD to region of Higher DPD
(4) Permeability
The extend to which a membrane permits of restricts the movement of a substance though it
Is called membrane permeability
· Depends of membrane composition and the chemical nature of the solute.
· Bases on permeability membranes are of three types –permeable ( eg: cellulose cell wall )Impermeable (eg :- cutinized and suberised walls) semi permeable (eg:- cell membrane ) or differentially permeable.