Plant Physiology:

The plant physiology is the branch of science that deal with physiology process or function of plant.

• Stephen Hales is considered as the father of plant physiology.

Plant Water Relation:

The movement of water from one cell to another depends upon the water relation of plant.

• Water is basic constituent of living cells.
• It is universal solvent.
• Water is important for all physiology activities of plants & play important role for all living organism.
• It acts as a reactant in no. of reaction in cell.
• It acts as a source of oxygen during photosynthesis.

WATER POTENTIAL:

It is the potential of water molecule to do some work. It is represented by Ψ (psi) and It is measured in pascal.

• Pure water has maximum energy and maximum potential.
• Water potential of pure water is maximum i.e. zero.
• So, water potential of solution will be less than zero (negative).

The factor that affect water potential are:

1. Solute Ψs: If the solute potential increase that water potential decrease.
2. Pressure Ψp: If the pressure is increases water potential is decrease increase. (Ψw = Ψs + Ψp)

Note: So water move from higher water potential to lower water potential region.

TRANSPORT IN PLANT

There are 3 thing that needs to be transported in plant:

1. water
2. minerals
3. food

So there are 2 types of transport in plant:

1. Short distance: It takes place by cytoplasmic streaming, diffusion.
2. Long distance: It takes place through Vascular tissue i.e. xylem and phloem this is normally called translocation.

Means of transport:

There are 2 mode of transport:

1. Passive: There is no use of ATP. The molecules moves from higher concentration to lower concentration until the equilibrium established. It is not sensitive to factors like temp, inhibitors.
2. Active: ATP is required for the transport. It can takes place even against concentration gradient. It is very sensitive to temp as well as inhibitor.
   Ex: Protein, enzymes.

DIFFUSION:

Movement of solute particles from higher Concentration to lower concentration untill it reaches to equilibrium is called diffusion. It is the passive process.

Ex: If a drop of ink is dropped into glass containg water soon its become distributed through out the glass untill it become faint in colour and the process is called Diffusion.

So the movement of molecule in diffusion is Spontaneously and is due to K.E. of molecule. It occurs untill it reaches the equilibrium.

Characteristics of diffusion:

• In diffusion no energy expenditure is involved. So it is a passive process.
• It is inversely proportional to distance.
• Rate of diffusion is determined by temp, concentration gradient and relative humidity.

FACTOR EFFECTING DIFFUSION:

There are several factor that effect diffusion such as:

1. Temp: Temp increases the K.E of diffusing molecule. So the rate of diffusion increases with the increase in temp.
2. Density of diffusing substance: Rate of diffusion is inversely proportional to the square root of its density. (Graham's Law)
   i.e. D ∝ 1/√d
   If the molecules of diffusing substance are larger slower will be their movement. So diffusion decrease with which the increase in the density of diffusing Substance.
3. Concentration of diffusion medium: Higher the concentration or density of the diffusion medium lower the rate of diffusion.
4. Diffusion pressure gradient: The rate of diffusion of a substance is directly proportional to the diffusion pressure gradient.

2) Facilitated diffusion:

It is a passive process but this process is fascilated by carrier proteins. Eg Porin, outer membrane.

Importance of diffusion in plant:

• Transpiration takes place due to the diffusion of water vapour from wet plant to dry atmosphere.
• During photosynthesis and respiration exchange of oxygen and Carbon dioxide takes place by the process of diffusion.
• Diffusion helps to transport the substances within the cell or betn the cell.
• Salt and ions are observed by plant by the process of diffusion.

OSMOSIS:

The movement of solvent particles from it's high Concentration to it's lower Concentration across a semi permeable membrane till its reaches equilibrium.

Note: i.e from dilute solution to the Concentration through a semipermeable membrane movement from hypotonic (lower) to hypertonic (higher) through Semi permeable membrane.

Osmotic Concentration:

On the basis of amount of solute Solution are 3 types:

1. Hypotonic Solution: The Solution has lower solute Concentration than the inside the cell is called hypotonic solution. So external solution is more dilute than the inside cell. So water move from solution into the cell. Hence, cell become turgit (swell) and may brust and this process it also called Endosmosis.
2. Hypertonic Solution: The solution has higher Concentration than inside the cell is called Hypertonic solution. So external Solution is more Concentrated than cell. So water move from cytoplasm of cell to the surrounding Solution by the Process called Exosmosis.
3. Isotonic: The solution has the same concentration of water and solutes as inside a cell or external Solution that balances the osmotic pressure of the cytoplasm of cell. So there is no net movement of water across the membrane.

Types of osmosis:

On the basis of movement of water from the cell or into the cell. Osmosis of two types:

1. Endosmosis: When a plant cell is place in pure water, the water enters the cell. This phenomenon is called Endosmosis. The water molecule moves in the living cells and cell soil become turgid.
   Movement of water from soils into root.
2. Exosmosis: When the plant cell is placed in Concentrated Soln (water) comes out of the cells. This is called Exosmosis. In this case cell can shrink (flaccid) Eg: When the graps is kept in the salt solution it shrink due to exosmosis.

In physical system osmosis depends upon 3 factor

1. Temperature: keeping pressure Constant when semipermeable membrane Seperates pure water on two side each being at different temp, the molecules of water will from the region of higher to the region of lower temp.
2. Pressure: If the pressure increase water moves from higher pressure to the lower pressure.
3. Concentration gradient: The liquid move from higher Concentration to lower Concentration.

Osmotic pressure (OP):

[Diagram of U-tube experiment with SPM]

The net movement of solvent molecule from solvent to solution can be stoped by applying Some extra maximum amount of pressure over solution side which stops osmosis. This is called osmotic pressure. It is represent by pascal.

In the above experiment the movement of water inside the funnel can be prevented by applying pressure to the Solution from upper part. This pressure required to stop the movement of water completely is called osmotic pressure. It is also refers as Osmotic potential or solute potential.

Reverse osmosis:

Reverse osmosis is also know as hyper filtration. It is a technique that allows the removal of water molecule from various Containment through semi-permeable membrane. The process requires driving force i.e pressure from pump to push the fluid through the membrane.

Eg: Disalination (Removal of salt molecule)

Sea water -> Drinking water (Fresh water)

Diffusion pressure defeceit:

The amount by which The diffusion pressure of a solution is less than its pure solvent is called diffusion pressure defeceit.

i.e In turgid cell: OP = 10, TP = 10 -> DPD = OP - TP = 10 - 10 = 0

Flaccid: OP=10, TP=0 -> DPD = 10-0 = 10

Turgor:

Turgor pressure of hydrostatic pressure is the pressure exerted by cytoplasm against the liquid it is also called Pressure Potential. Because of rigidity of cell wall the cell doesn't repture as cell was is rigid and elastic therefore it exerts equal an opposite pressure against expanding cytoplasm. This back pressure exerted by the cell wall is Called wall pressure (WP). These two pressure turgor and wall pressure are equal & opposite in direction.

Turgor pressure is max when the cell wall Can't stretch any more this such a cell is called turgid ie amount of water entering the cell is equal to the amount of water leaving the cells.

• Turgor pressure (TP) develops in plant cell only presence of cell wall.

Turgidity plays a very important role in the plant:

• The Turgor pressure helps to in maintaing the shape and forms of plant.
• The stem of Herbaceous plant ie non-woody tissue that is maize, sugarcan, banana are held stright by fully turgid cell pack tightly together.
• Turgor pressure holds the leaf in flat and horizontal position.
• Opening and closing of stomata is governed by the turgidity of the guard cell.
• Certain plants like beans and touchme not (mimosa pudica) show with response of drooping or straightening of leaf by controlling the turgidity.

TP = WP

water moves into the cell -> osmotic pressure.

Plasmolysis:

When cell is placed in hypertonic Solution exosmosis takes places due to the process of exosmosis the protoplasm of the plant cell shrink. The shrinkage of protoplasm of plant cell due to loss of water is called plasmolysis. And cell is called plasmolysed cell.

If we place the plasmolysed cell in the hypotonic solution water again enters into the cell and become turgid. This is called de-plasmolysis and cell is called deplasmolysed cell.

[Diagrams showing Normal Cell -> Incipient Plasmolysis -> Plasmolysed Cell]

Significance of Plasmolysis:

• Plasmolysis is the charactersitic features of living plant cell. All living cell plasmolysed when kept in hypertonic solution.
• Pickle, meat, Fish are preserved by salting. Similarly Gams & Jellies are preserved by Sweetening with Sugar. Salting Sweetening creates hypertonic So Condition in which fungi & bacteria gets killed by plasmolysis.
• Salty killed weeds of lawn by inducing plasmolysis in their cells.
• Plasmolytic method is applied for the determination of osmositic pressure of a cell in lab.

Imbibition:

Imbibition is the phenomenon of adsortion adsorption of water or any other liquid by the solid particle of a substance without forming a solution.

Eg: If dry piece of wood is placed in water it swolles and increases in volume.

• If agar-agar are placed in water the swolles and their volume increases.
• Wooden doors and window absorbes water in humid rainy seasons and increase in volume so they are hard to open or close.

The solid particle which adsorb water is called Imbibit and liquid which is imbibed is called imbibant.

Application of Imbibition to the plant:

1. It help in germination of seeds because the stored Food in seed swolles causing the seed cot to rupture.
2. Before absortion of water cell wall of root hairs b. Imbibed water.

Note:

1. Apoplast Pathway: In this Pathway, water moves from root hairs to xylem through the interconnecting cell and wall intercellular Spaces As living part of cell (cytoplasm) aren't included in this system so it is non-living System & is a fast process.
2. Symplast: The symplast system includes the living part of plant made up of interconnected cytoplasm of neighbouring cells.
   In this pathway water moves from one cell to another through plasmodesmata by which the cytoplasm of adjecent plant cell is connected.

Ascent of Sap:

After Water is absorp by the plant root it is transported to all part of plant and utilize for different purposes.

The water adsorb by the root from the soil is not pure water. It is dilute solution minerals, salt and water is Called as Sap.

So upward movement of Sap or dilute solution from Root to shoot of the plant against the gravational force is called ascent of Sap.

Mechanism of ascent Sap:

The sap is move upward against the force of gravity to great height. Many theories have been purposed to explain the ascent of sap:

1. Vital force theory
2. Root pressure theory
3. Physical force theory

1) Vital force theory:

These theory Support that the ascent of sap is due to vital activites in the stem (living cell) two theory are given here:

a) Relay pump theory:
These theory was purposed by Godlewski in 1884. According to him due to change in Osmotic pressure of xylem parenchyma (ie pumping activities of living cell) They are responsible for the upward movement of water.

Objection:
These theory was discarded by Strasburger (1893). He explain that ascent of sap continous in the stem though living cell are killed by poison.

b) Pulsation theory:
This theory was purposed by J.C Bose in 1923. According to him ascent of sap takes place due to Pulsatory activity. Pulsatory activities of living cell of inner most Corticle layer present near to the vessel and tracheid to xylem.
This theory was rejected due to no co relation betn Pulsatory activity and ascent sap was seen.

2) Root Pressure theory:

This theory was purposed by Pristely. The pressure developed by xylem cell by the absorp tion of water through root hair is called root pressure. So the water went in the xylem vessel and tracheids due to root pressure.

Eg: If tomato plant cut near its base the xylem Sap is seen to flow out through cut end and this is due to Root pressure.

According to this theory Root pressure develop in the xylem of root can raise water to a certain height but does't seen effective because of following reasons:

• Magnitude of root pressure is very low (at 2 atm).
• Even in the absence of root pressure ascent of sap continous.
• Eg (Sea) When a leafy twig is cut under water & placed in a beaker full of water it remains fresh and green for long time.
• In Germosperm root pressure has rarely been observed.

3) Physical force theory:

According the physical force theory the dead cell are responsible for ascent of sap. There are many theories which are explain below.

a) Atmospheric pressure theory:
According to this theory the ascent of sap in plant takes place due to atmospheric pressure.

Objection:
But it is not true for all plants as atmospheric pressure can risen water upto height of 34 feet. And there is no such expose area in plant to be acted by atmospheric pressure to rise the water.

b) Capillary force theory:
In plants the xylem vessel are placed one above the other forming of continouse channel. This can be compared with long Capillary tube. It is through that water rises in Capillary tube due to Capillary force. It was supported by Boehm (1809). There are many objection on this theory:

1. For capillary free surfaces required.
2. The magnitude of capillary force is very low.
3. The soil water is not connected with the xylem vessel directely.
4. In Gymnosperm and pterophytes Vessel are absent & other xylem element donot form continuous chanal.
5. Cross wall of xylem element may not allow the capillary movement.

c) Imbibition Theory:
Ungar (1868) supported view that ascent of sap can take place through the wall of xylem by imbibition. But now it is not supported because the ascent of sap take place through lumen not through wall of xylem.

d) Transpiration Pull & Cohesion of water theory:
This theory was orginally purposed by Dixon & Joly in 1894. The theory is base on the following features:

1. Cohesive and adhesive properties of water molecule to form and unbroken continuous water coloumn in the xylem.
2. Transpirtion Pull or tension exerted on this water coloumn.

1. Xylem vessel are tubular structure extended from root to the top of the plant. Cell are placed one above the other with their end wall perforated forming a Continuous tube.
2. These are supported by xylem treachied which have pores in their wall.
3. One End of xylem tube is Connected with root hair via parecycle, endodermis, & cortex and other end is connected with the Sub stomatal cavity in the leaves through mesophyll cell.
4. This tube is filled with water.
5. The water is filled inside the xylem capillary due to cohesion & adhesion properties of water which form Continous water coloum. The water coloumn Can't be broken or pulled away from xylem wall because of cohesion and adhesion of water.

2) Loss of water from mesophyll cell causes decrease in the water potential (ie the cell sap of mesophyll cell become more Concentrated & consequently its water potential decrease. The water moves from cell to cell along the water potential gradient. Finally the movement of water with in the leaves is transpritted to the water filled in the xylem element. These exerted a Pull and water fill in the xylem comes in a state of tension. These pull is called transpiration pull. These tension generated at the top of the unbroken water coloumn is transmitted downward from petiole, stem & finally reaches to the root. These tension or pull result in the upward movement of water.

Transpiration:

The loss of water in the vapour from the living tissue of the areail part the plant is turn is transpiration.

Mechanism of transpiration:

Water may be lost from cuticle, stomata or lenticels.
Transpiration may occurs 2

• Diffusion of water from the cell wall of mesophyll cell into intercellular spaces.
• Diffusion of water vapour present in the intercellular spaces into outer atomposhere.

Reason:

When the water vapour accumlate into inter cellular species vapour pressure increase and water vapour start diffussing Outside into dry atmosphere mainly through the stomata a minar amount of water is lost directly from the open surface of leaves through cuticle. The loss of water vapour continuous till the Stomatal apeture open. Therefore transpiration is regulated by opening & closing of stomata but if the transpiration lenticular, the lenticels is always open.

Types of Transpiration:

Transpiration may occurs Following 3 sides:

1. Stomatal Transpiration: It is the loss of water which occurs through specialized aperture which are present in leaves called stomata. In herbiscous plant, the stomata can also occur in the epidermis of green stem. It account from 80-90 percentage of the total water loss from plant.
2. Cuticle transpiration: It is the transpiration through the cuticle of the epidermal cell of leaves & stem. It rarely exceeds 5% of the total water loss. It various with the thickness of the cuticle. Thicker the Cuticle, Lesser is the transpiration.
3. Lenticels Transpiration: It is the evapouration of water through lenticels. Lenticels are minute pores present on the bark. They contain loose parenchymatous tissue with lots of air spaces through which water Vapour can escape.

Factor affecting Transpiration:

There are many external & internal factors that effects transpiration.

a) External factors:

1. Temperature: higher the temp more is the Transpiration because the rate of evaporation of water from the mesophyll cell increases the transpiration rate. The temp of leaves get raised by absorping the sun light. These also increases vaporiization of water in leaf which inturned increases transpiration.
2. Light: light affect transpiration by infilenc ing the open & closing of stomata. The most mesophytes it causes stomata to open & hence increase the water loss from the plant.
3. Wind velocity: The velocity of wind greater effect the transpiration rate. As air blows it increases transpiration by removing all the water vapours from the surface of transpiring leafs. high wind velocity some time decreases the rate of transpiration as it results in the stomatal closer.
4. Atmospheric pressure: low atmospheric pressure increase evaporation and increases the rate of transpiration. For eg: Plant growing at hill show higher rate of transpiration but this effect is neutilized by low temp Present at the hills. So transpiration is normal in hills.
5. Available of Soil water: If the available water in soil is not sufficient the rate of transpiration is decrease. i.e rate of transpiration is equivalent to the rate of water absorption.
6. Carbon dioxide (CO2): high amount of CO2 acts as anti-transperent. The chemical that prevent transpiration are called anti-transperent. As they result closing of stomata. Eg: wax, vaselin, asperin, abscissic acid etc.
7. Humidity: Humidity means the amount of water vapour present in atmosphere. if the conc. of water vapour is higher in the atmosphere than that in the leaf the vapour can't diffuse outside. So the rate of transpiration is low. i.e That is rate of transpiration is inversely proportional to the humidity.

b) Internal factor:

1. Leaf Area: By reducing the size of leaf plant decreases their rate of transpiration ie xerophytic character. larger leaves loss more water than small leaves.
2. Leaf structure: The following anatomical features reduces the rate of Transpiration.
   • Thick cuticle on the surface of plant parts.
   • Wax, resin & suberin coating on the surface of plant part.
   • Compact mesophyll cell in the leaves.
   • Reduction in the number of stomata.
   • Sunken stomata.
3. Age of plant: Rate of transpiration is slow at the seedling stage, maximum at maturity & gradualy decrease near the Senescence.

Significances:

• Transpiration influence the rate of absorption water from soil.
• By transpiration water move upward & it passes into cell vacuolar it make cell turgid. These gives form & shape to the cell & to the plant as a whole.
• Transpiration also help in the distribution of minerals through out the plant.
• The evaporation of water during transpiration cools the leaves.
• Some plant cacuts, retrain water by reducing transpiration. These save the plant from high temp & strong sun light.

Transpiration as a necessary evil:

Transpiration is a very important activities as it facilitated the movement of water & minerals up toward the leaves in a plant. At the same time if the water lose in more than the uptake of water by the root can cause wilting & even death of the plant. It is for reason that Curtis in 1926 had refered transpiration as a necessary evil.

Stomata & Transpiration

Stomata are tiny course present the epidermal layer of leaf leaves. the size of typical stomatal pores is 3-12 μm in wide & 10-14 μm in length. There would be as many as 2,000 to 50,000 stomata per cm2 of a leaf Surface.

In monocot leaves, they are almost equally distributed and are present on both the Surface of leaves. However, in dicot leaves their density is much more on the lower epidermis.

Rates of stomata in transpiration:

Since most of the water is lost from sto through stomata plant regulates the degree of stometal opening to reduce the water loss. It has been seen that stomata show periodic Opening & closing during the day depending upon the heat + light, water contains of the cell & humidity. They are generally close during the night.

Mechanism of Stomatal movement:

The opening & closing of stomata operates as a result of turgor changes in the guard cells. Then the guard cell become turgid their thin wall get extented & thick wall become Slightly Concave so that the stomata Opens.
On the other hand, the guard cell become flaccid when they lose water their thick wall goes to back to Original position resulting in the closing of stomatal pore.

Note: cellulose microfibric & micelles are arranged around circumference of guard cell & called radial micellation.

There are several hypothesis for explaning mechanism of stomatal movement.

a) Mohl's hypothesis (Photosynthetic theory):

According to Von Mohl's (1956) the chloroplast present in guard cell prepared sugar through photosynthesis. As a result their osmotic pressure increases with the increase in turgor pressure due to endosmosis. This result in Opening Stomata.

This theory is not accepted because in many cases gaurd cell are found to be less important for photosynthesis as compared to mesophyll. Hence the hypothesis is rejected.

b) Starch-Sugar hypothesis:

This hypothesis is given by Lloyd & explains that increase Concentration due to photosynthesis & endosmosis of water during the day leads to the opening of stomata & vice versa (decrease in sugar con. follow exosmosis leading to the closing of stomata at night.

Reaction in light:
Utilisation of CO2 during photosynthesis -> Drop in CO2 lead cytoplasm to be alkaline -> Conversion of starch into sugar -> Increased concn of Solute -> Endosmosis of water -> Increased Turgor pressure -> Stomata Open

Reaction in dark:
Accumulation of CO2 due to absence of photosynthesis -> Increased acidity due to formation of carbonic acid -> Conversion of Sugar into Starch -> Decreased concn of solute -> Exosmosis of water -> Decreased Turgor pressure -> Stomata closed

Action of Potassium (K+) Theory: (Role of K+ in stomatal movement)

This theory was purposed by Levitt Fujino & modified by Levitt.
It is Considered a modern theory. It has been proved that the accumulation of K+ alone brings the Opening of stomata & loss of potassium ions causes closing of stomata.

During light starch in guard cell is metabolized into PEP (phosphoenol pyruvic acid). This PEP combines with CO2 to produce oxaloacetic acid & finally mallic acid.
-> The organic acid that is malic acid dissociation into malate anion & H+ in the guard cell.
-> H+ transported from guard cell to subsidary cell and K+ are taken into guard cell activity this process is called ion exchange.
-> H+ = K+ exchange is an active process which required involvement of Energy ATP supplied either by respiration or by photo phosphorylation.
So, K+ ion increase in guard cell increases the osmotic pressure. As a result water enters the guard cell by endosmosis. Thus, turgor pressure increases and stomata gets open.

- At night CO2 is not utilized thus Concentration increased stomatal activities so organic acid are Converted back to starch. and inhibitor hormone abssissic acid which function as acidici medium and inhibit K+ uptake by changing the diffusion and permiability of guard cell. The K+ ions transport back to epidermal cell and thus OP of guard cell decreases causing exosmosis. The guard cell become flaccid & stomatal pore get closed.

Infact the actually stomatal closer still not clearly known.

Guttation:

The process exudation or Guttation is defined as the loss of water in the form of liquid drop from the edges of leaves.

• It occurs through stomata like pores called hydathodes.
• Exudation may Sometime Occurs from stem through scars of leaves & lenticels. It is the process by which fully tugid plant removes extra water.
• The cause of Guttation is mainly root pressure.
• Hydathodes pores are Surrounded by epithem which lies above a vein ending (ie xylem).
• Due to root pressure water is forced by xylem into intercellular Spaces & flows out a hydathodes.

Difference between Transpiration and Guttation