Crop Physiology note of 2nd sem

DIFFUSION AND OSMOSIS
DIFFUSION
The movement of gas, liquid or solid particles or ions from higher region of higher concentration to the region of their lower concentration is known as diffusion.
Thus, the exchange of CO2, O2 and water vapour between leaf and external atmosphere is the process of diffusion.
CHARACTERISTICS OF DIFFUSION
 The molecules or ions diffuse from the region of higher concentration to the region of lower concentration.
 The diffusion molecules move randomly towards all the regions of their lower concentration. This continues till the molecules get evenly distributed in the space available. The movement of molecules is due to their kinetic energy.
 The direction of diffusion of one substance is independent of the movement of another molecule.
 The rate of diffusion of molecules is proportional to their kinetic energy, their size, the density of medium through which they move and gradient of concentration over which they diffuse.
DIFFUSION PRESSURE
 The movement of molecules depends upon the internal kinetic energy. The molecules in the region of higher concentration contain more kinetic energy and they show fast movement.
 The movement of all the molecules collide themselves and produce a kind of pressure in the medium is known as diffusion pressure.
DIFFUSON PRESSURE OF LIQUID
 Like gases, solvent and liquid also posses diffusion pressure. The diffusion pressure of a pure solvent is always maximum and when solute particles are added in it, the diffusion pressure of solution is reduced.
 The difference between the diffusion pressure of a solvent and its solution is called diffusion pressure deficit (DPD).
 When the deficiency in diffusion pressure of a solution is created, it starts absorbing more solvent particles to overcome this deficiency.
 Thus can be found out the absorbing capacity of a solution through DPD and DPD of a solution gives on idea about the absorbing capacity of that solution.
 DPD is also called suction pressure (SP).
DPD = OP – TP where, OP = Osmotic pressure
TP = Turgor pressure
FACTORS AFFECTING THE RATE OF DIFFUSION
1. Temperature:
 Temperature is directly proportional to the rate of diffusion.
 On increasing the temperature, the rate of diffusion particles is also increased because of increase in the velocity of these particles.
2. Concentration of the medium:
 Medium is inversely proportional to the rate of diffusion.
 On increasing the concentration of medium, the rate of diffusion is reduced and vice versa.
3. The size and mass of diffusing particles:
 If the size and mass of diffusing particles is smaller, the rate of their diffusion will always be faster.
4. Solubility of solute:
 The rate of diffusion increase with the rate of dissolution of solute in solution.
 Thus, more the solubility of any solute in solution faster will be the rate of diffusion.
5. Density of the diffusion pressure:
 The rate or diffusion of gases is related with the density of diffusing particles.
 According to Graham’s law of diffusion, the rate of diffusion of any particles is inversely proportional to the square root of its density.
r = 1/√d
Where, r = Rate of diffusion of gas
d = Density of gas
 The gases having higher densities show slower rate of diffusion, where as those possessing lower density show faster rate of didifffusion.
Example:
The density of Hydrogen [H] is one and oxygen [O] is 16.
Therefore according to Graham’s law of diffusion,
rH/rO = √dO/√dH = √16/√1 = 4/1 = 4
Hydrogen will diffuse 4 times faster than Oxygen.
IMPORTANCE OF DIFFUSION OF PLANTS
 The exchange of O2 and CO2 gases in the atmosphere through stomata of leaves takes place by the process of diffusion.
 During stomatal transpiration, the water vapours from intercellular space diffuse in the atmosphere through stomata by the process of diffusion.
 The diffusion of ions of mineral salts during passive absorption also takes place by this process.
 The absorption of water through roots is also performed by diffusion.


OSOMOSIS
Osmosis may be defined as the passage of solvent molecules from a region of their higher concentration to the region of lower concentration through a differentially permeable membrane.
The solvent in all biological systems is water. Thus, in other words, it is the diffusion of water through a differentially permeable membrane.
PERMEABILITY:
 Permeability is the degree of diffusion of gases, liquid and dissolved substances through a membrane.
 The entrance or exist of any substances in the cell depends upon the permeability of the plasma membrane.
 The permeability membrane can be classified in the following types:
i. Impermeable:
 These are those membranes through which only exchange of gases take place.
Example: Cell wall with thick layer of cutin on its surface.
ii. Semi permeable:
 A membrane that is almost totally impermeable to solute molecules but permeable to the solvent is called semi permeable.
 These are the membranes through which only the exchange of water or solvent particles take place.
 Solute can neither enter nor can leave through such membranes.
Example: Egg membrane, urinary bladder of goat, etc.


iii. Selectively permeable:
 These are the membranes through which the exchange of only selected ions or small molecules takes place.
 Plasma membrane is mainly selectively permeable and not only semi permeable.
iv. Permeable:
 This type of membrane has free passage of water, other solvents and most of the dissolved substances.
Example: Plant cell wall
v. Dialyzing membrane:
 These posses other layers in the form of outer covering.
Example: Cell wall



FACTORS AFFECTING PERMEABILITY
External factors
1. Physical agents:
 High temperature, heat, low pressure of O2 and CO2 radiations, etc increase the permeability of plasma membrane.
2. Chemical agents:
 A number of chemicals such as ether, benzene, chloroform, acetone, toxic substance, etc. when added in the external medium or solution, increase the permeability.
3. Ageing of cells:
 Permeability varies at different age of cells.
 In young cells, it is low but at the time of senescence, it is increased.
 The older cells approaching death also show increase in permeability.
Internal factors
1. Membrane constitution:
The permeability of plasma membrane depends upon its constitution i.e. percentage of lipid, carbohydrates and phosphates, etc.

TYPES OF SOLUTION
From the biological point of view, the solution my be of following types.
1. Hypertonic solution:
 Those solutions whose concentration and osmotic pressure (O.P.) are more than the concentration and O.P. of cell sap are called hypertonic solution.
2. Hypotonic solution:
 Those solutions whose concentration and osmotic pressure (O.P.) are less than the concentration and O.P. of cell sap are called hypotonic solution.
3. Isotonic solution:
 Those solutions whose concentration and osmotic pressure (O.P.) are equal to the concentration and O.P. of cell sap are called hypertonic solution.

TYPES OF OSMOSIS
1. Endosmosis:
When water or solvent molecule enters into the cell through plasma membrane from outer medium, it is called endosmosis.




2. Exosmosis:
When water or solvent molecule exits from the cell through plasma membrane from outer medium, it is called endosmosis.









Osmotic pressure
 Osmotic pressure of a solution is the maximum hydrostatic pressure that a solution could develop when separated from its pure solvent by a selectively permeable membrane.
 Chamber A contains pure water and B contains sugar solution, two solutions are separated by selectively permeable membrane.
 Water molecules will diffuse through the membrane from both sides. When water move rapidly from A to B than from B to A.
 Liquid will raise in chamber B and decrease in A.
 Here, pressure is applied in B side piston. This pressure is required to resist the osmotic flow of water from A to B, called osmotic pressure.








FACTORS AFFECTING OSMOTIC PRESSURE
1. Concentration of solute particles:
 It is directly proportional to the O.P. The O.P. of concentrated solution is always greater than the O.P. of solution of low concentration.
 If the concentration of solute particles is increased in any solution, its O.P. will also increase.
2. Temperature:
 It is also directly related to the O.P. If the temperature of the solution is increased, its O.P. will also increase.
3. Ionization of solute particles:
 If the solute particles in the solution are present in ionic form and their concentration is increased. The osmotic pressure of the solution is also increased.
4. Light:
 Light plays an indirect role on O.P.
 In sunlight, the synthesis of carbohydrate takes place due to photosynthesis which increases the concentration of protoplasm resulting in increase in O.P. of the cell sap.
5. ¬Position of tissue:
 The tissue which is nearer to soil or water supply posses low O.P. in comparisons to those which are away from water supply.
 Due to this reason, leaves posses higher O.P. than roots.
 This pressure increase simultaneously from roots to upper portion of stem.
SIGNIFICANCE OF OSMOSIS IN CROP PLANTS
 Absorption of water from soil by roots hairs is due to osmosis.
 Osmosis helps in maintaining the turgidity of plant organs.
 The opening and closing of stomata is dependent on the turgidity of guard cell which is due to osmosis.
 Growth of young cells by increase in their size is due to O.P. and T.P
 Due to the higher osmotic concentration of cells, they become resistant to freezing and desiccation.
DIFFFERENCE BETWEEN DIFFUSION AND OSMOSIS
Diffusion Osmosis
The molecules always move from the region of higher concentration to the region of lower concentration. The water molecules move from less concentrated solution to high concentrated solution.
Diffusion occurs in solid, liquid and gases. Osmosis occurs in solvents only.
It doesn’t require semi permeable membrane. It takes place through semi permeable membrane.

THE CONCEPT OF WATER POTENTIAL:
• The water is a good solvent. The water molecules possess free energy and the difference between free energy of water molecule in pure and in any other system is called water potential.
• Any other system means the water in a solution or in a plant cell or tissue.
• The Greek letter ‘Psi’ is used as a symbol for water potential. The water potential is measured in terms of a pressure, eg. bars or atmosphere, 1 bar = 750mmHg or 0.987 atm.
• Water potential of pure water at atmospheric pressure is zero and this is considered to be the highest. The pressure of solute particles the decrease the water potential.
• The water moves from the system having higher free energy towards the system having lower free energy, usually the free energy of pure water is greater than the free energy of other solutions prepared in water.
• If the two regions in an aqueous system have water potential A and B respectively, the difference in water potential will be,
=

=

• If is greater than , will be +ve and the water moves from A to B.
• If is greater than A, will be –ve and the water will move from B to A.
• The water potential of a solution is usually measured using pure water as a standard. The water potential of pure water at atmospheric pressure is zero. When the solute particles are added in water and solution is prepared, they reduce the free energy of water.
• Thus the water potential of solution is decreased and comes in –ve value. i.e. less than zero.
• Due to this reason the water potential of a solution is always less than zero.
• If the two system having different water potential are separated by a semi permeable membrane, the movement of water molecules always takes place from the system having higher water potential (less concentrated soln) towards the system having lower water potential (more concentrated soln)
• The movement of water will continue till the water potentials of the two systems become equal. At this stage, the net transfer of water will cease.



COMPONENTS OF WATER POTENTIAL:
• When a typical plant cell containing cell wall, vacuole and cytoplasm is subjected to movement of water, a no. of factors are involved, Which determines the water potential of cell sap.
• The water potential of a living cell is determined by three major components or potentials.
i. Matric potential(ᵠm)
ii. Solute potential(ᵠs)
iii. Pressure potential(ᵠp)
• The water potential is actually the sum of all the above three potentials.
ᵠ=ᵠm+ᵠs+ᵠm

i. Matric potential:
• The term matric is used for such surface which can absorb water molecules, eg. cell wall, protoplasms and soil particles etc.
• While the matric potential refers to that component of water potential which is influenced by the presence of matric.
• Matric potentials are also –ve values. They reduce the water potential of a system (region).
• The matric potential in case of plant tissues and cells is often neglected because it is insignificant in osmosis.
• The above equation may be written in simplified form as follows;
ᵠ=ᵠs+ᵠp
• The equation indicates that water potential of plant cells and tissues is usually the sum of solute potential and pressure potential.
ii. Solute potential:
• It is also a component of water potential and is also known as osmotic potential. The amount of solute present in water is called solute potential.
• The presence of solute in water reduces the value of water potential and reduction value of ᵠ are directly proportional to the potential of water. Since the potential of pure water is zero.
• The value of solute potential or osmotic potential are always –ve i.e. less than zero.
• The solute potential expressed in bars with –ve sign and the term ᵠS has replaced the osmotic pressure. The term used earlier.


iii. Pressure potential:
• The cell wall of a plant cell, which is made up of cellulose, provides a definite shape to the cell and is elastic in nature.
• It is also exerts a pressure on the cellular contents inwards (in wall-wall pressure) resulting into development of hydrostatic pressure in the vacuole called turgor pressure.
• The value of ᵠP in plant cells are +ve and ᵠP is equivalent to wall pressure and turgor pressure.




OSMOTIC RELATIONS IN THREE PHYSICAL STATES: (ᵠ,ᵠS and ᵠP)
According to water potential,
1. In fully turgid cell:
• Net movement of water into cell stops.
• The cell will be at equilibrium state with water of outer medium.
• The water potential ᵠ will be zero.
• The cell at full turgor pressure ᵠS equal to ᵠP but with opposite sign. i.e. its ᵠ will be zero.
If ᵠP of cell is 5 bars,
Then, ᵠ=ᵠS+ᵠP
=-5+5=0 bar
2. In flaccid cell:
• The turgor becomes zero.
• At zero turgor, the cell shows osmotic potential(ᵠO) equal to its water potential(ᵠ)
• Flaccid cell has an osmotic potential(ᵠO) of -5 bars and pressure potential(ᵠP) of 0 bars, i.e. ᵠO=-5 and ᵠ=0
Then, ᵠ=ᵠO+ᵠP
=-5+0 bars
=-5 bars.
• Thus the water potential ᵠ of the cell will be -5 bars. This value is less than the ᵠ of pure water, i.e. zero.

3. In plasmolysed cell:
• The pressure potential ᵠP has negative value i.e. the cell shows negative turgor pressure.
• The water potential in such a cell will be more -ve. If in a plasmolysed cell
ᵠS=-5 bars and ᵠP=-1bars
ᵠ=ᵠS+ᵠP
=(-5)+(-1)=-6 bars.

PROBLEM REGARDING OSMOTIC ENTRY OF WATER:
There are two adjacent live cell A and B. cell A has an osmotic potential(ᵠS) of -10 bars and pressure potential(ᵠP) of 5 bars where cell B has an osmotic potential of -5 bars and pressure potential of 2 bars. What will be the direction of water flow in the cells.





Cell A Cell B
ᵠS=-10 bars
ᵠP=5 bars ᵠS=-5 bars
ᵠP=2 bars
ᵠ=ᵠS+ᵠP
=-10+5
=-5 ᵠ=ᵠS+ᵠP
=-5+2
=-3

• In the problem, the cell A has ᵠS=-10 bars and ᵠP=5 bars therefore, the water potential(ᵠ) of the cell, A will be -5 bars.
• The cell B has ᵠS=-5 and ᵠP=2 bars,
Therefore, the ᵠ of cell B will be -3 bars.
• Since, the osmotic entry of water always takes place from higher water potential to lower.
• The direction of water flow will be from cell B(-3 bars) to cell A(-5 bars).















Ascent of sap
• The water and soluble mineral salts absorb by the root reach to the leaves through roots, stem and branch of the plant.
• The phenomena of ascending of absorbed water against gravitation through the vessels and tracheids of xylem is called ascent of sap.

Path of ascent of sap
• The water ascent through the vessels and tracheids of xylem. In other word the path of ascent of sap is xylem.
• In young herbaceous plant almost all the trachery elements (tracheida and vessels) participate in this process but in large woody trees, the trachery elements of only sap woods are functional.
• It can be demonstrate by the following experiments…..

Experiment no.1
• It can be studied easily in white flowered lupin plant or rose plant.
• Cut a flowering twigs of either lupin or rose plant in water avoid the entry of air bubbles and place it in beaker containing a solution of eosine in water.
• After a few hours the minute vein of the petal of flower become reddish. Now cut the T.s of stem and absorb that xylem vessel and tracheids are red.
• It prove that ascent of sap in plant takes place through the vessel and tracheid of xylem.

Experiment no.2
• This experiment was performed for the first by Stephen kales.
• It also demonstrate the ascent of sap in stem through vessels and tracheids of xylem.
• For this experiment, take a plotted plant and remove in circular fashion at some place of stem, all the outer tissue (epidermis, cortex, endodermis, pericycle and phloem) except vessel and tracheids of xylem and pith.
• Leave the experiment for a few days and observe that the leaves of the plant are still green.
• It proves that the water and soluble salts ascend through the xylem tissue.
Mechanism of ascent of sap (Theories of ascent of sap):
• Many theories have been proposed to explain the mechanism of ascent of sap. They are divided into two main group.

1. Vital theory:
a. Root pressure theory
b. Godle wski theory
c. Vital force theory
2. Physical theory:
a. Imbibition theory
b. Capillary force theory
c. Cohesion theory of Dixon and Jolly

Root pressure theory:
• The pressure developed in the xylem cell by the absorption of water through root hairs is called root pressure.
• The water ascends in the xylem vessels and tracheids due to root pressure.
• The plant possess root pressure of only two atmospheres, which helps the water to ascend up to a maximum height of only 20m.
• It has been confirmed by the experiment that, if the plant is placed in water vertically after removing its root portion, even then the upward movement of water doesn’t stop.
• Thus the root pressure theory proves to be wrong.

Godle wski theory(1889):
• This theory proposed that the water ascend in the plant due to pumping action of the cell of xylem parenchyma and medullary rays.

Vital force theory:
• Well known Indian scientist sir J.c bose (1923) advocated that the cell of inner layer of cortex possess pulsating action like heart.










• When these cell expand, the water of adjacent cortex cell diffuse into them and they (cell of inner layer of cortex) becomes turgid.
• When this cell contract, the water ascend in the plant forcibly. Bose confirmed his observation with the help of apparatus, electric probe prepared by himself.
• He took the electric probe and connected it with the galvanometer through battery. When he inserted the needle of probe entered into the inner layer of cortex.
• But the needle of galvanometer did not show any movement during the entry of probe needle into various outer layer of cortex.
• Most of the modern scientist are against this view. Strasvurger (1893) prove all the vital theories wrong. He observed the continuous ascending movement of water even if the cell of parenchyma and midullary rays where destroyed with the help of poisonous chemical substance like picric acid.


,COHESION THEORY OF DIXON AND JOLLY( Transpiration Pull)
• This theory was proposed by Dixon and Jolly(1894) and has been supported by Curtis and Clark(1951) Milburn and Johnson(1966) and Levitt(1969)
• This theory is now popularly known by various names such as Cohesion hypothesis, Theory of Cohesive force, Dixon and Jolly theory or Transpiration pull theory, Cohesion tension theory or Transpiration pull theory.
What is Cohesion?
• Attraction between the similar molecules is called Cohesion. The water molecules have strong mutual attraction (Cohesion) due to which they can’t be easily separated from one another.
• The magnitude of cohesive force of water, which has been measured upto 350 atms. Is much in excess of the minimum required for the ascent of sap in the tallest trees.
Cohesion-Tension theory:
• Water forms a continuous column from base of the plant to its top and remains under Cohesive tension due to transpiration pull.
• And according to the need water is being pulled up to the top of the tree.

Characters of Cohesion-Tension theory:
This important and widely accepted theory has following essential features.
• Water forms a continuous column from the base of the plant to its top.
• Water is lost from mesophyll cell due to transpiration because of which a pulling force develop,it puts this cell under tension.
• The tension may cause a break in water column but due to tensile strength or cohesive properties of water molecules, the continuous column is not broken.
The tension or transpiration pull is transmitted to the root region to regulate absorption

Mechanism of ascent of sap
• The loss of water from the surface of leaf mesophyll cell due to transpiration reduce the water amount and causes an increase in the osmotic pressure of these cell.
• Thus a reduced water potential is developed in the mesophyll cell i.e D.PD increase.
• Water from the adjacent cell and ultimately from the conducting tissue is pulled to meet these losses of water and as a result a pull is developed in mesophyll cell and xylem cell of the leaves.
• Now water present in the xylem cell is placed under tension, which is ultimately transmitted to the root through the stem tracheids.
• This develop the transmission of tension is because of cohesive property of continuous water column in the vessels and tracheids from leaves to the root through the stem.
• The water column moves by mass flow due to transmission pull and simultaneously the process of ascent of sap is accomplished.

Objection of cohesion-tension
• There is only one relevant but refutable objection to this theory-due to variation temp. during day and night and in vessels of larger diameter.
• There are fair chances of gas bubble entering in water column from soil with water which may break the continuity of water column.
• It is true that such bubble are not rare among the plants but this objection has been successfully explained.

Explanation:
• The vessel are found gas filled during excessive tension this phenomena is known as cavitation and has been demonastrated by Mil born and Johnson(1966).
• This difficulty is overcome due to presence of many parallel column of vessel side by side and the injurious effect of temporary cavitation are eliminated.
• When the tension (by rain or simply at night).the gases are dissolved in solution and the column become continuous.


















TRANSPIRATION
Plants absorb a large amount of water by the roots and the excess water is lost in the form of water vapor. This process of loss of water from the aerial part of the plant is known as transpiration.
DIFFFERENCE BETWEEN TRANSPIRATION AND EVAPORATION
Transpiration Evaporation
It is a vital physiological process. It is a physical process in which water changes from liquid to a gaseous form.
It is controlled by guard cells. It is not controlled by guard cells.
It takes place through the surface of leaves. It takes place through the surface of various open water bodies and doesn’t requires the living organs of plant like leaves.
It takes place due to osmotic and suction pressure. Suction or osmotic pressures are no involved in it.
It takes place in living cells. Plant cells are not required for evaporation.
The temperature of the plant is maintained due to transpiration. It has no relation with plant temperature.



KINDS OF TRANSPIRATION
 The process of transpiration is more or less continuous but is much rapid during the day then at night.
 There are four types of transpiration.

i. Lenticular transpiration:
 It takes place through the lenticles which are present on the epidermal portion of the woody portion.
 Lenticles are the small pores present below the bark of old trees.
 Lenticular transpiration occurs continuously on day and night as there is no mechanism to stop or to reduce.
 According to Huber, this loss through lenticles is only 1% of the total transpiration.

ii. Cuticular transpiration:
 The loss of water in the form of water vapor from the cuticles of various aerial parts is called cuticular transpiration.
 The water vapor reaches to the cuticle through the internal tissues of aerial parts by diffusion and from cuticle, it diffuses in the atmosphere.
 The total transpired water is only about 5 to 10 % through cuticles.
 The plants growing in shady places transpire up to 15% of the total transpired water.
 The amount of water loss in xerophytic plants is quite little or negligible.
 In flowers, stems and fruits, mainly cuticular transpiration is found.













iii. Stomatal transpiration:
 The loss of water in the form of vapour through the stomata of leaves is called stomatal transpiration.
 The maximum amount of (80-90%) absorbed water is transpired through stomatal transpiration.
 It is commonly found in the leaves and stems of young plants.
 The crop plants like wheat, gram, maize, mustard and potato, etc also transpire through stomata.
 The water loss of 250 tones/day/acre has been recorded from wheat crop.


iv. Bark transpiration:
 This type of transpiration takes place through the bark or cork seen on the outside of woody stem.
 Huber (1956), demonstrated that bark losses 5 times more water than all to lenticles together.


IMPORTANCE OF TRANSPIRATION
 The additional water is transpired to the atmosphere through the aerial parts of the plant.
 The suction force is developed, because of transpiration which helps to the ascent of sap.
 The increase in transpiration increases the rate of absorption of water and minerals and also solute particles and they are distributed to all parts of the plants.
 The leaf temperature is maintained because of transpiration.
FACTORS AFFECTING TRANSPIRATION
Followings are the affect of transpiration:
1. External or environmental factors:
a. Humidity:
 Wet and dry air affects the transpiration. The dry air absorbs moisture.
 If the air present in the atmosphere is dry and air present in the intercellular space of leaves is wet, the diffusion of water vapor will take place from intercellular space of the leaves to the atmospheric air.
 Thus, less humidity in air increases the rate of transpiration. In contrast, high humidity in the decrease the rate of transpiration.
b. Temperature:
 The rate of transpiration is directly proportional to the temperature of atmosphere.
 Temperature also affects the humidity of the air. The rate of transpiration increases the temperature of the atmosphere.
 The high temperature of atmosphere lowers and low temperature increases the humidity.
c. Light:
 Transpiration increases in high light intensity and decreases in low light intensity.
 In high intensity of light, the water present in mesophyll cells diffuse rapidly resulting in increase in humidity of internal air.
 This increase the rate of transpiration. The stomata remains open during day hours and close during night hours.
d. Wind velocity:
 High wind velocity increases the rate of transpiration and low wind velocity decreases.
 In high wind velocity, the humid air surrounding the leaves moves all the side away from the plant, resulting in decrease in the humidity around the leaves and increase in the rate of transpiration.
e. Water content of soil:
 If excess water is present in the soil, more absorption of water will take place resulting in the high rate of transpiration.
 If the water deficient soil is present, there is decrement in the rate of transpiration.


2. Internal factors:
a. Presence of cuticle on epidermis:
 Some leaves posses thick cuticle on the epidermis which reduces the rate of transpiration.
b. Hairy leaves:
 Some leaves posses epidermal hairs which retain moisture or humid air resulting retardation in rate of transpiration.
c. Presence of shrunken stomata:
 The xerophytes’ leaves posses sunken stomata which also reduces the rate of transpiration.
d. Number of stomata on leaves:
 The rate of transpiration is related with the number of stomata.
 More the number of stomata present on the leaves more will be the transpiration rate and less number of stomata show lower transpiration rates.


STRUCTURE OF STOMATA









 Stomata are the openings found on the epidermis of the leaves and young stems. Each stoma is surrounded by two specialized epidermal cells known as Guard Cells.
 They differ from epidermal cells in their shapes (kidney or bean shaped) and in present of chloroplasts.
 The inner wall of guard cell is thick and inelastic whereas the outer wall is thin and elastic in nature.
 Guard cells are bordered by one or more modified epidermal cells called subsidiary cells or accessory cells.
 The stomata opens to the interior into a cavity called sub-stomatal cavity which remains connected with the intercellular spaces.
 The leaf surface, depending upon the species, may contain 1000 – 60,000 stomata/cm2.
 The size of each stomatal pore, when fully open, may measure 3 – 12 Ƞ in diameter an 10 – 40 Ƞ in length. On an average, fully open stomata occupy approx. 2% of the total leaf area.
DISTRIBUTION OF STOMATA
 The stomata are found distributed on upper and lower surface of the leaves.
 In dorsiventral leaf (dicot), they are mostly found in the lower side of the leaves.
 In isobilateral leaf (monocot), their number is equal on both lower and upper surfaces.
 In floating leaf (eg: Water lily), stomata are found on upper surface or epidermis.
 In Nerium and Pinus, the stomata are found sunken in the cavities.
 In submerged plants like Hydrilla and Potamogeton, non functional stomata are found.
 In xerophytes like Casurina, sunken stomata are found.
 In dicot leaves, generally the stomata are found scattered where as in monocot leaves they are arranged on parallel rows.
 All the stomata of a leaf cover about 1-2% of total area of leaf.
TYPES OF STOMATA
The stomata may be classified in following five types to their distribution on leaves.
1. Apple type:
 When the stomata are found only on the lower surface of the leaf, the condition is called hypostomatous. This condition is found in apple, peach, mulberry and walnut.
2. Potato type:
 In this type, stomata are found more on the lower surface than the upper surface.
Examples: Potato, Tomato, etc.
3. Oat type:
 In this type, stomata are found equally on both the surfaces of leaves.
Examples: Oat, Maize, Grasses etc.
4. Water lily type:
 In this type stomata are found only on upper surface of leaves.
Examples: Water lily, lotus, etc.
5. Potamogeton type:
 In this type, stomata are absent or functionless.
Examples: Potamogeton, etc.

GUTTATION
 The herbaceous flowering plants growing in moist places possess special types of structure as in vein ending margins of leaf called Hydathodes.
 The water exudates through hydathoides in the form of small liquid droplets. This phenomenon is called Guttation.
DIFFERENCE BETWEEN TRANSPIRATION AND GUTTATION
Transpiration Guttation
Water loss takes place in the form of vapour. Water loss takes place in the form of liquid drops.
Transpired water is pure. Liquid coming out of guttation is impure, it contains minerals, salts, etc.
It takes place via stomata, cuticle and lenticles. It takes place through hydathodes.
It takes place during day hours. It takes place during morning or night.
It is controlled by guard cells. It is not controlled by guard cells.
Root pressure is not involved. It takes place due to the root pressure.
It maintains the temperature of the plant. It has no relation with temperature.
It takes place in all higher terrestrial plants. It mainly takes place in herbaceous plants.
Mechanism of transpiration
 The mechanism of transpiration is completed in two stages.
1. The diffusion of water mesophyll cell into intercellular spaces.
2. The diffusion of water vapour of intercellular spaces into the water dry atmosphere.
 The roots of plant continuously absorbs water and mineral salt from the soil which ascend through the xylem vessel and reach to the leaves
 The mesophyll cells of leaves become turgid due to excess amount of this absorb water
 At this stage the T.P of the cell is increased and DPD is decreased which result in diffusion of water from mesophyll cells into intercellular spaces.
 The intercellular spaces now become saturated with water and the water vapour pressure becomes greater than the WVP of atmosphere.
 Simultaneously DPD of inter cellular space is decreased much than DPD of water vapour present in the atmosphere.
 Thus, the water from the intercellular spaces diffuses into the atmosphere in the forms of vapors through stomata,lenticles and cuticles.
 About 80-90% of absorbed water through stomata. The intercellular spaces of mesophyll cell remains connected with the sub stomatal chambers or respiratory chambers.
 Thus, of water vapour continuously diffuse from intercellular space into sub stomatal chambers and the air of these cavities remain saturated with watervapour.
 When the air of outer atmosphere is unsaturated the water diffuses from sub-stomatal chambers into the atmosphere. Thus the process of transpiration continuous.

Mechanism of opening and closing of stomata
 The stomatal transpiration occurs when stomata fully open. The opening and closing of stomata is a direct response to increase or decrease in the osmotic concentration of the guard cells.
 When the osmotic concentration of guard cell increases .They absorb water from the surrounding epidermal cells and become turgid.
 Increase turgidity causes the outer thin elastic wall of the guard cell to stretch towards outside.
 The inner thick and inelastic wall also gets pulled along with it and assumes a concave shape.
 The stomata or pore between the two guard cells is open in this condition ,loss in the turgidity of guard cell results result in stomatal closing.
 Thus, the turgidity of the guard cells, when is regulated by their osmotic concentration is the main cause of stomatal opening and closing.
 Various theories have been to explain these turgor changes. Some of these theories are described below.



1. THEORY OF PHOTOSYNTHESIS ON GUARD CELLS:
 Van nohl(1856) observed that the stomata remain open in the light or day time and closed in the dark or during night. On the basis he proposed the theory of photosynthesis in guard cells and told that the chloroplast present in the guard cells photosynthesis in light resulting in the formation of carbohydrates as increase O.P of guard cells.
 Due to which the water enters into the guard cells by the osmosis from the surrounding cells and then become turgid.
 The turgidity of cells .T.P also increase which results in opening of stomata .During light the O.P and T.P of guard cells are very much reduced become zero due to lack photosynthesis and stomata become closed.

Summary of Theory Of Photosynthesis In Guard Cells:
 Light – photosynthesis by guard cell – Formation of sugar – increase in osmot ic pressure of cell sap – endosmosis – increase in turgidity of guard cells – stomata open.
 Following are the objection regarding this theory
 The chloroplast of guard cells performs insufficient photosynthesis.
 The chloroplast of stomatal guard cells of certain plants is completely unable to photosynthesis carbohydrates.
 The concentration of cell sap of stomatal guard cells increase 2-3 times in 5-30 minutes, while the amount of chlorophyll present in the guard cell is quite less.
 The guard cell already possesses much amount of stored sugar.
 Sometimes the guard cell of stomata of young leaves also possesses starch grain before the opening and formation of buds.
 Some plants when are kept in dark,their leaves still posses starch.
 The leaves of same plant which are without chlorophyll also posses starch grain in the guard cells of stomata.

2.Theory of starch-sugar interconversion.
 According to lioyd(1905),Loftfied(1921) and sayre(1926).the amount of starch in the guard cell increases during night and decreases during day times.
 The insoluble starch presennt in the guard cell is hydrolysed into soluble glucose-1-phospatein the presence of phosphorylase enzyme during day time and soluble glucose-1-phospate is converted into insoluble starch during night.
 Thus both are reversible rxn.

Starch + phosphorylase Glucose-1 phospate
(insoluble) (soluble)

Sayre(1926)
 Observed that opening and closing of stomata depends upon the change in pH of guard cell. According to him stomata open at high pH(7) and become closed at low pH(5).
The pH of guard cell increases during the day and decreases during night. When the pH increase the starch is hydrolyzed into soluble sugar in the presence of phosphorylase resulting in decrease in the quantity of starch and increase in quantity of sugar.
Due to increase the sugar concentration the O.P of guard cell is increased and the water from surrounding mesophyll cell diffused in the guard cell resulting in increase of T.P. and opening of stomata.
When the pH of guard cell decreases during night,soluble glucose-1-phospate sugar is again converted into starch resulting in diffusion of water from guard cells.
Thus the guard cells become flaccid and stomata are closed.

Later on scarth(1932)
Explain the basis of change in pH of guard cell he proposed the theory starch –sugar interconversion.
According to him the respiration and photosynthesis are carried out simultaneously during daytime.
Thus, CO2 produced in respiration is utilized in photosynthesis by mesophyll cells resulting in increase in PH.
Whenever PH increase, The enzyme phosphorylase become active and hydrolyzed starch into soluble sugar.
 During night the CO2 produced in respiration instead of being utilized in photosynthesis accumulated in the intercellular spaces of mesophyll cells resulting in decrease in PhH of guard cells.
 Whenever PH decrease the soluble sugars are converted into starch resulting in decrease O.P.of guard cell and diffusion of water from guard cells. Thus the guard cells become flaccid and stomata are closed.

 CHANGES TAKING PLACE DURING CLOSING OF STOMATA.
1.The co2 becomes accumulated in intercellular space.
2.The pH of cell sap of guard cells is reduced to 5.0
3. Soluble sugar are converted into starch
4.op of guard cell is reduced.
5.The water of guard cells is diffused outside due to exosmosis resulting in flaccid stage of guard cell and closing of stomata.
CHANGES TAKING PLACE DURING OPENING OF STOMATA.
1.The concentration of CO2 in leaves is reduced much due to photosynthesis.
2.The ph of cell sap of guard cell is increased(pH 7)
3.the starch is converted into soluble sugar due to action of enzyme photosynthesis.
OP of guard cell is increased.
4.The water from mesophyll cell diffuse into guard cells due to endosmosis and the guard cells become turgid resulting in opening of stomata


 Starch + PO4 Glucose-1-phosphate
Insoluble and osmotically active

3. THEORY OF STARCH-GLUCOSE INTERCONVERSION:
 Steward (1964), critised the theory of starch sugar interconversion and proposed another modified theory for opening and closing of stomata called “Theory of starch glucose interconversion”.
 According to this theory, the stomata open when starch is hydrolyzed into glucose-1-phosphate in the presence of phosphorylase enzyme and glucose-1-p is converted into glucose and inorganic phosphate (Pi) in the presence of phosphoglucomutase and phosphatase enzymes.
 The stomata become closed when glucose and i.p are again converted into glucose-1-p in the presence of ATP and hexokinase enzyme and glucose-1-p into starch.
 When starch is converted into glucose and Pi, the O.P. of guard cells increases along with the PH of the cell sap which becomes 7. In this condition, stomata are open.
 When glucose and Pi are converted into starch, the O.P. of guard cells is reduced and the PH of cell sap becomes 5. In this condition, stomata are closed.
The summary of opening and closing of stomata is as follow:
A. Opening of stomata:
Starch + phospate Glucose-1-p

Glucose-1-p Glucose-6-p

Glucose-6-p Glucose + Pi

B. Closing of stomata:
Glucose + Pi + ATP Glucose-1-p

Glucose-1-p Starch + phosphate

Many physiologists do not agree with the theories of starch sugar interconversion and starch glucose interconversion due to following reasons.
i. The guard cells of monocot plants do not contain starch even though they function like other guard cells.
ii. Stomata are closed during noon without change in any quantity of starch.
iii. The rate of interconversion of starch and sugar and starch and glucose is insufficient for opening and closing of stomata.
iv. Sometimes starch is converted into malic acid in place of sugar
4. THEORY OF GLYCOLATE METABOLISM:
 This theory was proposed by Zelitch (1963). According to which glycolic acid plays an important role in opening of stomata.
 Glycolic acid is formed in the guard cells when the concentration of CO2 and glycolate also synthesize carbohydrate.
 The O.P. of guard cells increases with the formation of glycolate which requires ATP for its synthesis.

The whole process may be shown as below:
NADP + ADP +Pi +H2O NADP + H+ + ATP +1/2 O2


Glyoxylate + NADP + H+ Glycolate + NADP+

Glycolate + ½ O2 Glycolyxate + H2O2

H2O2 H2O + ½ O2
5. THEORY OF PROTON TRANSPORT:
 This theory was proposed by Levitt (1974).
 According to this theory, the opening and closing of stomata depends upon the entry and exit of potassium ions in the guard cells.
 At first, malic acid is formed from the starch in the guard cells which dissociates into cations and anions.
[R(COOH)2 R(COO-)2 + 2H+]
H+ K+
 The anions exit out from the guard cells and to replace those, K+ ions enters into the guard cells from surrounding mesophyll cells.
 K+ ions reacts with malic acid to form potassium malate which is transported into the cell vacuole.
 It increases the O.P. of guard cells resulting in diffusion of water from mesophyll cells into guard cells.
 Thus, the guard cell becomes turgid and due to increase in T.P. the stomata open.
 Noggle and Frintz (1976), supported proton transport theory. They summarized and proposed following scheme of opening and closing of stomata.
OPENING OF STOMATA:
 Light Starch Production of malic acid in guard cells Dissociation into H2 and malic ions Influx of K+ and efflux of H+ ions Formation of potassium malate Transport of potassium malate into vacuoles Osmotic entrance of water into guard into guard cells Increase of T.P. Stomata open
 During closing of stomata, reverse reaction takes place.

OPENING AND CLOSING OF STOMATA IN SUCCULENT PLANTS
 On succulent plants, the stomata open during night and remain closed during day time.
 In these plants, incomplete oxidation of carbohydrates takes place during night resulting in the formation of organic acid which accumulate in the guard cells.
 Thus, CO2 is not released outside the stomata and stomata remain open during night.
 During day time, the organic acids accumulated during night are oxidized resulting in liberation of large amount of CO2 which is utilized in photosynthesis.
 Thus, the stomata remain closed during day time.
During night (in Dark):
2C6H12O6 + 3O2 C4H6O5 + 3H2O

During day (in light):
C4H6O5 + 3O2 4CO2 + 3H2O















TRANSLOCATION OF ORGANIC SOLUTES IN PLANTS
Concept:
• In the lower green plants like spirogyra, ulothris, chlamydomonas, Euglina and all other algae, the food is synthesized in every cell of plants. Thus the question of its translocation does not arise in them.
• In higher green plants the food is not synthesized in all the cells of the plants but it is mainly synthesized in the leaves from where it is translocated into different part of plants.
• The process through which the synthesized food from the leaves is translocated into different part of the plant according to requirements is called translocation of food.
• The food materials excess than the required amount are stored in different organs of the plant like root, stem, leaves, seeds and fruits. Such organs are called storage organs.
• The food materials are always stored in insoluble form and are translocated in solution or soluble form. During translocation insoluble food is first converted into soluble form.

Storage of food:
• The carbohydrate and other food materials are synthesized in excess than the required amount inside the leaves.
• This excess food is translocated from leaves and stored in various storage organs like roots, stems, leaves and seeds of fruits. The storage mainly takes place in parenchyma cells, medullary rays and xylem parenchyma cells.
• These cells contain certain enzymes which convert soluble food material into insoluble food material when required.
• In carrot, radish and turnip, the food is stored inside the roots where as in others it is stored in underground stem, leaves, seeds, flowers, and fruits.

Food storage organs are as follows:
1. Leaves: In certain plants the food is stored inside the leaves. eg. Onion, Garlic, Cabbage and Bryophyllum etc.
2. Roots: In certain plants food is stored inside the roots. Eg. Carrot, Radish, Turnip, Beta vulgaris, Asparagus etc.
3. Stems: In certain plants food is stored in the stems only-
Eg. Phylloclade – Opuntia
Rhizome – Turmeric, Banana
Corn – Aulocacia
Tuber – Potato
Bulbil – Lily, Agava
4. Flowers: eg. Cauliflower
5. Seeds: Normally the seeds of all flowering plants contain stored food either inside the cotyledons or inside the endosperm.
• The food is utilized during germination of seed and formation of seedlings.

Forms of stored food:
The stored food may be stored inside plants in the following form,
1. Carbohydrates:
a. Starch: The food materials are stored in the form of starch. The soluble sugars synthesized in the leaves are converted into insoluble starch. During night it is stored in various storage organs. The starch is mainly found in underground stems, in the seed of wheat, maize, rice and in fleshy roots.
b. Sugars: It is found in sugarcane, Beta roots, Turnip and various type fruits.
c. Insulin: It is soluble carbohydrates and is found in the roots of Dahlia and in members of compositae family.
d. Hemicellulose: It is found in the cotyledons and endosperms of the Oat, Palm, Lupin, Coffee, Almond, Coconut and Ground nut etc.

2. Oil and fat:
They are mainly stored in the seeds of various plants like mustard, Almond, Coconut and Ground nut.
3. Protein:
It is most important and helps in the formation of protoplasm. In small amount it is found in almost all the seeds but in higher amount it is found in the seeds of Cajanus spp, Cicer spp, Pisum spp etc.

DIRECTION OF TRANSLOCATION:
The translocation of food in plants takes place in downward, upward and lateral direction.
1) Downward translocation:
According to this hypothesis, different organic food materials synthesized in the leaves are translocated downward in the soluble form due to which they are stored in stems and roots of the plants. In plants are food is utilized in the formation of new cells, some parts in the nutrition of old cells and remaining food is converted into insoluble form and is stored in different storage organs like stem. Eg. In potato tubers and in roots of Radish, Carrot and Beta roots.
2) Upward translocation:
Certain stages of the plants are found when the food materials are translocated upwardly. Some stages are as follows;
i. Germination of seeds.
ii. The formation of new stems and leaves from the underground storage organs.
iii. Formation and development of new buds;
iv. Development of fruits.

3) Lateral translocation:
i. In certain plants of stems and roots, the food is translocated inlateral direction.
ii. This is mainly performed by medullary rays.
Path of translocation:
1. In higher plants, the food is thranslocated in different organs of the plants.
2. Through vascular system which is made up of vascular bundles. The vascular bundles are made up of complex tissue, xylem and phloem.
3. The xylem possesses tracheids, xylem vessels, fibres and parenchyma cells.
4. Where as the phloem possesses sieve tube. Companion cells, phloem fibres and phloem parenchyma cells.
5. The xylem element are mainly involved in ascent of sap and phloem elements(sieve tube) in translocation of food.

Phloem anatomy:
1. Sieve tube:
• These are long slender tube like structures and in the transport of sucrose or glucose throughout the plants.
• These are formed by end to end fusion of cells called sieve tube elements.
• The wall of sieve tube elements are made up of cellulose and pectic substances, but their nuclei degenerated and lost as they mature.
• The cytoplasm is confined to a thin peripheral layer, two adjoining end walls of neighbouring sieve elements form a sieve plate.
• In fact, originally plasmodermata passed through the walls but later on those pores enlarged so that the walls look like a sieve allowing the flow of solution from one elements to the next.
2. Companion cells:
• A thin walled elongated cells called companion cells. It is associated with each sieve tube. Both are connected by simple pits.
• Each companion cell is living and contains dense protoplasm and a large elongated nucleus each.
• The sieve tube elements depends on the adjacent companion cell therefore they remain living.
3. Phloem parenchyma:
• It is living and often cylindrical in shape mostly absent in monocots. These mainly store food material.
4. Phloem fibres:
• It is made up of sclerenchymatous fibre cells. They provide mechanical support

SYMPLAST AND APOPLAST
• The movement of solute through the plant tissues can take place in two path way.one is cytoplasmic path way and other is cell wall path way.
• Solute movement may occur through channels in the cell walls and is therefore extracellular.
• In this way it pass the protoplasts and over comes the barriers in the cross membrane.
• In this process the solute can be freely exchanged with the external solution and this path way is also usually called free space.
• The whole of the cellwall continuity is referred to as apoplast.
Apoplast
: It is non-living continuous system made up of water filled cellular cellwall and intracellular spaces from epidermis to xylem.
:The ions or solute which enter the cellwall of epidermis move across the cell walls of cortex,cytosol,endodermis,cellwall of pericycle and finally accumulate in xylem vessels or phloem.
:Solute may also follow the route through cytoplasm of the protoplast and are transported to the adjacent cells through plasmodesmatos (a).The latter channels provide continum with the adjscent cells in a three dimensional way and is called symplast or symplasm.

Symplast
:It is living continuous system formed by cytoplasm or cytosol and plasmodesmata from epidermis to xylem parenchyma.An ion or solute which enters the cytosol of epidermis move across.

TRANSPORT OF PHOTOSYNTHATE PRODUCT:
• A plant needs a transport system to move photosynthetate from the area of synthesis to utilization.
• These photosynthetate move thoroughly the vascular system,the xylem and phloem where xylem is acropetal or besipetal both.
• Phloem loading and phloem unloading both plays a role to transfer organic as solute.

Pholem Loading:
• The transfer of photosynthate from the mesophyll cells of leaves to the phloem sieve tube elements.
• During phloem loading the mesophyll cells are typically at a lower osmotic potential(higher water potential)than the sieve tube elements thus the phloem loading requires an energy input to move sugars into an area of higher concentration.
• Phloem loading generates the increased osmotic potential in the sieve tube elements. supplying the driving force from mass flow of assimilate.
• It consists of movement of sugars from symplast (mesophyll cells) into apoplast (cell walls )and then into symplast (phloem cells).


Phloem unloading:
• The transfer of photosynthates from phloem sieve tube elements to the cell of a sink.
• Many investigation in the field of translocation of sucrose from chloroplast to sieve tube elements as shown in figure.
UDP

Mesophyll Chloroplast
UDPG

Fructose 6-P Sucrose-P Sucrose-P + ATP

Pi


Sucrose carrier


Transfer cell cytoplasm
Sieve tube elements
Sucrose
Carrier



Source sink concept and translocation of solute:
• In plant growth and development, materials are moved from the source where they are enter the plant or are synthesized to the sink where they are utilized.
• Inter organ translocation in plant is primarily through the vascular system, the xylem and the phloem.
• Movement in the xylam tissue is essentially a one way acropetal movement from the roots i.e. Transpiration.
• In contrast substance in the phloem have bidirectional movement, movement may be acropetal or besipetal.
• Assimilate produced in the leaves moves to sinks while substance absorbed by roots move upward.
• In both xylem and phloem there are lateral connections plasmodesmata, which allow some lateral movement.
MECHANISM OF TRANSLOCATION:
Following theories were proposed to explain the mechanism of translocation:
1) Protoplasmic streaming theory:
• According to De-Vries (1885) and Curtis, soluble food materials in sieve tube move from one end to another end due to cytoplasmic streaming and similarly, They move from one sieve tube to another through sieve plate by streaming movement.
• Although this view seems to be correct to certain extent but due to lack of proper evidences, it is also not accepted by the scientists.



2) Munch’s mass flow hypothesis:
• Some scientists are of the opinion that the soluble food materials in the phloem move just like blood vessels.
• Munch (1930) proposed a hypothesis, A/C to which the soluble food materials in the phloem show mass flow.
• The main reason behind this is that the sugars are synthesized in the mesophyll cells of leaves due to which the OP of mesophyll increase, resulting in absorption of water through xylem by endosmosis.
• Now, the turgor pressure of the mesophyll cell increase towards upperside which affects and produces mass flow in the protoplasm of sieve tube towards the lower side .
• Thus, the sugars move downwards into the roots where they are utilized during respiration and growth and their concentration is also reduced.
• Thus, the food materials always move from higher concentration to lower concentration continuously.
• The main drawback of this theory is that “it explains only unidirectional downward flow of soluble food materials.






Loss by transpiration
Mesophyll cells at high OP sugar from photosynthesis
Phloem

Dissolved sugar move downward


cambium Upward movement by water

xylam
Root cells

CO2








Sugar consumed water from soil


Diagrammatic representation of Munch hypothesis




GROWTH REGULATORS AND THEIR EFFECTS IN PLANTS

Hormone: A chemical messanger
 The term of hormones was first proposed by Hardy and applied by William Bayliss and Earnest Starling (1904-06) in animal physiology.
 An organic substance produced naturally in higher plants controlling growth or other physiological functions at a site remote from its place of production and active in minute amounts. (Thimann 1948)
 For practical purpose, plant growth regulators can be defined as either natural or synthetic compounds that are directly to a target plant to alter its life process or its structures to improve quality, increase yields or facilitates harvesting of green plants.
 Phytohormones are frequently found in relatively greater qualities in the growing reasons of apical buds, young leaves, root and shoot apices.
 There hormones have been given various names like growth regulators plant growth substances, plant hormones, growth promoters plant grown activators or phytohormones.
 Phytohormones: coined by Thimann (1948). A special kind of chemical substance occurring naturally in plants which regulate and control the plant physiology process.



Classification of plant hormones

Hormones


Natural Artificial Postulated Phenol



Indole Hormones: Non-Indole Hormones:
i. Auxin 1. Nitrogenous: 2. Non-Nitrogenous:
ii. IAA i. Cytokinins i. Gibberellins
iii. IAN ii. Zeatin ii. Ethylene
iv. Acetaldehyde iii. 2 IPA iii. ABA
v. Indoacetamide

Artificial Hormones: Postulated: Phenol:
i. IPA i. Rhizocaline i. Coumarine
ii. IBA ii. Caulocaline
iii. NAA iii. Florigen
iv. 2,4 D iv. Vernalin
v. 2,4,5 T v. Dormin
vi. IAA

Note: Florigen and Vernalin are flowering hormone.
Here,
IAA= Indole Acetic Acid
IAN=Indole 3- Acetonitrite
IPA=Indole Propionic Acid
IBA=Indole Butyric Acid
NAA=Nepthalene Acetic Acid
2,4 D=2,4- Dichlorophenoxy Acetic Acid
2,4,5 T=Trichlorophenoxy Acetic Acid

GENERAL FUNCTIONS OF PLANT GROWTH REGULATORS
 Initiation of cell division, cell enlargement
 Accelerating of root cutting, coloration of fruits and tissue culture.
 Controlling abscission of leaves plant, organ size, cambium activity, apical dominance, premature crop of fruits, attack of diseases and insect, pests and rate of respiration.
 Promoting flowering, tillering of crop, nucleic acid ctivities, protein synthesis and enzyme activities.
 Increase yield of crops.
 Stimulating callus formation and help in breaking dormancy of seeds and buds.
AUXIN
 Auxin is the most important phytohormone which promotes growth of stem and enlargement of plant cells.
 The first crystalline auxin was obtained from human urine by Kogl and Hagen Smith (1934). Chemically it was shown to be Indole 3 – acetic acid (IAA).
 Thiemann (1935) made study of Rhizopus shinus culture and isolated a different substance called IAA.

CHEMECAL STRUCTURE OF AUXIN










Auxin and related auxins are as follows:
IAA, IAN, IPA, IBA, PAA, 2, 4 D 2, 4, 5 T, NAA,IAC,IBA, etc.
 Auxina or auxentriolic acid (C18H32O5) occurs at the meristemic apices (buds and growing leaves).
 Auxinb or auxenolonic acid (C18H30O4) present in corn germ oil, other vegetable oils, malts and fungus.
 Heteroauxin (C10H9O2) occurs in higher plants, bacteria, yeasts and fungi.

BIOSYNTHESIS OF AUXIN
 IAA, the main naturally occurring auxin is synthesized from tryptophan.
 Tryptophan is first converted to Indole acetaldehyde either through Indole Pyruvic acid or through tryptomine.
 Indole acetaldehyde is then converted into IAA.
 Gorden and Sanchez Nieva (1949), Leopold (1955) and Audus (1959) have given the possible pathway and sequence of the formation of IAA from tryptophan.



















There is another alternative pathway of IAA synthesis, tryptophan have been suggested.
1. Tryptophan Indole-3-acetic acid IAA

2. Tryptophan Glucobrassin Indole acetonitril

IAA

PRACTICAL APPLICATION OF AUXIN IN AGRICULTURE
1. Fruiting:
 It plays significant role in fruit setting, fruit thinning, fruit dropping and fruit quality.
 The production of parthenocarpic fruit can be induced to develop successfully by the application of IAA, IBA, and NAA.
 NAA causes a decrease in fruit set, 2, 4, 5 T employ for fruit thinning in several fruit crops.
 Auxin helps to check pre-harvest drop of fruits.
 The application of 2,4 D, 2,4,5 T and IBA to facilitate the development of coloration, sweetening and ripening of many fruits.
2. Flowering:
 Auxin helps to alter earliness of many crops such as oat, corn, barley, mustard, peas, etc.
 The flowering in pineapple test by treating with NAA, 2,4 D and IAA at low concentration (5-10 ppm). The dropping of flower buds, flowering and berries has been successfully controlled by small doses of auxins.
3. Germination:
 NAA, MH (Malic Hydrazoides) inhibits the sprouting of potatoes, onion, garlic.
 The various crop seeds when treated with IAA, NAA, IBA, and IAN enhances the germination percentage.
4. Root initiation:
 Auxin inhibits the growth of root. However, litchi, mango, grapes, lime cutting treated with IBA, NAA found more rooting.
 Auxin induced rooting helps propagation of certain plants by cutting.



5. Weed control:
 Most of the weeds of field crops can be successfully controlled by the application of auxins. 2,4 D, 2,4,5 T, MCPA (2 methyl, 4-chloro phenoxy acetic acid) has proved to be an ideal weed killer.
6. Auxin and sex:
 Auxin plays a vital role in the increasement of female flowers in many Cucurbits, mango, etc when treated with MH, NAA, and IAA.

PHYSIOLOGICAL EFFECTS OF AUXIN
 Application of exogenous auxins causes stimulation of coleoptiles and stem growth.
 Initiation and promotion of cell division in cambium and apical growth.
 Inhibition of apical dominance
 Produce rooting in several stem cutting and formation of adventitious roots.
 Increase formation of female flowers and ovary wall growth leading to parthenocarpy in many fruit crops.
 Prevention of abscission layer of leaves, flowers and fruits from stem.
 Induce plant growth movements.
 Induce RNA synthase.



GIBBERELLINS
 GA are naturally occurring phytohormones. They are found in maturing seedsseedlings.Cotyledons and leaves of plants.
 In 1926, a Japanese pathologist e. Kurosawa first discovered the connection between the “Bakane” disease of rice caused by Giberella fugikuroi in 1929. T. Yobuta and T. Hayashi isolated a small quantity of highly active crystalline material from the filtrates of the fungus and gave the name Gibberellin A.
 In 1945, P.A. Brain et.al. isolated and chemically characterized a pure compound from culture filtrates of Gibberella fugikuroi. They called this new substance Gibberellic acid.
 At persent about 9o Gibberellins have been identified. They are abbreviated as GA1, GA2,……….. GA90.
 The original Gibberellic acid is GA3. The chemical structure of GA3 is as followed.

PHYSIOLOGICAL EFFECTS OF GA
 Promotion of plant growth
 Promotion of seed germination and bud growth
 Induction of flowering
 Prevention of senescence
 Mobilization of food and minerals in seeds
 Breaking dormancy of seeds
 Stimulation of enzyme activity in seeds

PRACTICAL APPLICATION OF GAs
GA3 have found extensive use in agriculture and food industry.
 Increase the number, size colour and quality of fruits (grapes, apple and pears).
 Stimulates bud formation and fruit set.
 Increase α- amylase activity in germinating barley seeds which is used for malt production in beer industry.
 Promote the elongation of cane internodes without decreasing the sugar content.
 Genetic dwarfism has been successfully overcome by GA3 treatment.
 GA is more efficient than auxin in inducing parthenocarpy.
 Breaking dormancy of seeds and buds.

BIOSYNTHESIS OF GIBBERILLINS
 Biogenetic relationship of GA3 to the different phase was proposed by Cross et.al. (1956), Birch et.al (1959) demonstrated the incorporation of acetate into mevalonic acid (MVA) and then into GA3 in culture of G. fugikuroi.
 The biosynthesis of GA3 froom MVA proceeds via 18 or more intermediates and about 15 related compounds.
 Cell free system of G. fujikuroi and system from immature seeds of Echinocystis macrocarpa and Cucurbita maxima have been in biosynthetic studies.

The following steps are involved in biosynthesis of GA3:
1. Formation of MVA from acetate.


Acetate Acetyl CoA Acetyl + CoA

Acetyl CoA 3- methyl, 3- hydroxyl glutryl CoA Mevalollic acid

Mevalollic acid Mevalonic acid

2. Formation of Isopentenyl pyrophosphate (IPP) from mevalonate.


Mevalonic acid 5- phosphomevalonate

5- phosphomevalonate 5 – diphospho mevalonate + Co2 + H3PO4

5 – diphospho mevalonate Isopentenyl pyrophosphate (IPP)

3. Condensation of IPP to form aeranyl pyrophosphate.

IPP Dimethylenl pyrophosphate
The two isomers condense to geranyl2 pyrophosphate by alkylation.
4. Cyclisation of Geranyl geranyl pyrophosphate.
5. Conversion of ent – kaurene to ent – 7 – α - hydroxyl kaurenric acid.
6. Concentration or contraction of β-ring and β-hydroxylation.
7. Loss of C-20 to form C-19 GA3.
CYTOKININS
 Cytokinins are natural chemical substances which can stimulates cell division in cells of various plant organs.
 Fruits (apple, tomato, plum, banana, peach, pears) endosperm tissues and coconut milk are the richest sources of cytokinins.
 Cytokinins are of various kinds:
Zeatin, 2 IP, 2IPA, Dihyrozeatin, Benzyl adenine

CHEMICAL STRUCTURE:






PHYSIOLOGICAL EFFECTS OF CYTOKININS
1. Promotion of cell division and organ formation
2. Promotion of seed germination
3. Expansion of cotyledons and leaves
4. Promotion of chloroplast development
5. Effect on overall plant growth
6. Increase nucleic acid metabolism and protein synthesis
7. Delaying of senescence

PRACTICAL APPLICATION OF CYTOKININS IN AGRICULTURE
1. The exogenous application of cytokinins helps to facilitate the development of flowers and fruits in many plants.
2. They break dormancy of tobacco, white cloves carpet grass, etc. They have been found quite effective in breaking dormancy of seed of many species.
3. They can accelerate and retard the process of abscission in leaves.
4. Stimulate root initiation of many plants.

ABSCISSIC ACID (ABA)
 ABA is natural and unique plant hormone and is widely present in angiosperms, gymnosperms, ferns and fungus.
 Fruits contain the highest ABA concentration.
CHEMEICAL STRUCTURE:






BIOSYNTHESIS OF ABA:
Two pathways for the biosynthesis of ABA have been identified.
i. From mevalonic acid
Direct synthesis of ABA from mevalonic acid through farnesyl pyrophosphate mainly in the water stressed tissues.
Mevalonic acid Iso- pentenyl pyrophosphate Farnesyl pyrophosphate Abscissic acid(ABA)

ii. From the oxidation of carotenoides(Xanthophyll)
 Indirect synthesis of ABA takes place by the oxidation of carotenoides or xanthophylls. The xanthophylls, vialaxanthin is converted to xanthoxin by the action of lipoxygenase or by a photo oxidation process.
 The xanthoxin is then oxidized to produce ABA.

Vialaxanthin Xanthoxin ABA



PHYSIOLOGICAL ROLES OF ABA
1. Inhibition of seed germination
2. Inhibition of seedling growth
3. Inhibition of bud growth
4. Stomatal closing
5. Stimulate positive geotropic response
6. Synthesis of nucleic acid and protein
PRACTICAL APPLICATION OF ABA IN AGRICULTURE
1. ABA promotes stomatal closing and thus reduces water loss due to transpiration.
2. It plays a significant role in water stressed plants.
3. Increase tuber yield and leaf tissues.
4. Stimulation of fruit ripening.
5. Delay in germination of seed.
6. Induce flowering in short day plants.

GROWTH INHIBITORS
The natural or synthetic compounds that inhibits or retard the physiological or biochemical process in plants is k/a growth inhibitors.
They may be of two types:
1. Natural growth inhibitors
i. Ethylene
ii. ABA
iii. Phenolic acid
iv. Caumarins
2. Synthetic growth inhibitors
i. Morphactins
ii. Chlorocholine chloride



ACTIVITIES OF INHIBITORS
i. Caumarins inhibit seed germination
ii. Dormin inhibits bud formation
iii. Chlorocholine chloride retards the enzyme activity within the seed and root during their development.
iv. Morphactins inhibit the elongation of nodes and internodes.
v. ABA inhibits seed germination and accelerates abscission in leaves.
vi. Ethylene inhibits plant growth.

AGRICULTURAL IMPORTANCE
i. Accelerate flower formation
ii. Suppress suckering in tobacco
iii. Eradicate weeds
iv. Prevent storage sprouting in onion, potato, garlic and certain other root crops.
ETHYLENE
 Ethylene is a gaseous hormone, highly soluble in water and can easily move through plant tissues.
 Normally a small amount of ethylene(< 0.1 ppm) is found to be present in plant tissue, although a high concentration may be present in the flowers of orchids.
 The ethylene is synthesized in ripening fruits, flowers, seeds, leaves and even in roots of plants.

Chemical Structure:
CH2=CH2
H H
C=C
H H


BIOSYNTHESIS OF ETHYLENE:
 All higher plants produce ethylene. The amino acid methionone is said to be an early precursor of ethylene formation.
 The enzyme responsible for catalyzing methionine to ethylene in vitro have been isolated from plants, some of the intermediate steps in the ethylene biosynthesis is given below.
1. Methionine α- keto, ϒ- methyl Methional Ethylene

2.
a. Methionine + ATP SAM + pyro phosphate

b. SAM 1- amino cyclopropane carboxylic acid(ACC)

c. ACC Ethylene + CO2 +HCN

HCN is ultimately converted to formic acid and ammonia.
PHYSIOLOGICAL EFFECTS OF ETHYLENE
 Enhance seed germination
 Growth inhibition and morphogenic effects
 Flowering inhibition and sex expression
 Ripening of fruits
 Acceleration of senescence and abscission
 Assist RNA and DNA synthesis

PRACTICAL APPLICATION OF ETHYLENE IN AGRICULTURE
The most common Trade Name of ethylene is ethrel or elephon which is 2-chloroethyl phosphoric acid.
 Ethylene has been used for synchronized flowering and ripening of fruits of many plants such as pineapple, mango, litchi, banana, grapes, lemons, orange, apple, melons, etc.
 The application of ethrel also increases the number of female flower in cucumber, melon in young stage.
 It reduces the incidence of disease and insects, pests.
 It prevents lodging and increase tillering of several sereal crops when applied in early stage.
 Increase in yield and earlier harvest in Cucurbitaceae family.
 Promotion of flowering and ripening of many fruit crops.
 Stimulation of germination.
GROWTH & DEVELOPMENT
DEFINATION OF GROWTH:
Growth is an important character of all the living beings. Each living organism increases in size, shape, volume and weight. This process is called growth.

DEFINATION OF DEVELOPMENT:
Development can be defined as a process in which growth, differentiation, maturation and senescence takes place in a regular sequence in the life history of a plant.

Growth involves one or more of the following parameters:
 Increase in size of the organs
 Increase in the number of cells of a plant or plant parts
 Increase in the quantity of protoplasm
 Increase in dry weight of the plant
 Increase in the amount of various cell organelles including size and thickness
The growth of a plant can be of two types:
1. Vegetative growth:
It’s responsible for growth in length or in other words the growth which takes place between the emergence of seedling and initiation of flowering is called vegetative growth.
2. Reproductive growth:
It involves floral structure, fruits and seeds, initiation of flowering, development of sex organs, fertilization and seed formation, constitute reproductive growth.

TYPES OF GROWTH:
 On the basis of their growth organs of the higher plants, they fall into two broad categories i.e. organs of limited growth and organs of unlimited growth.
 Leaves, flowers and fruits to the former type while stem and roots have unlimited growth.
 Organs of limited growth do not have a growing point while organs of unlimited growth have growing point called meristem.
 The meristem depending upon their position is of three types.
1. Apical meristem:
 It occurs at the stem and root apices. Growth produced as a result of the activity of apical meristem is called as primary growth because it produces only primary tissues.
 Primary growth increases the length of plant axis, causes the development and elongation of stem and root branches and gives rise to lateral appendages like root hairs, leaves and floral organs.
2. Intercallary meristems:
 They are considered as portion of apical meristems separated by permanent tissues and are temporary regions of growth. These are also meant for producing growth in length.
3. Lateral meristems:
 It occurs both in root and stem of dicot and gymnosperms. It brings about secondary growth to increase the thickness of plant in girth or in diameter.
Example: Vascular margin of young, expanding leaves

PHASE OF GROWTH:
 Growth is not a simple process. It occurs in meristem region before completion of this process, a meristematic cell has to part through following three phases:
i. Formation phase (Cell formation by cell division)
ii. Elongation phase (Cell elongation)
iii. Maturation phase (Cell differentiation and maturation)
 The above three phases can be seen clearly in a longitudinal section of root apes where cell formation phase is represented by meristematic and cell enlargement phase by cell elongation zone.






i. Formation phase:
 The meristematic cells are thin walled, dense cytoplasm and show continuous mitotic cell division.
ii. Cell elongation:
 The daughter cells formed by the division of meristematic cells undergo enlargement.
 Initially, the cell enlarge is a;; dimension but subsequently enlargement takes place only in a specific direction.
 During this stage, good quantity of protein protoplasm and cell wall material is synthesized, prominent central vacuole appear in the cells.
 Plasticity and elasticity of the cell walls increase.
 Permeability of cell wall to water increase, wall pressure decrease, synthesis of cell wall material increase, vacuole formation is the most important feature at this stage.
iii. Cell differentiation:
 As the cells enlarge, they gradually acquire permanent shapes and forms. This final phase of growth is usually called maturation.
 As maturation process continues, cells become fully differentiated. Thus, in this phase, development of wall thickening in xylem elements and formation of sieve pores in phloem takes place.
 A mature cell may be living or dead.
 During this stage, structural qualitative and quantitative change takes place and cell attains definite shape structure, function and properties.
GROWTH CURVE:
 The growth rate of cell, plant organs or a whole plant does not remain the same but always varies.
 This variation in growth is due to irregular change in initial stage during the phase of cell formation. The growth rate is quite slow while it increases rapidly during the phase of cell elongation and becomes maximum, later on it slow down during the phase of cell maturation.
 At last, a stage comes when the growth rate becomes zero i.e. the growth stops.
 Thus, the total period from initial to final stage of growth is called “Grand Period of Growth”.
 The total period of growth can be divided into following stages:
i. Lag phase
ii. Log phase
iii. Decline phase
iv. Senescence phase or Steady phase



Growth rate



Time
i. Lag phase:
During this period, the growth rate is quite slow because it is the initial stage of growth. In other words, growth starts from this phase.
ii. Log phase:
During this phase, the growth rate is maximum and reaches at the top because at this stage the cell division and physiological processes are quite fast.
iii. Decline phase:
This phase comes after log phase. During this phase, the growth rate is slow as the metabolic process slows down.
iv. Steady phase:
During this phase, the growth rate is almost complete and become static. Thus the growth rate becomes zero.

 If the growth rate is plotted against time, an “S” shaped curved is obtained known as Sigmoid curve or grand period curve.
 Environmental conditions may alter growth rate but not the sigmoid form of the curve.





FACTORS AFFECTING THE GROWTH OF PLANTS:
External factors:
1. Light:
 It is an essential factor for the growth of the plant. The effect of light on growth is dependent on intensity, quality, duration and direction of light.
a. Intensity:
 High light intensity retards the growth of plants due to increase in the rate of transpiration.
 Water deficiency in plants leads to stunted growth of internodes and reduction in leaf size whereas at the dark place, the stems become excessively long and the leaves become whitish or yellowish owing to the development of etiolion which leads to the pathological condition etiolation.
 In this condition, there is no increase in light intensity then the plant ultimately dies.
 Normally, maximum growth takes place under light intensity much less than that of summer day.
b. Quality:
 Different colors effect differentially on the growth of a plant. The visible light is mostly effective on the growth of plant whereas UV and infra red are determined to growth.
 In blue light, cell division takes place but ell enlargement stops.
 Red light improves cell enlargement but inhibits cell division.
 Green light enhances the expansion of leaf.
c. Duration:
 Duration of light has a marked effect on vegetative as well as reproductive growth of plants.
 Thus, the length of daily light period on growth and development of plant is called photoperiodism, observed for the first time by Gardener and Attard (1920).
 According to this phenomenon, flowering is formed in a number of plants by short day while in other by long day and the plants are named accordingly i.e. short day plant and long day plants respectively.
d. Direction:
 The roots, shoots and leaves show different orientation to the direction of light and cause curvature in the organ. Hence, these are called phototropic curvatures.



2. Food materials:
 The growth rate increases in the presence of excess food materials while decreases during shortage.
 They also increase the concentration of cytoplasm and the rate of cell division.
3. Temperature:
 The plant growing in different regions require different temperature for growth. The temperature has a pronounced effect in growth. It occurs between 4 – 450C.
 The best growth takes place between 28- 330C. In plants occurring in colder regions the best growth takes place between 35-400C while in plant growing in warmer regions it takes place between 38-440C.
 Some seeds show germination when they are kept at low temperature. Similarly some plants require low temperature in addition to the sufficient photoperiod for flowering.
 When they are given low temperature treatment at initial stage of life, they show an early flowering later on. Such a property of plant is called vernalization.
 It has been observed in wheat, rice, etc.
4. Oxygen:
 It is necessary for respiration during the food materials is oxidized to release energy.
 The growth is directly proportion to the amount of oxygen. In excess of oxygen, the growth is reduced.
5. Carbondioxide:
 CO2 chiefly effects the process of photosynthesis. Its rate increase in excess of CO2 and results in the manufacture of food materials like carbohydrates, etc.
 These food materials are most important for growth.
 The rate of photosynthesis is slowed down when the amount of CO2 is not sufficient, the growth is also slow.
6. Water:
 Water is the most important factor for growth. In its presence, various physiological activities like translocation of food materials, water absorption, photosynthesis, activation of enzymes and protoplasm takes place. All the processes are related with growth.

Internal factors:
Internal factors necessary for growth mainly include PGRs like auxin, GA3, cytokinins, etc. They are ¬required in traces and in their deficiency; the rate of growth is reduced.

Growth in unicellular and multicellular organisms and flowering plants
 In unicellular organisms, the growth is very simple but it is very much complex in multicellular organisms.
 In unicellular, there is increase in the volume of the cell and also increase in the number of organelles. Mitotic cell division is responsible.
 Seeds are the means for the multiplication of flowering plants. Perennial plants continue their growth more than one season but annuals die after flowering and seed formation.




note prepared by: Arjn Dev(nepalibruceme@yahoo.com)
contact no: 9849599439