transpiration_:- stomatal transpiration and opening and closing mechanism of stomata

Transpiration:- loss of excess amount of water from ariel part like stem, leaf etc. of the plant
Types of transpiration :-
Stomatal transpiration
Cuticular transpiration
Lenticular transpiration

Stomatal opening clossing mechanism

1. Pt. Ravishankar Shukla University Raipur
" Transpiration"
Presented by :-

Diksha Chandrakar
msc biochemistry 2nd sem ????????????

2. Transpiration :-
** The physiology process by which the excess water is lost from the living
tissues of plants in the form of vapour is called Transpiration.
** Transportation is the process water movement through a plant and it's
evaporation from Arial parts such as leaves, stem and flowers.
** almost 98-99% water absorbed by a plant is lost in transpiration.
** only 1 % of absorbed water is used during photosynthesis.

3. Overview of transpiration:
1) Water is passively
transported into the roots and
then into the xylem.
2) The forces of cohesion and
adhesion cause the water
molecules to form a column in
the xylem.
3) Water moves from the xylem
into the mesophyll cells,
evaporates from their surfaces
and leaves the plant by
diffusion through the stomata.

4. Types of Transpiration :-
There are three different types of Transpiration in plants:-
1) stomatal transpiration :-
** stomata are minutes pores confined to epidermis
of green shoot and leaves .
**the water near the surface of the leaves changes
into vapour and evaporated when stomata are open.
** opening and closing of stomata are controlled
by guard cells .
** Maximum 80%- 90 % of the water loss by
stomata transpiration.

5. 2) Lenticular transpiration :-
** Lenticular are minutes opening in the bark of branches and twigs.
** Evaporation of water from the lenticel cells of the plants is known
as lenticular transpiration.
** lenticels are not present in all the plants.
** A minimal 1% amount of water is lost through lenticels.
** Lenticels which are made up of parenchymatous cell and are
present on the epidermis of many plant parts ( stem , petiole, fruit) ,
are pores that always open .

6. ** constitutes major part of water loss by deciduous trees during leafless
stage.
** occurs continuously day and night and there is no mechanism to stop
or reduce it.

7. 3) cuticular transpiration :-
** About 5-10% of the water from the leaves
is lost through cuticular transpiration.
** Upper epidermis of plants secret thin layer of wax cuticles , which
minimise loss of water.
** cuticles prevents evaporation
of water from the leaf surface.
** Transpiration inversely proportional
to the thickness of the walls.

** ** xerophytic plants generally have
very thick cuticles and wax coating
on the leaves and stem .

8. Mechanism of stomatal transpiration :-
The mechanism of stomatal transpiration which take place during
day time can be studied in 3 steps .
1 ) osmotic diffusion of water from leaf xylem to intracellular
space above the stomatal through the mesophyll cells.
2 ) opening and closing of stomata ( stomata movement ).
3 ) simple diffusion of water vapour from intracellular space
to other atmosphere through stomata.

9. 1) Diffusion of water from leaf xylem to intracellular space :-
** Leaf xylem , in the vein supplies water to all the tissues.
** In the leaves vascular bundles are surrounded by mesophyll
tissue , which is composed of Palisades parenchyma and spongy
parenchyma .
* there are small intracellular space between the cells of Palisades
tissues but in the spongy parenchyma , intracellular space is large in size.
** since the mesophyll cells are photosynthetic , they accumulate sugar . So
their osmotic pressure is very high.

** the mesophyll cells draw water from the xylem tube through the cell wall
by osmosis.

10. ** heat from the sunlight,,
thermal radiation, and
warm air current are used
by leaves to vapourised
water.
Release water in the form of vapour in intracellular space close to
stomata by osmotic diffusion .
** now in the turn O. p. And
D.P.D. of mesophyll cells
become High and hence, they
draw water from xylem by
osmotic diffusion.
** As a result the mesophyll cells become turgid and their diffusion pressure
deficit ( DPD ) and osmotic pressure decrease with the result that they

11. ** so the stomatal pores are open.
**the turgidity of guard cells decrease when osmotically active
substances are transported to the surrounding cells.
** As a consequence the guard cells become flaccid and straight
because of low Op. And DPD.
** so inner cell membrane of guard cells come close to each other and the
stomatal pores is closed.
** osmotic diffusion of water into guard cells occurs when their osmotic
pressure increase and water potential decrease (more negative) related to
those surrounding epidermal and mesophyll cells.
** the guard cells become flaccid when their osmotic pressure decrease
relatively surrounding cells ( movement of water take place from higher
water potential to lower water potential).

12. 2) opening and closing of stomata ( stomata movement) :-
** opening and closing of stomata controlled by changes in the turger
pressure.
** turger changes due to gain or loss of solutes from the adjacent or
subsidiary cells. Or caused by osmotic flow of water in the guard cells.
** consequent to increase in the osmotic pressure (op) and diffusion pressure
deficit ( DPD) of the guard cells ( which is due to accumulation of ions by
active absorption).
** osmotic diffusion of water from surrounding epidermal cells moves into the
guard cells.
** This increase the turger pressure of the guard cells and they become turgid.
the guard cells swell , increase in length and curve at the middle due to
differential stretching of wall ( cellulosic microfibril) .

13. These maybe several agents or
mechanism which controls stomatal
movement.
** hydrolysis of starch into sugar in
guard cells.

** Synthesis of sugar or organic acid in
them.

** The active pumping of k+ H+ ion in
guard cells.

16. Significant of Transpiration :-
1) transportation of conduction of water and minerals to different parts of
the plant.
2) due to the continuous elimination of water from the plant body . There
is a balance of water maintained within a plant.
3) helps to keep the plant cool on hot weather
4) it maintain the turgidity of the cell.
5) A suction force is created by by Transpiration that helps in the upward
movement of water in the plant.
6) it maintain osmosis and keep the cell rigid.

17. Factor affecting Transpiration :-
Different factor affecting the rate of Transpiration are
Cellular factor Environment factor
**the orientation of leaf
** the water status of the plant
** Total number and distribution of stomata in leaf
* light
* Humidity
* Temperature
* Wind speed
Drawbacks of Transpiration :-
** Reduce growth

** Formation of AbA

** Reduce photosynthesis

** Fall in metabolism

19. Reference: :-

Taiz,L and zeiger, E.2010 plant physiology, 5th edition , sinauer Associates
an imprint of Oxford University press.

20. THANKS