Transpiration, stomatal movement

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Star Sugar Hypothesis, Levit theory, Potassium control on stomatal opening, factors affecting transpiration, transpiration as necessary evil, significance of transpiration

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Transpiration and Stomatal Movements:

Transpiration and Stomatal Movements Copyright © McGraw-Hill Companies Permission Required for Reproduction or Display Dinesh D Khedkar Deptt . Of Botany Shri Shivaji Science College Amravati

1.4 : Transpiration:

1.4 : Transpiration Types of transpiration Stomatal movements Mechanism of transpiration (Starch sugar hypothesis), Significance Antitranspirant Guttation .

Introduction:

Introduction

Slide4:

When transpiration take place in leaves, water evaporated from intercellular spaces of leaves to outer atm. through stomata. As more water releases from mesophyll cell to intercellular spaces, in turn mesophyll cell draw water from xylem of leaf. Due to this a tension is created in water in the xylem of leaves. This tension transmitted downward to water in xylem elements of roots through xylem of petiole and stem and the water is pulled upward in the form of continuous unbroken water column to reach transpiring surfcae- top of plant.

Transpiration:

Transpiration Loss of excess water from aerial parts of plants in the form of water vapours is C/a Transpiration Kinds of Transpiration Stomatal transpiration: Most of transpiration takes place through stomata, usually confined to more numbers on lower side of leaves (90%). Cuticular Transpiration ( Peristomatal transpiration): Although it is impervious to water, still some may water may lost through it (3-10%) Lenticular Transpiration: some water may lost by woody stem through lenticels, which is called as Lenticular Transpiration (1%).

Mechanism of Stomatal Transpiration:

Mechanism of Stomatal Transpiration Stomatal Transpiration takes place during day time can be studied in 3 steps: Osmotic diffusion of water in the leaf from xylem to intercellular space above stomata through mesophyll cells. Opening and closing of stomata Simple diffusion of water vapours from intercellular spaces to outer atm. through opened stomata.

V:

V

Slide16:

Confocal image of guard cells showing chloroplasts (in red) and microtubes (green)

Slide17:

There may be several different agents and mechanisms which creates O.P. in guard cell such as, Hydrolysis of starch into sugars in guard cell; synthesis of sugar and organic acids in guard cell and active pumping of K + ions in the guard cells. Opening and Closing of Stomata

Mechanism of Transpiration (Starch Sugar Hypothesis):

Mechanism of Transpiration (Starch Sugar Hypothesis)

Mechanism of Transpiration (Starch Sugar Hypothesis):

Mechanism of Transpiration (Starch Sugar Hypothesis)

Slide23:

High pH Low pH

ATP-Driven Proton (H+)-K+ Exchange Pump Mechanism in Guard Cell (Levitt 1974):

ATP-Driven Proton (H+)-K+ Exchange Pump Mechanism in Guard Cell (Levitt 1974) Photosynthesis produces hydrogen ions (H+). Hydrogen ions diffuse out of the guard cells.

Slide27:

Outward movement of hydrogen ions causes the active transport of potassium (K+) into the cell. This exchange of H+ and K+ is followed by entry of Cl- ion in guard cell, results in electrical differentiation in guard cell. H+ out of guard cell K+ into guard cell

Slide28:

Increased potassium [K+] inside the guard cells draws water in from the surrounding epidermal cells by osmosis The guard cell swells, changes shape, and opens the pore

Slide29:

Active potassium theory

Active potassium theory:

Active potassium theory

Abscisic Acid (ABA):

Abscisic Acid (ABA)

Factors affecting stomatal movement:

Factors affecting stomatal movement

Factors affecting stomatal movement:

Factors affecting stomatal movement

Significance:

Significance

Slide39:

An integrated scheme of the probable mechanism of stomatal opening

Significance of Transpiration:

Supposed role in movement of water: Although transpiration plays imp. Role in upward movement of water i.e. ascent of sap in plants, it does not means that translocation of water stopped with it. Even in the absence of transpiration water continues to rise upward to maintain turgidity of cells for various metabolic processes. Significance of Transpiration

Significance of Transpiration:

Significance of Transpiration Supposed role in Absorption and Translocation of Mineral Salts: Earlier it was thought that rapid rate of transpiration resulted in increase in rate of mineral salt absorption. Now it is established that these two processes are entirely independent processes. Therefore it has nothing to do with absorption of mineral salt. However, once the mineral salts have been absorbed by the plants, their further translocation or distribution may be facilitated by transpiration through translocation of water in the xylem element.

Significance of Transpiration:

Significance of Transpiration Supposed role in Regulation of Temperature: Some of the light energy absorbed by the leaves is utilized in Photosynthesis, rest is converted in to heat energy which raises their temperature. Rapid movement of water from aerial parts of plant through transpiration brings down their temp. and thus prevent from excessive heating. This view is not correct as Plants kept under intense sunlight with their stomata plugged by vaseline do not show much increase in their temp.

Transpiration as Necessary Evil - Curtis (1926) :

Transpiration as Necessary Evil - Curtis (1926)

Transpiration as Necessary Evil:

Transpiration as Necessary Evil

Significance:

Significance

Slide47:

Antitranspirants and Guttation

Slide48:

Thank You

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