Transpiration PDF
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Uploaded by CommendableSard7063
Loyola College
Dr. R. Ravindhran
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Summary
This document details various aspects of transpiration, including its types, mechanisms, and affecting factors. It provides information on stomatal transpiration, cuticular transpiration, and lenticular transpiration, along with a discussion on the opening and closing of stomata. It also covers the starch-sugar interconversion hypothesis and K+ ion transport mechanism. The document further elaborates on affecting factors like atmospheric humidity, temperature, wind, light, and available soil water. Finally, it briefly discusses plant antitranspirants.
Full Transcript
Transpiration Dr. R. Ravindhran Loyola College. Types of Transpiration 1. Stomatal Transpiration 2. Cuticular Transpiration 3. Lenticular Transpiration Types of Transpiration Mechanism of Stomatal Transpiration 1. Osmatic diffusion of water in the leaf from xylem to intercellular s...
Transpiration Dr. R. Ravindhran Loyola College. Types of Transpiration 1. Stomatal Transpiration 2. Cuticular Transpiration 3. Lenticular Transpiration Types of Transpiration Mechanism of Stomatal Transpiration 1. Osmatic diffusion of water in the leaf from xylem to intercellular space above the stomata through the mesophyll cells. 2. Opening and closing of stomata. 3. Simple diffusion of water vapours from intercellular spaces to outer atmosphere through stomata. Mechanism of Stomatal Transpiration Opening and Closing of Stomata Opening and Closing of Stomata 1. Starch - sugar interconversion hypothesis of stomata opening and closing. (a) During daytime: According to this theory, the CO released in respiration is utilized in the process of photosynthesis, which makes the medium of the guard cell alkaline. Due to this high pH, the starch produced in the night is converted into sugar in the presence of enzyme phosphorylase. Sugar is soluble in water and consequently increases to the OP of the guard cells. Therefore, the cells become turgid. In this state, the thin outer wall of guard cell stretches outward and opens the stomata. (b) During the night: During the night, the CO produced in respiration is not utilized and diffuses into the cytoplasm of guard cells. It makes the medium of the guard cells acidic (low pH). At this low pH, the sugar made during daytime is also converted into starch. Starch being insoluble in water reduces the osmotic pressure of the guard cell. Consequently, water moves from guard cells to the attached subsidiary cells. It makes the guard cells flaccid and therefore, stomata close. 2 2 Starch – Sugar Interconversion theory- Steward K+ ion Transport mechanism in Guard cell K +ion Transport mechanism in Guard cell K + ion Transport mechanism in Guard cell Factors Affecting Rate of Transpiration External – Atmospheric humidity – Temperature – Wind – Light – Available soil water – C02 Internal - Internal water condition Plant Antitranspirants Substance which retard their transpiration. ABA – Abscisic acid, Phenyl Mercuric Acetate Increase in C02 concentration.
