Lecture 9: Transpiration (BIOL3011) - PDF

L.9 Biology Department SQU College of Science Lecture 9 BIOL3011 Transpiration Plant Physiology  L.9 Biology Department...

L.9 Biology Department SQU College of Science Lecture 9 BIOL3011 Transpiration Plant Physiology  L.9 Biology Department SQU College of Science This lecture covers the process of transpiration, its advantages Outcome for plants, and the different types of transpiration mechanisms. It also explains stomatal structure, distribution and movement as key factors influencing transpiration, along with an overview of guttation, another form of water release in plants. Plant Physiology  L.9 Biology Department SQU College of Science 1 Transpiration 2 Advantages of transpiration Outline 3 Transpiration types 4 Stomatal structure, distribution and movements 5 Guttation Plant Physiology 1 Transpiration 1 1 Transpiration Transpiration is the process by which water is lost from plants (Aerial part) to the atmosphere, through the stomata. ▪ Water loss is crucial for water uptake. ▪ Water loss it creates a negative pressure (tension) in the leaf's vascular system, specifically in the xylem. ▪ This tension pulls water up from the roots, through the stem, and into the leaves. 1 Transpiration ▪ Water Loss: Evaporation of water from plant surfaces, mainly leaves, which helps to cool the plant and regulate internal water levels. ▪ Water Uptake: The loss of water through transpiration drives the uptake of water from the soil (Allow the plant to transport nutrients and maintain cellular hydration essential for photosynthesis and growth). 1 Transpiration Transpiration Evaporation 1 Modified physical phenomenon Physical process from any surface. present in plants. 2 Involves living cells, controlled by Occurs from both non- living and living guard cells surfaces controlled by physical factors. 3 Involves different forces i.e. vapor Does not involve these pressures pressure, osmotic pressure, diffusion pressure. 4 Keeps the surface of leaf cool and Causes dryness of surface protect from sun burning. 1 Transpiration Water loss differs between mesophytes and xerophytes. Mesophytes ▪Meso= middle /phyton=plants ▪Plants that thrive in environments with moderate water availability, neither too wet nor too dry. Xerophytes ▪Xero= dry /phyton=plants ▪Plants that are adapted to survive in environments with very limited water availability, such as deserts or arid regions. 1 Transpiration Large amount of water is lost by transpiration in the life cycle of a plant. Mesophytes –Zea mays (Maize) 20 kg per day. –Helianthus annuus (Sunflower) 56 kg per day. Xerophytes –Cactus loose less water (100 times less=estimation) than mesophytes. 2 Advantage of transpiration 2 2 Advantages of transpiration Creates suction force which helps in the conduction of water. It helps in absorption of minerals through roots due to transpiration pull. Evaporates excess of water. Translocation of food. Maintains temperature. Helps in opening and closing of stomata. Transpiration is necessary for dispersal of excess energy received from sun. 3 Transpiration types 3 3 Transpiration types Cuticular transpiration. Lenticular transpiration. Stomatal transpiration. 3 Transpiration types Cuticular transpiration -Water loss through the cuticle, the waxy layer on the epidermis of leaves and stems. -Cuticle helps reduce water loss 3 Transpiration types Lenticular transpiration. -Transpiration occurs through lenticels, which are small, spongy openings in the bark of woody stems. -Lenticels reduce water loss in stems and limit the gas exchange. 3 Transpiration types Lenticular transpiration Lenticels 3 Transpiration types Lenticular transpiration Cross-section of a woody stem 4 Stomatal distribution, structure, and movements 4 4 Stomatal structure, distribution and movements The stomata are apertures in the epidermis, each bounded by two guard cells. In Greek, stoma means “mouth,” and the term is often used with reference to the stomatal pore only. Kirkham et al., 2023 ( Advances in Botanical Research) 4 Stomatal distribution, structure and movements Stomatal distribution ▪Mesophytes Stomata are typically present on both the upper (adaxial) and lower (abaxial) surfaces of leaves. More on the lower surface (abaxial) than the upper surface (adaxial). ▪Xerophytes Lower surface (abaxial) only. 4 Stomatal structure, distribution and movements Stomatal structure 4 Stomatal structure, distribution and movements Stomatal structure 4 Stomatal structure, distribution and movements Stomatal structure Typeof stomatal complex Description Example families Examples Anomocytic Vicia faba Guard cells surrounded by cells (irregular celled) no different from epidermal cells Chenopodiaceae in size and shape, and may lack true subsidiary cell function. Cucurbitaceae Metcalfe & Chalk (1950) reported Apocynaceae these occur in 142 families. Boraginaceae Sometimes called ranunculaceous. Schlumbergera Diacytic/Paracytic (two celled) Guard cells surrounded by two Caryophyllaceae perpendicular (diacytic) or parallel Acanthaceae (paracytic) subsidiary cells. Illustration is Cactaceae diacytic, example given is paracytic. Nicotiana benthamiana Anisocytic (unequal celled) Guard cells surrounded by three unequally sized subsidiary cells, one of which is distinctly smaller than the Crassulaceae other two. Solanaceae Metcalfe & Chalk (1950) Brassicaceae reported these occur in 37 families. Lawson et al., 2020 (Annu Rev Plant Biol) 4 Stomatal structure, distribution and movements Typeof stomatal Description Stomatal structure complex Example families Examples Triticum aestivum Graminaceous (grass-like) Dumbbell-shaped guard cells surrounded by subsidiary cells that lie parallel to the long axis. Cyperaceae Metcalfe & Chalk (1950) Poaceae described different types. Tradescantia Tetracytic (four celled) Guard cells are surrounded by four Poaceae subsidiary cells—two lateral and two Asclepiadaceae polar. Found mostly in monocots but Asphodelaceae can occur in dicots such as Tilia. Commelinaceae Actinocytic Monstera deliciosa (star-celled) Typical pattern for Commelina Typical pattern: communis (monocotyledon with Typical pattern: kidney-shaped guard cells). Ebenaceae A great deal of early stomatal work Commelinaceae was conducted on this species due to the ease with which the epidermis Araceae peels. Alternate pattern: Alternate pattern: Araceae Guard cell Guard cells surrounded by four or more Musaceae subsidiary cells, elongated radially to the Subsidiary cell stomata. Epidermal cell Lawson et al., 2020 (Annu Rev Plant Biol) 4 Stomatal structure, distribution and movements Stomatal movement 4 Stomatal structure, distribution and movements Stomatal movement 4 Stomatal structure, distribution and movements Stomatal movement Opening and Closing of Stomata Depends on the turgidity of the guard cells Stomatal Opening: Pressure potential increases. Guard cells expand. The outer wall stretches and pulls the inner wall. Stoma opens. Stomatal Closing: Stoma closes when guard cells are flaccid. This process depends on photosynthesis. 4 Stomatal structure, distribution and movements Stomatal movement Opening of Stomata Triggered by Sunlight + CO₂. Photosynthesis begins. Water potential of guard cells becomes more negative. Water diffuses into guard cells. Guard cells become turgid. Increase in pressure potential. Stomata open. 4 Stomatal structure, distribution and movements Stomatal movement Closing of Stomata Starch is formed. Water potential becomes less negative. Guard cells become flaccid. Guard cells contract. Stomata close. 4 Stomatal structure, distribution and movements Stomatal movement Role of K⁺ Ions in Stomatal opening/closing: K⁺ ions help in the opening and closing of stomata. Process of stomatal opening: Water potential (ψ) becomes more negative. Water enters guard cells (cells become turgid). Process of stomatal closing: When K⁺ ions diffuse out: Water potential (ψ) becomes less negative. Guard cells lose water and become flaccid. 4 Stomatal structure, distribution and movements Stomatal movement Stomata open during day and close during night. ABA closes stomata Cytokinin opens stomata. 5 Guttation 5 5 Guttation Guttation is the exudation of water droplets from the tips or edges of leaves. ▪Process: Hydathodes: Guttation takes place through specialized structures called hydathodes. Hydathodes are stoma-like pores located at the tips or edges of leaves. They are typically positioned above the ends of leaf veins. ▪Conditions for Guttation: Guttation commonly occurs during warm, humid nights when transpiration is low, and root pressure forces water out through the hydathodes 5 Guttation TranspiratioN Guttation Occurs during day Occurs during night In vapor form In liquid form Vapor is pure Contain dissolved substances Through stomata Hydathodes Controlled by stomata Uncontrolled 5 Guttation Guttation or dew drops 5 Guttation Longitudinal section of leaf apex and hydathode