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Welcome WEL-COME Mechanism of water uptake by roots ,transport in roots,aquaporins ,movement of water in plants, mycorrhizal association on water uptake. Department of Agricultural Botany Post Graduate Institute, Dr. PDKV, Akola. MECHANISUM OF WATER UPTAKE BY ROOTS Plants absorb water from the soil by their roots . Roots play the principle role in absorption of water . ROOT : Root consist of five regions 1)Root cap region 2)Meristematic region 3)Region of elongation 4)Region of root hair 5)Mature region Regions Plant Root Roots absorb water mainly from the apical region. Apical organization of root shows three clear Demarcation. The zone of meristematic cells ,the zone of elongation and the zone of absorption or differentiation . The important one are described here Root hair : It consist of epidermis cells for the absorption of water. The wall of root hair consist of cellulose and pectic substances both are highly hdrophilic in nature.These substances have great capacity of water absorption . Mechanism of water absorption Water absorption have been explained by two different approaches. 1) Active absorption 2) Passive absorption Active absorption: When root are involved actively in water absorption and water absorbing forces in plant are developed primary in roots . It is found in those plant where transpiration is less and water present in sufficient amount. Active absorption requires ATP released during respiration. Two theories of active absorption 1) Osmotic Theories (At kins 1961 & priestley 1992) 2) Non -Osmotic Theories (Thimann 1951 & Kramer 1959) Pathway of water in Root Root hair Epidermal cellVarious successive cortex cells Endodermal cells (passage cells)Cell of pericycle Xylem cells Xylem ductUpward movement of water . Passive absorption: Absorption of water into the roots are governed by other cells.The governing force originate in the cells of transpiring shoots and other than in roots its self . This force develop due to transpiration . Thus passive absorption take place due to activity of upper part of plant such as shoot and leaves . ACTIVE ABSORPTION Active absorption of water take place due to the activity of root and root hair. Absorption occurs by osmotic and non osmotic pressure . The root hairs have high DPP as compare to soil solution and there for water is taken. In the movement of water living part of protoplast is involved. In non osmotic type of absorption respiratory type of energy is utilized. PASSIVE ABSORPTION It taks place due to activiy of upper part of plant,such as shoot and leaves . Water is absorbed due to active transpiration . The absorption occurs due to tension created in xylem sap by transpiration pull thus water is sucked in by tension . The movement of water is through free spaces or apoplast of root. energy is never required. FACTORS AFFECTING WATER ABSORPTION RATE External environmental factors a) Available soil water b) Concentration of soil solution c) Soil temperature d) Soil aeration FACTORS AFFECTING WATER ABSORPTION RATE Internal environmental factors a) Transpiration b) Absorption of root system c) metabolism AQUAPORINS Aquaporins : some integral membrane protein which form water selective channels in cell membranes and facilitate faster movement of water across the membranes into the plant cell this channel have been called as Aquaporins. The direction of water transport across the membrane however is not affected by Aquaporins Movement of water in plants The water has to move upward through the stem . this upward movement of water is called as ascent of sap . Mechanism of ascent of sap : no of theories have been put forward . a) Vital theories b) Root pressure theories c) Physical force theories d) Transpiration pull and cohesion of water theory. Transpiration pull and cohesion of water theory Proposed by dixon and jolly (1894) it based on following feature 1. Cohesive and adhesive 2. Transpiration pull Mycorrhizal association on water uptake The association of a fungus whith root of plant is called as Mycorrhizae . The relationship of mycorrhizae is symbiotic or mutual in which both parteners are benefitted . The fungus absorb water and mineral salt from the soil and release them into cells of host root .The host root supply carbohydrate to fungus . The mycorrhizae fungi grouped into two categoris a) Ectotrophic micorrhizae b) Vesicular arbuscular micorrhizae (VAM) Ectotrophic micorrhizal fungi infect exclusively gymnosperm and woody angiosperms VAM fungi infect roots of most spp.of herbaceus angiosperms.