Plant Growth Regulators

Plant Growth Regulators

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  Muhammad Zeeshan Nazar M.PhilAgriculture Entomology [email protected]
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  Phytohormones • Naturally occurringorganic compounds • Relatively low molecular weight • Active in small concentrations •Synthesized at one site and translocated to the site of action, where they regulate the activities of plant.
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  Plant Growth Regulators Chemicals (natural or synthetic) which show hormonal effects to plants.
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  Major Phytohormones  Auxin Cytokinin  Gibberellin  Abscisic acid  Ethylene  Cycocel  Maleic Hydrazide Growth promoters Growth Retardants Growth Inhibitors
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  Auxin  Darwin notedtropistic response of grass tip coleoptile in 1897  Went found these substances in Avena coleoptile.  These substances become known as Auxins and necessary for growth  Found in growing regions such as terminal and lateral buds, elongating internodes and the young embryo in its developing stage inside the seed.  Responsible for cell elongation and cell division
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   They aretranslocated through the vascular bundles to the other parts of the plant, especially from apical to basal regions.  The accumulation of auxins in the terminal bud inhibits the growth of lateral buds, which can be avoided by prunning.
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  Natural Auxin  Indoleacetic acid (IAA) Synthetic Auxin  indole‐3‐butyric acid (IBA)  ‐naphthalene acetic acid (NAA)
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  Uses of Auxins Rooting of cuttings of various fruit species e.g mulberry, pomegranate, fig, grapes and olives are treated with IBA and NAA for early initiation of adventitious roots.  Killing of weeds e.g 2,4 D is used for killing of broad leaf weeds.  Micropropagation of plant species  Setting of fruits in tomato, by spraying of auxin 4- Chlorophenoxyacetic acid (4-CPA) before flowering.  Pre-Harvest Drop Control by spray of NAA in oranges
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  Cytokinin  It wasidentified in 1955 and was called kinetin  It was an active cell division stimulator Natural cytokinin  –Zeatin obtained from maize seed and coconut Synthetic cytokinin  –Kinetin  –benzyladenine (BA or BAP) It is present in embryos, germinating seeds, in early stages of developing fruits and in meristematic tissues.
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  Uses of cytokinins To stimulate shoot development  Delaying senescence  Accelerating bud growth
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  Gibberellin  Gibberellin wasdiscovered in 1930, during studies on fungal disease of rice, which caused excessive growth.  The fungus which produce these substances was known as Gibberella fugikuroi.  So the new substance was known as gibberellin  Gibberellin stimulate shoot elongation and control ger mination and dormancy  Present in the apices of shoots and leaf primordia of the plant, in embryo and cotyledons of the immature seed and fruit tissues.
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  Uses of Gibberellins Enhancing seed germination and seedling growth  Eliminating cold treatment  Initiate male flowers in cucumber
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  Abscisic acid Plant growthhormone that plays a role in  Plant stress,  Controlling water relations,  Embryo development,  Germination and dormancy Found in various plant tissues; cotton fruits, leaves of plants under water stress, fruits of rose. It is believed to be anti-auxin and anti-gibberellin in growth promoting actions.
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  Ethylene Natural plant growthhormone involved with fruit maturity and stimulation of adventitious roots Ethylene in its gaseous form spreads easily through the plant and affects it even in small quantities. Produced in the meristematic tissues of the plant, germinating seeds, withering flowers, maturing and ripened fruits and in injured plant tissues. Synthetic product “Ethephon” produces good amount of ethylene, when applied to plants.
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  Uses  Inducing fruitmaturity  Initiating flowers  Altering the sex of flowers  Changing the green color of citrus fruits  Abscission inducing effects