Plant Growth Regulators
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This document discusses several major plant hormones (phytohormones), including their functions, locations of synthesis, and some uses. It describes auxins, cytokinins, gibberellins, abscisic acid, and ethylene - noting that they regulate growth, stress responses, germination, flowering, and fruit development. Specific hormones are discussed in more detail, outlining their natural and synthetic forms as well as some of their roles and applications in agriculture.
Plant Growth Regulators
- 1. Muhammad Zeeshan Nazar M.Phil Agriculture Entomology [email protected]
- 2. Phytohormones • Naturally occurring organic 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.
- 3. Plant Growth Regulators Chemicals (natural or synthetic) which show hormonal effects to plants.
- 4. Major Phytohormones Auxin Cytokinin Gibberellin Abscisic acid Ethylene Cycocel Maleic Hydrazide Growth promoters Growth Retardants Growth Inhibitors
- 5. Auxin Darwin noted tropistic 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
- 6. They are translocated 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.
- 7. Natural Auxin Indole acetic acid (IAA) Synthetic Auxin indole‐3‐butyric acid (IBA) ‐naphthalene acetic acid (NAA)
- 8. 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
- 9. Cytokinin It was identified 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.
- 10. Uses of cytokinins To stimulate shoot development Delaying senescence Accelerating bud growth
- 11. Gibberellin Gibberellin was discovered 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.
- 12. Uses of Gibberellins Enhancing seed germination and seedling growth Eliminating cold treatment Initiate male flowers in cucumber
- 13. Abscisic acid Plant growth hormone 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.
- 14. Ethylene Natural plant growth hormone 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.
- 15. Uses Inducing fruit maturity Initiating flowers Altering the sex of flowers Changing the green color of citrus fruits Abscission inducing effects