Plant growth hormones

Plant growth hormones

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  PLANT HORMONES
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  • In plants,many behavioral patterns and functions are controlled by hormones. • These are “chemical messengers” influencing many patterns of plant development. – Plant hormones – a natural substance (produced by plant) that acts to control plant activities. • Chemical messengers: Are produced in one part of a plant and then transported to other parts, where they initiate a response. – They are stored in regions where stimulus are and then released for transport through either phloem or mesophyll when the appropriate stimulus occurs.
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  • Plant growthregulators – include plant hormones (natural & synthetic), but also include non-nutrient chemicals not found naturally in plants that when applied to plants, influence their growth and development. • Organic compounds other than nutrients ,applied in low concentration, which may alter the morphological structure /physiological response of plants. • Containing native (endogenous) and synthetic (exogenous) subs. • 5 recognized groups of natural plant hormones and growth regulators. • Auxins • Gibberellins • Cytokinins • Ethylene • Abscisic acid
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  • Plant Growthregulators (PGR) refers to natural or synthetic substances influence the growth and development. • IAA (Auxin)- Both natural and synthetic. • IBA (Auxin) - Always synthetic. Classification • Natural hormone: Produced by some tissues in the plant. Also called hormones. e.g. IAA. • Synthetic hormone: Produced artificially and similar to natural hormone in physiological activity. Also called Exogenous hormones. e.g. 2,4-D, NAA etc.
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  • On theBasis of Nature of Function : • Growth promoting hormones/Growth promoter: Increase the growth of plant. e.g. Auxins. Gibberellins, Cytokinins etc. • Growth inhibiting hormones/Growth retardant: Inhibit the growth of plant. e.g. ABA, Ethylene.
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  AUXINS • Derived fromthe Greek word "auxein" means- "to grow/increase". • Auxins may be defined as growth promoting substances which promote growth along the vertical axis when applied in low concentration to the shoot of the plant.
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  Occurrence and Distributionof Auxins • Promote elongation of coleoptile tissues • Natural auxin : IAA(Indole acetic acid), IAN(Indole -3-acetonitrile), Phenyl acetic acid. • Synthetic Auxins • IBA (Indole Butyric Acid) , NAA (Napthalene Acetic Acid) , 2,4-D (2,4 – Dichlorophenoxy acetic acid) , 2,4,5-T (2,4,5 – Trichlorophenoxy acetic acid) , NOA, NAD,etc. • MECHANISM OF ACTION: • protein synthesis, • alter osmotically active contents pf cell vacuole during cell expansion or cell wall extension.
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  Effects of Auxinon Plant Growth and Development • Cell Elongation and Cell Division • internode elongation • Leaf growth, initiation of vascular tissues, cambial activity, • fruit setting in case of pollination, • fruit growth, apical dominance, • inhibition of root rowth, • influence physical and chemical properties in leaf abscission, • inhibition of lateral buds
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  APPLICATION OF AUXINSIN AGRICULTURE . IBA AND NAA: Rooting of Cuttings • Application of NAA (in Mango) and IBA (in Guava) in stem cutting causes 100% success in vegetative propagation. • Seedless Fruit Production (Parthenocarpy) • In case of Banana, Grapes, Strawberry, Brinjal, Grapes – Application of IAA, IBA, and NAA show 100% success. • Promotion of Flowering :Application NAA causes uniform flowering in Pineapple leading to development of uniform sized fruits. • 2, 4 -D is also used to increase the femaleness in monoecious Cucurbits. • Prevention of Premature Dropping of Fruits: In case of Apple and Cotton - NAA • In case of Citrus fruits – 2,4–D/ 2,4,5-T • Germination :IAA, IBA, is most widely used in soaking seeds for germination. • Fruit Setting: 2, 4, 5-T is used for improved fruit setting in berries.
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  GIBBERELLINS • Discovered byKurosawa, a Japanese Plant Pathologist in 1928. • Rice plants infected by the fungus Gibberella fujikuroi showed excessive stem elongation. • Symptom is called ‘Bakane’ diseases. • Chemical was extracted & purified and named as Gibberellic Acid (GA). Now 80 different Gibberellins are available- GA1 to GA80 is available. • The most commonly occurring gibberellins is GA3. • Gibberellic Acid: Have a regulatory function • OCCURRENCE: • in roots , shoots, buds, leaves, floral apices. • Are produced in the shoot apex primarily in the leaf primordial (leaf bud) and root system . • Stimulates stem growth dramatically .
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  EFFECT OF GA: •Stimulates cell division, cell elongation (or both) and controls enzyme secretions, stimulation seed germination, breaking dormancy of overwintering plants, of flwering, stem elongation, increase in size of leaves, induction of parthenocarpic fruits . APPLICATION OF GA: • Increasing fruit size of seedless grapes • Increse the yield of digitalis glycosides per shoot. • Higher production of digoxin • Increase the height of castor plant five times more. • Increase dry weight of shoot in senna. • Promoting male flowers in cucumbers for seed production.
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  CYTOKININS • Promotes celldivision • Found in young and actively dividing tissues in embryos, seedlings, apical meristems. EFFECTS OF CYTOKININS • Cell division, delaying breakdown of chlorophyll, degradation of proteins in ageing leaves, • Developing embryo during seed development, • Influencing the expansion of cells in leaf discs and cotyledons. • Leaf senescence • Promote lateral bud development. • Miller isolated crystalline sub. From autoclaved herring sperm DNA of inducing cell division in tobacco cultures ---Kinetin ( 6-furfuryladenine). • Later on called as kinins and finally known as Cytokinins.
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  • Naturally occurringcytokinins: zeatin, N6 dimethyl amino purine. • Synthetic cytokinins: adenine, Kinetin, 6-benzyl adenine benzimidazole. • MECHANISM OF ACTION : Involved in nucleic acid metabolism and protein synthesis. • APPLICATIONS OF CYTOKININS • Increased yield of sennoside content in Tinnevelly senna leaves, also enhances th dry weight of shoots. • Increased formation of elongated capsule in opium. • Increase in leaf content and hyoscine content in duboisia, also present in extract of seaweed.
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  ETHYLENE (CH2=CH2) • Growthretardant. • Ethylene promotes ripening. • Gaseous hormone. 0.1 ppm • Produced in the actively growing meristems of the plant, in senescing ripening or ageing fruits, in senescing (ageing or dying) flowers, in germinating seeds and in certain plant tissues as a response to bending, wounding or bruising. • Ethylene as a gas, diffuses readily throughout the plant. • May promote leaf senescing and abscission (leaf fall). • Increases female flowers in cucumbers (economically - will increase fruit production). • Degreening of oranges, lemons and grapefruit – ethylene gas breaks down chlorophyll and lets colors show through.
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  ABSCISSIC ACID (ABA) •Growth retardant. • Induce stomata closing. • Inhibition of bud growth and shoot formation. • Widespread in plant body – moves readily through plant . • ABA appears to be synthesized (made) by the leaves. • Interacts with other hormones in the plant, counteracting the growth – promoting the effects of auxins & gibberellins. • Involved with leaf and fruit abscission (fall), onset of dormancy in seeds and onset of dormancy (rest period) in perennial flowers and shrubs. • ABA is effective in inducing closure of stomata in leaves, indicating a role in the stress physiology in plants. (ex: increases in ABA following water, heat and high salinity stress to the plant).