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Gibberlins: The regulators of plant height.

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Gibberllins: are Endogenous plant harmones that regulate growth and influence various developmental processes, including stem elongation, germination, dormancy, flowering, sex expression, enzyme induction, and leaf and fruit senescence.

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Gibberlins: The regulators of plant height.

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  2. 2. GIBBERLINS: Regulators of Plant Height Any of a group of plant hormones that stimulate stem elongation, germination, and flowering.
  3. 3. In 1926, Japanese E. KUROSAWA investigated a rice disease that is known as the ‘foolish seedling’. • Grow extremely fast, look spindly and pale and break off • Grow extremely fast, look spindly and pale and break off • It is detected that this abnormal growth is caused by a chemical secreted from a fungi, Gibberella fujikuroi. • It was first isolated in 1935 by Teijiro Yabuta and Sumuki, from fungal strains (Gibberella fujikuroi) provided by Kurosawa. Yabuta named the isolate as GIBBERLLINS. • LESLIE PALEG identified these gibberllins contain GIBBANE SKELETON having biological activity of cell elongation or cell division or both. • Gibberllin A isolated in 1938 is a mixture of atlest 6 gibberllins (GA1, GA2, GA3, GA4, GA7, GA9.) • Today, there are more than 110 gibberellins. 30% of them are biologically active. GIBBERLLINS: Gibberllins are Endogenous plant harmones that regulate growth and influence various developmental processes,
  4. 4. including stem elongation, germination, dormancy, flowering, sex expression, enzyme induction, and leaf and fruit senescence. • They are found in all parts of the plant body, especially in roots, shoots, buds, leaf, young fruits, and germinating seeds are all rich in gibberllins. • Different gibberellins differ in structure and biological activity. • In a plant, different gibberellin types can be found. They can be both active or inactive. • Convertion to active form happens at root tips, inactive Gibberellin is transported to root and after convertion, it goes back to shoot. • gibberellins are classified on the basis of structure as well as function. All gibberellins are derived from the entgibberellane skeleton. The gibberellins are named GA1....GAn in order of discovery. Gibberellic acid, which was the first gibberellin to be structurally characterised , is GA3. • Gibberellic acid (also called Gibberellin A3, GA, and GA3) is a hormone found in plants. Its chemical formula is C19H22O6. When purified, it is a white to pale-yellow solid. • Gibberellic acid is a very potent hormone whose natural occurrence in plants controls their development. Since GA regulates growth, applications of very low concentrations can have a profound effect while too much will have the opposite effect. It is usually used in concentrations between 0.01 and 10 mg/L. • Gibberellins are produced in greater mass when the plant is exposed to cold temperatures. • Gibberellin induces stem elongation in rosette plants. Cabbage is a rosette plant with profuse leaf growth and retarded internodal length. Just prior to flowering, internodes elongate
  5. 5. enormously. This is called bolting. Bolting needs either long days or cold nights. When a cabbage head is kept under warm nights, it retains its rosette habit. Bolting can be induced artificially by the application of gibberellins under normal conditions. The mechanism of action of gibberllic acid appears mainly to induce activity of gluconeogenic enzymes during early stages of seed germination and this specificity ensures a rapid conversion of lipid to sucrose , which is further used in supporting growth and development of the embryonic axis to a competent root and shoot system. It is also found that gibberllins induce the synthesis of α-amylase and other hydrolytic enzymes during germination of monocot seeds . they are also involved in mobilising seed storage reserves during germination and seedling emergence.
  6. 6. APPLICATIONS OF GIBBERLLINS • It is also widely used in the grape-growing industry as a hormone to induce the production of larger bundles and bigger grapes, especially Thompson seedless grapes. • Gibberellic acid is used extensively to increase the sucrose yield of sugarcane. • Gibberellic acid is also used to boost cherry production. Sweet, bing cherries are sprayed 4 to 6 weeks before harvest to increase fruit size. Application of GA3 to tart cherries increases yield through enhanced bearing. • The use of gibberlins in lower dose has shown increased yield of digitalis glycosides per shoot . the harmone tried with leaf and root culture of digitalis , showed higher production of digoxin. • In case of Tinnevelly senna , GA shows a little positive effect on dry wieght of shoot , but reduction in sennoside content of leaves. • It is observed that GA treatment can cause an increase in hieght of castor plant upto five times , but does not show any changes in fixed oil content . • The treatment significantly causes reduction in alkaloid content of Vinca, Datura, Hyoscyamus, etc.
  7. 7. • Dwarf pea plant treated with gibberellin: “Foolish seedling disease” in rice
  8. 8. External application of gibberellins can also enlarge fruit size in grapes: • GA can induce parthenocartpy and fruit enlargement Functions of Gibberellins: Active gibberellins show many physiological effects, each depending on the type of gibberellin present as well as the species of plant.
  9. 9. • Stimulate stem elongation by stimulating cell division and elongation. • Stimulates bolting/flowering in response to long days. • Breaks seed dormancy in some plants which require stratification or light to induce germination. • Stimulates enzyme production (a-amylase) in germinating cereal grains for mobilization of seed reserves. • Gibberellins promote the production of male flowers, either in place of female flowers in monoecious plants or in genetically female plants such as cucurbits. (sex expression). • Can cause parthenocarpic (seedless) fruit development. • Can delay senescence in leaves and citrus fruits. This helps in storing the fruits.