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Hormones213-page12 - GA on dwarf tomato • Gibberellins...

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Plant Growth Regulators - 12 Many seeds contain a variety of different gibberellins. Over 100 different gibberellins (organic acids synthesized from mevalonic acid) are known. Gibberellins are produced in roots and younger leaves, but have their highest concentration in seeds. Most effects of gibberellins are shown only in concert with auxins. Gibberellin Functions Gibberellins work with auxins to promote rapid elongation and division of stem tissue. Gibberellins determine microtubule alignment in the preprophase band that determines the plane of cellulose expansion. Microtubule alignment in hypocotyls (Red dots are chloroplasts) The effects of gibberellins on elongation are seen in: Bolting of biennials, to produce flowers during the first growing season Reversal of genetic dwarfism GA and flower bolting GA and bolting cabbage
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Unformatted text preview: GA on dwarf tomato • Gibberellins are important to breaking dormancy after imbibition of water by the seed coat. Gibberellins signal germination activities. Application of gibberellins to seeds will counter the normal environmental cues, such as exposure to low temperatures. Gibberellins stimulate synthesis of enzymes that convert stored nutrients (starches) to sugars needed for rapid cell respiration during germination. Gibberellins secreted by embryos at the start of germination (imbibition of water) typically activate a set of genes found in the aleurone layer of seeds for this conversion. The malting industry uses gibberellins to enhance the barley's starch reserves conversion to malt and then to glucose. Abscisic acid can counter the effect of gibberllin to keep seeds dormant....
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