Hormones213-page14

Hormones213-page14 - Seeds germinate when ABA is degraded...

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Plant Growth Regulators - 14 Abscisic Acid Abscisic acid (ABA) is a hormone that functions by inhibiting growth activities in times of environmental stress rather than by promoting growth. It often serves as an antagonist to the other growth promoting hormones in plants. Abscisic acid, which is also synthesized from mevalonic acid, got its name from the erroneous belief that it promoted the formation of abscission layers in leaves and fruits. It does not, although leaf abscission accompanies dormancy in many plants. Abscisic Acid Functions ABA promotes seed dormancy activities. ABA levels are high when seeds mature, promoting lowered metabolism and synthesis of proteins needed to withstand the dehydration associated with dormancy.
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Unformatted text preview: Seeds germinate when ABA is degraded by some environmental action. Desert seeds must have the ABA washed out of the seed coat, as do plants of marshy areas; temperate area plants have ABA degraded by light-stimulated enzymes. In other cases breaking dormancy is relative to the ratio of ABA (which keeps seeds in dormancy) and gibberellins (which promote germination). Low levels of ABA in maturing seeds promote premature germination. Mangrove seeds naturally have low levels of ABA and germinate while still attached to the shoot system. Certain mutations affecting ABA synthesis may result in seeds germinating prematurely. Mangrove germination Premature corn germination...
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