Just as the forms of dormancy are complex and diverse, the explanations for dormancy are varied. Simple models attribute ecodormancy to balances of water, carbohydrates, and energy within the growing meristem. As environmental conditions become less favorable, metabolic functions slow or change. For instance, as temperatures go below or above those that are optimal for metabolism, the reactions slow and thus growth slows or stops. Also, as tissues dehydrate or carbohydrate content lowers, metabolism may slow. Paradormancy is generally explained by a simple mechanistic model relating the balance of apical meristem-produced auxins and root-translocated cytokinins. Hormonal and nutritional models are used to explain endodormancy within buds and seeds. Bud scales and seed coats may contain the hormone abscisic acid (ABA). The tissue concentration of ABA is often highest as endodormancy begins and dissipates with the exposure of tissues to cool temperatures over time. More recently, biochemical and molecular studies are shedding some new light on these dormancy mechanisms and their controls from a genetic standpoint.
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