Investigating the Control of Wheat Seed Dormancy and Germination By Plant Hormones.

It is essential to advance knowledge about the hormonal control of seed dormancy directly in wheat where problems with preharvest sprouting (PHS) of seed on the mother plant, due to insufficient dormancy under cold and/or moist conditions, cause economic losses for farmers, millers, bakers, and consumers.  Selection for rapid seedling emergence has led to loss of seed dormancy in wheat, resulting in susceptibility to PHS.  Identification and localization of the hormone signal for dormancy release could transform our current knowledge leading to new breeding strategies for PHS tolerance.  Previous work showed that loss of dormancy is associated with loss of ABA (abscisic acid, which promotes dormancy) sensitivity and increased GA (gibberellic acid, which stimulates germination) sensitivity. Loss of ABA sensitivity may result from turnover. If so, it should be associated with a decrease in internal ABA. This study performed plant hormone profiling experiments which investigated the hormonal control of the transition from seed dormancy to germination in the cereal crop wheat.  To address whether the ratio of ABA:GA controls the dormancy status of wheat this project measured hormone levels in embryos/scutellum and aleurones/endosperm from imbibed seeds to determine whether:  1) After-ripening of wheat seeds is associated with increased GA levels, and decreased ABA levels;  2) Cold stratification of wheat seeds is associated with increased GA levels and decreased ABA levels;  3) ABA hypersensitive mutants of wheat, Zak ERA8 and Warm4 are associated with elevated ABA levels or decreased GA levels.