IntroductionThe seeds of many plants are dormant and unable to germinate at maturity, but gain the ability to germinate through after-ripening during dry storage. The hormone abscisic acid (ABA) stimulates seed dormancy, whereas gibberellin A (GA) stimulates dormancy loss and germination.MethodsTo determine whether dry after-ripening alters the potential to accumulate ABA and GA, hormone levels were measured during an after-ripening time course in dry and imbibing ungerminated seeds of wildtype Landsbergerecta(Ler) and of the highly dormant GA-insensitive mutantsleepy1-2(sly1-2).ResultsThe elevatedsly1-2dormancy was associated with lower rather than higher ABA levels. Lergermination increased with 2-4 weeks of after-ripening whereassly1-2required 21 months to after-ripen. Increasing germination capacity with after-ripening was associated with increasing GA4levels in imbibingsly1-2and wild-type Lerseeds. During the same 12 hr imbibition period, after-ripening also resulted in increased ABA levels.DiscussionThe decreased ABA levels with after-ripening in other studies occurred later in imbibition, just before germination. This suggests a model where GA acts first, stimulating germination before ABA levels decline, and ABA acts as the final checkpoint preventing germination until processes essential to survival, like DNA repair and activation of respiration, are completed. Overexpression of the GA receptorGID1b(GA INSENSITIVE DWARF1b) was associated with increased germination ofsly1-2but decreased germination of wildtype Ler.This reduction of Lergermination was not associated with increased ABA levels. Apparently,GID1bis a positive regulator of germination in one context, but a negative regulator in the other.