Genetic and ontogenic changes in sensitivity to abscisic acid in Brassica napus seeds

Abscisic acid (ABA) sensitivity was compared in seeds of three rape cultivars by measuring the effectiveness of a broad range of ABA concentrations in inhibiting germination of mature seeds. The least sensitive cultivar showed a sensitivity to exogenous ABA reduced by up to 10 times compared with the most sensitive one. In all cultivars, there was high ABA sensitivity in immature seeds and a progressive loss of sensitivity upon seed maturation. Genetic or ontogenic changes in sensitivity could not be correlated with changes in endogenous ABA levels. Spraying leaves of the mother plant with ABA solutions, however, both delayed seed germination on water and decreased sensitivity to ABA. Moreover, manipulation of gibberellin (GA) levels by spraying chlorocholine chloride or triapenthenol on leaves of the mother plant transiently increased seed sensitivity to ABA. Thus, manipulation of maternal ABA or GA could modify seed sensitivity to ABA.