Response to abscisic acid application and hormone profiles in spring Brassica napus seed in relation to secondary dormancy

Abstract

The plant hormone abscisic acid (ABA) has been implicated in the inception and maintenance of seed dormancy, while gibberellins promote dormancy breakage and germination in some species. We investigated whether osmotic stress induced secondary dormancy in Brassica napus L. is associated with changes in ABA sensitivity and metabolism, as well as changes in gibberellin levels. Seeds of two genotypes, one with low dormancy potential (LDP) and one with high dormancy potential (HDP) for secondary dormancy, were exposed to a dormancy-inducing osmotic treatment for up to 4 weeks and then germinated in the presence of increasing ABA concentrations. Even at relatively high concentrations of supplied ABA, germination of LDP seed was not inhibited, while relatively low ABA concentrations inhibited the germination of HDP seed after osmotic treatment. Fluridone was highly effective in suppressing secondary dormancy development in HDP seed, but had no effect on germinability in LDP seed. Despite the lack of differences in nonosmotically treated seed, ABA and ABA-glucose ester accumulated to higher levels, and gibberellin A1 accumulated to lower levels, in HDP relative to LDP seed by the end of the osmotic treatment. Our findings indicate an association among ABA sensitivity, biosynthesis and accumulation, and secondary dormancy potential in B. napus seed.Key words: abscisic acid (ABA), Brassica napus, fluridone, induced dormancy, osmotic stress, sensitivity.