Control of seed dormancy in Nicotiana plumbaginifolia: post-imbibition abscisic acid synthesis imposes dormancy maintenance

The physiological characteristics of seed dormancy in Nicotiana plumbaginif olia Viv. are described. The level of seed dormancy is defined by the delay in seed germination (i.e the time required prior to germination) under fav ourable environmental conditions. A wild-type line shows a clear primary do rmancy, which is suppressed by afterripening, whereas an abscisic acid (ABA )-deficient mutant shows a non-dormant phenotype. We have investigated the role of ABA and gibberellic acid (GA(3)) in the control of dormancy mainten ance or breakage during imbibition in suitable conditions. It was found tha t fluridone, a carotenoid biosynthesis inhibitor, is almost as efficient as GA(3) in breaking dormancy. Dry dormant seeds contained more ABA than dry afterripened seeds and, during early imbibition, there was an accumulation of ABA in dormant seeds, but not in afterripened seeds. In addition, flurid one and exogenous GA(3) inhibited the accumulation of ABA in imbibed dorman t seeds. This reveals an important role for ABA synthesis in dormancy maint enance in imbibed seeds.