Studies on a Nondormant Sunflower Mutant

During the course of greenhouse studies, an unexpected sunflower mutant resulting from an interspecific cross of the wild perennial Helianthus divaricatus with cultivated HA 89 was found. In this mutant, dormancy is not induced in the developing embryo. Instead, developing seeds of the mutant sunflower begin to germinate in the head about 40 days after pollination (Fig. 1). Others have reported seed nondormancy in sunflower as well, but the phenotype in that case was albino, with visibly reduced pigmentation by carotenoids. Analysis showed that a defective ζcarotene desaturase was responsible for the loss of pigmentation (Conti et al, 2004). Because carotenoids are precursors of abscisic acid (ABA), the possibility exists that altered ABA biosynthesis was responsible for nondormancy in the albino mutant. ABA is a known inducer of dormancy in many plants, including sunflower (Le Page-Degivry and Garello, 1990). Although pigmentation appeared normal in our nondormant mutant, we investigated the levels of ABA in the developing seeds of the nondormant mutant at various stages after pollination. In addition, we report the results of in vitro studies on the effect of exposure of excised developing nondormant mutant seeds to ABA.