Regulation of Dormancy in Barley by Blue Light and After-Ripening: Effects on Abscisic Acid and Gibberellin Metabolism

White light strongly promotes dormancy in freshly harvested cereal grains, whereas dark and after-ripening have the opposite effect. We have analyzed the interaction of light and after-ripening on abscisic acid (ABA) and gibberellin (GA) metabolism genes and dormancy in barley ( Hordeum vulgare ‘Betzes’). Analysis of gene expression in imbibed barley grains shows that different ABA metabolism genes are targeted by white light and after-ripening. Of the genes examined, white light promotes the expression of an ABA biosynthetic gene, HvNCED1 , in embryos. Consistent with this result, enzyme-linked immunosorbent assays show that dormant grains imbibed under white light have higher embryo ABA content than grains imbibed in the dark. After-ripening has no effect on expression of ABA biosynthesis genes, but promotes expression of an ABA catabolism gene ( HvABA8 ′ OH1 ), a GA biosynthetic gene ( HvGA3ox2 ), and a GA catabolic gene ( HvGA2ox3 ) following imbibition. Blue light mimics the effects of white light on germination, ABA levels, and expression of GA and ABA metabolism genes. Red and far-red light have no effect on germination, ABA levels, or HvNCED1 . RNA interference experiments in transgenic barley plants support a role of HvABA8 ′ OH1 in dormancy release. Reduced HvABA8 ′ OH1 expression in transgenic HvABA8 ′ OH1 RNAi grains results in higher levels of ABA and increased dormancy compared to nontransgenic grains.