The role of endogenous gibberellins in the formation of α-amylase by aleurone layers of germinating barley caryopses.

Using sensitive and selective immunological assays we have shown that in germinating caryopses of Hordeum vulgare L. cv. Himalaya, the level of gibberellin A4 (GA4) rises approximately 18-to 20-fold shortly (2-4 h) before α-amylase activity increases. Gibberellin A4 is the predominant immunoreactive gibberelin during these developmental stages and reaches a peak amount of approximately 9 pmol per caryopsis about 48 h after imbibition. Isolated aleurone layers produce GA4 in the presence of an exogenous gibberellin, such as GA1, which is not a biosynthetic precursor for GA4. Experiments with inhibitors of gibberellin biosynthesis indicate that gibberellin synthesis is required in this tissue for the induction of α-amylase. The inductive effect of exogenously applied GA1 is indirect and appears to be mediated by GA4. Embryos form predominantly GA1; however, very little of this material is released by isolated embryos into the incubation medium. The results presented make it unlikely that the role of the embryo in the process of α-amylase induction in aleurone layers is to provide gibberellins or gibberellin precursors.