Dormancy Studies in Seed of Avena Fatua 4. : The Role of Gibberellin in Embryo Dormancy

Initiation of germination and subsequent growth of naked dormant embryos of Avena fatua L. require an exogenous source of sugar, amino acids, and gibberellic acid (GA). Non-dormant embryos can grow on sugar and amino acids, without exogenous GA, because they produce endogenously a gibberellin-like factor. This factor is absent in freshly matured dormant embryos but increases in amount with length of afterripening for several years, then decreases steadily. The action on embryos of exogenous GA and the endogenous GA-like factor is to promote the synthesis of enzymes or possibly to activate preformed enzymes necessary for the utilization of endosperm as the substrate for germination and growth. The levels of free phosphate and specific activity of 3′-nucleotidase, and ability to synthesize soluble protein between 24 and 48 hours, are markedly restricted in highly dormant embryos and GA can overcome these restrictions.