Induction of alpha-amylase inhibitor synthesis in barley embryos and young seedlings by abscisic Acid and dehydration stress.

An endogenous alpha-amylase inhibitor was found to be synthesized in embryos of developing barley grain (Hordeum vulgare cv Bonanza). Accumulation of this protein occurred late in development (stage IV), at the same time that endogenous abscisic acid (ABA) showed a large increase. The inhibitor could be induced up to 23-fold in isolated immature embryos (stage III) by culture in ABA. Precocious germination was also blocked in stage III embryos by ABA. Dehydration stress on the isolated immature embryos also induced higher levels of the inhibitor and ABA. An even greater response to dehydration stress was observed in young seedlings, where inhibitor content increased 20-fold and ABA increased 80-fold during water stress. The high degree of correlation between ABA and inhibitor contents in in situ embryos, dehydrated embryos and young seedlings, as well as the increase in inhibitor caused by exogenously applied ABA to isolated embryos, suggests that increased alpha-amylase inhibitor synthesis in response to dehydration stress is mediated by ABA.