Post-transcriptional regulation of bifunctional alpha-amylase/subtilisin inhibitor expression in barley embryos by abscisic acid.

Changes in bifunctional alpha-amylase/subtilisin inhibitor (BASI) expression induced by abscisic acid (ABA) were studied using in vitro cultured barley (Hordeum vulgare cv. Bonanza) embryos. The steady-state levels of BASI mRNA and BASI protein were increased by exogenously applied ABA. Accumulation of BASI protein was preceded by an increase in message level. The results suggest that ABA does not affect BASI mRNA translation. Nuclear run-on assays demonstrated that ABA had no effect on transcriptional activity. BASI mRNA was not detectable in the embryos treated with a protein synthesis inhibitor, cycloheximide, which had no inhibitory effect on BASI transcription rate. We propose that ABA increases the stability of BASI mRNA through synthesis of a short-lived protein that protects the message.