Regulation of alcohol dehydrogenase gene expression in barley aleurone by gibberellin and abscisic acid

The expression of the Adh1 gene (alcohol dehydrogenase, EC 1.1.1.1) was studied in the aleurone layer of barley (Hordeum vulgare cv. Himalaya). Expression increased markedly during grain development at the levels of activity, enzyme protein and mRNA, mRNA content, but not enzyme activity, could be increased further by exogenous abscisic acid (ABA) when isolated, de-embryonated developing grains were pre-treated with gibberellic acid (GA(3)) or fluridone. In isolated mature aleurone layers incubated with exogenous hormones, ADH mRNA was strongly up-regulated by ABA and down-regulated by GA(3) within 6 h, With ABA, this increase in mRNA was followed by an increase in ADH protein and activity peaking at 18 h, With GA(3), the decrease in mRNA was accompanied by simultaneous decreases in protein and activity. In general, GA(3) counteracted the effect of ABA and vice versa, In the aleurone of germinating grain, ADH activity decayed in a distal direction from the embryo, consistent with down-regulation by gibberellin(s) diffusing from it. It was concluded that ADH gene expression in the aleurone of the intact grain is regulated by an ABA/gibberellin interaction.