GIBBERELLIN A(3) CAUSES A DECREASE IN THE ACCUMULATION OF MESSENGER-RNA FOR ACC OXIDASE AND IN THE ACTIVITY OF THE ENZYME IN AZUKI-BEAN (VIGNA-ANGULARIS) EPICOTYLS

Differential screening, aimed at the isolation of cDNA clones of mRNAs whose accumulation is influenced by GA(3), resulted in the isolation of a cDNA clone of an mRNA whose level was decreased by GA(3) in segme nts of epicotyls of Vigna angularis. The putative protein encoded by t his cDNA resembled the 1-aminocyclopropane-1-carboxylate oxidases (ACC oxidases) identified in other plant species (about 80% homology at th e amino acid level). Thus, the corresponding gene was designated AB-AC O1 (azuki bean ACC oxidase). GA(3) also decreased the activity of ACC oxidase in azuki bean epicotyls, but it did not decrease the rate of e thylene evolution. In fact, GA(3) increased the rate of ethylene evolu tion and the level of ACC. Thus, GA(3) seemed to increase the producti on of ethylene by promoting the synthesis of ACC.