Plant Biotechnology 24, 231–235 (2007)

Storage proteins in cotyledons of legume plants are degraded by proteinases after germination. We examined whether abscisic acid (ABA), gibberellin (GA) and brassinosteroid (BR) are involved in the expression of cysteine proteinases in cotyledons of common bean seeds with RNA blotting using cDNAs for five papain-like proteinases, EP-C1, CP1, CP2, CP3, CP4 and two legumain-like proteinases, LLP1 and LLP2 as probes. Six genes, except for CP4, are activated after seed imbibition. These germination-induced cysteine proteinase genes (GICPs) are repressed by exogenously applied ( )-5 a , 8 -cyclo-ABA which is more resistant to hydroxylation than ABA. Either GA3 or epi-BR activated GICPs in the presence of ABA, suggesting that both of GA and BR are involved in the expression of GICPs. It is possible that GA biosynthesis is required for the activation of GICPs, because either GA-biosynthesis inhibitors, chloroethyltrimethylammonium chloride or prohexadione calcium repressed GICPs and this repression was restored by exogenously applied GA3.