α-Amylase Activity in DevelopingSorghumCaryopses from Sprouting Resistant and Susceptible Varieties. The Role of ABA and GAs on its Regulation

α-Amylase activity was analysed in developing caryopses fromSorghumvarieties showing contrasting susceptibility to preharvest sprouting. Unsprouted caryopses from variety Redland B2 (very susceptible) showed α-amylase activity from 31 d after pollination (DAP) onwards, that were 20-fold higher than those observed for variety IS 9530 (very resistant). When the caryopses were incubated the α-amylase activity predominately increased in the embryos. IS 9530 embryos were more sensitive to added GA3than those of Redland B2. Treating the panicles at 3 DAP with an inhibitor of GA biosynthesis (paclobutrazol) brought the α-amylase activity of Redland B2 caryopses down to the levels found in IS 9530 control caryopses. In contrast, treating the panicles at 3 DAP with an inhibitor of ABA biosynthesis (fluridone) increased the α-amylase activity of caryopses from the two varieties. These results show that differences between both varieties are not limited to differences in the susceptibility to germinate on the mother plant, but they include differences in the activity of α-amylase. In addition, these results suggest the participation of both GAs and ABA in the regulation of the α-amylase activity in developingSorghumcaryopses.