ALPHA-AMYLASE ACTIVITY IN DEVELOPING SORGHUM CARYOPSES FROM SPROUTINGRESISTANT AND SUSCEPTIBLE VARIETIES - THE ROLE OF ABA AND GAS ON ITS REGULATION

alpha-Amylase activity was analysed in developing caryopses from Sorgh um Varieties showing contrasting susceptibility to preharvest sproutin g. Unsprouted caryopses from variety Redland B2 (very susceptible) sho wed alpha-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 alpha-amylase activ ity predominately increased in the embryos. IS 9530 embryos were more sensitive to added GA(3) than those of Redland B2. Treating the panicl es at 3 DAP with an inhibitor of GA biosynthesis (paclobutrazol) broug ht the alpha-amylase activity of Redland B2 caryopses down to the leve ls found in IS 9530 control caryopses. In contrast, treating the panic les at 3 DAP with an inhibitor of ABA. biosynthesis (fluridone) increa sed the alpha-amylase activity of caryopses from the two varieties. Th ese results show that differences between both Varieties are not limit ed to differences in the susceptibility to germinate on the mother pla nt, but they include differences in the activity of alpha-amylase. In addition, these results suggest the participation of both GAs and ABA in the regulation of the alpha-amylase activity in developing Sorghum caryopses. (C) 1997 Annals of Botany Company