HORMONAL-REGULATION OF DORMANCY IN DEVELOPING SORGHUM SEEDS

The role of abscisic acid (ABA) and gibberellic acid (CA) in determini ng the dormancy level of developing sorghum (Sorghum bicolor [L.] Moen ch.) seeds from varieties presenting contrasting preharvest sprouting behavior (Redland B2, susceptible; IS 9530, resistant) was investigate d. Panicles from both varieties were sprayed soon after pollination wi th fluridone or paclobutrazol to inhibit ABA and CA synthesis, respect ively. Fluridone application to the panicles increased germinability o f Redland B2 immature caryopses, whereas early treatment with paclobut razol completely inhibited germination of this variety during most of the developmental period. Incubating caryopses in the presence of 100 mu M GA(4+7) overcame the inhibitory effect of paclobutrazol, but also stimulated germination of seeds from other treatments. IS 9530 caryop ses presented germination indices close to zero until physiological ma turity (44 d after pollination) in control and paclobutrazol-treated p articles. However, fluridone-treated caryopses were released from dorm ancy earlier than control and paclobutrazol-treated caryopses. Incubat ion in the presence of GA(4+7) stimulated germination of caryopses fro m all treatments. Our results support the proposition that a low dorma ncy level (which is related to a high preharvest sprouting susceptibil ity) is determined not only by a low embryonic sensitivity to ABA, but also by a high GA content or sensitivity.