Effects of Gibberellins and Prohexadione on the Activities of Oryzain and α-Amylase in Rice Seeds : PROTEINS, ENZYMES AND METABOLISM

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Oryzains, cysteine proteinases of rice seeds, are induced by GA_3 in germinating rice seeds [Abe et al. (1987) Agric. Biol. Chem. 51 : 1509]. The effects of GA_1 GA_3, GA_4, GA_9 and GA_20 On the production of oryzain and α-amylase were investigated in embryoless half- and whole-seeds of rice (cv. Nipponbare). When gibberellins (GAs) were incubated with embryoless half-seeds, GA_1, GA_3 and GA_4 induced oryzain and a-amylase, but GA_9 and GA_20 did not. GA_9 and GA_20 induced oryzain and a-amylase production in whole seeds, but this production was inhibited by the simultaneous application of prohexadione, an inhibitor of 2β- and 3β-hydroxylation of GAs. Prohexadione did not inhibit the activities of oryzain and a-amylase induced by GA_1 These results suggest that GAS possessing the 3β-hydroxyl group induce activities of oryzain and a-amylase in rice seeds and that GA_9 and GA_20 have activity only after they are converted metabolically to active GAs, probably GA_4 and GA_1 respectively. GA_1 was more active than GA_4 in both half seeds and whole seeds incubation. Oryzain and a-amylase activities induced by GA_4 Were significantly inhibited in the presence of 10^<-4> M prohexadione. This suggests that the conversion of GA_1 to GA_4 (13-hydroxylation) might be inhibited at a high dose of prohexadione in whole seeds.
日本植物生理学会の論文