Changes in Some Hydrolytic Enzymes Associated with the Redifferentiation of Shoots in Rice Callus Tissues

[摘要] Developmental processes of shoot formation in rice callus tissues of var. Aichi asahi and Te-Tep grown in the organ forming medium were investigated in detail. At the same time, the changes in various hydrolytic enzyme activities (α-amylase, RNase; catalase, acid phosphatase) and α-amylase isozyme patterns in these processes were studied and compared with the some biochemical changes in rice seedlings. For this purposes, the callus tissues with green or white shoot protuberances were divided into organ-forming regions and non-organ-forming callus parts. (1) The clear cut results on organogenesis in callus tissues were obtained by adding the casein hydrolysate (4 g/1) and 5×10-5 M kinetin to Maeda's medium containing 10-7 M 2, 4-D and by using the 3 passage callus tissues, in light (3, 000 lux) conditions of 25°C instead of 30°C. Such conditions as above mentioned inhibited early growth of callus parts showing organogenesis. The callus tissue in these conditions was designated as K-callus tissues. (2) In K-callus tissue, organ-forming regions and shoot primordia were observed after 6 days of callus innoculation. Also, various hydrolytic enzyme activities during these periods were rather inhibited in comparison with control callus tissue in the 10-5 M 2, 4-D medium without kinetin (C-callus). (3) Shoot formation began to start gradually after a week and became vigorous from 10 to 14 days in culture. But root formation was slight at this stage. As the shoots were formed, RNase and α-amylase activities in shooting regions increased rapidly. α-Amylase activity was maximum at 10 day-old. At the 10th day, RNase and (α-amylase activities were about 7- and 10-times as much as that of C-callus tissue, respectively (fig. 12, table 2). These data suggest that histological and biochemical "lag phase" in organogenesis present about one week after callus innoculation. (4) In the callus tissue grown in the GA3-treated (5×10<-5> M) organ-forming medium (KGcallus tissue), organogenesis and its related enzyme activities were strikingly decreased (fig. 13). (5) In the organ forming medium containing yeast extract (5 g/1), the shoot or root primordia of Te-Tep callus tissue were observed after about two week. The shoot primordia were initiated exogenously and root ones endogenously, and both primordia were formed independently to each other. The shoot primordia were circularly surrounded by a large number of vascular bundles, but the root ones were not. Their singularities were discussed. (6) From the observations on α-amylase banding patterns, the results were obtained that the activities of α-amylase "g" and "e" conspicuously increased and a new isozyme "1" was induced with organ developments in K-callus tissue and in the organ forming regions of KG-callus tissue. (7) Several hydrolytic enzyme activities in rice Seedlings of 2 to 4 day-old were studied to compare the changes in developmental processes in redifferentiation of shoot. Enzyme activities were lower than those of C-callus (10 day-old) or shoot-initiating regions of K-callus tissue except catalase. Only one isozyme of α-amylase which was considered to correspond with amylase "a" in callus tissue was isolated from rice seedlings. From the results mentioned above, the intimate relations between histological and gross morphological aspects and some biochemical changes in redifferentiation processes of rice callus tissues were suggested. The role of hydrolytic enzymes and vascular systems surrounding circularly shoot primordia in these processes were discussed.

[学科分类] 农业科学（综合）