Characteristics and Varietal Differences of α-Amylase Isozymes in Rice Callus Tissues

Abstract

The characterization and varietal differences of α-amylase isozymes in rice callus tissues were studied by disc electrophoresis and gel electricfocusing on polyacrylamide gel electrophoresis (isoelectricfocusing). (1) Amylase in callus tissues grown on a Maeda's chemical defined medium containing 10-5M 2, 4-D was resolved into six isozymes by disc electrophoresis and ten by isoelectricfocusing. From the investigations on heat (70°C, 15 min.) stability, Ca2+ -requirement and EDTA (5 × 10-3M)resistancy of ten isozymes by isoelectricfocusing, we found that all of these isozymes were α-amylase, and only one isozyme (band a), which was fastest-migrating and most acidic, was a new rice o'-amylase that was not required Ca2+ and not inactivated by EDTA. (2) Some biochemical changes in Aichi asahi callus tissues grown in the 10-5M 2, 4-D medium containing various carbon sourses (glucose, fructose, maltose, lactose, xylose, galactose, arabinose and soluble starch) which were added in place of sucrose, were investigated. The growth, α-amylase isozyme patterns and protein content in callus tissues grown in soluble starch were not different from sucrose medium. In all sugars, as only arabinose did not allow the callus growth, it was suggested that this sugar was inappropriate as carbon sourse. The banding patterns of α-amylase isozymes in arabinose medium were different from other sugars, that is, amylase "g" was strongly inhibited. (3) α-Amylase isozyme banding patterns in callus tissues of three normal varieties (Ginbozu, Aichi asahi, Te-Tep) and three dwarf varieties (Tan ginbozu, Waisei shinriki, Kotake tamanishiki), which were studied by isoelectricfocusing, were different from each others and these isozyme activities were changed in compliance with total α-amylase activity. α-Amylase activity in Tan ginbozu callus tissus was lowest in six varieties, but this callus tissus contains ten isozymes. Hence, this dwarfism is not elucidated by changes in isozyme banding patterns. (4) Changes in α-amylase activity and its isozymes in rice variety, Fujiminori and its four strains (Reimei, 71, 71L, and 71S) derived by 60Co-irradiation were studied. The callus tissue of strain "71", which showed the low plant height and was thus dwarf mutant, represented poor growth, low protein content and low enzyme activity. Beside, each activity of ten α-amylase isozymes were relatively low. The callus tissue of strain "71S", which showed the lowest plant height, represented the same biochemical changes as ones of Fujiminori.