The changes and biochemical characteristics of endopeptidase isozymes in non-heading Chinese cabbage under salt stress | 盐胁迫下不结球白菜幼苗叶片内肽酶同工酶变化及生化特性研究

Chinese. 研究了不同盐浓度胁迫下不结球白菜暑绿幼苗叶片中可溶性蛋白质含量、内肽酶同工酶及其活性的变化和内肽酶同工酶生化特性。结果表明，暑绿叶片中存在5种内肽酶同工酶（EP1～EP5），其中，EP3和EP5为半胱氨酸型内肽酶，EP1和EP2为丝氨酸型内肽酶，而EP4几乎不被所试的各种内肽酶抑制剂所抑制；内肽酶的最适pH为6．0，最适温度为50℃；EP3、EP4和EP5的热稳定性较好，在60℃下保温1h后还保留较高活性。100mmol・L-1NaCl处理暑绿4d后，EP4活性增强，其他4种同工酶活性变化不明显；200mmol・L-1NaCl处理相同时间，叶片1，5-二磷酸核酮糖羧化酶／加氧酶（Rubisco）等蛋白发生明显降解，EP2、EP4、EP5活性随着时间推进不断升高，而EP1、EP3活性明显降低，显示EP2、EP4、EP5可能在盐胁迫诱导的暑绿叶片衰老中起主要作用。[著者文摘]

English. The changes of soluble protein content, endopeptidase isozymes （EPs） and activity in seedling leaves of non-heading Chinese cabbage Shulu under salt stress, and EPs biochemical characteristics were studied. The results showed that five EPs （EP1 -EPS） in leaves were detected. Among them, EP3 and EP5 were cysteine endopeptidases, EP1 and EP2 were serine endo- peptidases, but EP4 was hardly inhibited by all the EP inhibitors used. The optimum pH and temperature of EPs were 6. 0 and 50 ℃. EP3, EP4 and EP5 still had high activities after their incubation at 60 ℃ for 1 h. The activity of EP4 gradually increased in leaves under 100 mmol ・L-1 salt stress during 4 days, but the other EPs were almost invariable. However, the activities of EP2, EP4 and EP5 increased and those of EP1 and EP3 declined obviously accompanied by the degrading of ribulose-1,5-bisphos- phate carboxylase/oxygenase （Rubisco） in leaves under 200 mmol ・L-1 salt stress during 4 days. It suggested that EP2, EP4 and EP5 might play an important role in salt stress-induced Shulu leaf senescence.