To understand the role of H2O2 in the damaging effect of UV-B radiation on ribulose- 1,5-bisphosphate carboxylase/oxygenase (Rubisco)content, the time courses of changes in Rubisco and H2O2 contents under UV-B treatment were measured in the primary leaves of two mung bean cultivars (Phaseolus raditus L. cv. Zhonglu-1 and Qindou-20). A 0.4 W/m2 UV-B treatment caused a drop of the former to about 1/3 and a 30%-40%rise in H2O2 content in a week in both cultivars but with Qindou-20 showing stronger responses. Such higher rate of increase in proteolytic activity under UV-B treatment implies that UV-B lowers Rubisco by activating proteolytic enzymes which hydrolizes Rubisco. Scavenging of H2O2 by exogenously added ascorbic acid (ASA) significantly inhibited the UV-B-induced decrease in Rubisco amount and increases in H2O2 level and proteolytic activity. It is shown that H2O2 participates in the UV-B-induced reduction of Rubisco amount. It is suggested that H2O2 stimulates the degradation of Rubisco by activation of proteolytic systems.%为了探讨UV-B辐射引起的Rubisco含量降低的可能机制,研究了两个绿豆品种(秦豆-20和中绿-1)幼苗在UV-B辐射下叶片Rubisco含量、蛋白水解酶活性和H2O2含量的变化.结果表明:UV-B辐射显著加速了两个绿豆品种幼苗叶片H2O2含量和蛋白水解酶活性上升,使Rubiscco含量下降.秦豆-20品种在UV-B辐射下H2O2含量和蛋白水解酶活性的上升程度明显大于中绿-1,相应其Rubisco含量的下降程度也大于中绿-1.抗坏血酸处理能明显降低UV-B辐射下两品种幼苗叶片H2O2含量,同时明显抑制蛋白水解酶活性的上升及Rubisco含量的下降.结果说明UV-B辐射诱导Rubisco含量的降低可能通过提高H2O2水平从而加强蛋白水解酶系统的活化而加速了Rubisco的降解.
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