NORMAL UNIV CENT CHINA,DEPT BIOL,WUHAN 430070,PEOPLES R CHINA; CHINESE ACAD SCI,INST HYDROBIOL,WUHAN 430072,PEOPLES R CHINA; CHINESE ACAD SCI,WUHAN INST BOT,WUHAN 430074,PEOPLES R CHINA
Superoxide dismutase activity in water hyacinth leaves was not sensitive to small changes in environmental pH, but declined markedly with greater pH changes. KCN inhibited superoxide dismutase activity, suggesting that the enzyme was mainly composed of the Cu-Zn form. Low temperature (2-degrees-C) treatment caused a decline in superoxide dismutase activity. This effect became more pronounced as the treatment time was prolonged. Furthermore, the decline was much more significant than reductions of glucose-6-phosphate dehydrogenase activity or respiration under comparable conditions. With increasing physiological age, superoxide dismutase activity declined and was significantly lower in old than in young leaves. Therefore, superoxide dismutase activity might be employed as one of physiological parameters in studying leaf senescence.