EFFECTS OF LOW-TEMPERATURE AND PHYSIOLOGICAL AGE ON SUPEROXIDE-DISMUTASE IN WATER HYACINTH (EICHHORNIA-CRASSIPES SOLMS)

Superoxide dismutase activity in water hyacinth leaves was not sensiti ve to small changes in environmental pH, but declined markedly with gr eater pH changes. KCN inhibited superoxide dismutase activity, suggest ing that the enzyme was mainly composed of the Cu-Zn form. Low tempera ture (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 re ductions of glucose-6-phosphate dehydrogenase activity or respiration under comparable conditions. With increasing physiological age, supero xide dismutase activity declined and was significantly lower in old th an in young leaves. Therefore, superoxide dismutase activity might be employed as one of physiological parameters in studying leaf senescenc e.