Effects of putrescine on senescence in detached leaves of Chinese cabbage (Brassica campestris L.) in the light were investigated. The putrescine as a potent antisenescence substance markedly inhibited chlorophyll and protein loss at the 10 mM concentration in the detached leaves during the dark incubation. In the light, however, putrescine showed the opposite effects to dark incubation. The chlorophyll loss by putrescine in the light was stopped with dark-transfer, and inhibited competitively by a divalent cation Ca^2+. In the light, putrescine reduced the protease activity. Putrescine, in the light, increased H_2O_2 content and reduced the activities of enzymes -superoxide dismutase (EC 1.15.1.1), peroxidase (EC 1.11.1.7), catalase (EC 1.11.1.6)- involved in inhibiting the accumulation of free radicals. These results suggest that the effects of puterscine on chlorophyll and protein loss in detached leaves of Chinese cabbage in the light are related to the cationic nature of putrescine and the accumulation of free radicals. Effects of putrescine on senescence in detached leaves of Chinese cabbage (Brassica campestris L.) in the light were investigated. The putrescine as a potent antisenescence substance markedly inhibited chlorophyll and protein loss at the 10 mM concentration in the detached leaves during the dark incubation. In the light, however, putrescine showed the opposite effects to dark incubation. The chlorophyll loss by putrescine in the light was stopped with dark-transfer, and inhibited competitively by a divalent cation Ca^2+. In the light, putrescine reduced the protease activity. Putrescine, in the light, increased H_2O_2 content and reduced the activities of enzymes -superoxide dismutase (EC 1.15.1.1), peroxidase (EC 1.11.1.7), catalase (EC 1.11.1.6)- involved in inhibiting the accumulation of free radicals. These results suggest that the effects of puterscine on chlorophyll and protein loss in detached leaves of Chinese cabbage in the light are related to the cationic nature of putrescine and the accumulation of free radicals.