Changes in Antioxidative Levels in Aging Cucumber (Cucumis sativus L.) Leaves

Abstract

To investigate the relationship between aging and antioxdative levels of fully developed, aging cucumber leaves, we measured the contents of protein, malondialdehyde, chlorophyll, reactive oxygen species (superoxide and hydrogen peroxide), and antioxidative compounds (ascorbic acid, β-carotene and flavonoid), then analyzed the activities of antioxidative enzymes, superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and peroxidase (POD). Protein, malondialdehyde and chlorophyll contents in the leaves decreased linearly for 22, 35, and 55 days, respectively, whereas superoxide and hydrogen peroxide contents accumulated for 35 and 25 days, respectively, and then decreased. These results suggest that the aging process after leaf development could be divided into two periods, the earlier one representing a growth process lasting until 25 to the 30th day, the later one is the senescence process beginning about the 35th day. Thus, SOD, CAT, and APX decreased rapidly after 35 days of development, while ascorbic acid and flavonoid contents decreased with time for 25 days. Our data indicate that SOD, CAT and APX, are closely related with the senescence process, whereas ascorbic acid and flavonoid are related with the growth process in developed cucumber leaves.