Abstract: Physiological indices such as contents of soluble protein (Pr), chlorophyll (Chl) and malondialdehyde (MDA), the dynamic changes of activities of catalase (CAT), peroxidase (POD), superoxide dismutase (SOD), and the changes of root vitality were analyzed in muskmelon during natural senescence using the varieties of Yugu and Xiami grown in plastic greenhouse. Results showed that the leaf senescence of different cultivars and leaf location were quite different. Contents of soluble Pr and Chl increased with leaf age and then decreased. However, the decreasing rate was different. Xiami has more Pr and Chl than Yugu and the functional leaves could sustain for more days. Content of MDA was low at the early development of leaves, and the change was relatively flat. However, MDA content was increased relatively rapidly during late growth stages. SOD activity in leaves has ‘M’ shaped curve, and the time of appearance of the inflection point differed between varieties and leaf locations. Xiami had stronger activity of SOD than Yugu and thus a higher antioxidant capacity and delay of senescence. POD activity increased as leaf gradually aged, and reached the highest value and then began to decrease until the death of the leaf. Because POD continuously increased during the most time of the whole development but decreased within a relatively short period, the POD activity probably has a greater impact on leaf senescence. CAT activity increased with the process of leaf development, reached the maximum at 21-28 days and then declined with the aging of the leaves. The rate of decline of CAT in Xiami was much slower than Yugu during the later stage of leaf development. Root activity reached the highest value in the first flowering, with Xiami showing higher activity of root viability than Yugu. After pollination, root activity began to decline and has the lowest value when fruit maturity．

Key words: muskmelon, senescence, physiological indices