Physiological indices such as contents of soluble protein (Pr), chlorophyll (Chi) 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 Chi increased with leaf age and then decreased. However, the decreasing rate was different. Xiami has more Pr and Chi 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.%以塑料大棚栽培的‘玉菇’和‘夏蜜’厚皮甜瓜品种为试验材料,研究甜瓜植株不同节位叶片在自然衰老过程中可溶性蛋白(Pr)、叶绿素(Chl)、丙二醛(MDA)含量的变化,过氧化氢酶(CAT)、愈创木酚过氧化物酶(POD)、超氧化物歧化酶(SOD)的活性变化以及根系活力变化规律.结果表明,厚皮甜瓜不同品种不同叶位叶片衰老差异较大.不同品种和不同叶位叶片中的可溶性Pr和Chl含量都随着叶龄的增加而升高然后下降,但下降的速度不同,其中‘夏蜜’的Pr和Chl含量比‘玉菇’高,功能叶片维持天数多.在甜瓜叶片发育初期,MDA含量不高,其变化也比较平缓,但随着叶龄的增加而升高,后期增加比较迅速.叶片SOD活性变化呈‘M’型曲线,出现拐点的位置因品种和节位不同而异.‘夏蜜’SOD活性比‘玉菇’的高,清除活性氧的能力强,植株衰老的也慢.POD活性随着叶龄的增加而逐渐升高,在达到最高值后开始下降,叶片也随之衰老死亡.由于POD活性在叶片发育过程中持续上升时间长,下降时间比较短,可能对叶片衰老的影响较大.CAT活性随着发育进程不断升高,在发育21 ～28 d后达到最大值,在叶片充分发育后随着叶龄增大而下降,其下降速度也不同,‘夏蜜’的叶片在发育后期相比‘玉菇’的要平缓.根系活力在始花期达到最高值,其中‘夏蜜’的根系活力比‘玉菇’的高,授粉后,根系活力开始下降,在果实成熟期达到最低值.
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