Photosynthesis And Carbohydrate Metabolism In Source Leaves In Response To Sink-Source Manipulations In Cucumis Melo L.cv. Hetao

Hetao melon is Inner Mongolia hetao area of good melon varieties. It has theoretic and practical significance to explore and illustrate its carbohydrate metabolism. This study based on the carbohydrate metabolism of Hetao melon fruits. Net photosynthetic rate, carbohydrate contents and the activities of related enzymes in source leaves were studied during fruit development (Cucumis melo L.cv. Hetao). Variations of net photosynthetic rate, sucrose contents, reducing sugar contents, starch contents and the activities of related enzymes in carbohydrate metabolism in source leaves in response to sink-source manipulation by defruiting and retaining fruits were studied. The results indicated that:1. Net photosynthetic rate in source leaves significantly increased during young fruit period and early stage of fruit expansion period (0-12d), stayed high level during the mid and late stage of fruit expansion period and the lag phase (12-32d), decreased gradually during mature period (32-44d). During the full growth stage, sucrose and reducing sugar contents in source leaves remained stable. The activities of sucrose phosphate synthase (SPS) and sucrose synthase on synthesis(SS+) higher in the early and last stage than that in the middle stage. The activities of sucrose synthase on cleavage(SS-) and invertase(Inv) showed no regular law but incrased during mature period. The activities of adenosine diphosphate-glucose pyrophosphorylase (AGPase) in source leaves significantly increased during young fruit period and early stage of fruit expansion period (0-12d) and then stayed low level.2. Day and night variation of net photosynthetic rate was typical single peak curve and showed no evidence of midday depression and the peak showed during11:00～13:00. Single peak curve variations in contents of sucrose, reducing sugar, starch in leaves were found in day and night changes and the peak showed around13:00. Day and night variations of activities of SPS and SS+in leaves showed bimodal curves and the activities of AGPase showed typical single peak. Day and night variations of activities of SS-and Inv showed no regular law.3. Contents of starch and activities of AGPase in leaves of defruiting treatment were higher than those of retaining fruits. There was no significant difference between defruiting and retaining fruits in net photosynthetic rate, contnents of sucrose, reducing sugar, starch and activities of sucrose metabolism-related enzymes. 4. Contents of sucrose in leaves increased were related to the activities of SPS and SS+and contents of starch in leaves increased were related to the activities of AGPase.