Abstract: Tomato leaf ( source organ) , transport system and fruit ( sink organ) were separated along tomato assimilate transport path in order to determinate the composition and content of carbohydrate and sucrosemetabolizing enzymes activities. The results indicated that carbohydrate composition and content and the activities of sucrose2metabolizing enzymes were different at different parts along the transport route from source to sink. Fructose contentwas the highest, whereas sucrose contentwas the lowest in mesophyll tissues. Glucose and fructose were the p redominant sugars in the midrib of leaf. Glucose was the highest and fructose the lowest in contents in the petiole vascular bundle, with sucrose standing in the medium. Sucrose was the main sugar in the internode and peduncle vascular bundle. In the fruit vascular and other parts of the fruit, glucose and fructose, rep resenting the p redominant sugar were nearly equal in amount, with sucrose being p resent in trace quantities. However, glucose was the highestwhile sucrose the lowest in contents in sepals. These three kinds of sugarwere almost equal in amount in the fruit pedicle. Invertase activity was retained at very lower level in mesophyll and transport tissues. In contrast, in the nonvascular tissues of the sink organ invertase showed higher activity. Among all tissues the activity of sucrose synthase ( SS) was the highest in the fruit pedicle and the lowest in the parts of fruits, with mesophyll and transport tissues standing in the medium. Sucrose phosphate synthase ( SPS) activity was higher in the mesophyll, the organ of sucrose synthesis, than in transport tissues, except in peduncle and fruit vascular bundles, which favor sucrose synthesis. SPS activity was the lowest at other parts of the fruit.

Key words: Tomato ( Lycopersicon esculentum Mill. ), Assimilate transport route, Carbohydrate, Sucrose-metabolizing enzymes