| 14C-tracing, tissue anatomical and modern analysis-testing techniques were employed in this study to investigate the change of sucrose, that is the translocation form of tomato assimilates, and the tune needed to transport them to the sink organ along the transport path. Sugar composition and content and the activities of four sucrose-metabolizing enzymes were measured systematically for the first time at different sites along the assimilate transport path from source to sink. It was clear that sugar composition and content, and the time and spatial expressions of activities of various sucrose-metabolizing enzymes were different during tomato fruit development. The sucrose-metabolizing key enzymes were identified in tomato cultivar (L esculen turn Mill .).Effects of cultural measures, such as deficit irrigation, foliage application and different nitrogen and potassium treatments of soil on photosynthesis, yield, quality, dry matter distribution and sucrose metabolism were studied and the feasibility of regulation of sucrose metabolism was discussed. The main results are as follows.1. 14C tracing test indicated that almost all photosynthates resulting from Ih of photosynthesis could be transported out of the leaf within 72h and more than 85% of them were exported within 24h after the start of photosynthesis. Assimilates were detected in small quantities entering the fruit through the internode and pedicel vascular bundles 2h after photosynthesis. Only the radio activity of sucrose but not that of glucose and fructose was detected, suggesting that some of the sucrose in the fruit came directly through the phloem at the early stage of fruit development, not through the synthesis of glucose and fructose. The greatest amount of sucrose transport occurred in the internode pedicel vascular bundle 8h after the start of photosynthesis.2. It was found that sugar composition and content and the activities of sucrose-metabolizing enzymes at different parts along the transport route from source to sink were different. Fructose content was the highest, whereas sucrose content was the lowest in mesophyll tissues. Glucose and fructose were the predominant sugars in the midrib of the leaf. Glucose had the highest and fructose the lowest content in the petiole vascular bundle, with sucrose standing in between. 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,representing the predominant sugar were nearly equal in amount, with sucrose being present i trace quantities. Among the three, glucose had the highest while sucrose the lowest content in sepals. These three kinds of sugar were almost equal hi amount hi the fruit pedicle.3. Invertase was inactive hi mesophyll and transport tissues. In contrast, sucrose synthase (SS) was quite active hi these parts. In the nonvascular tissues of the sink organ (fruit) invertase showed greater activity than SS. Among all tissues the activity of SS was highest hi the fruit pedicle. Sucrose phosphate synthase (SPS) activity was higher in the mesophyll, the organ of sucrose synthesis, than hi transport tissues, except peduncle and fruit vascular bundles, which favor sucrose synthesis. SPS activity at other parts of the fruit was the lowest.4. A negative correlation was found between glucose and fructose contents and SS activity during fruit development. The correlation coefficients were -0.9497*and -0.9598** (r(o.o5,3)=0.8783,r(o.oi,3)=0.9587) respectively. A positive correlation was found between invertase activity and glucose and fructose contents, but there was a significant negative correlation between the former and the sucrose content. The correlation coefficients were -0.9706**and -0.9669**(r(o.oi,3)=0.9587), respectively. There was a significant positive correlation between sucrose accumulation and SS activity, with the correlation coefficient was 0.8886* (r(o.o5,3)=0.8783) . hi the whole course of fruit development, no significant correlation existed between the contents of three...
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