| Applying 9 to 12-year old Roberson navel orange trees (Citrus sinensis Osbeck) grafted on Citrus tangerina as testing materials, using the methods of combining field biological and ecological investigation and indoor analysis, the activity changes of enzymes related to sugar metabolism during fruit growth and their relationships with the sugar accumulation, the comparisons of enzymes related to sugar metabolism in different habitats, the effects of ecological factors on enzymes related to sugar metabolism were studied, the result showed:1. Sugar in navel orange fruit began to accumulate at the stage of fruit inflation. During the mid- and late stages of fruit inflation, the content of reducing sugar increased faster than that of sucrose, which led to the content of reducing sugar higher than that of sucrose in the ripe fruit. The activity of sucrose phosphate synthase (SPS) was very low in the young fruit, and it increased gradually with fruit development and reached to the maximum at 150 days after anthesis, and then it declined rapidly, keeping at a lower level. The activity of sucrose synthase (SS) that included synthetic direction and cleavage direction was high at initial stage of fruit development, decreasing rapidly with fruit development. The activity of SS (synthetic direction) began to rise again at 150 days after anthesis, reaching to maximum at 195 days after anthesis, and then decreased rapidly. The activity of SS (cleavage direction) rose again from 105 days after anthesis to 150 days after anthesis, and then reaching to minimum at 165 days after anthesis, after which it rose again until 195 days after anthesis. The variance curve of activity of SS (synthetic direction) conformed with that of SS (cleavage direction), and they had a significant positive correlation coefficient.2. At the mid- and late stage of inflation, SS (synthetic direction) activity rose again immediately while SPS activity decreasing rapidly. And when the activities of SPS and SS (synthetic direction) increased gradually, that of SS (cleavage direction) rose againcorrespondently, having no invertase when sugar accumulating, SS (cleavage direction) became a key enzyme to regulate sucrose content, which adjusted fruit sink strength. So, it was comprehensive effects that related enzymes were involved in the sucrose metabolism during Robertson navel orange development.3. Before 150 days after anthesis, the variance curve of activity of SPS conformed with that of sugar content, and they had a significant positive correlation coefficient, which proved that SPS was a key enzyme of sugar accumulation in early and mid- stage of fruit inflation. And after 150 days after anthesis, the variance curve of activity of SS (synthetic direction) conformed to that of sugar content, and they also had a significant positive correlation coefficient, which proved that SS (synthetic direction) was a key enzyme of sugar accumulation in late stage of fruit development. SS (cleavage direction) was important to fruit sugar accumulation because it influenced fruit sink strength though regulating sucrose content in fruit.4. In different habitats, sugar content of Robertson navel orange showed much difference each other. But for the related enzymes, in every habitat, SPS and SS (cleavage direction) showed no changes in activity and SS (synthetic direction) had a significant difference in activity, which indicated that the differences of sugar content in different habitats resulted from activities of SS (synthetic direction) changing in every habitat.5. Though the gray system analysis of 16 ecological factors to the fruit sugar content, the results showed that the factors which influenced the sugar content were more seriously were temperature and sunshine. The sugar content of fruit was high in the eco-type habitat that had higher temperature and enough sunshine and quantity of heat. So, for the sugar content, temperature and sunshine were main ecological factors. Thus, they became the key indexes for navel orange ecological di...
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