Preliminary Research On Mechanism Of Sugar Metabolism In Root Of Sugar Metabolism In Root Of Sugar Beet(Beta Vulgaris L.)

The studies on the activities of Nitrate Reductase(NR), Invertase(Inv), Sucrose Synthetase(SS), Sucrose Phosphorus Synthetase(SPS) were conducted in both root and leaf blade of sugar beet of cultivar Tian Yan-7 under four kinds of nitrogen levels, i.e. commensurate with 0, 60,120 and 180kg N/bin2 of which were set two sorts of nitrogen forms: ammonium nitrogen and nitrate nitrogen. The pit culture was adopted in sugar beet planting and the measurement and determination were synchronously carried out during the whole period of sugar beet growth in 1999. The main objectives of this experiment were to preliminarily understand the mechanism of sugar metabolism and accumulation in the root of sugar beet by measuring and analyzing the activities of mainly related enzymes. Determine the roles of these enzymes and to analyze the dynamic changes of dry matter accumulation, root yield, sugar content and sugar production under different forms of nitrogen. The result could be drawn as follows: The activities of enzymes related to sugar and nitrogen metabolism demonstrated significant correlation, which varied at different stages, under four different nitrogen levels. Two forms of nitrogen also took different effects on the EA, root tuber production and sugar content. During the whole period of sugar beet growth, the activities of NR, SPS and 55 in leaf blade varied in coordination with the change trends similar to each other. The decomposition and synthesis activi6es emerged as almost opposite, showing a kind of self-regulation. The mechanism of nteraction of carbon and nitrogen, regulation in common?was reflected through their performance. Differences of the influences of the two forms of nitrogen on the studied enzymes were produced. Nitrate nitrogen can stimulate the growth of stems and leaves as well as the whole biological mass better than ainmonium nitrogen, by improving the key enzymes of carbon assimilation. Compared to ammonium nitrogen, nitrate nitrogen can increase the decomposition activities of SS even more, but inhibit its synthesis activities to some degree. Likewise, the dry matter accumulation at different growth stage, sugar content and root tuber production at harvest time all illustrated as follows: nitrate nitrogen increased the biological mass, but reduced the sugar content; aninionium nitrogen performed otherwise, good for the sugar content, but against the biological mass. As to the key enzyme regulating sugar in rootS, the change trend of its synthesis activities came to its only peak at the end of August and the beginning of September, decomposition activities at the middle stage of August. The top part of root tuber play an important role in regulating the assimilated matter, which was accomplished mainly by SS. The activities of SPS in root were generally lower than that of SS, but basically coincided with the sugar content distributed in the root, i.e. lower part>middle part>top part, and they took on an increasing trend. The neutral mv activities were high at early stage, then kept very low during the middle stage, rebounded a lit the late stage, which were allocated in root as: top part>middle part>lower part. The sugar metabolism in root is a relatively independent procedure to the upper part above ground, which was involved in the physiological structure and many other factors. However, to trace the newly absorbed carbon in beet body, along with determining those related enzymes would prove to be a working way in probing this problem thoroughly.