Sugar Metabolism And Related Enzyme During The Furity Development Of Qingzhhong Loquat Cultivar

The quality of sweet melon is mainly determined by sugar contents because it affects the tastes and color of fruit and serves as a precursor as well for synthesis of organic acid vitamin and carrotenoids. Therefore, it is very imperative to study the mechanism of sugar metabolism for the ultimate goal of improving the quality of fruit.Sugar accumulation and the activity of sucrose metabolism related enzyme during fruit development process were investigated in the fruit of loquat cultivars 'Qingzhong','Bahong' and 'Jidanbai'. The effect of pharmacy and bagging treatments on sugar accumulation, sucrose metabolism related enzyme and sorbitol metabolism related enzyme activities of the fruit in loquat cultivar 'Qingzhong' was analysed and the cDNA fragment of sucrose phosphate synthase gene was isolated and expression pattern was determined. The results are as follows:1. Before May 3rd three loquat cultivars, sucrose, glucose and fructose were slowly accumulated, but accumulated quickly and there was a clear turning point, after May 23rd accumulated slowly. During the fruit development of three loquat cultivars, the changes of the activity of neutral invertase (NI), acid invertase (AI), sucrose synthase (SS) and sucrose phosphate synthase (SPS) were accordance with the accumulation of three sugars. The activity of AI and NI were lower and no obvious changed before May 3rd, but the rapid increase occurred. And the activity of SS and SPS were low and almost unchanged before May 3rd, but the activity of the cultivar 'Jidanbai' increased rapidly, then rised slowly. The activities of the cultivars 'Qingzhong' and 'Bahong' increased with the maturity of the fruit, but below the activity of the 'Jidanbai'.2. The accumulation of fructose and glucose increased significantly with ethychlozate 200 mg·L-among seven treatments. The content of sorbitol decreased first and then increased during the fruit development. The activities of SS and SPS decreased significantly with ethychlozate 100 mg·L-1 after May 21st, and the activity of sucrose-metabolizing enzyme increased under other six treatments; the activity of sorbitol-metabolizing enzyme declined generally.3. The average fruit weight decreased in the bagged fruit; the contents of sucrose, glucose and soluble solids increased; and the contents of fructose, sorbitol and titratable acidity decreased. In addition, the activities of AI and NI in the bagged fruit were lower than for the non-bagged fruit, and the activities of SS and SPS in the bagged fruit were higher than in the non-bagged fruit, but the activities of sorbitol dehydrogenase (SDH) and sorbitol oxidase (SOX) were higher in the bagged fruit at the beginning of fruit development and then lower than non-bagged fruit during fruit development. The activities of SDH and SOX in the bagged fruit were lower than in the non-bagged fruit but there was no significant difference and the activities of SS and SPS in the bagged fruit were higher than in the non-bagged fruit and there was a significant difference.4. SPS1 (386 bp) and SPS2 (383 bp) cDNA encoding SPS gene fragment were isolated from fruit of loquat by the method of RT-PCR. Sequencing analysis showed that 91% identity in nucleotide sequence in the fruit of loquat and peach was observed. The method of half ration RT-PCR showed that the expression of SPS gene was gradually increased with the development of Qingzhong fruit.