Analysis On Activities Of Sugar-metabolization Related Enzymes And Its Gene Expressions During Fruit Ripening Of Jackfruit

Sugar contents are important factors determining fruit quality, and the metabolism of sugar in fruit is extremely complex, controlled by a variety of enzymes. In order to understand the sugar metabolizing processes and key enzymes involved during fruit ripening of jackfruit, fruits from genotypes of hard flesh jackfruit(12E、13D、13K、148-4) and soft flesh jackfruit(12As、12Cs、13Bs、13Ls) were used as materials, contents of soluble sugars and activities of sugar-metabolism related enzymes were determined during fruit ripening, and also expression levels of the genes were analyzed. Main results obtained as followings:1. Soluble sugar. during fruit ripening of soft and hard flesh jackfruit, sucrose was the main conmoponent of total soluble sugars, followed by fructose and glucose. Contents of soluble sugar and sucrose differed among genotypes. Contents of four kinds of soluble sugars increased constantly during fruit ripening, with the exception of the soft flesh jackfruit 12 Cs and the hard flesh jackfruit 13 K, which showed slight decreases in contents of 4 kinds of soluble sugar at the ripening stage IV. The ratio fructose versus glucose content was low in unripe fruit, but close to 1 after fruit was fully ripe.2. Acid invertase. changes in activities of AI were significant different between genotypes of soft and hard flesh jackfruit. In hard flesh jackfruits, the activities of AI were relatively constant at low levels during fruit ripening, while in soft flesh jackfruits, the activities of AI increased rapidly at different stages of fruit maturity, and especially showed a significant positive correlation to contents of glucose and fructose in fruits of 12 Cs and 13Bs; expression analysis of one acid invertase gene during fruit ripening of jackfruit revealed that, expression of Ah AI 1 gene was low, and may have little effects on sugar accumulation in fruit of jackfruit.3. Neutral invertase. activities of NI changed little during fruit ripening of jackfruit, and no difference revealed between genotypes of soft and hard flesh jackfruit. No significant correlation was detected between enzyme activities and contents of soluble sugars, therefore neutral invertase may not be the key enzyme determining contents of sugars in fruits of jackfruit. Four genes of neutral invertase were analyzed and results indicated that, expression level of Ah NI 1 gene was the highest among NI genes investigated during fruit ripening; expression of Ah NI 1 gene and Ah NI 2 gene showed similar changing patterns, with the high expression appeared in immature fruit for most genotypes; however, the peak of expression of Ah NI 3 and Ah NI 4 gene were found in fully ripe fruit, indicating that activity of NI during fruit ripening of jackfruit may be controlled by all of these four gene.4. Sucrose synthase. activities of SS-c changed little during fruit ripening, and maintained high levels in immature fruit of most genotypes. However, activities of SS-s were relatively stable at a low level during fruit ripening, indicated that, SS might play more important role in sucrose synthesis than sucrose hydrolysis. Expressions of 3 sucrose synthase genes were analyzed in this study, results indicated that, changes in expressions of these 3 genes during fruit ripening were similar, and the expression level of Ah SS 1 gene was the highest among them. The expression levels of these genes were high in immature fruits, which were similar to the changing patterns of enzyme activity, indicating that, sugar metabolism in fruit of jackfruit might be controlled by all these three genes.5. Sucrose phosphate synthase. during fruit ripening of jackfruit, correlation coefficients between sucrose contents and activities of SPS were higher than that between sucrose contents and activities of SS-s, but it was only significant in 13 D. Expressions of four sucrose phosphate synthase genes were investigated in this study, results showed that, the expression levels of Ah SPS 1 gene were the highest among these four genes; changes in expression levels of Ah SPS 1 gene was similar to that of Ah SPS 2 gene, both showed low expression level in immature fruit; changes in expression levels of Ah SPS 3 gene was similar to that of Ah SPS 4 gene, both showed high expression level in immature fruit.6. Amylase. expressions of one ɑ-AMY gene and 4 β-AMY genes during fruit ripening of jackfruit were investigated in this study, results showed that, expression levels of Ah AMYɑ 1 gene increased during fruit ripening, indicating a more important role in hydrolysis of starch; expression levels of Ah AMYb 6 gene was significantly higher than that of three AMYb gene, and the changing patterns of Ah AMYb 6 gene was similar to Ah AMYɑ 1 gene, but different from three other AMYb gene, indicated that Ah AMYb 6 gene and Ah AMYɑ 1 gene might be associated with the process of sugar metabolizing during fruit ripening of jackfruit.