Studies On Changes Of Sugar Accumulation And Related Enzymes Activities In Sand Pear Fruits And Leaves

With the improving of living standard and abundance of various fruits supply, there is a larger demand for higher quality fruits. So improving the quality of fruits is in the direction of cultivation and breeding. Sugar content is one of the important index of fruit quality. Among the sugar content in sand pear fruits, the sucrose content is closely related to the fruit quality. Most of the fine varieties fruits have high sucrose content. But some poor varieties fruits have low sucrose content. So studying the impact factors of high and low sucrose content is particularly important. Starting with the most important index of sugar accumulation that determined by the metabolizing enzymes, try to explore the key enzymes that sugar accumulation in different sand pear fruits from the different sucrose contents. And provide a basis for selecting the new varieties. In order to explore the roles of sugar accumulation and its metabolizing enzymes in sand pear fruits and leaves. Six kinds of sand pear fruits and two of their leaves were used. Three of them are high sucrose-accumulating cultivars, which are named 'Shinyu', 'Shinseiki' and 'Akaho' respectively. And the other are low sucrose-accumulating cultivars. which are named 'ba dong jing li', 'ba yue xue'and 'huang mi' respectively. Leaves of 'Shinseiki' and 'ba dong jing li' were used. The main findings are as follows:1. Dynamic changes of sugar contents in sand pear fruits(1) Sucrose: In the early stage of the fruit growth, the sucrose contents of two categories sand pear fruits were both little. There was no difference of sucrose contents in the two categories sand pear fruits. The difference of sucrose accumulation time between the two categories sand pear fruits was not significant. The sucrose started to accumulate from 105 days after anthesis. And the sucrose content reached the highest point at 135 days after anthesis in high sucrose-accumulating sand pear fruits. Then the sucrose content slowly declined in ripe fruit. Sucrose accumulated slowly throught fruit development in low sucrose-accumulating sand pear fruits.(2) Glucose: Glucose content was higher than sucrose content in the two categories sand pear fruits. Glucose started to accumulate from 60 days after anthesis in high sucrose-accumulating sand pear fruits. The glucose content reached the highest point at 105 days after anthesis in high sucrose-accumulating sand pear fruits. Then glucose content declined and the lowest point presented at 135 days after anthesis. Glucose accumulated slowly in the early stage of fruit development and started to accumulate from 90 days after anthesis in the low sucrose-accumulating sand pear fruits. (3) Fructose: The fructose started to accumulate in the early stage of the fruit growth in the high sucrose-accumulating sand pear fruits. And the highest point of fructose content presented at 105 days after anthesis. Then fructose content declined and the lowest point presented at 135 days after anthesis. Fructose accumulated quckily throughout the fruit development stage in low sucrose-accumulating sand pear fruits.(4) Total sugar: total sugar increased throughout the fruit development stage in the two categories sand pear fruits. The difference of total sugar content between the two categories sand pear fruits was not significant.2. Dynamic change of sugar metabolizing enzymes activities in sand pear fruits(1) Invertase: The activity of VIN and NIN decreased throughout the fruit development stage in the two categories sand pear fruits. And the activity of VIN and NIN maintained at a certain level in the late stage of fruit development. The difference of VIN and NIN activity between the two categories sand pear fruits was not significant. The activity of VIN and NIN had negative correlation with sucrose content.(2) SPS and SS: The activity of SPS and SS had positive correlation with sucrose content in high sucrose-accumulating sand pear fruits. No significant correlation was found between the activity of SPS and SS with sucrose content in high sucrose-accumulating sand pear fruits. And the activity of SPS and SS did not significantly change in the late stage of the fruit development in low sucrose-accumulating sand pear fruits. Also sucrose accumulated slowly throughout fruit development in the low sucrose-accumulating sand pear fruits.3. Dynamic changes of sugar contents in sand pear leaves(1) Sucrose: sucrose content in the two categories sand pear fruits decreased gradually with the development of fruit. The sucrose content of 'Shinseiki' was higher than 'ba dong jing li'. The same phenomenon was also presented in fruits.(2) Fructose and Glucose: Fructose and glucose contents in the two categories sand pear fruits increased slowly with the development of fruit. Then fructose declined slowly in the ripe fruit.4. Dynamic change of sugar metabolizing enzymes activities in sand pear leaves(1) SPS and SS: The activity of SPS and SS increased with the development of fruit in 'Shinseiki'. But the activity of SPS and SS in 'ba dong jing li' declined slowly in the ripe fruit. The activity of SPS and SS positively correlated with sucrose content in the two sand pear leaves. The activity of SPS and SS in 'ba dong jing li' was higher than 'Shinseiki'.(2) VIN and NIN: The activity of VIN and NIN in the two sand pear leaves increased gradually with the development of fruit. The correlation coefficient between VIN and NIN activity and sucrose was higher than SPS and SS.