Studies On Dynamic Changes Of Organic Acid Contents And Metabolizing Enzyme Activities In Sand Pear Fruit

Organic acids are the major facters in fruit affecting the quality of fruit.The studies previously showed that malate acid and citrate acid were the main organic acids in mature sand pear.Some breeds had more malate acid than citrate acid,and others had more citrate acid than malate acid.But no explanation has done to declare the difference.In this study,the contents of malate acid and citrate acid and their relative enzyme activities in six typical breeds of sand pear were assayed,the relationship between the two organic acids and their correlated enzyme activities were analysed to discuss the reason for the difference of composition and content in different sand pears and the impacts which correlated enzyme activities have on organic acids.The results are as followed:1.Dynamic change of malate acid in different sand pearsThe change of malate acid content shows a parabola-like rise-and-fall motif. The significant difference among different varieties lie in different speed when it rises and falls.Er Gongbai and Geng Touqing which have more malate acid fall quite slowly after they arrived their highest value,but Zhen Yu and Yan Dang Snow Pear fall much more quickly.2.Dynamic change of citrate acid in different sand pearsThere are many differences in the change of citrate acid content among different sand pears which also have different speed when it rises and falls.Zhen Yu has low citrate acid content,and the citrate acid content rises and falls slowly.Citrate acid content begins to rise quickly from eight weeks after anthesis,and rises at 13 times to eighteen weeks inYan Dang Snow Pear which has high citrate acid content.At the same stage,Geng Touqing rises at 1.8 times.3.Dynamic change of correlated enzyme activities of malate acidThe change of NAD-MDH activity has the same trend as the change of malate acid.The breed which has more malate acid has higher NAD-MDH activity.It has a big correlation with malate acid content during the development of sand pears.The biggest correlation cofficient 0.8964^**.At early stage of fruit growth,the activity of NADP-ME is low.Hardly when malate acid content start to fall,the activity of NADP-ME begun to rise quickly.It falls just before the mature.The breed which has lower malate acid content has higher NADP-ME activity.At late stage the correlation between them was from -0.9314^* to-0.8284.There is almost no consistence between PEPC activity and malate acid content, and the correlation is not notable.4.Dynamic change of correlated enzyme activities of citrate acidThe change of CS activity has the same trend as the change of citrate acid. When the fruit are mature,the breeds which have more citrate acid have higher CS activity.The correlation coefficient higher than 0.8284^** show a notable correlation between citrate acid and CS activity during fruit deveopments.The change of PEPC activity has simillar trend to the change of citrate acid.When the fruit are mature,the breeds which have more citrate acid have higher PEPC activity.The correlation coefficient is at the late stage is from 0.7056 to 0.9484^*.Cyt-ACO and Mit-ACO activity have no correlation with the change of citrate acid content,but same in different breeds.The change of NAD-IDH activity is different in breeds.There is no significant count between NAD-IDH activity and citrate acid content.