Study On The Changes Of Main Organic Acid Content And Acidmetabolism During The Development Of Jujube Fruits

By using the method of high performance liquid chromatography(HPLC),the components and content of organic acids in fruit of Junzao and Sour jujube were determined.In the meantime,the activities of organic acid-metabolizing enzymes,such as malate dehydrogenase(NAD-MDH),malic enzyme(NADP-ME),enol phosphate type pyruvate carboxylase(PEPC),citrate synthase(CS),were analyzed during the development of Junzao and Sour jujube fruit.The results showed that:(1)A high performance liquid chromatographic(HPLC)ZjMethod was established and validated for the fast simultaneous determination of organic acids and vitamin C(Vc)in jujube fruits.The coefficientsof determination(R2)of the standard calibration curves of the analyzed compounds were all above 0.998 9and the precisionexpressed as relative standard deviations were between 0.98% and 4.77%(n = 5)and the repeatability RSDs were in therange of 0.88% to 2.19%(n = 5).The mean recovery rates of seven organic acids and vitamin C were in the range of 91.35% to 105.74%.We got the results that malic acid、citric acid and tartaric acid were the main acids,especially the malic acid(19.21 mg·g-1)was account for 89.76 %,in jujube fruits.Except tartaric acid,the content of both malic acid and citric acid were increased during the early stages of jujube fruits development and decreased at the later stages.(2)The activities of NAD-MDH and CS had the same trend,that was increased during the early stages of jujube fruits development and decreased at the later stages,with malic acid and citric acid concentration during the development of jujube fruits.However,the change of NADP-ME activity was on the contrary.Correlation analyses showed that there was a positive correlation between the contents of malic acid and the activities of NAD-MDH,but the correlation between the contents of malic acid and the activities of NADP-ME was negative.The activities of CS showed a significant positive correlation which the correlation coefficient could reach 0.9260 with the contents of citric acid,while there was no same correlation between the activities of PEPC and the contents of malic acid and citric acid.Therefore,this research assumed that NAD-MDH、NADP-ME and CS activities might play significant roles in organicacids biosynthesis and degradation,but the role of PEPC activity was small.(3)The relative transcript of ZjCS showed the same trend with the citric acid,that was increased during the early stages of jujube fruits development and decreased at the later stages,during the development of jujube fruits.Therefore,the accumulation of citric acid was mainly regulated by ZjCS gene.Nevertheless the expression pattern of ZjMdh 、 ZjPEPC and ZjMe genes was not consistent in the jujube fruit,the accumulation of malic acid was mainly catalyzed by NAD-MDH enzyme and controlled by ZjMdh gene.ZjPEPC gene and ZjMe gene played an important role on the malic acid metabolism in Sour jujube.However,the expression patterns of ZjMdh、ZjPEPC and ZjMe genes were significantly different from those patterns of the metabolizing enzymes in Junzao fruit.