Study On Organic Acid Metabolism Of Majiayou And Taoxi Pomelo Fruits

Citrus fruits are fruits with citric acid as the main organic acid.Previous studies on citrus fruit organic acid metabolism showed that fruit quality and flavor were mainly affected by organic acids.Majia pomelo is a local characteristic variety of Jiangxi Province,and it is also a pomelo variety independent of the Wendan pomelo and Shatian pomelo varieties.Taoxi pomelo is a new type of Jiangxi early-maturing sweet pomelo.All of them have become Jiangxi’s characteristic business cards because of their unique taste and flavor.However,there are few studies on organic acid metabolism in fruits of Majia pomelo and Taoxi pomelo.This article studies the changes in the content of organic acid components and related genes during fruit development and storage.Preliminary study on the regulation mechanism affecting the change of citric acid content,and providing a theoretical basis for the improvement of fruit quality and storage quality of Majia pomelo and Taoxi pomelo.The findings are as follows:(1)Analysis of changes in organic acid content and expression of related genes during fruit development of Majia pomelo and Taoxi pomelo: Citric acid is the main organic acid in Majia pomelo and Taoxi pomelo.The change trend of citric acid and total acid content in Majia pomelo fruit is generally consistent,and can be divided into slow growth period(before 120 d after flowering),rapid growth period(120 d-195 d after flowering),and falling period(after flowering 195 d-210 d);the trend of citric acid content in Taoxi pomelo fruit is generally slow growth(before 90 d after flowering),rapid growth(90 d-105 d after flowering),stable period(after 105 d after flowering).The rapid accumulation of citric acid during fruit development of Majia pomelo was mainly related to the CS2 and VHA-c4 genes,while the decrease in citric acid content 15 days before harvest was mainly related to the Aco3,GAD5 and GABA genes in the GABA degradation pathway.Protein gene DIC plays an important role in citric acid metabolism during the development of Majia pomelo fruit.During the fruit development process of Taoxi pomelo,PEPC2 and CS1 genes jointly participated in the accumulation of citric acid in fruits,and the down-regulated expression of CHX genes during the rapid rise of citric acid promoted the rapid accumulation of citric acid.Then the up-regulated expression of degradation genes(ACL3,Aco3,NAD-IDH2/3,GS2 and GAD5)and transporter genes(CHX and DIC)and the down-regulated expression of VHP2 slowed down the accumulation of citric acid in the fruit and stabilized the citric acid content.(2)Measurement and analysis of the sugar-acid content,and sugar-acid ratio of Majia pomelo,Shatian pomelo,Jinsha pomelo,and Taoxi pomelo during storage indicate that the main organic acids of the four types of pomelo fruits are citric acid,followed by malic acid,tartaric acid and quinic acid are low,and the trends of total acid and citric acid are basically consistent.The citric acid content of Shatian pomelo and Jinsha pomelo fruit did not increase significantly compared to 0 d during storage,while the citric acid content of Majia pomelo and Taoxi honey pomelo fruit increased significantly during the early storage period.Sucrose was highest in the 4 types of pomelo fruit,followed by glucose and fructose.Analysis of sugar-acid ratio shows that the overall sugar-acid ratio of Shatian pomelo fruit does not change much during storage.The sugar-acid ratio of Jinsha pomelo fruit was significantly lower than that at 0 d after storage for 40 d.However,the fruit of Majia pomelo and Taoxi pomelo are significantly different from Shatian pomelo and Jinsha pomelo.The fruit showed obvious acid reversion in the early period of storage(0 d-60 d).Since the storage of Taoxi pomelo,the sugar-acid ratio level has been lower than before storage,and the fruit has returned to acid throughout the storage period,which is different from Majiayou.(3)Analysis of changes in organic acid content and related gene expression during the storage of Majia pomelo and Taoxi fruits:The citric acid content of Majiayou and Taoxi honey pomelo increased significantly at the beginning of storage,and reached a peak at 40 days after storage.The up-regulated expression of the synthetic genes PEPC1 / 2 and CS1 /2 and the transport genes VHA-c4 and VHP2 of Majiayou fruit,and the down-regulated expression of the degradation genes GS2,GAD5 and the transport gene DIC caused their citric acid content to increase significantly.The increase in citric acid in Taoxi honey pomelo was mainly It is related to the synthesis-related PEPC1 / 2 and CS1,the degradation gene GAD5,and the transporter genes CHX,VHA-c4,and VHP2.