Analysis Of Fruit Quality And Acid Metabolism Mechanism Of Three Orange Cultivars From Jiangjin District, Chongqing

Citric acid, the major organic acid in citrus fruit, is produced by the tricarboxylic acid (TCA) cycle and the way of degradation included the Gamma-amino butyric acid(GABA) pathway and glutamine synthesis (GS) pathway. In this paper, three sweet orange varieties from the Jiangjin local orange, including’Changyecheng’(low-acid and small size type),’Jincheng S-26’(normal) and’Daguojincheng’(high-acid and bigger size type) cultivar, were used in this study. The changes in fruit growth indexs and fruit quality as well as the expression of the genes related to acid metabolism were analyzed during fruit development. The characteristics of fruit development, fruit quality evaluation and regulation of citric acid metabolism were discussed. These results could offer the reference for improving fruit quality in practice, and lay foundation for the molecular genetic improvement in citrus breeding. The main results were as follows:1. Results showed that the fruit development of three cultivars was in a S-trend, and reached the maximum size in late October. During fruit development, fruit shape index (longitudinal meter/transverse meter) changed a little the shape index of ’Changyecheng’orange fruit is less than 1, exhibiting round-shapes; the’JinchengS-26’ and’Daguojincheng’orange fruit have oval shape, and their shape index was greater than comparison of the three varieties indicates that the average weight of Changye’ orange fruit is 79% of’JinchengS-26’orange fruit and the average weight of ’Daguojincheng’orange fruit is 68% bigger than JinchengS-26 fruit. With fruit ripening, the average content of TSS and pH value gradually increased, and TA decreased. After fruit maturity, JinchengS-26 fruit got the highest TSS content,’Changyecheng’orange lowest TSS content and smallest fruit size, and’Da guo jincheng’orange higher TA content and biggest fruit size.2. Organic acids are normal constituents of most citrus fruit juice. The composition and content offruit juice ofthree orange varieties were analyzed byhigh efficiency liquid chromate graphy. Three kinds of the organic acid were extracted from fruit juice of the three varieties and the citric acid is the major constituent of the organic acids. During fruit development, the citric acid was decreased gradually and malic acids increased. The quinic acid was increased in the earlier stage and then decreased. At the early November, These data showed that citric acid content was 19.0% higher in ’Daguojincheng’ orange fruit and 23.8% lower in’Changyecheng’ orange than that in the ’jinchengS-26’fruit. During the fast TA decreasing period, the TA content of presented the drop significantly in the fruit of the three varieties, and the result is that the citric acid content was 15.9% higher in’Daguojincheng’ orange fruit and 37.5% lower in’Changye’ orange than that in the’JinchengS-26’fruit. This result proved that the difference in TA content between the three varieties comes mainly from the difference of ability of the organic acid synthesise during the cell division period and that of organic acid degradation during the fruit maturity.3. Total 29 genes related with citrus acid metabolism were obtained, including 3 aconitase genes, one ATP-citrate lyase gene,5 citrate synthase genes,2 citrate synthase genes,6 isocitrate dehydrogenase genes,2 glutamine synthase genes,1 citrateH+ symporter gene,1 Malate channel gene,6 V-ATPase genes,2 V-Ppase genes, from the fruit tissue during the fruit maturity. Quantitative real-time PCR results showed that the transcript level of CitACO1, CitACO4, CitIDHs, CitGADs, CitGS4, CitATP-CL and citrateH+ symporter, MCL genes in’Changyecheng’ orange significantly higher than in ’Daguojincheng’ orange, suggesting that the difference of organic acids mainly involved in the citric acid degradation, rather than its biosynthesis during the fruit maturity. The results also indicated that citric acid in orange fruit were degraded via the GABA pathway and were coordinated controlled by poly-gene.In conclusion, acid contents of three orange varieties have obvious differences, and the organ acid content of’Daguojincheng’ orange fruit is the highest and that of ’Changyecheng’orange is the lowest. The difference of organic acids content in the three orange cultivars were mainly lie on the citric acid degradation rate, but the biosynthesis rate. The citric acid content significant effect on the total organic acids concentration in orange fruit, though the mechanisms varied for both cases. It indicated that GS and GABA degradation pathway of citric acid involved in the difference of citric acid levels in the three sweet orange varieties. The citric acid degradation were coordinated controlled by poly-gene and different mechanisms in the orange fruit.