The Analysis Of Metabolic Differences On Yanxiwanlu And Changtailugan And Effects Of Abscisic Acid On Ponkan Fruit Ripening

Even though the yield and acreage of the citrus industry in our country rank the first in the world, the competitiveness remains to be improved. Citrus fresh fruit is not able to achieve the annual supply in our country, which mainly results from the irrational citrus variety and maturity structure. Hence, it is of great significance to perfect the industry that we strengthen our understanding of the citrus fruit ripening process, regulate fruit ripening by means of cultivation and physiology and research the ripening molecular mechanism. In this study, the metabolic differences between ‘Changtailugan’ and its late ripening mutant ‘Yanxiwanlu’ were analyzed, and the effects of exogenous ABA and NDGA in the fruits of ‘E-gan No.1’ ponkan were investigated from physiological and molecular levels. The main results are as follows:1. The physiological qualities including soluble sugars, organic acids, carotenoids, lignin and ABA content in ‘Changtailugan’(WT) and ‘Yanxiwanlu’(MT) fruits at six ripening stages were measured. Sucrose content and TSS/TOA were much lower in MT than in WT; however, the content of citric acid, quininic acid and TOA were converse. MA/TOA is another important indicator of citrus fruit ripening; during the ripening process, MA/TOA decreased continuously in WT fruit, but kept relatively stable in MT fruit. The rise of malic acid in WT fruit pulp negatively affected the accumulation of fructose and glucose in the late ripening stages. The composition and content of carotenoids vary from citrus fruit tissues. Violaxanthin was the major carotenoid in the fruit peel of WT and MT; during the process of fruit ripening, the content of neoxanthin, violaxanthin and β-crytoxanthin were on the rise, and the content of these carotenoids in WT were apparently higher than MT; however, the content of α-carotene and β-carotene held decline trends, and kept a lower level in WT fruit peel. The content of seven carotenoids all increased with fruit ripening in WT and MT fruit pulp, and were significantly higher in WT fruit pulp than in MT. There existed two peaks of ABA accumulation in WT and MT fruit pulp at the beginning of fruit coloring and prior to full ripening; the content of ABA was significantly higher in WT than in MT at 180- 225 DAF. The content of lignin in MT fruit pulp kept higher than WT at the first three ripening stages, but remained no difference after that.2. Four gradients of ABA and NDGA concentration were set to dip the ponkan fruits, then the content of endogenous ABA and the expression level of CsNCED1 gene were analyzed; results showed that the lowest ABA and NDGA concentration which works for citrus is 500 μM, and the treatment should repeat every week to ensure the efficacy. The effects of exogenous ABA and NDGA on the color index H value and the content of soluble sugars, organic acids and endogenous hormones in the fruits of ‘E-gan No.1’ were examined and the expression profiles of genes involved in the ABA, sugar and organic acid metabolism and signal transduction pathway in fruits were also investigated. The results indicated that, 1) exogenous ABA could accelerate fruit coloring, significantly decrease the organic acid content, and up-regulate the transcript levels of CsACO1 and CsNADP-IDH which are involved in the degradation of organic acids, thus positively affected the ripening of citrus fruit, while treatment with NDGA could restrain fruit coloring and acid degradation; 2) A coordinate interaction was found between the ABA signaling pathway and sucrose signaling pathway to regulate citrus fruit ripening. Especially, Cs SUC 3 played a vital role in accumulation of sugars during the last ripening stage of citrus fruit, which could be induced by ABA treatment; 3) ABA could restrict its own accumulation at 14 DAY not only by inducing the expression of ABA 8’-hydroxylase 1 but also by reducing the expression of Cs NCED1.