Regulation of Sulfur Dioxide on Organic Acids Content and Malate Metabolism Pathway of Grapes in Postharvest
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Abstract:
The effects of sulfur dioxide (SO2) on the content of organic acids and the regulation of malate metabolism of ‘Munage’ grapes during postharvest storage were investigated. The changes in the contents of tartaric acid, L-malic acid, L-ascorbic acid and citric acid during fruit storage were measured by high performance liquid chromatography (HPLC), and RNA sequencing (RNA-Seq) was used to analyze the main pathways of SO2 to regulate malate metabolism. The differences in the expression of malate dehydrogenase (MDH), cytoplasmic malate dehydrogenase (cytMDH), mitochondrial malate dehydrogenase (mtMDH), lactate dehydrogenase (LDH), NADP-dependent malic enzyme (NADP-ME), pyruvate decarboxylase 1 (PDC1), pyruvate decarboxylase 2 (PDC2), and ethanol dehydrogenation enzyme dehydrogenase (ADH) genes were determined to verify further the results of RNA-Seq. The results showed that on the 60th day of storage, the contents of tartaric acid, L-ascorbic acid and citric acid in the fruits of the SO2-treatment group were 0.13 mg/g, 0.34 mg/100g, and 0.02 mg/g (which were all higher than those of the CK group), with the content of L-malic acid lower than that of the CK group by 0.64 mg/g. SO2 can maintain the contents of tartaric acid, L-malic acid, L-ascorbic acid and citric acid in ‘Munage’ grapes, through up-regulating the expressions of mtMDH, LDH, NADP-ME and PDC1, while down-regulating the expressions of MDH, cytMDH, PDC2 and ADH, to promote the decomposition of L-malic acid and preserve the flavor characteristics of the fruit. The study can provide a theoretical basis for the investigations on the regulatory role of SO2 in malate metabolism of grapes.
