Comparison of Malic Acid Metabolism between'Guozhenhao 1'and Its Parent'Dawuxing'Loquat Fruits
[Objective]The differences in organic acid metabolism between ′Dawuxing′ and its parent'Guozhenhao 1′ loquat fruits were studied,to clarify the differences in their accumulation patterns,related enzyme activities and related gene expressions,in order to provide a theoretical basis for the regulation of organic acids in the loquat production process and the cultivation of new low-acid varieties.[Method]The differences in organic acid contents and expression levels of metabolism-related genes in ′Dawux-ing′and ′Guozhenhao 1′ fruits at different developmental stages were analyzed to determine the differ-ences in organic acids.[Result]The fruits of the two loquat varieties mainly accumulated tartaric acid and succinic acid in the early stage of development,and malic acid in the late stage of development,and malic acid content increased first and then decreased with fruit development.Compared with the ′Dawux-ing′,the contents of titrable acid,organic acid and malic acid in the maturation stage of ′Guozhenhao 1′were significantly increased by 17.6%,25.2%and 35.6%,respectively.Additionally,the activity of ma-late synthetase NAD-MDH was significantly increased,while the activity of degradation enzyme NADP-ME was significantly decreased in'Guozhenhao 1'.The relative expression levels of EjPEPC,EjMDH and EjNADP-ME were significantly up-regulated compared with ′Dawuxing′ in mature ′Guozhenhao 1′fruit,while EjNADP-ME4 was significantly down-regulated.Correlation analysis showed that malic acid content was positively correlated with the activity of NAD-MDH and the expression levels of EjNAD-MDH,while significantly negatively correlated with the expression levels of EjPEPC2 and EjNADP-ME4 in both loquat varieties.[Conclusion]The high expression of EjNAD-MDH in ′Guozhenhao 1′ at the ma-turity stage led to an increase in NAD-MDH activity,while the high expression of EjNADP-ME4 in ′Dawuxing′ led to an increase in NADP-ME activity.This ultimately led to a high higher synthesis rate of malic acid and a slower degradation rate in ′Dawuxing′,ultimately resulting in a higher malic acid con-tent than ′Dawuxing′.
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