Organic acid is an important indicator of fruit quality, and malate is the predominant organic acid in apple fruit. However, the regulation of malate metabolism in postharvest fruit is rarely reported. Here, we found that, compared with a control treatment, a 10 mM γ-aminobutyric acid (GABA) treatment remarkably delayed the loss of tiftratable acidity and malate and increased the succinate and oxalate contents in “Cripps Pink” fruit stored in polyethylene bags at room temperature. The higher malate levels in GABA-treated fruit were accompanied by higher activities of cytosolic nicotinamide adenine dinucleotide-dependent malate dehydrogenase (cyNAD-MDH) and phosphoenolpyruvate carboxylase (PEPC) but lower cytosolic NAD phosphate-dependent malic enzyme (cyNADP-ME) and phosphoenolpyruvate carboxykinase (PEPCK) activities than those seen in control fruit. Notably, ethylene production was significantly reduced by GABA treatment, paralleling the downregulation of MdACS, MdACO, and MdERF expression. Meanwhile, GABA treatment also enhanced the activity of the GABA shunt and promoted the accumulation of GABA. This study provides new insights into the regulation of malate metabolism and reports for the first time the possible interplay between GABA and ethylene signaling pathways in apple fruit during postharvest storage.

中文翻译：

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外源γ-氨基丁酸处理有助于苹果果实在贮藏过程中苹果酸代谢和乙烯合成的调节

有机酸是水果品质的重要指标，苹果酸是苹果果实中的主要有机酸。然而，很少有关于收获后果实中苹果酸代谢的调控的报道。在这里，我们发现，与对照处理相比，10 mMγ-氨基丁酸（GABA）处理显着延迟了可tiftratable酸和苹果酸的损失，并增加了储存在聚乙烯袋中的“ Cripps Pink”水果中琥珀酸酯和草酸的含量。室内温度。GABA处理的水果中苹果酸水平较高，同时胞质烟酰胺腺嘌呤二核苷酸依赖性苹果酸脱氢酶（cyNAD-MDH）和磷酸烯醇丙酮酸羧化酶（PEPC）的活性较高，而胞质NAD磷酸依赖性苹果酸酶（cyNADP-ME）和磷酸烯醇丙酮酸的活性较低羧基激酶（PEPCK）的活性要比对照果实所见的高。值得注意的是，通过GABA处理，乙烯产量显着降低，与此同时，MdACS，MdACO和MdERF表达。同时，GABA处理还增强了GABA分流器的活性并促进了GABA的积累。这项研究为苹果酸代谢的调控提供了新见解，并首次报道了苹果果实采后贮藏期间GABA与乙烯信号传导途径之间可能存在的相互作用。