In this study, five genes involved in malic acid (MA) metabolism, including a cytosolic NAD-dependent malate dehydrogenase gene ( cyNAD-MDH), a cytosolic NADP-dependent malic enzyme gene ( cyNADP-ME), two vacuolar H+-ATPase genes ( vVAtp1 and vVAtp2), and one vacuolar inorganic pyrophosphatase gene ( vVPp), were characterized from pear fruit based on bioinformatic and experimental analysis. Their expression profile in "Housui" pear was tissue-specific, and their expression patterns during fruit development were diverse. During "Housui" pear storage, MA content decreased, which was associated with the downregulated transcripts of MA metabolism-related genes and cyNAD-MDH activity and higher cyNADP-ME activity. The response of MA metabolism to postharvest 1.5 μL L-1 1-MCP fumigation and 0.5 mL L-1 ethrel dipping was distinct: 1-MCP fumigation upregulated gene expression and cyNAD-MDH activity and suppressed cyNADP-ME activity, and thus maintained higher MA abundance when compared with those in the control; on the other hand, an opposite behavior was observed in ethrel-treated fruit.
Keywords: 1-MCP; enzyme activity; ethrel; gene expression; malic acid; pear.