Salicylic acid, ethephon, and methyl jasmonate enhance ester regeneration in 1-MCP-treated apple fruit after long-term cold storage

Volatile esters, primarily synthesized in peel tissues, are major aromatic components of apple fruits [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.]. The use of cold storage combined with 1-methylcyclopropene (1-MCP) treatment prolongs the life of apples but represses the regeneration of esters during poststorage ripening. In this study, the regeneration of total esters was significantly increased in apple fruits treated with salicylic acid (SA) and Ethephon (ETH) that had been treated once or twice with 1-MCP. However, methyl jasmonate (MeJA) treatment resulted in regeneration of total esters after a single 1-MCP treatment. To determine the mechanism by which SA, ETH, and MeJA regulate ester regeneration, the apple alcohol acyltransferase gene (MdAAT2) was investigated at the mRNA, protein, and enzyme activity levels. Genes associated with ethylene perception were also investigated by RT-PCR. The results suggest that MdAAT2 controls ester regeneration and that MdETR1 plays a key role in ethylene perception and regulation of downstream MdAAT2 gene expression during poststorage. Ester compounds and concentrations differed in peels treated with different signal molecules, indicating that regulation of the pathway upstream of straight-chain ester biosynthesis depended on the regulation of lipoxygenase (LOX) and alcohol dehydrogenase (ADH) activity by SA, ETH, and MeJA during poststorage ripening.