Phomopsis longanae-induced pericarp browning and disease development of longan fruit can be alleviated or aggravated by regulation of ATP-mediated membrane lipid metabolism

Compared to P. longanae-inoculated longan fruit, DNP-treated P. longanae-inoculated longans displayed higher fruit disease index, pericarp browning index and cell membrane permeability. Moreover, they exhibited higher activities of phospholipase D, lipase and lipoxygenase, lower amounts of phosphatidylcholine, phosphatidylinositol and USFA (unsaturated fatty acids) as well as higher amounts of phosphatidic acid and SFA (saturated fatty acids). Additionally, lower ratio of USFA to SFA and USFA index were shown in DNP-treated P. longanae-inoculated longans. However, ATP-treated P. longanae-inoculated longans exhibited the opposite results. These findings indicated that DNP stimulated longan pericarp browning and disease development caused by P. long-anae resulted from the increases in activities of membrane lipids-degrading enzymes, promoting degradation of membrane phospholipids and USFA, and disruption of membrane structural integrity. Whereas, the opposite results observed in ATP-treated P. longanae-inoculated longans were due to the reduction in activities of membrane lipids-degrading enzymes and the maintenance of membrane structural integrity.