DCC and ADP regulate the pulp breakdown in Phomopsis longanae Chi-inoculated longan via modulating energy levels and the metabolisms of reactive oxygen species and membrane lipids

Compared to P. longanae-inoculated longan, DCC + P. longanae-inoculated longan exhibited an elevated pulp breakdown index and higher cell membrane permeability, along with the reduced ATP levels and energy charge. Additionally, DCC + P. longanae-inoculated longan exhibited higher activities of membrane lipid-degrading enzymes (MLDEs), including PI-PLC, PC-PLC, PLD, DGK, PAP, lipase, and LOX, as well as higher levels of DAG, PA and SFAs. Conversely, the contents of PI, PC and USFAs were reduced, accompanied by lower U/S and IUFA. Besides, DCC + P. longanae-inoculated longan displayed lower activities of SOD, CAT, APX, GPX, MDHAR, DHAR, and GR, along with lower reducing power and DPPH radical scavenging ability, lower levels of AsA and GSH, and higher levels of DHA, GSSG, H₂O₂, O₂^·− production rate, and MDA. These outcomes indicate that DCC treatment expedited pulp breakdown in P. longanae-inoculated longan by exacerbating energy deficiency, which activated MLDEs activities and damaged cell membrane structure. Furthermore, the insufficient energy supply also impaired ROS-scavenging capacity, thereby leading to ROS accumulation, membrane lipid peroxidation, and loss of cell membrane integrity. In contrast, ADP + P. longanae-inoculated longans exhibited the opposite effects. The results of present work can provide new insight into the mechanism of longan pulp breakdown, and offer new strategies such as the application of ADP for suppressing longan pulp breakdown to extend the shelf life of fresh longan.