Salicylic acid treatment improves the storability of fresh longan by regulating the metabolisms of respiration and energy

This work investigated how salicylic acid (SA) treatment enhanced the storage quality of longan fruit by affecting its respiration and energy metabolism. Compared to control longan, SA-treated longan exhibited higher levels of commercially acceptable fruit rate, sucrose, vitamin C, TSS, and total soluble sugar, but lower levels of fruit disease index, pulp breakdown index, weight loss, TA, and reducing sugar. Additionally, SA treatment resulted in lower fruit respiration rate, lower activities of the critical enzymes involved in respiratory pathways (PGI, SDH, CCO, AAO), lower values of NADH and NAD, higher activities of enzymes (NADK, G-6-PDH + 6-PGDH), and higher amounts of NADPH and NADP. Besides, SA-treated longan showed higher levels of ATP, ADP, and energy charge, but lower AMP level, along with higher activities of H⁺-ATPase, Ca²⁺-ATPase, and Mg²⁺-ATPase in mitochondrial, plasma, and vacuolar membranes. These data indicated that SA treatment-maintained the storage attributes of postharvest longan was due to the weakened respiratory intensity, the reduced consumption of nutrients, the inhibited respiratory pathways of EMP-TCA cycle, and the enhanced respiratory pathway of PPP. Additionally, SA treatment retained higher levels of ATPase activity and energy status to maintain cellular ionic balance and protect membrane integrity, ultimately improved the storability of fresh longan during storage.