Abstract: Phospholipids are one of the major constituents of cell membranes. Cell membrane stability is affected by phospholipid metabolism, in turn affecting plant growth, senescence and secondary metabolism. The plant resistance inducer benzothiadiazole (BTH) can improve disease resistance in muskmelon (Cucumis melo L.) after harvest, delay fruit senescence, and affect the production of aroma-active secondary metabolites. In the present work, we studied the changes in the contents of phosphatidyl cholines (PC), phosphatidylinositol (PI) and phosphatidic acid (PA) and the activities and gene expression levels of phospholipase A2 (PLA2), phospholipase C (PLC) and phospholipase D (PLD) during the postharvest storage of muskmelon (Cucumis melo L. cv. Yujinxiang), and furthermore, we explored the mechanism of action of BTH in regulating phospholipid metabolism. The results showed that the activity and gene expression of phospholipase in pericarp were inhibited by BTH treatment during postharvest storage, and the activity peaks of PLA2, PLC and PLD in pericarp were reduced by 7.11%, 10.24% and 7.20%, respectively, as compared to the control. BTH treatment augmented the accumulation of PC and PI over the control; the peak values at the end of storage increased by 5.24% and 2.08%, respectively. BTH treatment decreased PA level in comparison to the control and distilled water treatment; PA levels in pericarp and flesh of BTH treated fruits were 20.72% and 8.51% lower than those in the control. BTH treatment inhibited unsaturated fatty acids less than saturated fatty acids. Accordingly, BTH treatment can control postharvest diseases in muskmelon by inhibiting the relative expression levels of PLC and PLD genes and reducing the enzyme activities and therefore decreasing fatty acid production and altering the degree of unsaturation of fatty acids, besides affecting the signal transduction pathways involved in cell membrane metabolism and the generation of secondary metabolites.

Key words: benzothiadiazole, thick-skinned muskmelon, phospholipid metabolism, phospholipase, gene expression, fatty acid