Preharvest L-phenylalanine sprays accelerated wound healing of harvested muskmelons by eliciting phenylpropanoid metabolism and enzymatic browning

L-phenylalanine (L-phe) is the initial substrate of phenylpropanoid metabolism. This study aimed to investigate the effect of four preharvest spray with 8 mM L-phe during fruit development and wound healing ability in harvested muskmelons (cv. Manao) and to explore the related mechanisms. The results revealed that preharvest L-phe sprays promoted phenylalanine ammonialyase, cinnamate-4-hydroxylase, 4-coumaric acid coenzyme A ligase and cinnamyl alcohol dehydrogenase activities, and elevated the level of four phenolic acids (p-coumaric, caffeic, cinnamic, ferulic acids), three lignin monomers (sinapyl, coniferyl, cinnamyl alcohols), total phenols, flavonoids and lignin at wounds of harvested fruit. L-phe treatment increased peroxidase activity, H2O2 level, and accelerated the deposition of suberin polyphenolic and lignin at wounds, which led to lower weight loss and disease index of harvested muskmelons during healing. Moreover, the treatment enhanced polyphenol oxidase activity and induced enzymatic browning at wounds. Thus, preharvest L-phe sprays promoted wound healing of harvested muskmelons by eliciting phenylpropannoid metabolism and enzymatic browning at wounds.