Attenuation of prochloraz phytotoxicity to postharvest mango fruit by melatonin is associated with the regulation of detoxification capacity

Excessive fungicide residues in crops threaten food safety, and may initiate oxidative stress and cause phyto-toxicity to products. Melatonin (Mel), a pleiotropic bioactive molecule, plays multiple physiological functions in plants. In this study, utilizing postharvest dipping with Mel and fungicide prochloraz (Pcz) as the model, we explored the effect of Mel on Pcz-triggered toxification and its underlying physiological mechanism in 'Guifei' mango fruit during storage at 25 degrees C. Results showed that pretreatment with 1 mmol L-1 Mel before exposure to 1.2 g L-1 Pcz (Mel + Pcz) reduced Pcz residues by 15.1% and 30.7% in mango fruit at 4 and 8 d, respectively, while ameliorating phytotoxicity to a greater extent than Pcz treatment alone. Microscopic observation revealed that Mel alleviated Pcz-triggered damage to lenticels on fruit exocarp tissue. Mel appreciably repressed Pcz-induced oxidative stress, as indicated by lower levels of reactive oxygen species, malondialdehyde, damaged DNA and carbonylated proteins and good maintenance of membrane integrity and mitochondrial membrane potential in Mel + Pcz fruit. Moreover, Pcz-induced increases in activities of antioxidant enzymes (superoxide dismutase, catalase and peroxidase), levels of ascorbate-glutathione cycle components and activities of pesticide degradative enzymes (cytochrome P450, glutathione S-transferase and glycosyltransferase) were further amplified after treatment with Mel + Pcz, which contributed to a stronger detoxification capacity in mango fruit. The study might provide a strategy for diminishing fungicide residues and attenuating phytotoxicity in post-harvest fruits.