Abstract: To investigate the effects of melatonin (MT) in combination with 1-methylcyclopropene (1-MCP) on postharvest proline metabolism and chilling injury in Hami melons, this study included four treatments: control (distilled water immersion + distilled water fumigation), MT (100 μmol/L MT immersion + distilled water fumigation), 1-MCP (distilled water immersion + 1 μl/L 1-MCP fumigation), and their combination (100 μmol/L MT immersion + 1 μl/L 1-MCP immersion). These treatments were assessed for their impact on physiological indices and the activities and gene expression of enzymes involved in proline synthesis and metabolism during cold storage. Results showed that the combined treatment maintained soluble solids and soluble protein content in the pericarp, suppressed the increase in electrolyte leakage and malondialdehyde (MDA) content, reduced respiratory intensity, and retarded the decrease in fruit firmness. Furthermore, this treatment significantly upregulated the expression of CmP5CS and CmOAT and downregulated CmProDH expression, consequently enhancing the enzymatic activities of Δ1-pyrroline-5-carboxylate synthase (P5CS) and ornithine-δ-aminotransferase (OAT) and inhibiting proline dehydrogenase (ProDH) activity. These biochemical changes promoted proline accumulation and reduced the chilling injury index. In conclusion, the combined application of MT and 1-MCP modulates proline metabolism and augments chilling tolerance in Hami melon fruits.

Key words: Hami melons; melatonin; 1-methylcyclopropene; chilling injury; proline metabolism