Exogenous Putrescine Application Mitigates Chill Injury in Melon Fruit During Cold Storage by Regulating Polyamine Metabolism and CBF Gene Expression

When kept at a low temperature, yellow melons are prone to chilling injury. It is widely known that applying putrescine (Put) after harvest can prevent chilling harm in fruit. The best dosage of Put for treating yellow melon remains unknown, and the underlying mechanisms are not well understood. This study aimed to investigate the effects of exogenous putrescine application on chilling injury in melons and to elucidate the underlying physiological and molecular mechanisms involved. In this study, melons were treated with various concentrations of Put (0, 1, 2, and 4 mM), and the phenotype, chilling injury index, endogenous polyamine content, activities of crucial enzymes, and expression levels of associated genes (CmADC, CmODC, CmSAMDC1-4, CmSPDS1-2, CmSPMS1-2, and CmCBF1-4) were measured during storage. In our study on yellow melon, we found that treatment with 2 mM Put optimally alleviated chilling injury. This effect was achieved by enhancing the activities of ADC, AIH, CPA, ODC, SAMDC, DAP, and PAO, thereby regulating the endogenous levels of Put, Spd, and Spm. Furthermore, Put mainly impacted the expression of CmCBFs, which might help regulate downstream cold-inducible genes, leading to the improvement of tolerance in yellow melon fruit. Exogenous Put enhances melon chilling tolerance by activating endogenous polyamine biosynthesis and the CBF signaling pathway. This provides an effective strategy for post-harvest preservation of melons and might serve as a guide for future research into the mechanism involved in Put-induced chilling tolerance in horticulture crops.