Melatonin (MLT) is a vital signaling molecule that regulates multiple physiological processes in higher plants. In the current study, the role of MLT in regulating chilling tolerance and its possible mechanisms in litchi fruit during storage at ambient temperatures after its removal from refrigeration was investigated. The results show that the application of MLT (400 μM, dipping for 20 min) to ‘Baitangying’ litchi fruit effectively delayed the development of chilling injury (CI) while inhibiting pericarp discoloration, as indicated by higher chromacity values (L*, a*, b*) and anthocyanin levels. MLT treatment suppressed the enhancements of the relative electrical conductivity (REC) and malondialdehyde (MDA) content, which might contribute to the maintenance of membrane integrity in litchi fruit. MLT treatment slowed the decline in cellular energy level, as evidenced by higher adenosine triphosphate (ATP) content and a higher energy charge (EC), which might be ascribed to the increased activities of enzymes associated with energy metabolism including H⁺-ATPase, Ca²⁺-ATPase, succinate dehydrogenase (SDH), and cytochrome C oxidase (CCO). In addition, MLT treatment resulted in enhanced proline accumulation, which was likely a consequence of the increased activities of ornithine-δ-aminotransferase (OAT) and Δ¹-pyrroline-5-carboxylate synthase (P5CS) and the suppressed activity of proline dehydrogenase (PDH). These results suggest that the enhanced chilling tolerance of litchi fruit after MLT treatment might involve the regulation of energy and proline metabolism.

“Zhongbai” papaya fruit were treated with 15 mmol/L glycine betaine (GB) and then refrigerated at 6°C for 40 days to study the influence of GB on chilling injury (CI) and possible mechanism associated with energy metabolism. The results exhibited that GB treatment remarkably reduced the CI severity as indicated by lower CI index during storage. GB treatment lowered electrolyte leakage and malondialdehyde content, which accounted for maintenance of membrane integrity and reduced lipid peroxidation. Moreover, GB treatment improved the energy status as revealed by increased adenosine triphosphate (ATP) level, energy charge, and activities of energy metabolism‐related enzymes including mitochondrial membrane H⁺‐adenosine triphosphatase (H⁺‐ATPase) and Ca²⁺‐adenosine triphosphatase (Ca²⁺‐ATPase), succinate dehydrogenase (SDH), and cytochrome C oxidase (CCO). The results indicate that enhanced chilling tolerance in papaya fruit by GB treatment during cold storage might be ascribed to improved energy status in association with increased activities of energy metabolism‐related enzymes.

β-aminobutyric acid (BABA) is a new environmentally friendly agent to induce disease resistance by priming of defense in plants. However, molecular mechanisms underlying BABA-induced priming defense are not fully understood. Here, comprehensive analysis of priming mechanism of BABA-induced resistance was investigated based on mango-Colletotrichum gloeosporioides interaction system using iTRAQ-based proteome approach. Results showed that BABA treatments effectively inhibited the expansion of anthracnose caused by C. gleosporioides in mango fruit. Proteomic results revealed that stronger response to pathogen in BABA-primed mango fruit after C. gleosporioides inoculation might be attributed to differentially accumulated proteins involved in secondary metabolism, defense signaling and response, transcriptional regulation, protein post-translational modification, etc. Additionally, we testified the involvement of non-specific lipid-transfer protein (nsLTP) in the priming acquisition at early priming stage and memory in BABA-primed mango fruit. Meanwhile, spring effect was found in the primed mango fruit, indicated by inhibition of defense-related proteins at priming phase but stronger activation of defense response when exposure to pathogen compared with non-primed fruit. As an energy-saving strategy, BABA-induced priming might also alter sugar metabolism to provide more backbone for secondary metabolites biosynthesis. In sum, this study provided new clues to elucidate the mechanism of BABA-induced priming defense in harvested fruit.