Exogenous melatonin ameliorates cold-induced damage in tomato plants

•Melatonin promotes photosynthetic carbon fixation in cold-stressed tomato plants.•Melatonin improves antioxidant potential in cold-stressed tomato plants.•Melatonin induces expressions of cold-responsive genes in tomato plants.•Melatonin increases accumulation of metabolites in cold-stressed plants.•Melatonin ameliorates cold-induced damage in tomato plants.

Low temperature is an adverse environmental factor posing damage to tomato plants and causing huge loss of yields. Thus, seeking an effective way of ameliorating cold damage is important for sustainable tomato production. Melatonin is a crucial molecule involved in plant abiotic stress responses. In this study, we investigated the role of exogenous melatonin in amelioration of cold damage in tomato plants. Lower malondialdehyde (MDA) content and electrolyte leakage, greater activities of antioxidant enzymes, and higher levels of non-enzymatic antioxidants were observed in melatonin-pretreated plants than in non-melatonin-pretreated plants under cold stress. Gene expression analyses showed that exogenous melatonin substantially promoted expression of cold-responsive genes, including SlICE, SlCBF and SlP5CS, under cold condition. Notably, SlSBP, a gene encoding a Calvin cycle enzyme sedoheptulose-1,7-bisphosphatase (SBPase), was considerably induced in melatonin-treated plants under cold stress, consistent with the observed increase in photosynthetic carbon assimilation. Analyses of metabolites revealed that levels of polyamines, sucrose, and proline were significantly enhanced following cold treatment in melatonin-pretreated plants. Collectively, our data provide evidence for the ameliorative effects of melatonin on cold-induced damage to tomato plants. Our work also provides a case study that exogenous application of melatonin may be potentially employed as a strategy to improve cold tolerance in tomato production.