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To better understand the function of melatonin in tomato fruit ripening and quality improvement, a label-free quantitation method was used to investigate the proteins that differ between the control ( CK) and 50 μ m melatonin treatment (M50) fruits. Proteomics data identified 241 proteins that were significantly influenced by melatonin. These proteins were involved in several ripening-related pathways, including cell wall metabolism, oxidative phosphorylation, carbohydrate, and fatty acid metabolism. Moreover, the application of exogenous melatonin increased eight proteins that are related to anthocyanin accumulation during fruit ripening. Additionally, the affected protein levels correlated with the corresponding gene transcript levels. Further, the total anthocyanin content from M50 increased by 52%, 48%, and 50% at 5, 8, and 13 DAT (day after melatonin treatment), respectively. The melatonin-mediated promotion of fruit ripening and quality might be due to the altered proteins involved in processes associated with ripening. In this work, we indicated that a senescence-related protein was downregulated in the M50 fruit, while a cell apoptosis inhibitor ( API5) protein was upregulated. In addition, peroxidases ( POD9, POD12, peroxidase p7-like) and catalase ( CAT3) significantly increased in the M50 fruits. Based on the previous studies and our data, we inferred that melatonin might be positively related to fruit ripening but negatively related to fruit senescence. This research provides insights into the physiological and molecular mechanisms underlying melatonin-mediated fruit ripening as well as the anthocyanin formation process in tomato fruit at the protein concentration level, and we reveal possible candidates for regulation of anthocyanin formation during fruit ripening. [ABSTRACT FROM AUTHOR]

Melatonin as a naturally synthesized molecule in plants takes part in regulation of stress resistance. The mechanisms by which melatonin alleviates abiotic stresses are discussed.In recent years melatonin has emerged as a research highlight in plant studies. Melatonin has different functions in many aspects of plant growth and development. The most frequently mentioned functions of melatonin are related to abiotic stresses such as drought, radiation, extreme temperature, and chemical stresses. This review mainly focuses on the regulatory effects of melatonin when plants face harsh environmental conditions. Evidence indicates that environmental stress can increase the level of endogenous melatonin in plants. Overexpression of the melatonin biosynthetic genes elevates melatonin levels in transgenic plants. The transgenic plants show enhanced tolerance to abiotic stresses. Exogenously applied melatonin can also improve the ability of plants to tolerate abiotic stresses. The mechanisms by which melatonin alleviates abiotic stresses are discussed. [ABSTRACT FROM AUTHOR]

Tomato fruits were treated by exogenous melatonin. The effect of melatonin on ethylene biosynthesis, ethylene perception, and ethylene signalling may contribute to fruit ripening and quality improvement in tomato.In this study, the effect of melatonin on the postharvest ripening and quality improvement of tomato fruit was carried out. The tomatoes were immersed in exogenous melatonin for 2h, and then the related physiological indicators and the expression of genes during post-harvest life were evaluated. Compared with control check (CK), the 50 µM melatonin treatment significantly increased lycopene levels by 5.8-fold. Meanwhile, the key genes involved in fruit colour development, including phytoene synthase1 (PSY1) and carotenoid isomerase (CRTISO), showed a 2-fold increase in expression levels. The rate of water loss from tomato fruit also increased 8.3%, and the expression of aquaporin genes, such as SlPIP12Q, SlPIPQ, SlPIP21Q, and SlPIP22, was up-regulated 2- to 3-fold under 50 µM melatonin treatment. In addition, 50 µM melatonin treatment enhanced fruit softening, increased water-soluble pectin by 22.5%, and decreased protopectin by 19.5%. The expression of the cell wall modifying proteins polygalacturonase (PG), pectin esterase1 (PE1), β-galactosidase (TBG4), and expansin1 (Exp1) was up-regulated under 50 µM melatonin treatment. Melatonin increased ethylene production by 27.1%, accelerated the climacteric phase, and influenced the ethylene signalling pathway. Alteration of ethylene production correlated with altered 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS4) expression. The expression of ethylene signal transduction-related genes such as NR, SlETR4, SlEIL1, SlEIL3, and SlERF2, was enhanced by 50 µM melatonin. The effect of melatonin on ethylene biosynthesis, ethylene perception, and ethylene signalling may contribute to fruit ripening and quality improvement in tomato. This research may promote the application of melatonin on postharvest ripening and quality improvement of tomato fruit as well as other horticultural productions in the future. [ABSTRACT FROM AUTHOR]

• Melatonin treatment triggered increased carotenoid accumulation. • Melatonin treatment did not enhance carotenoid levels in Nr tomato. • Ethylene acts in melatonin-induced biosynthesis of carotenoids. In tomato, red color is a key commercial trait and arises from the accumulation of carotenoids. Previous studies have revealed that melatonin promotes lycopene accumulation and ethylene production. However, it is unclear if melatonin similarly increases other carotenoids, and whether any increase of carotenoids in tomato fruit is directly related to ethylene production. In this study, changes in carotenoid profiles during fruit ripening were investigated in control (CK) and in fruits treated with melatonin (M50). The α, β-carotene, and lycopene levels were significantly increased in M50, and there was increased carotenoid biosynthetic gene expression. We also observed up-regulated transcript levels of SlRIN , SlCNR , and SlNOR in M50 compared to CK. To better understand the regulation of carotenoid biosynthesis by melatonin and its potential response to endogenous ethylene, we tested an ethylene-insensitive mutant, Never ripe (Nr). Melatonin-treated Nr failed to accumulate more carotenoids compared to CK, although there was significantly changed ethylene production. Additionally, there was no general upregulation of expression of ripening-related genes in this mutant under melatonin treatment. These results suggest melatonin function might require ethylene to promote carotenoid synthesis in tomato. [ABSTRACT FROM AUTHOR]

• Treatment with 1 mmol L−1 melatonin maintained postharvest quality of 'Fuji' apples. • Melatonin treatment reduced weight loss and peel injury in stored apples. • Melatonin decreased ethylene production by inhibiting ethylene synthesis genes. • Melatonin treatment reduced MDA concentrations in apples during storage. • Melatonin treatment promoted antioxidant capacity in apples during storage. The effects of treatment with melatonin on ripening of 'Fuji' apples during storage at 1 °C for 56 d were investigated. The apples were harvested at the commercial ripening stage and treated with 1 mmol L−1 melatonin. Compared with the control, melatonin treated apples had significant reduced ethylene production (28 d–56 d) and weight loss (14 d–56 d) during storage (p < 0.05). Also, the melatonin treatment maintained better apple skin structure throughout storage. The reduced ethylene production was regulated by the decreased expressions of MdACO1, MdACS1, MdAP2.4 and MdERF109 , based on RNA-Seq analysis, which was validated using qRT-PCR analysis. Moreover, the activity of 3 enzymes, including peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT), were significantly increased in melatonin treated fruit (p < 0.05). Taken together, this study highlights the inhibitory effects of melatonin in ethylene biosynthesis and factors influencing postharvest quality in apple. [ABSTRACT FROM AUTHOR]