BACKGROUND: Melatonin (MT) is an endogenous indoleamine that regulates senescence progression and stress response in plants. OBJECTIVE: Here, we investigated the effect of MT on the shelf-life and postharvest quality of table grapes (Vitis labrusca L. cv. ‘Fengzao’). METHODS: After harvesting, ‘Fengzao’ grapes were immersed in MT solution at various concentrations (0 [as control], 0.05, 0.1, 0.5 and 1.0 mM for 2 h and stored at 24±1 for 15 days. Physiological indicators including weight loss rate, firmness, contents of total soluble solids (TSSs), ascorbic acid (AsA), malondialdehyde (MDA), hydrogen peroxide (H2O2), and activities of catalase (CAT), ascorbate peroxidase (APX), and superoxide dismutase (SOD) were investigated. Additionally, the DNA methylation rate of ‘Fengzao’ grapes were measured using the methylation-sensitive amplification polymorphism (MSAP) technique. RESULTS: Application of MT effectively delayed grape senescence in all treatment groups compared with the control, with the longest delay observed in the 0.5 mM treatment. Additionally, the rate of DNA methylation decreased in all the 0.5 mM MT treatment groups, indicating a potential role of MT in demethylation. CONCLUSIONS: Our results suggest that the exogenous application of MT can delay the senescence of grapes during postharvest.

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‘Kyoho’ grape (Vitis viniera L. × Vitis labrusca L.) is the most widely cultivated table grape variety. However, it is prone to fruit abscission after harvest, which affects the development of the market. The aim of this study was to evaluate the effects of applying different concentrations of sodium lactate (0.1%, 0.5% and 1% NaL) on postharvest table grape preservation. After harvesting, ‘Kyoho’ grapes were immersed in sodium lactate solution at various concentrations (0 [as control], 0.1%, 0.5% and 1% NaL) for 2min and stored at 20±1℃ for 10 days. Physiological indicators including weight loss rate, browning level of rachis, contents of vitamin C, sugar, malondialdehyde (MDA), membrane permeability, and activities of polygalacturonase (PG), peroxidase (POD), cellulase (Cx) and lipoxygenase (LOX) were investigated. Additionally, it was also determined for ATP content, energy charge and activity of energy metabolism-related enzymes. These results showed that NaL treatment inhibited berry abscission and maintained berry quality due to the decrease of cell wall degrading enzyme activity, the increase of energy metabolism-related enzyme activities and high level of ATP content and energy charge. This study provides a new and effective method for the postharvest storage of table grapes that can help minimize economic losses.

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BACKGROUND: Powdery mildew affects grapevine growth and development and reduces grapevine fruit yield and quality. Plant U-box (PUB) E3 ubiquitin ligases play important roles in ubiquitin/proteasome-mediated protein degradation during plant development and in the plant defense response. OBJECTIVE: We cloned the VvPUB17 gene from Vitis vinifera and analyzed that VvPUB17 enhanced the resistance of grapevine to powdery mildew through the SA signal pathway. METHODS: Pathogen inoculation of Arabidopsis thaliana and grapevine plants was carried out by the tableting method. Gene expression was analyzed by quantitative real-time PCR. Sequence analysis and in vitro ubiquitination experiments show the structure and characteristics of VvPUB17. Exogenous salicylic acid, methyl jasmonate, ethylene and powdery mildew induced the expression of VvPUB17 in Arabidopsis leaves to verify the resistance of VvPUB17 to powdery mildew. RESULTS: Sequence analysis and in vitro ubiquitination experiments show that VvPUB17 contains U-box and Armadillo repeats (ARM repeat) and has E3 ubiquitin ligase activity dependent on the conserved U-box motif. Transgenic plants showed elevated levels of key genes related to the SA defense response pathway and high concentrations of salicylic acid. CONCLUSIONS: VvPUB17 functions as an E3 ubiquitin ligase that enhances the resistance of grapes to powdery mildew through the SA signal pathway.