Effects of Exogenous Nitric Oxide Treatment on Grape Berries Against Botrytis cinerea and Alternaria alternata Related Enzymes and Metabolites.

Postharvest losses of grape berries caused by the pathogenic fungi Botrytis cinerea and Alternaria alternata have been widely reported, and nitric oxide (NO) as a plant signaling molecule to control postharvest diseases has recently become an active research topic. This study aimed to investigate the regulatory effect of NO on the interaction between grape berries and fungi. During interactions between grape berries and pathogenic fungi, treatment with 10 mM sodium nitroprusside (SNP, an NO donor) delayed the decline of the physiological quality of the grape berries and had positive effects on the weight loss rate, firmness, and respiration intensity. SNP treatment increased the activities of superoxide dismutase (SOD) and polyphenol oxidase (PPO) and inhibited the activities of peroxidase (POD) and catalase (CAT) of grape berries during the resistance to fungal pathogen infection. In addition, the increase in browning degree and the accumulation of hydrogen peroxide were inhibited by SNP treatment. In the phenylpropane metabolic pathway, the activities of phenylalanine ammonia-lyase (PAL), cinnamate 4-hydroxylase (C4H), and 4-coumaric acid coenzyme A ligase (4CL) were increased during the activation of grape berries during the resistance to pathogen infection by SNP, and the intermediate metabolites lignin, flavonoids, and total phenols were accumulated. In addition, SNP treatment had a regulatory effect on the gene expression levels of SOD, POD, PPO, PAL, and 4CL. These results suggested that SNP treatment was effective for the preservation and disease reduction of grape berries.

Nitric Oxide Made a Major Contribution to the Improvement of Quality in Button Mushrooms (Agaricus bisporus) by the Combined Treatment of Nitric Oxide with 1-MCP.

Browning is one of the major effects of shelf-life responsible for the reduction in the commercial value of the button mushrooms (Agaricus bisporus). In this study, the individual and the combined effects of exogenous sodium nitroprusside (SNP, a nitric oxide donor) and 1-methylcyclopropene (1-MCP) on the quality of button mushrooms were evaluated. The results demonstrated that mushrooms treated with SNP+1-MCP promoted reactive oxygen species (ROS) metabolism thereby protecting cell membrane integrity, hindering polyphenol oxidase (PPO) binding to phenolic compounds, and downregulating the PPO activity. In addition, the SNP+1-MCP treatment effectively maintained quality (firmness, color, total phenol, and flavonoid) and mitigated oxidative damage by reducing ROS accumulation and malondialdehyde production through the stimulation of the antioxidant enzymes activities and the enhancement of ascorbic acid (AsA) and glutathione (GSH) contents. Moreover, the correlation analysis validated the above results. The SNP+1-MCP treatment was observed to be more prominent on maintaining quality than the individual effects of SNP followed by 1-MCP, suggesting that the combination of NO and 1-MCP had synergistic effects in retarding button mushrooms senescence, and NO signaling molecules might be predominant in the synergy.

Short-term hypobaric treatment alleviates chilling injury by regulating membrane fatty acids metabolism in peach fruit.

Short-term hypobaric treatment (SHT) on postharvest quality and membrane fatty acids metabolism were studied in peach fruit (Prunus persica [L.] Batsch., cv. Feicheng) during shelf life after cold storage. SHT was effective in alleviating chilling injury (CI) and maintaining postharvest quality. SHT reduced the production of malondialdehyde (MDA) and electrolyte leakage (EL), and increased membrane fluidity. In addition, SHT plays an imperative role in reducing saturated fatty acid (SFA), increasing unsaturated fatty acid (USFA), and keeping a higher unsaturation level in peach fruit. Meanwhile, SHT enhanced the activity of fatty acid synthetase (FAS), upregulated the expression levels of FAD2, FAD3-1, FAD3-2, and FAD7 genes at the early stage of storage, as well as inhibited the activity of lipoxygenase (LOX) and gene expression of LOX1. These results suggested that SHT could increase fatty acids unsaturation by regulating FAS activity, FAD and LOX1 gene expression, thus maintain high membrane stability and alleviate CI. PRACTICAL APPLICATIONS: CI is an important factor affecting the postharvest quality of peaches in cold storage, and metabolism of membrane fatty acids is one of the main CI response mechanisms. Our previous study has shown that SHT could alleviate CI in peach fruit. Therefore, it is of great significance to investigate the regulation of membrane fatty acids metabolism under SHT. Results from this study suggest that the enhancement of chilling tolerance by SHT in peaches could be explained, at least in part, as being due to enhanced FAS activity, upregulated the expression of FAD gene, and inhibited LOX1 to maintain higher unsaturation level. All in all, we explored the response mechanism of membrane fatty acids metabolism under SHT in peach fruit, and supplied theoretical guidance for application of the technology.

Improvement in storage quality of postharvest tomato fruits by nitroxyl liposomes treatment.

Nitroxyl (HNO) has attracted much attention due to its unique biological activity. To investigate the preservation effect of HNO on fruits, a nitroxyl liposome based on 1-nitrosocyclohexyl acetate was prepared and characterized by infrared spectroscopy and transmission electron microscopy. The optimal preparation conditions were explored, and then HNO liposomes were prepared under the optimal conditions to study the effect of HNO liposomes on postharvest quality of tomatoes. The tomato fruits were treated with different concentrations (0, 5, 10, 15 and 20 µmol L-1) of HNO liposomes and stored at room temperature. The results indicated that treatment with HNO liposomes can more effectively delay the browning and slow down the decrease in lightness of tomatoes. Additionally, HNO liposomes can reduce the activity of PPO and POD, inhibit the increase of MDA and total phenol content. These results suggest that treatment with HNO liposomes can effectively preserve the quality of tomatoes.