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.