Effect Of Nitric Oxide Fumigation On Reactive Oxygen Species Metabolism Of ‘Munage’ Table Grapes

‘Munage’table grape is one of the most popular varieties of fresh grapes in Xinjiang.As a non-climacteric fruit,the imbalance of reactive oxygen metabolism is considered to be an important factor in accelerating the senescence of the grape.Nitric oxide（NO）,as a signaling molecule,is found to be effective in regulating fruit respiration,ethylene release,active oxygen metabolism as well as delaying fruit ripening and senescence.Storage quality of postharvest‘Munage’table grape at 0^oC was evaluated.Effect of NO fumigation on enzymatic antioxidant and non-enzymatic antioxidant systems in different tissues of grape were analyzed.Regulation of NO fumigation on ROS metabolism related gene in different tissues of grape was studied.Effect of NO fumigation on ROS metabolism of grape is discussed.The main results were outlined as follows:（1）‘Munage’table grape was fumigated with 0,40,80,150,300,500 and 1000μL/L NO at0℃for 2 h per every 7 days.The proper concentration of NO fumigation was 300μL/L through the evaluation of weight loss,shattering rate and decay rate.NO fumigation could significantly keep the fruit firmness and stalk chlorophyll（Chl）,delay the decrease of total soluble solids（TSS）,titratable acid（TA）and pH.In addition,it also protected the integrity of the cell membrane.（2）The reactive oxygen species（ROS）content and ROS related enzymes showed different tendency in various parts of grape during the whole storage time.The catalase（CAT）activity,superoxide dismutase（SOD）activity,hydrogen（H₂O₂）content and superoxide anion(O₂^·-)production rate were higher in the stalk than in the peel and pulp,but the activitiy of ascorbate peroxidase（APX）and glutathione reductase（GR）were higher in the pulp than in the stalk and peel.In addition,MDA content was lower in the pulp than in the stalk and peel.300μL/L NO trearment could induced the increase of CAT、POD and SOD activities,inhibited the content of MDA,H₂O₂ and O₂^·-.Therefore,the scavenging ability to excessive ROS was enhanced,leading to retarde the senescence of‘Munage’grape.（3）The antioxidant compounds concentration were higher in the grape stalk than in the peel and pulp during storage.300μL/L NO fumigation could obviously decreased the content of total phenol（TP）,total flavonoids（TF）,proanthocyanidins（PC）,ascorbic acid（AsA）and Carotenoids（Car）.Antioxidant ability of eliminating the DPPH^·was improved in every parts of grapes.NO fumigation also kept the integrity of waxes on the peel by observing the ultrastructure of grape peel using SEM.（4）Through RT-PCR technology,VvMSD,VvCAT,VvGR,VvPOD2 and VvGPX2 fragments were obtained,which are 112 bp,181 bp,198 bp,200 bp and 227 bp,respectively.300μL/L NO fumigation could significantly induced genes expression level of VvMSD,VvCAT and VvGR in stalk.In peel of grape,NO fumigation induced the expression of these five genes related to ROS.NO fumigation also increased the level of gene expression in pulp,except VvGPX2.However,NO fumigation had no significant effect on the regulation of VvGPX2,VvPOD2 in stalk and VvGPX2in pulp.In summary,NO fumigation could reduced the accumulation of excess ROS and maintained the storage quality of grapes by regulatd the enzymatic antioxidant and non-enzymatic antioxidant systems and the related genes of ROS metabolism in different tissues.