The Roles Of Nitric Oxide And Abscisic Acid In Regulating The Responses To Chilling Injury Of Peach Fruit During Storage

As a climacteric fruit,peaches（Prunus persica（L.）Batsch）are inevitably affected by soft,perishable and deteriorate during storge and transport after harvest at ambient temperature.Refrigerated storage,which are useful method for retarding metabolism rate and prolonging the storage period of peach fruit.However,peach fruits are sensitive to low temperature,and easily suffer from chilling injury,which manifested as woolliness,browning and lose intrinsic flavor.Thus,chilling injury has become a limit factor in peaches storage and preservation.Nitric oxide（NO）and abscisic acid（ABA）have been shown to be important stress regulate factors and play critical roles in the tolerance of plants to cold stress.Cold conditions could induced endogenous NO and ABA production to relieve chilling injury symptoms of fruit during storage.In this experiment,the postharvest‘Xintaihong’peach fruit served as the material to investigate the roles of NO and ABA in regulating the responses of peach fruit to chilling stress and some key substances in endogenous synthesis.Furthermore,we also conducted to examine the roles of endogenous NO and ABA on the physiological regulation mechanism in cold-stored peach fruit.The main results were presented as follows:1.Under low-temperature storage,compared with the control,treatments with NO,ABA,NO+Fluridone（ABA biosynthesis inhibitor）could obviously restrained the decrease of the firmness and significantly inhibit the increase of chilling index,and also maintained the high levels of SSC and peel color of peaches during storage.The results showed that application of exogenous NO,ABA and NO+Fluridone could effectively alleviate the chilling injury symptoms of fruits under cold conditions.In contrast,the treatments of c-PTIO and Fluridone could exacerbate the chilling injury occurred in peaches throughout the cold storage period,when compared with those subjected to NO or ABA treatment alone;compared with the ABA treatment alone,ABA+c-PTIO could significantly increased the chilling index,and decreased the levels of firmness,peel color and SSC content in peaches during storage.It may suggest that such protective effects by ABA induced were reversed in the presence of the NO scavenger c-PTIO.2.Under low-temperature storage,compared with the control,treatments with NO,ABA,NO+Fluridone led to the increases in the activities of SOD,POD,APX,GR,MDHAR and DHAR to varying degrees,and also enhanced the contents of antioxidants（AsA and GSH）and the ratios of AsA/DHA and GSH/GSSG.Meanwhile,application of exogenous NO,ABA and NO+Fluridone also significantly inhibited the accumulation of ROS species(O₂^·-、H₂O₂and^·OH)and markedly alleviated the increase in electrolyte leakage and MDA content in peaches during storage.In contrast,the treatments of c-PTIO and Fluridone could decrease the antioxidant enzyme activities and antioxidant capacities,while obviously enhanced the ROS species,electrolyte leakage and MDA content,when compared with those subjected to NO or ABA treatment alone.Furthermore,ABA+c-PTIO could significantly increased the ROS species,electrolyte leakage and MDA content and maintained the low levels of antioxidant enzyme activities and antioxidant capacities,when compared to treatment with ABA alone.These results showed that both exogenous NO and ABA could enhance the efficiency of enzymatic and non-enzymatic systems,which resulted in improvement on scavenging capacity of ROS species,thereby eliminate these toxic substances to cell and alleviate lipid peroxidation,thus maintaining the integrity of the cell membrane and reducing the oxidative damage in peaches under chilling stress.Application of exogenous ABA could increase the resistance to cold-induced oxidative stress by enhancing the efficiency of antioxidant system,which are partially mediated by NO.3.Under low-temperature storage,the activity of NR and contents of NO,nitrite and nitrate in peaches treated with NO and ABA were markedly higher than those of the control,but had negative impact on the L-arginine content and NOS activity.Meanwhile,application of exogenous NO and ABA also maintained the relatively low levels of spermidine and spermine contents or SAMDC and ADC activities.Furthermore,the levels of NO content was markedly decreased by application of c-PTIO,NR inhibitor Sodium tungstate,Fluridone,but had not affected by NOS inhibitor _L-NAME;compared with the control and NO treatment alone,the content of ABA and some key substances in ABA synthesis（carotenoids contents,ZEP,NCED and AO activities）increased obviously in the presence of ABA under cold conditions.Moreover,we found that treatment with Fluridone significantly inhibited the ABA content,while NO,c-PTIO,_L-NAME and Sodium tungstate had no influence on it,when compared with the control.These results indicated that alteration of the endogenous NO level was associated with the NR activity up-regulated.ABA can mediate its synthesis by autocatalystic reaction and then induce NO production through nitrate reductase pathway in peaches under chilling stress.4.The rate of respiration and ethylene production in control peaches significantly lower than that of peaches among other treatments（c-PTIO,Sodium tungstate and Fluridone）during the cold storage period.Meanwhile,application of c-PTIO,Sodium tungstate and Fluridone also reduced the contents of proline and soluble sugar.Moreover,the levels of some key enzyme（P5CS and OAT）activities in proline accumulation were dramatically suppression by NO scavenger c-PTIO,NR inhibitors Sodium tungstate and ABA inhibitors Fluridone,but markedly increased the activity of PDH in proline degradation.Additionally,there were no significant differences in these results of peaches among treatments with _L-NAME and control.These results indicated that alteration of the endogenous NO and ABA level may directly regulate the important osmotic adjustment substances,thus alleviated the chilling injury in peach fruit under low-temperature stored,and such results most implications shown to be that NO synthesis in cold-stored peaches are mainly realized by nitrate reductase pathway.