Regulation Mechnism Of Antioxidant System On Reactive Oxygen Species During Development And Postharvest Storage Of Peach Fruit

Peach is one of the most popular fruits in the world because of its high nutrition and good flavor.As a typical climacteric fruit,peach is highly perishable after harvest,which limit its circulation and supply in the market and cause high economic loss.It has been reported that reactive oxygen species(ROS)metabolism and antioxidant system may act as molecular message in regulating fruit ripening and senescence.ROS and antioxidant system are easy to be regulated by postharvest treatment,which may affect fruit quality and oxidative stress tolerance.In this research,firstly,the main antioxidant genes in peach fruit were identified and analyzed.Secondly,we studied changes of ROS level during furit development and ripening and the regulation mechanism of antioxidant system on ROS level.Moreover,several postharvest treatments,including heat treatment and heat combined 1-MCP treatment,have been used to analyze their effect on fruit quality,ROS level and antioxidant system during fruit storage.We believe that this research can help us know more about fruit ripening and senescence and provide a guidline for selecting an optimal posrharvest treatment in the production practice.The main results are as follows:1.We identified eight SOD genes,eight GPX genes,two CAT genes,four APX genes,two MDHAR genes,two DHAR genes and 2 GR genes from "Xiahui 5" peach fruit using keword research and modif analysis.The results indicate that most antioxidant genes locate on cytoplasm and most H2O2-scavenging genes are distruibuted in chromosome 5.Moreover,the expression of different gene family members is significantly different in peach fruit.PpaSOD3,PpaSOD5,PpaCAT1,PpaGPX6and PpaGPX8 are key members with higher expression level among all the antioxidant genes.2.We investigate the changes of fruit quality,ROS level and antioxidant enzymes(SOD,CAT and GPX)during the development and ripening of "Xiahui 5" peach fruit.Our results showed that ROS were correlated with respiration reaction during fruit development and ripening.O2-and H2O2 matained high level during fruit development,while no oxidative damage was detected in that stage.This result indicates that O2-and H2O2 may act as potential signaling molecules during fruit fast development.In the late stage of fruit ripening,abundant H2O2 is accompanied by high MDA and EL level.The over-acculated H2O2 might have the function of a major toxic molecule to stimulate lipid peroxidation and oxidative stress,accelating fruit senescence.Moreover,Low temperature(4?)postponed and suppressed the climacteric peaks of respiration and ethylene,and significantly enhanced the activities of CAT and GPX and the expression of some antioxidant genes.The significantly up-regulated PpaCAT1 and PpaGPX6(>5 folds)were two key genes in alleviating oxidative stress in the late stage of fruit ripening.3.In this study,the effect of hot air(HA,38? for 3 h)and hot water(HW,48? for 10 min)treatments on CI,fruit quality,reactive oxygen species(ROS)and antioxidants in"Xiahui 5" peach fruit during storage at 4? was investigated.Compared with CK,HA and HW treatments maintained higher fruit firmness during the whole cold storage,and allivate chilling injury symptom.However,HW was more effective than HA in alleviating internal browning(IB)symptoms in fruit.HW treatment may be easier to regulate the AsA-GSH metabolism in peach fruit due to the higher heat transmission in water.Our results showed that HW treatment enhanced the concentrations of AsA and DHA in the early stage of storage,meanwhile HWtreatment increased the expression of PpaAPXs and decreased the expression of PpaDHARs on day 3.These results indicate that HW treatment can enhance AsA metabolism by promoting the conversion of DHA from AsA.During the late stage of storage,HM treated fruit maintined high concentrations of GSH and GSSG and high expression of PpaGRsand PpaGPXs,which contribute to maintain the high GSH metabolism in peach fruit.Moreover,enhanced AsA-GSH metabolism and up-regulated expressions of PpaSOD5,PpaCAT1,PpaGPX6 and PpaAPX2 in the HW treated fruit might play an important role in maintaining the lower ROS level and IB index during refrigerated storage.HA treatment also up-regulated the expression of PpaSOD5,PpaCAT1,PpaGPX6 and PpaAPX2,bu it had no effect on either AsA metabolism or GSH metabolism.Above results indicate that nnhanced AsA-GSH metabolism may play an important role in alleviateing chilling injury.4.In this study,a combined treatment with hot water and 1-MCP(HM)was applied to peach fruit to investigate its effect on the quality and antioxidant level during storage at room temperature(RT)and low temperature(LT).HM treatment is effective to slow fruit softening before day 5,increase soluble solid content(SSC)before day 3 and decrease respiration rate and ethylene production during RT storage.Meanwhile,HM treatment can reduce electrolyte leakage(EL)and suppress reactive oxygen species(ROS)accumulation by enhancing the activity and gene expression level of SOD,CAT,APX and GPX and the expression of PpaSODs,PpaCAT1,PpaAPX4 and PpaGPXs in the late stage of RT storage.During LT storage,HM treatment only maintains fruit firmness in the early stage,but it has no positive effect on delaying fruit ripening and even decreases SSC and TA content in the late stage.Moreover,long term cold storage causes higher EL and ROS level and induces the activity of antioxidant enzymes but not the expression of antioxidant genes in HM treated fruit,which indicate that HM treatment can only affect the antioxidant system at enzymatic level.In conclusion,HM treatment is more benefit for peach fruit stored at RT.