Ethylene Regulates Lipid Metabolism To Aleviate Chilling Injury Browning In Peach Fruits

Peach fruit is a typical cold-sensitive fruit.It is easy to cause chilling injury internal browning after harvesting.The phytohormone ethylene is closely related to fruit ripening and cold resistance,but its role in peach fruit chilling is still controversial.In this study,the fruit of the hard peach’Xiazhimeng’ was selected as the experimental material,which was treated with ethylene(ETH,100μL.L-1,24h,20℃)(CETH,after 14d storage at 0℃,14μL.L-1 ethylene was continuously fumigated).The control group(CK)fruit was not treated at all,and all the fruits were stored in a cold storage at 0℃ for 59 days and then transferred to a 20℃ 2d simulated shelf life.The effects of ethylene treatment on the internal browning-related metabolism,ROS,lipid components and key genes involved in sphingolipid synthesis of peach fruit were studied.1.This study found that ETH treatment can significantly reduce the internal browning of peach fruit,while down-regulating the peach fruit firmness and respiration rate;it has no effect on relative conductivity and H2O2 level,and significantly reduces the shelf life of 59+2d malondialdehyde(MDA).PPO and POD activities and total phenolic content had no effect.CETH treatment significantly reduced internal browning of peach fruit,but had no significant effect on peach fruit firmness and ethylene release,but significantly inhibited respiratory rate;inhibited relative conductivity increase,controlled H2O2 level,decreased MDA accumulation;had no effect on PPO activity,However,a significant reduction in POD activity results in an accumulation of total phenolic content.Conclusion,both treatments can reduce chilling injury of peach fruits,but CETH treatment is more effective.Both treatments can reduce the damage of cell membrane by reducing the accumulation of MDA,while CETH treatment can promote the accumulation of phenols by reducing the relative conductivity,reducing the accumulation of H2O2 and MDA.2.In order to further elucidate the lipid-regulating effect of ethylene on peach fruit under chilling injury,we used high-resolution liquid chromatography-mass spectrometry to detect lipid molecules in shelf-preserved peach fruit,including 16 major lipid components and more than 300 lipid molecules.There was no difference between the total lipid content of ETH treatment and the CK,while the total TG content of CETH treatment was significantly reduced.In the comparison of different lipid molecules(treatment group(ETH,CETH)and control group CK),the lipid molecules with different ETH changes(up 22,decrease 7)were equivalent to the total number of CETH(rise 26,decrease 5).Two groups of glycerol lipid molecules that are raised together include TG(4:0/9:0/16:0),TG(26:0/18:0/16:2),and DG(19:0/15).:2),PC(18:4/19:5),PE(19:1),PEt(6:0/16:0).During the ripening process of peach,TG and DGDG decreased,and MGDG increased.The more abundant TG(4:0/11:0/16:0,decreass)and DG(17:4/19:4,rise)changed significantly in CETH treatment,but had no significant effect in ETH;The lactose lipid molecule DGDG(16:0/18:3)was significantly increased in both ETH and CETH treatments.These results indicate that ETH,especially CETH,has significant regulatory effects on TG,DG,DGDG,and MGDG in chilling injury peach fruit.In addition,ETH and CETH add up to six kinds of sphingolipids,including CerP(d 12:0/24:5),CerP(d14:0),CerP(d21:1),Cer(d32:0),Cer(D34:0),Cer(d35:2+O);the sphingolipid molecule CerG3(d16:0)has the highest content in the detected sphingolipid molecules(0.24μmol.g-1 Fw),and CETH is 9.6%higher than CK.But there is no significant difference in ETH.3.Since the synthesis of sphingolipid Cer is further divided into two synthetic pathways of GIPC and CerG.To further understand the mechanism of sphingolipid synthesis,we investigated the expression levels of key enzyme genes PpIPCS1,PpIPCS3,PpΔ4SLD(GIPC pathway)and PpGCS,PpΔ8SLD(CerG pathway)during sphingolipid synthesis.ETH treatment can increase the relative expression of PpIPCS1,PpIPCS3 and PpΔ4SLD genes;the relative expression of PpGCS and PpΔ8SLD is also increased by ETH,resulting in a significant increase in CerGl(d18:1/12:0)content.CETH treatment inhibited the relative expression of PpIPCS1,PpIPCS3 and PpΔ4SLD genes,and increased the relative expression of PpGCS and PpΔ8SLD,which significantly increased the content of CerG3(d1 6:0).These results suggest that the CerG pathway may be one of the key regulatory steps for ethylene to alleviate chilling injury.Different pathways for ethylene to differentially regulate sphingolipid synthesis may be associated with different degrees of chilling browning.Through subcellular localization analysis,PpIPCS1 was found to be localized in the Golgi apparatus,and PpGCS was localized in the plasma membrane.In summary,exogenous ethylene treatment can inhibit POD activity,increase the accumulation of polyphenols,control H2O2 levels and MDA content,scavenge reactive oxygen species(ROS),and regulate storage lipid metabolism,especially sphingolipid synthesis.Exogenous ethylene treatment can regulate the key enzyme genes in the process of sphingolipid synthesis,maintain the proportion of sphingolipid synthesis in different ways,enhance the stability of the membrane,and thus slow down the chilling injury browning of peach fruit.In summary,both treatments can alleviate the chilling injury of peach fruit,but the effect of CETH treatment is more obvious.