Study On The Mechanisms And Regulation Measures Of Chilling Injury In Green Pepper Fruit Under Low Temperature Stress Based On Membrane Lipid Metabolism

Green pepper(Capsicum annuum),solanaceae capsicum,also known as pepper,bell pepper,which is rich in vitamin C and moisture.Green peppers are sensitive to low temperature because they are native to the tropics.Chilling injury occurs when the storage environment is below 7℃.The main manifestations are the sunken surface of the peel,calyx discoloration,water loss and nutrients,etc.,which seriously affect the commercial value of green peppers.It has been reported that chilling injury is closely related to changes in cell membrane composition,so it is of great scientific significance to investigate the effect of low temperature on membrane lipid metabolism of green pepper and the regulation of chilling injury.In this test,the components of membrane lipids,fatty acid content,proline content,cell membrane permeability,membrane lipid peroxidation product MDA content,and membrane lipid metabolism key enzymes activity and their gene expression under low temperature stress were analyzed.The change in expression explained the occurrence of chilling injury in green pepper under low temperature stress from the perspective of membrane lipid metabolism,and based on this,a transcription factor NAC100 that interacted with the key enzyme gene PLDα1 for membrane lipid metabolism was screened.Adopting salicylic acid treatment to control chilling injury of green pepper fruits under low temperature stress provides theoretical basis and technical support for low temperature storage and transportation of postharvest green pepper.The findings are as follows:1.Two types of glycolipids: MGDG and DGDG,six types of phospholipids: PA,PC,PE,PI,PS,and PG,respectively,and three types of lysophospholipids: LPC,LPE,and LPG were detected in the membrane lipid components of green pepper fruits.The main fatty acid components include linoleic acid,linolenic acid,stearic acid,and palmitic acid.We found that the content of PI,PC,PE and MGDG decreased in green pepper under low temperature stress,the content of PA,LPC and DGDG level increased,the content of linolenic acid,linoleic acid decreased,the content of stearic acid increased,membrane lipid unsaturated index decreased,and the activity of PLD,PLA1,LOX increased.The results of real-time quantitative PCR test showed that PLA1 family genes PLA1β1,PLA1γ2,PLD family genes PLDα1,PLDα4,and PLDβ1 had obvious responses to low temperature stress.At the same time,the relative conductivity and MDA content increased significantly,and proline accumulated significantly.It is believed that low temperature stress activated membrane lipid metabolism-related enzymes and gene expression,accelerated membrane lipid degradation,resulting indamage to cell membrane structure and function.2.Salicylic acid treatment can increase the activity of antioxidant enzyme such as superoxide dismutase(SOD),peroxidase(POD)and catalase(CAT)in green pepper fruits,and reduce superoxide anion radical(O2﹣)generation rate and hydrogen peroxide(H2O2)content.Salicylic acid treatment affected As A-GSH cycle and regulated the activities of related enzymes ascorbate peroxidase(APX)and glutathione reductase(GR),and maintained high level of As A and GSH,which can effectively inhibit the increase of chilling injury index in green pepper fruits.Salicylic acid treatment inhibited the increase of PA and LPC content and the degradation of PC and PE,kept the green pepper fruit with higher linoleic acid and linolenic acid content,reduced the increase of stearic acid,and maintained a higher film lipid Saturation index.At the same time,salicylic acid treatment inhibited the activity and gene expression of PLD,PLA1,and LOX,further delayed the degradation of membrane lipids and the reaction of membrane lipid peroxidation,reduced the accumulation of membrane lipid peroxidation products and the increase of relative conductivity.A yeast one-hybrid technique was used to screen the transcription factor NAC100 that interacts with the key enzyme gene PLDα1for membrane lipid metabolism.It was found that salicylic acid treatment can reduce the expression of the transcription factor NAC100.It is thought that salicylic acid treatment may regulate PLD activity by regulating the NAC transcription factor NAC100 gene encoding PLD.