Study On The Injury Mechanism Of High Concentration Of CO₂ To Actinidia Arguta

Actinidia arguta is a type of respiration jump fruit,which is easy to soften and corrupt after harvest,and has the characteristics of poor storage,production application in low temperature combined with gas storage,the method has the advantages of economy,convenience and no residue,but the method also has some disadvantages if the storage and use of gas in the process of packaging oxygen transmission effect is poorer or fruit respiration intensity bigger,make the CO₂is too much inside the packaging is not discharge in time,change the storage gas composition,for a long time,it will cause fruit CO₂damage and fruit quality decline.At present,most of the researches on air-controlled storage of soft date Actinidia arguta focus on the quality changes caused by different packaging materials,gas components or combined with other fresh-keeping methods,and there are few researches on the changes of the fruit damaged by CO₂in the adverse packaging effect.In this paper,the micro-environment air conditioning box pasted with different air-regulated element is used as the carrier,the formation of low CO₂（<5%）content（>5%）and high CO₂content in the storage environment,not to paste the air-regulated element（air）as the control group,transcriptome sequencing was used to explore the changes of differential gene expression and important metabolic pathways enriched by differential genes in Actinidia arguta at the end of storage under high CO₂stress,and the indexes of quality,flavor,cell wall and antioxidant system during 0～60 days of storage were determined.The experimental results are as follows:1.CK,CO₂-L and CO₂-H in the stable content of gas in the chamber of CK:O₂:20.9%,CO₂:0.03%;CO₂-L:O₂:17.00%～20.92%,CO₂:1.63%～2.78%;CO₂-H:O₂:11.22%～15.55%,CO₂:9.00%～11.93%.Compared with CK and CO₂-L treatment groups,CO₂-H treatment group accelerated the occurrence of flesh browning,and flesh browning degree was 3.80 at the end of storage,which was significantly higher than other groups（P<0.05）.The weight percentage and TSS content changed little,and thepericarp strength decreased,but TA content increased slightly at the end of storage.Fruit color change was obvious,L*,a*and b*values increased gradually at the end of storage,and chlorophyll a and chlorophyll b contents decreased significantly,which was not conducive to maintaining fruit skin color and serious chlorosis of flesh.Electronic nose analysis showed that the inflection point of fruit freshness was 15 days earlier than that of the control group,and the relative content of 2-hexenal,the flavor substance of fresh grass,in the volatile components decreased,while the relative content of ethanol increased,and the odor was obvious.In the CO₂-H treatment group,the damage of Actinidia arguta fruit was obvious,and the quality and flavor decreased rapidly.2.Transcriptome sequencing was performed on Actinidia arguta stored for 60 days.A total of 2855 differentially expressed genes were identified in CO₂-L and CK treatment groups,among which 103 genes were significantly up-regulated and 77 genes were significantly down-regulated.A total of 9495 differentially expressed genes were identified in CO₂-H and CK treatment groups,of which 102 genes were significantly up-regulated and 86 genes were significantly down-regulated.A total of 12461 differentially expressed genes were identified in CO₂-H and CO₂-L treatment groups,among which 182 genes were significantly up-regulated and 77 genes were significantly down-regulated.KEGG analysis showed that the differentially expressed genes were mainly concentrated in the pathways of plant hormone conduction and metabolism,energy metabolism and sugar metabolism,and there were also many differentially expressed genes in active reactive oxygen metabolism pathways.By analyzing the differently-expressed genes in the above metabolic pathways,the expression levels of MPK6 and PR1 genes increased,and the expression abundance of PK PDC ADH in fruit tissues increased and PL,PME,PG,β-Glu,β-amylase and starch synthase were down-regulated in Actinidia arguta under CO₂stress.The gene expression of GSR,GST,CAT,POD,CHS L-ascorbate oxidase decreased,while the gene expression of PLC increased,indicating that the tissue,glycolytic cell wall and reactive oxygen metabolism were affected under CO₂stress,and the antioxidant capacity was weakened,which had negative effects on the body.3.High concentrations of CO₂lead to abnormal cell wall metabolism,The softening results of Actinidia arguta under CK,CO₂-L,CO₂-H treatment showed that,compared with the other two groups,CO₂-H treatment group can maintain higher content of cell polysaccharide propectin,cellulose,hemicellulose,inhibit the conversion of propectin to water-soluble pectin,and inhibit softening enzyme activity.When 60 days PG,Cx,β-Gal and amylase activity were 97.81μg/（h·g）,91.52μg/（h·g）,50.50μmol/（h·g）and 1.42 mg/（min·g）;tissue collapse and cell damage were obvious in CO₂-H treatment group at the end of storage.These results indicated that high concentration of CO₂stress affected the cell wall metabolism of fruits,reduced the activity of cell wall degradation enzymes,and damaged the cell structure and tissue,while the CO₂-L treatment group could maintain the cell structure better,and did not affect the fruit ripening and softening process.4.High concentration of CO₂leads to abnormal metabolism of antioxidant system.In order to determine the changes of antioxidant system of Actinidia arguta under high CO₂stress,the indexes of reactive oxygen metabolism,ascorbic acid-glutathione circulation and antioxidant substances were determined during storage.The results showed that CO₂-H treatment caused a large accumulation of O₂.^-and H₂O₂in fruits,and the content of MDA increased rapidly at the later stage of storage,the relative conductivity,which indicates the permeability of cells,also increased significantly;the activities of SOD,CAT,POD and APX enzymes in the free radical scavenging enzyme system decreased,ascorbic acid-glutathione loop GSSG,reduce GSH content,at the same time can remove free radicals in organization directly As A and flavonoids content is lower than other treatment group,DPPH free radical clearance rate and total antioxidant capacity in the late storage for minimum 3 group.The results indicated that the Actinidia arguta of soft date stored for a long time under high concentration of CO₂stress had a large accumulation of free radicals,damage of antioxidant system,aggravation of membrane lipid peroxidation,and weakened resistance to stress and quality of fruit.