Molecular Mechanism Of Cold Pepper Damage Based On Membrane Lipid Metabolism And Its Control Of Chilling Injury

Green pepper(Capsicum frutescens Linn.)was originated from tropical and subtropical regions of Central and South America,which belongs to cold sensitive plants.The low temperature during postharvest storage and transportation will cause chilling damage to green pepper’s fruit,and the quality of fruit after harvest is reduced or even corrupt,which has seriously reduced the value of commodities and brought huge economic losses to the planting and processing industries of green pepper.Low temperature storage is an effective postharvest control technique to keep the freshness of vegetables by inhibiting respiration.This technique also has a good effect on storage of green pepper.Green pepper is a kind of cold-sensitive vegetable.In the process of low temperature storage,the unsuitable temperature will lead to chilling injury,the quality of green pepper will become worse,and the shelf life will be shortened.In this experiment,we systematically monitored the changes in primary physiological parameters of green pepper stored at different temperatures(0℃,4℃,7℃,10℃),and the most sensitive temperature of chilling injury was determined.The mechanism of chilling injury in green pepper was studied by membrane lipigraphy and histomorphological observation,and the PLD activity and related gene expression results were analyzed.By means of steaming different density(0μmol/L,1μmol/L,10μmol/L,100μmol/L)MeJA on green pepper,the experiiment researched primary physiological parameters about chilling injury of green pepper on 4℃,and the parameters include:relative conductivity,MDA and proline.Fatherore,the experiment analyzed the effect of MeJA on the changes of membrane lipid components and explored the regulatory techniques for reducing the chilling injury of green pepper.The main findings are as follows:1.The respiration intensity of green pepper is inhibited on low temperature.The degradation rate of chlorophyll,ascorbic acid and soluble solids of green pepper stored at 4℃ is rapid and the quality decreases rapidly.However,the membrane permeability,malondialdehyde and proline content increased significantly compared with the other three groups,the activity of trox was lower than that of the other three groups,and the membrane damage was serious.While the chilling injury index of green pepper stored at 10℃ was 0%,and no chilling injury occurred.2.By means of histomorphological observation,fresh green peppers(newly harvested)look bright,and had a clear line between the exocarp and mesocarp;the arrangement of pulp is clear.For fresh samples,the cell size was homogeneous,and the whole cellular profile was clearly visible;the chloroplasts attached tightly to the cell walls due to the pressure of the vacuole,and chloroplasts is shuttle-like.After the end of the storage period,it was found that stored green peppers at 10℃ apparently showed slight dehydration and turbidity,the peel line and pulp tissue were slightly blurred,the cells became uneven in size,slightly corrugated,the chloroplast-dependent cell walls were not compact,and they began to expand and become round.The green peppers stored at 4℃ appeared large cold lesions,and the peel lines and pulp tissue were completely blurred.The cells shrank significantly and the tissues were severely damaged.The chloroplasts and the cell walls were completely separated,and the chloroplasts showed a spindle-like shape,indicating that the organelles were severely damagedWe identified approximately 100 molecular species of polarlipids with different carbon numbers in pepper samples.Among the 100 lipid molecular species,there were two categories of galactolipids,monogalactosyl diacylglycerol(MGDG)and digalactosyldiacylglycerol(DGDG),six categories of phospholipids,phosphatidic acid(PA),phosphatidylcholine(PC),phosphatidylethanolamine(PE),phosphatidylglycerol(PG),phosphatidylinositol(PI)and phosphatidylserine(PS)and three categories of lysophosphatides,lysophosphatidylcholine(LPC),lyso-phosphatidylethanolamine(LPE)and lysophosphatidylglycerol(LPG).At 4℃,PA and three phospholipids increased significantly,and the total lipid content of the membrane decreased.The activity of PLD increased during storage.The activity of PLD in green peppers stored at 4℃ reached the maximum on the 20 th day,which was significantly higher than that of the other three groups,and its gene expression was also in an upward trend.3.The study found that methyl jasmonate immersion can significantly inhibit the increase of membrane permeability,reduce the accumulation of MDA,and reduce the content of proline in the tissue,reducing the incidence of chilling pepper.Through the analysis of the phospholipids,it was found that the content of total phospholipids in the green pepper treated with methyl jasmonate was higher than that in the control group,and the PA content was lower than that in the control group.The decrease of PI,PC,PG content was also lower than that of the control group.The PLD activity of the green pepper treated with methyl jasmonate was lower than that of the control group,and gene expression was also suppressed.