Endogenous GSH Participates In The Effects Of Exogenous Nitric Oxide On Photosynthetic Characteristics And Chloroplast Mechanism Of Cucumber Leaves Affected Under Low Temperature

Cucumber?Cucumis sativus L.?is an annual climbing or herb of the Cucurbitaceae with high cold sensitivity.It is widely cultivated in various parts of China.It often suffers from low-temperature damage during winter and spring cultivation in protected areas,which affects its growth,yield,and quality.Dehydration at low temperatures leads to damage to photosynthetic apparatus and plant membrane systems,inhibits the development of chloroplasts,promotes the accumulation of reactive oxygen species,resulting in disorders of metabolism and destruction of growth,etc.so it is of great significance to study the ability to enhance the low temperature tolerance of cucumber.Nitric oxide?NO?is not only a biologically active substance,but also a signaling molecule involved in many growth processes and stress responses.The appropriate concentration of NO is involved in the regulation of plant response to multiple abiotic stresses through various ways,such as salt damage,high temperature,low temperature,drought,etc.In this study,the soilless culture Jinyan No.4 cucumber seedlings was used as the test material,the photoperiod was set at 14 h/10 h,and the day and night temperature was25°C/20°C in a light incubator,and NO was applied to the foliar NO donor?SNP,Asia?.Sodium nitroferrocyanide),GSH synthetase inhibitor?BSO,butanamine phenylamine amine?,NADPH synthetase inhibitor?6-AN,6-aminoanthinylamine?,day and night temperatures dropped after 24 h at 10°C/6°C,the effects of exogenous NO on cell membrane permeability,gas exchange parameters,chlorophyll fluorescence parameters,and activities of antioxidant enzymes in chloroplasts and redox status of cucumber seedlings were studied 24 h after cold stress.Get the following conclusions:1.After 24 h of low temperature stress,compared with CK,water+SNP treatment significantly increased the relative water content and chlorophyll content of cucumber seedling leaves,significantly reduced the electrolyte leakage rate and malondialdehyde?MDA?content in leaves of cucumber seedlings,and treated with water and SNP.In contrast,BSO+SNP,6AN+SNP treatment significantly reduced the relative water content and chlorophyll content of cucumber leaves,while the MDA and electrolyte leakage rate increased significantly.The results indicated that GSH was involved in NO increase cucumber leaves relative water content at low temperature,improve water-holding capacity of seedlings,ensure normal water transport of plants;participate in the decline of membrane lipid peroxidation and cell membrane permeability,and degradation of chlorophyll,through the increase The content of various photosynthetic pigments in the leaves of the seedlings enhances the resistance to freezing,whereas the BSO+SNP,6AN+SNP treatment destroys the plant cell membranes,rendering the SNP ineffective.2.Compared with CK,water+SNP treatment significantly increased the net photosynthetic rate?Pn?,transpiration rate?Tr?,stomatal conductance?Gs?and maximum photochemical quantum yield?F_v/F_m?of cucumber seedlings compared with CK after 24 h.actual photochemical efficiency??PSII?,non-adjusted energy dissipated quantum yield Y?NO?,photochemical quenching coefficient?qP?,epitaxy and electron transport coefficient?ETR?,and a significant decrease in intercellular CO₂ concentration?Ci?and non-photochemical quenching coefficient?NPQ?;compared with water+SNP treatment,BSO+SNP,6AN+SNP treatment significantly reduced cucumber leaves Fv/Fm,?PSII,qP,ETR,Pn,Gs,Tr,and Y?NPQ?,Ci improved significantly.These results indicate that GSH participates in the regulation of physiological functions of PSII,improves the cold tolerance of cucumber leaves,and inhibits the decrease of photosynthetic activity of cucumber mesophyll cells,which fully indicates that GSH is necessary to participate in the maintenance of higher photosynthetic rate of NO in cucumber.3.After 24 h of low temperature stress,compared with CK,water+SNP treatment can maintain high fluorescence yield,so that the rapid chlorophyll fluorescence induction curve JIP phase gradually increased,while BSO+SNP,6AN+SNP treatment significantly reduced Effects of SNPs;Water+SNP Treatment of PSII Maximum Photochemical Efficiency??Po?in Leaves of Cucumber Seedlings,Energy Absorption of PSII Reaction Centers for Electron Transfer??Eo?,Capture of Excitons,Transfer of Electrons to Electron Transport Chain QA^-The probability of other downstream electron acceptors??o?and the fluorescence parameters related to the receptor side performance of the PSII reaction center include oxygen release complex?OEC?activity status(F_O-K),QA reducibility(F_K-J),QB(F_Q-I-I with rapid reduction)The ability to be reduced(F_J-I)and the ability to restore the slow-reduced PQ library(F_I-P)and the number of reactive centers per unit of light-receiving area?RC/CS?are significantly higher CK,but the maximum rate?M_o?of the fluorescence parameter QA associated with the shutdown of the reaction center and the relative variable fluorescence?V_J?of the J phase were significantly lower than CK;compared with the water+SNP treatment,BSO+SNP,6AN+SNP processing?Po,?Eo,?o,RC/CS,F_K-J,F_J-I,F_I-P,etc.Significantly decreased,while M_o and V_J significantly increased.4.After 24 h of low temperature stress,compared with CK,water+SNP treatment significantly increased the activities of GR,POD,APX,CAT,DHAR,and MDHAR in chloroplasts of cucumber,reduced the level of ROS,and promoted the absolute content of reduced antioxidants AsA and GSH.At the same time,maintaining a higher GSH/GSSG,AsA/DHA,NADPH/NADP⁺state,indicating that the regulation of GSH/GSSG,As A/DHA,NADPH/NADP⁺by exogenous NO is related to the participation of GSH,and exogenous NO affects low temperature AsA-GSH metabolic cycle of cucumber chloroplasts under stress,participate in mediating the balance of ROS,reduce the oxidative stress,thereby alleviating the damage of chilling stress on chloroplasts of cucumber;at the same time,it significantly reduces the content of H₂O₂ and O^-_2?,and BSO+SNP,6AN+SNP Treatment significantly reduced the effect of SNP.5.After 24 h of low temperature stress,compared with CK,water+SNP treatment significantly increased NO content and NOS specific activity of cucumber leaves;compared with water+SNP treatment,the effects of BSO+SNP and 6AN+SNP treatments were not significant.This shows that exogenous NO can reduce the content of oxygen free radicals in cucumber leaves.