Regulation Of Nitric Oxide On Photosynthetic Carbon Assimilation Mechanism In Cucumber Seedlings Under Low Temperature Stress

Horticultural facilities has become the agricultural advantage industry, FacilitiesHorticulture area of China has been the first place in the world, but in China facilityhorticulture development level is immature, less artificial greenhouse, facilities andequipment system is not perfect, leading to resist the ability to reduce the external stress.Studyon plant adapt to stress mechanism in facilities environment has important significance. Inthis study,’Jinyan4’ cucumber (Cucumis sativus L.) seedlings as experimental material, usingartificial sunlight greenhouse to cultivation of cucumber seedlings and artificial climate boxgreenhouse to low temperature treatment.Study on exogenous NO donor SNP on cucumberseedlings photosynthesis, carbohydrate metabolism, chlorophyll fluorescence, AsA-GSH,antioxidant enzymes and NO as a signaling molecule regulating related parts of the Calvineffect of gene expression under low temperature (10℃/6℃) stress. The main results are asfollows:1.We have studied the regulation function of nitric oxide(NO) on chlorophyllfluorescence and antioxidant enzyme activity of cucumber seedlings under low temperature(10℃/6℃)。The results showed that: NO donor SNP only significantly improved the Φ PS Ⅱ,POD and APX activity before low temperature treatment, but after the low temperature of24h,SNP increased the Φ PS Ⅱ, Fv/Fm, qP, NPQ, photochemical reactions of P share, improvedthe utilization rate of solar energy, reduced the non photochemical dissipation portions of Ex,improved the distribution of light energy imbalance, this trend had continued into the48h,while nitric oxide synthase (NOS) inhibitor L-NAME and nitric oxide scavenger PTIO canblock the effect of SNP. Low temperature after24h,48h, malondialdehyde (MDA) content ofeach treatment, conductivity values lower than the low temperature0h, SOD activityincreased, CAT activity decreased rapidly, POD firstly increased and then decreased, NOSinhibitor L-NAME and NO scavenger PTIO block SNP before low temperature and in lowtemperature treatment significantly induced the activity of antioxidant enzymes. It showedthat NO produced by the NOS path played an important role in the regulation of chlorophyllfluorescence and antioxidant enzyme activity increasing cold resistance in Cucumber, at thesame time in low temperature treatment the APX and POD play the main role of the H2O2regulation.2.Exogenous SNP can induced Nitric oxide(NO) production, and it can improvePn,Gs,Tr, Rubisco carboxylation rate and regeneration rate and initial Rubisco activity, totalactivity, reduce MDA production and accumulation, the conductivity decreases, the NOSinhibitor L-NAME and NO scavenger PTIO to block the effect of SNP on cucumber seedlingleaves under low temperature (10℃/6℃) stress. In addition, the expression of NO as the molecular signals that regulate the expression of Calvin cycle related genes Cytb6f、psaA、CHL、PRK、RCA、rbcS、FBPase、SBPase、RPE、FBP-aldolase、PGK，but downregulatedthe expression of rbcL, which can be explained in the NO plays an important role inimproving cold resistance in Cucumber by adjusting the expression of genes related tophotosynthesis and Calvin prompted redistribution of the light energy between photosystemⅠand Ⅱ.3.Effects of NO signaling molecules under low temperature stress on carbohydratemetabolism of cucumber seedlings and relative genes. The results showed that, sprayingexogenous SNP can improve the ratio of chlorophyll fluorescence parameters Fv/Fm underlow temperature stress. NO treatment could significantly reduced the content of MDA andconductivity values, the content of effective change of carbohydrate, sucrose, reducing sugar,promote the content of total soluble sugar, fructose and glucose content, induced the keyenzymes SPS, AI, SS in carbohydrate metabolism activity and starch accumulation. SNPexpression induced in cucumber leaves related genes of carbohydrate metabolism such asSUS, BAM, Invertase, UGDH, SUS2, SUS4, SPS1, SPS2, SUT2, SUT4, and down-regulatedthe expression of SUS1gene and RFS gene. Thus, NO through regulating the expression levelof chlorophyll fluorescence parameters, carbohydrate metabolism and related genes toimprove cucumber seedling acclimation to low temperature stress, cucumber seedlings underlow temperature to avoid causing damage caused in the processes, are important to thecucumber cooling mechanism.4.Exogenous NO donor SNP improved the peroxide ascorbic acid enzymes(APX),glutathione reductase (GR), dehydroascorbate reductase (DHAR) and Monodehydroascorbatereductase (MDAR) activity, induced H2O2and O2.-, promote reduced ascorbic acid (ASA),glutathione (GSH) content, reduced glutathione (GSSG) content and dehydroascorbic acid(DHA)of ASA-GSH cycle on cucumber seedlings under low temperature (10℃/6℃),adjustASA/DHA and GSH/GSSG ratio, improved the NADPH and the activity of NADP+, reducethe conductivity, MDA content, NOS inhibitor L-NAME,NO scavenger PTIO,NADPHoxidase inhibitor DPI and H2O2scavenger DMTU inhibited SNP regulation under lowtemperature stress. It can be concluded that the exogenous NO involved in the ASA-GSHcycle on cucumber leaves under low temperature stress adjustment, removal of H2O2,alleviate the oxidative damage of low temperature stress on cucumber, improve coldresistance of plant. Besides, it indicated that ROS is involved in the NO induced coldresistance of cucumber seedlings.