The Relationship Of DNA Methylation And Stress Resistance In Cucumber Seedlings Under Low Temperature

Recently, DNA methylation has been one of the hot research. Many studies have showedthat external adverse environmental conditions such as drought, salinity, cold, heavy metalsand other abiotic stress can induce plant genomic DNA methylation level and state (halfmethylation, the methylation, demethylation) get changed, which can affect the expression ofplant gene and the activity of transposons, then regulate the genetic information, and createfavorable conditions for plant to adapt to the adverse environment. And after the stress, DNAmethylation was restored to the level before the stress, avoiding the waste of energy and geneexpression activity which was unnecessary.In order to study the mechanism between cold resistance of cucumber DNA methylationand low temperature stress, we started our work from two sides: one was the correlations ofDNA methylation with the growth and development of cucumber, the photosynthetic functionof regulating and he membrane lipid peroxidation of plants. The other was the SNPpretreatment to the donor of NO to reduce variation of DNA methylation in CucumberSeedlings under low temperature stress, to reveal the mechanism of nitric oxide release stress,and lay the foundation for using methylation differential gene. According the experiment, wedraw the following conclusions:1. After5-azaC treatment, cucumber seeds were obviously inhibited effect on thegermination, and the growth of cucumber seedlings was indirectly affected later.Moreover, the germination, indicators of early growth, morphological index andchlorophyll content were lower than the control, and a significant difference (P<0.05).2. Under low temperature and weak light,500-800μmol/L5-azaC treatment to cucumberseeds had decreased significantly the cell membrane permeability and the content ofMDA of seedlings(P<0.05), increasing the leaf Pn, Gs, Tr and Ci, promoting Fv/Fm,ΦPSII, ETR and qP, and also reducing the NPQ and Y(NO).3. At the low temperature of24h and48h with500~800μmol/L5-azaC the MDA content inseedling leaves was significantly decrease with CK (P<0.05), the activities of antioxidantenzymes SOD, CAT, APX and GR was increased, the production and accumulation ofreactive oxygen species (H2O2and O2-) was decreased under low temperature and weaklight stress; but with the concentration increased,5-azaC with1000~5000μmol/L causedthe leaf membrane in cucumber lipid peroxidation, and the antioxidant enzyme activitywere significantly reduced, finally resulted in oxidative hurts on the plants.4. Before the low temperature, compared with the control the level of DNA methylation ofcucumber seedling leaves was significantly reduced (P<0.05), decreased by22.06%after12h by spraying NO donor SNP. This indicated that the SNP pretreatment can reduce thelevel of DNA methylation of cucumber seedling leaves. In terms of control, DNA methylation level of cucumber leaves was gradually decreased after6h and24h lowtemperature treatment, while the level of DNA methylation of the SNP treatment showelevated (6h) before falling trend (24h) compared with0h low temperature. After6htreatment of low temperature, compared with the control the level of DNA methylationwas significantly increased by5.65%(P<0.05). Therefore, the change of the status ofgenomic DNAmethylation was involved in the process of NO relieve cold stress.