Soybean Physiological And Biochemical Characteristics And DNA Methylation Variation Under Cadmium Stress

With the rapid development of modern industry, cadmium pollution has become a worldwide environmental problem. Cadmium toxicity, easy to accumulate, difficult to degrade, plant growth with serious harm. Soybean as the main food crops, cadmium pollution would seriously affect their growth and yield. The research on the response mechanism of soybean to Cd stress has great significance to the cultivation of cadmium tolerant soybean varieties. Taking soybean as material, using nutrient solution hydroponic method, treatment of soybean seedlings with different concentrations of Cd Cl2(0.5mg/ L, 5mg/ L, 15mg/ L), to study the effects of cadmium stress on growth, physiological and biochemical and genomic DNA methylation of soybean, to explore the relationship between DNA methylation and soybean response to Cd stress. The results are as follows:1. Cadmium Stress can cause toxic symptoms of soybean, as the stress time was prolonged, the toxic effect was spreading from the base to the top, and processing the higher the concentration the more serious poisoning, mainly for soybean leaves turn yellow, deformity; stem and leaf veins showing symptoms of toxic red-brown, plant small, slender stalk, withered and even death. Low concentration of Cd Cl2(0.5 mg/L) on soybean plant height, root length, underground fresh weight, underground dry weight low impact, medium concentration(5 mg/L) and high concentration(15 mg/L) was significantly inhibitory effect on growth.2. Cd stress resulted in the accumulation of superoxide anion, hydrogen peroxide, and MDA content, 0.5mg/L of Cd Cl2 has a low impact on the growth of soybean, 5mg/L and 15mg/L of Cd Cl2 caused soybean plants oxidative damage, soybean through the increase of 4 kinds of antioxidant enzyme activities(superoxide dismutase, catalase, peroxidase, ascorbate peroxidase) to resist cadmium stress produced by the reactive oxygen free radicals damage to the body. Changes of chlorophyll content in Soybean under Cd Stress, 0.5 mg / L Cd stress on the chlorophyll content of less impact, 5 mg / L and 15 mg / L Cd stress resulted in a significant decrease of chlorophyll content.3. MSAP methylation of soybean genomic DNA was analyzed by using 42 pairs of primers,The results showed that cadmium stress leads soybean genomic DNA methylation level and pattern has changed, the overall level of DNA methylation and methylation polymorphism of soybean genome were increased, and it was positively correlated with the concentration. The total methylation rate of Control(CK)、S1(0.5 mg/L Cd Cl2) 、S2(5 mg/LCd Cl2)、S3(15 mg/L Cd Cl2) was 27.92 %、29.78 %、33.2 %、35.79 %, soybean genomic DNA methylation polymorphism rate were 14.46 %、16.57 %、18.15 %.Changes in methylation patterns of cadmium stress mainly novo methylation based.4. The homology comparison of the 30 methylation differential fragment sequences, the results showed that there were 2 different fragments that did not find the homologous sequences, 28 differential fragments showed high homology with soybean genome, 15 of them are homologous with functional protein, 9 of them are unknown functional protein, 4 of them did not find the homologous protein. These functional proteins are widely involved in plant abiotic stress response process.