Effect Of Cd-induced DNA Damage And DNA Repair System On Arabidopsis Seedlings

DNA damage assay based on RAPD,ELISA-based global methylation analysis,and expression analysis of genes related to DNA damage,repair,and cell cycle were used to study genomic DNA damage and stress response of DNA repair and cell cycle in Arabidopsis plantlets exposed to Cd for 5 d.Sensitive indicators which could be sensitive biomarkers applied to early diagnosis and risk assessment of genotoxic effects of Cd pollution in ecotoxicology was also screened in this study.The results were as follows:1.After stress treatment for 5 days by different concentrations(0?0.125?0.25?1.0 and 2.5 mg·L-1)Cd,the number of leaves which kept constantly 2 of them was detected not a sensitive indicator for Cd stress.Instead,the root growth of the plant was more sensitive.The root length of seedlings in low does groups was significantly promoted(P<0.05),while ones in high concentration groups was significantly reduced(P<0.01 or P<0.05).2.After stress treatment for 5 days by different concentrations(0?0.125?0.25?1.0 ? 2.5 mg·L-1)Cd,DNA damage was increased significantly with the increased Cd dose,which showed a positive dose-dependent effect.3.After Cd stress for 5 days by different concentrations(0?0.125?0.25?1.0 ?2.5 mg·L-1)Cd,the global methylation rate was increased significantly with the increased Cd dose(P<0.01 or P<0.05).4.Stressed under Cd(0?0.125?0.25?1.0 ? 2.5 mg·L-1)for 5 d,the relative expression of cell division genes(PCNA1 and PCNA2),MMR genes(MLH1,MSH2 and MSH6),homologous recombination genes(RAD51 and BRCA1),and non-homologous end joining genes(KU70,MRE11 and GR1)were followed an obvious inverted U-shaped dose-response effect of Cd exposures and a MMR>HR>NHEJ sensitivity rule.The results showed that low-dose Cd result in easy-repaired mismatch damage,and high-dose Cd stress cause difficult-repaired chromoso me damage and double strand break,which could accumulate and aggravate with the stress duration.In addition,the expression of MSH6 and MLH1 is the most sensitive indicator which could be a sensitive biomarker,applied to early diagnosis and risk assessment of genotoxic effects of Cd pollution in ecotoxicology.