Difference Of Cadmium Enrichment Characteristics And Cadmium Related Genes Expression Between Two Varieties Of Ryegrass

With the continuous development of mine and the accumulation of tailings,the rapid development of transportation and industry and the abuse of pesticide and fertilizer,the problem of soil Cd pollution is becoming more and more serious.Therefore,the pollution caused by the heavy metal Cd to the soil environment has became a noticeable problem.As a new environmental treatment technology,phytoremediation is one of the main methods to treat and repair the heavy metal Cd pollution in soil.Phytoremediation technology is suitable for large scale Cd contaminated soil,which has great potential and can beautify the environment,and has high practical significance in repairing and managing Cd contaminated soil.Ryegrass（Lolium multiflorum L.）is a forage grass,with fast growth,strong tillering regeneration capacity,high yield,cold and drought tolerance and other characteristics.In addition,it could accumulated heavy metals and has a strong resistance in heavy metals contaminated soil,but also can survive and even grow in heavy metals polluted and severely polluted tailings.The pot experiment were carried out to investigate the influence of different Cd levels(0,75,150,300 and 600 mg·kg^-1)on biomass,activities of antioxidant enzymes,concentrations and accumulation of Cd in two varieties of ryegrass（included Bond and Abode）.Moreover,the different expression of Cd related genes in roots,stem and leaves of ryegrass were also detected by the qRT-PCR analysis techniques.It aims to clear that genes with the highest level of gene expression and better varieties in Cd absorb and translocation,and provide data for breeding cadmium tolerant crop varieties or cadmium hyperaccumulator plants through genetic engineering.The main results are summarized as follows:（1）Root dry weights in two varieties of ryegrass and shoot,plant dry weights in Abode increased at first and then decreased with the increasing Cd levels in soils.When exposed to 75mg·kg^-1 Cd,shoot and plant dry weights in Abode reached the maximum value(10.93 g·pot^-1 and12.03 g·pot^-1),which increased by 11.1%and 10.7%compared to the control,respectively.Compared with two varieties of ryegrass,shoot dry weight and plant dry weight of Abode were higher than that of bond under 75-600 mg·kg^-11 Cd stress.（2）The activities of SOD and CAT in shoot and roots and activities of POD in roots of two varieties of ryegrass increased at first and then decreased with the increasing Cd levels in soil.With increasing Cd levels in soil,shoot MDA content in ryegrass was increased.The increase of shoot MDA content in Bond variety was greater than that in Abode variety.Highest root MDA content in ryegrass was found at 75 mg·kg^-1 Cd,which increased by 81.5%（bond）and 111.1%（Arbor）compared to the control,respectively.Pn,Gs and Tr in the leaves of two ryegrass varieties increased at first and then decreased with the with the increasing Cd levels in soil.（3）The content of Cd in the shoot and root of two ryegrass varieties increased with the increasing Cd levels in soil.When exposed to 75 mg·kg^-1 Cd,the Cd content of the two ryegrass varieties reached the critical value of Cd hyperaccumulator(100 mg·kg^-1),which was 111.19mg·kg^-1（Bond）,133.69 mg·kg^-1（Abode）.The content of Cd in shoot and root,and the accumulation of Cd in shoot,root and total plant were higher than that of Bond.（4）The root of ryegrass has higher enrichment ability to Cd.The Cd bioconcentration coefficient of the shoot and root of ryegrass is greater than 1,and the Cd bioconcentration coefficient in the shoot increased gradually with the increasing Cd levels in soil,the root Cd bioconcentration coefficients also reached the maximum value under the maximum Cd(600 mg·kg^-1)stress level.With the increasing Cd levels in soil,the transport coefficient of Cd showed an upward trend.Comparing the Cd content and accumulation,the Cd bioconcentration coefficients and the Cd translocation coefficient of two ryegrass varieties,Abode’s enrichment ability to Cd was higher than that of Bond..（5）The main Cd chemical form in the shoot of two ryegrass varieties was F-NaCl,which accounted for the 57.8%-79.4%of the total extraction state,and followed by F-W and F-HAC.The soil of two varieties of ryegrass was mainly EXC-Cd,and Cd concentration in the shoot and root of two ryegrass varieties was significantly positively correlated with the EXC-Cd content in rhizosphere soil（p<0.01）.Moreover,the FDC of EXC-Cd increased from 51.4%to 83.3%under Cd stress.The content of EXC-CD in the soil of Abode was higher than that of Bond,which was consistent with Cd concentration in Abode higher than that of bond.（6）The IRT,MT,OAS family genes and the Nramp2 gene are the major genes associated with Cd.The expression level of 4 gene families showed single or double peak variation trend when exposed to Cd stress,and the highest value was reached at 75 or 150 mg·kg^-1 Cd level.The expression level of 4 gene families in leaves was significantly higher than that in roots and stems.The concentration of Cd in Abode is greater than that of Bond.It may be related to the higher expression of Cd absorption gene in the root of Abode,but the expression of gene in leaves and stems are lower,which indicates that the transport effect is lower than that of Bond,but the accumulation of Cd in the root of Abode is higher,so the upper part of the ground still has advantages.Comprehensive comparison,Abode has advantages in restoring soil pollution.The expression of Cd tolerance and transportion genes in root and stem can be strengthened to improve the ability of tolerance and transportion of Cd in ryegrass.