Genotypic Differences Of Cd Accumulation And Molecular Mechanisms Of Cd Enriched Plants

In recent years,with the large-scale and intensive development of urbanization,industrialization and agricultural,pollutants are introduced into soils through industrial emission,sewage irrigation,fertilizer contaminated and the use of urban sludge,etc.,which makes the soil cadmium（Cd）content increasing,and more attention has been paid to control and repair soil Cd pollution.Phytoremediation technology,as a new green biotechnology,is considered to be the best choice to repair heavy metal contaminated soil because of its simple operation and low cost of remediation.Ryegrass（Lolium multiflorum L.）,annual or perennial herb,with high biomass,rapid growth,strong tillering and can quickly covered the ground,which makes it have strong accumulation capability to heavy metals Cd;Brassica juncea L.,belongs to the family of cruciferae Brassica,with short growth cycle and high aboveground biomass,it can enrich many heavy metals and has great application potential in phytoremediation;Alfalfa（Medicago Sativa L.）,perennial leguminous grass,is a kind of economic crop yield.It also has high enrichment of Cd.Now,there are few reports on comparing the Cd absorption capacity of ryegrass,alfalfa and Brassica juncea L.,and rarely reports was found about the difference expression levels of Cd tolerance related genes in the three species of Cd-enrichment plants.The pot experiments 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 ryegrass（included Bangde and Abode）,Brassica juncea L.and alfalfa.Moreover,the expression levels of Cd tolerance related genes were also detected by the RT-PCR analysis techniques,which can explain why they enrich heavy metals from molecular mechanism level,and so as to provide theoretical basis for the prevention and remediation of Cd-contaminated soils.The main results are summarized as follows:（1）Shoot dry weights and the total dry weights in Bangde and Abode increased at first and then decreased with increasing levels of soil Cd.The highest shoot dry weights of Bangde and Abode were observed at Cd levels of 75 mg·kg^-1and 150 mg·kg^-1,increased by 10.06% and 25.84% compared to the control,respectively.Under various treatments,the shoot dry weights of Bangde and Abode were much higher than those of Brassica juncea L.and alfalfa.（2）With the increase of soil Cd levels,the photosynthetic system parameters in three species of plants have been significantly suppressed.The content of MDA in shoot and root of three species decreased with the increase of Cd levels.when the Cd level was 600 mg·kg^-1,the root MDA content of ryegrass（included Bangde and Abode）,alfalfa and Brassica juncea L.were significantly lower than contro（P<0.05）,decreased by 49.62%,44.44%,40.74% and 51.68% respectively compared to control.The activities of SOD and POD in leaf and root of three species of plants mainly decreased first,then increased with increasing Cd levels,while CAT activity of leaf and root in three species of plants decreased.（3）Ryegrass（included Bangde and Abode）,alfalfa and Brassica juncea L.all had strong ability of enriching Cd,and Cd concentration of root was higher than that of shoot.The shoot Cd concentration of ryegrass（included Bangde and Abode）were 171.827 mg·kg^-1 and 169.122 mg·kg^-1 in 150 mg·kg^-1 Cd level,while that of alfalfa and Brassica juncea L.were 356.463 mg·kg^-1 and 308.735 mg·kg^-1 in 75 mg·kg^-1 Cd level,all higher than the critical value of hyperaccumulation plants(100 mg·kg^-1 Cd),showed extremely strong potential enrichment.（4）The highest removal rate of Abode was 16.24% in 75 Cd mg·kg^-1 level,while the removal rate in other Cd levels were alfalfa best,19.82%,30.72% and 26.78% respectively.Considering factors such as accumulation and removal rate of Cd etc.,rotation way can enhance the overall removal rate of soil Cd.（5）EXC-Cd was the dominate Cd form in soil at the different Cd treatments and FDC of it was 55.09%-83.23%.The contents of Cd chemical forms in soil were in order of EXC-Cd > CAB-Cd > FeMn-Cd > RES-Cd > OM-Cd.With increasing levels of Cd,the percentage of EXC-Cd also increased.Significant positive correlation was found in soil Cd forms（except of OM-Cd）and Cd concentration of shoot and root in two varieties of ryegrass（P<0.01）.（6）The enrichment coefficient（BCF）of ryegrass（included Bangde and Abode）,alfalfa and Brassica juncea L were all over 1 in the different Cd treatments,the order was Brassica juncea L > alfalfa > Abode > Bangde,while the transfer factor（TF）of them were all below 1,the order was Abode < Bangde < alfalfa < Brassica juncea L.Under all Cd levels,Brassica juncea L.was the strongest of the three Cd-enrichment plants,and Abode can effectively gather soil Cd.（7）Significant differences of the expression levels of OAS and IRT were found in Bangde and Abode when exposed to Cd pollutions.The expression levels of OAS and IRT among different sub-species/varieties were still quite different under the same Cd treatments.The expression levels of OAS and IRT in Bangde significantly increased under Cd treatment 75 mg·kg^-1,while The expression levels of OAS and IRT in Abode significantly increased under Cd treatment 150 mg·kg^-1,and the amplitude of The expression levels of OAS and IRT in Abode was significantly lower than that in Bangde.The reaction trends among gene members within the same gene family were generally similar among each other.