Physiological And Molecular Responses Of Copper Inhibiting Cadmium Uptake And Accumulation In Polish Wheat

Due to the irrigation of sewage,industrial discharges of "three wastes" and the misuse of pesticides and fertilizers,increasing of arable soils in China are contaminated by cadmium(Cd).Cd in arable soils is is easily absorbed by crops,and then affecting crop growth to limit the crop yield and quality.As an important crop in China and even in word,increasing of wheat accumulate Cd in grain more than 0.2 mg/kg,and potentially poses a risk to human health.Therefore,it is urgent to reduce the grain Cd accumulation in wheat.Management of water and fertilisers is one of the fastest,simplest,convenient,and effective agronomic strategies to reduce crop Cd accumulation.As an essential metal for plants,copper(Cu)competes with Cd in crops by affecting Cd absorption,translocation,and distribution.However,it is unknown whether and how Cu influences Cd absorption,translocation and distribution in wheat.Dwarf Polish wheat(Triticum polonicum L.,2n =4x = 28,AABB;DPW)is one of the unique resources in China,carrying several excellent traits,such as long kernels and dwarfism,and low-Cd accumulated in grains.Thus,it is an ideal material for studying the mechanism of Cd absorption and accumulation.In the present study,DPW was used as the material to reveal the physiological and molecular responses of Cu on Cd absorption,accumulation,and transport.Plant growth,Cd uptake in root,Cd translocation from root to shoot,subcellular distribution,Cd chemical forms,transcript level of genes involved in cell wall synthesis,and metal chelate,as well as hormone signaling and metal transport under Cu deficiency,normal Cu concentration(CK),and high Cu concentration were investigated.The results would provide a theoretical basis for using Cu to reduce Cd absorption and accumulation in wheat.The main results are as follows:(1)Neither Cu deficiency nor Cu addition significantly affected the growth and development of DPW under Cd stress.(2)Under Cd stress,Cu deficiency increased the Cd absorption and accumulation in roots,but inhibited the Cd translocation from roots to shoots when compared with CK.While,Cu addition did not significantly change the Cd accumulation in roots and the Cd translocation from roots to shoots when compared with CK.(3)Under Cd stress,Cu deficiency down-regulated the expression of callose synthase related genes(CALS),and up-regulated the expression of several cell wall synthesis genes(Cht,CLP,CESA,XTH,and GLU)when compared with CK.The results suggested that Cu deficiency might increase the cellulose concentration of the root cell wall in DPW to promote Cd binding in the cell wall.Although Cu addition up-regulated the expression of 5cell wall synthesis genes(XTH,CSL,and GLU),it significantly repressed the expression of17 cell wall synthesis genes(Cht,CLP,GLU,CALS,and XTH)when compared with CK.The cellulose concentration in root cell wall in DPW would be reduced to limit Cd binding in the cell wall.(4)Under Cd stress,although Cu deficiency repressed the expression of 3 Cd uptake genes(IRT),it significantly up-regulated the expression of 11 Cd uptake genes(HIPP,ZIP,and COPT)when compared with CK.Thus,Cd uptake was promoted by Cu deficiency in DPW roots.Additionally,Cu deficiency promoted the expression of 8 Cd efflux genes(ABCG,ZIP,CCX,and HMA)and 3 Cd sequestration genes(ABCC)when compared with CK,ultimately inhibited the Cd translocation from roots to shoots.Although Cu addition reduced the expression of 7 Cd uptake genes(IRT,NRAMP,COPT,and HIPP),it also increased the expression of 4 Cd uptake genes(NRAMP,HIPP)compared with CK.Thus,the Cd concentration in DPW roots was not altered.At the same time,Cu addition reduced the expression of 13 Cd efflux genes(ABCG and ZIP),and 13 Cd transport genes(YSL,ABCB,OPT,and CAX),increased the expression of 3 Cd sequestration genes(MTP,ABCC,and CAX)when compared with CK,and then promoted Cd sequestration in root vacuoles.