Effects Of Burkholderia Bacteria And Genotype On Cadmium Accumulation Of Rice And Barley

Cadmium (Cd) is a heavy metal which nonessential for both plants and human being. But it imposesa threat to human’s health by its easy entrance into the food chain. With the continuous expansion of Cdcontaminated farmland and the reduction of available arable land, the food safety in Cd contaminatedarea becomes a prominent problem. Cultivating low Cd accumulation varieties is a cost-effective way tosolve the food security problems in medium or low Cd contaminated farmland. Studing the interactioneffects between genotypes and rhizosphere factors on Cd accumulation of crop could provide atheoretical basis for developing low-Cd-accumulation crops and safety production techniques in Cdcontaminated land. In this study, we chose different rice and barley genotypes as plant materials, a plantgrowth-promoting rhizobacteria Burkholderia sp.D54and Cd stress as rhizosphere factors to researchthe effects of inoculating Burkholderia sp.D54on Cd uptake and translocation in rice, the relationshipsamong subcellular distribution and chemical forms of Cd, phytochelatins (PCs) in the root and shoot,and Cd accumulation in different barley genotypes. The major results were summarized as follows:1. Two bacterial strains separated from Cd contaminated paddy soil could grow normally under500mg/L Cd stress as Burkholderia sp.D54. Inoculation with Burkholderia sp.D54could promote theseedling growth of Cd-sensitive rice cultivar X24. Its biomass, root length, root volume, root surfacearea and root tip numbers increased significantly. But Inoculation with Burkholderia sp.D54had noeffect on other tested rice cultivars.2. Inoculation with Burkholderia sp.D54could enchance Cd uptake in roots of X24seedlings, bothCd concentration and accumulation were significantly increased. However, Cd concentration in shoot ofinoculated seedlings was significantly lower than that of uninoculated seedlings. It indicated thatinoculation with Burkholderia sp.D54could enchance Cd-root retention but reduce Cd translocationfrom roots to shoots. Inoculation with Burkholderia sp.D54remarkably enhanced Cd accumulation inthe cell walls, but had little effect on the accumulation in cell organelles and soluble fractions.Total PCsin rice roots were closely associated with Cd stress but not with inoculation of Burkholderia sp.D54.3. The results of pot experiment for whole growth period showed that inoculation with Burkholderiasp.D54remarkably enhanced Cd accumulation in the rice roots, but produced different effects on Cdaccumulation in aboveground organs, depending on Cd amounts in soil. Cd concentrations in stems,leaves, and kernels of the inoculated rice plants were significantly higher than that of uninoculatedplants in the pots with soil of0.1mg/kg Cd. When Soil Cd concentration increased to1.2-4.8mg/kg, Cdconcentrations in stems, leaves and kernels of the inoculated rice plants were significantly lower thanthat of uninoculated plants.4. Cd transport rate and concentration in shoots of hua10118(Cd-tolerance barley cultivar) werelower than that of hua2255(Cd-sensitive barley cultivar). Cd was mainly distributed in the cell wall andsoluble fractions of roots and shoots in both of the varieties, which took about35%-44%, respectively.Cd in organelles only took about5%-26%. Cd concentration in cell organelles of hua2255was higherthan that of hua10118，which probably resulted in the sensitivity of hua2255to Cd. The predominant form of Cd in the roots was HAc-extractable Cd but NaCl-extractable Cd in the shoots. The amount ofethanol-extractable, water-extractable and NaCl-extractable Cd in hua2255was higher than that inhua10118, which was probably the main reason of different Cd transport and tolerance between them.The concentrations of PC2and PC3both in the roots and shoots of hua2255were remarkably higher thanthat of hua10118.5. Cd concentration of each organ at mature stage was significantly changed with barley genotypesand different Cd treatments. Cd concentration in roots has little difference between different barleygenotypes but Cd concentration in kernel was greatly different among different barley genotypes. Cdconcentration in each organ of Cd-sensitive cultivars was higher than that of Cd-tolerance cultivarsunder low Cd level treatment. In the soil with0.3mg/kg Cd, Cd concentrations in roots, stems, leavesand kernels of Cd-sensitive cultivar hua6were16.2%,22.3%,176.8%and62.2%higher than that ofCd-tolerance cultivar hua8, respectively. With the increase of Cd level in soil, Cd concentration ofCd-tolerance cultivar was increased rapidly. Kernel Cd concentration of hua8was34.3%significantlyhigher than that of hua6in the pots with soil of2.4mg/kg Cd, root Cd concentration had no differencebetween them. Kernel Cd concentration was closely associated with Cd concentration in rachis and flagleaves.