Selection Of Cadmium-tolerant Plant Growth-promoting Rhizobacteria And Their Effect On Cadmium Uptake And Accumulation By Loliummultiflorum Lam.

Ryegrass(Lolium multiflorum Lam.)is considered as one of high biomass production and high value energy plant.In addition,ryegrass also exhibited high levels of both heavy mental tolerance and phytoextraction capacity in heavy mental contaminated fileds.The objectives of this study were(a)to investigate the effects of Cd(cadmium)-tolerant PGPR(plant growth-promoting rhizobacteria)on the growth,Cd uptake and accumulation of ryegrass in Cd-contaminated soil and the extractable Cd concentration in the rhizosphere and(b)to examine the feasibility to develop ryegrass as bioenergy plant in Cd-polluted soil.Thirty-two Cd-tolerant PGPR were isolated from different plants rhizosphere soil through adding various concentrations of Cd in the LB(Luria-Bertani)media.After assessed for potentially useful characteristic with ability to secrete 3-indoleacetic acid(IAA),ACC deaminase and phosphate solubilisation,and rescreening through plant growth promoting assay on filter paper culture for Cd-tolerant strains,three rhizobacterias(Ca02,Oj06 and Ps08)with plant growth promoting traints were chosen for regulation of Cd-tolerant PGPR on ryegrass seedling growth under Cd stress.The bacteria were identified as Pseudomonas sp.(Ca02)and Enterobacter sp.(Oj06 and Ps08),respectively by physiological characteristics,morphology and 16SrDNA sequential analysis.In order to further study the Cd-tolerant PGPR's colonazation in roots of ryegrass,this experiment has labeled Ca02 with gfp gene successfully by using the electricity transformation method,and observed Ca02 colonize in roots of ryegrass.The result indicated that Ca02 may colonize in the ryegrass root surely.Hydroponic experiment has been carried out to research the affects of PGPR on ryegrass under Cd stress.The results of experiment showed that the adjunction of Ca02,Oj06,Ps08 and J62 demonstrated obvious promoting effect on ryegrass with 20?m·L-1(final Cd concentration).Shoot and root length,root fresh and dry weight,shoot fresh and dry weight,chlorophyll content,and Cd accumulation of ryegrass enhanced dramatically and MDA content reduced after PGPB treat.Pot culture test was carried out in soil with a Cd concentration of 20±0.33 mg·kg-1,and the three strains were inoculated in ryegrass.The results showed that the shoot dry weights and Cd accumulation in shoot of ryegrass treated with Ca02,Oj06 and Ps08 increased markedly,and peroxide level of leaves(MDA content)decreased dramatically(P<0.05),compared touninoculated control.Extractable Cd concentration of rhizosphere were increased,especially for the inoculation of Ca02.The test indicated that Cd-tolerant PGPR could promote ryegrass seedling growth significantly under Cd stress,and enhance Cd uptake and accumulation by improving available Cd in soil.