title: The endophytic bacterium, Sphingomonas SaMR12, improves the potential for zinc phytoremediation by its host, Sedum alfredii.
abstract: The endophytic bacterium, Sphingomonas SaMR12, isolated from Sedum alfredii Hance, appears to increase plant biomass and zinc-extraction from contaminated soil; however, the mechanism by which this occurs is not clear. Here, the ability of SaMR12 to promote zinc extraction and its effects on root morphology and exudation were examined in hydroponics. Zinc treatment increased shoot biomass by 30 to 45%, and by a further 10 to 19% when combined with SaMR12 inoculation. Zinc treatment also increased zinc accumulation modestly and this too was enhanced with SaMR12. Both biomass and zinc levels increased in a dose-dependent manner with significant effects seen at 50 µM zinc and apparent saturation at 500 µM. Zinc and the endophyte also increased levels of auxin but not at 50 µM and zinc increased levels of superoxide and hydrogen peroxide but mainly at 500 µM. As for root morphology, SaMR12 increased root branching, the number of root tips, and surface area. Zinc and SaMR12 also increased the exudation of oxalic acid. For most assays the effects of the endophyte and zinc were additive, with the notable exception of SaMR12 strongly reducing the production of reactive oxygen species at 500 µM zinc. Taken together, these results suggest that the promotion of growth and zinc uptake by exposure to zinc and to SaMR12 are independent of reactive oxygen and do not involve increases in auxin.
authors.affiliation: MOE Key laboratory of Environment Remediation and Ecosystem Health, College of Environmental and Resource Sciences, Zhejiang University, Zijingang Campus, Hangzhou, China.
authors.forename: Bao
authors.initials: B
authors.lastname: Chen
authors.affiliation: Agricultural Ecology and Plant Protection Management Station, Yuhang County, Hangzhou, China.
authors.forename: Jianguo
authors.initials: J
authors.lastname: Shen
authors.affiliation: MOE Key laboratory of Environment Remediation and Ecosystem Health, College of Environmental and Resource Sciences, Zhejiang University, Zijingang Campus, Hangzhou, China.
authors.forename: Xincheng
authors.initials: X
authors.lastname: Zhang
authors.affiliation: MOE Key laboratory of Environment Remediation and Ecosystem Health, College of Environmental and Resource Sciences, Zhejiang University, Zijingang Campus, Hangzhou, China.
authors.forename: Fengshan
authors.initials: F
authors.lastname: Pan
authors.affiliation: MOE Key laboratory of Environment Remediation and Ecosystem Health, College of Environmental and Resource Sciences, Zhejiang University, Zijingang Campus, Hangzhou, China.
authors.forename: Xiaoe
authors.initials: X
authors.lastname: Yang
authors.affiliation: MOE Key laboratory of Environment Remediation and Ecosystem Health, College of Environmental and Resource Sciences, Zhejiang University, Zijingang Campus, Hangzhou, China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Feng
mesh_terms: D001673:Biodegradation, Environmental; D018533:Biomass; D007210:Indoleacetic Acids / Q000378:metabolism; D018384:Oxidative Stress; D010100:Oxygen / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism; D031963:Sedum / Q000378:metabolism*; D020578:Sphingomonas / Q000502:physiology*; D015032:Zinc / Q000378:metabolism*
chemical_list: D007210:Indoleacetic Acids; C030737:indoleacetic acid; D015032:Zinc; D010100:Oxygen