title: Chromium immobilization by extra- and intraradical fungal structures of arbuscular mycorrhizal symbioses.
abstract: Arbuscular mycorrhizal (AM) fungi can enhance plant Cr tolerance through immobilizing Cr in mycorrhizal roots. However, the detailed processes and mechanisms are unclear. The present study focused on cellular distribution and speciation of Cr in both extraradical mycelium (ERM) and mycorrhizal roots exposed to Cr(VI) by using field emission scanning electron microscopy equipped with energy dispersive X-ray spectrometer (FE-SEM-EDS), scanning transmission soft X-ray microscopy (STXM) and X-ray absorption fine structure (XAFS) spectroscopy techniques. We found that amounts of particles (possibly extracellular polymeric substances, EPS) were produced on the AM fungal surface upon Cr(VI) stress, which contributed greatly to Cr(VI) reduction and immobilization. With EDS of the surface of AM fungi exposed to various Cr(VI) levels, a positive correlation between Cr and P was revealed, suggesting that phosphate groups might act as counter ions of Cr(III), which was also confirmed by the XAFS analysis. Besides, STXM and XAFS analyses showed that Cr(VI) was reduced to Cr(III) in AM fungal structures (arbuscules, intraradical mycelium, etc.) and cell walls in mycorrhizal roots, and complexed possibly with carboxyl groups or histidine analogues. The present work provided evidence of Cr immobilization on fungal surface and in fungal structures in mycorrhizal roots at a cellular level, and thus unraveled the underlying mechanisms by which AM symbiosis immobilize Cr.
authors.affiliation: State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, People's Republic of China; University of Chinese Academy of Sciences, Beijing, 100049, People's Republic of China; Department of Environmental Geosciences, Faculty of Environmental Sciences, Czech University of Life Sciences Prague, Kamycká 129, Prague 6-Suchdol 165 21, Czech Republic.
authors.forename: Songlin
authors.initials: S
authors.lastname: Wu
authors.affiliation: State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, People's Republic of China.
authors.forename: Xin
authors.initials: X
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, People's Republic of China; University of Chinese Academy of Sciences, Beijing, 100049, People's Republic of China.
authors.forename: Yuqing
authors.initials: Y
authors.lastname: Sun
authors.affiliation: State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, People's Republic of China; University of Chinese Academy of Sciences, Beijing, 100049, People's Republic of China.
authors.forename: Zhaoxiang
authors.initials: Z
authors.lastname: Wu
authors.affiliation: State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, People's Republic of China.
authors.forename: Tao
authors.initials: T
authors.lastname: Li
authors.affiliation: State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, People's Republic of China; Key Laboratory of Agro-ecological Processes in Subtropical Region, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha, 410125, People's Republic of China.
authors.forename: Yajun
authors.initials: Y
authors.lastname: Hu
authors.affiliation: State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, People's Republic of China.
authors.forename: Jitao
authors.initials: J
authors.lastname: Lv
authors.affiliation: State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, People's Republic of China.
authors.forename: Gang
authors.initials: G
authors.lastname: Li
authors.affiliation: State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, People's Republic of China.
authors.forename: Zhensong
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, People's Republic of China.
authors.forename: Jing
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, People's Republic of China.
authors.forename: Lirong
authors.initials: L
authors.lastname: Zheng
authors.affiliation: Shanghai Synchrotron Radiation Facility, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201204, People's Republic of China.
authors.forename: Xiangjun
authors.initials: X
authors.lastname: Zhen
authors.affiliation: State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, People's Republic of China. Electronic address: bdchen@rcees.ac.cn.
authors.forename: Baodong
authors.initials: B
authors.lastname: Chen
mesh_terms: D002857:Chromium / Q000032:analysis* / Q000737:chemistry; D056229:Fungal Structures; D008855:Microscopy, Electron, Scanning; D025282:Mycelium / Q000378:metabolism*; D038821:Mycorrhizae / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism* / Q000382:microbiology*; D010944:Plants / Q000378:metabolism; D013052:Spectrometry, X-Ray Emission; D013499:Surface Properties; D013559:Symbiosis
chemical_list: D010710:Phosphates; D002857:Chromium; C074702:chromium hexavalent ion
keywords: Arbuscular mycorrhizal fungi; Chromium; SEM-EDS; STXM; XAFS