Transformation and Immobilization of Chromium by Arbuscular Mycorrhizal Fungi as Revealed by SEM–EDS, TEM–EDS, and XAFS

Arbuscular mycorrhizal fungi (AMF), ubiquitous soil fungi that form symbiotic relationships with the majority of terrestrial plants, are known to play an important role in plant tolerance to chromium (Cr) contamination. However, the underlying mechanisms, especially the direct influences of AMF on t...

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Bibliographic Details
Published in:	Environmental science & technology 2015-12, Vol.49 (24), p.14036-14047
Main Authors:	Wu, Songlin, Zhang, Xin, Sun, Yuqing, Wu, Zhaoxiang, Li, Tao, Hu, Yajun, Su, Dan, Lv, Jitao, Li, Gang, Zhang, Zhensong, Zheng, Lirong, Zhang, Jing, Chen, Baodong
Format:	Article
Language:	eng
Subjects:	Chromium Chromium - analysis Chromium - metabolism Chromium - pharmacokinetics Contamination Daucus carota - drug effects Daucus carota - metabolism Daucus carota - microbiology Fungi Histidine - chemistry Histidine - metabolism Mass spectrometry Microscopy, Electron, Scanning Microscopy, Electron, Transmission Mycelium - metabolism Mycorrhizae - drug effects Mycorrhizae - physiology Phosphates - chemistry Plant Roots - drug effects Plant Roots - metabolism Plant Roots - microbiology Scanning electron microscopy Soil - chemistry Soil Microbiology Soil Pollutants - analysis Soil Pollutants - metabolism Soil Pollutants - pharmacokinetics Spectrometry, X-Ray Emission Symbiosis X-Ray Absorption Spectroscopy - methods
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Summary:	Arbuscular mycorrhizal fungi (AMF), ubiquitous soil fungi that form symbiotic relationships with the majority of terrestrial plants, are known to play an important role in plant tolerance to chromium (Cr) contamination. However, the underlying mechanisms, especially the direct influences of AMF on the translocation and transformation of Cr in the soil–plant continuum, are still unresolved. In a two-compartment root-organ cultivation system, the extraradical mycelium (ERM) of mycorrhizal roots was treated with 0.05 mmol L–1 Cr(VI) for 12 days to investigate the uptake, translocation, and transformation of Cr(VI) by AMF using inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy equipped with energy-dispersive spectroscopy (SEM–EDS), transmission electron microscopy equipped with energy-dispersive spectroscopy (TEM–EDS), and X-ray-absorption fine structure (XAFS) technologies. The results indicated that AMF can immobilize quantities of Cr via reduction of Cr(VI) to Cr(III), forming Cr(III)–phosphate analogues, likely on the fungal surface. Besides this, we also confirmed that the extraradical mycelium (ERM) can actively take up Cr [either in the form of Cr(VI) or Cr(III)] and transport Cr [potentially in the form of Cr(III)-histidine analogues] to mycorrhizal roots but immobilize most of the Cr(III) in the fungal structures. Based on an X-ray absorption near-edge spectroscopy analysis of Cr(VI)-treated roots, we proposed that the intraradical fungal structures can also immobilize Cr within mycorrhizal roots. Our findings confirmed the immobilization of Cr by AMF, which plays an essential role in the Cr(VI) tolerance of AM symbioses.
ISSN:	0013-936X 1520-5851