title: Ultrastructural localization of heavy metals in the extraradical mycelium and spores of the arbuscular mycorrhizal fungus Glomus intraradices.
abstract: Arbuscular mycorrhizal fungi, obligate symbionts of most plant species, are able to accumulate heavy metals, thereby, protecting plants from metal toxicity. In this study, the ultrastructural localization of Zn, Cu, and Cd in the extraradical mycelium and spores of the arbuscular mycorrhizal fungus Glomus intraradices grown in monoxenic cultures was investigated. Zinc, Cu, or Cd was applied to the extraradical mycelium to final concentrations of 7.5, 5.0, or 0.45 mmol/L, respectively. Samples were collected at time 0, 8 h, and 7 days after metal application and were prepared for rapid freezing and freeze substitution. Metal content in different subcellular locations (wall, cytoplasm, and vacuoles), both in hyphae and spores, was determined by energy-dispersive X-ray spectroscopy. In all treatments and fungal structures analysed, heavy metals accumulated mainly in the fungal cell wall and in the vacuoles, while minor changes in metal concentrations were detected in the cytoplasm. Incorporation of Zn into the fungus occurred during the first 8 h after metal addition with no subsequent accumulation. On the other hand, Cu steadily accumulated in the spore vacuoles over time, whereas Cd steadily accumulated in the hyphal vacuoles. These results suggest that binding of metals to the cell walls and compartmentalization in vacuoles may be essential mechanisms for metal detoxification.
authors.affiliation: Departamento de Microbiologia del Suelo y Sistemas Simbioticos, Estacion Experimental del Zaidin, Consejo Supertableior de Investigaciones Cientificas (CSIC), Profesor Albareda 1, 18008 Granada, Spain. manuelgg@wpi.edu
authors.forename: Manuel
authors.initials: M
authors.lastname: González-Guerrero
authors.forename: Lewis H
authors.initials: LH
authors.lastname: Melville
authors.forename: Nuria
authors.initials: N
authors.lastname: Ferrol
authors.forename: John N A
authors.initials: JN
authors.lastname: Lott
authors.forename: Concepción
authors.initials: C
authors.lastname: Azcón-Aguilar
authors.forename: R Larry
authors.initials: RL
authors.lastname: Peterson
mesh_terms: D002104:Cadmium / Q000378:metabolism; D002473:Cell Wall / Q000737:chemistry; D003300:Copper / Q000378:metabolism; D003593:Cytoplasm / Q000737:chemistry; D005658:Fungi / Q000737:chemistry* / Q000502:physiology / Q000648:ultrastructure; D019216:Metals, Heavy / Q000032:analysis*; D046529:Microscopy, Electron, Transmission; D025282:Mycelium / Q000737:chemistry* / Q000648:ultrastructure; D038821:Mycorrhizae / Q000737:chemistry* / Q000502:physiology / Q000648:ultrastructure; D013052:Spectrometry, X-Ray Emission; D013172:Spores, Fungal / Q000737:chemistry* / Q000648:ultrastructure; D013997:Time Factors; D014617:Vacuoles / Q000737:chemistry; D015032:Zinc / Q000378:metabolism
chemical_list: D019216:Metals, Heavy; D002104:Cadmium; D003300:Copper; D015032:Zinc