Sequestration of heavy metals and radionuclides in ectomycorrhiza
The involvement of microorganisms such as fungi, present in the environment, take part in the process of element re-distribution. Ectomycorrhiza (ECM) was investigated concerning metal and radionuclide distribution within the system soil-ECM. The development of the ECM tree partners Picea abies and Pinus sylvestris was studied in relation to a symbiosis with the early colonizer ectomycorrhizal fungi Paxillus involutus and Pisolithus tinctorius, as well as the late colonizer fungus Tricholoma vaccinum. With pot experiments, the influence of ECM on metal distribution in soil was analyzed. High bioconcentration factors (BCF) associated with metal enrichment in the fungal cell was found to correlate with low glutathione S-transferase (GST) activities. While early colonizers showed higher GST activity in the mycelium as well as in mycorrhizal roots, the late colonizer T. vaccinum had lower or even lacking GST activity. In this study was shown that basidiomycetes excrete secondary metabolites and nutrients, like sugars or amino acids, via guttation. Additionally, high Pb values were measured in guttation droplets after cultivation in Pb supplemented media, which shows detoxification for survival under harsh environmental conditions. An involvement of aquaporin proteins in guttation, by forming water channels in the membrane, could be shown too. The transfer of water as well as gases or soluble substances can be inhibited by acetazolamide and silver ions which led to less guttation and altered element contents in the guttation fluid. Here, fungi could be shown to determine element concentrations in their host plant, and keep homeostasis within their cells by support of the GST enzyme as well as excreting metals with guttation. Thus, the role of fungi in element cycling can be followed and furthermore potentially find applications.
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