NITROGEN-METABOLISM IN THE ECTOMYCORRHIZAL FUNGUS LACCARIA-BICOLOR (R MRE) ORTON

Blended colonies of the ectomycorrhizal fungus, Laccaria bicolor (R. Mre.) Orton, grew axenically as a suspension of fine hyphae in a defined buffered medium with glucose (doubling time 1–2 d) but not acetate as the carbon source, and either ammonium or nitrate as nitrogen sources. A number of amino acids were found to be excellent nitrogen sources for this basidiomycete, but were less effective as sources of carbon. During post‐exponential growth in medium containing inorganic nitrogen, the fungal symbiont released amino acids. L. bicolor has the enzymatic potential to assimilate ammonium by the activities of glutamine synthetase, NADH‐glutamate dehydrogenase and NADPH‐glutamate dehydrogenase. It also contains highly active aspartate and alanine aminotransferases. The activities of glutamine synthetase, NADPH‐glutamate dehydrogenase and aspartate aminotransferase were greater in the presence of nitrate than in the presence of ammonium and declined as the culture aged, suggesting a biosynthetic role for these enzymes. In contrast, the activities of NADH‐glutamate dehydrogenase and alanine aminotransferase increased during post‐exponential growth, and also in cultures growing on amino acids as a carbon source, suggesting a catabolic role for these enzymes. Copyright © 1990, Wiley Blackwell. All rights reserved