Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp Original article đề tài: The role of glutamine synthetase, glutamate synthase and glutamate dehydrogenase in ammonia assimilation by the mycorrhizal fungus Pisolithus tinctorius. | 706s Ann. Sci. For. 1989 46 suppl. 706s-710s Forest Tree Physiology E. Dreyer etal. eds. Elsevier INRA The role of glutamine synthetase glutamate synthase and glutamate dehydrogenase in ammonia assimilation by the mycorrhizal fungus Pisolithus tinctorius . Kershaw and . Stewart Departement of Biology Darwin University College London Gower St. London WC1E . Introduction Of the major nutrients required by trees nitrogen appears to be the most important for increasing forest productivity. Nitrogen is obtained from inorganic forms present in the soil solution and thus the root is an important centre for inorganic nitrogen assimilation. There is evidence that ectomycorrhizae ECM stimulate ammonia uptake by woody plants. The fungal partner contributes nitrogen to the tree root in two ways by translocation of nitrogenous compounds from the soil N-pool to the root and by conversion of absorbed N into forms more easily utilised by the root. Studies of the assimilation of nitrogen by pure cultures of ECM fungi provide the basis for investigation of fungal-based nitrogen metabolism within the ECM. In most fungi and higher plants inorganic nitrogen is assimilated into the amino acids glutamate and glutamine which then donate nitrogen to other metabolites. The route of ammonia assimilation found in both mycorrhizal and non-mycorrhizal roots appears to be the glutamate synthase cycle whereas ammonia assimilation in fungi is generally held to occur via the glutamate dehydrogenase GDH pathway Fig. 1 . Previous studies have shown that some yeasts are capable of utilising the glutamate synthase cycle for ammonia assimilation Roon et al. 1974 Johnson and Brown 1974 but in the ectomycorrhizal fungus Cenococcum gra-niforme the GDH pathway was the primary route of ammonia incorporation Genetet etal. 1984 . Materials and Methods Pure cultures of Pisolithus tinctorius an ecto-mycorrhizal basidiomycete were grown for 18 d in half-strength modified Melin-Norkrans medium 1 2MMN .
