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Ammonium assimilation by spruce— Hebeloma sp. ectomycorrhizas
Author(s) -
CHALOT M.,
STEWART G. R.,
BRUN A.,
MARTIN F.,
BOTTON B.
Publication year - 1991
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/j.1469-8137.1991.tb01046.x
Subject(s) - glutamine synthetase , glutamate synthase , glutamate dehydrogenase , nitrogen assimilation , glutamine , biochemistry , asparagine , asparagine synthetase , biology , alanine , amino acid , ammonium , glutamic acid , methionine , glutamate receptor , enzyme , chemistry , organic chemistry , receptor
summary In order to investigate the relative contribution of glutamine synthetase and NADP‐glutamate dehydrogenase to the assimilation of ammonium (NH 4 + ) by spruce ectomycorrhizas, changes in free amino acid content and kinetics of 15 N incorporation into free amino acids were measured together with the effect of specific enzyme inhibitors. Exposure of detached ectomycorrhizas to ( 15 NH 4 ) 2 SO 4 showed that the greatest flow of 15 N enters into the amido group of glutamine. Label was also detected in glutamic acid, alanine and γ‐aminobutyric acid. Large amounts of alanine and glutamate accumulated in response to the addition of methionine sulfoximine (MSX) together with a decrease in 15 N incorporation into both amido‐ and ammo‐nitrogen of glutamine. These results are consistent with a major role of glutamate dehydrogenase and glutamine synthetase in nitrogen assimilation in the symbiosis and do not suggest any significant role for glutamate synthase in the synthesis of glutamate. A large accumulation of unlabelled asparagine in response to MSX and albizziine inhibition suggests the occurrence of an unlabelled NH 4 + pool in the host plant. The transfer of nitrogen compounds between the fungal cells and the host tissues is discussed.