title: Nitrogen transfer and assimilation between the arbuscular mycorrhizal fungus Glomus intraradices Schenck & Smith and Ri T-DNA roots of Daucus carota L. in an in vitro compartmented system.
abstract: Nitrogen metabolism was examined in monoxenic cultures of carrot roots (Daucus carota L.) colonized with the arbuscular mycorrhizal (AM) fungus Glomus intraradices Schenck & Smith. Glutamine synthetase and glutamate dehydrogenase activities were significantly increased in mycorrhizal roots for which only the extraradical mycelium had exclusive access to NH4NO3 in a distinct hyphal compartment inaccessible to the roots. This was in comparison with the water controls but was similar to the enzyme activities of non-arbuscular-mycorrhizal (non-AM) roots that had direct access to NH4NO3. In addition, glutamate dehydrogenase activity was significantly enhanced in AM roots compared with non-AM roots. Carrot roots took up 15NH4+ more efficiently than 15NO3-, and the extraradical hyphae transfered 15NH4+ to host roots from the hyphal compartment but did not transfer 15NO3-. The extraradical mycelium was shown, for the first time, to have a different glutamine synthetase monomer than roots. Our overall results highlight the active role of AM fungi in nitrogen uptake, transfer, and assimilation in their symbiotic root association.
authors.affiliation: Department of Biology, University of Ottawa, ON, Canada.
authors.forename: Jean-Patrick
authors.initials: JP
authors.lastname: Toussaint
authors.forename: Marc
authors.initials: M
authors.lastname: St-Arnaud
authors.forename: Christiane
authors.initials: C
authors.lastname: Charest
mesh_terms: D046508:Culture Techniques; D004269:DNA, Bacterial; D018552:Daucus carota / Q000382:microbiology*; D005658:Fungi / Q000502:physiology*; D009584:Nitrogen / Q000378:metabolism*; D013559:Symbiosis / Q000502:physiology*
chemical_list: D004269:DNA, Bacterial; C036483:T-DNA; D009584:Nitrogen