Toussaint Jean-Patrick, St-Arnaud Marc, Charest Christiane
Department of Biology, University of Ottawa, ON, Canada.
Can J Microbiol. 2004 Apr;50(4):251-60. doi: 10.1139/w04-009.
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.
在接种丛枝菌根（AM）真菌根内球囊霉（Glomus intraradices Schenck & Smith）的胡萝卜根（Daucus carota L.）单菌培养物中研究了氮代谢。对于菌根根，只有根外菌丝体能在根无法进入的独特菌丝隔室中单独接触NH₄NO₃，其谷氨酰胺合成酶和谷氨酸脱氢酶活性显著增加。与水分对照相比是这样，但与能直接接触NH₄NO₃的非丛枝菌根（non-AM）根的酶活性相似。此外，与非AM根相比，AM根中的谷氨酸脱氢酶活性显著增强。胡萝卜根吸收¹⁵NH₄⁺比¹⁵NO₃⁻更有效，根外菌丝体从菌丝隔室向宿主根转运¹⁵NH₄⁺，但不转运¹⁵NO₃⁻。首次表明根外菌丝体具有与根不同的谷氨酰胺合成酶单体。我们的总体结果突出了AM真菌在其共生根关联中氮吸收、转运和同化中的积极作用。
