Abstract
To investigate nitrogen assimilation and translocation in Zea mays L. colonized by the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus fasciculatum (Thax. sensu Gerd.), we measured key enzyme activities, 15N incorporation into free amino acids, and 15N translocation from roots to shoots. Glutamine synthetase and nitrate reductase activities were increased in both roots and shoots compared with control plants, and glutamate dehydrogenase activity increased in roots only. In the presence of [15N]ammonium, glutamine amide was the most heavily labeled product. More label was incorporated into amino acids in VAM plants. The kinetics of 15N labeling and effects of methionine sulfoximine on distribution of 15N-labeled products were entirely consistent with the operation of the glutamate synthase cycle. No evidence was found for ammonium assimilation via glutamate dehydrogenase. 15N translocation from roots to shoots through the xylem was higher in VAM plants compared with control plants. These results establish that, in maize, VAM fungi increase ammonium assimilation, glutamine production, and xylem nitrogen translocation. Unlike some ectomycorrhizal fungi, VAM fungi do not appear to alter the pathway of ammonium assimilation in roots of their hosts.
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Selected References
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- Dunn-Coleman N. S., Robey E. A., Tomsett A. B., Garrett R. H. Glutamate synthase levels in Neurospora crassa mutants altered with respect to nitrogen metabolism. Mol Cell Biol. 1981 Feb;1(2):158–164. doi: 10.1128/mcb.1.2.158. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Genetet I., Martin F., Stewart G. R. Nitrogen Assimilation in Mycorrhizas : Ammonium Assimilation in the N-Starved Ectomycorrhizal Fungus Cenococcum graniforme. Plant Physiol. 1984 Oct;76(2):395–399. doi: 10.1104/pp.76.2.395. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hummelt G., Mora J. NADH-dependent glutamate synthase and nitrogen metabolism in Neurospora crassa. Biochem Biophys Res Commun. 1980 Jan 15;92(1):127–133. doi: 10.1016/0006-291x(80)91529-6. [DOI] [PubMed] [Google Scholar]
- Rhodes D., Rich P. J., Brunk D. G. Amino Acid Metabolism of Lemna minor L. : IV. N-Labeling Kinetics of the Amide and Amino Groups of Glutamine and Asparagine. Plant Physiol. 1989 Apr;89(4):1161–1171. doi: 10.1104/pp.89.4.1161. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Robinson S. A., Slade A. P., Fox G. G., Phillips R., Ratcliffe R. G., Stewart G. R. The role of glutamate dehydrogenase in plant nitrogen metabolism. Plant Physiol. 1991 Feb;95(2):509–516. doi: 10.1104/pp.95.2.509. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Roon R. J., Even H. L., Larimore F. Glutamate synthase: properties of the reduced nicotinamide adenine dinucleotide-dependent enzyme from Saccharomyces cerevisiae. J Bacteriol. 1974 Apr;118(1):89–95. doi: 10.1128/jb.118.1.89-95.1974. [DOI] [PMC free article] [PubMed] [Google Scholar]
- SIMS A. P., FOLKES B. F. A KINETIC STUDY OF THE ASSIMILATION OF (15N)-AMMONIA AND THE SYNTHESIS OF AMINO ACIDS IN AN EXPONENTIALLY GROWING CULTURE OF CANDIDA UTILIS. Proc R Soc Lond B Biol Sci. 1964 Feb 18;159:479–502. doi: 10.1098/rspb.1964.0015. [DOI] [PubMed] [Google Scholar]