PLANT PHYSIOLOGY , Vol 101, Issue 3 865-871, Copyright © 1993 by American Society of Plant Biologists
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PLANT-MICROBE INTERACTIONS |
Ammonia Assimilation in Zea mays L. Infected with a Vesicular-Arbuscular Mycorrhizal Fungus Glomus fasciculatum
J. B. Cliquet and G. R. Stewart
Biology Department, University College London, Gower Street, London WC1, United Kingdom
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.
