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Carbon Metabolism in Spores of the Arbuscular Mycorrhizal Fungus
Glomus intraradices as Revealed by
Nuclear
Magnetic Resonance Spectroscopy1
Berta Bago,
Philip E. Pfeffer*,
David D. Douds Jr.,
Janine Brouillette,
Guillaume Bécard, and
Yair Shachar-Hill
United States Department of Agriculture-Agricultural Research
Service, Eastern Regional Research Center, 600 East Mermaid Lane,
Wyndmoor, Pennsylvania 19038 (B.B., P.E.P., D.D.D., J.B.); Unité
Mixte de Recherche, Centre National de la Recherche Scientifique
(Strasbourg, France)/Université de Paris-Sud 5546, Pôle de
Biotechnologie Végétale, 24 chemin de Borde-Rouge 31326, Castanet Tolosan, France (G.B.); and New Mexico State University,
Department of Chemistry and Biochemistry, Las Cruces, New Mexico 88001 (Y.S.-H.)
Arbuscular mycorrhizal (AM) fungi are
obligate symbionts that colonize the roots of over 80% of plants in
all terrestrial environments. Understanding why AM fungi do not
complete their life cycle under free-living conditions has significant
implications for the management of one of the world's most important
symbioses. We used 13C-labeled substrates and nuclear
magnetic resonance spectroscopy to study carbon fluxes during spore
germination and the metabolic pathways by which these fluxes occur in
the AM fungus Glomus intraradices. Our results indicate
that during asymbiotic growth: (a) sugars are made from stored lipids;
(b) trehalose (but not lipid) is synthesized as well as degraded; (c)
glucose and fructose, but not mannitol, can be taken up and utilized;
(d) dark fixation of CO2 is substantial; and (e) arginine
and other amino acids are synthesized. The labeling patterns are
consistent with significant carbon fluxes through gluconeogenesis, the
glyoxylate cycle, the tricarboxylic acid cycle, glycolysis,
non-photosynthetic one-carbon metabolism, the pentose phosphate
pathway, and most or all of the urea cycle. We also report the presence
of an unidentified betaine-like compound. Carbon metabolism during
asymbiotic growth has features in between those presented by
intraradical and extraradical hyphae in the symbiotic state.
1
This work was supported in part by grant no.
97-35107-4375 from the National Research Initiative Competitive
Grants Program/U.S. Department of Agriculture and via a fellowship
under the Organisation for Economic Co-operation and Development
Co-operative Research Program: Biological Resource Management for
Sustainable Agriculture Systems (to G.B.). The research utilized in
part the Resource for Solid-State NMR of Proteins at the University of
Pennsylvania: A National Institutes of Health Supported Research Center
(grant no. P41RR09731 from the Biomedical Research Technology Program, National Center for Research Resources, National Institutes of Health).
*
Corresponding author; e-mail ppfeffer{at}arserrc.gov; fax
215-233-6581.
Plant Physiol. (1999) 121: 263-272
Copyright Clearance Center: 0032-0889/99/121//10
© 1999 American Society of Plant Physiologists
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