title: Metabolic origin of the delta13C of respired CO2 in roots of Phaseolus vulgaris.
abstract: Root respiration is a major contributor to soil CO2 efflux, and thus an important component of ecosystem respiration. But its metabolic origin, in relation to the carbon isotope composition (delta13C), remains poorly understood. Here, 13C analysis was conducted on CO2 and metabolites under typical conditions or under continuous darkness in French bean (Phaseolus vulgaris) roots. 13C contents were measured either under natural abundance or following pulse-chase labeling with 13C-enriched glucose or pyruvate, using isotope ratio mass spectrometer (IRMS) and nuclear magnetic resonance (NMR) techniques. In contrast to leaves, no relationship was found between the respiratory quotient and the delta13C of respired CO2, which stayed constant at a low value (c. -27.5 per thousand) under continuous darkness. With labeling experiments, it is shown that such a pattern is explained by the 13C-depleting effect of the pentose phosphate pathway; and the involvement of the Krebs cycle fueled by either the glycolytic input or the lipid/protein recycling. The anaplerotic phosphoenolpyruvate carboxylase (PEPc) activity sustained glutamic acid (Glu) synthesis, with no net effect on respired CO2. These results indicate that the root delta13C signal does not depend on the availability of root respiratory substrates and it is thus plausible that, unless the 13C photosynthetic fractionation varies at the leaf level, the root delta13C signal hardly changes under a range of natural environmental conditions.
authors.affiliation: Laboratoire d'Ecologie, Systématique et Evolution (ESE), CNRS-UMR 8079 - IFR 87, Bâtiment 362, Université Paris-Sud, 91405-Orsay Cedex, France;Plateforme Métabolisme-Métabolome, IFR87 La Plante et son Environnement, Institut de Biotechnologie des Plantes, Bâtiment 630, Université Paris-Sud, 91405-Orsay Cedex, France;Laboratoire de Physiologie Cellulaire Végétale CEA-Grenoble 17, rue des Martyrs, 38054 Grenoble Cedex 9, France.
authors.forename: Camille
authors.initials: C
authors.lastname: Bathellier
authors.affiliation: Laboratoire d'Ecologie, Systématique et Evolution (ESE), CNRS-UMR 8079 - IFR 87, Bâtiment 362, Université Paris-Sud, 91405-Orsay Cedex, France;Plateforme Métabolisme-Métabolome, IFR87 La Plante et son Environnement, Institut de Biotechnologie des Plantes, Bâtiment 630, Université Paris-Sud, 91405-Orsay Cedex, France;Laboratoire de Physiologie Cellulaire Végétale CEA-Grenoble 17, rue des Martyrs, 38054 Grenoble Cedex 9, France.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Tcherkez
authors.affiliation: Laboratoire d'Ecologie, Systématique et Evolution (ESE), CNRS-UMR 8079 - IFR 87, Bâtiment 362, Université Paris-Sud, 91405-Orsay Cedex, France;Plateforme Métabolisme-Métabolome, IFR87 La Plante et son Environnement, Institut de Biotechnologie des Plantes, Bâtiment 630, Université Paris-Sud, 91405-Orsay Cedex, France;Laboratoire de Physiologie Cellulaire Végétale CEA-Grenoble 17, rue des Martyrs, 38054 Grenoble Cedex 9, France.
authors.forename: Richard
authors.initials: R
authors.lastname: Bligny
authors.affiliation: Laboratoire d'Ecologie, Systématique et Evolution (ESE), CNRS-UMR 8079 - IFR 87, Bâtiment 362, Université Paris-Sud, 91405-Orsay Cedex, France;Plateforme Métabolisme-Métabolome, IFR87 La Plante et son Environnement, Institut de Biotechnologie des Plantes, Bâtiment 630, Université Paris-Sud, 91405-Orsay Cedex, France;Laboratoire de Physiologie Cellulaire Végétale CEA-Grenoble 17, rue des Martyrs, 38054 Grenoble Cedex 9, France.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Gout
authors.affiliation: Laboratoire d'Ecologie, Systématique et Evolution (ESE), CNRS-UMR 8079 - IFR 87, Bâtiment 362, Université Paris-Sud, 91405-Orsay Cedex, France;Plateforme Métabolisme-Métabolome, IFR87 La Plante et son Environnement, Institut de Biotechnologie des Plantes, Bâtiment 630, Université Paris-Sud, 91405-Orsay Cedex, France;Laboratoire de Physiologie Cellulaire Végétale CEA-Grenoble 17, rue des Martyrs, 38054 Grenoble Cedex 9, France.
authors.forename: Gabriel
authors.initials: G
authors.lastname: Cornic
authors.affiliation: Laboratoire d'Ecologie, Systématique et Evolution (ESE), CNRS-UMR 8079 - IFR 87, Bâtiment 362, Université Paris-Sud, 91405-Orsay Cedex, France;Plateforme Métabolisme-Métabolome, IFR87 La Plante et son Environnement, Institut de Biotechnologie des Plantes, Bâtiment 630, Université Paris-Sud, 91405-Orsay Cedex, France;Laboratoire de Physiologie Cellulaire Végétale CEA-Grenoble 17, rue des Martyrs, 38054 Grenoble Cedex 9, France.
authors.forename: Jaleh
authors.initials: J
authors.lastname: Ghashghaie
mesh_terms: D000064:Acclimatization; D002245:Carbon Dioxide / Q000737:chemistry / Q000378:metabolism*; D002247:Carbon Isotopes / Q000032:analysis / Q000378:metabolism*; D019069:Cell Respiration / Q000502:physiology; D003624:Darkness; D009682:Magnetic Resonance Spectroscopy; D027805:Phaseolus / Q000378:metabolism*; D010730:Phosphoenolpyruvate Carboxylase / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism*
chemical_list: D002247:Carbon Isotopes; D002245:Carbon Dioxide; D010730:Phosphoenolpyruvate Carboxylase