title: Metabolic origin of carbon isotope composition of leaf dark-respired CO2 in French bean.
abstract: The carbon isotope composition (delta(13)C) of CO(2) produced in darkness by intact French bean (Phaseolus vulgaris) leaves was investigated for different leaf temperatures and during dark periods of increasing length. The delta(13)C of CO(2) linearly decreased when temperature increased, from -19 per thousand at 10 degrees C to -24 per thousand at 35 degrees C. It also progressively decreased from -21 per thousand to -30 per thousand when leaves were maintained in continuous darkness for several days. Under normal conditions (temperature not exceeding 30 degrees C and normal dark period), the evolved CO(2) was enriched in (13)C compared with carbohydrates, the most (13)C-enriched metabolites. However, at the end of a long dark period (carbohydrate starvation), CO(2) was depleted in (13)C even when compared with the composition of total organic matter. In the two types of experiment, the variations of delta(13)C were linearly related to those of the respiratory quotient. This strongly suggests that the variation of delta(13)C is the direct consequence of a substrate switch that may occur to feed respiration; carbohydrate oxidation producing (13)C-enriched CO(2) and beta-oxidation of fatty acids producing (13)C-depleted CO(2) when compared with total organic matter (-27.5 per thousand). These results are consistent with the assumption that the delta(13)C of dark respired CO(2) is determined by the relative contributions of the two major decarboxylation processes that occur in darkness: pyruvate dehydrogenase activity and the Krebs cycle.
authors.affiliation: Laboratoire d'Ecophysiologie Végétale, Unité Propre de Recherche et d'Enseignement Supérieur Associé 8079, Bâtiment 362, Université Paris XI, 91405 Orsay, France. guillaume.tcherkez@ese.u-psud.fr
authors.forename: Guillaume
authors.initials: G
authors.lastname: Tcherkez
authors.forename: Salvador
authors.initials: S
authors.lastname: Nogués
authors.forename: Jean
authors.initials: J
authors.lastname: Bleton
authors.forename: Gabriel
authors.initials: G
authors.lastname: Cornic
authors.forename: Franz
authors.initials: F
authors.lastname: Badeck
authors.forename: Jaleh
authors.initials: J
authors.lastname: Ghashghaie
mesh_terms: D050260:Carbohydrate Metabolism; D002245:Carbon Dioxide / Q000378:metabolism*; D002247:Carbon Isotopes / Q000378:metabolism; D019069:Cell Respiration / Q000502:physiology; D002952:Citric Acid Cycle / Q000502:physiology; D003624:Darkness; D005227:Fatty Acids / Q000378:metabolism; D010084:Oxidation-Reduction; D027805:Phaseolus / Q000378:metabolism*; D018515:Plant Leaves / Q000378:metabolism*; D011768:Pyruvate Dehydrogenase Complex / Q000378:metabolism; D013696:Temperature; D013997:Time Factors
chemical_list: D002247:Carbon Isotopes; D005227:Fatty Acids; D011768:Pyruvate Dehydrogenase Complex; D002245:Carbon Dioxide