title: The intramolecular ¹³C-distribution in ethanol reveals the influence of the CO₂ -fixation pathway and environmental conditions on the site-specific ¹³C variation in glucose.
abstract: Efforts to understand the cause of ¹²C versus ¹³C isotope fractionation in plants during photosynthesis and post-photosynthetic metabolism are frustrated by the lack of data on the intramolecular ¹³C-distribution in metabolites and its variation with environmental conditions. We have exploited isotopic carbon-13 nuclear magnetic resonance (¹³C NMR) spectrometry to measure the positional isotope composition (δ¹³C(i) , ‰) in ethanol samples from different origins: European wines, liquors and sugars from C₃, C₄ and crassulacean acid metabolism (CAM) plants. In C₃-ethanol samples, the methylene group was always ¹³C-enriched (∼2‰) relative to the methyl group. In wines, this pattern was correlated with both air temperature and δ(18)O of wine water, indicating that water vapour deficit may be a critical defining factor. Furthermore, in C₄-ethanol, the reverse relationship was observed (methylene-C relatively ¹³C-depleted), supporting the concept that photorespiration is the key metabolic process leading to the ¹³C distribution in C₃-ethanol. By contrast, in CAM-ethanol, the isotopic pattern was similar to but stronger than C₃-ethanol, with a relative ¹³C-enrichment in the methylene-C of up to 13‰. Plausible causes of this ¹³C-pattern are briefly discussed. As the intramolecular δ¹³C(i) -values in ethanol reflect that in source glucose, our data point out the crucial impact on the ratio of metabolic pathways sustaining glucose synthesis.
authors.affiliation: 1Interdisciplinary Chemistry: Synthesis,Analysis, Modelling (CEISAM), University of Nantes – CNRS UMR 6230, 2 rue de laHoussinière, BP 92208, F-44322 Nantes, France.
authors.forename: Alexis
authors.initials: A
authors.lastname: Gilbert
authors.forename: Virginie
authors.initials: V
authors.lastname: Silvestre
authors.forename: Nicolas
authors.initials: N
authors.lastname: Segebarth
authors.forename: Guillaume
authors.initials: G
authors.lastname: Tcherkez
authors.forename: Claude
authors.initials: C
authors.lastname: Guillou
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Robins
authors.forename: Serge
authors.initials: S
authors.lastname: Akoka
authors.forename: Gérald S
authors.initials: GS
authors.lastname: Remaud
mesh_terms: D000388:Air; D002244:Carbon / Q000737:chemistry / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism*; D002247:Carbon Isotopes / Q000032:analysis / Q000378:metabolism; D019069:Cell Respiration; D029627:Crassulaceae / Q000378:metabolism / Q000502:physiology; D000431:Ethanol / Q000737:chemistry*; D005285:Fermentation; D005947:Glucose / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D010788:Photosynthesis; D011891:Rain; D013472:Sunlight; D013696:Temperature; D027843:Vitis / Q000737:chemistry* / Q000378:metabolism; D014867:Water; D014920:Wine / Q000032:analysis
chemical_list: D002247:Carbon Isotopes; D014867:Water; D002245:Carbon Dioxide; D000431:Ethanol; D002244:Carbon; D005947:Glucose