Abstract
Carbon isotope composition in respired CO2 and organic matter of individual organs were measured on peanut seedlings during early ontogeny in order to compare fractionation during heterotrophic growth and transition to autotrophy in a species with lipid seed reserves with earlier results obtained on beans. Despite a high lipid content in peanut seeds (48 %) compared with bean seeds (1.5 %), the isotope composition of leaf- and root-respired CO2 as well as its changes during ontogeny were similar to already published data on bean seedlings: leaf-respired CO2 became 13C-enriched reaching −21.5 ‰, while root-respired CO2 became 13C-depleted reaching around −31 ‰ at the four-leaf stage. The opposite respiratory fractionation in leaves vs. roots already reported for C3 herbs was thus confirmed for peanuts. However, contrarily to beans, the peanut cotyledon-respired CO2 was markedly 13C-enriched, and its 13C-depletion was noted from the two-leaf stage onwards only. Carbohydrate amounts being very low in peanut seeds, this cannot be attributed solely to their use as respiratory substrate. The potential role of isotope fractionation during glyoxylate cycle and/or gluconeogenesis on the 13C-enriched cotyledon-respired CO2 is discussed.
Acknowledgements
The authors are grateful to the Laboratoire d'Ecologie, Systématique et Evolution (ESE, CNRS-UMR 8079) at the University of Paris-Sud (Orsay) for financial support for isotope analyses, the platform ‘Métabolisme-Métabolome’ of the IFR87 (Orsay) for technical assistance for isotope analyses of water-soluble fraction, and the Laboratoire de Biogéochimie et Ecologie des Milieux Continentaux (BIOEMCO, INRA, Thiverval-Grignon) for providing both plant culture and IRMS facilities as well as for technical assistance for isotope analyses of respired CO2 and bulk OM.
Disclosure statement
No potential conflict of interest was reported by the authors.