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On-line analysis of the {13}CO(2) labeling of leaf isoprene suggests multiple subcellular origins of isoprene precursors

Project ID: 1973
Funded under: FP5-JRC


Isoprene (2-methyl-1,3-butadiene) is the most abundant biogenic hydrocarbon released from vegetation, and there is continuing interest in understanding its biosynthesis from photosynthetic precursors in leaf chloroplasts. We used on-line proton-transfer-reaction mass spectrometry (PTR-MS) to observe the kinetics of {13}C-labelling of isoprene following exposure to {13}CO(2) and then the loss of {13}C after a return to normal {12}CO(2) in oak (Quercus agrifolia Nee) and cottonwood (Populus deltoides Barr.) leaves. Assignments of labelled isoprene species were verified by gas chromatography-mass spectrometry. For the first time, it was possible to observe the half-lives of individually {13}C-labeled isoprene species during these transitions, and to trace some of the label to a C3 fragment that contained the two isoprene carbons derived from pyruvate via the deoxyxylulose-5-phosphate (DOXP) pathway. At steady state (under {13}CO(2)), approximately 80% of isoprene carbon was labeled, with fully labeled isoprene as the major species (approx. 60%). The source of the unlabeled C is suggested to be extrachloroplastic, but not from photorespiratory carbon. After a transfer to {12}CO(2), {13}C-labelling persisted in one isoprene carbon for several hours; this persistence was much more pronounced in (i) leaves inhibited by fosmidomycin, a specific inhibitor of the DOXP pathway, and (ii) in sun leaves which have higher ratios of soluble sugars to starch. Other sources of cytosolic isoprene precursors (i.e. dimethylallyl diphosphate or pentose phosphate) could not be excluded. The data obtained shed light on the half-lives of photosynthetic metabolites, exchanges of carbon between cellular pools, and suggest multiple origins of isoprene precursors in leaves.

Additional information

Authors: KARL T, Insitut für Ionenphysik, Universität Innsbruck (AT);PRAZELLER P, Insitut für Ionenphysik, Universität Innsbruck (AT);LINDINGER W, Insitut für Ionenphysik, Universität Innsbruck (AT);FALL R, Department of Chemistry and Biochemistry and the Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder (US);ROSENSTIEL T N, Department of EPO Biology, University of Colorado, Boulder (US);LARSEN B, European Commission, Joint Research Centre, Institute for Environment and Sustainability, Ispra (IT);SEUFERT G, European Commission, Joint Research Centre, Institute for Environment and Sustainability, Ispra (IT)
Bibliographic Reference: An article published in: Planta, vol 215, no. 6 (October 2002), pp. 894-905
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