PLANT PHYSIOLOGY , Vol 110, Issue 4 1317-1322, Copyright © 1996 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Evidence of the Photosynthetic Origin of Monoterpenes Emitted by Quercus ilex L. Leaves by 13C Labeling
F. Loreto, P. Ciccioli, A. Cecinato, E. Brancaleoni, M. Frattoni, C. Fabozzi and D. Tricoli
Consiglio Nazionale delle Ricerche (CNR)-Istituto di Biochimica ed Ecofisiologia Vegetali (F.L, D.T.) and CNR-Istituto per I'Inquinamento Atmosferico (P.C., A.C., E.B., M.F., C.F.), Via Salaria, Km 29,300-00016 Monterotondo Scalo, Rome, Italy
The carbon of the four main monoterpenes emitted by Quercus ilex L. leaves
was completely labeled with 13C after a 20-min feeding with 99% 13CO2. This
labeling time course is comparable with the labeling time course of
isoprene, the terpenoid emitted by other Quercus species and synthesized in
leaf chloroplasts. It is also comparable with that of phosphoglyceric acid.
Our experiment therefore provides evidence that monoterpenes emitted by Q.
ilex are formed from photosynthesis intermediates and may share the same
synthetic pathway with isoprene. By analyzing the rate and the distribution
of labeling in the different fragments, we looked for evidence of
differential carbon labeling in the [alpha]-pinene emitted. However, the
labeling pattern was quite uniform in the different fragments, suggesting
that the carbon skeleton of the emitted monoterpenes comes from a unique
carbon source.
