© 2004 Heron Publishing—Victoria, Canada
Impact of ozone on monoterpene emissions and evidence for an isoprene-like antioxidant action of monoterpenes emitted by Quercus ilex leaves
Francesco Loreto (1, 2), Paola Pinelli (1), Fausto Manes (3) and Hannes Kollist (4)
1. CNR-Istituto di Biologia Agroambientale e Forestale, Monterotondo Scalo, Italy / 2. Corresponding author (francesco.loreto@ibaf.cnr.it) / 3. Universita’ di Roma I, Dipartimento di Biologia Vegetale, Roma, Italy / 4. Department of Biology, University of Turku, FIN-20014 Turku, Finland / Received June 20, 2003; accepted September 13, 2003; published online February 2, 2004
Summary
Quercus ilex (L.) leaves emit monoterpenes, particularly α-pinene, β-pinene and sabinene. Apart from the monoterpene pools that are stored
in specialized structures and have a clear defensive or attractive role, the function of monoterpenes in Q. ilex leaves is unknown. We tested whether monoterpenes have an antioxidant role, as has previously been found for isoprene in
isoprene-emitting leaves. We exposed Q. ilex leaves to either mild and repeated ozone exposure (Experiment I) or to a single acute ozone exposure (Experiment II) at temperatures
ranging between 20 and 32 °C. Both ozone treatments rapidly stimulated monoterpene synthesis, but had no effect on photosynthesis
and caused no visible damage to leaves maintained at 25, 30 or 32 °C. Ozone inhibited both photosynthesis and monoterpene
synthesis in leaves maintained at 20 °C. To characterize the relationship between monoterpenes and ozone-induced damage, we
fed detached leaves fosmidomycin, a selective inhibitor of isoprene synthesis. Fosmidomycin caused rapid and complete inhibition
of monoterpene emissions in leaves maintained at 30 °C, confirming that monoterpenes are synthesized by the same biochemical
pathway as isoprene. However, over the experimental period, fosmidomycin did not affect concentrations of compounds that are
formed from chloroplastic isoprenoids and that might have conferred antioxidant protection, either directly (carotenoids)
or indirectly (chlorophylls, xanthophylls). In leaves whose monoterpene synthesis had been inhibited by fosmidomycin, ozone
rapidly and significantly inhibited photosynthesis and increased the production of hydrogen peroxide and malonyldialdehyde.
We conclude that monoterpenes produced by Q. ilex leaves share the same biosynthetic pathway and function as isoprene. Furthermore, all volatile isoprenoids may have similar
antioxidant properties and may be stimulated by the same stress-inducing conditions.
Keywords:
chlorophyll fluorescence, fosmidomycin, isoprenoids, photosynthesis, reactive oxygen species.
