Wound
VOCs
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Wound
VOCs
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Wound
VOCs--surprising chemistry in leaves revealed by PTR-MS.
It is well known that physical wounding of green leaves leads to the production
of VOCs in the cis-3-hexenal family as shown in the scheme below (right). These
six-carbon VOCs appear to be antimicrobial compounds, so their formation after
wounding may inhibit invasion of the leaf by opportunistic microbes that abound
on leaf surfaces. Progress in understanding biochemical aspects of leaf wound
VOC formation has been hindered by the analytical challenge of measuring their
formation. We have collaborated with scientists at NOAA (Boulder) and the University
of Innsbruck (Austria) to use proton-transfer-reaction mass spectrometry (PTR-MS)
to measure wound VOC formation. The method eliminates the need for pre-concentration
or chromatography; instead PTR-MS allows continuous on-line analysis of almost
all biogenic VOCs with high sensitivity. Some highlights of recent published
or submitted work are the following. (1) Wound VOCs are generally not released
from pre-existing pools in leaves, but are formed within seconds of wounding
by the lipoxygenase (LOX) system. Thus wound VOC release is controlled by wound
signaling reactions that lead to release of chloroplast fatty acids. 2) Formation
of wound VOCs is much higher during the drying phase following cutting (see
the figures on the following page). This has implications for the release of
reactive VOCs following lawn mowing and hay crop harvesting, and during leaf
drying associated with leaf senescence in major crops like corn, wheat and soybean.
3) Leaf damage induced by frost events in the Autumn triggers LOX-dependent
formation of five-carbon VOCs, like 1-penten-3-ol and 1-penten-3-one, which
have been detected in high amounts in air at a mountain peak in Austria. We
have shown that leaves from a diverse array of plants in the Innsbruck, Austria
area catalyze pentenyl VOC formation after a freeze-thaw event, and suggest
that leaf LOX is responsible, catalyzing the free radical cleavage of fatty
acids shown below (left)
References. R. Fall, T. Karl, A. Hansel, A. Jordan, and W. Lindinger (1999)
Volatile organic compounds emitted after leaf wounding. On-line analysis by
proton-transfer-reaction mass spectrometry. J. Geophys. Res. 104, 15963-15974.
J.A. de Gouw, C.J. Howard, T.G. Custer, and R. Fall (1999). ) Emissions of volatile
organic compounds from cut grass and clover are enhanced during the drying process.
Geophys. Res. Lett. 26, 811-814. J.A. de Gouw, C.J. Howard, T.G. Custer, B.M.
Baker, and R. Fall (2000) Proton-transfer chemical ionization mass spectrometry
allows real-time analysis of volatile organic compounds released from cutting
and drying of crops. Environ. Sci. Technol., in press. T. Karl, R. Fall, P.
J. Crutzen, A. Jordan, and W. Lindinger (2000) High concentrations of reactive
biogenic VOCs in the free troposphere during the late Autumn. Submitted.