Detection of plant volatiles after leaf wounding and darkening by proton transfer reaction "time-of-flight" mass spectrometry (PTR-TOF).
Bottom Line: In the strong isoprene-emitter Populus alba, light-dependent isoprene emission was sustained and even enhanced for hours after photosynthesis inhibition due to leaf cutting.Thus isoprene emission can uncouple from photosynthesis and may occur even after cutting leaves or branches, e.g., by agricultural practices or because of abiotic and biotic stresses.This observation may have important implications for assessments of isoprene sources and budget in the atmosphere, and consequences for tropospheric chemistry.
Affiliation: Ionicon Analytik G.m.b.H., Innsbruck, Austria.
Proton transfer reaction-time of flight (PTR-TOF) mass spectrometry was used to improve detection of biogenic volatiles organic compounds (BVOCs) induced by leaf wounding and darkening. PTR-TOF measurements unambiguously captured the kinetic of the large emissions of green leaf volatiles (GLVs) and acetaldehyde after wounding and darkening. GLVs emission correlated with the extent of wounding, thus confirming to be an excellent indicator of mechanical damage. Transient emissions of methanol, C5 compounds and isoprene from plant species that do not emit isoprene constitutively were also detected after wounding. In the strong isoprene-emitter Populus alba, light-dependent isoprene emission was sustained and even enhanced for hours after photosynthesis inhibition due to leaf cutting. Thus isoprene emission can uncouple from photosynthesis and may occur even after cutting leaves or branches, e.g., by agricultural practices or because of abiotic and biotic stresses. This observation may have important implications for assessments of isoprene sources and budget in the atmosphere, and consequences for tropospheric chemistry.
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Mentions: In vivo information on the enzymatic activity leading to GLVs production cannot be provided according to Michealis-Menten model due to difficult estimation of substrate availability. This is the consequence of the continuous conversion of enzymatic products into further substrates which occurs once the cascade of multi-step enzymatic reaction (catalyzed by LOX, HPL, ADH and AD) has been initiated. However, by exploiting PTR-TOF highly resolved GLVs analysis, it may be possible to indirectly analyze differences in the activation of the lipoxygenase pathway by following the rate of conversion over the time between ratios of protonated ions. In particular the time course of the ratios between m/z = 83.085/81.070 (hexenols + hexanal/hexenals) and between m/z = 143.107/81.070 (hexenyl acetates/hexenals) may provide information about the speed of conversion of the classes of GLVs. We performed this analysis on GLVs emitted after cutting and after transition from light to dark transition by D. glomerata and P. alba leaves (Fig. 7 a,b). Our results show that wounding induces a differential production of the main GLVs over the time with respect to light-dark transition in both plant species. The instantaneous oxidation of linoleic and α-linolenic acids occurring when wounded cellular membranes are exposed to the air contact efficiently catalyzed the first step of the lipoxygenase reactions leading to the production of m/z = 81.070 (hexanal/hexenals) that is slowly converted to m/z = 83.085 (hexenols) and then to m/z = 143.107 (hexenyl acetates); differently the condition created by sudden darkening induces a production of both m/z = 81.070 than m/z = 83.085 (or m/z = 143.107) with similar time-courses.