Abstracts now available online - Euro Fed Lipid

Profiling of labile plant oxylipins by in situ derivatization with
pentafluorobenzyl-hydroxylamine
Birgit Schulze, Paulina Dąbrowska, Wilhelm Boland,
Max-Plank-Institut für chemische Ökologie
Jena, Germany
Signaling compounds derived from the family of unsaturated C18-fatty acids play an
important role during plant development and stress response. Although the oxylipins
comprise a broad range of chemically diverse compounds, most previous studies focus
on the analysis of classical phytohormones such as jasmonic acid and 12oxophytodienoic
acid. We developed a rapid and reliable GC-MS-based method for the
identification and quantification of oxylipins which includes labile and highly reactive
compounds. A key feature of the method is the in situ derivatization of leaf extracts with
pentafluorobenzyl hydroxylamine (PFBHA) yielding stable PFB-oximes that prevent
degradation and rearrangements during sample preparation. The raw extract is
partitioned with hexane and CH2Cl2 to separate less polar from polar compounds
followed by aminopropyl solid phase extraction and derivatization with diazomethane
and N-methyltrimethylsilyltrifluoroacetamide (MSTFA).
Moreover, PFB-oximes exhibit characteristic mass spectra and can be analyzed with
high sensitivity by negative ionization mass spectrometry (NCI-MS). This approach
greatly facilitates the identification of unknown oxylipins in complex plant matrices and
allows monitoring of temporal and spatial changes of the oxylipin pattern in response to
stress factors. High levels of oxylipins were observed locally in caterpillar damaged leaf
tissue. Some of the oxylipins were already produced after mere mechanical wounding;
whereas others required an additional action of herbivore-characteristic elicitors.
Additionally, the in situ derivatization completely suppresses the isomerization of cis-JA
to the less active trans-JA. After wounding, cis-JA is produced by de novo biosynthesis
via the octadecanoid pathway. Then, cis-JA is slowly converted into its less active transisomer
until a resting level is reached. Although substantial differences in physiological
activity of various JA isomers have been reported, it is not entirely clear to which extend
the epimerization is under enzymatic control or occurs spontaneously.
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