Formation of a new class of oxylipins from N-acyl(ethanol)amines by the lipoxygenase pathway

N-Acylethanolamines (NAEs) constitute a new class of plant lipids and are t hought to play a role in plant defense strategies against pathogens. In pla nt defense systems, oxylipins generated by the lipoxygenase pathway are imp ortant actors. To date, it is not known whether plants also use endogeneous oxylipins derived from NAEs in their defense reactions. We tested whether members of the NAE class can be converted by enzymes constituting this path way, such as (soybean) lipoxygenase-1, (alfalfa) hydroperoxide lyase and (f lax seed) allene oxide synthase. We found that both alpha-N-linolenoylethan olamine and gamma-N-linolenoylethanolamine (18:3), as well as alpha-N-linol enoylamine and gamma-N-linolenoylamine were converted into their (13S)-hydr operoxide derivatives by lipoxygenase. Interestingly, only the hydroperoxid es of alpha-N-linolenoyl(ethanol)amines and their linoleic acid analogs (18 :2) were suitable substrates for hydroperoxide lyase. Hexanal and (3Z)-hexe nal were identified as volatile products of the 18:2 and 18:3 fatty acid (e thanol)amides, respectively. 12-Oxo-N-(9Z)-dodecenoyl(ethanol)amine was the nonvolatile hydrolysis product. Kinetic studies with lipoxygenase and hydr operoxide lyase revealed that the fatty acid ethanolamides were converted a s readily or even better than the corresponding free fatty acids. Allene ox ide synthase utilized all substrates, but was most active on (13S)-hydroper oxy-alpha-N-linolenoylethanolamine and the (13S)-hydroperoxide of linoleic acid and its ethanolamine derivative. alpha-Ketols and gamma-ketols were ch aracterized as products. In addition, cyclized products, i.e. 12-oxo-N-phyt odienoylamines, derived from (13S)-hydroperoxy-alpha-N-linolenoylamines wer e found. The results presented here show that, in principle, hydroperoxide NAEs can be formed in plants and subsequently converted into novel phytooxy lipins.