N-Acylethanolamines (
NAEs) are fatty-acid derivatives with potent biological activities in a wide range of eukaryotic organisms. Polyunsaturated
NAEs are among the most abundant
NAE types in seeds of
Arabidopsis thaliana, and they can be metabolized by either fatty acid amide hydrolase (
FAAH) or by lipoxygenase (
LOX) to low levels during seedling establishment. Here, we identify and quantify endogenous oxylipin metabolites of
N-linolenoylethanolamine (
NAE 18:3) in
Arabidopsis seedlings and show that their levels were higher in
faah knockout seedlings. Quantification of oxylipin metabolites in
lox mutants demonstrated altered partitioning of
NAE 18:3 into 9- or 13-
LOX pathways, and this was especially exaggerated when exogenous
NAE was added to seedlings. When maintained at micromolar concentrations,
NAE 18:3 specifically induced cotyledon bleaching of light-grown seedlings within a restricted stage of development. Comprehensive oxylipin profiling together with genetic and pharmacological interference with
LOX activity suggested that both 9-hydroxy and 13-hydroxy linolenoylethanolamides, but not corresponding free fatty-acid metabolites, contributed to the reversible disruption of thylakoid membranes in chloroplasts of seedling cotyledons. We suggest that
NAE oxylipins of linolenic acid represent a newly identified, endogenous set of bioactive compounds that may act in opposition to progression of normal seedling development and must be depleted for successful establishment.
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