Lipoxygenase-mediated production of fatty acid hydroperoxides is a specific signature of the hypersensitive reaction in plants

Lipoxygenase (LOX)-dependent massive production of (9S) fatty acid hydroperoxides was previously observed in cryptogein-elicited tobacco leaves and proposed as being an actor of cell death during the hypersensitive reaction (HR). In this work, we have further investigated the occurrence of this metabolism for biotic, compatible and incompatible interactions in tobacco, and also in Arabidopsis thaliana. Our methodology, based on metabolite analysis (isomer distribution and chirality), is sufficient to assess for the induction of a LOX metabolism. In both plants, a (13S) oxylipin metabolism is initially operating in control leaves. In tobacco, the (9S) LOX-dependent oxylipin metabolism was shown to be induced by tobacco mosaic virus and an avirulent bacterial strain of Ralstonia solanacearum. In Arabidopsis, accumulation of the oxylipin metabolites in leaves was also observed in response to harpin, and during different incompatible interactions. However, in the latter model, the metabolites are mainly (13S), suggesting the involvement of a specific (13S) LOX. In all cases studied so far, accumulation of the oxylipin metabolites is correlated with HR cell death and is not observed during compatible interactions. In many plant species, LOX transcript accumulation precedes, and LOX activity correlates, the induction of the HR symptoms. Thus, accumulation of the oxylipin metabolites can be considered as a marker of HR cell death in plant-pathogen interactions. Both 9 or 13 oxylipin metabolism can be apparently activated, depending on the plant species. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.