The
lipoxygenase pathway is responsible for the production of
oxylipins, which are important compounds for plant defence responses.
Jasmonic acid, the final product of the
allene oxide synthase/
allene oxide cyclase branch of the pathway, regulates
wound-induced gene expression. In contrast, C6 aliphatic
aldehydes produced via an alternative branch catalysed by
hydroperoxide lyase, are themselves toxic to pests and pathogens. Current evidence on the subcellular localization of the
lipoxygenase pathway is conflicting, and the regulation of metabolic channelling between the two branches of the pathway is largely unknown. It is shown here that while a
13-lipoxygenase (LOX H3),
allene oxide synthase and
allene oxide cyclase proteins accumulate upon wounding in potato, a second
13-lipoxygenase (LOX H1) and
hydroperoxide lyase are present at constant levels in both non-wounded and wounded tissues.
Wound-induced accumulation of the
jasmonic acid biosynthetic
enzymes may thus commit the
lipoxygenase pathway to
jasmonic acid production in damaged plants. It is shown that all
enzymes of the
lipoxygenase pathway differentially localize within chloroplasts, and are largely found associated to thylakoid membranes. This differential localization is consistently observed using confocal microscopy of GFP-tagged
proteins, chloroplast fractionation, and western blotting, and immunodetection by electron microscopy. While LOX H1 and LOX H3 are localized both in stroma and thylakoids, both
allene oxide synthase and
hydroperoxide lyase protein localize almost exclusively to thylakoids and are strongly bound to membranes.
Allene oxide cyclase is weakly associated with the thylakoid membrane and is also detected in the stroma. Moreover,
allene oxide synthase and
hydroperoxide lyase are differentially distributed in thylakoids, with
hydroperoxide lyase localized almost exclusively to the stromal part, thus closely resembling the localization pattern of LOX H1. It is suggested that, in addition to their differential expression pattern, this segregation underlies the regulation of metabolic fluxes through the alternative branches of the
lipoxygenase pathway.