Activation of NADPH Oxidase by Linolenic Acid Derived from Chloroplast Lipids

Abstract

Pathogen invasion of plants induces a transient production of reactive oxygen species (e.g., O₂^-, H₂O₂). O₂^- generation is catalyzed by NADPH oxidase. Molecular mechanism underlying activation of NADPH oxidase remains unclear. As reported previously (Yaeno et al. (2003) Plant Cell Physiol. 44: suppl, s149), α-linolenic acid (LA), the most abundant trienoic fatty acids (TAs) in the chloroplast membrane lipids, is involved in the activation of NADPH oxidase. In Arabidopsis wild-type leaves inoculated with Pseudomonas syringae pv. tomato DC3000 (avrRpm1), the levels of free LA increased coincident with H₂O₂ accumulation. Further, the LA levels of extrachloroplast membrane phospholipids increased substantially. This increase was accompanied by the transfer of hexadecatrienoic acid, a TA species usually acylated in chloroplast galactolipids, to extrachloroplast phospholipids. These results suggest that LA liberated from chloroplast membrane lipids is utilized for the activation of NADPH oxidase which is localized in the plasma membrane.