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.