Abstract
Pathogen invasion of plants induces a transient production of reactive oxygen species (e.g., superoxide) in the oxidative burst. Superoxide generation is probably catalyzed by NADPH oxidase. Animal NADPH oxidase is well characterized, but the molecular mechanism underlying activation of NADPH oxidase in plants remains unclear. Trienoic fatty acids (TAs) are the major polyunsaturated fatty acid in the membrane lipids in plant cells. TAs are crucial for adaptation to abiotic stresses, especially to low- or high-temperature stress. We report that α-linolenic acid (LA), the most abundant TA species in the chloroplast membrane lipids, is critical for generation of superoxide. Impairment of LA synthesis in the chloroplast membranes impaired superoxide accumulation in the oxidative burst, leading to reduced resistance to avirulent bacterial pathogens. LA was the most effective fatty acid for stimulating NADPH oxidase activity in vitro.
