Active Oxygen in Plants

Plant cells produce active oxygen during interactions with potential pathogens. Active oxygen species, including superoxide, hydrogen peroxide, and the hydroxyl radical, could potentially affect many cellular processes involved in plant/pathogen interactions. Active oxygen can be difficult to monitor in plant cells because many of the species are short-lived and are subject to cellular antioxidant mechanisms such as superoxide dismutases, peroxidases, the ascorbate/glutathione cycle, and catalase. Modifications of the luminol-dependent chemiluminescence assay have facilitated studies on both the production and scavenging of active oxygen that occurs during incompatible plant/bacteria interactions. Many potential sources for active oxygen production have been identified such as NADPH oxidases and peroxidases, but it is still unclear which mechanisms predominate during plant/ pathogen interactions. The active oxygen produced in response to pathogens and elicitors has been hypothesized to have direct antimicrobial effects and to playa role in other defense mechanisms including lignin production, lipid peroxidation, phytoalexin production, and the hypersensitive response.