Reactive Oxygen Species metabolism in plants: production, detoxification and signaling in the stress response.

The production of reactive oxygen species (ROS), such as superoxide radical (O2•-), hydroxyl radical (OH•) and hydrogen peroxide (H2O2), in plants is a common event in metabolic and physiological processes. ROS are normally formed in photosynthesis and respiration by the chloroplast and mitochondrial electron transfer chains, respectively, and in metabolic reactions taking place in the peroxisomes. As these active oxygen species are destructive to cellular components such as lipids, nucleic acid and proteins, plant cells are equipped with non-enzymatic and enzymatic antioxidant defense systems comprising ascorbate, glutathione, phenols, catalases, superoxide dismutases and peroxidases. Biotic and abiotic stress, such as salinity stress, excess of heavy metals, mechanical shock, UV light, exposure to ozone, water deficiency and pathogen attack, also increase ROS production. In the latter case the release of ROS, referred to as the “oxidative burst”, is one of the earliest responses activated following pathogen recognition and has been suggested to play a pivotal role in the integration and the coordination of the plant defense responses. In this review we summarize the current knowledge about ROS production and oxidative defense in plants. The role of ROS will be discussed in the frame of stress responses, with emphasis on the plant-pathogen interaction.