Oxidative burst is a very quick plant defense response after pathogen recognition, leading to hypersensitive reaction (HR). This response is due to generation of reactive oxygen species (ROS), such as H2O2 , O2-, and OH-. Several roles in plant defense have been proposed for ROS. Hidrogen peroxide (H2O2), apart from being directly toxic to pathogens, is also involved in cell wall strengthening, since it is necessary for lignin biosynthesis. Hidrogen peroxide acts as a second messenger, being responsible for the activation of the benzoic acid 2-hydrolase, enzyme responsible for benzoic acid conversion to salycilic acid. Oxidative burst is not only confined to the macroscopic site of HR, since secondary bursts can occur in distant tissues, causing micro-HR's and leading to systemic acquired resistance (SAR), which is mediated by salycilic acid as a signal. Therefore, occurrence of both HR and SAR are dependent on signaling cascades derived from oxidative burst, as an early event in plant response against pathogen invasion.
