- NADPH oxidases (NOX) catalyze the production of superoxides, a type of reactive oxygen species (ROS). The dramatic induction of ROS production by human NOX2 in activated blood phagocytic cells and its role in promoting pathogen killing has long motivated research in this area (Babior et al., 2002). In plants, the NOX homologs have been named respiratory burst oxidase homologs (Rboh) and they are also involved in ROS production in response to pathogens (Sagi and Fluhr, 2001; Torres et al., 2002). However, the discovery of new types of animal NOX genes and new functions for plant Rboh genes underlines diverse roles for NOX-generated ROS in eukaryotic cell biology, including animal and plant defense, development, hormone biosynthesis, and cellular signal transduction (Foreman et al., 2003; Kwak et al., 2003; Lambeth, 2004; Sagi et al., 2004; Torres et al., 2005). This Update will focus on recent advances in our understanding of intrinsic molecular properties of Rboh as they are related to their function in plants.