Plant catalases: Peroxisomal redox guardians

While genomics and post-genomics studies have revealed that plant cell redox state is controlled by a complex genetic network, available data mean that catalase must continue to be counted among the most important of antioxidative enzymes. Plants species analyzed to date contain three catalase genes, and comparison of expression patterns and information from studies on mutants suggests that the encoded proteins have relatively specific roles in determining accumulation of H2O2 produced through various metabolic pathways. This review provides an update on the different catalases and discusses their established or likely physiological functions. Particular attention is paid to regulation of catalase expression and activity, intracellular trafficking of the protein from cytosol to peroxisome, and the integration of catalase function into the peroxisomal antioxidative network. We discuss how plants deficient in catalase are not only key tools to identify catalase functions, but are also generating new insight into H2O2 signalling in plants and the potential importance of peroxisomal and other intracellular processes in this signalling.