Hydrogen peroxide homeostasis: Activation of plant catalase by calcium/calmodulin

Abstract

Environmental stimuli such as UV, pathogen attack, and gravity can induce rapid changes in hydrogen peroxide (H₂O₂) levels, leading to a variety of physiological responses in plants. Catalase, which is involved in the degradation of H₂O₂ into water and oxygen, is the major H₂O₂-scavenging enzyme in all aerobic organisms. A close interaction exists between intracellular H₂O₂ and cytosolic calcium in response to biotic and abiotic stresses. Studies indicate that an increase in cytosolic calcium boosts the generation of H₂O₂. Here we report that calmodulin (CaM), a ubiquitous calcium-binding protein, binds to and activates some plant catalases in the presence of calcium, but calcium/CaM does not have any effect on bacterial, fungal, bovine, or human catalase. These results document that calcium/CaM can down-regulate H₂O₂ levels in plants by stimulating the catalytic activity of plant catalase. Furthermore, these results provide evidence indicating that calcium has dual functions in regulating H₂O₂ homeostasis, which in turn influences redox signaling in response to environmental signals in plants.