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Ca²⁺/CALMODULIN-MEDIATED SIGNALING: ACTIVATION OF PLANT CATALASE BY CALCIUM/CALMODULIN.   T. Yang and B.W. Poovaiah.   Department of Horticulture, Washington State University, Pullman, WA. 

     Environmental stimuli 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 environmental changes.  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 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 the first evidence indicating that calcium has dual functions in regulating H₂O₂ homeostasis, which in turn influences redox signaling in response to environmental signals in plants.

     (Supported by NASA grant NAG5-4841 and NSF grant MCB 0082256)