Ascorbate Peroxidase Functions in Higher Plants: The Control of the Balance Between Oxidative Damage and Signaling

Ascorbate peroxidases (APXs) catalyze the reduction of H2O2 into water using ascorbate as an electron donor in photosynthetic eukaryotes. In higher plants, APX isoforms are distributed among the cytosol, chloroplasts (stroma and thylakoid membrane), mitochondria, and peroxisomes to fine-tune organellar and cellular levels of H2O2. If it were not for these isoforms, plants would be unable to efficiently use ascorbate, the most abundant soluble antioxidant, for H2O2 scavenging because of their weak chemical interaction. This is one of the plausible explanations for why plants accumulate a large amount of ascorbate. Their substrate H2O2 is a relatively stable form of a reactive oxygen species with both cytotoxicity and signaling function. The balance of the opposite actions of H2O2 is a key determinant for plant acclimation to changing environments. In this chapter, we described how APXs are involved in the balance control of H2O2 and how they modulate plant stress acclimation.