Occurs in almost all aerobically respiring organisms and serves to protect cells from the toxic effects of hydrogen peroxide. Responsible for the redox homeostasis in leaves. Prevents nitric oxide (NO) accumulation and subsequent NO-mediated leaf cell death as well as the S-nitrosylation of specific proteins (e.g. glyceraldehyde 3-phosphate dehydrogenase and thioredoxin) by degrading H(2)O(2). Involved in photorespiration. Promotes drought stress tolerance and recovery. Involved in NO-mediated enhanced tolerance to zinc oxide nanoparticles (ZnO NPs)-induced phytotoxicity. Participates in melatonin-mediated detoxification. 2 H2O2 = 2 H2O + O2 Homotetramer (By similarity). Interacts with GLO1 and GLO4; these interactions are disturbed by alpha-hydroxy-2-pyridinemethanesulfonic acid (HPMS) and salicylic acid (SA). Interacts with STRK1 at the plasma membrane (By similarity). Activated by STRK1-mediated phosphorylation at Tyr-210 upon salt and oxidative stress. Belongs to the catalase family.