Horseradish Peroxidase (HRP) is an enzyme commonly used as an indicator for chemical reactions which produce peroxide. The enzyme is routinely conjugated to antibodies for use in enzyme-based immunoassay systems. HRP functions in the removal of H2O2 (hydrogen peroxide), oxidation of toxic reductants, biosynthesis and degradation of lignin, suberization, auxin catabolism, response to environmental stresses such as wounding, pathogen attack and oxidative stress. These functions might be dependent on each isozyme/isoform in each plant tissue.