Produces developmental and stress-related release of hydrogen peroxide in the apoplast. May play an important role in several aspects of plant growth and defense mechanisms. 2 H(+) + O2 + oxalate = 2 CO2 + H2O2 Oligomer (believed to be a pentamer but probably hexamer). Found in the apoplast and the cytoplasm of germinating embryo cells. Associated with the cell wall. By auxin, pathogens and heavy metal ions. Associated mostly with highly substituted forms of glucuronogalactoarabinoxylans. Belongs to the germin family.