SECRETED CATALASE ACTIVITY FROM ROOTS OF DEVELOPING MAIZE (ZEA-MAYS L) SEEDLINGS

Hydrogen peroxide generation by cell wall and plasma membrane has been demonstrated in several plant materials. However, we do not find appreciable concentrations of hydrogen peroxide in corn (Zea mays L.) roots, but a relatively high catalase activity was observed. The activity was released to the incubation medium and increased with time, while the activity remaining in roots was constant. When external H2O2 was added, rapid enzymatic decomposition led to levels of hydrogen peroxide below limits of detection. Both activities found in the incubation medium and in root apoplast were inhibited by boiling, NaN3, and KCN. The results indicate that the found catalase activity is able to maintain H2O2 at very low levels in extracellular spaces. It is supposed that this H2O2 scavenging system avoids the formation of high toxic hydroxyl radicals which would be generated by interactions of Fe II and peroxide.