The role of ascorbate peroxidase-3 in oxidative stress
The Arabidopsis gene APX3 that encodes a putative peroxisomal membrane-bound ascorbate peroxidase was overexpressed In Escherichia coli and transgenic tobacco plants. APX3 expressing bacterial cells showed high APX activity, whereas no APX activity could be detected in bacterial cells alone. APX3 expressing plants had substantial levels of APX3 mRNA and protein. The H2O2 can be converted to more reactive toxic molecules, e.g. OH, if it is not quickly removed from plant cells. Expression of APX3 in tobacco can protect leaves from oxidative stress damage caused by aminotriazole which inhibits catalase activity that is found mainly in glyoxisomes and peroxisomes and leads to accumulation of H2O2 in those organelles. However, these plants did not show increased protection from oxidative damage caused by paraquat which leads to ROS production in chloroplasts. Therefore, protection provided by expression of APX3 seems to be specific against oxidative stress originating in peroxisomes, not from chloroplasts, which is consistent with the hypothesis that APX3 is a peroxisomal membrane-bound antioxidant enzyme.