Involvement of heme oxygenase as antioxidant defense in soybean nodules

Objective: We have previously demonstrated that the inducible form of heme oxygenase plays a critical role in protecting against oxidative stress in mammals. To gain further insight into the functions of this enzyme in plants, we have tested its activity and expression in soybean nodules subjected to cadmium (Cd) stress. Materials and methods: Four-weeks-old soybean nodulated plants were treated with different cadmium chloride concentrations (0, 50 and 200 mu M) during 48 h. Oxidative stress parameters such as TBARS content, GSH levels and antioxidant enzyme activities were measured as well as heme oxygenase activity and expression. Besides, the effect of biliverdin and Zn-protophorphyrin IX were analized. Results: Treatment with 200 mu M Cd during 48 h caused a 67% increase in TBARS content, whereas GSH decreased 44%, and total superoxide dismutase, gluthatione reductase and guaiacol peroxidase were also inhibited 54,20 and 60%, respectively. A total of 200 mu M Cd produced the overexpression of heme oxygenase-1, as well as a 10-fold enhancement of its activity. Co-administration of biliverdin (10 mu M) completely prevented the effects caused by Cd. Treatment with Zn protoporphyrin IX, a strong inhibitor of heme oxygenase, expectedly decreased heme oxygenase-1 activity to half. When the inhibitor was given together with Cd, completely prevented the enzyme induction and oxidative stress parameters were significantly enhanced. Conclusion: Taking together, these results are indicating that heme oxygenase plays a protective role against oxidative cell damage in soybean nodules.