Heme Oxygenase is Involved in the Protection Exerted by Jasmonic Acid Against Cadmium Stress in Soybean Roots

The present study was undertaken to test the influence of exogenously applied jasmonic acid (JA) upon the oxidative stress exerted by Cd in soybean plants. It was found that depending on its concentration, JA can improve plant antioxidant responses against Cd. Pretreatment with 20 mu M JA effectively ameliorated Cd-induced oxidative stress as indicated by the decrease in thiobarbituric reactive substance (TBARS) levels, enhancement of glutathione (GSH) content, and diminution of H2O2 and O-2 (-) formation. On one hand, the activities of classic antioxidant enzymes such as catalase (CAT) and superoxide dismutase (SOD) were also augmented by JA treatment. This behavior was not observed in plants treated with Cd alone. On the other hand, 20 mu M JA caused the enhancement of heme oxygenase (HO) activity (71% with respect to controls) and the amount of protein (60% with respect to controls). However, no gene induction was observed. Pretreatment with 20 mu M JA before the addition of Cd provoked the highest values of HO activity and protein expression (138 and 122%, respectively). Once again, these enhancements were not correlated with transcript levels. Plants pretreated with Zn-protoporphyrin IX (ZnPPIX), a well-known irreversible HO-1 inhibitor, could not cope with the oxidative damage caused by Cd. This indicates that HO-1 is involved in the protection exerted by JA against the oxidative stress due to Cd treatment.