Heme oxygenase activity and oxidative stress signaling in soybean leaves

We have previously demonstrated that the induction of heme oxygenase-1 (EC 1.14.99.3) plays a protective role for soybean plants against oxidative stress. Here, we have investigated for the first time the possible signal transduction pathways involved in heme oxygenase-1 induction in leaves of soybean plants. Treatment with 200 μM Cd during 48 h increased 87% thiobarbituric acid reactive substances, whereas GSH decreased 70%, respect to controls. These effects were prevented by preincubation with diphenyleneiodonium (DPI, NADPH oxidase inhibitor), cantharidin (protein phosphatases inhibitor), LaCl3 (calcium channel blocker) and [1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ, guanylate cyclase inhibitor). Two hundred micromoles Cd produced increased concentrations and in situ accumulation of H2O2 and O2−, which were again prevented by DPI, cantharidin, LaCl3 and ODQ. Moreover, Cd-induced heme oxygenase-1 activity was also totally or partially abolished by pretreatment with the different inhibitors. These results clearly demonstrated that the signal transduction pathways involved in oxidative stress, triggered by cadmium ions were similar to those implicated in heme oxygenase-1 induction, and supported the proposal of a close relationship between oxidative stress generation and heme oxygenase induction in higher plants.