Signal transduction pathways and haem oxygenase induction in soybean leaves subjected to salt stress

We have previously demonstrated that the induction of haem oxygenase-1 (EC 1.14.99.3) plays a protective role for soybean plants against cadmium and UV-B stress. Here, we have investigated the possible signal transduction pathways involved in haem oxygenase-1 induction in leaves of soybean plants subjected to salt stress. Treatment with 100 mM NaCl during 48 h increased thiobarbituric acid reactive substances by 30%, whereas GSH decreased by 50%, with respect to controls. These effects were prevented by pre-incubation with diphenyleneiodonium (DPI; an NADPH oxidase inhibitor), [1,2,4] oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ; a guanylate cyclase inhibitor) or LaCl3 (calcium channel blocker). NaCl at 100 mM produced in situ accumulation of H2O2 and O-2(sic), which were also prevented by DPI, ODQ or LaCl3. Moreover, salt-induced haem oxygenase-1 activity was also totally abolished by pretreatment with the different inhibitors. These results clearly demonstrated that the signal transduction pathways involved in oxidative stress triggered by salt stress were similar to those implicated in haem oxygenase-1 induction, and provide additional information suggesting that haem oxygenase might play a key role in the anti-oxidative protection machinery of higher plants.