INDUCTION OF ENZYME-ACTIVITIES AND ANTIOXIDANT PRODUCTION IN BARLEY PLANTS AS A RESULT OF SO2 FUMIGATION

Two cultivars (Arda and Plaisant) of barley (Hordeum vulgare) were exposed continuously to fumigation with low concentrations of SO, (115, 220 and 350 mu g/m(3)) for 34 days. The increases observed in the activities of catalase (EC 1.11.1.6.), superoxide dismutase (EC 1.15.1.1.), glutathione synthetase (EC 6.3.2.3.), glutathione reductase (EC 1.6.4.2.), glutathione peroxidase (EC 1.11.1.9.) and glutathione transferase (EC 2.5.1.18,) following fumigation were higher in Arda than in Plaisant. The ratio of reduced glutathione to oxidized glutathione (GSH/GSSG) increased significantly in Plaisant, and even more so in Arda. The antioxidant levels in lipid extracts were higher than in the control only after exposure to SO2 at the lowest concentration, while at higher concentrations no significant changes were observed. As to free radicals, only after fumigation with the highest levels of SO2 a 5% increase in free organic radicals was found in Plaisant, compared to the non-treated control. In previous studies it had been shown that Arda is more resistant to drought than Plaisant. Our data show that also in response to low SO2 concentrations Arda has a higher potential to activate anti-oxidative stress defences. These results suggest that the phenotype that proved to be more resistant to drought may have a higher ability than the sensitive one to activate antioxidative defences when exposed to SO2 at low concentrations.