Antioxidant responses of barley (Hordeum vulgare L.) genotypes to lead toxicity

The effects of lead toxicity were studied in the leaves of two barley cultivars. Plants were grown for 32 days in perlite and then exposed to 10- and 15-mM Pb(NO3)2 for additional 6 days. Lead toxicity decreased the photosynthetic pigment contents in the leaves of Tokak 157/37. The phenolic content of the leaves was reduced in Tarm-92 and increased in Tokak 157/37. The malondialdehyde content in leaves showed that lipid peroxidation in Tokak 157/37 was lower than in Tarm-92. H2O2 accumulation was more remarkable in the leaves of Tokak 157/37 exposed to 15 mM lead. Significantly higher superoxide dismutase activity observed in our study indicates a likely higher rate of superoxide radical dismutation. Lower ascorbate peroxidase activities were observed at 10 mM lead in Tarm-92 and at 15 mM lead in Tokak 157/37. The glutathione reductase activity in Tarm-92 was lower whereas it was induced by 10 mM lead treatment in Tokak 157/37. Lead toxicity resulted in increased level of the guaiacol peroxidase activity in both cultivars. Our results suggest that lead toxicity induced membrane damage in barley leaves, led to photosynthetic pigment loss and that guaiacol peroxidase activity may be critical for lead tolerance at early stage of seedling oxidative stress development.