Antioxidant Responses of Helianthus annuus L. under Vanadium Stress

Vanadium (v) is a transition metal consistently distributed in the earth’s crust. at trace concentrations, it has been described as a beneficial element for some organisms; however, it is toxic at higher concentrations. this study was conducted hydroponically in a complete randomized design to investigate effects of v (0, 3.25, 7.5, and 15 mg l^-1 ) on antioxidant system of sunflower. results showed that all applied concentrations of v significantly decreased the plant growth, but increased the free amino acids, proline, malondialdehyde and h2o2 contents of plants. the antioxidant enzymes activities increased in response to the increase in v concentration. the activity of (guaiacol) peroxidase showed a significant increase at 15 mg l^-1 v while the activities of catalase, glutathione reductase, and ascorbate peroxidase decreased significantly by application of v. there was a slight increase in the superoxide dismutase activity at different concentrations of v. the study concludes that the applied concentrations of v induced oxidative stress in sunflower and (guaiacol) peroxidase was a more effective antioxidant enzyme in scavenging the free radicals in this plant.