Effect of selenium on growth and antioxidant capacity of Triticum aestivum L. during development of lead-induced oxidative stress

Effects of two selenium concentrations-0.4 and 0.8 mg Se6+ per kilogram of soil (treatments Se0.4 and Se0.8)-on seedling growth, chlorophyll content (Chl (a + b)), the content of thiobarbituric acidreactive substances (TBARs) indicative of peroxidation rates, and the activities of antioxidant enzymes (ascorbate peroxidase, AsP; glutathione reductase, GR; and guaiacol peroxidase, GPX) were studied in roots and leaves of wheat (Triticum aestivum L., cv. Triso) plants that were exposed for 14 days to oxidative stress induced by 50 and 100 mg Pb2+ per kilogram of soil (treatments Pb50 and Pb100, respectively). The pollution of soil with Pb2+ inhibited growth, lowered Chl (a + b) content, and intensified peroxidation. The content of TBARs increased by 44 and 72% in leaves and by 25 and 45% in roots for treatments Pb50 and Pb100, respectively. Activities of the antioxidant enzymes GR and GPX were higher in Pb2+-treated than in untreated (control) plants. The introduction of Se6+ into Pb2+-free soil (treatment Se0.4) was found to promote growth, stimulate AsP activity by 40% in leaves, and enhance AsP, GR, and GPX activities in roots by 38, 33, and 74%, respectively. The content of TBARs was reduced in Se6+-treated plants. By contrast, the treatment Se0.8 suppressed growth, elevated TBARs content, and stimulated activities of antioxidant enzymes in roots and leaves. The addition of 0.4 mg Se6+/kg to Pb2+-contaminated soil alleviated the negative influence of lead on plant growth, whereas the addition of 0.8 mg Se6+/kg aggravated the effect of Pb2+ contamination, especially in treatment (Pb100+Se0.8). Thus, the effectiveness of exogenous Se6+ application on growth and adaptive potential of plants cultivated under optimal pollutant-free conditions and on soils contaminated with lead depended on the concentration of Se6+ supplemented to soil and on the content of the stressor agent.