Growth and some physiological characteristics of alfalfa (Medicago sativa L.) in response to lead stress and Glomus intraradices symbiosis

Lead is a nonessential element that has a negative effect on plant growth and development. Plant symbiosis with arbuscular mycorrhizal fungi (AMF) in soils contaminated with heavy metals can affect growth of plant, nutrition and tolerance against heavy metals. In this study, the effect arbuscular mycorrhizal fungi Glomus intraradices on the growth, photosynthetic pigments, protein content, proline, phenol and activities of antioxidant enzymes in alfalfa plants under Pb toxicity were examined. The experiment was performed by using two treatments (mycorrhizal and non-mycorrhizal) and five lead concentrations (0, 60, 120, 180 and 240 µm Pb(NO3)2). Results showed that Pb stress decreased plant growth, photosynthetic pigments and protein content, however AMF improved them. Amount of proline, phenol and antioxidant enzymes activity increased with lead increasing. Amount of them in roots of AMF plants in comparison with non-AMF plants increased. Leaves of AMF plants had more superoxide dismutase activity comparison with non-AMF plants. However proline content, activity of catalase and guaiacol proxidase in leaves of mycorrhizal plants, were lower than those of non-mycorrhizal plants. In addition, mycorrhizal colonization significantly decreased with Pb exposure. These results, suggested that G. intraradices can decrease Pb toxicity in alfalfa plants.