en تنش فلزات سنگین Toxic ions stress پژوهشي Research <div style="text-align: justify;"><strong>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 <em>Glomus intraradices</em> on the growth, photosynthetic pigments, protein content, proline, pheno</strong><strong>l</strong><strong> and </strong><strong>activities of antioxidant enzymes</strong><strong> in </strong><strong>alfalfa plants under Pb toxicity were examined.</strong><strong> The experiment was performed by using two treatments (mycorrhizal and non-mycorrhizal) and five lead concentrations (0, 60, 120, 180 and 240 &micro;m Pb(NO₃)₂).</strong> <strong>Results showed that Pb stress decreased plant growth, </strong><strong>photosynthetic pigments </strong><strong>and protein content, however AMF improved them. Amount of proline, phenol and</strong><strong> antioxidant enzymes activity increased with lead increasing. </strong><strong>Amount of them</strong><strong> in roots of AMF plants in comparison with non-AMF plants increased. </strong><strong>Leaves of AMF plants had more superoxide dismutase activity comparison with non-AMF plants.</strong><strong> However </strong><strong>proline content, </strong><strong>activity of catalase and guaiacol proxidase in leaves of mycorrhizal plants, were lower than those of non-mycorrhizal plants</strong><strong>. In addition, mycorrhizal colonization significantly decreased with Pb exposure. These results, suggested that </strong><strong><em>G. intraradices </em></strong><strong>can decrease Pb toxicity in alfalfa plants.</strong></div> <div style="text-align: justify;"></div> Mycorrhiza, Lead, Heavy metals, Antioxidant enzymes, Alfalfa 1 12 http://jispp.iut.ac.ir/browse.php?a_code=A-10-333-6&slc_lang=en&sid=1 Samaneh Kahromi Kahromi.s@gmail.com No Department of Plant Sciences, Kharazmi University, Tehran Farzaneh Najafi Najafi_f@khu.ac.ir Yes Department of Plant Sciences, Kharazmi University, Tehran