Histological and ultrastructure changes in Medicago sativa in response to lead stress

In the recent years, human activities such industry and agriculture promote heavy metal release into the environment. Lead is the most contaminant metals in environment which adversely affects both plant and human life. The present study was undertaken to determine the effects of Pb on structural characteristics in Medicago sativa L. 30 days plants treated with Pb in 5 treatments (0,120, 240, 500, 1000μM Pb) with 3 repeat in per treatment for 10 days. Histochemical method of lead detection revealed significant accumulation of this metal in cortex and xylem tissues in roots and in stems lead deposits on cell wall of collenchymas tissues. The analysis of scanning electron micrographs of the leaf surface of M. sativa grown on hydroponic culture treated with Pb showed an increase in the size of guard cells in adaxial surface and decrease in abaxial surface, decrease in size of stomata aperture and closure of stomata in 1000 μM Pb in medium. Alternation of epicuticular waxes is one of the most important of pollution symptoms, in our study, alteration in structure and deposition of epicuticular waxes were observed. Also anatomical characteristics of stem and root affected by Pb contamination. Under Pb toxicity, anatomical symptoms including increase the diameter of stems and root as well as amplified vascular bundles and pith area were obsreved.