Effect of different concentrations of lead on anatomical structure of Matricaria chamomilla L. in different developmental stages

In recent decades, increased human industrial activities and enormous fertilizer application in agriculture section has promoted heavy metal release into the environment. Pb is one of the most prominent heavy metal contaminant in the ecosystem. In spite of its global importance, there is little knowledge regards mechanisms of lead toxicity in plants. Regarding industrial and medicinal importance of Matricaria chamomilla, the response of this species to lead toxicity was investigated at rosette, shooting and flowering stages. To examine this, plants were transplanted to hydroponic culture at rosette stage and were exposed to different Pb nitrate treatments including 0, 60, 120, 180, 240 μM. Plants were harvested after completing each developmental stages for analysis and studying. The results revealed that the root Pb concentration was greater than that of above ground parts at all studied stages. Examining leaf, stem and root cross sections showed that increased Pb absorption caused similar changes in leaf and stem anatomy at all investigated stages. However, Pb influence on root anatomy was dissimilar at different developmental stages, so that Pb pollution increased the diameter of xylem and vascular tissues at rosette stage but it reduced these traits at shooting stage.