Abstract

Currently, human health and ecosystems are at serious risk because of environmental contamination by heavy metals as a result of human, industrial and agricultural activities. Plants were also affected by this pollution as one of the main components of the ecosystem. To evaluate the effects of different concentrations of lead heavy metal on valerian growth as a medicinal herb, plants were grown under hydroponic culture and stressed with lead nitrate, Pb(NO₃)₂, at concentrations of 0, 75 and 150 mg l^-1 for one month. This research carried out in a completely randomized design with three replications at greenhouse condition. The results showed that the increase of Pb concentrations in the nutrient solution decreased significantly shoot and root fresh weight, shoot and root dry weight, total fresh weight of plant, shoot length, root to shoot dry weight ratio and leaf area. The lowest content of growth parameters observed at 150 mg l^-1 level. Root dry weight of 150 mg l^-1 level in comparison with control decreased about %65. Generally, our results showed that Pb treatments had adverse effects on plant growth parameters, especially on root biomass.  Keywords: heavy metals, medicinal plant, growth parameters