Cadmium (Cd) is one of the most common toxic metals present in the environment that induces various toxic effects in plants even at low doses. Medicinal plants may be easily contaminated with heavy metals during growing period. A laboratory experiment was conducted out to determine the effects of cadmium on seed germination percentage, seedling growth parameters and proline content of Milk thistle (Silybum marianum) medicinal plant at Biotech Research Center of University of Zabol in Iran during 2010. The seedlings were treated with concentrations of 0, 100, 200, 400 and 600 mg L-1 of cadmium chloride. The experiment was done in a completely randomized design with four replications. The parameters were measured included of: germination percentage, germination rate, root and shoot length, soot/root length ratio, seedling fresh weight and proline content of leaves. Our results indicated that a significant inhibitory effect was observed at all levels of cadmium compared to control. Increasing the concentration of cadmium to 600 mg L-1 showed a significant decrease in seed germination, shoot and root length and fresh weight of seedlings, while shoot/root length ratio and proline content increased by increasing Cd concentration.
