Effect of Different Concentrations of Copper and Lead on Stomata Changes, Morphological and Biochemical Characteristics of Four O’Clock (Mirabilis jalapa)

In recent decades cultivation of plants as a tool to manage the polluted areas by heavy metals has received an increased attention. In order to evaluate the possibility of using Four o’clock plant as a phytoremediator in soils polluted by Cu and Pb, an experiment was conducted using four levels of Cu and Pb (0, 200, 400, and 800 mg/kg) concentrations, as a factorial experiment based on a completely random design in the Research Greenhouse of Shahid Bahonar University of Kerman, Iran. Results showed that pollution by each of these metals alters photosynthetic pigments concentration and morphological traits of plants. Stomatal characteristics were significantly decreased by these heavy metals. Significant increases were also found in concentration of reducing sugars and proline, Pb and Cu accumulation in stems and roots and also activities of antioxidative enzymes. High levels of metal accumulation were found in roots. Compared to the control condition, plants which were grown under the highest levels of pollutions accumulated 32 and 22 times more Cu and Pb, respectively, in root tissue and 6 and 3.6 times more in the shoot tissue. Superoxide dismutase, catalase and ascorbate peroxidase activities were also increased up to 2.7, 2.5 and 2.4 times in plants grown in the soil polluted with the highest level of both metals. Meanwhile, proline concentration increased 9 times in plants grown under the same conditions. These Results showed that this species can be used as a Cu and Pb tolerant ornamental plant in Cu and Pb polluted conditions.