C3 and C4 plants as potential phytoremediation and bioenergy crops for stabilization of crude oil and heavy metal co-contaminated soils-response of antioxidative enzymes

Abstract

Metal accumulation in 15 (C3 and C4) plants growing on crude oil spill laden soil and the responses of antioxidative enzymes were examined. In this study, the synergistic effect of four different metals was examined to find out the antioxidative stress responses. Plants were collected from their natural habitat (crude oil spill laden soil) during the rainy season at the vegetative stage (before flowering) and analyzed for shoot metal concentrations and activities of catalase (CAT), superoxide dismutase (SOD), and malondialdehyde (MDA). The shoot metal concentrations (mg kg) of all the individual metals (Mn, Co, Cd, and Zn) were found in different concentration. All the metal accumulating plants, CAT and SOD activities were found to be high in comparison to the control plants. The highest SOD activity was found in Cynodon dactylon (47 μg FW) whereas the lowest was found in Fimbristylis dichotoma (13 μg FW). The SOD activity increased considerably in all the metal accumulating plants, and the increase ranges 13–47 μg FW. Catalase activity was also found to be high (2–18 μg FW) in all the grass and sedges, of which the highest was recorded in Echinochloa colonna (18 μg FW) and lowest in Arundo donax (2 μg FW). The significant decrease in MDA activity (between 1–0.04 nmol g FW) in the leaves of all metal accumulating plants, suggested metals in soil induced oxidative damage. The antioxidant responses among the species grown in a contaminated site displayed higher levels of activity in all the enzymes compared to no-polluted plants. Therefore, it can be assumed that the heavy metal uptake and bio-productivity (the coordinated manifestation of the efficiency that operates at various molecular and cellular level of these species) is sustained through antioxidative defense system in the examined plants.