Copper phytoremediation potential of Calandula officinalis L. and the role of antioxidant enzymes in metal tolerance.

Cu phytoremediation potential of an ornamental plant, Calandula officinalis, was explored in terms of growth responses, photosynthetic activities and antioxidant enzymes such as SOD, CAT and GPX. The results showed that this plant had high Cu tolerance of up to 400 mg/kg, which is far above the phytotoxic range for non hyperaccumulators. It grew normally in soils at all the doses (150-400 mg/kg) without showing external signs of phytotoxicity. At 150 mg/kg, flowering was augmented; root and shoot biomass, root lengths and leaf soluble protein contents remained same as that of the control. However, chlorophyll and carotenoid pigment contents declined significantly along with significant elevations in lipid peroxidation, at all the doses. Elevations of antioxidant enzymes reflected stress as well as probable mitigation of reactive oxygen species due to Cu stress. Except for the highest conc. (400 mg/kg), leaf accumulation of Cu was higher than root accumulations. The Cu accumulation peaked at 300 mg/kg Cu in soil, with leaf and root accumulations to be respectively, 4675 and 3995 µg/g dry wt., far more than the minimum of 1000 µg/g dry wt. for a Cu hyperaccumulator. The plant root at all the doses tolerated Cu, with the tolerance index ranging from 94-62.7. The soil to plant metal uptake capacity, indicated by extraction coefficient and the root to shoot translocation, indicated by translocation factor, at all the doses of Cu were >1, pointed towards efficient phytoremediation potential.