Effect of zinc and lead on the physiological and biochemical properties of aquatic plant Lemna minor: its potential role in phytoremediation

Abstract

Plants have gained importance in situ bioremediation of heavy metals. In the present study, different concentrations of zinc (Zn²⁺) (0.5, 5, 10, 15, 20 mg/l) and lead (Pb²⁺) (1, 2, 4, 6, 8 mg/l) were used to evaluate metal tolerance level of Lemna minor. L.minor were exposed to metals for 4 days and tested for its dry to fresh weight ratio (DW/FW), photosynthetic pigments production and protein content. The oxidative damage was detected by measuring catalase activity. L.minor showed tolerance against Zn²⁺ and Pb²⁺ at a concentration of 10 and 4 mg/l, respectively. Among the metals, Pb²⁺ showed a significant toxicity at 8 mg/l. High concentration (20 mg/l of Zn²⁺ and 8 mg/l of Pb²⁺) of the metals displayed a considerable negative effect on soluble proteins (13 fold decrease with Zn²⁺ and 4 fold decrease with Pb²⁺) and photosynthetic pigments (twofold decrease with Zn²⁺ and onefold decrease with Pb²⁺) and lead to a consequent reduction in number of fronds. Further, the catalase was greatly increased (twofold decrease with Zn²⁺ and sixfold decrease with Pb²⁺) under metal stress. The results indicate that L.minor withstands Zn²⁺ and Pb²⁺ toxicity up to the concentration of 10 and 4 mg/l, respectively. Hence, the metal tolerant property of this plant shall be exploited for bioremediation of Zinc and Lead in polluted water. Further, the detailed and wide range of heavy metal toxicity studies should be done to reveal the possible use of this plant on large scale bioremediation purpose.