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

Appl Water Sci (2017) 7:1247–1253 DOI 10.1007/s13201-015-0376-x ORIGINAL ARTICLE Effect of zinc and lead on the physiological and biochemical properties of aquatic plant Lemna minor: its potential role in phytoremediation M. A. Jayasri1 • K. Suthindhiran1 Received: 10 June 2014 / Accepted: 28 December 2015 / Published online: 21 January 2016 Ó The Author(s) 2016. This article is published with open access at Springerlink.com 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. & K. Suthindhiran ; 1 Marine Biotechnology and Bioproducts Lab, Marine Biotechnology and Biomedicine Lab, School of Bio Sciences and Technology, VIT University, Vellore 632 014, Tamil Nadu, India Keywords Lemna minor
Zinc
Lead
Tolerance
Phytoremediation Abbreviations Zn2? Zinc Pb2? Lead L. minor Lemna minor CAT Catalase DW/FW Dry to fresh weight ratio Introduction Urbanization and industrialization had triggered extreme water pollution by draining effluents directly into water bodies without prior treatment. Industries such as smelters, tanneries, metal refineries and mining operations are the major sources of metal release into the environment (Gardea et al. 2004; Srivastava and Thakur 2006). These effluents generally contain metals that can be toxic even in trace amounts and it is very difficult to purify these water bodies due to its large volume. Heavy metal pollution is an important environmental problem in the world because, unlike organic materials, heavy metals cannot be transformed by microorganisms and, therefore, accumulates in water, soil, bottom sediments and living organisms (Miretzky et al. 2004). Most of the heavy metals have been found to be carcinogenic in nature and hence it poses a threat to human health too (Shakibaie et al. 2008; Vinodhini and Narayanan 2009). Metals induce deleterious effect on physiology of aquatic plants by effecting some of the essential phenomenon such as photosynthesis, enzymatic activity, etc. (Teisseire and Vernet 2000; 123 1248 Appl Water Sci (2017) 7:1247–1253 Prasad et al. 2001; Vaillant et al. 2005; Kanoun et al. 2009; Zhou et al. 2009) Hence, some eco-friendly and economic methods shall be considered to treat heavy metal polluted water. Plants have been found to accumulate and concentrate the heavy metals within. Phytotolerance studies are used to determine metal tolerant property of plants and also to determine the detrimental effect of metals on physiological response of plants (Basile et al. 2012; Radić et al. 2010). L.minor, commonly known as Duckweeds are aquatic plants that float on or just beneath the surface of still or slow-moving fresh water bodies and often form dense floating mats in eutrophic ditches and ponds (Driever et al. 2005). It is also used in wastewater treatment to remove mineral and organic contamination and radionuclides (Chaudhary and Sharma 2014; Axtell et al. 2003). The present work deals with the study of the potential of duckweed to grow in different concentrations of metals, viz. Zinc (Zn2?) and lead (Pb2?) and to assess the tolerance level exhibit by the plant. The metal tolerant efficiency of L. minor was evaluated with reference to: (1) dry to fresh weight ratio (DW/FW) (2) changes in soluble protein content; (3) changes in contents of chlorophyll a, chlorophyll b, anthocyanin and carotenoid; (4) changes in enzymatic activity of catalase (CAT) activity. Measurement of dry to fresh weight ratio (DW/FW) The number of fronds, fresh weight, and dry weight was calculated as per the ISO/DIS 20079 protocol (2004). Dry to fresh weight ratio (DW/FW) was calculated using the formula dry weight (g)/fresh weight (g). Determination of photosynthetic pigments The contents of chlorophyll a, chlorophyll b, and carotenoid content of both control and metal treated fronds were determined as described earlier (Lichtenthaler 1987). Briefly, 150 mg of L. minor frond was homogenized with 80 % cold acetone. The homogenate was centrifuged, and the absorbance of the supernatant was measured at 470, 537, 647, 663 and 730 nm with a spectrophotometer (Wenhua et al. 2007). Anthocyanin content of both control and metal treated fronds were determined spectrophotometrically as explained by Suzuki (1995). Catalase assay Duckweed (L.minor) was collected from natural pond water of Vellore Institute of Technology, Vellore. Catalase activity in fronds was measured as described by Wenhua et al. (2007). Approximately 500 grams of L. minor fronds treated with lead and zinc of different concentrations were homogenized in 5 ml of cold potassium phosphate buffer, pH 7.8. The homogenate was centrifuged at 9000 rpm for 15 min with a temperature of 4 °C and supernatant were stored at 4 °C for analysis. The reaction mixture (1 ml) containing potassium phosphate buffer (50 mM, pH 7.5, 750 ll), H2O2 (200 mM, 100 ll) and enzyme extract (150 ll) was evaluated for catalase activity by measuring the consumption of H2O2 spectrophotometrically at 240 nm (Wenhua et al. 2007). Plant sample preparation Protein estimation Lemna minor fronds were prepared and disinfected in 1 % of sodium hypo chloride solution and 2 g fronds were then inoculated in synthetic media, i.e., Quarter Coic and Lessaint solution (Khellaf and Zerdaoui 2009) along with various concentrations of lead (1, 2, 4, 6 and 8 mg/l) and zinc (0.5, 5, 10, 15, and 20 mg/l) to induce metal stress. Aeration was provided, and fronds were allowed to grow at 25 °C in an incubator with 16 h illumination per day provided from fluorescent tubes for 4 days (...truncated)