Evaluation of Accumulation Capacity, Mineral Nutrient Status and Photosynthetic Pigment Contents in Aquatic Plant Bacopa Monnieri in Relation to Heavy Metal Exposures
Heavy metals are one of the major contaminants in marine ecosystems in the world. Present study has investigated the heavy metal accumulation capacity, mineral nutrient status and photosynthetic pigment concentrations of aquatic plant Bacopa monnieri (L.) Pennel in relation to treatment with different concentrations (100, 200 and 400 μM) of heavy metals such as Cd, Cu, Ni and Pb in artificially contaminated solutions. The concentrations of heavy metals and mineral nutrients such as Ca, Cd, Cu, Fe, K, Mg, Mn, Na, Ni, Pb and Zn were measured in root, stem and leaf samples of B. monnieri using ICP-OES. Before heavy metal treatments, all samples were supplied with 1% Hoagland solution to balance the mineral nutrient status. Treatments have caused to increase in accumulation of heavy metals such as Ca, Cd, Cu, Ni and Pb, while with exception of Ca, they led to decrease in all mineral elements, including Fe, K, Mg, Mn, Na and Zn. Measured lowest and highest (dw-mg/kg) element values, respectively include 3527.530±56.677 (stem; 100 μM)-6443.469±121.771 (leaf; 400 μM) for Ca; 14.703±0.464 (stem; 100 μM)-68.450±1.316 (root; 400 μM) for Cd; 78.688±1.528 (stem; 100 μM)-258.928±5.029 (root; 400 μM) for Cu; 174.586±3.391 (stem; 400 μM)- 580.065±11.267 (leaf; 100 μM) for Fe; 9745.227±189.134 (stem; 400 μM)- 14917.742±289.765 (root; 100 μM) for K; 560.450±10.940 (stem; 100 μM)-781.562±15.117 (leaf;100 μM) for Mg; 39.846±0.774 (stem; 400 μM)-105.455±2.048 (leaf;100 μM) for Mn; 669.875±13.012 (stem; 400 μM)- 815.876±15.848 (root;100 μM) for Na; 17.104±0.332 (stem; 100 μM)-65.090±1.264 (root; 400 μM) for Ni; 51.662±1.003 (stem; 100 μM)-143.791±2.793 (root; 400 μM) for Pb; and 19.352±0.376 (stem; 400 μM)- 39.255±0.762 (leaf;100 μM) for Zn. Results have demonstrated that B. monnieri could accumulate Cd as 620.4, 494.1 and 1014.0 more times than control in leaf, stem and root samples, respectively. Thus, B. monnieri appears a good candidate as an accumulator plant in cleaning of polluted water, mainly for Cd-polluted waters. Besides, photosynthetic pigment analyses were performed using plants leaves. Interestingly, 100 μM heavy metal treatments have caused the chlorophyll a and b concentrations to considerably increase in contrast to other treatments (200 and 400 μM samples). Increase in chlorophyll a and b concentrations in response to initial 100 μM treatment could be derived from the shock-state induced upregulated gene expression in B. monnieri plants. In addition, photosynthetic pigments are used as stress indicators in some plant species thereby partially explaining the increased chlorophyll contents in initial stress treatments. However, 400 μM treatments have caused a substantial decrease in chlorophyll a, b, total chlorophyll and carotenoid levels, indicating the adverse effects of increased heavy metal concentrations on plant pigments.
Keywords- Macrophyte, abiotic stress, aquatic plant, phytoremediation, heavy metal accumulation.