BIOACCUMULATION AND BIOCHEMICAL EFFECTS OF MERCURY IN THE PLANT BACOPA-MONNIERI (L)

Plants of Bacopa monnieri were treated with six different concentratio ns of Hg (0.01, 0.5, 1.0, 2.0, 3.0, and 5.0 mu g mL(-1)) for 4, 7, and 14 d under laboratory conditions. The metal accumulation in the root tissues was about five times more than in the shoots. At all the conce ntrations of Hg, cysteine, total -SH, reduced glutathione, and ascorbi c acid contents increased in the roots of B. monnieri up to 7 d of exp osure except the ascorbic acid content, which decreased above 2 mu g m L(-1) Hg. The malondialdehyde content decreased at all the concentrati ons of Hg; however, protein and sugar contents decreased above 0.1 and 2.0 mu g mL(-1) Hg, respectively, after 4 d of exposure in the roots of the plant. The chlorophyll content in leaves decreased significantl y with an increase in metal concentrations and durations of exposure. The results suggest that an increase in cysteine, total -SH, reduced g lutathione, and ascorbic acid content by Hg treatment at the initial e xposure period are part of the overall expression of Hg tolerance in t he plant, and the decrease in chlorophyll and protein content is a con sequence of Hg toxicity at higher metal concentrations and increased p eriod of exposure. (C) 1996 by John Wiley & Sons, Inc.