The effect of mercury (Hg) on growth, photosynthesis, accumulation and antioxidative responses were studied in Sesbania drummondii, cultivated on different concentrations of Hg (0 - 100 ppm) for one week. At lower concentrations of Hg plants growth was not significantly affected; however, at higher concentrations growth affected significantly. A concentration of 100 ppm Hg inhibited growth by 36.8%, with respect to control. Hg concentration in shoot as well in root increased with increasing Hg concentrations in the growth medium. Hg accumulated more in root than shoot. At 100 ppm Hg concentration shoot accumulated 1911 mg Hg/ kg of their dry weight while root accumulated 62166 mg Hg/ kg dw. Photosynthetic activity was assessed by measuring chlorophyll a fluorescence by determination of Fv/Fm and Fv/Fo values. Photosynthetic integrity was not affected upto 50 ppm Hg concentration, however, concentrations higher than 50 ppm affected photosynthetic integrity. S. drummondii plants responded to Hg induced oxidative stress by modulating non-enzymatic antioxidants (glutathione, other non-protein thiols) and enzymatic antioxidants: superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR). The content of glutathione (GSH) and GSH/GSSG ratio increased upto a concentration of 50 ppm while slight down at 100 ppm Hg. The content of other non-protein thiols significantly increased with increasing Hg concentrations in the growth medium. The activities of antioxidative enzymes, SOD, APX and GR followed the same trends as antioxidants first increasing upto a concentration of 50 ppm Hg and then slight decrease. The results suggest that Sesbania plants were able to tolerate Hg induced stress using an effective antioxidative defense mechanism.
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