Interactive effects of selenium and mercury on the restoration potential of leaves of the medicinal plant, Portulaca oleracea Linn

Leaves of Portulaca oleracea have the potential of regeneration, when grown in a distilled water medium. The two heavy metals, Se and Hg individually and in combination affected both shoot and root development. They completely arrested shoot development at all concentrations. However, they produced concentration-dependent changes in the development of roots, which ranged from their complete inhibition to variation in their initiation time, number and length. Leaf decay was initiated on day 46 in control leaves. Concentration-dependent changes were also observed in the time of initiation and magnitude of decay of leaves. The data indicates that Hg was more toxic than Se. The protective effect of Se against Hg toxicity was evident only at very low concentrations. With further increases in the concentration of both Se and Hg, the protective effect decreased and simultaneously the toxicity increased. Following the decay of leaves, a pink colour development was observed only on leaves exposed to Se. Microbial analysis of leaves showed the presence of Acinetobacter only in Se-exposed leaves. Acinetobacter was therefore considered as probably involved in the formation of elemental Se, which produced a pink colour.