The phytotoxic effects of selenium-mercury interactions on root growth in Brassica rapa (LvLing)

Rapid industrial and agricultural development has dramatically increased the emission of selenium (Se) and mercury (Hg) into the environment. Combined soil pollution by Se and Hg poses a potential threat to crop production. However, no toxic effects of Hg-Se interactions on plants have been reported previously. In this study, we investigated the effects of Hg-Se interactions on biochemical and physiological indices in the roots of Brassica rapa (LvLing). Seedlings were treated hydroponically with solutions of mercury chloride (1 mu M), sodium selenite (4 mu M), or a combination of the two. Combined Hg+Se treatment significantly inhibited root growth, reduced root biomass, and enhanced reactive oxygen species (ROS) and malondialdehyde accumulation and led to a loss of plasma membrane integrity. The combined treatment increased glutathione peroxidase, glutathione S-transferase, and peroxidase activity, reduced superoxide dismutase activity, and had no effect on catalase activity. In addition, we detected increased glutathione concentrations in root tips and reduced ascorbic acid concentrations in the presence of Hg+Se relative to individual treatments with these elements. Thus, Hg-Se interactions enhanced oxidative injury, cell death, and phytotoxicity in B. rapa roots.