Stress protein synthesis and peroxidase activity in a submersed aquatic macrophyte exposed to cadmium

Sago pondweed ( Potamogeton pectinatus L.) was exposed to CdCl, to evaluate peroxidase (POD) activity and stress protein (SP) synthesis as potential biomarkers of contaminant stress in an aquatic plant. Peroxidase activity did not increase in sago pondweed incubated for 24 h in a liquid culture medium containing 0.5, 0.75, or 1 mM CdCl,. By contrast, at each of these CdCl, concentrations, SPs of 162, 142, 122, 82, and 61 kDa were preferentially synthesized, and synthesis of a 66‐kDa protein was reduced relative to controls. Peroxidase activity also did not change in sago pondweed rooted for 21 d in agar containing 1 mM CdCl 2 , despite the lower growth rate, lower protein content, and brown discoloration of the plants. Only when the plants were grown 7 or 21 d on agar containing 10 mM CdCl, were the growth retardation and phenotypic deterioration accompanied by significantly increased POD activity. In contrast, plants rooted for 7 d in agar containing 1 mM CdCl, were not significantly discolored or retarded in growth, yet they preferentially synthesized SPs of 122, 82, and 50 kDa and synthesized proteins of 59 and 52 kDa at reduced rates relative to controls. Similar changes in protein synthesis were accompanied by signs of depressed growth after 21 d of incubation with 1 mM CdCl, and with 7 or 21 d of exposure to 10 mM CdCl,. These data indicate that changes in SP synthesis may precede detectable alterations in growth of aquatic plants and, therefore, may be a potentially useful early biomarker of contaminant stress. However, further studies will be required to determine whether the SP response is measurable during exposure to environmentally relevant contaminant levels.