STRESS PROTEIN-SYNTHESIS AND PEROXIDASE-ACTIVITY IN A SUBMERSED AQUATIC MACROPHYTE EXPOSED TO CADMIUM

Sago pondweed (Potamogeton pectinatus L.) was exposed to CdCl2, to eva luate peroxidase (POD) activity and stress protein (SP) synthesis as p otential biomarkers of contaminant stress in an aquatic plant. Peroxid ase activity did not increase in sage pondweed incubated for 24 h in a liquid culture medium containing 0.5, 0.75, or 1 mM CdCl2. By contras t, at each of these CdCl2 concentrations, SPs of 162, 142, 122, 82, an d 61 kDa were preferentially synthesized, and synthesis of a 66-kDa pr otein was reduced relative to controls. Peroxidase activity also did n ot change in sage pondweed rooted for 21 d in agar containing 1 mM CdC l2, despite the lower growth rate, lower protein content, and brown di scoloration of the plants. Only when the plants were grown 7 or 21 d o n agar containing IO mM CdCl2 were the growth retardation and phenotyp ic deterioration accompanied by significantly increased POD activity. In contrast, plants rooted for 7 d in agar containing 1 mM CdCl2 were not significantly discolored or retarded in growth, yet they preferent ially synthesized SPs of 122, 82, and 50 kDa and synthesized proteins of 59 and 52 kDa at reduced rates relative to controls. Similar change s in protein synthesis were accompanied by signs of depressed growth a fter 21 d of incubation with 1 mM CdCl2 and with 7 or 21 d of exposure to 10 mM CdCl2. These data indicate that changes in SP synthesis may precede detectable alterations in growth of aquatic plants and, theref ore, may be a potentially useful early biomarker of contaminant stress . However, further studies will be required to determine whether the S P response is measurable during exposure to environmentally relevant c ontaminant levels.