Perturbation of monovalent cation composition in Ulva lactuca by cadmium, copper and zinc

Discs of thallus cut from the macroalga Ulva lactuca were incubated in filtered seawater containing cadmium, zinc, copper or cobalt (30 μM). The metal uptake rates differed for each metal in the order Cu > Zn > Cd > Co. Exposure of the macroalga to metals resulted in a disruption of intracellular monovalent cation composition. Intracellular potassium was irreversibly lost and sodium was accumulated by cadmium- or copper-treated U. lactuca, which was assumed to indicate irreversible disruption of the plasmalemma. Exposure to zinc caused an increase in sodium concentrations, whereas potassium concentrations were not significantly different from the controls, suggesting that the integrity of the plasmalemma had been maintained at the zinc concentration used. Intracellular magnesium was also lost from copper-treated algae, which again indicated a loss of integrity of the cell membrane.