| Abstract: | We investigated how Prorocentrum micans Ehrenberg, a planktonic dinoflagellate common in Portuguese coastal waters, is able to tolerate and recover from sublethal concentrations of copper(II). The experimental design simulated events in inshore waters, where P. micans is subjected to high levels of pollutants, including copper. Decrease in growth rate, induction of a growth lag phase, temporary loss of motility, and potassium leakage were the effects induced in P. micans cultures by 90 nM labile copper. A 10–20-fold increase in cellular copper concentration was observed in toxicity experiments. Copper efflux (representing a 50% decrease in cellular metal content) was a short-term tolerance mechanism. A 25-kDa protein was detected after only 3 h of exposure to copper, but there was no evidence of phytochelatin synthesis. Ultracytochemical labeling of metals with the sulfide-silver procedure showed that copper was associated with the thecal plates, starch grains, and, to a lesser extent, lipid droplets. High values affixation capacities and average conditional stability constants for copper binding by starch, amylopectin, and cellulose support the location of copper in thecal plates and starch grains. We conclude that P. micans responds rapidly to copper toxicity and has two tolerance mechanisms for copper: copper efflux and sequestration in polymeric substances. |
