POTENTIAL TOLERANCE MECHANISMS OF PROROCENTRUM MICANS (DINOPHYCEAE) TO SUBLETHAL LEVELS OF COPPER

We investigated how Prorocentrum micans Ehrenberg, a planktonic dinofl agellate 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 subjecte d to high levels of pollutants, including copper. Decrease in growth r ate, 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 concentrat ion was observed in toxicity experiments. Copper flux (representing a 50% decrease in cellular metal content) was a short-term tolerance mec hanism. A 25-kDa protein was detected after only 3 h of exposure to co pper, but there was no evidence of phytochelatin synthesis. Ultracytoc hemical labeling of metals with the sulfide-silver procedure showed th at copper was associated with the thecal plates, starch grains, and, t o a lesser extent, lipid droplets. High values of fixation capacities and average conditional stability constants for copper binding by star ch, amylopectin, and cellulose support the location of copper in theca l plates and starch grains. We conclude that P. micans responds rapidl y to copper toxicity and has two tolerance mechanisms for copper: copp er efflux and sequestration in polymeric substances.