Level of intracellular calcium in U. compressa (A) cultivated in control condition (white circles) and with 10 μm copper (black circles). Calcium level is expressed as the ratio of Fluo 3 fluorescence and chloroplast autofluorescence. Level of calcium in the alga cultivated in control condition (control), exposed to 10 μm copper (copper), or treated with 10 μm ned-19, 100 μm ryanodine (rya), 10 μm xestospongin C (xes), 1 mm ASC, or 0.1 mm cPTIO and exposed to 10 μm copper for 2 h (B), 3 h (C), and 12 h (D). Bars represent mean values of three independent experiments ± sd. Different letters indicate significant differences (P < 0.05).