Effect of cadmium on growth, ATP content, carbon fixation and ultrastructure in the marine diatom Phaeodactylum tricornutum Bohlin

Cadmium toxicity to the diatom Phaeodactylum tricornutum Bohlin has been st udied on the basis of the effect of this metal on growth, ATP content, C-14 uptake and cellular ultrastructure. The microalga was exposed to 1, 5, 10, 25, 50, 75 and 100 mg l(-1) of cadmium and showed a concentration- depende nt inhibition in those physiological parameters. At cadmium concentrations of 5 mg l(-1) or higher, a significant effect on growth of P. tricornutum w as observed. After 8 hours of exposure to the different cadmium concentrati ons, the decrease in the ATP content was significant only at cadmium concen trations of 25 mg l(-1) or higher. C-14 uptake was more susceptible to cadm ium than the decrease in the ATP content, as 5 mg l(1)(-) of cadmium caused a severe decrease in this parameter. Cadmium also caused ultrastructural c hanges in P. tricornutum cells: deposition of cadmium on the surface of cel l, increase in the chloroplast size, appearance of electrodense granulation s, and reduction in lipid inclusions.