COPPER TOXICITY ON THE MARINE MICROALGA PHAEODACTYLUM-TRICORNUTUM - EFFECTS ON PHOTOSYNTHESIS AND RELATED PARAMETERS

Essential heavy metals, as copper, can be toxic for microalgae at high concentrations. Copper affected growth and other parameters closely r elated to photosynthesis of the marine diatom Phaeodactylum tricornutu m. A copper concentration of 0.10 mg l-1 provoked about 50% growth red uction and 1 mg l-1 inhibited the growth. Copper also interfered with photosynthesis and ATP production. A copper concentration of 0.5 mg l- 1 reduced in a 50% the photosynthetic rate. Therefore, growth is more affected by copper than photosynthesis. Results of chlorophyll a fluor escence obtained by flow cytometry showed that copper's inhibitory eff ect on PS II activity is located on its oxidizing side. The lower copp er concentration assayed provoked a significant decrease in the cellul ar pool of ATP. Pigment analysis by HPLC showed that copper affected t he pigment pattern of P. tricornutum. Important changes were observed for chlorophyll a and its allomer: chlorophyll a proportion decreased while its allomer increased with the copper concentration, being maxim um at 1 mg Cu 1-1. The study of the intracellular pH by flow cytometry revealed that P. tricornutum cells exposed to 0.5 and 1 mg Cu 1-1 sho wed an intracellular pH higher than control cultures cells, explaining the high proportion of the chlorophyll a allomer in these cells.