Flow cytometry determination of acute physiological changes in a marine diatom stressed by copper.

Flow cytometry (FCM) was used to determine changes in cellular volume, transmembrane potential, mitochondrial membrane potential and intracellular pH in the marine microalga Phaeodactylum tricornutum immediately (5 to 10 seconds) after the addition of selected concentrations of copper. An acute increase in the forward scatter signal of this diatom was detected after the addition of 10 mg 1-1 of copper. Stress produced by the copper addition resulted in various physiological alterations that can be easily and quickly detected by FCM: (i) the hyperpolarization of the cell membrane, as a result of an immediate increase in the cytoplasmic membrane potential, (ii) the increase of the mitochondrial membrane potential, being maximum at the higher copper concentration assayed, and (iii) the increase in the intracellular pH with the highest copper concentration assayed (10 mg 1-1).