Mercury-induced oxidative stress in marine phytoplankton Tetraselmis tetrathele (Prasinophyceae).

Mercury-induced oxidative stress was observed in the cells of marine phytoplankton Tetraselmis tetrathele
(Prasinophyceae) using the fluorescent probes 2' 7-dichlorofluorescindiacetate (DCFH-DA) and fluorescein
diacetate (FDA). When the cells were exposed to 1μM of HgCl2， the fluorescence intensity of 2'
7' -dichlorofluorescin (DCF) was three times higher than that of the control level 60 min after the treatment，
indicating H202 accumulation，and it gradually decreased. Moreover，exposure to 0.3μM of HgCl2 caused an
increase in fluorescence 6h after the treatment. However，exposure to HgCl2 at concentrations of 3.0μM or
greater did not cause an increase in fluorescence. It is thought that H202 was also generated at these
concentrations，but could not be detected due to inactivation of the cellular esterase necessary to convert
DCFH-DA to DCFH，and/or leakage from the cells due to membrane damage caused by HgCl2. The maximum
level of fluorescence was approximately two times higher under light conditions than under dark conditions，
suggesting that H202 was derived partly from photosynthesis. These results indicate that accumulation of H202 is
involved inconsequence of the toxicity of mercury.