Effect of Methylmercury on the Light

The effect of a dangerous toxic substance, methylmercury, on light dependence curves of chloro phyll fluorescence in Chlamydomonas moewusii was studied. We found low concentration of methylmercury (10–7 M) to cause a decrease in the relative rate of the non cyclic electron transport activity of PS2, a decline in the maximum utilization of light energy (α), and a decline in the saturation light intensity (Es). Nonpho tochemical fluorescence quenching increased after short term exposure and decreased in the course of pro longed incubation. These parameters were more sensitive to the action of the toxic substance than the widely used parameter FV/FM, which reflects the maximum quantum yield of PS2. We propose the use of the method of fast measurement of light dependence curves of fluorescence to detect the changes in algal cells at the early stages of exposure to mercury salts.