Flow fluorometric study of DNA content in nonproliferative Euglena gracilis cells and during proliferation

Ethanol-fixed Euglena gracilis cells have been analyzed by flow microfluorometry during the lag, logarithmic and stationary phases. The histogram of a plateau stage culture reveals, as expected, an unimodal distribution, but the peak is at lower fluorescence intensity as compared to G1 logarithmic cells. The fluorescence intensity drops as the cells enter the stationary stage. Ultimately the decrease represents a change of about 25%. When cells recover from the plateau stage, the fluorescence intensity increases during the lag phase, and climbs to the level found in a G1 logarithmic population. The reason for the decrease in the fluorescence intensity during the stationary stage may be due to a possible loss of DNA or to a decrease in the number of chromatin-binding sites for intercalating ethidium bromide.