Flow fluorometric study of DNA content in nonproliferative Euglena gracilis [Algae] 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 a 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 Gl 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.