[Action of actinomycin D on Euglena gracilis ultrastructure].

Effects of 1 and 10 mkg/ml concentrations of actinomycin D, an inhibitor of RNA synthesis, on the ultrastructure of a phytoflagellate Euglena gracilis were followed during 48 hours. Similar changes were observed with both the concentrations, but the effect of the higher dose appeared in a short time and was more expressed. The effect of actinomycin D becomes obvious as early as half an hour after its adding; the cell nucleus, chloroplasts and mitochondria show definite responses. Chromatin condensation is seen in the nucleus, the nucleolus is enlarged in size, compressed and fragmented. Chloroplasts react to the action of actinomycin D by swelling, accumulation of osmiophilic globuli, disorganization and reduction of lamellar systems, formation of the myelin figures and gran-like structures and by the decomposition of pyrenoid. The mitochondrial matrix is compressed, the structure and orientation of the cristae become abnormal, and some electron-dense bodies appear.