Sensitivity of Chloroplast Development in Euglena to Acridine Orange: Bleaching and Recovery from Damage

Treatment of light-grown Euglena cells with acridine orange(AO) at non-lethal concentrations resulted in the permanentloss of their ability to form chloroplasts. However, dark-growncells were insensitive to AO. Starvation of the cells underlight culture or the addition of chloramphenicol (CM) deformedthe chloroplasts and made them less AO sensitive. Cells withmature chloroplasts seemed to show the most sensitivity to AO.Illumination with intense visible light of the AO-treated cells,whether they had been light- or dark-grown, made a greater proportionof them liable to be bleached or to be killed. The photosensitizationwas evident over the range of wavelengths of 450–500 nm,where the absorption maximum of AO is located. When light-grown cells, after AO treatment, were held in darknessin a nongrowth medium for 24 hr, the bleaching effect was reduced.However, if held under a light of 620–670 nm, where cellswere not photosensitized but were able to form chloroplasts,the AO-damage was not reversed. The possibility of repair afterAO-treatment is discussed. (Received May 15, 1981; Accepted October 8, 1981)