Effect of Actinomycin D on Euglena Chloroplast Formation

Abstract

THE fact that some chloroplast mutations are inherited in a non-Mendelian fashion indicates that chloroplasts possess a degree of genetic autonomy¹. Treatment of Euglena gracilis with any one of a variety of chemical or physical agents leads to the permanent loss of chloroplasts and results in permanently ‘bleached’ but viable cells². While the chemical nature of the hereditary units of chloroplasts remains uncertain, Schiff et al. and Gibor and Granick have concluded from work on the ultra-violet inactivation of the Euglena chloroplast-forming system that cytoplasmic or chloroplast nucleoprotein is involved³. The action spectrum for the photoreactivation of the chloroplast-forming system is similar to that found for systems in which thymine dimer formation has been shown to be the primary result of ultra-violet irradiation⁴. The report that the ultra-violet resistance of the Euglena chloroplast-forming system is increased in cells which have been grown in the presence of 6-azathymine also suggests that DNA is the ‘target’ in ultra-violet inactivation⁵. Chemical and histochemical experiments to detect DNA in the chloroplasts of various organisms have led to conflicting views⁶. Two reports of the incorporation of tritiated thymine into chloroplasts⁷ provide further evidence for the involvement of DNA in chloroplast heredity.