Effect of streptomycin on greening and biosynthesis in Euglena gracilis

Abstract

1. 1. An experimental system is described in which etiolated cells of Euglena gracilis, under conditions which do not support growth, synthesise chlorophyll in the light, rapidly and reproducibly, without a lag period. The synthesis of chlorophylls a and b, and of carotenoids, is inhibited by high concentrations of streptomycin. 2. 2. During greening there is little or no fall in the level of the free amino compounds of the cells. Streptomycin sulphate causes an increase in the level of the free amino compounds of the cells. Inorganic sulphates have a similar, although smaller, effect. 3. 3. At concentrations which inhibit greening, streptomycin also inhibits the incorporation of [1- 14C]acetate into the protein and nucleic acid of the cells, both in the light and in the dark. Incorporation of acetate carbon into polysaccharide, however, is markedly stimulated by streptomycin in the light. 4. 4. The various effects of streptomycin on chlorophyll and carotenoid synthesis, and on acetate incorporation, are all annulled if MnCl 2 is added at the same molar concentration as the drug; MgCl 2 is ineffective. 5. 5. It is suggested that streptomycin has a general effect on biosynthesis and that its inhibition of greening is not due to a specific inhibition of chloroplast formation, but is merely one consequence of the effect on general biosynthesis.