Resistance and Sensitivity of Chloroplast Ribosomes to Streptomycin in Mutants of Chlamydomonas reinhardi

Abstract

Abstract In a mendelian (sr3) and an uniparental (sr35) streptomycin resistant mutant of Chlamydomonas reinhardi the influence of streptomycin on protein synthesis on the chloroplast and cytoplasmic ribosomes was investigated in vitro. Hetero‐, mixo‐ and phototrophic agar cultures and heterotrophic liquid cultures were used. Protein synthesis on the cytoplasmic ribosomes, measured by the activity of glyceraldehyde‐3‐phosphate: NADP dehydrogenase (EC 1.2.1.9), was not inhibited, but rather stimulated by streptomycin. Protein synthesis on the chloroplast ribosomes of sr3, measured by the activity of ribulose‐1,5‐diphosphate carboxylase (EC 4.1.1.39), was greatly inhibited by streptomycin, especially in hetero‐ and mixotrophic cultures. In sr35 the chloroplast ribosomes were resistant to streptomycin. Heterotrophically grown cultures of sr3 and of a streptomycin‐sensitive strain are yellow in the presence of streptomycin and form no or only reduced thylakoids on solid media. But 70‐S organelle‐ribosomes are present in a normal amount. The relationship between chloroplast protein synthesis and thylakoid formation is discussed.