RNA and protein synthesis in protoplasts isolated from tobacco leaves

Abstract

RNA and protein synthesis in the protoplasts isolated from tobacco mesophyll were studied by measuring the incorporation of labeled precursors. 1. 1. Incorporation of [ 14C]uracil into protoplast RNA was accounted for almost entirely by RNA synthesis in the nucleus. Little radioactivity was incorporated into rRNA's of the chloroplasts. 2. 2. Incorporation of [ 14C]uracil was inhibited by actinomycin D, chromomycin A 3 and 2-thiouracil, but not by rifampicin and daunomycin. 3. 3. Rate of protein synthesis was found to be 2 · 10 −6 nmole leucine per protoplast per h, corresponding to a turnover rate of 0.5 % per h. 4. 4. Incorporatio of [ 14C]leucine was inhibited by cycloheximide, blasticidin S and enomycin. Only partial inhibition was obtained with chloramphenicol and puromycin. 5. 5. [ 14C]Leucine was incorporated into both cytoplasmic and chloroplast protein. Incorporation into cytoplasmic protein was inhibited by cycloheximide, while that into chloroplast protein was sensitive to chloramphenicol. 6. 6. Average half-life of mRNA was estimated to be 4 h.