An autoradiographic comparison of the effects of enucleation and actinomycin D on the incorporation of nucleic acid and protein precursors by Acetabularia chloroplasts

Abstract

Surgical enucleation of the giant, unicellular alga ( Acetabularia mediterranea) eliminates the genetic material of the nucleus, while treatment with actinomycin D is presumed to prevent the transcription of the genetic material within the chloroplasts as well as that of the nucleus. An autoradiographic comparison of the effects of both treatments on the incorporation of radioactive thymidine, uridine and leucine by the chloroplasts gave the following results. 1. 1. Enucleation does not prevent the incorporation of thymidine into the DNA of the chloroplasts. 2. 2. Enucleation has little effect on the incorporation of uridine into the RNA of the chloroplasts while actinomycin abolished this incorporation in both normal and enucleate plants. 3. 3. Enucleation has only a minor effect on the incorporation of leucine by the chloroplasts while actinomycin greatly reduced such incorporation in normal and enucleate plants. These results are compatible with the hypothesis of almost complete autonomy of chloroplasts in replicating their DNA and in the production of most, if not all, plastid RNA and protein species from this DNA template.