Synthesis of ribosomal RNA in ribosome-deficient plastids of the mutant "albostrians" of Hordeum vulgare L.

The nuclear gene-induced plastome mutant "albostrians" of Hordeum vulgare L. is characterized by a plastid ribosome-deficiency. This ribosome deficiency could be caused by the lack of or a defect in chloroplast RNA polymerase. However in our investigations we found an activity of chloroplast RNA polymerase in wild-type and mutant leaves of "albostrians" barley by (1) electron microscopic autoradio-graphy after in vivo labelling of RNA, (2) determination of RNA polymerase activity in isolated plastids, and (3) characterization of the newly synthesized RNA by electrophoresis in polyacrylamide gels. The genes of 23S and 16S rRNA are transcribed in mutant plastids and the RNAs are processed. From these results we conclude that the enzymes involved in transcription and processing of chloroplast rRNA are synthesized on cytoplasmic ribosomes and that the plastid ribosome deficiency in albostrians barley is probably not caused by a defective chloroplast DNA dependent RNA polymerase or by a mutation in the genes of 23S and 16S chloroplast rRNA.