Transcriptional activity of isolated maize chloroplasts.

Chloroplasts and etioplasts, isolated from light- or dark-grown Zea mays plants, respectively, can incorporate labeled UTP into RNA in a reaction stimulated by light or ATP. This in organello RNA synthesis proceeded at a linear rate for up to 2 h. When expressed per unit protein, plastids from dark-grown plants incorporated more UTP than those from light-grown plants, and the highest rate of UTP incorporation was found in plastids from light-stimulated leaves (grown previously in the dark). The in organello newly synthesized RNA was heterodispersed, with most transcripts smaller than 14 S. Specific transcripts were detected in organelles from both dark- and light-grown plants that contain sequences that are homologous to the mRNAs for the rbcL gene (coding for the large subunit of ribulose bisphosphate carboxylase (LS-RuBPCase] and for the psbA gene (32-kDa thylakoid membrane protein). Qualitatively, the newly synthesized in organello transcripts were similar from the dark and light organelles.