BLUE LIGHT-DEPENDENT CHLOROPLAST DIFFERENTIATION IN CULTURED PLANT-CELLS - EVIDENCE FOR TRANSCRIPTIONAL CONTROL OF PLASTID GENES

A DNA‐protein complex capable of RNA synthesis (transcriptionally active chromosome, TAC) was isolated from plastids of dark‐grown and blue light irradiated cell cultures of Chenopodium rubrum. The transcriptional activity of TAC increased rapidly upon irradiation of dark‐grown cells with blue light. Analysis of the RNA synthesized showed that plastid rRNA genes as well as genes coding for membrane and stroma proteins were specifically transcribed; their quantities depended on the developmental stage of the plastids produced by blue light exposure. The in vitro transcription rate seems to reflect fairly well the in vivo situation insofar as its enhancement in blue light irradiated cells is in good accordance with the observed steady‐state level of plastid mRNAs. The results obtained support the notion that the blue light‐dependent accumulation of plastid mRNAs in vivo is caused by an increase in the transcription rate of the corresponding genes. Thus an alternative exists to the light‐induced transformation of etioplasts to chloroplasts in seedlings where primarily posttranscriptional and translational controls are effective. 1990 Deutsche Botanische Gesellschaft/German Botanical Society