Differential Regulation of Nuclear Genes during Blue Light‐dependent Chloroplast Differentiation in Cultured Plant Cells

Abstract

AbstractNuclei capable of RNA synthesis were isolated from both dark‐grown and blue light‐irradiated cell cultures of Chenopodium rubrum. Analysis of the heterodisperse RNA sequences synthesized showed that the SSU and LHCP gene as well as early light‐induced genes were specifically transcribed. The relative transcription rate of their mRNAs increased with the onset of blue light irradiation reaching a maximum at about 12 h, then dropped to the dark level. A comparison with the steady‐state concentration of the same mRNAs in vivo revealed a substantial difference between the two groups of genes: For the three early light‐induced genes the in vitro transcription rate is in good accordance with the observed steady‐state level of their transcripts supporting the notion that the blue light‐dependent rapid and transient accumulation in vivo is caused by a temporary increase in the transcription rate of the corresponding genes. In contrast, for the SSU and LHCP gene, the changes in transcription rate do not follow those in steady‐state concentration; thus the observed steady increase of the latter in blue light cannot be explained as an enhancement in the transcription rates of both genes, but is a likely consequence of post‐transcriptional events.