Phytochrome regulation of mRNA levels of ribulose-1,5-bisphosphate carboxylase in etiolated rye seedlings (Secale cereale).

The effect of red light and far-red light on the appearance of mRNA for the small and large subunit of ribulose-1,5-bisphosphate carboxylase in rye seedlings has been analysed. Irradiation of etiolated seedlings with a pulse of red light increased the mRNA level of the small subunit by a factor of 7-10 and that of the large subunit by a factor of 3. A pulse of far-red light resulted in a much lower, but measurable increase. The effect of red light is reverted by an immediate far-red pulse, demonstrating the classical phytochrome response.In vitro transcription experiments with nuclei isolated from red light-treated seedlings showed that the transcription rate of the small subunit mRNA was increased only by a factor of 1.5-2.5, indicating posttranscriptional as wells as transcriptional regulations of the small subunit of ribulose-1,5-bisphosphate carboxylase.