In-vivo phytochrome control of in vitro transcription rates in isolated nuclei from oat seedlings.

The transcription rate of isolated nuclei from oat seedlings was analysed by measuring the incorporation of radioactive label in trichloroacetic-acid-pelletable material. It was observed that this transcription rate depends on the light pretreatment of the plants: 7.5 h after a 5-min red or far-red light pulse maximum rates were found, but at this time far-red light induced only about half of the stimulation observed after a red light pulse. The far-red reversibility of the effect of the red light pulse indicates that phytochrome controls the capacity for transcription by isolated nuclei. Besides this slow reaction, phytochrome regulated the transcription rates in a very fast response when homogenates were irradiated.