Phytochrome control of in vitro transcription of specific genes in isolated nuclei from barley (Hordeum vulgare).

The transcriptional rates of four different genes in shoots of barley grown under different light regimes were quantified by monitoring nuclear RNA transcripts using gene-specific hybridization probes. Isolated nuclei were pulse-labelled with [alpha-32P]UTP and the relative rates of light-harvesting chlorophyll a/b protein (LHCP) mRNA, NADPH:protochlorophyllide oxidoreductase mRNA, B1 hordein mRNA, and 26-S rRNA synthesis were measured. Irradiation of dark-grown plants with a red light pulse increased the rate of LHCP mRNA synthesis tenfold within 3 h, and the rate of rRNA synthesis more than twofold within 9 h. The relative rate of synthesis of the oxidoreductase mRNA decreased following a red light pulse reaching a minimum after 3-6 h. As a direct proof of phytochrome involvement in the light-induced stimulation of LHCP and the repression of the oxidoreductase transcripts for both responses, red/far-red reversibility could be demonstrated. We conclude that phytochrome is able both to increase the transcription of certain nuclear genes and decrease the transcription of others.