Phytochrome control of <i>in vitro</i> transcription of specific genes in isolated nuclei from barley (<i>Hordeum vulgare</i>)

Abstract

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.