PHOTORECEPTORS CONTROLLING TRANSCRIPTION OF rbcS GENES IN GREEN LEAF TISSUE OF Pisum sativum

Abstract

We have investigated the photoreceptors controlling transcription of genes encoding the small subunit (rbcS) of ribulose 1,5-bisphosphate carboxylase-oxygenase in green leaf tissue of pea (Pisum sativum). RbcS transcription was measured by hybridising labelled transcripts of isolated nuclei to rbcS cDNA clones. Transfer of green Pisum leaf tissue to darkness for 5 h causes a substantial decrease in the rate of rbcS transcription and the rate is restored rapidly when the plants are returned to white light. Low fluence rates of red light are ineffective in restoring the rate of rbcS transcription, suggesting that phytochrome alone does not fully mediate the response. Blue light is similarly effective to white light of an equal fluence rate (120 mumol m-2 s-1) in restoring the rate of rbcS transcription in the dark-treated plants, indicating that a blue light photoreceptor is involved. However, red light at the same fluence rate produces about 65% of the effect of blue or white light, showing that the blue light photoreceptor is not the only photoreceptor controlling rbcS transcription in the green leaf tissue. The identity of the photoreceptor responsible for the red light effect is discussed. Similar effects of blue and red light are observed at the level of transcript abundance in dark-grown pea leaf tissue given a brief illumination with red light, which potentiates the tissue for rapid transcript accumulation in white light.

A blue-light photoreceptor mediates the fluence-rate-dependent expression of genes encoding the small subunit of ribulose 1,5-bisphosphate carboxylase/oxygenase in light-grown Phaseolus vulgaris primary leaves

“…Previous studies of the role of blue light in sun/shade adaptation (see Senger and Bauer 1987) have often compared the effectiveness of red and blue light at single fluence rates and a contradictory picture has resulted. Moreover, the results show a clearer blue-light effect than found by Clugston et al (1990). The present observations extend those of Fluhr and Chua (1986) with pea in that they do not involve the use of extensively dark-adapted seedlings and they demonstrate the importance of the blue-light photoreceptor as a fluence-rate sensor.…”

“…Plants grown for 16 d in low white light (15 lamol -m 2. s -l ) were illuminated for 30 min with either the red or blue light source described above at a fluence rate of 75 lamol -m -z. s-1 prior to measurements being made. Nuclear transcripts from 106 nuclei were synthesised in the presence of 1.85 MBq [a-32p]UTP (110 TBq-mmol 1) and extracted and hybridised as described previously (Gallagher and Ellis 1982;Clugston et al 1990). Three separate measurements were made of the time (T) taken to for the resistance to rise from 30 to 70 mA for each leaf.…”

“…Finally, a blue-light photorecep-tor may act as the fluence-rate detector. Clugston et al (1990) obtained evidence for bluelight stimulation of rbcS transcription in pea leaves that had received minimal dark adaptation and higher fluence rates of blue light, but a significant response was also induced by red light. It has been shown that blue/ UV-A illumination increases translatable rbcS mRNA in dark-grown Sorghum seedlings (Drumm-Herrel and Mohr 1988).…”

Arabidopsis rbcS Genes Are Differentially Regulated by Light

“…The results are consistent with regulation of at least the rbcS 3B gene by a blue-light photoreceptor in 10-d-old red light-grown seedlings. Because these seedlings show Chl accumulation, the involvement of a blue-light photoreceptor in the effect of LF blue light on the expression of three Arabidopsis rbcS genes is probably correlated with the developmental stage of the seedlings, as was described for pea (Fluhr and Chua, 1986;Clugston et al, 1990).…”

“…In young, etiolated pea seedlings, the light-induced changes in rbcS gene expression are phytochrome mediated, and there is no evidence for action of other photoreceptors. However, in mature leaves, a blue-light receptor acts in concert with phytochrome (Fluhr and Chua, 1986;Sasaki et al, 1988;Clugston et al, 1990). Blue-light receptors have been implicated in other species as well (Wehmeyer et al, 1990).…”