RED: FAR-RED RATIO DOES NOT MODULATE THE ABUNDANCE OF TRANSCRIPTS FOR TWO MAJOR CHLOROPLAST POLYPEPTIDES IN LIGHT-GROWN Pisum sativum TERMINAL SHOOTS

Photoreceptors controlling transcription of rbcS genes in green leaf tissue of Pisum sativum

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.

REVERSAL OF CAESIUM INHIBITION OF GROWTH BY POTASSIUM IN HYPOCOTYLS OF TOMATO SEEDLINGS (LYCOPERSICON ESCULENTUM L.)

Stunted, misshapen, necrotic hypocotyls of tomato seedlings (Lycopersicon esculentum L.) germinated on caesium cations in continuous red or white light indicated caesium-associated hypocotyl photo-injury. Continuous, far red irradiation inhibited seedling germination in control and caesium treatments but was reversed by continuous white light. Hypocotyl photo-injury also occurred in far red pretreated seedlings germinated on caesium in continuous white light. Except for suppressed elongation, hypocotyls of caesium-treated seedlings were normal in appearance. Etiolated caesium-treated seedlings placed in continuous white light also exhibited hypocotyl photo-injury. The effects of caesium cations were reversed by potassium cations but not by cations of other alkali metals.

Expression of two nuclear genes encoding chloroplast proteins during early development of cucumber seedlings

Cloned complementary DNA probes have been used to measure steady-state transcript levels for the small subunit of ribulose bisphosphate carboxylase-oxygenase (SSU) and the chlorophyll a/b-binding protein (LHCP) in cotyledons during early development of cucumber seedlings. Initial accumulation of trancripts to SSU occurs 2d after germination and is independent of light and developmentally programmed. Although transcripts accumulate in dark-grown tissues, their levels increase rapidly in light-grown cotyledons from day 4, coinciding with emergence above the soil, so that by day 6 levels are 2.4 times higher in light-grown compared with dark-grown cotyledons. In contrast, accumulation of transcripts to LHCP occurs only in light-grown cotyledons. Southern blot analysis of genomic DNA indicates that in cucumber there are one and two genes encoding SSU and LHCP, respectively, considerably fewer than in those other plant species that have been examined. Both LHCP genes are expressed in light-grown cotyledons.