Phytochrome Levels in Light-Grown Avena Change in Response to End-of-Day Irradiations

Abstract

The effect of 15-minute end-of-day irradiations on photoreversible phytochrome levels in light-grown oat (Avena sativa L., cv Garry) seedlings was investigated. Oat seedlings were grown in a cycle of 8 hours of natural daylight and 16 hours of complete darkness, from sowing until harvest at day 10. The level of extractable, photoreversible phytochrome per unit fresh weight was 60% higher after end-of-day far-red irradiation than after either endof-day red irradiation or end-of-day far-red followed by end-ofday red. Seedlings irradiated with end-of-day far-red also exhibited a small but significant increase in shoot height and fresh weight per seedling. Extracts of seedlings given each of these end-of-day treatments were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, electroblotted, and immunostained with monoclonal antibodies specific to different phytochromes.

Phytochrome-Mediated Light Regulation of PHYA- and PHYB-GUS Transgenes in Arabidopsis thaliana Seedlings

“…Preliminary results have also shown that PHYB-GUS expression under red light in the phyB background was similar to the GUS activity level in etiolated seedlings (data not shown). In oat the levels of one or more light-stable phytochromes increased in abundance after end-of-day far-red irradiation (Stewart et al, 1992). Since the end-of-day far-red response is phyB mediated (Smith, 1994), this result is also consistent with phyBmediated regulation of PHYB transcription.…”

Phytochrome Levels in the Green Alga Mesotaenium caldariorum Are Light Regulated

“…For this reason, the light regulation of Mesotaenium phytochrome abundance observed here contrasts with the apparent lack of light regulation of type I1 phytochrome in higher plants. As was discussed above, however, the recent studies of Stewart et al (1992) suggest that the lack of light regulation may not be true for a11 of the green plant phytochromes. Although the light regulation of Mesotaenium phytochrome levels is qualitatively similar to that for type I phytochrome of higher plants, our analyses also reveal significant differences.…”

“…In that study, a monoclonal antibody to maize phytochrome was used to show that the level of an immunologically cross-reacting 125-kD polypeptide was nearly 3-fold higher in 3-d dark-adapted fern tissue compared with light-grown tissue. More recently, Stewart et al (1992) have presented evidence that the levels of non-phyA phytochromes in green oat seedlings are also photoregulated. In their study, monoclonal antibodies, which recognize phytochromes found in light-grown oat tissue, were utilized to show an end-of-day red/far-red light dependency on the increase of these phytochrome species in green oat seedlings placed in darkness.…”

Photoresponses of Light-Grown phyA Mutants of Arabidopsis (Phytochrome A Is Required for the Perception of Daylength Extensions)

“…The levels of immunochemically detectable phytochrome A in light-grown Arabidopsis seedlings are at the limits of detection, so we did not detect any such oscillation in phytochrome A levels. Oscillations in the levels of an immunochemically detectable, low-abundance, type I1 phytochrome have been reported for oat seedlings grown in light/dark cycles, with the magnitude of phytochrome reaccumulation in the dark being increased by an E,OD FR treatment (Stewart et al, 1992).…”