Spectrophotometric phytochrome measurements in light-grown Avena sativa L.

Abstract

Phytochrome was studied spectrophotometrically in Avena sativa L. seedlings that had been grown for 6 d in continous white fluorescent light from lamps. Greening was prevented through the use of the herbicide San 9789. When placed in the light, phytochrome (Ptot) decreased with first order kinetics (τ1/2 ≈ 2 h) but reached a stable low level (≈2.5% of the dark level) after 36 h. This concentration of phytochrome remained constant in the light and during the initial hours of a subsequent dark period, but increased significantly after a prolonged dark period. Evidence suggests that the constant pool of phytochrome in the light is achieved through an equilibrium between synthesis of the red absorbing (Pr) and destruction of the far-red absorbing form (Pfr) of phytochrome. It is concluded that the phytochrome system in light-grown oat seedlings is qualitatively the same as that known from etiolated monocotyledonous seedlings, but different than that described for cauliflower florets.

Autoregulatory control of translatable phytochrome mRNA levels

“…The level of Pr remains essentially constant throughout this period, consistent with the slow turnover rate estimated for this form of the molecule (8). The steady-state level ofphytochrome established in continuous white light at 1-3% of that initially present in etiolated tissue (10,13) is also consistent with the notion that 0ks is constant and that 'k5's is 50-100 times greater than lkdr (8).…”

“…The 80 (1983) translatable mRNA. Why then are the new steady-state levels of the photoreceptor in continuous light observed to be as high as 1-3% of the initial, etiolated tissue concentration (10,13)? If the rate of destruction of the chromoprotein increases 50-to 100-fold and the rate of synthesis declines >20-fold upon Pfr formation, the level of phytochrome in continuous light should be more than an order of magnitude lower than observed.…”

“…Photoconversion of Pr to Pfr in vivo results in a rapid decline in phytochrome concentration because Pfr has a much greater rate of degradation than Pr (7,8,10,11). Three hours after the onset of irradiation the concentration of phytochrome is decreased by == 80% in Avena (11,12), eventually reaching a new steady state in continuous light at 1-3% of the initial etiolated-tissue concentration (10,13). Return of the tissue to the dark results in reaccumulation of the photoreceptor as Pr (8,14).…”

Phytochrome‐mediated responses in light‐grown corn showing rapid, reverse reciprocity failure*

“…To test this assumption, direct spectrophotometric phytochrome measurements on light-grown corn were made with plants grown in the presence of Norflurazon. The herbicide has no effect on the sensitivity of the phytochrome system of several plants, but the chlorophyll, which would normally make spectrophotometric phytochrome measurement impossible, is completely photobleached (Jabben & Deitzer, 1978, 1979. Fluenceresponse curves for all three responses to end-of-day FR in light-grown corn are unaltered by the herbicide (Gorton & Briggs, 1980a).…”

Phytochrome Responses to End-of-Day Irradiations in Light-grown Corn Grown in the Presence and Absence of Sandoz 9789

“…Screening by Chl prevents complete photoconversion of phytochrome and Chl fluorescence causes an apparent decrease in the signal size (10, I 1). Jabben and Deitzer (6,7) have developed a method to extend the spectral assay to light-grown plants through the use of the chlorosis-inducing herbicide San 9789. The herbicide blocks carotenoid synthesis (1, 2) so that Chl is not protected from photooxidation.…”