Phytochrome: First-order phototransformation kinetics in vivo

The deviation from first order commonly observed in phototransformation kinetics of phytochrome in vivo is due to a light-intensity gradient within the sample. This gradient was measured and was found to approach that predicted by the Kubelka-Munk theory of light scatter in turbid materials. The influence of this gradient is eliminated and first-order phototransformation kinetics are obtained, when either (i) thin samples of translucent (low optical density) material of high phytochrome content are measured directly; or (ii) thin samples of opaque (high optical density) or translucent material are sandwiched between two layers of light-scattering material. This result is consistent with the existence of only one population of photoreversible phytochrome molecules in vivo.

Turnover of phytochrome in pumpkin cotyledons

By using density labeling, it was found that the protein moiety of phytochrome is synthesized de novo in the red-absorbing form in cotyledons of dark-grown pumpkin (Cucurbita pepo L.) seedlings, as well as those irradiated with red light and returned to the dark. The rate of synthesis appears to be unaffected by the light treatment. Turnover of the red-absorbing form was also detected in dark grown seedlings using density labeling, while turnover of the far red-absorbing form is already implied from the well known "destruction" observed in irradiated seedlings. In both cases, true degradation of the protein is involved, but the rate constant of degradation of the far red-absorbing form may be up to two orders of magnitude greater than that of the red-absorbing form. The data indicate that, in pumpkin cotyledons, phytochrome levels are regulated against a background of continuous synthesis through divergent rate constants of degradation of the red and far red-absorbing forms and the relative proportions of the two forms present.

De novo synthesis of phytochrome in pumpkin hooks

Phytochrome becomes density labeled in the hook of pumpkin (Cucurbita pepo L.) seedlings grown in the dark on D(2)O, indicating that the protein moiety of the pigment is synthesized de novo during development. Red light causes a rapid decline of the total phytochrome level in the hook of etiolated seedlings but upon return to the dark, phytochrome again accumulates. These newly appearing molecules are also synthesized de novo. Newly synthesized phytochrome in both dark-grown and red-irradiated seedlings is in the red-absorbing form. Turnover of the red-absorbing form is indicated by the density labeling of phytochrome during a period when the total phytochrome level in the hook of dark-grown seedlings remains constant. However, it was not possible to determine whether this results from intracellular turnover or turnover of the whole cell population during hook growth.

A Study on the Immunoglobulin Class of the Anti-A1 Isoagglutinin

It is shown by DEAE-cellulose chromatography, gel filtration on Sephadex G-200 and by density gradient ultracentrifugation that there are IgG isoantibodies in O sera, which can differentiate between A1 and A2 red cells quite well. From this it is concluded that the difference between A1 and A2 red cells must be qualitative.

A detailed analysis of phytochrome decay and dark reversion in mustard cotyledons

During the first 10 min after a saturating dose of red light, 72 h dark-grown mustard cotyledons show no phytochrome decay. Within the same time interval there exists a transient form of P fr (=P fr (T) ) which is no longer photoconvertible at 0°C, but is at 25°C. This P fr (T) converts in the dark to P fr and P r . These "dark reversions" take about 10 min. After a lag phase of 10 min the P fr decay can be described by a single, first order kinetic curve. The time courses of these reactions are functions of the time of etiolation.

The demonstrationin vivo of more than one form ofP fr

Phototransformation studies of pumpkin phytochromein vivo indicate two populations, a slow and a fast one. The ratio between the two populations can be altered by different light-dark-pretreatments. The destruction kinetics ofP fr also show a deviation from a first order curve which indicates the existence of two populations ofP fr with respect to decay. No significantP fr →P r dark reversion could be detected. Two models are discussed, which could explain the shape of the destruction kinetics observed and the different ratios of the two populations obtained from phototransformation measurements.

On the phytochrome phototransformation kinetics in mustard seedlings

The in vivo phototransformation kinetics of mustard hook and cotyledon phytochrome exhibit a deviation from a single first order curve, quite similar to that for pumpkin hooks as reported in a previous paper (Boisard, Marmé and Schäfer, 1971). The P fr→Prkinetics can be characterized by the ratios ɛ fr,λ (I) · P fr (I) /ɛ fr,λ (II) · P fr,λ (II) and [Formula: see text] where P fr (I) and P fr (II) are two populations of phytochrome molecules which convert to P rwith a first order half-life of [Formula: see text] and [Formula: see text]. These ratios depend on the length of time of etiolation. The ratio ɛ fr,λ (I) · P fr (I) /ɛ fr,λ (II) · P fr,λ (II) is independent of the amount of total P frpresent at the beginning of the P fr→Prphototransformation after a non-saturating dose of red light. The half-lives of the two populations, however, depend on the concentration of total P frinitially present. P fr→Prphototransformation kinetics with different light intensities show that reciprocity holds.