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L H Pratt

Publications and source records attributed to L H Pratt.

At least 55 records · Page 3Linked to original sources
PubMed1978

Phytochrome destruction: apparent inhibition by ethylene.

Phytochrome destruction begins immediately following actinic irradiation of 4-day-old, dark-grown oat (Avena sativa L., cv. Garry) shoots grown in open containers. When grown in closed containers, otherwise identical oat shoots exhibit a delay of about 40 minutes between irradiation and the onset of destruction. This delay can be attributed to accumulation of ethylene by several criteria, including elimination of the delay by mercuric perchlorate. These data provide an explanation for otherwise contradictory observations concerning the presence of a delay prior to the onset of destruction.

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PubMed1976

Red Light-enhanced Phytochrome Pelletability: Re-examination and Further Characterization.

Red light-enhanced pelletability of phytochrome was observed in extracts of all 11 plants tested: Avena sativa L., Secale cereale L., Zea mays L., Cucurbita pepo L., Sinapis alba L., Pisum sativum L., Helianthus anuus L., Raphanus sativus L., Glycine max (L.) Merr., Phaseolus vulgaris L., and Lupinus albus L. This enhanced pelletability was observed in all 11 plants following in situ irradiation (in vivo binding) but only in Sinapis and Cucurbita after irradiation of crude extracts (in vitro binding). In vivo binding was not strongly dependent upon pH and, with few exceptions, was not markedly sensitive to high salt concentration, whereas in vitro binding was completely reversed by both high pH and high salt concentration. However, both binding phenomena were observed only with a divalent cation in the extract buffer. In vivo binding was further characterized using Avena which showed an increase in pelletability from less than 10% in dark control extracts to more than 60% in extracts of red light-irradiated shoots. The half-life for binding was 40 seconds at 0.5 C and was strongly temperature-dependent, binding being complete within 5 to 10 sec at 22 C. If pelletable phytochrome in the far red-absorbing form was photoconverted back to the red-absorbing form in situ, phytochrome was released from the pelletable condition with a half-life of 25 minutes at 25 C and 100 minutes at both 13 C and 3 C. No cooperativity in red light-enhanced pelletability with respect to phytochrome-far red-absorbing form was observed.

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PubMed1975

Reversible redistribution of phytochrome within the cell upon conversion to its physiologically active form.

The intracellular localization of phytochrome was seen in dark-grown oat (Avena sativa L., cv. Garry) and rice (Oryza sativa L., cv. unknown) shoots after various light treatments using an indirect peroxidase-antiperoxidase antibody labeling method. Phytochrome is generally distributed throughout the cytoplasm in cells of tissue that had not been exposed to light prior to fixation. Within, at most, 8 min after the onset of saturating red irradiation, phytochrome, now present in the far-red-absorbing form, becomes associated with discrete regions of the cell. These regions do not appear to be nuclei, plastids, or mitochondria. After phototransformation back to the red-absorbing form originally present, phytochrome slowly resumes its general distribution. It is possible that this discrete localization of the far-red-absorbing form of phytochrome represents a physiologically significant binding with a receptor site in the cell.

Cytoplasm↗
PubMed1975

Phytochrome Characterization by Rabbit Antiserum against High Molecular Weight Phytochrome.

Both small and large sizes of phytochrome purified from Garry oat (Avena sativa L. ev. Garry) as well as large phytochrome purified from Newton oat (A. sativa L. cv. Newton), rye (Secale cereale L. cv. Balbo), barley (Hordeum vulgare L. cv. Harrison), and pea (Pisum sativum L. cv. Alaska) seedlings are characterized by a specific antiserum against large Garry oat phytochrome. A spur is observed by double diffusion assay against large and small Garry oat phytochrome indicating only partial identity. In micro-complement fixation assays, large Garry oat phytochrome yields greater activity than small Garry oat phytochrome. In addition, the peak of activity is shifted to a higher antigen concentration with small phytochrome. Phytochrome, red-absorbing form, and phytochrome, far redabsorbing form, are indistinguishable by both double diffusion and micro-complement fixation assay. The different grass phytochromes are antigenically identical by double diffusion assay. Immunoelectrophoretic analyses of oat and rye large phytochrome, after proteolysis, suggest that there are one or a few regions of the molecule especially susceptible to hydrolysis by a wide variety of endopeptidases.

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PubMed1975

Immunological and physical characterization of the products of phytochrome proteolysis.

The relationship between high molecular weight (large) and low molecular weight (small) forms of phytochrome has been shown earlier to be one of proteolysis. The products of such proteolysis are characterized here by chromatography through Bio-Gel P-200 using specific antiphytochrome sera as an assay system. Degradation of large oat (Avena sativa L. cv. Garry) phytochrome as phytochrome, red-absorbing form, phytochrome, far red-absorbing form, or under cycling conditions in crude preparations containing one or more proteases, always yields one fragment with the immunochemical, electrophoretic, spectroscopic, and size characteristics of small phytochrome. In addition, other fragments are detected which may account, in part, for the different molecular weight estimates reported by others for purified, photoreversible phytochrome. The small phytochrome produced by proteolysis with trypsin of a purified large phytochrome preparation is similar to that produced by the endogenously derived protease(s). A large (estimated molecular weight = 90,000), apparently nonphotoreversible peptide is also identified which is electrophoretically and immunochemically distinct from small phytochrome. Thus, it seems that small phytochrome may not represent more than approximately one-half of the native molecule.

Journal Article↗
PubMed1973

Comparative immunochemistry of phytochrome.

Partially purified high molecular weight preparations of phytochrome, estimated to be close to 440,000 molecular weight based upon chromatography through a calibrated Bio-Gel P-300 column, were obtained from Garry and Newton oats (Avena Sativa L., cv. Garry and cv. Newton), rye (Secale cereale L., cv. Balbo), barley (Horedum vulgare L., cv. Harrison), and pea (Pisum sativum L., cv. Alaska) by a sequence of three chromatographic steps: brushite, diethylaminoethyl cellulose, and Bio-Gel P-300. No significant differences were observed between these preparations during purification or subsequent handling. In addition, a low molecular weight form of phytochrome was purified from Garry oats. Two specific antisera against a low molecular weight form of phytochrome (60,000 molecular weight) obtained from etiolated Garry oat seedlings are characterized and used to compare the phytochrome preparations. Double diffusion assays indicated antigenic identity between all preparations except that pea phytochrome yielded a spur when compared to oat phytochrome. Micro complement fixation assays yielded complete identity between Garry and Newton oat phytochrome, reduced activity with rye and barley phytochrome, and a complete lack of activity with pea phytochrome at the serum dilutions assayed. Immunoelectrophoretic assays indicated that all high molecular weight phytochrome preparations were homogeneous by this criterion and that there were only slight differences between the preparations in electrophoretic mobility. Large and small forms of phytochrome isolated from Garry oats were found to be very similar antigens when tested with the anti-small phytochrome sera, although the small form was observed to electrophorese at a much slower rate than the large.

Journal Article↗
PubMed1973

Phytochrome destruction: an apparent requirement for protein synthesis in the induction of the destruction mechanism.

Examination of the phytochrome destruction reaction as a function of age in etiolated oat (Avena sativa L. cv. Garry) seedlings demonstrates that following illumination of 3-day-old shoots there is a lag, not observed in 4- or 5-day-old oats, prior to the onset of destruction. This light-mediated induction of the phytochrome destruction mechanism in 3-day-old shoots is inhibited by chloramphenicol, actinomycin D, and puromycin suggesting that protein synthesis is required. In 4-day-old shoots, actinomycin D and puromycin do not alter the kinetics of destruction while chloramphenicol partially inhibits the process. Thus, the inhibitors have a specific effect on the induction of the destruction mechanism but not its subsequent operation.

Journal Article↗
PubMed1971

Immunocytochemical localization of phytochrome.

An immunocytochemical assay, which localizes phytochrome in situ, indicates that this plant chromoprotein is associated with both nuclei and plastids, in addition to the cytoplasm. In an etiolated oat shoot, phytochrome is most abundant just behind the apex of the coleoptile, where it is associated with parenchyma cells; it is apparently absent at the extreme apx of the coleoptile. Further back from the tip, phytochrome is found in the epidermal cells of the coleoptile; it decreases in concentration toward the node, where it is again abundant. Phytochrome is also abundant in the extreme apical cells of young adventitious roots and in association with the procambium of the mesocotyl.

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