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W R Briggs

Publications and source records attributed to W R Briggs.

At least 109 records · Page 6Linked to original sources
PubMed1970

Some spectral properties of pea phytochrome in vivo and in vitro.

The transformation difference spectrum for phytochrome (Pr spectrum minus Pfr spectrum) in pea tissue is determined below 560 nanometers and compared with similar data on phytochrome in vitro The difference spectrum in vivo between phytochrome intermediates and Pfr is also shown for comparison with the data on phytochrome solutions. These comparisons show that the peaks in the spectra occurring in the blue wave lengths are shifted to shorter wave lengths and are much enhanced when phytochrome is extracted from the cell and placed in solution. The results indicate that the physicochemical state of phytochrome in the cell may be different from that of the extracted pigment.

Journal Article↗
PubMed1969

Long-lived Intermediates in Phytochrome Transformation I: In Vitro Studies.

Irradiation of phytochrome solutions with a high-intensity mixed red and far red light source causes measurable absorbancy increases at 543 nm. Evidence is presented that these absorbancy increases are caused by accumulation of intermediates on the P(R) to P(FR) pathway with relatively slow thermal decay constants. Kinetic analysis of the decay signals is consistent with the interpretation that the signals represent simultaneous independent and parallel decay of 2 species by first order kinetics to P(FR). If actinic light intensity is kept constant and exposure time changed, the relative amounts of the 2 components change, with proportionately more of the rapidly decaying species present following short exposure times. If the amount of the intermediates is decreased by decreasing actinic light intensity at constant exposure time, however, the relative amounts of the 2 remain constant. The Q(10) for intermediate decay following illumination is approximately 2.0, while that for complete phototransformation of the pigment in either direction is very close to 1.0. Incomplete transformation of P(R) to P(FR), caused by overlapping absorption of the 2 forms, is shown by the presence of intermediates (indicating cycling of the pigment) in continuous red light. Such intermediates do not appear in continuous far red, indicating a rate of pigment cycling below detection by the available instrumentation.

Journal Article↗
PubMed1969

Long-lived Intermediates in Phytochrome Transformation II: In Vitro and In Vivo Studies.

Conditions of illumination which cause phytochrome to cycle rapidly from P(R) to P(FR) and back lead to the accumulation in vivo of detectable amounts of long-lived intermediates on the P(R) to P(FR) pathway in oat coleoptile tissue. They appear to decay independently and in parallel to P(FR). Their behavior under different intensities of illumination and exposure time suggests that they are homologous with 2 similar intermediates previously observed in vitro. Available evidence favoring this suggestion is discussed. Equivalent illumination apparently causes far higher steady state levels of absorption by intermediates in vivo than in vitro, suggestion that native phytochrome is in a different physical state in the cell than it is in solution. A difference spectrum for the intermediates in vitro between 365 and 580 nm is presented. It has a maximum at 380 nm, a minimum at 418 nm, and crossover points at 398 and 485 nm. Glycerol in the phytochrome sample enhances the signal without otherwise changing the spectrum in any way. The difference spectrum represents the difference in absorption between the combined intermediates and P(FR).

Journal Article↗
PubMed1968

Effect of Low-intensity Red and Far-red Light and High-intensity White Light on the Flowering Response of the Long-day Plant Lemna gibba G3.

The long-day plant Lemna gibba L., strain G3 exhibits a relatively low sensitivity to short, white-light interruptions given during the dark period of a short-day cycle. However, the plants are fairly sensitive to low-intensity red light treatments given during a 15-hour dark period on the third day of a 2LD-(9L:15D)-2LD-7SD schedule. Far-red light is almost as effective as red light, and attempts to reverse the red light response with subsequent far-red light treatments have not been successful. Blue light proved to be without effect. When plants were grown on a 48-hour cycle with 15 minutes of red light every 4 hours during the dark period, the critical daylength was reduced from about 32 hours to slightly less than 12 hours.Continuous red light induced a fairly good flowering response. However, as little as 1 hour of white light each day gave a significant improvement in the flowering response over that of the continuous red light control. White light of 600 to 700 ft-c was more effective than white light of 60 to 70 ft-c. The white light was much more effective when divided into 2 equal exposures given 8 to 12 hours apart. These results suggest an increase in light sensitivity with regard to flower induction about 8 to 10 hours after the start of the light period.

Journal Article↗
PubMed1968

Some Properties of Phytochrome Isolated From Dark-grown Oat Seedlings (Avena sativa L.).

Phytochrome was partially purified from etiolated seedlings of Avena sativa L. Several properties of the red-absorbing (P(R)) and far-red absorbing (P(FR)) forms of the pigment were compared. The 2 forms could not be shown to differ with respect to their sedimentation velocity in sucrose density gradients, elution volume from Sephadex G-200 columns, binding properties on calcium phosphate, or electrophoretic mobility. P(FR), however, was more labile than P(R) during precipitation with 50% ammonium sulfate. Sephadex G-200 elution diagrams obtained with fresh phytochrome preparations revealed 2 components of different molecular weights, 1 roughly 180,000, and 1 roughly 80,000. Native phytochrome had an absorption spectrum in vivo showing an absorption maximum for P(R) of 667 nm. Both the large and small forms of phytochrome mentioned above can be maintained with an absorption maximum for P(R) of 667 nm. However, allowing them to remain for several hours as P(FR), even at 4 degrees , shifted this peak to 660 nm. The protein conformational change during phytochrome transformation may be quite small, though the various comparative techniques used do not strictly rule out a fairly large one. The need for maintaining the pigment as P(R) during all steps of purification, but particularly during ammonium sulfate precipitation is underscored.

Journal Article↗
PubMed1968

Kinetically distinguishable populations of phytochrome.

Two or more kinetically distinguishable populations of phytochrome molecules were observed in living tissues of oat, pea, maize, and cauliflower, as well as in extracts of oat. At least 3 different populations occurred in cauliflower florets, while 2 were observed in each of the other species. In extracted oat phytochrome, the relative proportions of the 2 forms remained constant during successive stages of purification. The physiological significance of this multiplicity of forms remains unclear.

Journal Article↗
PubMed1967

The effects of light on a circadian rhythm of conidiation in neurospora.

The expression of a circadian rhythm of conidiation by timex, a strain of Neurospora crassa, is inhibited by growth in continuous white light. The action spectrum for this effect has a strong peak (with minor subpeaks) in the blue region of the visible spectrum, and a broad shoulder in the near ultraviolet. This action spectrum suggests that a carotenoid or flavin compound may be the photoreceptor, but does not allow one to determine conclusively whether the receptor is indeed a carotenoid, flavin, or some other unrelated pigment. Two lines of evidence suggest that a carotenoid is not the photoreceptor. First, the in vivo absorption spectrum of timex (representing the sum of the spectra of the individual pigments present, predominantly carotenoids) has peaks at wavelengths 10 to 20 mmu longer than those of the action spectrum peaks. Second, an albino-timex has normal photosensitivity, a situation requiring that the photoreceptor, if carotenoid, be a quantitatively minor constituent of the total carotenoid complement.The magnitude and direction of phase-shift resulting from a standard dose of white light given at different times in the daily cycle of timex varies in the manner reported for other organisms. Additional phase-shift experiments have shown that there are no major transients in the attainment of a new equilibrium after a phase-shifting perturbation, and that 2 light reactions (rapidly and slowly saturating) may be involved in the phase-shift response.

Journal Article↗
PubMed1967

Flowering Responses of the Long-day Plant Lemna gibba G3.

Lemna gibba L., strain G3, exhibits a qualitative long-day flowering response with a critical daylength on a 24-hour cycle of about 10 hours. Evidence is presented that the onset of daughter frond formation in a given frond inhibits the activity of the flowering meristem. Consequently, flower induction can only occur in fronds smaller than about 0.05 to 0.07 mm long. Although a minimum of 1 long day seems to be sufficient to induce the formation of flower primordia, at least 6 long days are required to obtain mature flowers since long days are also required for the early stages of flower development. The critical night length on 24, 48 and 72-hour cycles is respectively 14, 16, and 18 to 22 hours. The close similarity between the critical night length for the different cycle lengths is explained in terms of an inhibitory effect of darkness both on flower initiation and flower development. A 10-hour dark period is more inhibitory to flowering on a 36-hour cycle than on 24, 48, 60 or 72-hour cycles. It is suggested that darkness inhibits flowering through the formation of a light-labile flower inhibitor which acts to inhibit the functioning of the flowering stimulus.

Journal Article↗
PubMed1966

Effect of red light on the phototropic sensitivity of corn coleoptiles.

The effect of red light in alteration of the phototropic sensitivity of corn coleoptiles (Zea mays L., cultivar Burpee Barbecue Hybrid) is investigated. Phototropic dosage-response curves for etiolated coleoptiles are compared with those for coleoptiles receiving 1 hour of continuous red light immediately prior to phototropic induction. In the former case, only curvature comparable to the first positive curvature of oat coleoptiles is obtained. There is no evidence for first negative curvature and only minimal second positive curvature. The reciprocity law proved valid for all curvatures obtained. With red light, the sensitivity of the first positive curvature was decreased over ten-fold and there was clear appearance of second positive curvature for which the reciprocity law was not valid. Once again there was no evidence for negative curvature. Time course studies indicated that within 1 hour of the beginning of red light treatment at 25 degrees , reactions leading to the decrease in phototropic sensitivity of the first positive component had gone to completion whether the red light was continuous or consisted of a single 1 second exposure followed by a 1 hour dark period. An action spectrum for the red-induced change in phototropic sensitivity showed a marked peak near 660 mmu with a small broad shoulder between 610 and 630 mmu, characteristic of phytochrome-mediated responses. The effect of red light could be fully reversed by low dosages of far-red light, but longer doses of far red were less effective. Large dosages of far-red light alone induced the same alteration in phototropic sensitivity as did red light.

Journal Article↗
PubMed1966

Photochemical and Nonphotochemical Reactions of Phytochrome in vivo.

The nonphotochemical reactions of phytochrome in the coleoptiles of dark-grown corn seedlings were studied at 3 temperatures: 14 degrees , 24 degrees , and 34 degrees . The data obtained show that the destruction of P(fr) is the only measurable reaction occurring; reversion of P(fr) to P(r) was not found. The Q(10)'s (2.7 and 3.5) and zero order kinetics found for the destruction reaction are consistent with the hypothesis that the reaction is enzyme-mediated.In vivo action spectra for phytochrome transformation in the coleoptiles of darkgrown corn seedlings were obtained which agree qualitatively with those obtained by other workers for phytochrome-mediated physiological responses and in vitro action spectra. In vivo conversion of phytochrome by blue light, as determined from spectrophotometric measurements of phytochrome itself, is reported. Action peaks for P(r) were found at 667 mmu and in the blue in the region of 400 mmu, with a broad shoulder from 590 mmu to 640 mmu. Action peaks for P(fr) were found at 725 mmu and in the blue in the region of 400 mmu with a minor peak at 670 mmu, and a broad shoulder from 590 mmu to 640 mmu. The ratio of the quantum efficiencies of P(r) at 667 mmu and P(fr) at 725 mmu (Phi(r667)/Phi(fr725)) was estimated to be 1.0.

Journal Article↗
PubMed1966

The physiological versus the spectrophotometric status of phytochrome in corn coleoptiles.

The influence of red light in altering the phototropic sensitivity of corn coleoptiles (Zea mays L., cultivar Burpee Barbecue Hybrid) is compared with the spectrophotometric status of the phytochrome they contain. The distribution of measurable phytochrome corresponds roughly with the distribution of sensitivity to red light for physiological change. Both phytochrome concentration and red light sensitivity are maximal in the coleoptile tips. Red light pretreatments which reduce total phytochrome by about 50%, however, do not alter subsequent red light sensitivity of the phototropic system. Dosages of red light sufficient to saturate the physiological system are two orders of magnitude too small to induce measurable phytochrome transformation. The log-dosage-response curves for physiological change and for phytochrome transformation do not have the same slopes. The time course for appearance, mainconcentration of the far-red-absorbing form of phytochrome over a broad range of tenance, and decay of the physiological response is independent of the measurable concentrations. The following hypothesis is proposed: the phytochrome mediating the alteration in phototropic sensitivity is only a small proportion of the total present. This small active fraction is physically and kinetically independent of the bulk measurable, and is packaged in some manner which facilitates its transformation in both directions.

Journal Article↗
PubMed1966

Circadian nature of a rhythm expressed by an invertaseless strain of Neurospora crassa.

A new strain of Neurospora crassa which exhibits a rhythm of conidiation when growing along an agar surface in a growth tube is described. The rhythm has been shown to be circadian for it meets the following criteria: A) the period under constant environmental conditions in the dark is about 24 hours (22.7 hours at 25 degrees ); B) the period is relatively temperature-independent (Q(10) is between 0.95 and 1.21 for temperature range of 18 to 35 degrees ); C) the rhythm persists in continuous darkness at constant temperature for a minimum of 14 days without damping out; and D) the phase of the rhythm can be shifted by a single brief exposure to light. The sensitivity of this strain to light has been demonstrated further by the entrainment of the rhythm to a period of 24.0 hours using a suitable light-dark regime, and by the inhibition by light of the appearance of a rhythm; i.e., continuous conidiation occurs when the strain is subjected to continuous light. The new strain is compared to 2 other strains of Neurospora which also express a rhythm, patch and clock.

Circadian Rhythm↗