Biomedical subjects

W R Briggs

Publications and source records attributed to W R Briggs.

At least 73 records · Page 4Linked to original sources

PubMed1984

Indole-3-acetic acid sensitization of phytochrome-controlled growth of coleoptile sections.

Addition of 6 muM indole-3-acetic acid (IAA) to incubation buffer increases the sensitivity of coleoptile sections cut from dark-grown Avena sativa L. cv. Lodi to red light by a factor of 10,000, relative to the response in the absence of added IAA, without changing the maximum amount of light-induced growth. From 0.03 to 4 muM IAA sections show at least a 100-fold increase in sensitivity to red light relative to the response in the absence of added IAA. In this IAA concentration range, the light-induced increase in elongation shows two phases of response to red-light fluence, which are separated by a plateau. The biphasic fluence-response curve is also characteristic of the red-light-induced stimulation of coleoptile growth in intact dark-grown seedlings. The effect of IAA on the sensitivity of the phytochrome-mediated growth response appears to be on some step in the transduction of the phytochrome signal, rather than on the growth response itself.

Journal Article↗

PubMed1984

Auxin concentration/growth relationship for Avena coleoptile sections from seedlings grown in complete darkness.

A biphasic auxin dose-response curve has been obtained for indole-acetic acid (IAA)-stimulated growth of subapical sections of coleoptiles from totally dark-grown oats (Avena sativa L. cv Lodi). The curve for growth at 6 h is composed of a log-linear phase and a modified bell-shaped phase separated by a plateau. The curve is log-linear from 0.003 to 0.4 micromolar IAA when sections are incubated in pH 5.9 buffer. The plateau of IAA concentration-neutral growth is seen from 0.4 to 4.0 micromolar IAA. Further increase in growth occurs from 4.0 to 10 micromolar IAA. Changing the pH of the buffer from 5.9 to 5.5 or 6.2 changes the shape of the curve, shifting the plateau to lower IAA concentration, or abolishing it, respectively. The synthetic auxin 2,4-dichlorophenoxyacetic acid also shows a biphasic dose-response curve, but the synthetic auxin 1-naphthalene acetic acid does not. The plateau is not affected by the auxin-transport inhibitor 2,3,5-triiodobenzoic acid. The plateau is eliminated by taking sections from coleoptiles grown under continuous dim red light. We advance a model to account for these results based on two modes of auxin uptake into the cell: carrier-mediated uptake and uptake via chemiosmotic diffusion.

Journal Article↗

PubMed1984

Photobiology of diagravitropic maize roots.

Light-induced modification of gravitropism in etiolated roots of Zea mays cv Bear x W38 is a low fluence response mediated by phytochrome. This cultivar has a threshold of 10(-6) mol m(-2) and becomes saturated with 10(-2) mol m(-2) of red light. The maximum light-mediated response of 32 degrees downward from horizontal occurs in roots 10 to 30 millimeters in length, 120 to 165 minutes after irradiation. Reciprocity is valid from 2 to at least 9,000 seconds and the response can be about 90% reversed by far red light. Photoreversibility is lost (;escape' occurs) about 20 minutes after red irradiation but appears to be regained 60 to 80 minutes later. A red light-induced (or synchronized) nutation in the apparent curvature rather than unusual escape characteristics may explain these results.

Journal Article↗

PubMed1983

Phytochrome-mediated cellular photomorphogenesis.

Red light-induced cell elongation and division in intact, etiolated oat (Avena sativa cv Lodi) seedlings have been assessed. The middle of coleoptile was especially responsive in the very low fluence range whereas the region immediately below the coleoptile tip and the two regions just above the coleoptilar node were more responsive than the entire organ in the low fluence range. These responses in the coleoptile are both the result of an increase in cell elongation. Coleoptile cell division is slightly inhibited in the very low and slightly stimulated by red light in the low fluence range.The one-sixth of the mesocotyl closest to the node is more suppressed in its growth than is any other region in the very low fluence range. However, the low fluence response involved the entire mesocotyl equally. In the apical one-sixth of the mesocotyl, a strong suppression of cell division and a weak suppression of cell elongation occurs. In the lower five regions of the mesocotyl, red light in both fluence ranges suppresses only cell elongation. Apparently, the difference between red light-induced oat growth stimulation and suppression primarily involves differences in the response of the cell elongation process.

Journal Article↗

PubMed1983

Rhythmic chloroplast migration in the green alga Ulva: dissection of movement mechanism by differential inhibitor effects.

The chloroplasts of the green alga, Ulva lactuca L., migrate rhythmically between the outer (periclinal) cell walls in the daytime ("face" position) and the anticlinal cell walls at night ("profile" position). Both NaN3 and colchicine inhibit chloroplast movement mainly in the direction from profile towards face position. Differential drug sensitivity is suggestive of different mechanisms for the two directions of chloroplast migration. UV light reverses the inhibition by colchicine, presumably through the formation of lumicolchicine, the non-tubulin-binding isomer of colchicine. This result is indicative of microtubule involvement. Interpretation of the effects of azide is complicated by changes in the biological clock (phase delay and lengthening of the period). Cytochalasin B has no effect on chloroplast movement when added alone, but when added with colchicine it prevents colchicine inhibition of movement. We hypothesize that chloroplast position is controlled by a balance between two opposing movement systems with differential drug sensitivity.

Azides↗

PubMed1982

Optical properties of etiolated plant tissues.

Etiolated tissues of several plants are multiple bundles of fiber optics capable of coherent transfer of light over at least 20 mm. The acceptance angles (the angles at which light can be intercepted and then internally reflected longitudinally) for mung beans, oats, and corn are 47 degrees , 59 degrees , and 52 degrees -54 degrees , respectively. The shapes of the curves that describe the acceptance angles are the same for various tissues of the same plant but differ between species. The pattern of light transmitted longitudinally through a tissue is dependent on the angle at which the light intercepts the side of the tissue and is strongly influenced by the tissue geometry. When 0.5 mm of the tip is irradiated, the amount of light traveling down the "shaded" side of the coleoptile is equal to or 2- to 3-fold greater than the amount traveling down the "lighted" side.

Journal Article↗

PubMed1982

Evidence from studies with acifluorfen for participation of a flavin-cytochrome complex in blue light photoreception for phototropism of oat coleoptiles.

The diphenyl ether acifluorfen enhances the blue light-induced absorbance change in Triton X100-solubilized crude membrane preparations from etiolated oat (Avena sativa L. cv. Lodi) coleoptiles. Enhancement of the spectral change is correlated with a change in rate of dark reoxidation of a b-type cytochrome. Similar, although smaller, enhancement was obtained with oxyfluorfen, nitrofen, and bifenox. Light-minus-dark difference spectra in the presence and absence of acifluorfen, and the dithionite-reduced-minus oxidized difference spectrum indicate that acifluorfen is acting specifically at a blue light-sensitive cytochrome-flavin complex. Sodium azide, a flavin inhibitor, decreases the light-induced absorbance change significantly, but does not affect the dark reoxidation of the cytochrome. Hence, it is acting on the light reaction, suggesting that the photoreceptor itself is a flavin. Acifluorfen sensitizes phototropism in dark-grown oat seedlings such that the first positive response occurs with blue light fluences as little as one-third of those required to elicit the same response in seedlings grown in the absence of the herbicide. Both this increase in sensitivity to light and the enhancement of the light-induced cytochrome reduction vary with the applied acifluorfen concentration in a similar manner. The herbicide is without effect either on elongation or on the geotropic response of dark-grown oat seedlings, indicating that acifluorfen is acting specifically close to, or at the photoreceptor end of, the stimulus-response chain. It seems likely that the flavin-cytochrome complex serves to transduce the light signal into curvature in phototropism in oats, with the flavin moiety itself serving as the photoreceptor.

Journal Article↗

PubMed1981

Phytochrome control of two low-irradiance responses in etiolated oat seedlings.

Light-induced coleoptile stimulation and mesocotyl suppression in etiolated Avena sativa (cv. Lodi) has been quantitated. Etiolated seedlings showed the greatest response to light when they were illuminated 48 to 56 hours after imbibition. Two low-irradiance photoresponses for each tissue have been described. Red light was 10 times more effective than green and 1,000 times more effective than far red light in evoking these responses. The first response, which resulted in a 45% mesocotyl suppression and 30% coleoptile stimulation, had a threshold at 10(-14) einsteins per square centimeter and was saturated at 3.0 x 10(-12) einsteins per square centimeter of red light. This very low-irradiance response could be induced by red, green, or far red light and was not photoreversible. Reciprocity failed if the duration of the red illumination exceeded 10 minutes. The low-irradiance response which resulted in 80% mesocotyl suppression and 60% coleoptile stimulation, had a threshold at 10(-10) einsteins per square centimeter and was saturated at 3.0 x 10(-8) einsteins per square centimeter of red light. A complete low-irradiance response could be induced by either red or green light but not by far red light. This response could be reversed by a far red dose 30 times greater than that of the initial red dose for both coleoptiles and mesocotyls. Reciprocity failed if the duration of the red illumination exceeded 170 minutes. Both of these responses can be explained by the action of phytochrome.

Journal Article↗

PubMed1981

Partial purification and characterization of a blue light-sensitive cytochrome-flavin complex from corn membranes.

A membrane fraction which contains a blue light-sensitive flavin-cytochrome complex (Brain et al. 1977 Plant Physiol 59:948) has been partially purified by sucrose and Renografin gradient centrifugations. Assays for marker enzymes show that this membrane fraction is distinct from endoplasmic reticulum, golgi, and mitochondria. This membrane fraction co-sedimented with glucan synthetase II activity, a proposed marker for plasma membrane in higher plants. The purified membrane fraction shows virtually identical light minus dark and dithionite reduced minus oxidized difference spectra with difference bands near 427 and 557 nanometers, suggesting that contamination by other cytochrome-containing membrane fractions is not significant. The photoactivity can be completely solubilized by 0.1% Triton X-100, leaving the bulk of the membrane undissolved. The kinetics for cytochrome photoreduction are not significantly affected by solubilization, indicating that both flavin and cytochrome could be associated with the same protein moiety.

Journal Article↗

PubMed1980

Phytochrome Pelletability Induced by Irradiation in Vivo: MIXING EXPERIMENTS.

Samples of irradiated and control Avena sativa shoot tissue were homogenized together to determine whether, during homogenization phytochrome from irradiated tissue can bind to the particulate material simultaneously extracted from the control tissue. The level of phytochrome pelletability for such mixed tissue homogenizations is equal to: (a) the values obtained when the extracts from separate homogenizations of the two batches of tissue are mixed and then centrifuged; and (b) the arithmetic mean of the values obtained when the two batches of tissue are separately homogenized and separately tested for pelletability. This relationship is observed regardless of the ratio of control to irradiated tissue over the range from 4:6 to 9:1. These data indicate that the observed limit to the level of pelletability inducible in irradiated tissue (about 60%) does not result from a limited number of nonspecific particulate binding sites to which in vivo-modified phytochrome molecules have access at, or after, the moment of cell disruption. The possibility that pelletability may represent preservation of an association established in vivo is discussed.

Journal Article↗

PubMed1980

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

Corn seedlings were grown in white light in the absence and presence of the chlorosis-inducing herbicide San 9789. The resulting green and achlorophyllous seedlings were used to investigate phytochrome-mediated responses to end-of-day far red irradiation and reversal of these responses by subsequent red irradiation. Mesocotyl and coleoptile elongation increased in response to end-of-day far red irradiation, whereas the anthocyanin content of the coleoptiles was decreased. All three responses were reversible by red irradiation following the far red. Dose-response curves for far red induction and red reversal of these responses did not differ significantly for plants grown in the presence or absence of San 9789. Thus, San 9789 appears to affect neither phytochrome itself nor the response system involved. Chlorophyll screening likewise does not affect phytochrome relationships for these responses.

Journal Article↗

PubMed1979

Red Light-inhibited Mesocotyl Elongation in Maize Seedlings: II. Kinetic and Spectral Studies.

Red light induces two distinct inhibition responses in mesocotyls of etiolated corn seedlings. A light dose of 10 nanoeinsteins per square centimeter is saturating for the more sensitive response, whereas doses above 1,000 nanoeinsteins per square centimeter are required to exceed the threshold sensitivity of the less sensitive one. The sensitive response can be detected within 20 minutes of the onset of illumination whereas the other response does not become apparent until more than 4 hours after the beginning of irradiation. The reciprocity law is valid for the first response, but probably not for the second. An action spectrum for the first response shows two maxima, one at 640 nanometers and the other between 660 and 670 nanometers, with a pronounced minimum near 650 nanometers. The effects both of 640 and 665 nanometers of light were reversible by far red light, but doses of far red required for full reversibility were almost three orders of magnitude greater than the doses of red required either to saturate the initial inhibition or to reverse the effect of far red light. The results suggest that corn may contain a red-absorbing pigment other than phytochrome which in some way interacts with phytochrome in the inhibition of mesocotyl elongation by red light.

Journal Article↗

PubMed1978

Application of higher derivative techniques to analysis of high-resolution thermal denaturation profiles of reassociated repetitive DNA.

We have analyzed high-resolution denaturation profiles of reassociated repetitive DNA sequences by using a combination of higher derivative analysis and curve-fitting techniques. Procedures originally used for resolution of components in complex absorption spectra were found to be applicable to high-resolution analysis of melting profiles of reassociated repetitive DNA sequences from pea DNA. Under conditions that eliminate the base composition effect on thermal stability (2.4 M tetraethylammonium chloride), such an anlysis can distinquish "thermal classes" of repetitive DNA duplexes exhibiting different amounts of base pair mismatch. Only a single thermal class is observed in reassociated Escherichia coli DNA whereas at least five classes can be reproducibly distinguished in pea and mung bean DNAs.

Base Sequence↗

PubMed1978

Red Light-inhibited Mesocotyl Elongation in Maize Seedlings: I. The Auxin Hypothesis.

Red light-inhibited mesocotyl elongation, which occurs in intact Zea mays L. seedlings, was studied in excised segments which included the coleoptile (or parts therefrom) and apical centimeter of the mesocotyl. Experiments took into account, first, the ability of the segments to regenerate auxin supply sites, and, second, that auxin uptake can be greatly reduced if there is no cut surface, apical to the elongating cells, to act as a port of entry. In all cases, auxin completely reversed the inhibition of elongation by light. The results support the hypothesis that light regulates mesocotyl elongation by controlling auxin supply from the coleoptile. Sucrose concentration had no effect on auxin reversal of light-inhibited elongation, but relatively high concentrations of gibberellic acid (10 mum) could substitute for auxin in this system.

Journal Article↗

PubMed1978

Auxin receptors of maize coleoptile membranes do not have ATPase activity.

Membrane-localized auxin-binding sites from coleoptiles and primary leaves of Zea mays L. which may be auxin receptors can be fully solubilized by 1 to 1.5 mg of Triton X-100 per mg of membrane protein (about 1 mg per gram of original tissue fresh weight), while 70% of the basal (Mg(2+))-ATPase and 85% of the K(+)-stimulated (Mg(2+))-ATPase (pH 6) remain pelletable. Gel exclusion chromatography on Bio-Gel A-1.5m indicates that the solubilized receptors occur as detergent-protein micelles of about 90,000 daltons equivalent molecular weight. Solubilized ATPase activities occur (a) as very large particles excluded from the gel, and (b) as particles of a size substantially smaller than the particles that exhibit auxin binding. The auxin-binding receptor therefore appears not to be an ATPase.

Journal Article↗

PubMed1978

Properties of a Solubilized Microsomal Auxin-binding Protein from Coleoptiles and Primary Leaves of Zea mays.

An auxin-binding protein can be solubilized from microsomal membranes of Zea mays using either Triton X-100 extraction of the membranes or buffer extraction of the acetone-precipitated membranes. This paper describes the properties of the binding protein solubilized by these two methods. The binding is assayed by gel filtration chromatography in the presence of naphthalene [2-(14)C]acetic acid. Binding is rapid and reversible with an optimum at pH 5. Both preparations show similar molecular weights by gel filtration (80,000 daltons) at pH 7.6 and 0.1 molar NaCl, and both aggregate at low ionic strength. They appear to be the same active molecular species. The binding activity is destroyed by trypsin, pronase or para-chloromercuribenzoic acid, but not significantly reduced by phospholipase C, DNase, RNase, or dithioerythritol. Since saturating amounts of naphthalene acetic acid protect the molecule from inhibition by para-chloromercuribenzoic acid, it is concluded that the binding protein has a sulfhydryl group at the binding site, or protects such a group in its binding conformation. The dissociation constant of the protein for naphthalene acetic acid is 4.6 x 10(-8) molar with 30 picomoles of sites per gram of tissue fresh weight. Binding constants were estimated for 13 other natural and synthetic auxins by competition with naphthalene[2-(14)C]acetic acid. Their dissociation constants are in general agreement with published values for their binding to intact membranes and their biological activity, although several exceptions were noted. A supernatant factor from the same tissue changes the apparent affinity of the protein for naphthalene acetic acid. This factor may be the same one as has been previously reported to alter the affinity of intact microsomes for auxin.

Journal Article↗

PubMed1978

Irradiation-enhanced Phytochrome Pelletability: Requirement for Phosphorylative Energy in Vivo.

Short, high intensity pulses of red and far red light are used to study, at room temperature, the kinetics of the in vivo dark reaction responsible for irradiation-enhanced phytochrome pelletability. The t((1/2)) for this reaction is 2 seconds at 25 C in both Avena shoots and Zea mays coleoptiles. This is the most rapid phytochrome-far red-absorbing form (Pfr)-mediated cellular response thus far reported. Anoxia, KCN, NaN(3) and carbonyl cyanide p-trifluoromethoxyphenylhydrazone reduce the rate (but not the final extent) of the reaction by more than an order of magnitude. The rate of the reaction under these conditions is strongly correlated with the inhibitor-induced reductions in cellular ATP levels. Likewise, recovery in ATP levels upon withdrawal of the inhibitors is accompanied by a parallel recovery in the rate of the reaction. Cytochalasin B blocks cytoplasmic streaming without diminishing the pelletability response. Colchicine is likewise without effect. These data suggest a requirement for phosphorylative energy in one or more of the Pfr-dependent intracellular events leading to enhanced phytochrome pelletability. The possibility that this event might represent an ATP-dependent modification of the pigment protein itself in the Pfr form is discussed.

Journal Article↗

PubMed1977

Labeling of membranes from erythrocytes and corn with fluorescamine.

Fluorescamine was used as a fluorescent label for intact human erythrocytes and slices of corn coleoptile tissue. This reagent has a greater affinity for membranous than for soluble proteins, and also labels membrane lipids which contain primary amine groups. In addition, some membrane fractions from labeled coleoptiles have a higher affinity for fluorescamine than do others. The relative labeling of the various fractions can be altered by changing the pH of the external labeling medium. Because the pH of the medium determines the rate of hydrolysis of fluorescamine to an unreactive form, this result suggests that the specificity of this reagent towards different cellular structures is determined by the lifetime of the active reagent. Fluorescamine was not found to be a specific reagent for the cell surface.

Cell Fractionation↗