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1Latest Papers from Table of Contents or Articles in PressL. A. Rocha ; A. Aleixo ; G. Allen ; F. Almeda ; C. C. Baldwin ; M. V. Barclay ; J. M. Bates ; A. M. Bauer ; F. Benzoni ; C. M. Berns ; M. L. Berumen ; D. C. Blackburn ; S. Blum ; F. Bolanos ; R. C. Bowie ; R. Britz ; R. M. Brown ; C. D. Cadena ; K. Carpenter ; L. M. Ceriaco ; P. Chakrabarty ; G. Chaves ; J. H. Choat ; K. D. Clements ; B. B. Collette ; A. Collins ; J. Coyne ; J. Cracraft ; T. Daniel ; M. R. de Carvalho ; K. de Queiroz ; F. Di Dario ; R. Drewes ; J. P. Dumbacher ; A. Engilis, Jr. ; M. V. Erdmann ; W. Eschmeyer ; C. R. Feldman ; B. L. Fisher ; J. Fjeldsa ; P. W. Fritsch ; J. Fuchs ; A. Getahun ; A. Gill ; M. Gomon ; T. Gosliner ; G. R. Graves ; C. E. Griswold ; R. Guralnick ; K. Hartel ; K. M. Helgen ; H. Ho ; D. T. Iskandar ; T. Iwamoto ; Z. Jaafar ; H. F. James ; D. Johnson ; D. Kavanaugh ; N. Knowlton ; E. Lacey ; H. K. Larson ; P. Last ; J. M. Leis ; H. Lessios ; J. Liebherr ; M. Lowman ; D. L. Mahler ; V. Mamonekene ; K. Matsuura ; G. C. Mayer ; H. Mays, Jr. ; J. McCosker ; R. W. McDiarmid ; J. McGuire ; M. J. Miller ; R. Mooi ; R. D. Mooi ; C. Moritz ; P. Myers ; M. W. Nachman ; R. A. Nussbaum ; D. O. Foighil ; L. R. Parenti ; J. F. Parham ; E. Paul ; G. Paulay ; J. Perez-Eman ; A. Perez-Matus ; S. Poe ; J. Pogonoski ; D. L. Rabosky ; J. E. Randall ; J. D. Reimer ; D. R. Robertson ; M. O. Rodel ; M. T. Rodrigues ; P. Roopnarine ; L. Ruber ; M. J. Ryan ; F. Sheldon ; G. Shinohara ; A. Short ; W. B. Simison ; W. F. Smith-Vaniz ; V. G. Springer ; M. Stiassny ; J. G. Tello ; C. W. Thompson ; T. Trnski ; P. Tucker ; T. Valqui ; M. Vecchione ; E. Verheyen ; P. C. Wainwright ; T. A. Wheeler ; W. T. White ; K. Will ; J. T. Williams ; G. Williams ; E. O. Wilson ; K. Winker ; R. Winterbottom ; C. C. Witt
American Association for the Advancement of Science (AAAS)
Published 2014Staff ViewPublication Date: 2014-05-24Publisher: American Association for the Advancement of Science (AAAS)Print ISSN: 0036-8075Electronic ISSN: 1095-9203Topics: BiologyChemistry and PharmacologyComputer ScienceMedicineNatural Sciences in GeneralPhysicsKeywords: Animals ; Biology/*methods ; Classification/*methods ; *Endangered Species ; *Extinction, BiologicalPublished by: -
2Latest Papers from Table of Contents or Articles in PressS. Simmons ; R. M. Brown ; H. Riemann ; N. V. Abrosimov ; P. Becker ; H. J. Pohl ; M. L. Thewalt ; K. M. Itoh ; J. J. Morton
Nature Publishing Group (NPG)
Published 2011Staff ViewPublication Date: 2011-01-21Publisher: Nature Publishing Group (NPG)Print ISSN: 0028-0836Electronic ISSN: 1476-4687Topics: BiologyChemistry and PharmacologyMedicineNatural Sciences in GeneralPhysicsPublished by: -
3Latest Papers from Table of Contents or Articles in PressM. Kaur, L. J. Barbano, E. M. Suen-Lewis, J. E. Shrock, A. D. Light, M. R. Brown, and D. A. Schaffner
American Physical Society (APS)
Published 2018Staff ViewPublication Date: 2018-01-11Publisher: American Physical Society (APS)Print ISSN: 1539-3755Electronic ISSN: 1550-2376Topics: PhysicsKeywords: Plasma PhysicsPublished by: -
4Articles: DFG German National LicensesWhite, K. D. ; Ashton, R. ; Brown, R. M. D.
London, etc. : Periodicals Archive Online (PAO)
Published 1977Staff ViewISSN: 0007-1269Topics: PsychologyURL: -
5Articles: DFG German National LicensesBROWN, G. K. ; BROWN, R. M. ; SCHOLEM, R. D. ; KIRBY, D. M. ; DAHL, H-H. M.
Oxford, UK : Blackwell Publishing Ltd
Published 1989Staff ViewISSN: 1749-6632Source: Blackwell Publishing Journal Backfiles 1879-2005Topics: Natural Sciences in GeneralType of Medium: Electronic ResourceURL: -
6Articles: DFG German National LicensesBiagi, S. F. ; Bourquin, M. ; Britten, A. J. ; Brown, R. M. ; Burckhart, H. J. ; Carter, A. A. ; Doré, Ch. ; Extermann, P. ; Gailloud, M. ; Gee, C. N. P. ; Gibson, W. M. ; Gordon, J. C. ; Gray, R. J. ; Igo-Kemenes, P. ; Jacot-Guillarmod, P. ; Louis, W. C. ; Modis, T. ; Rosselet, Ph. ; Saunders, B. J. ; Schirato, P. ; Siebert, H. W. ; Smith, V. J. ; Streit, K. -P. ; Thresher, J. J. ; Tovey, S. N.
Springer
Published 1985Staff ViewISSN: 1434-6052Source: Springer Online Journal Archives 1860-2000Topics: PhysicsNotes: Abstract Results are presented from experiment WA62, which searched for charmed strange baryon states produced inΣ − interactions in the SPS charged hyperon beam at CERN. Properties of theA + (csu) baryon at 2.46 GeV/c2 are summarized and upper limits are given for decay branching ratios into various channels. Three events observed at 2.74 GeV/c2 in theΞ − K − π + π + mass spectrum are interpreted as the first evidence for theT 0 baryon with quark content css. Results of a search for theA 0 (csd), the isospin partner of theA +, are presented. The results are discussed in the context of current theoretical understanding, and a comparison with other experiments on hadroproduction of charmed baryons is made.Type of Medium: Electronic ResourceURL: -
7Articles: DFG German National LicensesStaff View
ISSN: 1572-882XKeywords: β-Glycosyltransferases ; Acetobacter xylinum ; cellulosesynthase ; higher plantsSource: Springer Online Journal Archives 1860-2000Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, NutritionProcess Engineering, Biotechnology, Nutrition TechnologyNotes: Abstract More than ten β-glycosyltransferases are now recognized that have limited similarity to the amino acid sequence of cellulose synthase from Acetobacter xylinum. Using hydrophobic cluster analysis (HCA), we recently identified two domains and putative catalytic residues in the processive β-glycosyltransferases. In this study, we have found expressed sequence tags (ESTs) from higher plants (Arabidopsis thaliana, Brassica campestris, and Oryza sativa) that exhibit a limited sequence similarity to the A. xylinum cellulose synthase. These ESTs contain some of the conserved residues identified in the processive β-glycosyltransferases. Complete sequencing of an EST clone (T88271) from A. thaliana led to the identification of all the conserved residues in the derived truncated polypeptide which appears to be part of a putative cellulose synthase. Sequence comparison of proteins with known function and several unidentified proteins have the ‘D, D, D35Q(R,Q)XRW’ motif which is considered a strong predictor for β-glycosyltransferasesthat includes, among other proteins, cellulose and chitin synthases. The first two conserved aspartic acid residues in this motif were analysed by site-directed mutagenesis, and their replacement by another amino acid led to a loss of cellulose synthase activity in A. xylinum, suggesting that they are essential for enzyme activity. A correlation between the second residue (R or Q) in the Q(R,Q)XRW sequence and the synthesis of along glucan chain (polysaccharide) or a short glucan chain(oligosaccharide) suggests that this residue may be involved in the degree of processivityType of Medium: Electronic ResourceURL: -
8Articles: DFG German National LicensesBourquin, M. ; Brown, R. M. ; Chatelus, Y. ; Chollet, J. C. ; Degré, A. ; Froidevaux, D. ; Fyfe, A. R. ; Gaillard, J. -M. ; Gee, C. N. P. ; Gibson, W. M. ; Gray, R. J. ; Igo-Kemenes, P. ; Jeffreys, P. W. ; Merkel, B. ; Morand, R. ; Ott, R. J. ; Plothow, H. ; Repellin, J. -P. ; Saunders, B. J. ; Sauvage, G. ; Schiby, B. ; Siebert, H. W. ; Smith, V. J. ; Streit, K. -P. ; Strub, R.
Springer
Published 1982Staff ViewISSN: 1434-6052Source: Springer Online Journal Archives 1860-2000Topics: PhysicsNotes: Abstract The charged hyperon beam at the CERN Super Proton Synchrotron (SPS) has been used to collect data on semileptonic decays ofΣ −,Ξ − andΛ. A magnetic channel selects 100 GeV/c negatively charged particles produced in the forward direction by interaction of the 200 GeV/c SPS proton beam on a BeO target. TheΣ − andΞ − hyperons are concurrently identified in a DISC Čerenkov counter, and their decay products are analysed by a magnetic spectrometer. Electron-hadron discrimination is achieved by the combined use of lead-glass and lead/scintillator counters, transition radiation detectors, and a Čerenkov counter. In this article we report results on the $$\Sigma ^ - \to \Lambda e^ - \bar v$$ decay mode. Measurements of the Λ polarization and of the centre-of-mass distributions (baryon kinetic energy, electron-neutrino correlation, and Dalitz plot distributions) yield the vector to axialvector form factor ratiof 1/g 1=+0.034±0.080, in agreement with the value expected from the conserved vector current hypothesis (f 1/g 1=0). TheΣ −→Λe − v→ branching ratio measurement gives a value of (5.41±0.30)×10−5. The effects of radiative corrections are not included in these results. They are discussed in the text. Results on the otherΞ −,Σ −, andΛ semileptonic decays are reported in separate articles.Type of Medium: Electronic ResourceURL: -
9Articles: DFG German National LicensesBourquin, M. ; Brown, R. M. ; Chatelus, Y. ; Chollet, J. C. ; Degré, A. ; Froidevaux, D. ; Fyfe, A. R. ; Gaillard, J. -M. ; Gee, C. N. P. ; Gibson, W. M. ; Gray, R. J. ; Igo-Kemenes, P. ; Jeffreys, P. W. ; Merkel, B. ; Morand, R. ; Ott, R. J. ; Plothow, H. ; Repellin, J. -P. ; Saunders, B. J. ; Sauvage, G. ; Schiby, B. ; Siebert, H. W. ; Smith, V. J. ; Streit, K. -P. ; Strub, R.
Springer
Published 1983Staff ViewISSN: 1434-6052Source: Springer Online Journal Archives 1860-2000Topics: PhysicsNotes: Abstract Results on five different hyperon semileptonic decays from the WA2 experiment, performed in the CERN SPS charged hyperon beam, have been analysed within the framework of the Cabibbo model. For the first time, the inconsistencies, which inevitably occur when the results from different experiments are combined, have been avoided in these comprehensive fits to high statistics data from a single hyperon decay experiment. Excellent agreement with the basic Cabibbo model has been obtained using the WA2 data either alone or together with neutron lifetime measurements. These results contrast strongly with other recent Cabibbo analyses which have indicated the presence ofSU(3) breaking effects. Including radiative corrections we have obtained the results,F=0.477±0.012,D=0.756±0.011 and sinθ c =0.231±0.003. The ratio (D/D+F) is 0.613±0.009, which is close to theSU(6) prediction of 3/5. Using additional information onft values for superallowed nuclear Fermi transitions, an upper limit on the mixing parameter sinθ3 in the Kobayashi-Maskawa six quark scheme has been obtained: |sinθ3|〈0.20.Type of Medium: Electronic ResourceURL: -
10Articles: DFG German National LicensesBiagi, S. F. ; Bourquin, M. ; Brown, R. M. ; Burckhart, H. J. ; Extermann, P. ; Gailloud, M. ; Gee, C. N. P. ; Gibson, W. M. ; Jacot-Guillarmod, P. ; Perrier, J. ; Ragan, K. J. ; Rosselet, Ph. ; Schirato, P. ; Siebert, H. W. ; Smith, V. J. ; Streit, K. P. ; Thresher, J. J. ; Wood, A. T. ; Yanagisawa, C.
Springer
Published 1987Staff ViewISSN: 1434-6052Source: Springer Online Journal Archives 1860-2000Topics: PhysicsNotes: Abstract In an experiment at the CERN-SPS charged hyperon beam, we have investigated the inclusive $$\Lambda \bar K^0 $$ and $$\Sigma ^0 \bar K^0 $$ final states formed in Ξ− Be interactions. In the $$\Lambda \bar K^0 $$ channel, we observe a signal at 1826 MeV/c2 which can be identified with the known Ξ(1820) resonance. We determine its mass and width to be:M=1826±4 MeV/c2, Г=12±14 MeV/c2. A moment analysis is consistent with a spin of 3/2 and indicates a negative parity for this spin assignment. Also in the $$\Lambda \bar K^0 $$ channel, we observe a 3.6σ signal with the following parameters:M=1963±5 MeV/c2, Г=25±15 MeV/c2. This state, which we call Ξ(1960), is not observed in the $$\Sigma ^0 \bar K^0 $$ channel, leading to an upper limit on the ratio of partial widths $$\Sigma \bar K/\Lambda \bar K$$ of 2.3 (90% confidence level). A moment analysis of the $$\Lambda \bar K^0 $$ final state indicates a spin of 5/2 or greater in the natural spin-parity series 5/2+, 7/2−, etc.Type of Medium: Electronic ResourceURL: -
11Articles: DFG German National LicensesBiagi, S. F. ; Bourquin, M. ; Brown, R. M. ; Burckhart, H. J. ; Extermann, P. ; Gailloud, M. ; Gee, C. N. P. ; Gibson, W. M. ; Jacot-Guillarmod, P. ; Modis, Th. ; Perrier, J. ; Ragan, K. J. ; Rosselet, Ph. ; Schirato, P. ; Siebert, H. W. ; Smith, V. J. ; Streit, K. -P. ; Thresher, J. J. ; Wood, A. T. ; Yanagisawa, C.
Springer
Published 1987Staff ViewISSN: 1434-6052Source: Springer Online Journal Archives 1860-2000Topics: PhysicsNotes: Abstract The cross sections for Ξ− and Ω− inclusive production in Ξ− Be collisions at 116 GeV/c have been measured in the kinematic domain [0.1〈x F 〈0.9, 0〈p T 〈1.7 GeV/c]. The integrated cross sections per nucleon are found to be about twice as large as in Ξ− p collisions. The invariant cross sections increase by a factor of 70 for the Ξ− s and of 100 for the Ω− s between the central region (x F ∼0.2) and the projectile fragmentation region (x F ∼0.8). In the central region, they have about the same magnitude as the ones for Ξ− and Ω− inclusive production inp nucleon collisions. The Ξ− and Ω− polarisations have been measured over the same kinematic domain and are found to be compatible with zero.Type of Medium: Electronic ResourceURL: -
12Articles: DFG German National LicensesStaff View
ISSN: 1435-1463Source: Springer Online Journal Archives 1860-2000Topics: MedicineNotes: Summary Hypoxia, with or without hypercapnia, was induced by exposing rats to various gas mixtures for 45 min. In addition, some of the rats were exposed to electrical foot shocks for 15 min. Rats were either untreated by drugs or received inhibitors of catecholamine synthesis or metabolism. The adrenals and blood plasma were analyzed for dopa, and the adrenals for dopamine (DA) and adrenaline + noradrenaline. Adrenal DA was elevated by severe (6 % O2) but was slightly decreased by moderate hypoxia (8 % O2). The addition of 5 % CO2 to 8 % O2 caused a moderate increase in DA. Foot shock stress raised adrenal DA under normoxia and the effect was markedly potentiated by moderate hypoxia. The accumulation of dopa in the adrenals of animals treated with 3-hydroxybenzylhydrazine (NSD 1015), an inhibitor of the aromatic amino acid decarboxylase, was closely correlated to the levels of adrenal DA in the corresponding experimental groups receiving no drug treatment, supporting the usefulness of adrenal DA as an indicator of catecholamine synthesis. In NSD 1015-treated rats dopa was found in the plasma and levels were increased after foot shock stress. The data indicate that moderate hypoxia may retard the conversion of tyrosine to dopa, which may be related to the O2 requirement of this reaction. However, this effect can be overcome by neurogenic stimuli, presumably via an activation of adrenal tyrosine hydroxylase. Apparently such stimuli are induced by foot shock stress, severe hypoxia, hypercarbia and most markedly, by the combination of shock stress and hypoxia.Type of Medium: Electronic ResourceURL: -
13Articles: DFG German National LicensesStaff View
ISSN: 1435-1463Source: Springer Online Journal Archives 1860-2000Topics: MedicineNotes: Summary Rats were exposed to 21, 8 or 6% O2 or to 8% O2 with 5% CO2. After 30 min equilibration, groups of normoxic and hypoxic rats received electrical foot shocks for 15 min through a grid floor. The initial, rate-limiting steps in brain monoamine synthesis were measuredin vivo by determining the accumulation in different brain regions of dopa and 5-hydroxytryptophan (5-HTP), induced by the inhibitor of the aromatic amino acid decarboxylase, NSD 1015 (3-hydroxybenzylhydrazine HCl 100 mg/kg i.p.). In other rat groups a different approach to measuring catecholamine turnover was used, i.e. the depletion of brain dopamine and noradrenaline, induced by the tyrosine hydroxylase inhibitorα-methyltyrosine (400 mg/kg of the methylester HCl i.p.). Hypoxia retarded the formation of dopa and 5-HTP. Shock had the opposite action, though with considerable regional differences with respect to dopa formation. The effect of shock on dopa formation was still present under hypoxia, whereas the effect on 5-HTP formation was completely prevented. Hypercapnia reversed the effect of hypoxia on dopa formation but left 5-HTP formation unchanged. The depletion of dopamine and noradrenaline, induced byα-methyl-tyrosine, was enhanced by shock, but the effect was completely prevented by moderate hypoxia. While hypoxia may in part influence monoamine metabolism directly, by reducing the availability of oxygen for oxidative processes, the biochemical consequences of changes in physiological neuronal activities probably contribute to the overall effect and especially to the complex interaction between hypoxia and shock stress.Type of Medium: Electronic ResourceURL: -
14Articles: DFG German National LicensesStaff View
ISSN: 1432-1904Source: Springer Online Journal Archives 1860-2000Topics: BiologyChemistry and PharmacologyNatural Sciences in GeneralType of Medium: Electronic ResourceURL: -
15Articles: DFG German National LicensesStaff View
ISSN: 1433-9285Source: Springer Online Journal Archives 1860-2000Topics: MedicineNotes: Summary A consecutive series of 176 referrals from family doctors to psychiatrists conducting their outpatient clinics im primary care was studied. The presence of psychological symptoms was the stated reason for referral in only half of the patients, although chronic illnesses and the psychotic disorders were well represented. Female sex, attending the GP with physical ill-health and the absence of personality disorder were influential but unacknowledged factors in the referral process. The implications of these findings for the development of community psychiatric services and the relationship between primary and secondary care is discussed.Type of Medium: Electronic ResourceURL: -
16Articles: DFG German National LicensesMatthews, P. M. ; Brown, R. M. ; Morten, K. ; Marchington, D. ; Poulton, J. ; Brown, G.
Springer
Published 1995Staff ViewISSN: 1432-1203Keywords: Mitochondrial DNA ; MELAS ; Leber's hereditary optic neuropathy ; Mitochondrial diseaseSource: Springer Online Journal Archives 1860-2000Topics: BiologyMedicineNotes: Abstract Studies in vitro have shown that a respiratorydeficient phenotype is expressed by cells when the proportion of mtDNA with a disease-associated mutation exceeds a threshold level, but analysis of tissues from patients with mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes (MELAS) have failed to show a consistent relationship between the degree of heteroplasmy and biochemical expression of the defect. One possible explanation for this phenomenon is that there is variation of heteroplasmy between individual cells that is not adequately reflected by the mean heteroplasmy for a tissue. We have confirmed this by study of fibroblast clones from subjects heteroplasmic for the MELAS 3243 (A→ G) mtDNA mutation. Similar observations were made with fibroblast clones derived from two subjects heteroplasmic for the 11778 (G→A) mtDNA mutation of Leber's hereditary optic neuropathy. For the MELAS 3243 mutation, the distribution of mutant mtDNA between different cells was not randomly distributed about the mean, suggesting that selection against cells with high proportions of mutant mtDNA had occurred. To explore the way in which heteroplasmic mtDNA segregates in mitosis we followed the distribution of heteroplasmy between clones over approximately 15 generations. There was either no change or a decrease in the variance of intercellular heteroplasmy for the MELAS 3243 mutation, which is most consistent with segregation of heteroplasmic units of multiple mtDNA molecules in mitosis. After mitochondria from one of the MELAS 3243 fibroblast cultures were transferred to a mitochondrial DNA-free (ρ0) cell line derived from osteosarcoma cells by cytoplast fusion, the mean level and intercellular distribution of heteroplasmy was unchanged. We interpret this as evidence that somatic segregation (rather than nuclear background or cell differentiation state) is the primary determinant of the level of heteroplasmy.Type of Medium: Electronic ResourceURL: -
17Articles: DFG German National LicensesStaff View
ISSN: 1573-1472Source: Springer Online Journal Archives 1860-2000Topics: GeosciencesPhysicsNotes: Abstract The calibration of a sailplane variometer to measure vertical velocity fluctuations in the atmospheric boundary layer is described. Its usefulness is demonstrated with typical results from a boundary-layer development study. The atmospheric calibrations gave the ratio of standard deviations of vertical velocity fluctuations measured by a standard tower-mounted turbulence instrument to the values measured by variometer as 2.5 m s−1 V−1.Type of Medium: Electronic ResourceURL: -
18Articles: DFG German National LicensesStaff View
ISSN: 1615-6102Keywords: Boergesenia forbesii ; Cellulose microfibrils ; Cell wall ; Fluorescent brightening agent ; Freeze fracture ; Terminal synthesizing complexSource: Springer Online Journal Archives 1860-2000Topics: BiologyNotes: Summary Wounding cells ofBoergesenia forbesii (Harvey) Feldmann induces the synchronous formation of numerous protoplasts which synthesize large cellulose microfibrils within 2–3 hours after wounding. The microfibrils appear to be assembled by linear terminal synthesizing complexes (TCs). TC subunits appear on both E- and P-faces of the plasma membrane, thus suggesting the occurrence of a transmembrane complex. The direction of microfibril synthesis is random during primary wall assembly and becomes ordered during secondary wall assembly. The average density of TCs during secondary wall deposition is 1.7/μm2, and the average length of the TC is 510 nm. TC organization is similar to that ofValonia macrophysa; however, the larger TCs ofBoergesenia (510 nm vs. 350 nm) produce correspondingly larger microfibrils (30 nm vs. 20 nm). The effects of a fluorescent brightening agent (FBA), Tinopal LPW, on cell wall regeneration ofBoergesenia protoplasts was investigated. The threshold level of Tinopal LPW for interfering with microfibril assembly is 1.5 μM. At 95 μM Tinopal (for short periods up to 15 minutes), microfibril impressions have atypical spherical impressions at their termini. At longer incubations (24 hours), TCs and microfibril impressions are absent. When washed free of Tinopal, the protoplasts eventually resume normal wall assembly; however, TCs do not reappear until at least 30 minutes after the removal of Tinopal. In consideration of the presence of ordered TCs before FBA treatment, their random distribution upon recovery implies an intermediate stage of assembly or possiblyde novo synthesis.Type of Medium: Electronic ResourceURL: -
19Articles: DFG German National LicensesStaff View
ISSN: 1615-6102Keywords: Fluorescent brighteners ; Inhibitors ; Cell wall ; Cellulose microfibrilsSource: Springer Online Journal Archives 1860-2000Topics: BiologyNotes: Summary Calcofluor White ST is a fluorescent brightener that has previously been shown to alter cellulose ribbon assembly in the bacteriumAcetobacter xylinum. In this report, we demonstrate that Calcofluor also disrupts cell wall assembly in the eukaryotic algaOocystis apiculata. When observed with polarization microscopy, walls altered by Calcofluor show reduced birefringence relative to controls. Electron microscopy has shown that these altered walls contain regions which consist primarily of amorphous material and which generally lack organized microfibrils. We propose that wall alteration occurs because Calcofluor binds with the glucan chains polymerized by the cellulose synthesizing enzymes as they are produced. As a consequence, the glucan chains are prevented from co-crystallizing to form microfibrils. Synthesis of normal walls resumes when Calcofluor is removed, which is consistent with our proposal that Calcofluor acts by direct physical interaction with newly synthesized wall components. Several types of fluorescent patterns at the cell wall/plasmalemma interface have also been observed following Calcofluor treatment. Fluorescent spots, striations; helical bands, and lens-shaped thickenings have been documented. Each of these patterns may be the result of the interaction of Calcofluor with cellulose at different spatial or temporal levels or from varying concentrations of the brightener itself. Helical bands and lens-shaped thickenings also have been examined with the electron microscope. Like other regions of wall alteration, they are found to contain primarily amorphous material. Finally, we note that cells with severely disrupted walls are unable to complete their normal life cycle.Type of Medium: Electronic ResourceURL: -
20Articles: DFG German National LicensesStaff View
ISSN: 1615-6102Keywords: Cellulose formation ; 2,6-Dichlorobenzonitrile ; Freeze etching ; Plasma membrane ; Cellulose synthesizing enzyme complex ; Tinopal LPW ; Vaucheria hamataSource: Springer Online Journal Archives 1860-2000Topics: BiologyNotes: Summary The effects of 2,6-dichlorobenzonitrile (DCB, a known inhibitor of cellulose synthesis) and Tinopal LPW (TPL, an agent which disrupts glucan crystallization) on the structure of cellulose synthesizing complexes (terminal complexes, TCs) in the xanthophycean algaVaucheria hamata were investigated. DCB (10 μM) inhibits nascent fibril formation from the TC subunit (based on the absence of impressions) although it does not alter the overall shape of the rectangular TC during the short treatment of 20 min. With a prolonged treatment (60 min), the arrangement of TC subunits becomes disordered, and particles generally exhibited as doublets of subunits are released from each other. DCB also interferes with the formation of the overall shape of the TC although it does not disturb the conversion into TC rows of the subunits (the zymogenic precursor of the TC) packed in the globules. A 15 min treatment with TPL (1 mM) destroys the TC integrity by reducing the subunits into small fragments or particulate aggregates. The particulate rows of the TC are interrupted at many points, and fragments and particulate aggregates are dispersed by prolonged treatment (45 min) with TPL. Unlike DCB, TPL inhibits the conversion of globule subunits into TC rows. New insights on the structural characteristics necessary for cellulose microfibril assembly and possible mechanisms for the biogenesis of theVaucheria TC come from these data.Type of Medium: Electronic ResourceURL: