Showing papers by "University of Leicester published in 1979"

Elemental and Sr isotope variations in basic lavas from Iceland and the surrounding ocean floor

Abstract: Major and trace element data are used to establish the nature and extent of spatial and temporal chemical variations in basalts erupted in the Iceland region of the North Atlantic Ocean. The ocean floor samples are those recovered by legs 38 and 49 of the Deep Sea Drilling Project. Within each of the active zones on Iceland there are small scale variations in the light rare earth elements and ratios such as K/Y: several central complexes and their associated fissure swarms erupt basalts with values of K/Y distinct from those erupted at adjacent centres; also basalts showing a wide range of immobile trace element ratios occur together within single vertical sections and ocean floor drill holes. Although such variations can be explained in terms of the magmatic processes operating on Iceland they make extrapolations from single basalt samples to mantle sources underlying the outcrop of the sample highly tenuous.

Paravertebral thoracic block-a reappraisal.

Abstract: An accurate, simple and safe method, based upon cadaver studies, of obtaining a thoracic paravertebral block, suitable for repeated administration by catheter or for permanent accurate neurolytic block, and which carries significant advantages over intercostal or epidural block, is described in theory and practice.

A systematic relationship between phytochrome-controlled development and species habitat, for plants grown in simulated natural radiation.

Abstract: A survey of the responsiveness of plant species, typical of open and shade habitats, to simulated natural shade-light quality (i.e. white light plus supplementary far-red) has demonstrated a systematic relationship between habitat and certain developmental responses. Supplementary far-red light has a much greater effect on stem extension rate, petiole length, and leaf dry weight: stem dry weight ratio of the open habitat, shade-intolerant species. Far-red effects on leaf chlorophyll content show no such systematic grading. These results are discussed in relation to habitat adaptation. In most cases, the relationship between developmental response and the estimated phytochrome photoequilibrium, which is established by the radiation treatment, is linear. This is taken as an indication of phytochrome involvement in shade perception.

Phonolic components of the primary cell wall and their possible rôle in the hormonal regulation of growth.

Abstract: The insoluble cell wall polymers of cultured spinach cells contained esterified ferulic acid at 2–5 mg g-1 dry weight. Gibberellic acid (GA3, 10-11–10-6 M) promoted the expansion of these cells and simultaneoulsy suppressed peroxidase secretion, reduced the activity of cellular phenylanine ammonia-lyase and favoured the accumulation of wall-esterified ferulate and of extracellular soluble phenolic aglycones. When growth was prevented with 0·7 M sorbitol, GA3 still evoked the phenolic and peroxidase effects. It is suggested that peroxidase restricts growth by rigidifying the cell wall in two ways: (a) covalently by catalysing the conversion of feruloyl side-chains into diferuloyl cross-links and (b) non-covalently by catalysing the conversion of soluble phenolics into hydrophobic quinones (or polymers). GA3 is hypothesised to prevent this rigidification by inhibiting peroxidase secretion.

143 Nd/ 144 Nd and 87 Sr/ 86 Sr ratios from the Azores and their significance in LIL-element enriched mantle

Abstract: Basalts from Sao Miguel are displaced to higher 87Sr/86Sr ratios, and have a significantly shallower slope, compared with the main correlation between 143Nd/144Nd and 87Sr/86Sr for most mantle-derived volcanic rocks. Available data on young magmatic rocks indicate that large ionic lithophile (LIL)-element enrichment in the upper mantle involves two readily distinguishable components which reflect different histories.

Distribution of fibronectin in the ectoderm of gastrulating chick embryos

Abstract: A GLYCOPROTEIN known as large external transformation-sensitive (LETS) protein, cell surface protein (CSP) or fibronectin1–3 can be identified on the surface of various cell types1. This protein has a molecular weight of 210,000–250,000 and is closely related to the cold-insoluble globulin found in serum and to the factor needed for cell spreading in vitro4,5. In culture many cells secrete fibronectin into the growth medium and on to the substratum6–8; fibroblasts and other cells of mesodermal origin produce particularly large amounts. However, in the early mammalian embryo fibronectin is present in basement membranes before the mesoderm has formed, when the embryo consists only of ectoderm and endoderm9. Adult epithelia also produce fibronectin in vitro10, and it forms a component of epithelial basement membranes in vivo11–13. We have applied an immunofluorescent technique to whole mounts of early chick embryos to examine the distribution and possible morphogenetic function of fibronectin. We discuss our results here, and suggest that fibronectin is involved in morphogenetic movement during early development.

Relationships between Stomatal Behavior and Internal Carbon Dioxide Concentration in Crassulacean Acid Metabolism Plants

Abstract: Measurements of internal gas phase CO(2) concentration, stomatal resistance, and acid content were made in Crassulacean acid metabolism plants growing under natural conditions. High CO(2) concentrations, sometimes in excess of 2%, were observed during the day in a range of taxonomically widely separated plants (Opuntia ficus-indica L., Opuntia basilaris Engelm. and Bigel., Agave desertii Engelm., Yucca schidigera Roezl. ex Ortiges, Ananas comosus [L.] Merr., Aloe vera L., Cattleya sp. and Phalanopsis sp.) and below ambient air concentrations were observed at night.Stomatal resistance was always high when CO(2) concentration was high and experiments in which attempts were made to manipulate internal CO(2) concentrations gave data consistent with stomatal behavior in Crassulacean acid metabolism being controlled by internal CO(2) concentration. Exogenous CO(2) applied in darkness at a concentration similar to those observed in the light caused stomatal resistance to increase.In pads of Opuntia basilaris Engelm. and Bigel. subjected to severe water stress internal gas phase CO(2) concentrations exhibited fluctuations opposite in phase to fluctuations in acid content. Stomatal resistance remained high and the opening response to low CO(2) concentration was almost entirely eliminated.

Isolation and characterisation of a strain carrying a conditional lethal mutation in the cou gene of Escherichia coli K12

Abstract: A strain which carries a mutation conferring clorobiocin resistance and temperature sensitivity for growth was isolated from Escherichia coli K12 Genetic mapping and the molecular weight of the gene product suggest that the mutation is in the cou gene, specifying a sub-unit of DNA gyrase Nuclear organisation and segregation and placement of septa are grossly abnormal in the mutant at 42°C RNA synthesis and initiation of DNA replication are also affected at the restrictive temperature but the rate of DNA chain elongation continues almost undisturbed

Primary structure of a chloramphenicol acetyltransferase specified by R plasmids

Abstract: Naturally occurring isolates of chloramphenicol-resistant bacteria commonly synthesise chloramphenicol acetyltransferase (EC 2.3.28; CAT) in amounts which are sufficient to account for the resistance phenotype and often harbour plas-mids which carry the structural gene for CAT1,2. The finding of CAT in such diverse prokaryotes as Proteus mirabilis, Agrobacterium tumefaciens, Streptomyces sp., and a soil Flavobacterium has led to speculation concerning the origin and evolution of the more commonly observed CAT variants specified by plasmids in clinically important bacteria2. To provide a more solid basis for studying the evolution and spread of CAT within prokaryotes we chose to determine the complete amino acid sequence of a type I variant of CAT, the variant known to be associated with most F-like plasmids conferring chloramphenicol resistance. The sequence has been determined by combining the results obtained from manual and automated sequential degradation with those obtained by mass spectrometry of peptides generated by enzymatic digestion. The directly determined primary structure is identical with that predicted by the DNA sequence analysis3 of the chloramphenicol resistance transponson Tn9 known to specify a type I variant of chloramphenicol acetyltransferase.

Binding of Thiostrepton to a Complex of 23‐S rRNA with Ribosomal Protein L11

Abstract: Thiostrepton binds with high affinity and with a 1:1 stoichiometry to a complex formed between Escherichia coli 23-S ribosomal RNA and ribosomal protein L11 of E. coli or the homologous protein BM-L11 of Bacillus megaterium. In the presence of T1 ribonuclease, protein BM-L11 and thiostrepton protect from degradation a fragment of E. coli 23-S RNA estimated to be about 50 nucleotides in length.

Anomalous Properties of [3H]Spiperone Binding Sites in Various Areas of the Rat Limbic System

Abstract: [3H]Spiperone, a neuroleptic/dopamine receptor ligand, binds with high affinity (Kd 0.15 nM) to a single specific site on rat corpus striatum membranes. The "specific" binding represents about 80% of the total binding and is displaced by dopamime, apomorphine, and stereospecifically by neuroleptics such as butaclamol and flupenthixol. However, in contrast to the striatum, only 30-40% of the binding of [3H]spiperone to limbic forebrain membranes is displaced stereospecifically by butaclamol or flupenthixol, whereas dopamine and certain spiperone analogues compete with high affinity for about 70% of the labeled sites. These additional sites are saturable, reversible, and of high affinity. Kinetic analysis of association and dissociation rates yields a Kd value (1.5 nM) in agreement with equilibrium saturation data for these sites. They also possess a precise distribution, with high amounts being found in the hippocampus, septum, and nucleus accumbens, but they are completely absent in areas such as the corpus striatum, olfactory tubercles and hypothalamus. Moreover, these [3H]spiperone binding sites show strict structure-affinity relationships in that only spirodecanone butyrophenone derivatives and dopamine are capable of displacing this binding with relatively high affinities. The results emphasize the complex nature of neuroleptic/dopamine "receptor" binding sites in brain and the need for precise definition of such "specific" binding sites.

Demystifying Social Statistics

Abstract: . . . ,^ . . . . dlrectlons ot ratlona lty; eplstemo Oglcally, Weber's neo-Kantian assumptions implied a value-related diagnostic concern with modern occidental culture. Hence, for Schluchter, Weber's work develops neither a comparative structural analysis of world history, nor a universal theory of evolution; rather, it is a 'societal history' of the West. To demonstrate and clarify this 'developmental-historical' approach, Schluchter devotes the bulk of the book to

Migration in england during the late seventeenth and early eighteenth centuries

Abstract: The author examines the current state of research on migration in early modern England and reviews existing sources of data and their problems. He then presents new data on migration for the years 1660 to 1730 from biographical material provided by some 7000 witnesses appearing before church courts. Regional and social variations in migration and the factors affecting it are discussed (ANNOTATION)

Prediction of the Timing of the Adolescent Growth Spurt from Ossification Events in Hand—Wrist Films

Abstract: The prediction of the timing of the pubertal growth spurt could be helpful in planning some types of orthodontic treatment. It has been suggested that information from hand—wrist radiographs could be used for this purpose. Insufficient attention has been paid to the distinction between ossification events and bone stages. In the present paper it is shown that the uncertainty of prediction of the timing of the peak height Velocity from ossification events in the hand and wrist, is generally large and so they are of limited value for this purpose.

Hydraulic Resistance of Artificial Strip Roughness

Abstract: An experimental study of two-dimensional flow over non-uniform roughness is reported in which artificial strip roughness was employed. The roughness elements were square in cross section and placed at different relative spacings. A six-fold classification system is suggested based upon the ideas of Morris and Adachi. Resistance data from other investigators is also considered, and the variation of resistance coefficient with Reynolds number, relative spacing, and relative depth examined. The general resistance parameter, X, first introduced by Sayre and Albertson is found to be particularly helpful in synthesizing the various sets of resistance data. Logarithmic resistance equations involving X are validated over a wide range of roughness wavelength to height ratio. The relationship between roughness height and Nikuradse's equivalent sand roughness size is also examined.

Endogenous and Exogenous Auxin in the Control of Root Growth

Abstract: The endogenous indol-3yl-acetic acid (IAA) of detipped apical segments from roots of maize (cv ORLA) was greatly reduced by an exodiffusion technique which depended upon the preferential acropetal transport of the phytohormone into buffered agar. When IAA was applied to the basal cut ends of freshly prepared root segments only growth inhibitions were demonstrable but after the endogenous auxin concentration had been reduced by the exodiffusion technique it became possible to stimulate growth by IAA application. The implications of the interaction between exogenous and endogenous IAA in the control of root segment growth are discussed with special reference to the role of endogenous IAA in the regulation of root growth and geotropism.

Freeze Preservation of Somatic Embryos and Clonal Plantlets of Carrot (Daucus carota L).

Abstract: Cell suspensions of carrot (Daucus carota L.) can be cryopreserved by slow freezing (about 2 C per minute) in medium containing dimethylsulfoxide as a cryoprotectant. After storage in liquid nitrogen and thawing they demonstrate a high viability and are able to resume growth. Such a method entirely fails to preserve clonal plantlets; somatic embryos cease organized development at the time of freezing and recover growth only by secondary embryogenesis. Modification of the procedure, involving the removal of superficial moisture from cryoprotectant-treated embryos and plantlets and enclosing them in a foil envelope before freezing, greatly improves their survival potential. The use of dimethylsulfoxide at levels between 2.5 and 20% (v/v) and freezing at rates between 1 and 5 C per minute yielded viable preparations under appropriate thawing conditions. In general, treatments which increased tissue dehydration before or during freezing were most successful when followed by relatively slow thawing. Conversely where dehydration to a lesser degree was achieved, more rapid thawing was advantageous. Postthawing washing or inoculation into liquid media was inhibitory to recovery. On semisolid regrowth medium, somatic embryos resumed normal development, whereas in plantlets the root and shoot meristem regions gave rise to new growth. In both cases, inclusion of activated charcoal in the medium promoted organized growth.

Ribose methylation and resistance to thiostrepton

Abstract: THE antibiotic, thiostrepton, produced by Streptomyces azureus, inhibits bacterial protein synthesis by binding to 50S ribosomal subunits with 1:1 stoichiometry. Recently1, we showed that S. azureus prevents its own death by methylating 23S ribosomal RNA (rRNA) so that its ribosomes do not bind the drug. Intact ribosomes are not substrates for the methylase and those experiments involved methylation of ‘core particles’ derived from the (thiostrepton-sensitive) ribosomes of Streptomyces coelicolor. Ribosomes can be reconstituted from core particles by adding back the missing ‘split proteins’. Presumably, in S. azureus, methylation of 23S rRNA occurs before assembly of the 50S ribosomal subunit is completed. Here we report that the ‘thiostrepton-resistance’ methylase of S. azureus is an RNA-ribose methylase which introduces a single methyl group into adenosine in 23S rRNA. This is a novel antibiotic-resistance mechanism.

Some Psychological Processes in String Quartets

Abstract: The music of the emergent Classical era, with its gradual repudiation of the baroque functions of the continuo, its development of instrumental technique and its widening social appeal, saw the emergence of an ever-increasing variety of instrumental combinations. Of these, the string quartet attracted among major composers an unrivalled popularity which was maintained throughout the Romantic era and has continued unabated amidst the dissolution of tonality up to the present day. Other musical ensembles have survived over this period, but none without some alteration of its instrumentation; the basic structure of two violins, a viola and a 'cello has, however, remained unchanged since its emergence in the middle of the eighteenth century.

Open Channel Flow with Varying Bed Roughness

Abstract: The distribution of velocity and boundary shear stress in a rectangular flume has been examined experimentally, and the influence of varying the bed roughness and aspect ratio assessed. The resistance of the channel bed was varied by means of artificial strip roughness elements, and measurements made of the wall and bed shear stresses. Dimensionless plots of both shear stress and shear force parameters are presented for different bed roughnesses and aspect ratios, and these serve to illustrate the complex way in which such parameters vary. The definition of a wide channel is also examined, and a graph giving the limiting aspect ratio for different roughness conditions is presented. The boundary shear stress distributions and isovel patterns are used to examine one of the standard side-wall correction procedures. One of the basic assumptions underlying the procedure is found to be untenable due to the cross channel transfer of linear momentum.

Characterization and comparison of chloramphenicol acetyltransferase variants.

Abstract: 1 Variants of chloramphenicol acetyltransferase from a variety of bacterial species have been isolated and purified to homogeneity. They constitute a heterogeneous group of proteins as judged by analytical affinity and hydrophobic (‘detergent’) chromatography, native and sodium dodecyl sulfate electrophoresis, sensitivity to sulfhydryl specific reagents, steady state kinetic analysis, and reaction with antisera. 2 The most striking observation is that three variants of chloramphenicol acetyltransferase (R factor type III, Streptomyces acrimycini, and Agrobacterium tumefaciens) possess an apparent subunit molecular weight (24500) which is significantly greater than that of all other variants examined (22500). The three atypical variants are not identical since they show marked differences in a number of important parameters. 3 Although the fundamental mechanism of catalysis may prove to be identical for all chloramphenicol acetyltransferase variants, there is a wide range of sensitivity to thiol-directed inhibitors among the enzymes studied. 4 Amino acid sequence analysis of the N-termini of selected variants suggests that the qualitative differences among chloramphenicol acetyltransferase variants is a reflection of structural heterogeneity which is most marked in comparisons between variants from Gram-positive and Gram-negative species.