Showing papers by "University of Dundee published in 1985"

TANSLEY REVIEW No. 2

Abstract: Summary The benefits which this paper addresses are those of maintaining the intracellular acid-base balance during growth, and of generating osmolarity related to regulation of turgor in environments of low water potential. These benefits may incur costs in terms of the quantity of potentially growth-limiting resources (photons, water, nitrogen) which are needed to produce unit quantity of ‘baseline’ plant biomass. The direction (excess H+ or excess OH−) and magnitude of acid–base perturbation during growth depends on the nature of the N-source (NH4+, N2 or NO3−), so that the costing of pH homoiostasis involves consideration of the costs of overall N-assimilation for comparison with the other costs of growth of a terrestrial C3 plant. Photon costs for the various biochemical and transport processes involved in overall growth, N-assimilation, pH regulation and osmolarity generation are computed using known stoichiometries of coupled reactions. Water costs are deduced from the C-requirements for the various processes (including C lost in associated decarboxylations) by assuming a constant value of water lost in transpiration per unit net C fixed in an illuminated shoot. Nitrogen costs are deduced from the N-content of the plants or compounds under consideration. The computed costs for N-assimilation and the generation of osmolarity are referred to the costs of ‘baseline’ plant synthesis using the cheapest mechanisms (NH4+ as source for N-assimilation; inorganic ions as the basis for osmolarity generation) so that the increment of cost related to assimilation of N2or NO3−, or of osmolarity generation using an organic compatible solute, can be presented. Photon costs of growth with N2 fixation and the processes associated with regulation of pH are (granted the assumptions made as to stoichiometries and plant composition) 9 % higher than are those of growth with NH4+ as N˜ source. The predicted cost of growth with NO3− as N source depends on the location of NO3− reduction and the mechanism of OH− disposal, and ranges from 5 to 12% more than that for growth with NH4+ as N source. H2O (transpiration) costs follow a similar pattern, with growth on N2 as N source costing 12% more, and growth on NO3− costing to 1–2 to 167 % more, than growth with NH4+ as N source. The extra costs in photons of using compatible solutes (sorbitol, proline or glycine betaine) to generate an osmolarity of 500 osmol m−3 in all of the non-apoplastic water of the plant add 21·5 to 26·1 % to the total costs of growth, while use of compatible solutes to generate osmolarity in ‘N’ phases (i.e. cytosol, plastid stroma, mitochondrial matrix) alone would add 5·2 to 6·2% The costs of growth in terms of transpirational water are increased 7·9 to 98 % by the use of compatible solutes for osmolarity generation in the ‘N’ phases only. The increments for the N-containing solutes are higher when NO3− is the N-source rather than NH4+. The N-cost of growth with N-containing compatible solutes generating 500 osmol m−3 in ‘N’ phases increases the N cost of growth by 33%. These predicted costs are under-estimates of ‘real’ costs which take into account the occurrence of alternate oxidase activity under some growth conditions and the production of additional organic acid anions with N2 as opposed to NH4+ as N source. Nevertheless, the predicted minimum costs of attaining the benefits of pH regulation and of turgor generation are of use in suggesting where selectively significant (i.e. low requirement for a scarce resource) alternative mechanisms may occur. Examples include a possible photon saving by using NH4+ rather than N2 or NO3− where all three are available; a possible water saving by use of photoreduction of NO3− in leaves in arid environments; and a possible N saving by use of non-N-containing compatible solutes (polyols) in environments of low water potential. Proof of these suggestions involves comparisons of inclusive fitness of genotypes possessing the trait under consideration with that of genotypes lacking the trait.

Comparision of the new emulsion formulation of propofol with methohexitone and thiopentone for induction of anaesthesia in day cases

Abstract: The new emulsion formulation of di-isopropyl phenol (propofol) was compared with metho-hexitone and thiopentone for induction of anaesthesia in day cases. Propofol produced significantly smoresearch-article induction of anaesthesia, but caused more cardiovascular and respiratory depression. Pain on injection was significantly less than with methohexitone. Post-anaesthetic recovery was superior with propofol, with virtual absence of side effects, and rapid recovery with little impairment of psychomotor function 30 min after anaesthesia.

Osmotic adjustment and organic solute accumulation in unicellular cyanobacteria from freshwater and marine habitats

Abstract: The intracellular concentrations of low-molecular weight carbohydrates and quaternary ammonium compounds present in 26 axenic isolates of unicellular cyanobacteria have been studied over a range of external salinity from freshwater up to 300% seawater (100%=35‰ S). In all cases, a single carbohydrate, either sucrose or glucosylglycerol, was identified as the principal organic osmoticum, showing major variation in response to the external salt concentration; quaternary ammonium compounds were present in osmotically insignificant amounts. Glucosylglycerol was accumulated as primary osmoticum by nine of the isolates from saline habitats and by five of the freshwater isolates; trace amounts of sucrose were also prsent. The remaining twelve freshwater strains accumulated sucrose as sole osmoticum. Glucosylglycerol-accumulating strains grew over the widest salinity range (up to 200 to 250% seawater), whether isolated from saline or non-saline habitats. Sucrose-accumulating strains were more stenohaline, growing only in up to 50 to 100% seawater and showing no sustained growth in hypersaline media (>100% seawater). The data suggest that (1) glycosylglycerol accumulation is not unique to marine cyanobacteria, and (2) the upper salinity limit for growth may be linked to organic solute accumulation, rather than habitat, with glucosylglycerol-accumulating isolates having a greater potential for growth in salt-stressed conditions than sucrose accumulators.

Lipid peroxidation products and antioxidant proteins in plasma and cerebrospinal fluid from multiple sclerosis patients.

Abstract: Lipid peroxidation (LPx) products were measured as thiobarbituric acid-reactive substances (TS) and lipid-soluble fluorescent pigments (FP) in both plasma and CSF from MS patients and controls. Although no significant changes were found in MS plasma, we report here for the first time increases in both TS and FP in MS CSF (p<0.05 and p<0.01, respectively, compared with patients with other neurological diseases), indicating that increased LPx in CNS may be a feature of MS. Levels of transferrin were normal but caeruloplasmin (CP), a major antioxidant plasma protein, was significantly raised in MS patients (p<0.01) and this may represent an adaptive response to increased oxidative challenge. Neither of these proteins was detectable in CSF using radial immunodiffusion. There was no significant correlation between the severity or duration of the disease nor the period since the last relapse and either LPx products of CP suggesting that the changes observed in this work are not simply the direct result of demyelination and tissue damage.

Transport and fixation of inorganic carbon by marine algae

Abstract: Publisher Summary Marine algae have interesting characteristics relating to the transport and fixation of inorganic carbon and this chapter summarizes some of the recent findings. Researchers' understanding of the pathway of carbon metabolism in marine algae has been aided by the use of carbon isotopes. In 1952, Steeman Nielsen introduced the “C-14 technique” for measuring primary productivity in aquatic systems. This technique has its problems and many of the problems and uncertainties can be attributed to the fact that measurements are made in the absence of precise information on the transport and subsequent assimilation of inorganic carbon. Additionally, the use of carbon isotopes has helped elucidate the pathway of carbon assimilation in a number of marine algae and has shown that the photosynthetic carbon reduction cycle (PCRC) is operational with ribulose-1,5-bisphosphate carboxylase/oxygenase (RUBISCO) as the carboxylase. However, other early labeled products of photosynthesis, in particular C4 acids, have given rise to the notion that certain marine algae may have a C4 type of photosynthesis similar to that in specialized angiosperms. During recent years, certain advances have been made and various enzyme activities have been demonstrated in extracts of marine algae. Furthermore, certain enzymes have been purified but the number so far purified is extremely low. For these reasons, the contribution to the basic understanding of the processes involved in plant carbon assimilation by marine algae is comparatively small. The chapter shows some of the properties of the inorganic carbon system in seawater that are relevant to the assimilation of inorganic carbon by marine algae and cyanobacteria.

Target decomposition theorems in radar scattering

Abstract: By converting the coherent scattering matrix into a target vector, the concept of a coherency matrix may be introduced for characterising statistical scattering problems involving polarised waves. This technique is compared with the more conventional Mueller matrix formalism and a unique decomposition theorem developed for modelling dynamic scattering problems.

The switching mechanism in amorphous silicon junctions

Abstract: Extensive new results have been obtained on memory switching in a-Si p + ni junctions It is shown that the ON-state has its origins in a highly conducting filament less than lμm in diameter The physical mechanisms that could play a role in the switching operations are discussed

Evolution of nitrogen-fixing symbioses

Abstract: Because of both the energy costs and the slowness of the reactions of the nitrogenase complex compared with those involving some form of combined nitrogen (oxidised or reduced), we argue that the evolution of nitrogen-fixing organisms required an environment which was very limited in combined nitrogen. This is thought to have occurred after phototrophy evolved, but before water was used as a hydrogen donor (and therefore oxygen was present in the atmosphere). After oxygenic photosynthesis evolved, the need for a high level of biological nitrogen-fixation remained, since abiotic inputs were insufficient to keep pace with the rapidly evolving biomass (flora and fauna). Symbiotic fixation probably first evolved in the form of casual associations between cyanobacteria and most other groups of plants. By inhabiting the sporophytic generation of evolving land plants (cycads in particular), protection against nitrogenase-inactivating oxygen and a more desiccating environment was achieved simultaneously.We envisage nodulated plants arising by the transfer of nif genes into tumour-forming bacteria. In the case of legumes, these would be ancestors of extant agrobacteria, which gain entry into their hosts via wounds. Co-evolution of symbionts from nitrogen-fixing tumours has taken several routes, leading to extant nodules differing in mode of infection, structure and physiology. Evolution towards optimisation of oxygen usage is continuing.Nitrogen-fixing symbiosis in animal systems is only advantageous in specialised ecological niches in which wood is the sole dietary intake. In the case of shipworms, the symbiosis has many of the advanced features associated with nitrogen fixing root nodules.

DNA bending induced by cruciform formation.

Abstract: Cruciform structures1,2 in DNA are of considerable interest, both as extreme examples of sequence-dependent structural heterogeneity and as models for four-way junctions such as the Holliday junction3 of homologous genetic recombination. Cruciforms are of lower thermodynamic stability than regular duplex DNA, and have been observed only in negatively supercoiled molecules4–6, where the unfavourable free energy of formation is offset by the topological relaxation of the torsionally stressed molecule. From an experimental viewpoint this can be a disadvantage, as cruciform structures can be studied only in relatively large supercoiled DNA circles, and are destabilized when a break is introduced at any point. We therefore set out to construct a pseudo-cruciform junction—by generating hereroduplex formation between two inverted repeat sequences. Stereochemically, this should closely resemble a true cruciform but remain stable in a linear DNA fragment. We have now created such a junction and find that it has the expected sensitivities to endonucleases. These DNA fragments exhibit extremely anomalous gel electrophoretic mobility, the extent of which depends on the relative position of the pseudo-cruciform along the length of the molecule. Our results are very similar to those obtained by Wu and Crothers7 using kinetoplast DNA, and we conclude that the pseudo-cruciform junction introduces a bend in the linear DNA molecule.

Multisite phosphorylation of glycogen synthase from rabbit skeletal muscle. Identification of the sites phosphorylated by casein kinase-I.

Abstract: Glycogen synthase is a substrate for five distinct protein kinases in skeletal muscle which phosphorylate seven different serine residues on the enzyme. Cyclic-AMP-dependent protein kinase phosphorylates sites 1a, 1b and 2, phosphorylase kinase, site 2, glycogen synthase kinase 3, sites 3a, 3b and 3c, glycogen synthase kinase 4, site 2 and glycogen synthase kinase 5 site 5. Site 2 is seven residues from the N-terminus of glycogen synthase and is located in a cyanogen bromide peptide termed CB1 (apparent Mr= 9000). The other six phosphorylation sites are located in a cyanogen bromide peptide termed CB 2 (apparent Mr= 24000) at the C-terminal end of the molecule. The sequence of the N-terminal 123 residues of peptide CB2, has been completed. Sites 3a, 3b, 3c, 5. la and 1b are located at residues 30, 34, 38, 46, 87 and 100 from the N-terminus of CB2 respectively. Sitc l a is the next serine residue after site 5. The region surrounding sites 3a, 3b and 3c is very rich in proline residues while that surrounding sites la and 1b contains many serine and threonine residues. The 23 residues following site 5 contain 15 aspartic acid and glutamic acid residues, while the region immediately N-terminal to site 1a is very basic. The whole region is remarkably hydrophilic and is the region at which the native enzyme is attacked by proteinases. The sites at which glycogen synthase is cleaved by trypsin, chymotrypsin and thermolysin have been identified. The finding that trypsin cleaves the enzyme C-terminal to site 3c while chymotrypsin cleaves N-terminal to site 3a has formed the basis of a simple procedure for determining the state of phos- phorylation of the seven serine residues in vivo [Parker, P. J., Embi, N., Caudwell, F. B., and Cohen, P. (1982) Eur.j. Biochem. 124, 47–551.

Techniques of Identifying Competencies Needed of Doctors

Abstract: (1985). Techniques of Identifying Competencies Needed of Doctors. Medical Teacher: Vol. 7, No. 1, pp. 15-25.

Uptake of CO2 by aquatic vegetation

Abstract: Photosynthesis by aquatic plants based on the supply of CO2 from air-equilibrated solutions may be limited by the low diffusion coefficient of CO2 in water. For plants in which the transport of CO2 from the bulk medium is by diffusion, and the initial carboxylation uses RUBISCO, CO2 supply can be increased by growth in habitats with fast water flow over the surface (reducing unstirred layer thickness), or with heterotrophically-augmented CO2 levels, including the direct use of sediment CO2. Many aquatic plants using RUBISCO as their initial carboxylase counter the limitations on CO2 supply via the operation of biophysical CO2 concentrating mechanisms which are based on active transport of HCO−3, CO2 or H+ at the plasmalemma, and use bulk-phase HCO−3 or CO2 as the C source. A final group of aquatic plants use biochemical CO2 concentrating mechanisms based on auxiliary carboxylation by PEPc: C4-like and Crassulacean Acid Metabolism–like processes are involved. These various mechanisms for increasing CO2 supply to RUBISCO also help to offset the low specific reaction rate of aquatic plant RUBISCOs at low [CO2] and low [CO2]: [CO2]. In addition to overcoming restrictions on CO2 supply, the various methods of increasing inorganic C availability may also be important in alleviating shortages of nitrogen or photons.

A role for the mitochondrion in the protection of cells against calcium overload

Abstract: Publisher Summary This chapter describes the pathways that are responsible for mitochondrial calcium transport and discusses these pathways that act in concert to limit the extra-mitochondria1 free Ca 2+ concentration, [Ca 2+ ] e , in in vitro models, and discusses the validity of the synaptosome as a model for studying the integration of mitochondrial and plasma membrane transport systems in the brain The extents to which these model systems provide an insight into the events during brain ischemia are discussed The chapter considers the two aspects, the mechanism by which Ca 2+ gets out of the mitochondrial matrix, and whether Ca 2+ transport by such an obviously aerobic organelle as the mitochondrion can have any relevance in the ischemic condition The chapter explains that the Ca 2+ transport properties of isolated mitochondria are ideally suited to a role in limiting any increase in [Ca 2+ ] e that might otherwise damage the integrity of the cell, unless both oxidative phosphorylation and glycolysis are interrupted The chapter discusses the isolated nerve terminal as a model in which to study the mitochondrial and plasma membrane that transport properties are integrated in intact neuronal tissue

Accurate estimation of stomatal aperture from silicone rubber impressions

Abstract: Summary The potential of low viscosity silicone-based impression material for measuring stomatal aperture on intact leaves was investigated. It was found that the probability of successful replication of Commelina communis L. stomata depended on the width of the stomatal pores. The wider pores in a sample were more likely to be measured, so the resulting estimated mean was an overestimate of the true mean. This bias in estimates of stomatal aperture from impressions was studied and quantified. A transformation is described which was used to adjust apparent aperture measurements from impressions to give more accurate estimates of stomatal apertures on intact leaves of C. communis. Maximum absolute errors due to the bias usually occurred at apparent apertures on impressions of between 2 and 5 μm but were proportionally greatest below 3μm, where they often exceeded 40%. At a given aperture, the error depended upon the dispersion of the stomatal apertures about their mean and was greatest when this was large.

Multiphasic osmotic adjustment in a euryhaline cyanobacterium

Abstract: Transfer of Synechocystis PCC6714 from a freshwater medium to a saline medium caused the cells to shrink; rapid entry of NaCl resulted in a partial recovery of cellular volume within 2 min. Active extrusion of internal Na+ in exchange for extracellular K+ then occurred (within 20 min). Finally, the low-Mr carbohydrates sucrose and glucosylglycerol were accumulated and internal KC1 levels declined. In long-term growth experiments, the relative importance of sucrose as a component of the low-Mr organic solute fraction decreased and glucosylglycerol became the single most important intracellular solute. These observations demonstrate that several inorganic and organic solutes are involved in osmotic adjustment in this cyanobacterium, with sequential changes in the relative importance of each solute following transfer to a saline medium.

Osmotic adjustment in Spirulina platensis.

Abstract: The filamentous cyanobacterium Spirulina platensis has been examined for salt tolerance and osmotic adjustment. Salinities up to 150% seawater had little effect on growth yield or photosynthetic O2 evolution; higher salinities were markedly inhibitory. Osmotic adjustment was achieved by the intracellular accumulation of the low-molecular-weight carbohydrate glucosyl-glycerol in response to increased external salinity: in fullstrength (100%) seawater glucosyl-glycerol accounted for approximately 5.0% of the dry weight of the cyanobacterium. Trehalose was also present, particularly in cells at low salt concentration, and in 50% seawater medium accounted for up to 1.0% of the dry weight of the cyanobacterium. For cells grown in 100% seawater the ratio of trehalose to glucosyl-glycerol varied with temperature: at 37°C trehalose comprised 31% (w/w) of the low-molecular-weight carbohydrates while at 20°C only 9% of the total was trehalose. When subjected to hypo-osmotic shock the intracellular concentration of glucosyl-glycerol decreased and this was mirrored by an increase in glycogen. An understanding of the osmotic adjustment of S. platensis has implications both for the mass culturing of this and other strains of Spirulina and possibly also for the quality of the harvested product.

The toxicity of the cyanobacterium Microcystis aeruginosa to rainbow trout, Salmo gairdneri Richardson

Abstract: . Microcystis aeruginosa is a common cyanobacterium of nutrient-rich fresh waters. It has been implicated in a large number of poisoning incidents involving wild and domesticated terrestrial animals. The study showed that a pure strain of M. aeruginosa toxic to mice was non-toxic to rainbow trout immersed in a culture for 10 days. In contrast, when presented by intraperitoneal injections Microcystis caused an acute toxic response with 100% mortality of fish within 36 h. The histopathology of the response is described and contrasted with that to another cyanobacterium, Anabaena cylindrica, which was shown to be non-toxic by immersion or injection.

Direct determination of leucine metabolism and protein breakdown in humans using L‐[1‐13C, 15N]‐leucine and the forearm model

Abstract: We have used the forearm model to study protein metabolism in six normal healthy subjects in the fed state using L-[1-13C, 15N]-leucine as the substrate tracer. Deep venous and arterialized venous blood samples from the forearm were collected at 10-min intervals 2.5 h into a primed-continuous infusion of the dilabelled tracer. Arterialized venous blood was obtained using a 'hot-box' technique and forearm blood flow was measured by mercury strain-gauge plethysmography. The concentration and isotope enrichment of leucine and its metabolites, alpha-ketoisocaproic acid and CO2, in deep venous and arterialized venous blood were measured by gas chromatography-mass spectrometry and isotope ratio-mass spectrometry. The rates of leucine deamination and reamination were 388 +/- 24 (mean +/- SEM) and 330 +/- 23 nmol (100 ml)-1 min-1 respectively, whilst protein synthesis and breakdown rates were 127 +/- 11 and 87 +/- 10 nmol (100 ml)-1 min-1 respectively across the forearm in the fed state. We have demonstrated that the use of doubly labelled leucine as tracer and application of the mathematical model developed in this study, permits the comprehensive quantification of leucine kinetics including protein breakdown.

Quantitative exfoliative cytology of normal oral squames: an age, site and sex-related survey.

Abstract: This study describes the development of quantitative cytological techniques and their application to oral smears. Nuclear and cell size has been measured and matched with age, sex and site in an attempt to produce a baseline for comparison with identical measurements carried out on pathological smears. The results displayed a significant variation in nuclear and cytoplasmic area between different sites. Nuclear size varied significantly with advancing age; however, this was not the case for cytoplasmic area. There was no significant variation in either criterion between males and females.

The kinetic properties of cruciform extrusion are determined by DNA base-sequence

Abstract: The extrusion kinetics of two cruciforms derived from unrelated DNA sequences differ markedly. Kinetic barriers exist for both reactions, necessitating elevated temperatures before extrusion proceeds at measureable speeds, but the dependence upon temperature and ionic strength is quite different for the two sequences. One, the ColE1 inverted repeat, exhibits a remarkably great temperature dependence of reaction rate and is suppressed by moderate amounts of NaCl or MgCl2. In contrast, the other, a synthetic inverted repeat present in pIRbke8, shows more modest temperature dependence and has a requirement for the presence of salt, with optimal concentrations being 50 mM NaCl or 100 microM MgCl2. Under optimal conditions, cruciform extrusion rates are fast (t1/2 less than 60m) at 37 degrees C for both sequences at native superhelix densities. In 50 mM NaCl the pIRbke8 inverted repeat is characterised by an Arrhenius activation energy of 42.4 +/- 3.2 kcal mole -1. The differences in kinetic properties between the two sequences indicate that DNA base sequence is itself an important factor in determining cruciform kinetics, and possibly even in the selection of the mechanistic pathway.

A projected lagrangian algorithm for semi-infinite programming

Abstract: A globally convergent algorithm is presented for the solution of a wide class of semi-infinite programming problems. The method is based on the solution of a sequence of equality constrained quadratic programming problems, and usually has a second order convergence rate. Numerical results illustrating the method are given.