Showing papers by "University of Exeter published in 1993"

The role of active oxygen in the response of plants to water deficit and desiccation.

Abstract: Water deficits cause a reduction in the rate of photosynthesis. Exposure to mild water deficits, when relative water content (RWC) remains above 70%, primarily causes limitation to carbon dioxide uptake because of stomatal closure. With greater water deficits, direct inhibition of photosynthesis occurs. In both cases limitation of carbon dioxide fixation results in exposure of chloroplasts to excess excitation energy. Much of this can be dissipated by various photoprotective mechanisms. These include dissipation as heat via carotenoids, photorespiration, CAM idling and, in some species, leaf movements and other morphological features which minimize light absorption. The active oxygen species superoxide and singlet oxygen are produced in chloroplasts by photoreduction of Oxygen and energy transfer from triplet excited chlorophyll to oxygen, respectively. Hydrogen peroxide and hydroxyl radicals can form as a result of the reactions of superoxide. All these species are reactive and potentially damaging, causing lipid peroxidation and inactivation of enzymes. They are normally scavenged by a range of antioxidants and enzymes which are present in the chloroplast and other subcellular compartments. When carbon dioxide fixation is limited by water deficit, the rate of active oxygen formation increases in chloroplasts as excess excitation energy, not dissipated fay the photoprotective mechanisms, is used to form superoxide and singlet oxygen. However, photorespiratory hydrogen peroxide production in peroxisomes decreases. Increased superoxide can be detected by EPR (electron paramagnetic resonance) in chloroplasts from droughted plants. Stiperoxide formation leads to changes suggestive of oxidative damage including lipid peroxidation and a decrease in ascorbate. These changes are not, however, apparent until severe water deficits develop, and they could also be interpreted as secondary effects of water deficit-induced senescence or wounding. Non-lethal water deficits often result in increased activity of superoxide dismutase, glutathione reductase and monodehydroascorbate reductase. Increased capacity of these protective enzymes may be part of a general antioxidative response in plants involving regulation of protein synthesis or gene expression. Since the capacity of these enzymes is also increased by other treatments which cause oxidative damage, and which alter the balance between excitation energy input and carbon dioxide fixation such as low temperature and high irradiance, it is suggested that water deficit has the same effect. Light levels that are not normally excessive do become excessive and photoprotective/antioxidative systems are activated. Some of the photoprotective mechanisms themselves could result in active oxygen formation. Photoinhibitory damage also includes a component of oxidative damage. During normally-encountered degrees of water deficit the capacity of the antioxidant systems and their ability to respond to increased active oxygen generation may be sufficient to prevent overt expression of damage. Desiccation-tolerant tissues such as bryophytes, lichens, spores, seeds, some algae and a few vascular plant leaves can survive desiccation to below 30-40% RWC, A component of desiccation damage in seeds and bacteria is oxygen-dependent. Desiccation causes oxidation of glutathione, a major antioxidant, and appearance of a free radical signal detected by EPR in a number of tissues suggesting that oxidative damage has occurred. In photosynthetic cells damage may arise from photooxidation. Disruption of membrane-bound electron tranport systems in partially hydrated tissue could lead to reduction of oxygen to superoxide. Oxidation of lipids and sulphydryl groups may also occur in dry tissue. Tolerant cells recover upon rehydration and arc able to reduce their glutathione pool. Non-tolerant species go on to show further oxidative damage including lipid peroxidation. It is difficult to attribute this subsequent damage to the cause or effect of death. Embryos in seeds lose desiccation tolerance soon after imbibition. This is associated with membrane damage that has been attributed to superoxide-mediated deesterification of phospholipids and loss of lipophilic antioxidants. These effects are discussed in relation to other mechanisms involved in desiccation tolerance. Contents Summary 27 I. Introduction 28 II. Generation of active oxygen and defence mechanisms in plant cells 29 III. The effect of water deficit on photosynthesis 31 IV. Mechanisms for active oxygen generation during water deficit 36 V. Evidence for oxidative damage during water deficit 39 VI. Desiccation 47 VII. Conclusions 52 Acknowledgements 53 References 53.

John Bowlby and attachment theory

Abstract: Part I: Origins Chapter Introduction Biographical Maternal Deprivation Part II: Attachment Theory Attachment, Anxiety, Internal Working Models Loss, Anger and Grief Attachment Theory and Personality Development: The Research Evidence Part III: Implications Bowlby and the Inner World: Attachment Theory and Psychoanalysis Attachment Theory and the Practice of Psychotherapy Attachment Theory and Psychiatric Disorder Attachment Theory and Society Epilogue

The genetics of metal tolerance in vascular plants.

Abstract: SUMMARY In many parts of the world soils are detrimental to plant growth owing to elevated levels of metal ions, caused either by natural processes or by the result of man's activities. Many plants have evolved ecotypes or varieties that are able to grow more-or-less normally on these soils. This paper reviews our knowledge of the genetics of this phenomenon. The nature of tolerance and the problems of its measurement are discussed. Tolerance is frequently measured by an index produced by comparing growth in a contaminated environment with growth in a control environment. It is argued that this measurement is inappropriate for many genetical studies, and that it is frequently more useful to use growth at a single critical level of metal as a measure of tolerance. Polygenic inheritance provides a null hypothesis that has to be tested in a genetical analysis. Examples of major genes for tolerance to aluminium, arsenic, boron, cadmium, copper and manganese are discussed. Even where major genes have been demonstrated, it is probable that other minor genes, ‘modifiers’, are present as well. Because of the nature of tolerance as a character, dominance and epistasis are likely to vary with the level of metal at which an analysis is performed. Tolerance is generally found to be dominant at some levels of the metal. Studies which have mapped tolerance genes, particularly to aluminium and salt, are discussed. The specificity of tolerance is a matter of some confusion. Some studies indicate that tolerances evolve independently to different metals, but others have suggested that tolerance to one metal may often confer a degree of tolerance to some other metals. Very little is known about the molecular genetics of tolerance, and the mechanisms of tolerance to most metals. The possible role of phytochelatins and metallothionein-like proteins in metal tolerance is discussed. The distribution of tolerance in natural populations suggests that tolerance is a disadvantage in uncontaminated environments, but how this ‘cost’ arises is not known. There is some evidence that the disadvantage to tolerance may be associated more with the modifiers of tolerance than with the primary tolerance gene. The study of the genetics of tolerance is of importance in planning breeding programmes to produce tolerant crops for use in areas where metal contamination is a limiting factor in productivity. It can also assist in understanding the mechanisms of tolerance, as exemplified by the study of the mechanism of arsenic tolerance in Holcus lanatus. Important areas for further research are discussed.

Influence of the Earth's inner core on geomagnetic fluctuations and reversals

Abstract: IN view of its relatively small size (one-third the radius of the outer core), many geodynamo models neglect the inner core entirely1, or otherwise treat it as a non-conducting insulator2,3. In a previous steady-state model4, we considered some effects of a finitely conducting inner core, in particular the resulting electromagnetic coupling between inner and outer core. Here we include a prescribed buoyancy force, which is geophysically more realistic, and also yields time-dependent rather than time-independent solutions. The field in the finitely conducting inner core does not then adjust instantaneously to the field in the outer core, but has a diffusive timescale of its own of a few thousand years. Rather large, rapid fluctuations in the outer core are then effectively averaged out by the inner core, producing a relatively stable external dipole field. We speculate that a geomagnetic reversal could only occur as a result of a particularly large fluctuation, large enough and lasting long enough to reverse the field throughout the inner core as well.

Imperfect mimicry: a pigeon’s perspective

Abstract: Despite the dearth of field-based evidence from natural model-mimic communities, theory suggests that Batesian mimicry should have limits placed upon the model:mimic ratio for mimics to benefit. Paradoxically, hoverflies that are apparently mimics are often superabundant, many times more abundant than their supposed models. One possible solution to this paradox is that perhaps they are not mimics at all. We use discriminative operant conditioning methods to measure the similarity perceived by pigeons between wasps and various species of supposedly mimetic hoverflies, and an image processing technique to measure objective similarity. We demonstrate that pigeons rank mimics according to their similarity to a wasp model, in an orderly broadly similar to our own intuitive rankings. Thus pigeons behave as if many hoverflies are indeed wasp mimics. However, they rank the two commonest hoverflies as very similar to wasps, despite these looking decidedly poor mimics to the human eye. In these species, ‘poor’ mimicry may have been sustainable because it exploits some constraint in birds’ visual or learning mechanisms, or some key feature used in pattern recognition. Furthermore, the relation between similarity and mimicry is nonlinear: small changes in similarity can lead to dramatic increases in the degree of mimicry.

Factors Affecting the Formation of Audit Committees in Major UK Listed Companies

Abstract: This research investigates the proposition that there are differences between companies which have voluntarily formed audit committees and those which have not. The results of univariate and multivariate tests reveal statistically significant differences between the two groups for variables representing: (i) agency costs of equity, (ii) agency costs of debt, and (iii) director pressure to reduce information asymmetries.

Abdominal fat deposition in 11-year-old children

Abstract: Although the metabolic complications accompanying visceral deposition of fat are well-established, the onset and extent of such fat patterning in children has not been fully documented. This has been due to the problem of computerized tomography exposing children to a prohibitive radiation risk. Nuclear magnetic resonance imaging (MRI) has provided a feasible alternative. Specifically, the purposes of this study were to use MRI (i) to assess the extent of intra-abdominal (IA) and subcutaneous abdominal (SA) fat deposition in 11-year-old boys and girls, and (ii) to identify the most useful anthropometric indicators of IA adiposity in children. Twenty-five boys and 25 girls were selected to represent, by quintiles, the body mass index range for their age. IA fat, SA fat, and total cross-sectional areas were measured from an MRI scan at the umbilicus. Body density was assessed by hydrostatic weighing, and skinfold thicknesses, circumferences and related ratios, and stage of sexual maturity were measured. Results showed that a wide variation in IA fat deposition was present with amounts ranging from 6 to 58 cm2 (mean = 17.8 +/- 10.0) for boys and 15 to 50 cm2 (mean = 24.8 +/- 8.8) for girls. Percentage of cross-sectional area taken up by visceral fat appears to be less than in normal weight adults. Fourteen children had intra-abdominal/subcutaneous abdominal fat ratios that have been associated with higher health risk in obese adults. Waist-hip circumference ratio (WHR), which is widely used as an indicator of IA deposition in adults, was not a useful predictor in these children.(ABSTRACT TRUNCATED AT 250 WORDS)

Confidence Intervals for the Mean of a Poisson Distribution: A Review

Abstract: The paper provides a comprehensive review of methodology for setting confidence intervals for the parameter of a Poisson distribution. The results are illustrated by a numerical example.

Death from cancer at home: the carers' perspective.

Abstract: OBJECTIVES--To collect information from principal carers of people who had died at home with cancer; to identify areas of support which need improvement. DESIGN--Semistructured interviews with carers two to four months after the death. SETTING--38 general practices in the Exeter, Torbay, and Plymouth health districts. SUBJECTS--207 carers. MAIN OUTCOME MEASURES--Services received by carers and quality of support. RESULTS--161 of 207 patients were aged 60 or over. 88 carers were aged under 60, 110 were 60-80, and 9 were > 80. Carers had difficulty in getting urgent professional help in only 15 out of 177 cases. 124 carers were not given advice on financial help and 174 were not told of support available from local charities. Although pain was well controlled, 25% of patients had no relief of other symptoms. Overall, 150 carers considered the support excellent, 45 good, 8 moderate, 2 poor, and 2 had no comment. CONCLUSIONS--Although care has improved in recent years, health professionals need to give carers more advice about help available outside health services. Domestic help was often needed earlier. Better appreciation of carers9 problems is needed.

The role of the plasmalemma in metal tolerance in angiosperms

Abstract: Evidence for the role of the plasmalemma in metal tolerance of metal resistant ecotypes, cultivars and clones is presented. A range of tolerance mechanisms involving the plasmalemma are discussed including alterations to protein carrier and channel function and synthesis, efflux pumps and maintenance of plasmalemma integrity. Specific examples of such alterations from the literature on Al, As and Cu tolerance, where the plasmalemma has been shown to have a role in tolerance are considered. Tolerance by alterations to plasmalemma function in tolerant ecotypes may also rely on internal metal detoxification mechanisms constitutive in tolerant and non-tolerant plants.

H2* defect in crystalline silicon.

Abstract: Detailed infrared studies have been carried out on proton- and deuteron-implanted Si. A dominant trigonal defect involving a pair of inequivalent hydrogen atoms has been identified, with local modes at 2061.5, 1838.3, 1599.1, and 817.2 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. The structure, the local modes, and the isotopic shifts of the ${\mathrm{H}}_{2}^{\mathrm{*}}$ defect have been calculated using ab initio pseudopotential cluster theory. The structure is consistent with channeling and uniaxial stress experiments. The calculated frequencies and isotopic shifts are in close agreement with those observed.

Temporal variability in the impact of river regulation on thermal regime and some biological implications

Abstract: SUMMARY 1 Ten years of hourly water temperature data for three river sites in south-west England were used to investigate the longer-term thermal effects of river regulation The impact of reservoir impoundment on downstream invertebrate and trout development were simulated using daily mean temperature data in conjunction with published biological models 2 The main effects of regulation on water temperature were to increase the mean value, eliminate freezing conditions, depress summer maxima, delay the annual cycle and reduce diel fluctuation These impacts persisted over a distance of at least 5km below the dam but declined downstream, especially for seasonal and diurnal variations 3 Simulations suggested that regulation is likely to have had a greater impact on the development of brown trout (Salmo trutta) than on the development of one Ephemeroptera and four Plecoptera species Trout fry were predicted to emerge up to 57 days earlier, and to weigh up to 67% more by the end of the year following swim-up, in the regulated compared with the unregulated river 4 Marked inter-annual contrasts in the physical and biological consequences of impoundment were evident, indicating that long-term studies are required to define properly the effects of river regulation

The dynamics of intestinal helminth communities in eels Anguilla anguilla in a small stream: long-term changes in richness and structure

Abstract: The prediction that species richness and diversity of intestinal helminth communities in eels would change over time in response to habitat changes was tested over a period of 13 years in a small stream subjected to extensive human management. Nearly all measures of helminth community structure adopted indicated a decline in richness and diversity over the first 6 years followed by a recovery over the last few years to levels unexpectedly close to those at the start of the investigation. Changes in total number of species suggested that the component community was far richer (from 3–9 species) at the end of the period. By contrast, changes in diversity and dominance measures revealed less variation than expected and suggested that there was an underlying stability of community structure characterized by high dominance by a single species, although the identity of this changed, low diversity and a large proportion of the eel population harbouring 0 or only 1 species. A similar pattern of changes was recorded in the infra-communities, where values of species richness and diversity were very similar at the commencement and termination of the study. It appeared that those helminths that colonized in the recovery period contributed to community richness but had little impact on community structure. The helminth communities clearly did change in response to habitat changes, and the evidence for a fixed number of niches and an underlying constancy in helminth community structure in eels is evaluated.

Urbanization and human health

Abstract: Urbanization involves a physical change in which increasing proportions of populations live in urban settings, however defined. It also implies considerable changes in the ways in which these people live, how they earn their livelihoods, the food which they eat, and the wide range of environmental factors to which they are exposed. There is another underlying assumption that, increasingly, urban populations will be more healthy than their rural counterparts and that higher levels of urbanization will equate with better health status. This paper discusses some of the assumptions underlying this contention. It takes issue with certain of them, particularly the assumption that urbanization affects the health of all residents equally. It is manifestly evident that in many cities, particularly in the developing world, the poor are exposed to greater risks and have much lower health status than their richer neighbours. In addition, whilst urban residents may theoretically have a better access to health care and services than do residents in many rural areas, and whilst many indicators of health do appear better in more highly urbanized societies than ones less so, there are caveats. The paper introduces the concept of epidemiological transition, which suggests that, whilst life expectancy might be higher in many urbanized countries and in certain cities, the inhabitants are often merely suffering from different forms of ill-health, often chronic or degenerative, rather than infective. In certain cities in middle-income countries, residents, particularly the poor, are exposed to a double risk of both infection and chronic degenerative ailments. The paper concludes with a consideration of more general recent statements from the World Health Organization among others, on the impact of urbanization on health. The 'Healthy Cities' project is also discussed. WHO identifies a range of general determinants of urban health: physical, social, cultural and environmental. Many represent the by-products of modernization and especially industrialization. It is emphasized that urbanization, and the concentration of human beings into new areas in particular, can bring exposure to new risk factors for large numbers of people. The growth of infectious and parasitic disease in some urban settings must therefore be recognized, as must the emergence of chronic diseases, with the concomitant need for investment in new types of health and social care. However, a number of constraints militate against the achievement of improved urban health, especially in developing countries.(ABSTRACT TRUNCATED AT 400 WORDS)

Development of the biocatalytic resolution of 2-azabicyclo[2.2.1]hept-5-en-3-one as an entry to single-enantiomer carbocyclic nucleosides

Abstract: For the resolution of the bicyclic lactam 2-azabicyclo[2.2.1]hept-5-en-3-one, efficient whole cell biocatalysts have been identified and from these, enzymes (lactamases) have been isolated. While the two enzymes obtained act on different enantiomers of the lactam, either can be used in scaleable processes to obtain synthons for carbocyclic nucleosides having the natural configuration.

Optimal layout of tree networks using genetic algorithms

Abstract: Two alternative Genetic Algorithm methods for the optimal selection of the layout and connectivity of a dendritic pipe network are presented and compared. Both methods assume that the layout is selected from a directed base graph defining all feasible arcs. The first method uses a conventional binary string to represent the network layout, with the second method using a more efficient integer representation. Comparison with an exact Dynamic Programming formulation is made. The Genetic Algorithm techniques are shown to be very effective search procedures for the class of network optimization problem investigated.

Soil hydrophobicity effects on rainsplash: Simulated rainfall and photographic evidence

Abstract: Laboratory rainfall simulation experiments indicate greater splash losses for hydrophobic (water repellent) than for wettable sandy loam soils at different rainfall intensities, durations and soil surface inclinations. Using synchronized video cameras with different shutter speeds and stroboscopically illuminated 35 mm still photography, differences in splash droplets and ejection trajectory characteristics are examined. For hydrophobic soil, raindrop impact gives rise to fewer, larger, slower-moving daughter ejection droplets which carry more sediment and hence follow shorter range trajectories compared with wettable soil. Implications for erosion of hydrophobic soils are discussed.

Participation in community sports centres: motives and predictors of enjoyment.

Abstract: Research into why people engage in sport and physical recreation has received relatively little attention in both recreation planning and sport psychology. Although there has been a steady flow of North American literature related to participation motivation in competitive youth sport settings, such evidence is of limited value in explaining adult involvement in sport and recreation in Britain. The purpose of this exploratory study was to determine why people participate in sport and exercise in community sports centres and to identify whether these motives predict sport enjoyment. The study was based on a questionnaire‐interview of approximately 5 min duration conducted in six community sports centres in Leicester. The sample comprised 336 respondents aged 16 years and over. The subjects were presented with 15 motives for sports participation and indicated their degree of agreement on a 5‐point scale. The three most commonly endorsed motives were to maintain health, develop physical fitness and aid relax...

The genetics of malignant hyperthermia.

Abstract: Malignant hyperthermia susceptibility remains the commonest cause of death owing to general anaesthesia. This is despite the availability of presymptomatic testing, admittedly by a highly invasive method, and a recognised treatment for implementation immediately a patient shows signs of developing a crisis. Recently the finding of linkage to markers from chromosome 19q13.1-13.2 and the identification of mutations in a candidate gene held out hope of genetic diagnosis being available. However, it is likely that only about 50% of families have a mutation of the skeletal muscle calcium release channel gene. With this degree of genetic heterogeneity, presymptomatic testing based on DNA markers can only be offered at present to a limited number of families where linkage to markers from 19q13.1-13.2 has been clearly shown.

Maximum local helminth parasite community richness in British freshwater fish: a test of the colonization time hypothesis.

Abstract: The investigation of Price & Clancy (1983), which demonstrated a significant positive correlation between total helminth species number per host species and geographical range of freshwater fish host species in Britain, was re-examined using a different measure of parasite species richness. Re-calculation of the correlations between the two parameters after controlling for the effect of the composition of the list of fish by excluding, on biological and distributional grounds, 2 species of agnathans and 7 species of introduced teleosts, and for the effect of sampling effort by using helminth richness in the richest component community of each fish species rather than check-list data, reveals no significant relationship between helminth species richness and host range. Habitat and an omnivorous host diet now appear more significant determinants of helminth richness than the accumulation of parasites by predation. The findings provide little support for the interpretation of the relationship between helminth species richness and host range in terms of island biogeographic theory, but do support an alternative explanation in terms of the colonization time hypothesis, i.e. that helminth species richness is related to the time since the fish host arrived in Britain.

Enzyme-catalysed carbon–carbon bond formation: use of transketolase from Escherichia coli

Abstract: Transketolase has been obtained in greater quantities from an over-expressed E. coli transformant carrying the transketolase gene. Crude extracts of this organism are suitable for use in small scale biotransformations to provide mmol quantities of product. Initial results indicate that the transketolase from E. coli is relatively non-specific for the aldehyde component of the reaction.

Assessment of children's physical self-perceptions

Abstract: Two studies are reported on the use of Fox and Corbin's (1989) Physical Self-Perception Profile (PSPP) modified for use with children (PSPP-C). The current studies used British children of 12 and 15 years of age. Study I found that after factor analysis the proposed four subdomains of physical self-worth (sport competence, body attractiveness, perceived strength and physical condition) were not clearly represented, although some similarities emerged. However, the subscales showed adequate internal reliability for the younger sample, but less so for the adolescents, and no association with a measure of social desirability was found. Correlations between subdomains and a measure of physical self-worth (PSW) were moderate and similar to those reported in other research with American children. Finally, a small group of 12 year-old boys took part in Study II. They completed the PSPP-C and also performed an endurance run task. Performance was associated with scores on sport competence, physical conditi...