Showing papers by "University of Hertfordshire published in 1999"

Water stress inhibits plant photosynthesis by decreasing coupling factor and ATP

Abstract: Water stress substantially alters plant metabolism, decreasing plant growth and photosynthesis1,2,3,4 and profoundly affecting ecosystems and agriculture, and thus human societies5 There is controversy over the mechanisms by which stress decreases photosynthetic assimilation of CO2 Two principal effects are invoked2,4: restricted diffusion of CO2 into the leaf, caused by stomatal closure6,7,8, and inhibition of CO2 metabolism9,10,11 Here we show, in leaves of sunflower (Helianthus annuus L), that stress decreases CO2 assimilation more than it slows O2 evolution, and that the effects are not reversed by high concentrations of CO212,13 Stress decreases the amounts of ATP9,11 and ribulose bisphosphate found in the leaves, correlating with reduced CO2 assimilation11, but the amount and activity of ribulose bisphosphate carboxylase-oxygenase (Rubisco) do not correlate We show that ATP-synthase (coupling factor) decreases with stress and conclude that photosynthetic assimilation of CO2 by stressed leaves is not limited by CO2 diffusion but by inhibition of ribulose biphosphate synthesis, related to lower ATP content resulting from loss of ATP synthase

Dual pathways for regulation of root branching by nitrate.

Abstract: Root development is extremely sensitive to variations in nutrient supply, but the mechanisms are poorly understood. We have investigated the processes by which nitrate (NO3−), depending on its availability and distribution, can have both positive and negative effects on the development and growth of lateral roots. When Arabidopsis roots were exposed to a locally concentrated supply of NO3− there was no increase in lateral root numbers within the NO3−-rich zone, but there was a localized 2-fold increase in the mean rate of lateral root elongation, which was attributable to a corresponding increase in the rate of cell production in the lateral root meristem. Localized applications of other N sources did not stimulate lateral root elongation, consistent with previous evidence that the NO3− ion is acting as a signal rather than a nutrient. The axr4 auxin-resistant mutant was insensitive to the stimulatory effect of NO3−, suggesting an overlap between the NO3− and auxin response pathways. High rates of NO3− supply to the roots had a systemic inhibitory effect on lateral root development that acted specifically at the stage when the laterals had just emerged from the primary root, apparently delaying final activation of the lateral root meristem. A nitrate reductase-deficient mutant showed increased sensitivity to this systemic inhibitory effect, suggesting that tissue NO3− levels may play a role in generating the inhibitory signal. We present a model in which root branching is modulated by opposing signals from the plant’s internal N status and the external supply of NO3−.

Climate change and trophic interactions.

Abstract: With confirmation of anthropogenically induced climate change, the spotlight is on biologists to predict and detect effects on populations. The complexity of interactions within and between the biotic and abiotic components involved makes this a tough challenge, and most studies have consequently considered effects of only single climate variables on single species. However, some have gone further, and recently published long-term datasets now offer opportunities that complement new experimental approaches that span trophic levels. With these datasets, predicting relative shifts in temporal and spatial associations could be among the most tractable problems.

A landscape-scale study of bumble bee foraging range and constancy, using harmonic radar

Abstract: Summary 1. Bumble bees play a vital role in the pollination of many crops and wild flowers, and plans for their conservation require a knowledge of the dynamics and spatial scale of their foraging flights, which are, at present, poorly understood. 2. We investigated the foraging range and constancy of two colonies of bumble bees Bombus terrestris L. on a mixed arable farm using harmonic radar, which has a unique capability to record the trajectories of insects flying at low altitude in the field. 3. Foraging bees were fitted with lightweight radar transponders and tracked as they flew to and from the nest to forage. The resulting tracks gave information on length, direction and straightness of foraging routes. Superimposition onto a map of the foraging landscape allowed interpretation of the bees’ destinations in relation to the spatial distribution of forage. 4. Outward tracks had a mean length of 275·3 ± 18·5 m (n = 65) and a range of 70–631 m, and were often to forage destinations beyond the nearest available forage. Most bees were constant to compass bearing and destination over successive trips, although one bee was tracked apparently switching between forage patches. Both outward and return tracks had a mean straightness ratio of 0·93 ± 0·01 (n = 99). The bees’ ground speeds ranged from 3·0 m s–1 to 15·7 m s–1 (n = 100) in a variety of wind conditions. 5. The results support the hypothesis that bumble bees do not necessarily forage close to their nest, and illustrate that studies on a landscape scale are required if we are to evaluate bee foraging ranges fully with respect to resource availability. Such evaluations are required to underpin assessments of gene flow in bee-pollinated crops and wild flowers. They are also required when making decisions about the management of bees as pollinators and the conservation of bee and plant biodiversity.

Nicotianamine chelates both FeIII and FeII. Implications for metal transport in plants

Abstract: Nicotianamine (NA) occurs in all plants and chelates metal cations, including FeII, but reportedly not FeIII. However, a comparison of the FeII and ZnII affinity constants of NA and various FeIII-chelating aminocarboxylates suggested that NA should chelate FeIII. High-voltage electrophoresis of the FeNA complex formed in the presence of FeIII showed that the complex had a net charge of 0, consistent with the hexadentate chelation of FeIII. Measurement of the affinity constant for FeIII yielded a value of 1020.6, which is greater than that for the association of NA with FeII (1012.8). However, capillary electrophoresis showed that in the presence of FeII and FeIII, NA preferentially chelates FeII, indicating that the FeIINA complex is kinetically stable under aerobic conditions. Furthermore, Fe complexes of NA are relatively poor Fenton reagents, as measured by their ability to mediate H2O2-dependent oxidation of deoxyribose. This suggests that NA will have an important role in scavenging Fe and protecting the cell from oxidative damage. The pH dependence of metal ion chelation by NA and a typical phytosiderophore, 2′-deoxymugineic acid, indicated that although both have the ability to chelate Fe, when both are present, 2′-deoxymugineic acid dominates the chelation process at acidic pH values, whereas NA dominates at alkaline pH values. The consequences for the role of NA in the long-distance transport of metals in the xylem and phloem are discussed.

Cellular Compartmentation of Zinc in Leaves of the Hyperaccumulator Thlaspi caerulescens

Abstract: Cellular compartmentation of Zn in the leaves of the hyperaccumulator Thlaspi caerulescens was investigated using energy-dispersive x-ray microanalysis and single-cell sap extraction. Energy-dispersive x-ray microanalysis of frozen, hydrated leaf tissues showed greatly enhanced Zn accumulation in the epidermis compared with the mesophyll cells. The relative Zn concentration in the epidermal cells correlated linearly with cell length in both young and mature leaves, suggesting that vacuolation of epidermal cells may promote the preferential Zn accumulation. The results from single-cell sap sampling showed that the Zn concentrations in the epidermal vacuolar sap were 5 to 6.5 times higher than those in the mesophyll sap and reached an average of 385 mm in plants with 20,000 μg Zn g−1 dry weight of shoots. Even when the growth medium contained no elevated Zn, preferential Zn accumulation in the epidermal vacuoles was still evident. The concentrations of K, Cl, P, and Ca in the epidermal sap generally decreased with increasing Zn. There was no evidence of association of Zn with either P or S. The present study demonstrates that Zn is sequestered in a soluble form predominantly in the epidermal vacuoles in T. caerulescens leaves and that mesophyll cells are able to tolerate up to at least 60 mm Zn in their sap.

Unsupervised Data Base Clustering Based on Daylight's Fingerprint and Tanimoto Similarity: A Fast and Automated Way To Cluster Small and Large Data Sets

Abstract: One of the most commonly used clustering algorithms within the worldwide pharmaceutical industry is Jarvis−Patrick's (J−P) (Jarvis, R. A. IEEE Trans. Comput. 1973, C-22, 1025−1034). The implementation of J−P under Daylight software, using Daylight's fingerprints and the Tanimoto similarity index, can deal with sets of 100 k molecules in a matter of a few hours. However, the J−P clustering algorithm has several associated problems which make it difficult to cluster large data sets in a consistent and timely manner. The clusters produced are greatly dependent on the choice of the two parameters needed to run J−P clustering, such that this method tends to produce clusters which are either very large and heterogeneous or homogeneous but too small. In any case, J−P always requires time-consuming manual tuning. This paper describes an algorithm which will identify dense clusters where similarity within each cluster reflects the Tanimoto value used for the clustering, and, more importantly, where the cluster cen...

Nitrate and ammonium nutrition of plants: physiological and molecular perspectives

Abstract: Nitrogen is the mineral nutrient that plants need in the greatest quantities and the one that most frequently limits plant growth and crop yields. Most plants get their nitrogen (N) from the soil as either nitrate or ammonium, with some species showing a strong preference for one ionic form over the other. The uptake of nitrate and ammonium ions by roots involves a complex set of membrane transport systems that includes both high- and low-affinity transporters; net uptake rates can also be strongly influenced by the rate at which these ions efflux from root cells. Here we review our current picture of the mechanisms responsible for the uptake and efflux of nitrate and ammonium, attempting to integrate the large body of physiological data with the recent advances in the molecular biology of nitrate and ammonium transporters in bacteria and algae as well as in higher plants. We also review what is known at the physiological and molecular levels about the regulation of the N uptake systems, a process which involves both positive signals from soil nitrate or ammonium and feedback inhibitory signals that are generated by the plant's internal N status

Upregulation of a silent sodium channel after peripheral, but not central, nerve injury in DRG neurons.

Abstract: After transection of their axons within the sciatic nerve, DRG neurons become hyperexcitable. Recent studies have demonstrated the emergence of a rapidly repriming tetrodotoxin (TTX)-sensitive sodium current that may account for this hyperexcitability in axotomized small (<27 microm diam) DRG neurons, but its molecular basis has remained unexplained. It has been shown previously that sciatic nerve transection leads to an upregulation of sodium channel III transcripts, which normally are present at very low levels in DRG neurons, in adult rats. We show here that TTX-sensitive currents in small DRG neurons, after transection of their peripheral axonal projections, reprime more rapidly than those in control neurons throughout a voltage range of -140 to -60 mV, a finding that suggests that these currents are produced by a different sodium channel. After transection of the central axonal projections (dorsal rhizotomy) of these small DRG neurons, in contrast, the repriming kinetics of TTX-sensitive sodium currents remain similar to those of control (uninjured) neurons. We also demonstrate, with two distinct antibodies directed against different regions of the type III sodium channel, that small DRG neurons display increased brain type III immunostaining when studied 7-12 days after transection of their peripheral, but not central, projections. Type III sodium channel immunoreactivity is present within somata and neurites of peripherally axotomized, but not centrally axotomized, neurons studied after <24 h in vitro. Peripherally axotomized DRG neurons in situ also exhibit enhanced type III staining compared with control neurons, including an accumulation of type III sodium channels in the distal portion of the ligated and transected sciatic nerve, but these changes are not seen in centrally axotomized neurons. These observations are consistent with a contribution of type III sodium channels to the rapidly repriming sodium currents observed in peripherally axotomized DRG neurons and suggest that type III channels may at least partially account for the hyperexcitibility of these neurons after injury.

Association of circulating TNF‐α and IL‐6 with ageing and parkinsonism

Abstract: Introduction - We propose that the increase in TNF-α and IL-6 in the brain in idiopathic parkinsonism is in response to a peripheral immune/ inflammatory process, so ubiquitous as to be responsible for the resemblance between ageing and parkinsonism. Methods - Circulating cytokine was measured in 78 subjects with idiopathic parkinsonism and 140 without, aged 30 to 90 years, all obeying inclusion/exclusion criteria. Results - Serum TNF-α increased (P 10 years of ageing (28(-3, 69)%), but was not immediately related to between-subject differences in performance. Conclusion -Ageing and pathogenetic insult may be confounded, age being a progression, not a risk, factor.

The Knowledge Bases of the Expert Teacher

Abstract: In the late twentieth century, accountability and value for money are two of the major themes influencing developments in education. Reflecting these themes, recent government legislation has produced a set of teaching competences, later revised as standards, for use in initial teacher education and assessment of teaching performance. They are used as criteria for teacher training, in some cases forming the theoretical underpinning of courses. This article argues that that model of knowledge essential for teaching presented by the 10197 standards is impoverished. Instead there will be presented a comprehensive model of knowledge bases for teaching, which can inform our understanding of teaching and provide a more sophisticated theoretical underpinning than that imposed by government legislation. The model was developed through a recent doctoral study of subject knowledge and teaching competences. The model is illustrated by an example of teaching in history, which shows how it can act as a theore...

The Editors and Authors of Economics Journals: a Case of Institutional Oligopoly?

Abstract: This paper examines data on the institutional backgrounds of editors and authors of the top 30 economics journals, identified by their 1995 citation impact. It is revealed, for example, that 70.8% of the journal editors were located in the United States, and twelve U.S. universities accounted for the location of more than 38.9%. Concerning journal article authors, 65.7% were located in U.S. institutions and twelve U.S. universities accounted for 21.8%. Arguably, the degree of institutional and geographical concentration of editors and authors may be unhealthy for innovative research in economics. The number of academic journals in economics is large and increasing rapidly. The Judge Institute (1994) compiled a list of no less than 1,431 journals in management and social science, a large proportion of which were devoted to economic issues.2 Given this rapidly growing abundance of titles, more and more attention is being devoted to the identification of, and greater relative status bestowed upon, the top 30 or 'core' journals in the subject. It is likely that the explosion in the number ofjournals will lead to much higher relative prestige being bestowed on work published in the perceive 'core'. Accordingly, questions of institutional affiliation and control relating to these 'core' journals are of major and increasing importance. A list of the 30 most visible and well-known economics journals is compiled here. It is shown that a large number of the editors and authors related to these journals come from a few, predominantly U.S.-based, academic institutions. Although the degree of institutional concentration revealed here may be surprising, some might wish to attempt to explain this phenomenon by supposing that

Strategic pooling of compounds for high-throughput screening.

Abstract: Bringing new medicines to the market depends on the rapid discovery of new and effective drugs, often initiated through the biological testing of many thousands of compounds in high-throughput screening (HTS). Mixing compounds together into pools for screening is one way to accelerate this process and reduce costs. This paper contains both theoretical and experimental data which suggest that careful selection of compounds to be pooled together is necessary in order to reduce the risk of reactivity between compounds within the pools.

Changes in soil chemistry accompanying acidification over more than 100 years under woodland and grass at Rothamsted Experimental Station, UK

Abstract: Summary We have examined the effect that acid deposition and other sources of acidity have had over the last 110–140 years on soil under woodland (Broadbalk and Geescroft Wildernesses) and grassland (Park Grass) comprising some of the Classical Experiments at Rothamsted Experimental Station. Changes in soil chemistry have been followed by analysing some of the unique archive of stored samples for pH, water-soluble and exchangeable base cations, aluminium, iron and manganese, exchangeable acidity, cation exchange capacity (CEC) and soluble anions. Proton balances and historical data show the importance of acid deposition to acidification and concomitant changes in the chemistry of the soil. The pH of the surface soil of Geescroft Wilderness has fallen from 6.2 to 3.8 since 1883. The decrease in the pH of the unlimed, unfertilized plot on Park Grass was less over a similar period (from pH 5.2 to 4.2), illustrating the significant effect of the woodland canopy on the interception of acidifying pollutants. The effect of increasing acidity on the soil chemistry of Geescroft Wilderness is seen in its decreasing base saturation and CEC, with base cations moving down the soil profile. Clay minerals are being irreversibly weathered, and Mn and Al progressively mobilized, so that today Al occupies 70% of the exchange complex in the surface soil. Even with present reductions in sulphur deposition critical loads for sulphur, nitrogen and acidity are still exceeded. Such semi-natural ecosystems are unsustainable under the current climate of pollution.

Use of molecular and isotopic techniques to monitor the response of autotrophic ammonia-oxidizing populations of the β subdivision of the class Proteobacteria in arable soils to nitrogen fertilizer

Abstract: This study examined the effects of NH4NO3 fertilizer on the size and activity of nitrifying, autotrophic, ammonia-oxidizing populations of the β subdivision of the class Proteobacteria in arable soils. Plots under different long-term fertilizer regimes were sampled before and after NH4NO3 additions, and the rates of nitrification were determined by 15N isotopic pool dilution assays. Ammonia-oxidizing populations in the plots were quantified by competitive PCR assays based on the amoA and ribosomal 16S genes. Prior to fertilizer addition, ammonium concentrations and nitrification rates in the plots were comparatively low; ammonia-oxidizing populations were present at 104 to 105 gene copies g of soil−1. Three days after the application of fertilizer, nitrification rates had risen considerably but the size of the ammonia-oxidizing population was unchanged. Six weeks after fertilizer treatment, ammonium concentrations and nitrification rates had fallen while the ammonia-oxidizing populations in plots receiving fertilizer had increased. The rapidity of the rise in nitrification rates observed after 3 days suggests that it results from phenotypic changes in the ammonia-oxidizing bacterial population. Associated increases in population sizes were only observed after 6 weeks and did not correlate directly with nitrifying activity. Phylogenetic analyses of PCR products from one of the plots revealed a population dominated by Nitrosospira-type organisms, similar to those prevalent in other soils.

Erp1p and Erp2p, partners for Emp24p and Erv25p in a yeast p24 complex.

Abstract: Six new members of the yeast p24 family have been identified and characterized. These six genes, named ERP1–ERP6 (for Emp24p- and Erv25p-related proteins) are not essential, but deletion of ERP1 or ERP2 causes defects in the transport of Gas1p, in the retention of BiP, and deletion of ERP1 results in the suppression of a temperature-sensitive mutation in SEC13 encoding a COPII vesicle coat protein. These phenotypes are similar to those caused by deletion of EMP24 or ERV25, two previously identified genes that encode related p24 proteins. Genetic and biochemical studies demonstrate that Erp1p and Erp2p function in a heteromeric complex with Emp24p and Erv25p.

The amino terminus of receptor activity modifying proteins is a critical determinant of glycosylation state and ligand binding of calcitonin receptor-like receptor.

Abstract: The calcitonin receptor-like receptor (CRLR) can function as either a receptor for calcitonin gene-related peptide (CGRP) or for adrenomedullin (ADM), depending upon the coexpression of a novel family of single transmembrane proteins, which we have called receptor activity modifying proteins or RAMPs. RAMPs 1, 2, and 3 transport CRLR to the plasma membrane with similar efficiencies, however RAMP1 presents CRLR as a terminally glycosylated, mature glycoprotein and a CGRP receptor, whereas RAMPs 2 and 3 present CRLR as an immature, core glycosylated ADM receptor. Characterization of the RAMP2/CRLR and RAMP3/CRLR receptors in HEK293T cells by radioligand binding (125I-ADM as radioligand), functional assay (cAMP measurement), or biochemical analysis (SDS-polyacrylamide gel electrophoresis) revealed them to be indistinguishable, even though RAMPs 2 and 3 share only 30% identity. Chimeric proteins were created with the transmembrane and cytosolic portions of RAMP1 associated with the amino terminus of RAMP2 (RAMP2/1) and vice versa (RAMP1/2). Coexpression of RAMP2/1 with CRLR formed a core glycosylated ADM receptor, whereas the RAMP1/2 chimera generated both core glycosylated and mature forms of CRLR and enabled both ADM and CGRP receptor binding. Hence, the glycosylation state of CRLR appears to correlate with its pharmacology.

The evolution of barred spiral galaxies in the Hubble Deep Fields North and South

Abstract: The frequency of barred spiral galaxies as a function of redshift contains important information on the gravitational influence of stellar disks in their dark matter halos and also may distinguish between contemporary theories for the origin of galactic bulges. In this paper we present a new quantitative method for determining the strength of barred spiral structure, and verify its robustness to redshift-dependent effects. By combining galaxy samples from the Hubble Deep Field North with newly available data from the Hubble Deep Field South, we are able to define a statistical sample of 18 objectively-defined low-inclination barred spiral systems with $I_{814W}<23.2$ mag. Analysing the proportion of barred spiral galaxies seen as a function of redshift, we find a significant decline in the barred fraction beyond redshifts $z\simeq 0.5$. The physical significance of this effect remains unclear, but several possibilities include dynamically hotter (or increasingly dark-matter dominated) high-redshift discs, or an enhanced efficiency in bar destruction at high redshifts. By investigating the formation of the ``orthogonal'' axis of Hubble's classification tuning fork, our result complements studies of evolution in the early--late sequence, and pushes to later epochs the redshift at which the Hubble classification sequence is observed to be in place.

A Meta-analytic Review of Wisconsin Card Sort Studies in Schizophrenia: General Intellectual Deficit in Disguise?

Abstract: A majority of studies show that schizophrenics perform poorly on so-called tests of executive or frontal lobe function‐ the paradigmatic case being the Wisconsin Card Sort Test (WCST). Nevertheless, the specific character of this deficit in schizophrenia remains underspecified. In particular, it seems premature to assume that schizophrenia is characterised by an executive dysfunction and/or a disorder of frontal lobe function before determining whether any deficit is: selective; disproportionate to the general level of intellectual functioning; or qualitatively comparable with that of frontal lobe patients. A meta-analysis was conducted on 29 studies comparing the performance of schizophrenics and normal controls on the WCST. This showed that the mean weighted effect size was large for categories achieved (d= 0.91), medium for absolute level of perseveration (d= 0.53), but only small for the proportion of perseverative errors (d= 0.18). By contrast, the effect size for Wechsler Adult Intelligence Scale Intelligence Quotient (WAIS IQ) in a subset of these studies (d= 1.23) was significantly larger than for any WCST measures. This pattern of findings challenges notions that schizophrenia is characterised by an executive dysfunction that is: selective; disproportionate to IQ level; and analogous to that found in frontal lobe patients. Rather, the poor WCST performance of schizophrenics appears to reflect a generalised intellectual deficit.

The effect of magnetic fields on γ-ray bursts inferred from multi-wavelength observations of the burst of 23 January 1999

Abstract: Gamma-ray bursts (GRBs) are thought to arise when an extremely relativistic outflow of particles from a massive explosion (the nature of which is still unclear) interacts with material surrounding the site of the explosion. Observations of the evolving changes in emission at many wavelengths allow us to investigate the origin of the photons, and so potentially determine the nature of the explosion. Here we report the results of γ-ray, optical, infrared, submillimetre, millimetre and radio observations of the burst GRB990123 and its afterglow. Our interpretation of the data indicates that the initial and afterglow emissions are associated with three distinct regions in the fireball. The peak flux of the afterglow, one day after the burst, has a lower frequency than observed for other bursts; this explains the short-lived radio emission. We suggest that the differences between bursts reflect variations in the magnetic-field strength in the afterglow-emitting regions.

Pharmacokinetics of valganciclovir and ganciclovir following multiple oral dosages of valganciclovir in HIV- and CMV-seropositive volunteers.

Abstract: Ganciclovir is commonly used in the treatment of cytomegalovirus (CMV) disease in patients who are immunocompromised and for the prevention of CMV disease in solid organ transplant recipients Owing to limited bioavailability and saturable absorption, the use of oral ganciclovir in CMV retinitis is restricted to maintenance therapy only As induction therapy must be given intravenously, an oral formulation which could be used for induction would offer significant benefits A previous study of valganciclovir, a valyl ester prodrug of ganciclovir showed a 10-fold increase in plasma ganciclovir concentrations compared with the oral formulation However, before studies can be conducted to confirm the utility of oral valganciclovir for the treatment and prevention of CMV disease, a dose must be selected for use in these studies This study was designed to investigate the pharmacokinetics of ganciclovir and valganciclovir The study was an open-label, randomised, 4-way crossover, dose-ranging pharmacokinetic study, conducted in 39 patients who were HIV- and CMV-seropositive The participants were randomised to one of 2 groups: fasted (n = 19) and fed (n = 20) In both groups, participants received 450, 875, 1750 and 2625mg oral valganciclovir once daily for 3 days in a randomised order In the 32 participants who completed the study, valganciclovir was rapidly absorbed and converted into ganciclovir (maximum ganciclovir concentrations occurred after 10 to 175 hours in the fasted group and 15 to 20 hours in the fed group) Systemic exposure to valganciclovir was low [with an area under the concentration-time curve to 24 hours (AUC24) of 13 to 25% that of ganciclovir] The mean plasma concentrations of ganciclovir were dose-related Peak concentrations of ganciclovir were achieved approximately 30 minutes after those for valganciclovir In the fed state, the AUC24 of ganciclovir increased proportionally with dose The mean AUC24 values for ganciclovir were slightly higher following food (24 to 56%) than in the fasted state Based on linear regression of AUC24 values from the fed group, a dose of valganciclovir of 900 mg/day is expected to produce a daily expo sure (AUC24) comparable with an intravenous dose of ganciclovir 5 mg/kg/day These results show that once daily oral valganciclovir can produce exposures of ganciclovir (AUC24) exceeding those attained using intravenous ganciclovir 10 mg/kg This suggests that oral valganciclovir may be suitable in many circumstances currently requiring intravenous ganciclovir, allowing for more convenience in the management of patients with CMV retinitis by utilising a 2 or 4 tablet daily regimen to cover all phases of treatment

Effects of infection time and moisture on development of ear blight and deoxynivalenol production by Fusarium spp. in wheat

Abstract: Summary Wheat ears were inoculated with conidia of Fusarium spp. at different growth stages between ear emergence and harvest and moist conditions were maintained for up to 7 days subsequently by mist irrigation. Of the fungi tested (Fusarium culmorum, F. avenaceum, F. tricinctum, F. sporotrichioides and Microdochium nivale), only F. culmorum produced ear blight symptoms and grain samples were found subsequently to contain deoxynivalenol. Most ear infection and deoxynivalenol formation occurred following inoculation at about mid-anthesis. Small amounts of deoxynivalenol were formed and some F. culmorum was isolated even in the absence of ear blight symptoms. An overnight wet period was sufficient to initiate infection and deoxynivalenol formation but both were increased by extending the wet period up to at least 3 days. Recovery of Fusarium spp. from harvested grain was usually possible whether or not symptoms developed. F. culmorum usually persisted and often increased to moderately high levels after storage for 7 wk in a range of moisture conditions.

Analysis and elucidation of soil variation using wavelets

Abstract: Summary A wavelet is a compact analysing kernel that can be moved over a sequence of data to measure variation locally. There are several families of wavelet, and within any one family wavelets of different lengths and therefore smoothness and their corresponding scaling functions can be assembled into a collection of orthogonal functions. Such an assemblage can then be applied to filter spatial data into a series of independent components at varying scales in a single coherent analysis. The application requires no assumptions other than that of finite variance. The methods have been developed for processing signals and remote imagery in which data are abundant, and they need modification for data from field sampling. The paper describes the theory of wavelets. It introduces the pyramid algorithm for multiresolution analysis and shows how it can be adapted for fairly small sets of transect data such as one might obtain in soil survey. It then illustrates the application using Daubechies’s wavelets to two soil transects, one of gilgai on plain land in Australia and the other across a sedimentary sequence in England. In both examples the technique revealed strongly contrasting local features of the variation that had been lost by averaging in previous analyses and expressed them quantitatively in combinations of both scale and magnitude. Further, the results could be explained as the spatial effects of change in topography or geology underlying the variation in the soil. Analyse et eclairissement sur la variation du sol en utilisant les ondelettes Resume Une ondelette est un noyau compact d’analyse qu’on peut passer sur une sequence de donnees pour quantifier la variation localement. Plusieurs familles d’ondelettes existent. Chaque famille est caracterisee par des fonctions d’echelle de longueurs d’ondes et de degres de lissage differents, le tout constituant un ensemble de fonctions orthogonales. L’application de ces fonctions sur des donnees spatiales est une methode d’analyse unique et coherente qui permet de filtrer des donnees spatiales en identifiant des composantes independentes a differentes echelles. L’application n’exige que l’hypothese d’une variance bornee. Ces methodes ont ete developpees pour le traitement de signaux qui contiennent enormement de donnees comme des images de teledetection. Elles necessitent des modifications avant de les appliquer sur des donnees d’echantillonage provenant du terrain. Cet article decrit la theorie d’ondelettes. Il introduit l’algorithme pyramidal pour une analyse a quelques resolutions. Il montre ensuite comment on peut adapter l’algorithme pour un ensemble de donnees peu nombreuses comme celles qu’on peut obtenir lors d’une prospection du sol sur des transects. Les resultats montrent l’application des ondelettes de Daubechies a deux transects pedologiques, lepremier situe sur une plaine marquee de gilgai en Australie, et le second a travers une sequence de sediments jurassiques en Angleterre. Dans les deux exemples, la technique a revele des contrastes bien marques de certain traits locaux qui ont ete totalement occultes dans des analyses anterieures basees sur le calcul des moyennes. La technique des ondelettes permet aussi une quantification de ces traits locaux, en fonction de l’echelle d’observation et de la magnitude. De plus, ces resultats peuvent etre interpretes par les effets d’une variation spatiale de la topographie ou de la geologie qui sont a l’origine de la variation du sol.