bluuebunny/crossref_metadata_2025 huggingface dataset:
Testicular and Somatic Growth in Siberian Hamsters Depend on the Melatonin‐Free Interval Between Twice Daily Melatonin Signals
Authors: Freeman D. A. , Larkin J. E. , Seliby L.
Published: March 2003

In Siberian hamsters, day length is encoded by the duration of the nocturnal melatonin signal; short and long melatonin signals over the course of several weeks stimulate and inhibit somatic and gonadal development, respectively, in prepubertal males. We sought to determine whether juvenile male Siberian hamsters respond to multiple melatonin signals each day and the manner in which the sequence of melatonin signals and the duration of the melatonin‐free interval between signals affects development. Twenty‐one day old male Siberian hamsters, gestated and maintained in a short‐day photoperiod of 10 h light/day (10 L), were transferred to constant light to suppress endogenous melatonin secretion and received s.c. infusions of melatonin or saline for 12 days. Hamsters infused with saline retained small testes, whereas one short melatonin infusion each day resulted in significant testicular growth. Other hamsters were provided with two melatonin signals each day, one long (9 h) and one short (4 or 5 h); the order in which these signals was administered and the duration of the melatonin‐free interval after each signal varied between groups. In asymmetrical melatonin infusions, the first and second daily infusions were followed by 3‐h and 7‐h melatonin‐free intervals, respectively, whereas in symmetrical infusions, each melatonin signal was followed by a 5‐h melatonin‐free interval. In the asymmetrical sequence, the melatonin signal that immediately preceded the longer melatonin‐free interval determined the rate gonadal growth. Equal melatonin‐free intervals after each of the long and short daily melatonin infusions produced intermediate increases in gonadal and somatic development. The hypothalamic‐pituitary‐gonadal axis of Siberian hamsters can respond to multiple melatonin signals each day, with the rate of testicular growth determined primarily by the duration of the melatonin‐free interval following each infusion.
Water deficits and hydraulic limits to leaf water supply
Authors: Sperry J. S. , Hacke U. G. , Oren R. , Comstock J. P.
Published: March 2003

Many aspects of plant water use – particularly in response to soil drought – may have as their basis the alteration of hydraulic conductance from soil to canopy. The regulation of plant water potential (Ψ) by stomatal control and leaf area adjustment may be necessary to maximize water uptake on the one hand, while avoiding loss of hydraulic contact with the soil water on the other. Modelling the changes in hydraulic conductance with pressure gradients in the continuum allows the prediction of water use as a function of soil environment and plant architectural and xylem traits. Large differences in water use between species can be attributed in part to differences in their ‘hydraulic equipment’ that is presumably optimized for drawing water from a particular temporal and spatial niche in the soil environment. A number of studies have identified hydraulic limits as the cause of partial or complete foliar dieback in response to drought. The interactions between root:shoot ratio, rooting depth, xylem properties, and soil properties in influencing the limits to canopy water supply can be used to predict which combinations should optimize water use in a given circumstance. The hydraulic approach can improve our understanding of the coupling of canopy processes to soil environment, and the adaptive significance of stomatal behaviour.
Arabidopsis thaliana contains two phosphoenolpyruvate carboxylase kinase genes with different expression patterns
Authors: Fontaine V. , Hartwell J. , Jenkins G. I. , Nimmo H. G.
Published: March 2003

We have already reported the cloning of one phosphoenolpyruvate carboxylase kinase gene from Arabidopsis thaliana (Hartwell et al. 1999, Plant Journal 20, 333–342), hereafter termed PPCK1. A second putative phosphoenolpyruvate carboxylase kinase gene (PPCK2) was identified in the Arabidopsis genome. The corresponding cDNA was amplified from flower tissue by reverse transcriptase (RT)‐polymerase chain reaction (PCR). This cDNA was transcribed and translated in vitro. The translation products possessed high phosphoenolpyruvate carboxylase kinase activity, confirming the identity of the PPCK2 gene. The expression of both phosphoenolpyruvate carboxylase kinase genes was examined by RT‐PCR. PPCK1 is mainly expressed in rosette leaves whereas PPCK2 is expressed in flowers and, at a lower level, in roots and cauline leaves. Light increased the expression of PPCK1 in rosette leaves and that of PPCK2 in flowers. The expression of both genes in an Arabidopsis cell culture was increased by treatment with cycloheximide. The data suggest that the two genes may have different roles in tissue‐specific regulation of phosphoenolpyruvate carboxylase.
Body mass patterns of Little Stints at different latitudes during incubation and chick‐rearing
Authors: Tulp Ingrid , Schekkerman Hans , Chylarecki Przemek , Tomkovich Pavel , Soloviev Mikhail , Bruinzeel Leo , Van Dijk Klaas , Hildén Olavi , Hötker Hermann , Kania Wojciech , Van Roomen Marc , Sikora Arkadiusz , Summers Ron
Published: March 2003

Due to the ‘double‐clutch’ mating system found in the arctic‐breeding Little Stint Calidris minuta, each parent cares for a clutch and brood alone. The resulting constraint on feeding time, combined with the cold climate and a small body size, may cause energetic bottlenecks. Based on the notion that mass stores in birds serve as an ‘insurance’ for transient periods of negative energy balance, but entail certain costs as well, body mass may vary in relation to climatic conditions and stage of the breeding cycle. We studied body mass in Little Stints in relation to breeding stage and geographical location, during 17 expeditions to 12 sites in the Eurasian Arctic, ranging from north Norway to north‐east Taimyr. Body mass was higher during incubation than during chick‐rearing. Structural size, as estimated by wing length, increased with latitude. This was probably caused by relatively more females (the larger sex) incubating further north, possibly after leaving a first clutch to be incubated by a male further south. Before and after correction for structural size, body mass was strongly related to latitude during both incubation and chick‐rearing. In analogy to a similar geographical pattern in overwintering shorebirds, we interpret the large energy stores of breeding Little Stints as an insurance against periods of cold weather which are a regular feature of arctic summers. Climate data showed that the risk of encountering cold spells lasting several days increases with latitude over the species’ breeding range, and is larger in June than in July. Maintaining these stores is therefore less necessary at southern sites and during the chick‐rearing period than in the incubation period. When guarding chicks, feeding time is less constrained than during incubation, temperatures tend to be higher than in the incubation period, reducing energy expenditure, and the availability of insect prey reaches a seasonal maximum. However, the alternative interpretation that the chick‐tending period is more energetically stressful than the incubation period, resulting in a negative energy balance for the parent, could not be rejected on the present evidence.
Comparative activity pattern during foraging of four albatross species
Authors: Weimerskirch Henri , Guionnet Tatiana
Published: March 2003

The activity patterns of foraging Yellow‐nosed Diomedea chlororhynchos, Sooty Phoebetria fusca, Black‐browed D. melanophris impavida and Grey‐headed Albatross D. chrysostoma were compared using loggers recording the timing of landing and take‐offs, as well as the duration of bouts in flight or on the water, and the overall time spent in flight. The four species spent a similar proportion of their foraging time in flight (56–65%). During the day they were mostly flying (77–85% of the daylight period) whereas at night they were mainly (61–71%) sitting on the water. The amount of time spent in flight during the daytime foraging period was related to the amount of time spent sitting on the water at night. Differences between species occurred in the duration of bouts in flight and on the water as well as in the frequency of landings and in the time elapsed between successive landings. Yellow‐nosed Albatrosses were more active than the other species, with more frequent short bouts in flight and more frequent successive landings at short intervals. Sooty Albatrosses landed or took‐off less often than the other species and were more active just before dusk. Black‐browed and Grey‐headed Albatrosses were more active at night, especially the first part of the night and far from the colonies. Their trips consisted of a commuting part and a foraging part. Black‐browed Albatrosses landed more often during the foraging than the commuting part, suggesting that they were not searching when travelling. The study suggests that there is no fundamental difference between the overall activity budgets of the four species although they show distinctive diet, morphology and life history traits. The differences observed between the four species were related mainly to differences in foraging technique. Comparison with the Wandering Albatross, the only species for which data were available previously, suggest that this larger species might differ completely in foraging technique from the smaller albatrosses.
Differential post‐fledging survival of great and coal tits in relation to their condition and fledging date
Authors: Naef‐Daenzer Beat , Widmer Fritz , Nuber Maria
Published: March 2003

We present a multivariate model of the post‐fledging survival of juvenile great and coal tits (Parus major L., P. ater L.) in relation to chick body condition and timing of breeding. Radio‐telemetry and colour marks were used to track tit families during 20 days from fledging, that is, the period of post‐fledging dependence. Data on 342 chicks of 68 broods were obtained.

 Forty‐seven per cent of juveniles died during the observation period, predation being the main cause of mortality. In the first 4 days after fledging the mortality rate was 5–10% per day.

 Survival of juveniles was positively correlated with fledging mass. Furthermore, survival strongly decreased during the season. In the second half of June, mortality was five times the rate of mid‐May. The differential survival resulted in selection for both early fledging and high fledging mass. Juvenile condition was less important for survival in birds that had fledged early in the season. Their survival rates exceeded 70% in all weight classes, whereas in late broods only the heaviest individuals survived equally well. The survival of birds fledging both late and in poor condition was below 20%. Thus, selection for high fledging mass was much stronger in the late season than in early broods.

 We conclude that the impact of predation after leaving the nest results in selection for early breeding and, particularly in the late season, for high fledging mass. This may explain why the earliest broods have been found to produce most recruits into the breeding population even if they did not profit from maximum food availability during the nestling period. On the other hand, energetic limitations may constrain the begin of egg laying in adult birds. Thus, counteracting evolutionary responses to the seasonal development of food availability (the caterpillar peak) and to the risk of post‐fledging mortality (the peak in post‐fledging mortality) may have focused the period of optimal reproduction to a narrow time‐window.
Monitoring a marine ecosystem using responses of upper trophic level predators
Authors: Boyd I. L. , Murray A. W. A.
Published: March 2003

This study examined the changing status of the marine ecosystem at the island of South Georgia (Southern Ocean) using up to 27 variables measured over 22 years from three upper trophic level predators that specialize in foraging upon krill (Eupuasia superbaDana). These variables included population size, breeding performance, offspring growth rate, foraging behaviour and diet. A method was developed for reducing these multivariate time‐series to a single vector, called a combined standardized index (CSI).

Sensitivity analyses showed that missing values had a large effect upon the accuracy of the CSI but this effect was reduced if the individual variables were highly correlated. The level of correlation and proportion of missing values within the empirical data set were within the acceptable range. Individual variables had widely varying influence upon the CSI but, in general, those with longer time‐series had the greatest influence.

Principal components analysis showed that variables representing offspring growth tended to explain the greatest proportion of the variability in the CSI and this was followed by variables representing diet.

There were 3 years in which the CSI showed extreme and significantly low values. There was a significant non‐linear functional response (similar to the Holling Type II functional response) between the overall CSI and krill biomass and a similar relationship existed when the CSI was calculated for each species individually.

Separate analysis of variables that were likely to be representative of changing population size showed the presence of a significant decline between 1977 and 1998. There was no trend in the CSI from variables representative of foraging conditions during the summer breeding season. The study has shown that the marine ecosystem at South Georgia shows acute but transient variability that is amplified in the response of upper trophic‐level predators. There is less certainty that trends in populations are a consequence of shifts in the degree to which the ecosystem can support krill‐feeding seals and penguins.
Models of open populations with space‐limited recruitment: extension of theory and application to the barnacle Chthamalus montagui
Authors: Hyder Kieran , Åberg Per , Johnson Mark P. , Hawkins Stephen J.
Published: March 2003

Barnacles are a good model organism for the study of open populations with space‐limited recruitment. These models are applicable to other species with open supply of new individuals and resource limitation. The inclusion of space in models leads to reductions in recruitment with increasing density, and thus predictions of population size and stability are possible.

Despite the potential generality of a demographic theory for open space‐limited populations, the models currently have a narrow empirical base. In this study, a model for an open population with space‐limited recruitment was extended to include size‐specific survival and promotions to any size class. The assumptions of this model were tested using data from a pan‐European study of the barnacle Chthamalus montagui Southward. Two models were constructed: a 6‐month model and a periodic annual model. Predicted equilibria and their stabilities were compared between shores.

Tests of model assumptions supported the extension of the theory to include promotions to any size class. Mortality was found to be size‐specific and density independent. Studied populations were open, with recruitment proportional to free space.

The 6‐month model showed a significant interaction between time and location for equilibrium free space. This may have been due to contrasts in the timing of structuring processes (i.e. creating and filling space) between Mediterranean and Atlantic systems. Integration of the 6‐month models into a periodic annual model removed the differences in equilibrium‐free space between locations.

Model predictions show a remarkable similarity between shores at a European scale. Populations were persistent and all solutions were stable. This reflects the apparent absence of density‐dependent mortality and a high adult survivorship in C. montagui. As populations are intrinsically stable, observations of fluctuations in density are directly attributable to variations in the environmental forcing of recruitment or mortality.
Synchrony and second‐order spatial correlation in host–parasitoid systems
Authors: Bjørnstad Ottar N. , Bascompte Jordi
Published: March 2003

Recent theoretical studies on population synchrony have focused on the role of dispersal, environmental correlation and density dependence in single species. Trophic interactions have received less attention. We explored how trophic interactions affect spatial synchrony.

We considered a host–parasitoid coupled map lattice to understand how the self‐organizing spatial patterns generated by such dynamics affect synchrony. In particular, we calculated the spatial correlation functions (SCF) associated with travelling waves, spatial chaos and crystal lattices.

Travelling waves were associated with cyclic SCF (called second‐order SCF) that differed greatly from those seen in spatial chaos or crystal lattices. Such U‐shaped patterns of spatial synchrony, which have not been predicted by single‐species models, have been reported recently in real data. Thus, the shape of the SCF can provide a test for trophically generated spatiotemporal dynamics.

We also calculated the cross‐correlation function between the parasitoid and the host. Relatively high parasitoid mobility resulted in high within‐patch synchrony of the dynamics of the two species. However, with relatively high host mobility, the parasitoid dynamics began to lag spatially behind those of the host.

We speculated that this spatial lag between the host and parasitoid is the ultimate source of travelling waves, because the spatial cross‐correlation in turn affects host dynamics.

A new method to estimate the spatial cross‐correlation function between two species was developed as an integral part of the study.
Compartmentalization in plant–insect flower visitor webs
Authors: Dicks L. V. , Corbet S. A. , Pywell R. F.
Published: March 2003

Interactions between entomophilous flowering plants and their insect visitors were recorded at two mesotrophic grassland communities in Norfolk, and a diagrammatic quantitative web produced for each community.

The systems were analysed for compartmentalization using the method ofRaffaelli & Hall (1992), based on trophic similarity between pairs of species. Good evidence was found for compartmentalization at both sites.

Ordination of the data was used to suggest how the species fall into compartments. The likelihood that groups of plants and insects implied by this method represent real compartments in the web was assessed quantitatively, using trophic similarity indices, and qualitatively, by consideration of the species involved.

The compartments reflected classic pollination syndromes to some extent, dividing the insect fauna into a group of butterflies and bees, and a group of flies, at both sites. The compartmentalization was also affected by phenology.

Dominant interactions fell within compartments in the web, as might be expected in mutualistic systems.
Aggregation, habitat quality and coexistence: a case study on carrion fly communities in slug cadavers
Authors: Woodcock B. A. , Watt A. D. , Leather S. R.
Published: March 2003

The aggregation model of coexistence for discrete patches of ephemeral resources was tested with Diptera communities in slug cadavers.

Slugs were exposed to the necrophagous fauna present at each of 32 birch woodlands. After 3 days the slugs were removed and emerging adult insects were retained and identified.

Density‐specific aggregation (J), association between species (Cxy) and the necessary and sufficient condition for coexistence (Txy) were used to test the model. Woodlands were ranked on the basis of habitat quality that was defined by the diversity of species associated with each site.

Overall community and species‐specific responses to resource mass were investigated. Results provided evidence for multispecies coexistence by interspecific aggregation, although there was also evidence of alternative mechanisms that promote coexistence.

Differences aggregation and interspecific association were found between high and low quality sites. The implications of these findings are discussed with particular reference to how differences in habitat quality affect aggregation and interspecific association.
Helping does not enhance reproductive success of cooperatively breeding rufous vanga in Madagascar
Authors: Eguchi Kazuhiro , Yamagishi Satoshi , Asai Shigeki , Nagata Hisashi , Hino Teruaki
Published: March 2003

In many studies on cooperative breeding, helping by auxiliary individuals is considered to enhance the reproductive success of breeders. However, confounding factors other than helping could cause the differences.

The endemic Madagascan rufous vangaSchetba rufa(Vangidae) is known as a cooperatively breeding species. In order to evaluate the effect of helping in this species, we compared the reproductive success of breeding pairs helped by auxiliary birds, and pairs breeding alone, based on a 6‐year study of an individually colour‐banded population in the Ampijoroa Forest Station, western Madagascar.

This species is single‐brooded. Brood reduction was rare and most cases of nesting failure were due to total loss of clutches and broods, probably as a result of predation.

Monogamous pairs with one to four auxiliary birds comprised 24–43% of all breeding groups. Most auxiliary birds were male offspring remaining in their natal territory. Auxiliary males provided a considerable contribution towards antipredator defence, territory defence and to the provisioning of nestlings. In about one‐third of the groups, however, the auxiliary males did not help at all. Male offspring may remain in their natal territory in order to avoid harassment by other territorial individuals, and to increase the probability of territory acquisition and of copulation with unrelated breeding females.

The probability of breeding successfully was higher, and the number of fledglings produced was larger among pairs with auxiliary birds than among those breeding alone. However, provisioning by auxiliaries neither enhanced the growth rate of nestlings, nor reduced the number of days they required to fledge.

A pair‐match comparison of the same pairs between years with and without auxiliaries showed no effect of group size on their reproductive success. Even provisioning by auxiliaries did not affect the reproductive success.

Pairs accompanied by auxiliary birds for more than 1 year enjoyed higher reproductive success even in those years when they were without auxiliaries than did pairs always breeding alone.

Neither the simple presence of auxiliaries nor their helping behaviour enhanced the reproductive success of breeding pairs. The quality of the breeding pair and/or their territory may have affected their reproductive success and, as a result, increased the number of auxiliaries.
Glutathione decreases in dopaminergic PC12 cells interfere with the ubiquitin protein degradation pathway: relevance  for Parkinson's disease?
Authors: Jha Nandita , Kumar M. Jyothi , Boonplueang Rapee , Andersen Julie K.
Published: March 2003

Parkinson's disease (PD) is characterized by the presence of proteinaceous neuronal inclusions called Lewy bodies in susceptible dopaminergic midbrain neurons. Inhibition of the ubiquitin‐proteasome protein degradation pathway may contribute to protein build‐up and subsequent cell death. Ubiquitin is normally activated for transfer to substrate proteins by interaction with the E1 ubiquitin ligase enzyme via a thiol ester bond. Parkinson's disease is also characterized by decreases in midbrain levels of total glutathione which could impact on E1 enzyme activity via oxidation of the active site sulfhydryl. We have demonstrated that increasing reductions in total glutathione in dopaminergic PC12 cells results in corresponding decreases in ubiquitin‐protein conjugate levels suggesting that ubiquitination of proteins is inhibited in a glutathione‐dependent fashion. Decreased ubiquitinated protein levels appears to be due to inhibition of E1 activity as demonstrated by reductions in endogenous E1‐ubiquitin conjugate levels as well as decreases in the production of de novo E1‐ubiquitin conjugates when glutathione is depleted. This is a reversible process as E1 activity increases upon glutathione restoration. Our data suggests that decreases in cellular glutathione in dopaminergic cells results in decreased E1 activity and subsequent disruption of the ubiquitin pathway. This may have implications for neuronal degeneration in PD.
Substrate specificity, inhibition and enzymological analysis of recombinant human glutamate carboxypeptidase II
Authors: Barinka Cyril , Rinnová Markéta , Šácha Pavel , Rojas Camilo , Majer Pavel , Slusher Barbara S. , Konvalinka Jan
Published: March 2003

Glutamate carboxypeptidase II (GCPII, EC 3.4.17.21) is a membrane peptidase expressed in a number of tissues such as kidney, prostate and brain. The brain form of GCPII (also known as NAALADase) cleavesN‐acetyl‐aspartyl glutamate to yield free glutamate. Animal model experiments show that inhibition of GCPII prevents neuronal cell death during experimental ischaemia. GCPII thus represents an important target for the treatment of neuronal damage caused by excess glutamate. In this paper we report expression of an extracellular portion of human glutamate carboxypeptidase II (amino acids 44–750) inDrosophilaSchneider's cells and its purification to homogeneity. A novel assay for hydrolytic activity of recombinant human GCPII (rhGCPII), based on fluorimetric detection of released alpha‐amino groups was established, and used for its enzymological characterization. rhGCPII does not show dipeptidylpeptidase IV‐like activity assigned to the native form of the enzyme previously. Using a complete set of protected dipeptides, substrate specificity of rhGCPII was elucidated. In addition to the previously described substrates, four novel compounds, Ac‐Glu‐Met, Ac‐Asp‐Met and, surprisingly, Ac‐Ala‐Glu and Ac‐Ala‐Met were identified as substrates for GCPII, and their respective kinetic constants determined. The glycosylation of rhGCPII was found indispensable for the enzymatic activity.
The production of macrophage inflammatory protein‐2 induced by soluble intercellular adhesion molecule‐1 in mouse astrocytes is mediated by src tyrosine kinases and p42/44 mitogen‐activated protein kinase
Authors: Otto Vivianne I. , Gloor Sergio M. , Frentzel Stefan , Gilli Urs , Ammann Emerita , Hein Andreas E. , Folkers Gerd , Trentz Otmar , Kossmann Thomas , Morganti‐Kossmann Maria C.
Published: March 2003

Severe traumatic brain injury stimulates the release of soluble intercellular adhesion molecule‐1 (sICAM‐1) into CSF. Studies in cultured mouse astrocytes suggest that sICAM‐1 induces the production of macrophage inflammatory protein‐2 (MIP‐2). In the present study, we investigated the underlying mechanisms for MIP‐2 induction. sICAM‐1 induced MIP‐2 in astrocytes lacking membrane‐bound ICAM‐1, indicating that its action is due to heterophilic binding to an undescribed receptor rather than homophilic binding to surface ICAM‐1. Signal transduction may be mediated by src tyrosine kinases, as the src tyrosine kinase inhibitors herbimycin A and PP2 abolished MIP‐2 induction by sICAM‐1. Phosphorylation of p42/44 mitogen‐activated protein kinase (MAPK), but not of p38 MAPK, occurred further downstream, as evidenced by western blot analysis combined with the use of herbimycin A and specific MAPK inhibitors. By contrast, induction of MIP‐2 by tumour necrosis factor‐α (TNF‐α) involved both p42/44 MAPK and p38 MAPK. Following stimulation with either sICAM‐1 or TNF‐α, astrocyte supernatants promoted chemotaxis of human neutrophils and incubation of these supernatants with anti‐MIP‐2 antibodies more efficiently suppressed the migration induced by sICAM‐1 than by TNF‐α. These results show that sICAM‐1 induces the production of biologically active MIP‐2 in astrocytes by heterophilic binding to an undefined receptor and activation of src tyrosine kinases and p42/44 MAPK.
Ceramide activates microglia to enhance the production/secretion of brain‐derived neurotrophic factor (BDNF) without induction of deleterious factors in vitro
Authors: Nakajima Kazuyuki , Tohyama Yoko , Kohsaka Shinichi , Kurihara Tadashi
Published: March 2003

In analyzing the regulation of neurotrophin production/secretion from microglia, C8‐ceramide (d‐erythro‐sphingosine, N‐octanoyl‐) was found to induce secretion of brain‐derived neurotrophic factor (BDNF) from microglia in vitro. In the present study, the action of C8‐ceramide in secreting neurotrophic and harmful factors was investigated and compared with the effects of lipopolysaccharide (LPS). C8‐ceramide as well as LPS enhanced the production/secretion of BDNF but, different from LPS, did not induce tumor necrosis factor α, interleukin‐1β, or nitric oxide. The C8‐ceramide‐induced BDNF release was significantly suppressed by protein kinase C (PKC) inhibitor, bisindolylmaleimide, which targets PKC isoforms, α, β, γ, δ and ε. However, it was not suppressed by a specific inhibitor of PKCα. Furthermore, PKCβ and γ were undetected in the microglia. Therefore, PKCδ and/or ε appear to be functioning PKC isoforms. In contrast, none of the mitogen‐activated protein kinases (MAPKs) and none of the transcription factors, including the cAMP response element‐binding transcription factor (CREB) and nuclear factor κB (NFκB) were activated in the microglia in response to C8‐ceramide. These results indicate that ceramide‐induced BDNF release in microglia is mediated by a signaling pathway associated with PKCδ and/or ε, but not with activation of MAPKs, CREB and NFκB.
Refsum's disease: a peroxisomal disorder affecting phytanic acid α‐oxidation
Authors: Wierzbicki Anthony S. , Lloyd Matthew D. , Schofield Christopher J. , Feher Michael D. , Gibberd F. Brian
Published: March 2003

Refsum's disease (hereditary motor sensory neuropathy type IV, heredopathia atactica polyneuritiformis) is an autosomal recessive disorder the clinical features of which include retinitis pigmentosa, blindness, anosmia, deafness, sensory neuropathy, ataxia and accumulation of phytanic acid in plasma‐ and lipid‐containing tissues. The transport and biochemical pathways of phytanic acid metabolism have recently been defined with the cloning of two key enzymes, phytanoyl‐CoA 2‐hydroxylase (PAHX) and 2‐hydroxyphytanoyl‐CoA lyase, together with the confirmation of their localization in peroxisomes. PAHX, an iron(II) and 2‐oxoglutarate‐dependent oxygenase is located on chromosome 10p13. Mutant forms of PAHX have been shown to be responsible for some, but not all, cases of Refsum's disease. Certain cases have been shown to be atypical mild variants of rhizomelic chondrodysplasia punctata type 1a. Other atypical cases with low‐plasma phytanic acid may be caused by α‐methylacyl‐CoA racemase deficiency. A sterol‐carrier protein‐2 (SCP‐2) knockout mouse model shares a similar clinical phenotype to Refsum's disease, but no mutations in SCP‐2 have been described to‐date in man. This review describes the clinical, biochemical and metabolic features of Refsum's disease and shows how the biochemistry of the α‐oxidation pathway may be linked to the regulation of metabolic pathways controlled by isoprenoid lipids, involving calcineurin or the peroxisomal proliferator activating α‐receptor.
Timothy growth in Scandinavia: combining quantitative information and simulation modelling
Authors: Höglind M. , Schapendonk A. H. C. M. , Van Oijen M.
Published: March 2003

Timothy (Phleum pratense) is the most widely grown sown grass species for silage and hay production in the Nordic countries; it is also common in many other areas with a cold maritime climate. Research on timothy has identified many environmental factors and plant characteristics that determine timothy growth. However, much of the literature that analyses timothy growth presents only qualitative estimates of the importance of the different growth‐determining factors. Here we present a review of quantitative information on timothy. Moreover, we analyse to what extent this quantitative information is sufficient to permit the construction of a simple process‐based model of timothy growth. We then use such a model to identify the major growth‐determining factors. Simulations with the model showed that the major processes to be elucidated in future research on timothy are tillering dynamics and the formation and loss of leaves from tillers. We conclude that a combination of literature review and analysis by means of simulation modelling, such as we attempted here, is an effective approach to identify and prioritize research goals.
Phosphorus modifies the effects of nitrogen on nodulation in split‐root systems of Hippophaë rhamnoides
Authors: Gentili Francesco , Huss‐Danell Kerstin
Published: March 2003

The effects of N (ammonium nitrate), P (phosphate) and their interactions on nodulation were studied in the intercellularly infected actinorhizal plant Hippophaë rhamnoides.

 A split‐root design, with pots receiving different concentrations of N and P, was used to determine whether the effects of N and P are local or systemic, if they are specific to nodulation or general, and whether P could counteract N inhibition. H. rhamnoides plants were grown for 6–10 wk after inoculation with Frankia.

 Inhibition of nodulation by N was systemic for both nodule number and nodule biomass in H. rhamnoides.

 By contrast, high P had a systemic stimulation on nodule number and biomass and P prevented systemic, but not local, N inhibition. Stimulation by P was specific to nodulation and not simply mediated via plant growth. Whether N and P alter not only nodulation but also N2‐fixation in the nodules requires further investigation.
Growth depression of mycorrhizal Citrus seedlings grown at high phosphorus supply is mitigated by elevated CO2
Authors: Jifon John L. , Graham James H. , Drouillard Diana L. , Syvertsen James P.
Published: March 2003

Gas exchange and growth responses of pot‐grown sour orange (Citrus aurantium) and sweet orange (C. sinensis) were studied at high soil‐P where growth depression is predicted.

 Seedlings were either inoculated (AM) with the arbuscular mycorrhizal fungus Glomus intraradices or not inoculated (NM), and grown at elevated (eCO2) or ambient CO2 (aCO2) for 11 wk.

 At aCO2, growth of AM sour orange was depressed (18%) compared with NM seedlings, but at eCO2, AM sour orange plants were 15% larger than NM plants. Growth depression coincided with increased rhizosphere respiration, reduced root starch concentration, and lower relative growth rates. Net photosynthesis (Pn) of both genotypes was enhanced by eCO2. For sour orange, the stimulation was greater in AM than in NM seedlings and this may have compensated for the carbon (C) expenditure on mycorrhizas. Gas exchange and growth of sweet orange were unresponsive to colonization by G. intraradices.

 Differential responses to treatments suggest that C expenditure on mycorrhizas is more tightly regulated in citrus genotypes of low mycorrhizal dependency (MD) such as sweet orange than in high MD genotypes (e.g. sour orange).
Uptake and metabolism of glucose in the Nostoc–Gunnera symbiosis
Authors: Black K. G. , Parsons R. , Osborne B. A.
Published: March 2003

The transition of Nostoc colonies from free‐living to symbiotic conditions, in the Nostoc–Gunnera association, involves increased heterocyst frequency and a reliance on carbon imported from the host for metabolic processes, including N2 fixation.

 Here the uptake of a glucose analogue, 3‐[14C]‐O‐methyl‐glucose (14C‐OMG), in freshly isolated symbiotic and free‐living Nostoc cells was characterized. In situ isotope enrichment coupled with GC–MS was used to elucidate the primary pathway(s) of 1‐[13C]‐glucose metabolism in the Nostoc–Gunnera symbiosis.

 The characteristics of 14C‐OMG uptake by symbiotic clusters suggested a respiratory driven process mediated by a hexose transporter. However, uptake by various Nostoc isolates decreased with increasing heterocyst frequency and was specifically associated with vegetative cells. In isolated and symbiotically intact Nostoc cells, 1‐[13C]‐glucose was imported and converted to various intermediates of the incomplete citric acid cycle, glycolysis and N2‐assimilating pathways. Labelling profiles indicated that C metabolism was altered in infected, but not in uninfected, rhizome tissue.

 Although it has been proposed that cyanobacteria such as Nostoc metabolise glucose using enzymes of the oxidative pentose phosphate cycle, our results suggest that glucose is also metabolised via glycolysis as well as the incomplete citric acid cycle in symbiotic cells.
Tourmaline breakdown in the migmatite zone of the Ryoke metamorphic belt, SW Japan
Authors: Kawakami T.
Published: March 2003

A sharp line delimitating the distribution of tourmaline (termed as a ‘tourmaline‐out isograd’) is defined in the migmatite zone of the Ryoke metamorphic belt, Japan. The trend of the tourmaline‐out isograd closely matches that of the isograds formed through the regional metamorphism, suggesting that it represents the breakdown front of tourmaline during regional metamorphism. This is confirmed by the presence of the reaction textures of tourmaline to sillimanite and cordierite near the tourmaline‐out isograd. The breakdown of tourmaline would release boron into associated melts or fluids and be an important factor in controlling the behaviour of boron in tourmaline‐bearing high‐temperature metamorphic rocks.

Near the tourmaline‐out isograd, large tourmaline crystals occur in the centre of interboudin partitions containing leucosome. In the melanosome of the intervening matrix, reaction textures involving tourmaline are locally observed. These observations imply that tourmaline breakdown is related to a melting reaction and that the boron in the leucosome is derived from the breakdown of tourmaline in the melanosome during prograde metamorphism.

Boron released by tourmaline breakdown lowers both the solidus temperature of the rock and the viscosity of any associated melt. Considering that the tourmaline‐out isograd lies close to the schist–migmatite boundary, these effects might have enhanced melt generation and segregation in the migmatite zone of the Ryoke belt.

The evidence for the breakdown of tourmaline and the almost complete absence of any borosilicates throughout the migmatite zone suggest that boron was effectively removed from this region by the movement of melt and/or fluid. This implies that the tourmaline‐out isograd can reflect a significant amount of mass transfer in the anatectic zones.
Retrograde metamorphism of eclogite in the southern Appalachian Mountains, U.S.A.–A case involving seamount subduction?
Authors: Abbott R. N. , Greenwood J. P.
Published: March 2003

This work supports a growing body of evidence that the Ashe Metamorphic Suite (AMS) of the eastern Blue Ridge province in North Carolina has an ensimatic origin and is part of a subduction‐related accretionary mélange, marking the Taconic suture between the North American craton and the Inner Piedmont. In a palinspastic reconstruction, the thrust fault at the base of the AMS appears to have intercepted the greatest depths (i.e. highest‐P metamorphic rocks) beneath parts of the AMS now exposed adjacent to the Grandfather Mountain window. The greatest volume of mafic rock is found in these same areas. We suggest that the nascent, subduction‐related, basal thrust fault was deflected downward by an obstacle in the form of an isolated, mafic volcanic edifice on the oceanic crust–a sea mount.

Pelitic and mafic rocks dominate the AMS. North of the Grandfather Mountain window, retrograded eclogite occurs in the amphibolite near the base of the AMS. Textures and mineralogy indicate that an original eclogite assemblage was subjected to the following sequence of parageneses:

(a) Eclogite(I) facies: omphacite+garnet+quartz,

(b) Eclogite(II) facies: omphacite+garnet+epidote+quartz,

(c) Symplectic (diopside+plagioclase)+garnet+epidote+quartz,

(d) Amphibolite facies: (diopside+plagioclase)+garnet+epidote+hornblende+quartz,

(e) Amphibolite facies: plagioclase+garnet+epidote+hornblende+quartz.

P–T conditions, estimated from geothermobarometry applied to relevant mineral compositions, are c.720 °C and c.16 kbar for (b) eclogite(II) facies; c.655 °C and c.8.5 kbar for (e) amphibolite facies.
Reaction pathways and reaction progress for the smectite‐to‐chlorite transformation: evidence from hydrothermally altered metabasites
Authors: Robinson D. , Schmidt S. Th. , De Zamora A. Santana
Published: March 2003

The transformation from smectite to chlorite has been interpreted as involving either a disequilibrium chlorite/smectite mixed‐layering sequence, or an equilibrated discontinuous sequence involving smectite–corrensite–chlorite. Here, analysis of the smectite to chlorite transition in different geothermal systems leads us to propose that the transformation proceeds via three contrasting reaction pathways involving (i) a continuous mixed‐layer chlorite/smectite series; (ii) a discontinuous smectite–corrensite–chlorite series and (iii) a direct smectite to chlorite transition. Such contrasting pathways are not in accord with an equilibrium mineral reaction series, suggesting that these pathways record kinetically controlled reaction progress. In the geothermal systems reviewed the style of reaction pathway and degree of reaction progress is closely correlated with intensity of recrystallization, and not to differences in thermal gradients or clay grain size. This suggests a kinetic effect linked to variation in fluid/rock ratios and/or a contrast between advective or diffusive fluid transport. The mode of fluid transport provides a means by which the rates of dissolution/nucleation/growth can control the reaction style and the reaction progress of the smectite to chlorite transition. Slow rates of growth are linked to the first reaction pathway involving mixed‐layering, while increasing rates of growth, relative to nucleation, promote the generation of more ordered structures and ultimately lead to the direct smectite to chlorite transition, representative of the third pathway.
A problem‐solving based computer‐assisted tutorial for the earth sciences
Authors: Chang C.Y.
Published: March 2003

Abstract This study investigated the effects of a Problem‐Solving based Computer‐Assisted Tutorial (PSCAT) on earth science achievement and attitudes toward earth science of tenth graders (16‐year olds) in a senior high school in Taiwan. A total of 137 students who were enrolled in four earth science classes participated in this pre‐test/post‐test control‐group experiment. The experimental groups received the PSCAT; whereas the comparison groups received a Lecture‐Internet‐Discussion (LID) teaching approach. A multivariate analysis of covariance on the post‐test scores of the Earth Science Achievement Test and Attitudes Toward Earth Science Inventory, with students' pre‐test scores as the covariates, suggested that PSCAT produced (almost) significantly greater gains on students' earth science achievement than did the LID approach and that no statistically significant increase or decrease in student attitudes toward earth science was found for either group.
Pupils' recall of an interactive storybook on CD‐ROM
Authors: Trushell J. , Maitland A. , Burrell C.
Published: March 2003

Abstract This small‐scale study compares two groups of Year 4 (8/9 year‐old) pupils either reading or playing an interactive storybook. The study considered pupils' recall of propositions, which formed the story setting and episodes, and of micro‐propositions and characters' names, and pupils' responses to inferential items derived from the ‘interactive storybook’. The study indicates that, whether reading or playing, pupils' recall of the story setting was sound, but pupils who had read the interactive storybook demonstrated greater recall of the story event structure than those who had engaged in interactive picture‐play. Pupils who had played the interactive storybook demonstrated significantly greater recall of micro‐propositions and names.
Learning with ICT at primary level: pupils' perceptions
Authors: Goodison T.A.
Published: March 2003

Abstract  This study investigated primary schoolchildren's awareness of the linkage between ICT and the way they learn within the context of a school that has been particularly successful in integrating ICT into the curriculum. Pupils were interviewed by their teacher and, extracts from the dialogue, identify examples of good practice and describe some of the challenges that still lie ahead..
Innovative uses of ICT in Chilean schools
Authors: Hinostroza J.E. , Guzmán A. , Isaacs S.
Published: March 2003

Abstract This paper presents some of the results of the study of seven cases of innovative pedagogical practices using ICT. The study was performed in the framework of the application of SITES M2 in Chile. The results are divided in two sections. First is a summary of each case, highlighting its innovative characteristics that serve as models of ‘good practice’ for Chilean teachers. Second, the results of the analysis of what teachers did are outlined; the impact on students and the type of teaching and learning activities in use. Results show that these projects did not provide evidence of having impact on students' learning as defined in the national curriculum. However, they show that students participating in these projects could learn other things, had the opportunity to develop abilities defined as cross‐curricular and practised ICT related skills. The analysis of the teaching and learning activities highlights some deficiencies in the way that teachers implement new teaching strategies.
L‐lactic acid: a human‐signifying host cue for the anthropophilic mosquito Anopheles gambiae
Authors: Dekker T. , Steib B. , Cardé R. T. , Geier M.
Published: March 2003

Abstract Using a dual‐choice olfactometer, the role of l‐lactic acid was investigated in relation to host‐seeking and selection by female Anopheles gambiae Giles sensu stricto (Diptera: Culicidae) mosquitoes in a Y‐tube bioassay. l‐lactic acid alone was not attractive, but it significantly augmented the attractiveness of CO2, skin odour and skin‐rubbing extracts from humans and other vertebrates. Comparing the left and right index fingers of the same person, one could be made more attractive than the other by adding l‐lactic acid to the air stream over that finger. The difference in l‐lactic acid concentration between the two air streams offered to the mosquitoes fell within the natural range of variation emanating from a human hand, suggesting that l‐lactic acid modulates intraspecific host selection by An. gambiae. Analysis of skin rubbings from various vertebrates (carnivores, chickens, primates, rodents, ungulates) indicated that humans have uniquely high levels of l‐lactic acid on their skin. Tests with extracts of skin rubbings from cows and humans, with and without added l‐lactic acid, suggest that naturally lower levels of l‐lactic acid contribute to the lesser attractiveness of non‐humans to An. gambiae s.s.