bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photosynthetic carbon assimilation and associated metabolism in relation to water deficits in higher plants
Authors: Lawlor D. W. , Cornic G. 
Published: March 2003

SummaryExperimental studies on CO2 assimilation of mesophytic C3 plants in relation to relative water content (RWC) are discussed. Decreasing RWC slows the actual rate of photosynthetic CO2 assimilation (A) and decreases the potential rate (Apot). Generally, as RWC falls from c. 100 to c. 75%, the stomatal conductance (gs) decreases, and with it A. However, there are two general types of relation of Apot to RWC, which are called Type 1 and Type 2. Type 1 has two main phases. As RWC decreases from 100 to c. 75%, Apot is unaffected, but decreasing stomatal conductance (gs) results in smaller A, and lower CO2 concentration inside the leaf (Ci) and in the chloroplast (Cc), the latter falling possibly to the compensation point. Down‐regulation of electron transport occurs by energy quenching mechanisms, and changes in carbohydrate and nitrogen metabolism are considered acclimatory, caused by low Ci and reversible by elevated CO2. Below 75% RWC, there is metabolic inhibition of Apot, inhibition of A then being partly (but progressively less) reversible by elevated CO2; gs regulates A progressively less, and Ci and CO2 compensation point, Γ rise. It is suggested that this is the true stress phase, where the decrease in Apot is caused by decreased ATP synthesis and a consequent decreased synthesis of RuBP. In the Type 2 response, Apot decreases progressively at RWC 100 to 75%, with A being progressively less restored to the unstressed value by elevated CO2. Decreased gs leads to a lower Ci and Cc but they probably do not reach compensation point: gs becomes progressively less important and metabolic limitations more important as RWC falls. The primary effect of low RWC on Apot is most probably caused by limited RuBP synthesis, as a result of decreased ATP synthesis, either through inhibition of Coupling Factor activity or amount due to increased ion concentration. Carbohydrate synthesis and accumulation decrease. Type 2 response is considered equivalent to Type 1 at RWC below c. 75%, with Apot inhibited by limited ATP and RuBP synthesis, respiratory metabolism dominates and Ci and Γ rise. The importance of inhibited ATP synthesis as a primary cause of decreasing Apot is discussed. Factors determining the Type 1 and Type 2 responses are unknown. Electron transport is maintained (but down‐regulated) in Types 1 and 2 over a wide range of RWC, and a large reduced/oxidized adenylate ratio results. Metabolic imbalance results in amino acid accumulation and decreased and altered protein synthesis. These conditions profoundly affect cell functions and ultimately cause cell death. Type 1 and 2 responses may reflect differences in gs and in sensitivity of metabolism to decreasing RWC.
Identification of canine helper T‐cell epitopes from the fusion protein of canine distemper virus
Authors: Ghosh Souravi , Walker John , Jackson David C. 
Published: March 2003

SummaryThe fusion protein of canine distemper virus (CDV‐F), a 662 amino‐acid envelope protein, was used as the target molecule for identification of canine T helper (Th) epitopes. A library of 94 peptides, each 17 residues in length overlapping by 10 residues and covering the entire sequence of CDV‐F, was screened using a lymphocyte proliferation assay with peripheral blood mononuclear cells (PBMC) obtained from dogs inoculated with canine distemper virus (CDV) vaccine. Initially we observed low and inconsistent proliferation of PBMC in response to these peptides, even when using cells obtained from dogs that had received multiple doses of CDV. Subsequently, the use of expanded cell populations derived by in vitro stimulation of canine PBMC with pools of peptides allowed the identification of a number of putative canine Th‐epitopes within the protein sequence of CDV‐F. There were two major clusters of Th‐epitopes identified close to the cleavage site of the F0 fusion protein, while some others were scattered in both the F1 and F2 fragments of the protein. Some of these peptides, in particular peptide 35 (p35), were stimulatory in dogs of different breeds and ages. The identification of such promiscuous canine Th‐epitopes encouraged us to assemble p35 in tandem with luteinising hormone releasing hormone (LHRH) a 10 amino‐acid residue synthetic peptide representing a B‐cell epitope which alone induces no antibody in dogs. The totally synthetic immunogen was able to induce the production of very high titres of antibodies against LHRH in all dogs tested. These results indicate that p35 could be an ideal candidate for use as a Th‐epitope for use in outbred dogs.
Signalling pathways induced by protease‐activated receptors and integrins in T cells
Authors: Bar‐Shavit Rachel , Maoz Miriam , Yongjun Yin , Groysman Maya , Dekel Idit , Katzav Shulamit 
Published: March 2003

SummaryRecent characterization of the thrombin receptor indicates that it plays a role in T‐cell signalling pathways. However, little is known regarding the signalling events following stimulation of additional members of the protease‐activated receptor (PAR) family, i.e. PAR2 and PAR3. Most of the postligand cascades are largely unknown. Here, we illustrate that in Jurkat T‐leukaemic cells, activation of PAR1, PAR2 and PAR3 induce tyrosine phosphorylation of Vav1. This response was impaired in Jurkat T cells deficient in p56lck (JCaM1.6). Activation of PARs also led to an increase in tyrosine phosphorylation of ZAP‐70 and SLP‐76, two key proteins in T‐cell receptor (TCR) signalling. We also demonstrated that p56lck is meaningful for integrin signalling. Thus, JCaM1.6 cells exhibited a marked reduction in their adherence to fibronectin‐coated plates, as compared to the level of adherence of Jurkat T cells. While the phosphorylation of Vav1 in T cells is augmented following adhesion, no additional increase was noted following treatment of the adhered cells with PARs. Altogether, we have identified key components in the postligand‐signalling cascade of PARs and integrins. Furthermore, we have identified Lck as a critical and possibly upstream component of PAR‐induced Vav1 phosphorylation, as well as integrin activation, in Jurkat T cells.
On the development of the shoulder girdle in Crocidura russula (Soricidae) and other placental mammals: evolutionary and functional aspects
Authors: Großmann Martin , Sánchez‐Villagra Marcelo R. , Maier Wolfgang 
Published: March 2003

AbstractThe development of the shoulder girdle was studied in embryonic stages and a neonate of Crocidura russula using histological sections and 3‐D reconstructions. Neonatal stages of Suncus etruscus and Mesocricetus auratus, both altricial placentals, were also studied. The earliest stage of C. russula, in which the scapula is still partially blastematous, has already a supraspinous fossa. The dorsal portion of the scapular spine does not develop from the anterior margin of the scapula. Its mode of development varies among the placentals studied to date. In some it is completely appositional bone, in others it consists of bone formed mostly by endochondral ossification of a dorsal cartilaginous process stemming from the acromium. During development the supraspinatus muscle increases in size in proportion to the infraspinatus muscle and the humeral head increases in size in relation to the glenoid fossa. Placentals have secondary cartilage in the sternal and acromial ends of the clavicle, a derived feature absent in Marsupialia. Even the most altricial placentals have a more developed shoulder girdle at birth than any newborn marsupial studied to date.
Climate and population density induce long‐term cohort variation in a northern ungulate
Authors: Forchhammer Mads C. , Clutton‐Brock Tim H. , Lindström Jan , Albon Steve D. 
Published: March 2003

Summary

Density‐dependent and climatic conditions experienced by individuals before and after birth differ considerably between cohorts. Such early environmental variability has the potential to create persistent fitness differences among cohorts. Here we test the hypothesis that conditions experienced by individuals in their early development will have long‐term effects on their life history traits.
We approached this by analysing and contrasting the effects of climate (the North Atlantic Oscillation, NAO) and population density at year of birth on cohort birth weight, birth date, litter size, age of maturity, survival and fecundity of Soay sheep, Ovies aries L., ewes in the population on the island of Hirta, St Kilda, Scotland.
Significant intercohort variations were found in life history traits. Cohorts born after warm, wet and windy (high NAO) winters were lighter at birth, born earlier, less likely to have a twin and matured later than cohorts born following cold and dry (low NAO) winters. High population densities in the winter preceding birth also had a negative effect on birth weight, birth date and litter size, whereas high postnatal densities delayed age of first reproduction.
High NAO winters preceding birth depressed juvenile survival but increased adult survival and fecundity. The negative influence of high NAO winters on juvenile survival is likely to be related to mothers’ compromised physical condition while the cohort is in utero, whereas the positive influence on adult survival and fecundity may relate to the improved postnatal forage conditions following high NAO winters. High pre‐ and postnatal population densities decreased juvenile (neonatal, yearling) and adult (2–4 years) survivorship but had no significant effect fecundity.
Density dependence and colony growth in the ant speciesFormica neorufibarbis
Authors: Billick Ian 
Published: March 2003

SummaryProduction of cocoons and numbers of workers in 25–40 colonies of the ant speciesFormica neorufibarbiswere tracked from 1993 to 1998 in order to test for density dependence in either production or survivorship of workers.The percentage of workers lost by colonies over winter increased with increasing worker numbers.There was no evidence that worker production was density‐dependent.Food supplementation did not affect worker‐cocoon production.Colonies forced to live under small nest rocks produced fewer cocoons, but this effect was never seen under natural conditions.In the field, colonies preferentially utilized large rocks for nests and worker number was positively correlated with nest‐rock area.
Root proliferation in decaying roots and old root channels: a nutrient conservation mechanism in oligotrophic mangrove forests?
Authors: McKee Karen L. 
Published: March 2003

SummaryIn oligotrophic habitats, proliferation of roots in nutrient‐rich microsites may contribute to overall nutrient conservation by plants. Peat‐based soils on mangrove islands in Belize are characterized by the presence of decaying roots and numerous old root channels (0.1–3.5 cm diameter) that become filled with living and highly branched roots ofRhizophora mangleandAvicennia germinans. The objectives of this study were to quantify the proliferation of roots in these microsites and to determine what causes this response.Channels formed by the refractory remains of mangrove roots accounted for only 1–2% of total soil volume, but the proportion of roots found within channels varied from 9 to 24% of total live mass. Successive generations of roots growing inside increasingly smaller root channels were also found.When artificial channels constructed of PVC pipe were buried in the peat for 2 years, those filled with nutrient‐rich organic matter had six times more roots than empty or sand‐filled channels, indicating a response to greater nutrient availability rather than to greater space or less impedance to root growth.Root proliferation inside decaying roots may improve recovery of nutrients released from decomposing tissues before they can be leached or immobilized in this intertidal environment. Greatest root proliferation in channels occurred in interior forest zones characterized by greater soil waterlogging, which suggests that this may be a strategy for nutrient capture that minimizes oxygen losses from the whole root system.Improved efficiency of nutrient acquisition at the individual plant level has implications for nutrient economy at the ecosystem level and may explain, in part, how mangroves persist and grow in nutrient‐poor environments.
The influence of nutrient loading, dissolved inorganic carbon and higher trophic levels on the interaction between submerged plants and periphyton
Authors: Jones J. Iwan , Young Johnstone O. , Eaton John W. , Moss Brian 
Published: March 2003

Summary

We studied the growth of a submerged aquatic plant in relation to periphytic and planktonic algae over a range of nutrient and dissolved inorganic carbon (DIC) availabilities.
In consecutive years two factorial experiments were conducted in 48 artificial ponds (each 3.14 m3), comprising four concentrations of DIC (1.5, 2.5, 3.5 or 4.5 mm) each crossed with three separate nutrient loadings (10 µg L−1 P and 0.2 mg L N, 50 µg L−1 P and 1 mg L N, or 200 µg L−1 P and 4 mg L N). The second experiment differed by the inclusion of fish in the ponds.
In the first year DIC had no effect on plant growth, but nutrient loading did. Plants failed to grow in treatments where phytoplankton density was high (> 100 µg L−1). Where phytoplankton was low, high numbers of invertebrates colonized the ponds, and periphyton abundance on the plants was low. In the second year, where phytoplankton never achieved the densities of the previous year, there was a significant effect of DIC concentration on plant growth but not of nutrients. Invertebrate abundance was lower and periphyton on the plants correspondingly higher.
In both years increased nutrient loading had no effect on the abundance of periphyton growing on the surface of the plants. Periphyton abundance was determined by the density of grazing invertebrates in the ponds.
There was a negative relationship between periphyton density and final plant density, which became significantly less steep with increasing DIC, indicating that periphyton and plants were competing for carbon.
DIC concentration has the potential to influence community structure in shallow lakes, altering competitive interactions between periphyton and plants and rendering low DIC lakes more prone to loss of plants when nutrient loading increases. However, the expression of this competition between periphyton and plants will depend on the density of grazing invertebrates present, which is itself influenced by the intensity of fish predation on those invertebrates.
Counting dendritic spines in brain tissue slices by image correlation spectroscopy analysis
Authors: Wiseman P. W. , Capani F. , Squier J. A. , Martone M. E. 
Published: March 2003

SummaryGrowth of new micrometre sized projections called dendritic spines in neurones has been linked to the encoding of long‐term memories in vertebrates. Numerous studies have been carried out at both the light and electron microscopy level to quantify dendritic spine densities in brain tissue in laboratory animals. Currently, such efforts using light microscopy have relied on manual counting of spines in confocal or two‐photon optical slice images of tissue containing fluorescently labelled spines. This manual approach can be slow and tedious, especially for samples with high spine densities. We introduce an alternative way of performing spine counting that uses an applied image intensity threshold followed by spatial image correlation spectroscopy (ICS) analysis. We investigated the effect of particle sizes above the diffraction limit on the autocorrelation analysis as well as the influence of background fluorescence. Our results show that, for well labelled cerebellar tissue samples imaged with a signal‐to‐noise ratio of 5 or greater, ICS‐based spine counts can be conducted with the same 15–20% precision as manual counting, but much more rapidly.
P‐glycoprotein expression in rat brain endothelial cells:  evidence for regulation by transient oxidative stress
Authors: Felix Robert A. , Barrand Margery A. 
Published: March 2003

AbstractDuring ischaemia/reperfusion, cells of the blood–brain barrier are subjected to oxidative stress. This study uses primary cultured rat brain endothelial cells to examine the effect of such stresses on expression of multidrug transporters. H2O2 up to 500 µm applied to cell monolayers caused a concentration‐dependent increase in expression of P‐glycoprotein (Pgp) but not of multidrug resistance‐associated protein (Mrp1). Concentrations > 250 µm H2O2 decreased cell viability. Application of 100 µm H2O2 caused a significant increase after 48 h in Pgp functional activity, as assessed from [3H]vincristine accumulation experiments. At this concentration, H2O2 produced a transient increase within 10 min followed by a sustained decrease in levels of intracellular reactive oxygen species (iROS), detectable by flow cytometry. Reoxygenation of cell monolayers after 6 h hypoxia gave rise to a similar transient increase in iROS and this also led to increased Pgp expression by 24 h. Increases were also observed within 4 h after both H2O2 and hypoxia/reoxygenation treatments in mdr1a and mdr1b mRNA. Evidence suggests this was due to enhanced transcription rather than mRNA stabilization. Therefore, oxidative stress, by changing Pgp expression, may affect movement of Pgp substrates in and out of the brain.
A new role for apolipoprotein E: modulating transport of polyunsaturated phospholipid molecular species in synaptic plasma membranes
Authors: Igbavboa Urule , Hamilton Jillonne , Kim Hee‐Yong , Sun Grace Y. , Wood W. Gibson 
Published: March 2003

AbstractPhospholipids and their acyl group composition are important in providing the proper membrane environment for membrane protein structure and function. In particular, the highly unsaturated phospholipids in synaptic plasma membranes in the CNS are known to play an important role in modulating receptor function and neurotransmitter release processes. Apolipoprotein E (apoE) is a major apolipoprotein in the CNS, mediating the transport of cholesterol, phospholipids and their fatty acids, particularly in reparative mechanisms during neuronal injury. This study was performed to determine whether deficiency in the apoE gene contributes to an alteration of the phospholipids in synaptic plasma membranes. Phospholipid molecular species were identified and quantitated by HPLC/electrospray ionization‐mass spectrometry. Analysis of the different phospholipid classes in membranes of apoE‐deficient and C57BL/6 J mice indicated no obvious differences in the distribution of different phospholipid classes but substantial differences in composition of phospholipid molecular species. Of special interest was the prevalence of phospholipids (phosphatidylcholine, diacyl‐phosphatidylethanolamine, and phosphatidylserine) with 22:6n‐3 in both the sn‐1 and sn‐2 positions of SPM and these phospholipid species were significantly higher in apoE‐deficient mice as compared to control mice. Since polyunsaturated fatty acids in neurons are mainly supplied by astrocytes, these results revealed a new role for apoE in regulating polyunsaturated phospholipid molecular species in neuronal membranes.
Regulation of tumor necrosis factor‐α expression  by CD40 ligation in BV‐2 microglial cells
Authors: Jana Malabendu , Dasgupta Subhajit , Liu Xiaojuan , Pahan Kalipada 
Published: March 2003

AbstractLigation of CD40 has been shown to induce/stimulate the expression of tumor necrosis factor‐α (TNF‐α) in microglial cells. This study delineates the mechanism by which CD40 ligation regulates the expression of TNF‐α in BV‐2 microglial cells. There was very little induction of TNF‐α by ligation of CD40 alone by either cross‐linking antibodies against CD40 or␣recombinant CD40 ligand (CD154). The absence of any increase in TNF‐α production by CD40 ligation alone even in CD40‐overexpressed BV‐2 microglial cells suggest that signal transduced by the ligation of CD40 alone is not sufficient for strong induction of TNF‐α. However, CD40 ligation markedly induced the production of TNF‐α as well as the expression of TNF‐α mRNA in interferon‐γ (IFN‐γ)‐stimulated BV‐2 glial cells. Ligation of CD40 in CD40‐overexpressed cells markedly enhanced the expression of TNF‐α in the presence of IFN‐γ. To understand the mechanism of CD40 ligation‐mediated induction/stimulation of TNF‐α, we investigated the role of nuclear factor‐κB (NF‐κB) and C/EBPβ. IFN‐γ alone was able to induce the activation of NF‐κB as well as C/EBPβ. However, CD40 ligation alone in the presence or absence of CD40 overexpression induced the activation of only NF‐κB and not that of C/EBPβ, suggesting that the activation of NF‐κB alone by CD40 ligation is not sufficient to induce the expression of TNF‐α and that the activation of C/EBPβ is also necessary for strong induction of TNF‐α. Consistently, a dominant‐negative mutant of p65 (Δp65) and that of C/EBPβ (ΔC/EBPβ) inhibited the expression of TNF‐α in BV‐2 microglial cells stimulated with the combination of IFN‐γ and CD40 ligand. Taken together, these studies suggest that activation of both NF‐κB and C/EBPβ is important for strong induction of TNF‐α and that CD40 ligation regulates the expression of TNF‐α by modulating the activation of only NF‐κB but not that of C/EBPβ.
Activation of caspase‐3 alone is insufficient for apoptotic morphological changes in human neuroblastoma cells
Authors: Racke Margaret M. , Mosior Marian , Kovacevic Steve , Chang Chan Hsin S. , Glasebrook Andrew L. , Roehm Neal W. , Na Songqing 
Published: March 2003

AbstractActivated caspase‐3 is considered an important enzyme in the cell death pathway. To study the specific role of caspase‐3 activation in neuronal cells, we generated a stable tetracycline‐regulated SK‐N‐MC neuroblastoma cell line, which expressed a highly efficient self‐activating chimeric␣caspase‐3, consisting of the caspase‐1 prodomain fused to the caspase‐3 catalytic domain. Under expression‐inducing conditions, we observed a time‐dependent increase of processed caspase‐3 by immunostaining for the active form of the enzyme, intracellular caspase‐3 enzyme activity, as well as poly(ADP‐ribose) polymerase (PARP) cleavage. Induced expression of the caspase fusion protein showed predominantly caspase‐3 activity without any apoptotic morphological changes. In contrast, staurosporine treatment of the same cells resulted in activation of multiple caspases and profound apoptotic morphology. Our work provides evidence that auto‐activation of caspase‐3 can be efficiently achieved with a longer prodomain and that neuronal cell apoptosis may require another caspase or activation of multiple caspase enzymes.
Are flowers morphologically adapted to take advantage of electrostatic forces in pollination?
Authors: Vaknin Yiftach , Gan‐mor Samuel , Bechar Avital , Ronen Beni , Eisikowitch Dan 
Published: March 2003

Summary

The relationship between floral morphology and electrostatic pollination was studied here. To test the effects of floral morphology on pollen deposition on the stigma and other floral parts by means of electrostatic forces, metal replicas of almond (Amygdalus communis) flowers were constructed and then dusted with electrostatically charged and uncharged almond pollen. The pollen was applied to the flowers with a specially designed electrostatic powder‐coating device.
Pollen deposition on the flower was found to be higher when the pollen was electrostatically charged than when it was not. Most of the charged pollen grains were deposited on the corolla extremities and on the stigma, whereas uncharged pollen grains were evenly distributed on the entire flower.
Stigma exsertion was the most important morphological feature of the flower promoting pollen deposition on the stigma when electrostatic charge was used. Large flowers with corollas showed higher electrodeposition on the corolla than smaller, narrower ones.
These results collectively imply that morphological features of a plant might be adaptations to take advantage of electrostatic forces. This provided us with a very important tool for future research on floral morphology and pollination biology.