bluuebunny/crossref_metadata_2025 huggingface dataset:
Laryngeal reflex responses are not modulated during human voice and respiratory tasks
Authors: Henriquez Victor M. , Schulz Geralyn M. , Bielamowicz Steven , Ludlow Christy L.
Published: October 2007

The laryngeal adductor response (LAR) is a protective reflex that prevents aspiration and can be elicited either by electrical stimulation of afferents in the superior laryngeal nerve (SLN) or by deflection of mechanoreceptors in the laryngeal mucosa. We hypothesized that because this reflex is life‐sustaining, laryngeal muscle responses to sensory stimuli would not be suppressed during volitional laryngeal tasks when compared to quiet respiration. Unilateral electrical superior laryngeal nerve stimulation was used to elicit early (R1) and late (R2) responses in the ipsilateral thyroarytenoid muscle in 10 healthy subjects. The baseline levels of muscle activity before stimulation, R1 and R2 response occurrence and the integrals of responses were measured during each task: quiet inspiration, prolonged vowels, humming, forced inhalation and effort closure. We tested whether R1 response integrals during tasks were equal to either: (1) baseline muscle activity during the task added to the response integral at rest; (2) the response integral at rest minus the baseline muscle activity during the task; or (3) the response integral at rest. R1 response occurrence was not altered by task from rest while fewer R2 responses occurred only during effort closure and humming compared to rest. Because the R1 response integrals did not change from rest, task increases in motor neuron firing did not alter the LAR. These findings demonstrate that laryngeal motor neuron responses to sensory inputs are not gated during volitional tasks confirming the robust life‐sustaining protective mechanisms provided by this airway reflex.
Stochastic Averaging and Optimal Prediction
Authors: Park Jun H. , Namachchivaya N. Sri , Neogi Natasha
Published: October 2007

This work is concerned with the similarity between the two important reduction schemes: optimal prediction and stochastic averaging. To this end, we consider a randomly perturbed Hamiltonian system and derive a generalized Langevin equation from a Kolmogorov backward equation. We then show the similarity by adopting conditional expectation as our projection operator in the generalized Langevin equation. The characteristics of the conditional expectation play a central role in our study.
Frequency Range Selection for Impedance-Based Structural Health Monitoring
Authors: Peairs Daniel M. , Tarazaga Pablo A. , Inman Daniel J.
Published: October 2007

Impedance-based structural health monitoring uses collocated piezoelectric transducers to locally excite a structure at high frequencies. The response of the structure is measured by the same transducer. Changes in this response indicate damage. Frequency range selection for monitoring with impedance-based structural health monitoring has, in the past, been done by trial and error methods or has been selected after analysis by engineers familiar with the method. This study aims to determine if, in future applications, it is possible to automatically select preferred frequency ranges based on sensor characteristics, perhaps even before installing the system. In addition, the paper demonstrates a method for determining preferable frequency ranges for monitoring. The study examines the analysis of the measurement change through a damage metric and relates the results of the analysis to characteristics of the measurement. Specifically, outlier detection concepts were used to statistically evaluate the damage detection ability of the transducers at various frequency ranges. The variation in undamaged measurements is compared to the amount of change in the measurement upon various levels of damage. Testing was performed with both solid piezoceramic transducers and macrofiber composite piezoelectric devices of different sizes bonded to aluminum and fiber reinforced composite structures. The results indicate that characteristics of the structure, not the sensor alone, determine the optimal monitoring frequency ranges.
Anterior Prefrontal Function and the Limits of Human Decision-Making
Authors: Koechlin Etienne , Hyafil Alexandre
Published: October 2007

The frontopolar cortex (FPC), the most anterior part of the frontal lobes, forms the apex of the executive system underlying decision-making. Here, we review empirical evidence showing that the FPC function enables contingent interposition of two concurrent behavioral plans or mental tasks according to respective reward expectations, overcoming the serial constraint that bears upon the control of task execution in the prefrontal cortex. This function is mechanistically explained by interactions between FPC and neighboring prefrontal regions. However, its capacity appears highly limited, which suggests that the FPC is efficient for protecting the execution of long-term mental plans from immediate environmental demands and for generating new, possibly more rewarding, behavioral or cognitive sequences, rather than for complex decision-making and reasoning.
Plant Pathogen Recognition Mediated by Promoter Activation of the Pepper
Bs3
Resistance Gene
Authors: Römer Patrick , Hahn Simone , Jordan Tina , Strauß Tina , Bonas Ulla , Lahaye Thomas
Published: October 2007

Plant disease resistance (R) proteins recognize matching pathogen avirulence proteins. Alleles of the pepper
R
gene
Bs3
mediate recognition of the
Xanthomonas campestris
pv.
vesicatoria
(
Xcv
) type III effector protein AvrBs3 and its deletion derivative AvrBs3Δrep16. Pepper
Bs3
and its allelic variant
Bs3-E
encode flavin monooxygenases with a previously unknown structure and are transcriptionally activated by the
Xcv
effector proteins AvrBs3 and AvrBs3Δrep16, respectively. We found that recognition specificity resides in the
Bs3
and
Bs3-E
promoters and is determined by binding of AvrBs3 or AvrBs3Δrep16 to a defined promoter region. Our data suggest a recognition mechanism in which the Avr protein binds and activates the promoter of the cognate
R
gene.
Inactivation of the Interoceptive Insula Disrupts Drug Craving and Malaise Induced by Lithium
Authors: Contreras Marco , Ceric Francisco , Torrealba Fernando
Published: October 2007

Addiction profoundly alters motivational circuits so that drugs become powerful reinforcers of behavior. The interoceptive system continuously updates homeostatic and emotional information that are important elements in motivational decisions. We tested the idea that interoceptive information is essential in drug craving and in the behavioral signs of malaise. We inactivated the primary interoceptive cortex in amphetamine-experienced rats, which prevented the urge to seek amphetamine in a place preference task. Interoceptive insula inactivation also blunted the signs of malaise induced by acute lithium administration. Drug-seeking and malaise both induced Fos expression, a marker of neuronal activation, in the insula. We conclude that the insular cortex is a key structure in the perception of bodily needs that provides direction to motivated behaviors.
Hold Your Horses: Impulsivity, Deep Brain Stimulation, and Medication in Parkinsonism
Authors: Frank Michael J. , Samanta Johan , Moustafa Ahmed A. , Sherman Scott J.
Published: October 2007

Deep brain stimulation (DBS) of the subthalamic nucleus markedly improves the motor symptoms of Parkinson's disease, but causes cognitive side effects such as impulsivity. We showed that DBS selectively interferes with the normal ability to slow down when faced with decision conflict. While on DBS, patients actually sped up their decisions under high-conflict conditions. This form of impulsivity was not affected by dopaminergic medication status. Instead, medication impaired patients' ability to learn from negative decision outcomes. These findings implicate independent mechanisms leading to impulsivity in treated Parkinson's patients and were predicted by a single neurocomputational model of the basal ganglia.
A Cosmic Microwave Background Feature Consistent with a Cosmic Texture
Authors: Cruz M. , Turok N. , Vielva P. , Martínez-González E. , Hobson M.
Published: October 2007

The Cosmic Microwave Background provides our most ancient image of the universe and our best tool for studying its early evolution. Theories of high-energy physics predict the formation of various types of topological defects in the very early universe, including cosmic texture, which would generate hot and cold spots in the Cosmic Microwave Background. We show through a Bayesian statistical analysis that the most prominent 5°-radius cold spot observed in all-sky images, which is otherwise hard to explain, is compatible with having being caused by a texture. From this model, we constrain the fundamental symmetry-breaking energy scale to be ϕ
0
≈ 8.7 × 10
15
gigaelectron volts. If confirmed, this detection of a cosmic defect will probe physics at energies exceeding any conceivable terrestrial experiment.
GPCR Engineering Yields High-Resolution Structural Insights into β
2
-Adrenergic Receptor Function
Authors: Rosenbaum Daniel M. , Cherezov Vadim , Hanson Michael A. , Rasmussen Søren G. F. , Thian Foon Sun , Kobilka Tong Sun , Choi Hee-Jung , Yao Xiao-Jie , Weis William I. , Stevens Raymond C. , Kobilka Brian K.
Published: October 2007

The β
2
-adrenergic receptor (β
2
AR) is a well-studied prototype for heterotrimeric guanine nucleotide–binding protein (G protein)–coupled receptors (GPCRs) that respond to diffusible hormones and neurotransmitters. To overcome the structural flexibility of the β
2
AR and to facilitate its crystallization, we engineered a β
2
AR fusion protein in which T4 lysozyme (T4L) replaces most of the third intracellular loop of the GPCR (“β
2
AR-T4L”) and showed that this protein retains near-native pharmacologic properties. Analysis of adrenergic receptor ligand-binding mutants within the context of the reported high-resolution structure of β
2
AR-T4L provides insights into inverse-agonist binding and the structural changes required to accommodate catecholamine agonists. Amino acids known to regulate receptor function are linked through packing interactions and a network of hydrogen bonds, suggesting a conformational pathway from the ligand-binding pocket to regions that interact with G proteins.
Dense-Granule Protein NcGRA7, a New Marker for the Serodiagnosis ofNeospora caninumInfection in Aborting Cows
Authors: Huang Penglong , Liao Min , Zhang Houshuang , Lee Eung-goo , Nishikawa Yoshifumi , Xuan Xuenan
Published: October 2007

To investigate whether the production of an antigen-specific antibody is associated withNeospora caninum-induced bovine abortion, 62 serum samples were tested with an enzyme-linked immunosorbent assay using the recombinant antigens NcSAG1, NcSRS2, and NcGRA7. Our study suggested that NcGRA7 would be a new marker for the serodiagnosis ofN. caninuminfection resulting in abortion.
Rapid Onset of Intestinal Epithelial Barrier Dysfunction in Primary Human Immunodeficiency Virus Infection Is Driven by an Imbalance between Immune Response and Mucosal Repair and Regeneration
Authors: Sankaran Sumathi , George Michael D. , Reay Elizabeth , Guadalupe Moraima , Flamm Jason , Prindiville Thomas , Dandekar Satya
Published: October 2007

Gut-associated lymphoid tissue (GALT) is an early target for human immunodeficiency virus type 1 (HIV-1) infection and is a site for severe CD4
+
T-cell depletion. HIV-associated enteropathy is well-documented in chronic HIV-1 infection. However, the initial host responses to HIV infection in GALT and the early molecular correlates of HIV enteropathogenesis have not been characterized during primary HIV infection. In this study, we provide evidence of viral replication in GALT resident CD4
+
T cells and macrophages in primary-stage patients and identify early patterns of host mucosal responses and changes in the molecular microenvironment through gene expression profiling. High levels of viral replication in GALT and marked CD4
+
T-cell depletion correlated with decreased expression levels of genes regulating epithelial barrier maintenance and digestive/metabolic functions. These changes coincided with a marked increase in the transcription of immune activation-, inflammation-, and apoptosis-associated genes. Our findings indicate that HIV-induced pathogenesis in GALT emerges at both the molecular and cellular levels prior to seroconversion in primary HIV infection, potentially setting the stage for disease progression by impairing the ability to control viral replication and repair and regenerate intestinal mucosal tissues.
Inhibition of Translation by a Short Element in the 5′ Leader of the Herpes Simplex Virus 1 DNA Polymerase Transcript
Authors: Bryant Kevin F. , Coen Donald M.
Published: October 2007

Many viruses regulate gene expression, both globally and specifically, to achieve maximal rates of replication. During herpes simplex virus 1 infection, translation of the DNA polymerase (Pol) catalytic subunit is inefficient relative to other proteins of the same temporal class (D. R. Yager, A. I. Marcy, and D. M. Coen., J. Virol. 64:2217-2225, 1990). To investigate the mechanisms involved in the inefficient translation of Pol and to determine whether this inefficient translation could affect viral replication, we performed a mutagenic analysis of the 5′ end of the
pol
transcript. We found that a short sequence (∼55 bases) in the 5′ leader of the transcript is both necessary and sufficient to inhibit translation in rabbit reticulocyte lysates and sufficient to inhibit reporter gene translation in transfected cells. RNase structure mapping experiments indicated that the inhibitory element adopts a structure that contains regions of a double-stranded nature, which may interfere with ribosomal loading and/or scanning. Pol accumulated to ∼2- to 3-fold-higher levels per mRNA in cells infected with a mutant virus containing a deletion of the ∼55-base inhibitory element than in cells infected with a control virus containing this element. Additionally, the mutant virus replicated less efficiently than the control virus. These results suggest that the inhibitory element regulates Pol translation during infection and that its inhibition of Pol translation is beneficial for viral replication.
Herpes Simplex Virus Type 1 Immediate-Early Protein ICP27 Is Required for Efficient Incorporation of ICP0 and ICP4 into Virions
Authors: Sedlackova Lenka , Rice Stephen A.
Published: October 2007

Early in infection, herpes simplex virus type 1 (HSV-1) immediate-early (IE) proteins ICP0 and ICP4 localize to the nucleus, where they stimulate viral transcription. Later in infection, ICP0 and to a lesser extent ICP4 accumulate in the cytoplasm, but their biological role there is unknown. Previously, it was shown that the cytoplasmic localization of ICP0/4 requires the multifunctional IE protein ICP27, which is itself an activator of viral gene expression. Here, we identify a viral ICP27 mutant,
d
3-4, which is unable to efficiently localize ICP0 and ICP4 to the cytoplasm but which otherwise resembles wild-type HSV-1 in its growth and viral gene expression phenotypes. These results genetically separate the function of ICP27 that affects ICP0/4 localization from its other functions, which affect viral growth and gene expression. As both ICP0 and ICP4 are known to be minor virion components, we used
d
3-4 to test the hypothesis that the cytoplasmic localization of these proteins is required for their incorporation into viral particles. Consistent with this conjecture,
d
3-4 virions were found to lack ICP0 in their tegument and to have greatly reduced levels of ICP4. Thus, the cytoplasmic localization of ICP0 and ICP4 appears to be a prerequisite for the assembly of these important transcriptional regulatory proteins into viral particles. Furthermore, our results show that ICP27 plays a previously unrecognized role in determining the composition of HSV-1 virions.
Removal of a Single N-Linked Glycan in Human Immunodeficiency Virus Type 1 gp120 Results in an Enhanced Ability To Induce Neutralizing Antibody Responses
Authors: Li Yun , Cleveland Bradley , Klots Igor , Travis Bruce , Richardson Barbra A. , Anderson David , Montefiori David , Polacino Patricia , Hu Shiu-Lok
Published: October 2007

Glycans on human immunodeficiency virus (HIV) envelope protein play an important role in infection and evasion from host immune responses. To examine the role of specific glycans, we introduced single or multiple mutations into potential N-linked glycosylation sites in hypervariable regions (V1 to V3) of theenvgene of HIV type 1 (HIV-1) 89.6. Three mutants tested showed enhanced sensitivity to soluble CD4. Mutant N7 (N197Q) in the carboxy-terminal stem of the V2 loop showed the most pronounced increase in sensitivity to broadly neutralizing antibodies (NtAbs), including those targeting the CD4-binding site (IgG1b12) and the V3 loop (447-52D). This mutant is also sensitive to CD4-induced NtAb 17b in the absence of CD4. Unlike the wild-type (WT) Env, mutant N7 mediates CD4-independent infection in U87-CXCR4 cells. To study the immunogenicity of mutant Env, we immunized pig-tailed macaques with recombinant vaccinia viruses, one expressing SIVmac239 Gag-Pol and the other expressing HIV-1 89.6 Env gp160 in WT or mutant forms. Animals were boosted 14 to 16 months later with simian immunodeficiency virusgagDNA and the cognate gp140 protein before intrarectal challenge with SHIV89.6P-MN. Day-of-challenge sera from animals immunized with mutant N7 Env had significantly higher and broader neutralizing activities than sera from WT Env-immunized animals. Neutralizing activity was observed against SHIV89.6, SHIV89.6P-MN, HIV-1 SF162, and a panel of subtype B primary isolates. Compared to control animals, immunized animals showed significant reduction of plasma viral load and increased survival after challenge, which correlated with prechallenge NtAb titers. These results indicate the potential advantages for glycan modification in vaccine design, although the role of specific glycans requires further examination.
OBSERVATIONS ON THE GROWTH OF THE MARINE HYPHOMYCETE VARICOSPORINA RAMULOSA
Authors: Meyers Samuel P. , Hoyo Lydia
Published: October 2007

Varicosporina ramulosa, a staurospore-producing fungus, shows a range of morphological characteristics in response to salinity, pH, nutrients, and other changes in the culture medium. Variations in sporulation include encystment of mycelia and conidia, production of chlamydospores, and differences in concentrations of conidium production. Optimal conditions for mycelial growth differ from those stimulating reproduction. These factors possibly affect distribution of the species in the sea and may be significant in the observed paucity of morphologically adapted aquatic Hyphomycetes in estuarine localities.
VEGETATIVE PROPAGATION OF POPULUS SPP.: I. INFLUENCE OF TEMPERATURE ON FORMATION AND INITIAL GROWTH OF ASPEN SUCKERS
Authors: Maini J. S. , Horton K. W.
Published: October 2007

Populus tremuloides Michx. (trembling aspen), a commercially valuable tree, generally reproduces vegetatively by shoots (suckers) that arise adventitiously on lateral roots. Among various ecological factors, temperature plays a significant role in sucker initiation. The influence of five temperature regimes on suckering is reported here. Root cuttings of aspen, 10 cm long and 1.2 to 2.5 cm thick, were grown in the dark in fine sand. The temperature of the sand was kept at 58°, 64°, 74°, 87°, and 95 °F, and the moisture content near field capacity. The earliest emergence of suckers was at 87°. The maximum incidence and growth of suckers was at 74°, declining gradually below and above this temperature. Sufficient food material is stored in short root sections to sustain suckers for more than 3 weeks. These data agree with our field observations and indicate that after such disturbances as cutting and burning, insolation-induced increase in soil temperature is the cardinal factor for sucker stimulation.
The occurrence of wall deposits in phloem cells of cherry trees infected with little cherry disease
Authors: Verbeek Rosalinda Boasson
Published: October 2007

Phloem cells of cherry trees with little cherry show deposits on the cell walls which stain with acridine orange and can be observed with the fluorescent microscope. A survey of healthy and infected trees showed that there was a strong correlation between the occurrence of numerous wall deposits and the presence of the disease. Although wall deposits are found occasionally in the phloem of healthy petioles, an arbitrary cutoff point of five deposits per section was set as the distinguishing point between healthy and diseased material. The deposits develop in the petioles during the first 2 months after flowering. The color of the fluorescence seems to indicate that they do not contain RNA. It is suggested that the presence of numerous wall deposits could be useful as a diagnostic tool for the detection of little cherry.
Water relations of cassava: water content, water, osmotic and turgor potential relationships
Authors: Ike I. F. , Thurtell G. W.
Published: October 2007

The water content, water potential, osmotic potential, and turgor pressure relationships of two cultivars of indoor-grown cassava (Manihot esculenta) were examined. The two cultivars (CMC9 and MCOL113) represent low and high starch yielding varieties, respectively.Leaf water potentials were measured insitu with a dew-point hygrometer. A pressure chamber was used to estimate ψL in excised leaves. Relative water content (RWC) of intact leaves was measured with a beta-gauge but was calculated from the pressure chamber data for excised leaves. Osmotic potentials at water contents between 0 and 100% were calculated and the corresponding turgor pressures were obtained by difference.At low soil moisture tension, RWC and ψL dropped to minimum values during the day but recovered considerably at night. Osmotic potentials of turgid leaves were −970 kPa in cv. CMC9 and −1000 kPa in cv. MCOL113. Diurnal variations ψπ were small in both cultivars. However, daily fluctuations in ψP were larger and paralleled changes in ψL. A marked hysteresis was evident in the water content-potential and the water content-turgor pressure data obtained during the drying cycle. However, when water potentials and turgor pressures were changed rapidly by switching the lights off and on at short-time intervals, no hysteresis was observed in the data.
Use of cluster analysis in the systematics of the algal genus Cryptomonas
Authors: Anton Ann , Duthie Hamish C.
Published: October 2007

Sixteen species and one variety of the algal genus Cryptomonas Ehrenberg were identified from a large number of samples collected from lakes, ponds, and marshes in eastern Canada and the Northwest Territories. A description, including photographs and drawings, is given for each taxon. Cluster analysis statistics were used to determine the taxonomic value of certain characters and the affinities between the species. It was found that binary (two-state) characters gave a more realistic diagnosis than quantitative (continuous) data because of the large variation and overlap in measurements of the latter. The following characters were considered to be of taxonomic significance in separating the species: (i) cell shape and size, (ii) number of chloropasts, (iii) number and position of chloroplasts, (iv) flagella and gullet system, and (v) number and position of other included bodies. Based on these characters, a new taxonomic key was constructed for the identification of the common freshwater species of Cryptomonas.
Ultrastructure of teliospore germination and basidiospore formation in the rust fungus Gymnosporangium clavipes
Authors: Mims Charles W.
Published: October 2007

A mature teliospore of Gymnosporangium clavipes is two celled with a long pedicel. The spore wall appears multilayered and a germ pore region is present in the wall at each end of the teliospore. The cytoplasm of the spore is dense and packed with lipid droplets. A single, dense, prophase nucleus is present in each cell. Synaptonemal complexes were observed in younger spores but not in mature, germinable spores. The cytoplasm of a germinating spore appears less dense than that of a nongerminating spore. During germination a germ tube emerges from the germ pore region of each cell. Cytoplasmic vesicles are numerous in the tip of the rapidly elongating promycelium. The nucleus enters the promycelium and divides meiotically. Centripetally developing septa divide the promycelium into four uninucleate cells each of which gives rise to a sterigma at the tip of which a basidiospore initial develops. Cytoplasmic vesicles are prominent in the tip of the developing sterigma and in the basidiospore initial. Once the nucleus has entered the basidiospore initial it divides mitotically. During this time time a septum develops within the sterigma and the spore is delimited from the sterigma by the formation of a second septum at the base of the spore.
Effects of carbohydrate deprivation on rejuvenation, apospory, and regeneration in ostrich fern (Matteuccia struthiopteris) sporophytes
Authors: Materi Doug M. , Cumming Bruce G.
Published: October 2007

Propagules derived from mature ostrich fern (Matteuccia struthiopteris) sporophytes were rejuvenated by culture under conditions of carbohydrate deprivation, resulting in expression of the juvenile phenotype. The capacity of the excised, cultured leaves of these juvenile-type sporophytes to produce gametophytes by apospory or sporophytes by regeneration indicated that the rejuvenated sporophytes were ontogenetically equivalent, not just morphologically similar, to zygotic juvenile sporophytes. Both apospory and regeneration were promoted in leaves cultured on semisolid media. Compared with 0% sucrose, 1% sucrose greatly promoted the regeneration of sporophytes but reduced aposporous development. Rejuvenated sporophytes of different clones and ploidy levels exhibited a similar degree of juvenility, and their excised leaves expressed a similar capacity for aposporous and regenerative development. Key words: Matteuccia, rejuvenation, juvenility, apospory, regeneration.
Chromosomal evidence for autotetraploidy in the Turnera ulmifolia complex (Turneraceae)
Authors: Shore Joel S.
Published: October 2007

The hypothesis that tetraploids of two taxonomic varieties of the Turnera ulmifolia complex, vars. elegans and intermedia, have had autopolyploid origins, was tested. Chromosome counts within each variety show that two cytotypes occur with somatic numbers of 2n = 10 and 2n = 20. Tetrapoloids of both var. intermedia and var. elegans have pollen fertility approximately 13% less than that of diploids. Synthetic tetraploids produced by colchicine doubling exhibit pollen fertilities virtually identical to those of the natural tetraploids. While diploids exhibited only bivalent formation, tetraploids showed varying frequencies of univalents, bivalents, trivalents, and quadrivalents. The chromosome pairing model of R. C. Jackson and D. P. Hauber (1982. Am. J. Bot. 69: 644–646) and a minor modification of the goodness-of-fit test for that model, were used to test the hypothesis of an autopolyploid origin. For four of the six populations studied meiotically, the data fit the model. The data indicate that the tetraploid cytotypes of T. ulmifolia vars. elegans and intermedia have had autopolyploid origins. Key words: Turnera ulmifolia, autotetraploid, chromosome pairing model.
Interactions of the nonhost French bean plant (Phaseolus vulgaris) with parasitic and saprophytic fungi. IV. Effect of preinoculation with the bean rust fungus on growth of parasitic fungi nonpathogenic on beans
Authors: Fernandez Myriam R. , Heath Michèle C.
Published: October 2007

Bean leaves inoculated 24 h previously with the bean rust fungus were inoculated with spores of Cochliobolus heterostrophus, Stemphylium sarcinaeforme, Stemphylium botryosum, or Cladosporium fulvum. For all species except C. fulvum, hyphal growth resulting from stomatal penetrations was greater than that in leaves that were not rust-infected but did not continue for more than about 24 h. The incidence of direct penetrations for these three fungi also was increased by prior rust infection, and the incidence of epidermal wall appositions was reduced. Growth of C. fulvum in rust-infected leaves only exceeded that in control leaves when spores were injected into the intercellular spaces of the mesophyll tissue. Rust infection either had little effect on the incidence of cell death, normally induced by all of the tested fungi except C. fulvum, or it enhanced this response in association with greater fungal growth. From this and previous studies, it seems that successful rust infection increases the growth of a wider array of fungi nonparasitic to beans than treatments with growth regulators or intercellular washing fluids from rusted tissue. Its effect is most closely mimicked by preinoculation treatments with heat or protein synthesis inhibitors, but it does not induce indiscriminate susceptibility. Its effect may, in part, be due to the suppression of defenses involving wall modifications. Key words: Uromyces appendiculatus, induced susceptibility, nonhost resistance.
Structure and function of a specialized cell wall in the trichomes of the carnivorous bromeliad Brocchinia reducta
Authors: Owen Jr. T. Page , Thomson William W.
Published: October 2007

The leaves of the carnivorous bromeliad, Brocchinia reducta, are clustered in a tight vertical rosette, forming a water-collecting tank in which insects are trapped. Evidence in the literature indicates that nutrient uptake into the leaves occurs primarily, if not entirely, via trichomes located at the base of the leaves on the tank side. The outer cell wall in the trichomes from the carnivorous bromeliad B. reducta has an unusual ultrastructure. This wall has a labyrinthine-like appearance of light and dark-staining regions that suggests a highly specialized function. This study examined three structural aspects of this wall. First, the limiting porosity of the trichome wall was examined with fluorescently labelled dextrans and shown to permit the transport of molecules as large as 6.6 nm. Second, structural changes in a dehydrated wall were observed using freeze-substitution techniques. Specifically, the electron transparent wall "regions" were collapsed when the trichome was dried. Last, the presence of periodic acid soluble polysaccharides was detected throughout the electron-dense wall protuberances, but occurred only as thin, dispersed strands in the more electron-transparent regions. We have concluded from these studies that in the hydrated state, these electron-transparent regions represent the channels through which solutes move through the wall to the cap cell surface. A pore size of 6.6 nm would also permit the movement of modest-size proteins, and based on previous observations, we suggest that protein uptake into the cells would occur by pinocytosis. We found channels can vary in size and thus porosity; in the dehydrated state, the wall is considerably shrunken and the channels collapse. We hypothesize that the shrunken wall restricts the loss of water from leaves through trichomes to the atmosphere. Key words: Bromeliaceae, cell wall porosity, fluorescently labelled dextrans, freeze-substitution, Thiéry staining.
Development of Tubakia dryina on host tissue
Authors: Munkvold G. P. , Neely D.
Published: October 2007

Excised leaves of Quercus rubra were inoculated with suspensions of conidia of Tubakia dryina and the development of the fungus on the leaf tissue was observed by scanning electron and light microscopy. Conidial germination was 2% after 6 h, 53% after 12 h, and 54% after 24 h. Germ tubes formed appressorium-like structures directly on the leaf cuticle or over stomata, or entered stomata directly. Development of conidiomata was first evident 24–72 h after inoculation. Conidiomata first appeared as a small mass of hyphal cells, which then proliferated in a radial fashion, with simultaneous formation of conidia. Conidiogenous cells later ceased to form conidia and became thick walled and pigmented, forming a dark scutellum. Conidiogenous cells continued to proliferate ventrally to the scutellum, producing a ring of conidia embedded in a sticky matrix, surrounding the conidioma. Leaf tissue colonized by the fungus became water soaked, and later turned brown and necrotic. Key words: Actinopelte, leaf spot, oak, pycnothyrium.
The microfungal communities of a mixed mire in northern Sweden
Authors: Nilsson M. , Bååth E. , Söderström B.
Published: October 2007

The microfungal communities of a mire in northern Sweden were studied. Three plant communities were sampled at two depths, one dry ombrotrophic, one wet ombrotrophic, and one wet minerotrophic site. The fungi were isolated on malt agar using the dilution-plate technique. The most commonly isolated species were Chaunopychnis alba, Mortierella isabellina, Mortierella pulchella, Mycelium radicis atrovirens, Penicillium spinulosum, and a sterile isolate. Penicillium spinulosum, Penicillium thomii, and Mortierella pulchella were dominant in the hummocks, whereas Mycelium radicis atrovirens, Cladosporium sp., and one unidentified isolate were found more often in the wet plant communities. Chaunopychnis alba was isolated more frequently at the minerotrophic site compared with the other two sites. Cladosporium sp., Verticillium bulbillosum, a sterile isolate, and several yeast taxa were most abundant close to the surface. Species composition was most different between the dry hummocks and the two wet sites. In the hummocks the fungal community was more similar between the two depths than in the lawns where the groundwater surface was close to the vegetation surface. Key words: microfungi, groundwater, mire, peat, plant communities.
An analysis of morphological variation in Senecio cymbalaria (Asteraceae)
Authors: Whitton Jeannette , Bain John F.
Published: October 2007

Senecio cymbalaria Pursh is an arctic-alpine perennial that exhibits a broad range of morphological variation and occurs in four disjunct regions within North America. In this study, a morphological analysis of herbarium material is undertaken to determine whether the observed morphological variation is primarily attributable to morphological discontinuities among geographically isolated groups. Eighty individuals representing the total geographic range of the species were scored for 24 morphological characters and the data matrix subjected to principal components and cluster analyses. Individuals from the southern Rocky Mountains, previously recognized as Senecio conterminus, are separated from the remainder of S. cymbalaria in both analyses. Our results support recognition of two species, S. conterminus and S. cymbalaria. Although populations from the Gaspé and from Newfoundland form somewhat distinct clusters, neither can clearly be distinguished from populations of S. cymbalaria from Alaska, the Yukon, and Northwest Territories. Chromosome counts of 2n = 138 were obtained from two individuals from the Gaspé peninsula. Key words: biogeography, phenetics, Gulf of St. Lawrence, Senecio, disjunction, chromosome numbers.
Ultrastructure of virus-like particles in Plasmopara halstedii
Authors: Gulya T. J. , Freeman T. P. , Mayhew D. E.
Published: October 2007

Virus-like particles were observed in five North Dakota isolates of Plasmopara halstedii race 2, the causal agent of sunflower downy mildew. Virus-like particles were observed in fungal mycelium within sunflower seedlings showing typical symptoms of systemic infection as well as from seedlings displaying "twisted leaf syndrome." Virus-like particles were never observed in sunflower cells. The particles were isometric in shape and measured 23–26 nm in thin sections and 32 nm after phosphotungstic acid staining. Virus-like particles occurred dispersed throughout the cytoplasm and in membrane-bound organelles. Both crystalline and noncrystalline arrays were common. The particles were observed in haustoria, intercellular hypha, sporangiophores, zoosporangia, and oospores. Four species of double-stranded RNA were detected in sunflower tissue infected with P. halstedii; none were detected in healthy sunflower tissue. This is only the second report of an isometric, virus-like particle occurring in a member of the Peronosporales. Key words: mycovirus, downy mildew, Helianthus annuus.
Differential axis architecture in Thuja occidentalis (eastern white cedar)
Authors: Briand Christopher H. , Posluszny Usher , Larson Douglas W.
Published: October 2007

Quantitative architectural variation was investigated among the axes of Thuja occidentalis. Forty axes of each axis order were randomly sampled and for each axis: length, excurrency index, basal diameter, number of daughter axes, number of basal reiterated axes, dorsiventrality index, and percentage of length partitioned into photosynthetic (bearing green leaves) and nonphotosynthetic (nongreen) components was determined. The crown exhibited six axis orders. Both axis length and basal diameter declined with increasing axis order, and crown form was excurrent. The number of daughter axes was highest on axis order 1 (trunk) and lowest on axis order 5. Axis orders 2 through 4 had a similar number of daughter axes. The frame of the tree was composed of axis orders 1 and 2. These axes were radially symmetrical in midpoint cross section, exhibited indeterminate growth, and only a small percentage of their length was devoted to photosynthetic tissue. Axis orders 3 through 6, taken together, had many characteristics of compound leaves. They were dorsiventrally flattened, exhibited determinate growth (axis terminated by a cone or abscised), and the majority of their length was devoted to photosynthetic tissue. In autumn these axes were often abscised as a unit. Both male and female cones were located terminally on axis orders through 6, with 82.7% of male cones occurring on axis order 6, and 86.0% of female cones occurring on axis order 5. The architectural unit of T. occidentalis resembled that of Thuja plicata. Attims' model most closely resembles the architectural pattern of these two species. Key words: Thuja occidentalis, eastern white cedar, architecture.
Interrelationships of Oryza species based on electrophoretic patterns of alcohol dehydrogenase
Authors: Grover Anil , Pental Deepak
Published: October 2007

Nineteen different species belonging to the genus Oryza were studied for variation in electrophoretic patterns of alcohol dehydrogenase (ADH) extracted from germinating seeds. The ADH patterns were similar for aerobically and anaerobically germinating seeds of all the species. Oryza saliva accessions, both indica and japonica, revealed a five-band pattern on polyacrylamide gels. African cultivated rice, Oryza glaberrima, had an alcohol dehydrogenase pattern similar to that of O. sativa. Oryza perennis complex comprising of Oryza nivara, Oryza rufipogon in Asia, Oryza barthii, Oryza longistaminata in Africa, and some of the accessions of O. rufipogon from America had ADH patterns similar to that of O. sativa. In a few accessions of O. rufipogon from America, only three bands were visualized. Oryza minuta, Oryza officinalis, Oryza punctata, Oryza alta, Oryza grandiglumis, and Oryza latifolia had similar patterns with one major band at the same Rf value as the major band of O. sativa and two minor bands corresponding to the two bands found in O. sativa. Oryza australiensis, Oryza brachyantha, and Oryza granulata had distinct patterns. Oryza ridleyi had a six-band pattern with three major and three minor bands. The three major bands correspond to the major band of O. granulata, O. officinalis, and O. australiensis. Based on alcohol dehydrogenase data, six major groups were identified amongst Oryza species. Key words: Oryza species, alcohol dehydrogenase, phylogenetics.
Development and decline of chloroplasts in exocarp of Carica papaya
Authors: Sanxter Suzanne S. , Yamamoto Harry Y. , Fisher David G. , Chan Jr. Harvey T.
Published: October 2007

Photosynthetic and ultrastructural changes of plastids in papaya fruit exocarp (Carica papaya L.) from immature to ¾-ripe stages were characterized. Pulse-modulated chlorophyll fluorometry indicated primary photochemical yield developed maximally by the dead-green stage and did not decrease thereafter, even in ¾-ripe fruit. Nonphotochemical quenching, a reflection of ΔpH, also developed maximally by the dead-green stage but began declining at the ¼-ripe stage. The pattern of photochemical quenching, an indicator of oxidation of primary electron acceptors, was similar to nonphotochemical quenching. Chlorophyll a to b ratio was 2.25 in immature fruits and about 1.70 in more mature stages. Immature fruit plastids contained loosely appressed thylakoids with few grana, whereas more mature fruits up to the ¼-ripe stage had well-developed grana. Grana of ¾-ripe fruit were destacked; thylakoids often formed vesicles. These results, along with the fluorescence properties, suggest papaya-fruit chloroplasts are mature at the dead-green and mature-green stages and at these stages resemble chloroplasts in green leaf mesophyll tissue. When internal fruit ripening began (¼-ripe), photosynthetic and ultrastructural qualities of the exocarp remained relatively unchanged, indicating external ripeness lagged considerably behind internal ripeness. Although grana of ¾-ripe fruits were structurally disorganized, the ability for primary photochemistry was retained. Key words: chlorophyll fluorescence, ultrastructure, fruit development, ripening.
Mass loss and nitrogen dynamics of decaying litter of grasslands: the apparent low nitrogen immobilization potential of root detritus
Authors: Seastedt T. R. , Parton W. J. , Ojima D. S.
Published: October 2007

Litter-bag studies and simulation modeling were used to examine the relationship between mass loss and nitrogen content of decaying prairie foliage and root litter. In contrast with forest studies, grassland roots were low in lignin and nitrogen, decayed more rapidly than foliage, and demonstrated very low nitrogen immobilization potentials. Our findings agree with reports indicating that buried substrates with high C:N ratios do not immobilize substantial amounts of nitrogen and that nitrogen-limited environments induce steeper slopes in the mass loss – nitrogen concentration relationship. However, results suggesting rapid nitrogen mineralization contradict our own studies demonstrating reduced inorganic nitrogen availability in soils of frequently burned prairie. Simulation of observed patterns using the CENTURY grassland model indicated that these results could not occur without creating soil organic matter with unrealistically high C:N ratios. Litter-bag studies of buried substrates therefore may provide an incomplete perspective on the mass loss and nitrogen dynamics of buried litter in grassland and agroecosystem soils. Key words: Andropogon gerardii, C:N ratio, decomposition, immobilization, mineralization, nitrogen.
Populus forest characterization in Elk Island National Park relative to herbivory, prescribed fire, and topography
Authors: Bork Edward W. , Hudson Robert J. , Bailey Arthur W.
Published: October 2007

Wild ungulate herbivory and prescribed fire can modify the vegetational characteristics of Populus forest plant communities and alter their potential to meet conservation objectives. Effective management of these areas depends on understanding the impact of these disturbances across natural landscapes. Our objective was to quantify various overstory and understory plant community characteristics in the Populus forests in and around Elk Island National Park, Alberta, under different disturbance regimes. Vegetation from 36 sites, stratified by four topographic positions and three historical treatment combinations of fire and native ungulate herbivory, were sampled. In these sites, we quantified tree density, basal area and cover, understory species richness and diversity, shrub density and height, as well as grass, forb, and browse annual net primary production (ANPP). Although tree canopy characteristics were similar under all three disturbances, small-diameter trees (< 5 cm) were nearly absent within the Park. The reference area outside the Park had greater browse-leaf and -twig ANPP, as well as shrub height, but lower grass ANPP. Inside the Park, burned areas had greater shrub density and ANPP of grass and forb components. Topographically, tree stand basal area, cover, and shrub height were greatest on the northern slope, as was browse-leaf ANPP. Species diversity and richness were relatively greater on the toe slope. Within the plant community variables examined, the disturbances and positions frequently interacted, particularly the burned treatment with the crest position and level of herbivory with the south-facing and north-facing slopes. The structure, composition, and ANPP of Populus forest in Elk Island National Park has been significantly affected by both ungulate herbivory and prescribed burning. These factors, along with topography, influence the vegetation and are consequently important for management of the park's habitat and ungulate populations. Key words: ANPP, national park, prescribed fire, structure, topography, ungulate herbivory.
COLLECTIVE POLITICAL OPINION FORMATION IN NONLINEAR SOCIAL INTERACTION
Authors: KIM SOO YONG , PARK CHUNG HYUN , KIM KYUNGSIK
Published: October 2007

We have presented a numerical model of a collective opinion formation procedure to explain political phenomena such as two-party and multi-party systems in politics, political unrest, military coup d'etats and netizen revolutions. Nonlinear interaction with binary and independent decision making processes can yield various collective behaviors or collective political opinions. Statistical physics and nonlinear dynamics may provide useful tools to study various socio-political dynamics.
AN ALTERNATIVE ACCURATE SOLUTION OF THE EXPONENTIAL COSINE SCREENED COULOMB POTENTIAL
Authors: BAYRAK O. , BOZTOSUN I.
Published: October 2007

In this paper, we show an alternative and accurate solution of the radial Schrödinger equation for the exponential cosine screened Coulomb potential within the framework of the asymptotic iteration method. Unlike other methods, which require approximations for the centrifugal or exponential terms, we show that it is possible to solve the full potential without making any approximations within the framework of this method. The bound state energy eigenvalues are obtained for any n and l values and the results are compared with the findings of different methods for several screening parameters. Moreover, we study the screening parameter δ = 0 case to obtain the energy eigenvalues and corresponding eigenfunctions of this potential in a closed-form.
EFFECTS OF MASS MEDIA AND CULTURAL DRIFT IN A MODEL FOR SOCIAL INFLUENCE
Authors: MAZZITELLO KARINA I. , CANDIA JULIÁN , DOSSETTI VÍCTOR
Published: October 2007

In the context of an extension of Axelrod's model for social influence, we study the interplay and competition between the cultural drift, represented as random perturbations, and mass media, introduced by means of an external homogeneous field. Unlike previous studies [J. C. González-Avella et al., Phys. Rev. E72, 065102(R) (2005)], the mass media coupling proposed here is capable of affecting the cultural traits of any individual in the society, including those who do not share any features with the external message. A noise-driven transition is found: for large noise rates, both the ordered (culturally polarized) phase and the disordered (culturally fragmented) phase are observed, while, for lower noise rates, the ordered phase prevails. In the former case, the external field is found to induce cultural ordering, a behavior opposite to that reported in previous studies using a different prescription for the mass media interaction. We compare the predictions of this model to statistical data measuring the impact of a mass media vasectomy promotion campaign in Brazil.