bluuebunny/crossref_metadata_2025 huggingface dataset:
Underwater tunable organ-pipe sound source
Authors: Morozov Andrey K. , Webb Douglas C.
Published: July 2007

A highly efficient frequency-controlled sound source based on a tunable high-Q underwater acoustic resonator is described. The required spectrum width was achieved by transmitting a linear frequency-modulated signal and simultaneously tuning the resonance frequency, keeping the sound source in resonance at the instantaneous frequency of the signal transmitted. Such sound sources have applications in ocean-acoustic tomography and deep-penetration seismic tomography. Mathematical analysis and numerical simulation show the Helmholtz resonator’s ability for instant resonant frequency switching and quick adjustment of its resonant frequency to the instantaneous frequency signal. The concept of a quick frequency adjustment filter is considered. The discussion includes the simplest lumped resonant source as well as the complicated distributed system of a tunable organ pipe. A numerical model of the tunable organ pipe is shown to have a form similar to a transmission line segment. This provides a general form for the principal results, which can be applied to tunable resonators of a different physical nature. The numerical simulation shows that the “state-switched” concept also works in the high-Q tunable organ pipe, and the speed of frequency sweeping in a high-Q tunable organ pipe is analyzed. The simulation results were applied to a projector design for ocean-acoustic tomography.
Individual differences in source identification from synthesized impact sounds
Authors: Lutfi Robert A. , Liu Ching-Ju
Published: July 2007

Impact sounds were synthesized according to standard textbook equations given for the motion of freely vibrating membranes, bars, and plates. In a two-interval, forced-choice procedure, highly practiced listeners identified from these sounds predefined target sources based on their material and size, the hardness of the striking mallet, and the presence or absence of light damping applied to the center of the source. Listener decision strategy in each case was determined from a discriminant analysis of trial-by-trial responses resulting in a vector of regression weights given to different acoustic parameters. The analysis revealed significant differences in decision strategy across listeners within identification task, but similarity in decision strategy within listeners across variations in task. Only when the acoustic information for identification was highly constrained (identification of damping) did listeners adopt similar decision strategies approaching that of an ideal observer. Despite the large individual differences in decision strategy, identification accuracy was, in most cases, similar across listeners. Where there were differences in identification accuracy the differences appeared largely related to differences in internal noise and not decision strategy. The results are generally comparable to those obtained for the discrimination of arbitrary tone patterns.
Theory construction in auditory perception: Need for development of teaching materials
Authors: Durlach Nathaniel I. , Gallun Frederick J.
Published: July 2007

Beginning investigators in the field of auditory perception receive essentially no instruction in how to go about constructing new and useful theories. This article considers some of the characteristics of good theory in this field and is intended to serve as a call for further discussion of the processes by which such theory is created and for the development of appropriate theory-construction teaching materials.
Enhancing low frequency sound transmission measurements using a synthesis method
Authors: Bravo Teresa , Maury Cédric
Published: July 2007

The characterization of low frequency sound transmission between two rooms via a flexible panel is investigated experimentally in this work. Previously, the individual effects of the transmission suite on the measured sound reduction index have been studied analytically, and the results have been compared with the ideal case of having free field radiation conditions on both sides of the panel. A new approach is proposed using a near-field array of loudspeakers driven by a set of optimized signals such that a diffuse pressure field is reproduced on the surface of the partition to be tested. The practical effectiveness of this method is assessed when using a set of 16 acoustic sources located in the source reverberant room in close proximity to an aluminium panel. The experimental results obtained confirm the dependence of the characterized sound reduction index on the particular test chamber considered in the low frequency range. They also validate the proposed synthesis method for providing an estimate that only depends on the properties of the partition itself.
Statistical analysis of sound transmission results obtained on the New Jersey continental shelf
Authors: Dediu Simona M. , Siegmann William L. , Carey William M.
Published: July 2007

Experiments have been conducted near the site of AMCOR Borehole 6010 on the New Jersey Shelf to evaluate propagation predictability in sandy shallow-water environments. The influence of a nonlinear frequency dependence of the sediment volume attenuation in the uppermost sediment layer at this location is examined. Previously it was determined that a frequency power-law exponent of 1.5 was required for the best modeling of experimental results over the band 50–1000Hz. The approach here references the attenuation to an accepted value at 1kHz and makes extensive comparisons between measurements and calculations, to determine a power-law exponent of 1.85±0.15.
Identifying Mutator Phenotypes among Fluoroquinolone-Resistant Strains of
Streptococcus pneumoniae
Using Fluctuation Analysis
Authors: Gould Carolyn V. , Sniegowski Paul D. , Shchepetov Mikhail , Metlay Joshua P. , Weiser Jeffrey N.
Published: July 2007

The occurrence of mutator phenotypes among laboratory-generated and clinical levofloxacin-resistant strains of
Streptococcus pneumoniae
was determined using fluctuation analysis. The in vitro selection for levofloxacin-resistant mutants of strain D39, each with point mutations in both
gyrA
and
parC
or
parE
, was not associated with a significant change in the mutation rate. Two of eight clinical isolates resistant to levofloxacin (MIC, >8 μg/ml) had estimated mutation rates of 1.2 × 10
−7
and 9.4 × 10
−8
mutations per cell division, indicating potential mutator phenotypes, compared to strain D39, which had an estimated mutation rate of 1.4 × 10
−8
mutations per cell division. The levofloxacin-resistant isolates with the highest mutation rates showed evidence of dysfunctional mismatch repair and contained missense mutations in
mut
genes at otherwise highly conserved sites. The association of hypermutability in levofloxacin-resistant
S. pneumoniae
clinical isolates with mutations in DNA mismatch repair genes provides further evidence that mismatch repair mutants may have a selective advantage in the setting of antibiotic pressure, facilitating the development of further antibiotic resistance.
Targeting Fatty Acid Biosynthesis for the Development of Novel Chemotherapeutics against
Mycobacterium tuberculosis
: Evaluation of A-Ring-Modified Diphenyl Ethers as High-Affinity InhA Inhibitors
Authors: Boyne Melissa E. , Sullivan Todd J. , amEnde Christopher W. , Lu Hao , Gruppo Veronica , Heaslip Darragh , Amin Anita G. , Chatterjee Delphi , Lenaerts Anne , Tonge Peter J. , Slayden Richard A.
Published: July 2007

Structure-based design was used to develop a focused library of A-ring-modified diphenyl ether InhA inhibitors. From this library of analogs, two high-affinity alkyl-substituted diphenyl ethers, 6PP and 8PP, were selected for advanced study into their in vitro activity against
Mycobacterium tuberculosis
clinical isolates, their in vivo properties, and their signature response mode of action. 6PP and 8PP demonstrated enhanced activity against whole bacteria and showed activity in a rapid macrophage model of infection. In addition, transcriptional profiling revealed that the A-ring modifications of 6PP and 8PP increased the specificity of each analog for InhA. Both analogs had substantially longer half-lives in serum than did the parent compound, exhibited a fivefold reduction in cytotoxicity compared to the parent compound, and were well tolerated when administered orally at 300 mg/kg of body weight in animal models. Thus, the A-ring modifications increased the affinity and whole-cell specificity of the compounds for InhA and increased their bioavailability. The next step in optimization of the pharmacophore for preclinical evaluation is modification of the B ring to increase the bioavailability to that required for oral delivery.
Plasmid-Encoded ACC-4, an Extended-Spectrum Cephalosporinase Variant from
Escherichia coli
Authors: Papagiannitsis Costas C. , Tzouvelekis Leonidas S. , Tzelepi Eva , Miriagou Vivi
Published: July 2007

ACC-4, an omega loop mutant (Val
211
→Gly) of the
Hafnia alvei
-derived cephalosporinase ACC-1, was encoded by an
Escherichia coli
plasmid. The genetic environment of
bla
ACC-4
shared similarities with plasmidic regions carrying
bla
ACC-1
. Kinetics of β-lactam hydrolysis and levels of resistance to β-lactams showed that ACC-4 was more effective than ACC-1 against expanded-spectrum cephalosporins.
Effects of Human Immunodeficiency Virus Protease Inhibitors on the Intestinal Absorption of Tenofovir Disoproxil Fumarate In Vitro
Authors: Tong Leah , Phan Truc K. , Robinson Kelly L. , Babusis Darius , Strab Robert , Bhoopathy Siddhartha , Hidalgo Ismael J. , Rhodes Gerald R. , Ray Adrian S.
Published: July 2007

Human immunodeficiency virus protease inhibitors (PIs) modestly affect the plasma pharmacokinetics of tenofovir (TFV; −15% to +37% change in exposure) following coadministration with the oral prodrug TFV disoproxil fumarate (TDF) by a previously undefined mechanism. TDF permeation was found to be reduced by the combined action of ester cleavage and efflux transport in vitro. Saturable TDF efflux observed in Caco-2 cells suggests that at pharmacologically relevant intestinal concentrations, transport has only a limited effect on TDF absorption, thus minimizing the magnitude of potential intestinal drug interactions. Most tested PIs increased apical-to-basolateral TDF permeation and decreased secretory transport in MDCKII cells overexpressing P-glycoprotein (Pgp; MDCKII-MDR1 cells) and Caco-2 cells. PIs were found to cause a multifactorial effect on the barriers to TDF absorption. All PIs showed similar levels of inhibition of esterase-dependent degradation of TDF in an intestinal subcellular fraction, except for amprenavir, which was found to be a weaker inhibitor. All PIs caused a dose-dependent increase in the accumulation of a model Pgp substrate in MDCKII-MDR1 cells. Pgp inhibition constants ranged from 10.3 μM (lopinavir) to >100 μM (amprenavir, indinavir, and darunavir). Analogous to hepatic cytochrome P450-mediated drug interactions, we propose that the relative differences in perturbations in TFV plasma levels when TDF is coadministered with PIs are based in part on the net effect of inhibition and induction of intestinal Pgp by PIs. Combined with prior studies, these findings indicate that intestinal absorption is the mechanism for changes in TFV plasma levels when TDF is coadministered with PIs.
Orally Administered Combined Regimens for Treatment of
Mycobacterium ulcerans
Infection in Mice
Authors: Ji Baohong , Chauffour Aurélie , Robert Jérôme , Lefrançois Sébastien , Jarlier Vincent
Published: July 2007

Eight weeks of treatment with rifampin-streptomycin sterilizes
Mycobacterium ulcerans
infection in mice. Because the bactericidal activity against
M. ulcerans
of the combination rifampin-moxifloxacin, rifampin-clarithromycin, or moxifloxacin-clarithromycin was similar to that of rifampin-streptomycin, these combinations might be considered as alternative, orally administered combined regimens for treatment of Buruli ulcer in humans.
Enhancement of Apoptosis of THP-1 Cells Infected withMycobacterium tuberculosisby Inhalable Microparticles and Relevance to Bactericidal Activity
Authors: Yadav Awadh Bihari , Misra Amit
Published: July 2007

The relevance of apoptosis to killing of intracellularMycobacterium tuberculosiswas studied with phorbol-differentiated THP-1 cells. Microparticles containing isoniazid and rifabutin induced intrinsic apoptosis and bacterial killing equivalent to that with dissolved drugs and maximally enhanced purinergic P2 receptor activity, while drug-free microparticles induced apoptosis via a different mechanism without killing bacteria.
The Ssk1p Response Regulator and Chk1p Histidine Kinase Mutants of
Candida albicans
Are Hypersensitive to Fluconazole and Voriconazole
Authors: Chauhan Neeraj , Kruppa Michael , Calderone Richard
Published: July 2007

Hypersensitivity to the triazoles fluconazole and voriconazole associated with two-component signal transduction proteins has not been reported in
Candida albicans
. Herein, we show that strains of
C. albicans
lacking the response regulator Ssk1p or the Chk1p histidine kinase signal transduction proteins are hypersensitive to fluconazole and voriconazole compared to wild-type (wt) as well as gene-reconstituted strains, reflecting an increased hypersensitivity to these drugs of about 16- to 500-fold. In comparison to wt cells, both mutants had elevated levels of fluconazole accumulation and reduced viability upon incubation with either drug, suggesting that in the absence of Ssk1p or Chk1p, fluconazole and voriconazole have significantly increased fungicidal effects on
C. albicans
.
Intracellular Pharmacokinetics of Once versus Twice Daily Zidovudine and Lamivudine in Adolescents
Authors: Flynn Patricia M. , Rodman John , Lindsey Jane C. , Robbins Brian , Capparelli Edmund , Knapp Katherine M. , Rodriguez Jose F. , McNamara James , Serchuck Leslie , Heckman Barbara , Martinez Jaime
Published: July 2007

Zidovudine (ZDV) and lamivudine (3TC) metabolism to triphosphates (TP) is necessary for antiviral activity. The aims of this study were to compare ZDV-TP and 3TC-TP concentrations in adolescents receiving twice daily (BID) and once daily (QD) regimens and to determine the metabolite concentrations of ZDV and 3TC during chronic therapy on a QD regimen. Human immunodeficiency virus-infected patients (12 to 24 years) taking ZDV (600 mg/day) and 3TC (300 mg/day) as part of a highly active antiretroviral therapy regimen received QD and BID regimens of ZDV and 3TC for 7 to 14 days in a crossover design. Serial blood samples were obtained over 24 h on the QD regimen. Intracellular mono-, di-, and triphosphates for ZDV and 3TC were measured. The median ratio of BID/QD for ZDV-TP predose concentrations was 1.28 (95% confidence interval [CI] = 1.00 to 2.45) and for 3TC-TP was 1.12 (95% CI = 0.81 to 1.96). The typical population estimated half-lives (± the standard error of the mean) were 9.1 ± 0.859 h for ZDV-TP and 17.7 ± 2.8 h for 3TC-TP. Most patients had detectable levels of the TP of ZDV (24 of 27) and 3TC (24 of 25) 24 h after dosing, and half-lives on a QD regimen were similar to previously reported values when the drugs were given BID. Lower, but not significantly different, concentrations of ZDV-TP were demonstrated in the QD regimen compared to the BID regimen (
P
= 0.056). Although findings were similar between the BID and QD groups, the lower concentrations of ZDV and the number of patients below the level of detection after 24 h suggests that ZDV should continue to be administered BID.
Aerosol Infection of BALB/c Mice with
Brucella melitensis
and
Brucella abortus
and Protective Efficacy against Aerosol Challenge
Authors: Kahl-McDonagh M. M. , Arenas-Gamboa A. M. , Ficht T. A.
Published: July 2007

Brucellosis is a zoonotic disease with a worldwide distribution that can be transmitted via intentional or accidental aerosol exposure. In order to engineer superior vaccine strains against
Brucella
species for use in animals as well as in humans, the possibility of challenge infection via aerosol needs to be considered to properly evaluate vaccine efficacy. In this study, we assessed the use of an aerosol chamber to infect deep lung tissue of mice to elicit systemic infections with either
Brucella abortus
or
B. melitensis
at various doses. The results reveal that
B. abortus
causes a chronic infection of lung tissue in BALB/c mice and peripheral organs at low doses. In contrast,
B. melitensis
infection diminishes more rapidly, and higher infectious doses are required to obtain infection rates in animals similar to those of
B. abortus
. Whether this difference translates to severity of human infection remains to be elucidated. Despite these differences, unmarked deletion mutants BAΔ
asp
24 and BMΔ
asp
24 consistently confer superior protection to mice against homologous and heterologous aerosol challenge infection and should be considered viable candidates as vaccine strains against brucellosis.
I/St Mice Hypersusceptible toMycobacterium tuberculosisAre Resistant toM. avium
Authors: Kondratieva E. V. , Evstifeev V. V. , Kondratieva T. K. , Petrovskaya S. N. , Pichugin A. V. , Rubakova E. I. , Averbakh M. M. , Apt A. S.
Published: July 2007

We previously demonstrated that mice of the I/St strain are extremely susceptible toMycobacterium tuberculosis, as well as to the taxonomically distant intracellular bacteriaChlamydia pneumoniaeandSalmonella enterica. To broaden our knowledge about the control of susceptibility to intracellular pathogens, we studied the infection caused byMycobacterium aviumvirulent strain 724 in a panel of inbred mouse strains and found that I/St mice are resistant toM. avium. By comparing I/St mice with B6 mice, we demonstrated that (i) B6 mice are much more susceptible to infection caused byM. aviumin terms of bacterial multiplication in the lung tissue and severity of lung pathology; (ii) in B6 mice but not in I/St mice infection leads to prolonged leukocyte infiltration of the lung tissue, development of necrotic lung granulomata, and lethality; and (iii) the unfavorable infectious course in B6 mice is accompanied by elevated production of gamma interferon, tumor necrosis factor alpha, and especially interleukin-12 in the lungs. Importantly,M. avium-resistant I/St mice carry a functionalrallele of theSlc11a1(formerlyNramp1) gene, while B6 mice have theSlc11a1sgenotype. Segregation genetic analysis of (I/St × B6) F2 hybrids demonstrated that susceptibility or resistance to infection caused byM. aviumlargely depended upon theSlc11a1genotype and that other genetic traits had a relatively weak influence. This close-to-monogenic pattern differs sharply from the host control of many other intracellular bacterial infections, for which the involvement of numerous quantitative trait loci has been ubiquitously observed.
c-Jun N-Terminal Kinase 1 Is Required for Toll-Like Receptor 1 Gene Expression in Macrophages
Authors: Izadi Hooman , Motameni Amirreza T. , Bates Tonya C. , Olivera Elias R. , Villar-Suarez Vega , Joshi Ila , Garg Renu , Osborne Barbara A. , Davis Roger J. , Rincón Mercedes , Anguita Juan
Published: July 2007

The regulation of innate immune responses to pathogens occurs through the interaction of Toll-like receptors (TLRs) with pathogen-associated molecular patterns and the activation of several signaling pathways whose contribution to the overall innate immune response to pathogens is poorly understood. We demonstrate a mechanism of control of murine macrophage responses mediated by TLR1/2 heterodimers through c-Jun N-terminal kinase 1 (JNK1) activity. JNK controls tumor necrosis factor alpha production and TLR-mediated macrophage responses toBorrelia burgdorferi, the causative agent of Lyme disease, and the TLR1/TLR2-specific agonist PAM3CSK4. JNK1, but not JNK2, activity regulates the expression of thetlr1gene in the macrophage cell line RAW264.7, as well as in primary CD11b+cells. We also show that the proximal promoter region of the humantlr1gene contains an AP-1 binding site that is subjected to regulation by the kinase and binds two complexes that involve the JNK substrates c-Jun, JunD, and ATF-2. These results demonstrate that JNK1 regulates the response to TLR1/2 ligands and suggest a positive feedback loop that may serve to increase the innate immune response to the spirochete.
Impaired Expression of Perforin and Granulysin in CD8+T Cells at the Site of Infection in Human Chronic Pulmonary Tuberculosis
Authors: Andersson Jan , Samarina Arina , Fink Joshua , Rahman Sayma , Grundström Susanna
Published: July 2007

Protective immunity in tuberculosis is dependent on the coordinated release of cytolytic effector molecules from effector T cells and the subsequent granule-associated killing of infected target cells. In this study, we investigated the expression of cytolytic (perforin and granzyme A) and antimicrobial (granulysin) molecules at the single-cell level in cryopreserved lung tissue from patients with chronic, progressive tuberculosis disease. Quantification of protein-expressing cells was performed by in situ imaging, while mRNA levels in the infected tissue were analyzed by real-time PCR. Persistent inflammation, including excessive expression of inducible nitric oxide synthase in CD68+macrophages and significant infiltration of CD3+, CD8+and CD4+T cells, was evident in tuberculosis lesions in all patients. However, despite the accumulation of CD3+T cells, perforin- and granulysin-expressing CD3+T cells were detected at two- to threefold-lower ratios in the tuberculosis lesions than in distal lung parenchyma and uninfected control lungs, respectively. This was evident at both the protein and mRNA levels. Moreover, perforin- and granulysin-expressing CD8+T cells were scarce in individual granulomas within the tuberculosis lesions. In contrast, significant up-regulation of granzyme A-expressing CD3+T cells was evident in the lesions from all patients. Confocal microscopy revealed coexpression of perforin and granulysin, primarily in CD8+T cells; however, this expression was lower in the tuberculosis lesions. These findings suggest that symptomatic, chronic tuberculosis disease is associated with insufficient up-regulation of perforin and granulysin coexpression in CD8+T cells at the local site of infection.
T-Cell-Independent Humoral Immunity Is Sufficient for Protection against Fatal Intracellular Ehrlichia Infection
Authors: Bitsaktsis Constantine , Nandi Bisweswar , Racine Rachael , MacNamara Katherine C. , Winslow Gary
Published: July 2007

Although humoral immunity has been shown to contribute to host defense during intracellular bacterial infections, its role has generally been ancillary. Instead, CD4 T cells are often considered to play the dominant role in protective immunity via their production of type I cytokines. Our studies of highly pathogenicEhrlichiabacteria isolated fromIxodes ovatus(IOE) reveal, however, that this paradigm is not always correct. Immunity to IOE infection can be induced by infection with a closely related weakly pathogenic ehrlichia,Ehrlichia muris.Type I cytokines (i.e., gamma interferon, tumor necrosis factor alpha, and interleukin-12) were not necessary forE. muris-induced immunity. In contrast, humoral immunity was essential, as shown by the fact thatE. muris-infected B-cell-deficient mice were not protected from IOE challenge and becauseE. murisimmunization was effective in CD4-, CD8-, and major histocompatibility complex (MHC) class II-deficient mice. Immunity was unlikely due to nonspecific inflammation, as prior infection withListeria monocytogenesdid not induce immunity to IOE. Antisera from both wild-type and MHC-II-deficient mice provided at least partial resistance to challenge infection, and protection could also be achieved following transfer of total, but not B-cell-depleted, splenocytes obtained fromE. muris-immunized mice. The titers of class-switched antibodies in immunized CD4 T-cell- and MHC class II-deficient mice, although lower than those observed in immunized wild-type mice, were significant, indicating thatE. muriscan induce class switch recombination in the absence of classical T-cell-mediated help. These studies highlight a major protective role for classical T-cell-independent humoral immunity during an intracellular bacterial infection.
Genetic Alteration ofMycobacterium smegmatisTo Improve Mycobacterium-Mediated Transfer of Plasmid DNA into Mammalian Cells and DNA Immunization
Authors: Mo Yongkai , Quanquin Natalie M. , Vecino William H. , Ranganathan Uma Devi , Tesfa Lydia , Bourn William , Derbyshire Keith M. , Letvin Norman L. , Jacobs William R. , Fennelly Glenn J.
Published: July 2007

Mycobacteria target and persist within phagocytic monocytes and are strong adjuvants, making them attractive candidate vectors for DNA vaccines. We characterized the ability of mycobacteria to deliver transgenes to mammalian cells and the effects of various bacterial chromosomal mutations on the efficiency of transfer in vivo and in vitro. First, we observed green fluorescent protein expression via microscopy and fluorescence-activated cell sorting analysis after infection of phagocytic and nonphagocytic cell lines byMycobacterium smegmatisorM. bovisBCG harboring a plasmid encoding the fluorescence gene under the control of a eukaryotic promoter. Next, we compared the efficiencies of gene transfer usingM. smegmatisor BCG containing chromosomal insertions or deletions that cause early lysis, hyperconjugation, or an increased plasmid copy number. We observed a significant—albeit only 1.7-fold—increase in the level of plasmid transfer to eukaryotic cells infected withM. smegmatishyperconjugation mutants.M. smegmatisstrains that overexpressed replication proteins (Rep) of pAL5000, a plasmid whose replicon is incorporated in many mycobacterial constructs, generated a 10-fold increase in plasmid copy number and 3.5-fold and 3-fold increases in gene transfer efficiency to HeLa cells and J774 cells, respectively. Although BCG strains overexpressing Rep could not be recovered, BCG harboring a plasmid with a copy-up mutation inoriMresulted in a threefold increase in gene transfer to J774 cells. Moreover,M. smegmatisstrains overexpressing Rep enhanced gene transfer in vivo compared with a wild-type control. Immunization of mice with mycobacteria harboring a plasmid (pgp120hE) encoding human immunodeficiency virus gp120 elicited gp120-specific CD8 T-cell responses among splenocytes and peripheral blood mononuclear cells that were up to twofold (P< 0.05) and threefold (P< 0.001) higher, respectively, in strains supporting higher copy numbers. The magnitude of these responses was approximately one-half of that observed after intramuscular immunization with pgp120hE.M. smegmatisand other nonpathogenic mycobacteria are promising candidate vectors for DNA vaccine delivery.
Effects of elevated carbon dioxide and sucrose concentrations onArabidopsis thalianaroot architecture and anatomy
Authors: Lee-Ho Elaine , Walton Linda J. , Reid David M. , Yeung Edward C. , Kurepin Leonid V.
Published: July 2007

The objective of this study was to evaluate the effects of elevated carbon dioxide and sucrose concentrations on Arabidopsis thaliana L. Heynh root growth, morphology, and architecture. Two levels of CO2, 360 (ambient) and 900 (elevated) μmol·mol–1, and various sucrose concentrations were used. A. thaliana plants grown on a phytagar medium in small chambers with elevated CO2had longer roots, more lateral root growth and a more dichotomous branching pattern than plants grown in ambient CO2. Roots in elevated CO2had wider root diameters, and showed considerably more secondary growth such as larger diameter vascular cylinders and better-developed periderm. Addition of sucrose to the media closely resembled the effects of elevated CO2. Further, the increase in sucrose concentration had a more pronounced effect on root morphology under ambient, than elevated CO2. Thus, both elevated CO2and increased sucrose concentrations promote root growth by increasing their number, length, and diameter, and by changing the branching pattern from herringbone to dichotomous.
Floral development, fruit set, and dispersal of the Gulf of St. Lawrence Aster (Symphyotrichum laurentianum) (Fernald) Nesom
Authors: Lacroix Christian R. , Steeves Royce , Kemp Joni F.
Published: July 2007

The Gulf of St. Lawrence aster, Symphyotrichum laurentianum (Fernald) Nesom is listed as “threatened” according to the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). This rare halophyte is found in only a few locations in New Brunswick, Prince Edward Island, and the Magdalen Islands in Quebec. Developmental evidence confirms that there are two types of florets within each flower head and that each floral type has a biseriate pappus. The centrally located “disk” florets are distinctly larger than the more numerous peripheral “pistillate” florets throughout their development. The disk florets are bisexual and consist of an ovule, a style with a bifid stigma, and four to five stamens. The peripheral florets are pistillate and consist of an ovule and a style with a bifid stigma but no stamens. The main goals of this study were to assess fruit set in both types of florets, and the wind dispersal potential of their fruit (achenes). Pistillate flowers had a lower percentage of embryo-containing (filled) achenes (15.1%) than hermaphroditic florets (27.8%) in plants grown ex situ. The majority (68.3%) of filled achenes were produced by pistillate florets. Heads grown in situ had 64.9% filled achenes. Although the achenes of this plant have structures to aid dispersal by wind, in situ observations and experimental data show that this method of dispersal may be affected by the influence of the surrounding vegetation and flooding events. The impact of other factors that may affect the reproductive biology of this rare plant are discussed.
Trametes gibbosa (Basidiomycetes, Polyporales) in the USA and Canada
Authors: Kout J. , Vlasák J.
Published: July 2007

The polypore Trametes gibbosa (Pers.) Fries, common in Europe and Asia, is reported from eastern North America for the first time. Single basidiospore cultures from Pennsylvania, United States, and Quebec, Canada, were paired with each other and with cultures from the Czech Republic. The North American intercollection crosses were 60% compatible and 100% compatible with the Czech cultures. All the crosses among the Czech cultures were 100% compatible. The recent introduction of T. gibbosa to North America is suggested as a possible explanation for the limited number of mating-type alleles and subsequent incompatibility among the North American cultures.
Combining alders, frankiae, and mycorrhizae for the revegetation and remediation of contaminated ecosystems
Authors: Roy Sébastien , Khasa Damase P. , Greer Charles W.
Published: July 2007

Alder shrubs and trees that are capable of forming symbioses with mycorrhizal fungi and the nitrogen-fixing actinomycete Frankia sp. are particularly hardy species found worldwide in harsh and nutrient-deficient ecosystems. The mycorrhizal symbiosis may assist alders in nutrient and water uptake, while the actinorhizal symbiosis provides assimilable nitrogen. It is through these highly efficient symbioses, in which microsymbionts benefit from plant photosynthates, that actinorhizal plants such as alders colonize poor substrates, enrich soil, and initiate plant succession. These natural capabilities, combined with careful screening of microsymbionts and host plants, may prove useful for the rehabilitation of disturbed ecosystems. Although alders have been used extensively at industrial scales in forestry, nurse planting, and contaminated land revegetation, relatively little research has focussed on their actinorhizal and mycorrhizal plant–microbe interactions in contaminated environments. To study such a topic is, however, critical to the successful development of phytotechnologies, and to understand the impact of anthropogenic stress on these organisms. In this review, we discuss two alder-based phytotechnologies that hold promise: the stimulation of organic contaminant biodegradation (rhizodegradation) by soil microflora in the presence of alders, and the phytostabilization of inorganic contaminants. We also summarize the plant–microbe interactions that characterize alders, and discuss important issues related to the study of actinorhizal and (or) mycorrhizal alders for the rehabilitation of disturbed soils.
Vegetation responses to conifer encroachment in a western Cascade meadow: a chronosequence approach
Authors: Haugo Ryan D. , Halpern Charles B.
Published: July 2007

Conifer invasion of mountain meadows is pervasive in western North America, but its consequences for plant composition and diversity have not been studied. We used a chronosequence approach to reconstruct temporal patterns of vegetation change in response to ~200 years of conifer encroachment of a dry, montane meadow in the western Cascade Range, Oregon. Tree age distributions, forest structure, light, and vegetation composition were determined for three hundred and fifty-six 10 m × 10 m samples representing a gradient from open meadow to old forest (>90 years). Nonmetric multidimensional scaling revealed strong turnover in species composition from open meadow to old forest. Ordination axes were highly correlated with light availability and density/basal area of encroaching grand fir, Abies grandis (Dougl. ex D. Don) Lindl., and lodgepole pine, Pinus contorta Dougl. ex Loud. Cover of meadow species declined steeply with establishment of A. grandis ; richness declined more gradually and extirpations of meadow species were rare. Forest herbs colonized within two decades of tree establishment and within 60–80 years dominated the understory flora. In contrast with meadow species, changes in richness and cover of forest herbs were weakly related to changes in forest structure. Rapid replacement of meadow by forest species and long-term effects of trees on soils may limit potential for restoration of these unique habitats.
The association between floral longevity and pollen removal, pollen receipt, and fruit production in flame azalea (Rhododendron calendulaceum)
Authors: Blair Amy C. , Wolfe Lorne M.
Published: July 2007

Floral longevity is an important feature of a plant’s reproductive strategy. The goal of this study was to examine flower life span in the shrub flame azalea ( Rhododendron calendulaceum (Michx.) Torr.) to determine if it is fixed or plastic and to evaluate its association with pollen removal and receipt. Unmanipulated flowers remained open for ~10 days, while hand-pollinated flowers closed earlier (~7 days), indicating that these flowers are subject to pollination-induced senescence. In 2002, pollen removal was rapid (~70% of pollen was removed in the first 2 h of anthesis), while female function was a slower process (pollen accumulated on stigmas for up to 4 days). Fruit set was pollen limited, as 80% of hand-outcrossed flowers set fruit versus 35% of naturally pollinated flowers. This is likely the result of the pollen-collecting behavior of a common solitary bee, which did not contact stigmas. In sharp contrast, 2003 was a cooler and wetter spring, few flower visitors were observed, and virtually no pollen was removed from or deposited on stigmas after 48 h. These results suggest that the flower life span of flame azalea is a result of selection for increasing the probability of pollen receipt rather than pollen dispersal.
From genes to patterns: Auxin distribution and auxin-dependent gene regulation in plant pattern formation
Authors: Krogan Naden T. , Berleth Thomas
Published: July 2007

It has long been recognized that the plant hormone auxin plays integral roles in a variety of plant processes. More recently, it has become clear that these processes include some of the most basic pattern formation mechanisms needed to establish a functional plant body. Considerable insight into how this regulation plays out at the molecular level has been attained in recent years. Of special note are the complementary actions of the auxin efflux carrier proteins responsible for the formation of instructive auxin concentration gradients and the transcription factor complexes required for the appropriate interpretation of such instructions. The numerous players involved and the complexity of their regulation provide insight into how a single plant hormone can operate in such a multifunctional fashion. Many new features of auxin action can now be quantified and visualized, and three-dimensional models of auxin patterning can be tested and mathematically modeled. With these new advances, the developmental biology of auxin-mediated patterning has turned into a subject of plant systems biology research.
Pollen-mediated gene flow in a small, fragmented natural population of Fagus crenata
Authors: Hanaoka So , Yuzurihara Jungo , Asuka Yamashita , Tomaru Nobuhiro , Tsumura Yoshihiko , Kakubari Yoshitaka , Mukai Yuzuru
Published: July 2007

Pollen-mediated gene flow was analyzed in a small, fragmented, natural population of Fagus crenata Blume by surveying five microsatellite markers in seedlings derived from open-pollinated crosses. Paternity of 162 seedlings derived from two maternal trees was assigned by the maximum-likelihood method using CERVUS 2.0, and pollen dispersal patterns within the study site were determined. Most of the trees within the site sired seeds, although we found evidence of limited pollen-mediated gene flow from outside the stand; 92% of the matings that generated the seedlings occurred between trees within the population, and 8% of the matings were mediated by pollen derived from trees located outside the study site. Although the pollen-mediated gene flow within the site was not strongly limited, mating frequencies of paternal trees were found to be weakly negatively correlated with their distance from the mother trees, positively correlated with their stem diameter at breast height, and uncorrelated with their relatedness to the mother trees.
Seasonal variation in plant nutritive quality for Greater Snow Goose goslings in mesic tundra
Authors: Audet Benoît , Lévesque Esther , Gauthier Gilles
Published: July 2007

Variation in nutritive quality over time and among forage plants is important for herbivores such as geese. We examined the seasonal variation of some nutritive attributes (nitrogen, neutral detergent fibre, and phenolic compounds) of five plant species consumed by Greater Snow Geese ( Chen caerulescens atlantica ) L. in mesic tundra, a habitat where goose feeding ecology has been little studied compared with wetlands. We sampled ungrazed, aboveground plant tissues five times at 10–14 d intervals between 1 July and 15 August 2003 on Bylot Island, Nunavut. The species were Arctagrostis latifolia (R. Br.) Griseb. (Gramineae), Luzula nivalis (Laest.) Beurl. (Juncaceae), Oxytropis maydelliana Trautv. (Leguminosae), Oxyria digyna (L.) Hill, and Polygonum viviparum L. (both Polygonaceae). All species showed a seasonal decline in nitrogen content in both leaves and flowering heads (includes flowers and fruits) but the amplitude was variable among species (from 10% to 62% decline depending on the species). Neutral detergent fibre concentration in leaves remained stable or increased slightly over time in contrast to flowering heads where it increased in all species (from 7% to 94%). Fibre content was higher in flowering heads than in leaves. The total content of phenolic compounds varied throughout the summer. In some cases, the content of phenolic compounds remained stable but in others it initially increased and then decreased later on, or it increased throughout the summer. Seasonal variations in plant nutritive quality were smaller than interspecific differences. The nitrogen content of forbs (especially Oxytropis ) was high and their fibre content low compared with the grass and rush species (Luzula), particularly during the early summer.
Xylem production in six tree species growing on an island in the boreal forest region of western Quebec, Canada
Authors: Ko Heinrichs Derrick , Tardif Jacques C. , Bergeron Yves
Published: July 2007

Xylem production was studied by repeatedly taking microcore samples from the stems of six tree species growing on the “réserve écologique des Vieux-Arbres”, on Lake Duparquet, Québec, throughout the 1999 growing season. Species examined were paper birch ( Betula papyrifera Marsh.), white spruce ( Picea glauca (Moench) Voss), black spruce ( Picea mariana (Mill.) BSP), jack pine ( Pinus banksiana Lamb.), red pine ( Pinus resinosa Ait.), and eastern white cedar ( Thuja occidentalis L.). Onset of xylem cell production was observed in all species by 22 May 1999, and ended as early as mid-July and early August for white spruce and eastern white cedar, respectively. Xylem cell production in the remaining species ended between late August and mid-September. In general, the onset of latewood production ranged from the start of July to the first week of August. Typical sigmoidal curves were characteristic of ring width, number of cells, and number of earlywood cells over the growing season. Completion of the annual growth increment was quickest for white spruce and eastern white cedar, while it continued longest in both pine species. Numerous similarities in xylem production and tree ring formation over the course of the growing season were observed among the six species, suggesting that weather, along with photoperiod, plays a critical role in xylem production.
Mycorrhizal associations in Polylepis woodlands of Central Argentina
Authors: Menoyo Eugenia , Becerra Alejandra G. , Renison Daniel
Published: July 2007

Polylepis woodlands are one of the most threatened mountain ecosystems of South America, and their restoration is a high priority. To assess the mycorrhizal status in Polylepis woodlands of “Quebrada del Condorito” National Park (Córdoba Mountains, Central Argentina), we examined the roots of 22 plant species, belonging to 14 families and determined morphological types of arbuscular mycorrhiza (Arum and Paris type) and colonization level. The 22 species were colonized by arbuscular mycorrhizal fungi and dark septate endophytes. Different arbuscular mycorrhizal structures and colonization patterns were observed, although Paris-type colonization was predominant. Fourteen plant species are reported for the first time as hosts of arbuscular mycorrhizal fungi. We conclude that arbuscular mycorrhizal fungi and dark septate endophyte hosts are widespread in the Polylepis woodlands of Central Argentina and should receive special attention in future revegetation programs.
Macromolecular dynamics of the photosynthetic system over a seasonal developmental progression in Spartina alterniflora
Authors: Morash Andrea J. , Campbell Douglas A. , Ireland Robert J.
Published: July 2007

Spartina alterniflora Loisel. is a dominant primary producer in salt marsh intertidal zones along the Bay of Fundy of New Brunswick and Nova Scotia, Canada, where it has a 5-month growing season from May to September. We quantified key subunits of the S. alterniflora photosynthetic system (chlorophyll, PsbA, PsaC, AtpB, RbcL) over a seasonal developmental progression to determine resource allocations and estimate capacities for key subprocesses of photosynthesis catalyzed by light-harvesting antennae, photosystems I and II (PSI and PSII, respectively), ATP (adenosine triphosphate) synthase, and RuBisCO (ribulose bisphosphate carboxylase–oxygenase). Early in the season, all of the macromolecules peaked in concentration around day 159, but then declined as leaves elongated. Later in the season, just after flowering, chlorophyll b, PsbA, PsaC, and AtpB peaked again before declining at the end of the season. RbcL, however, did not exhibit a second late-season peak, but continually declined from the early-season peak. Estimates of metabolic flux per PSII and per RuBisCO were closely parallel until late in the season, indicating coordinated regulation of catalytic turnover per complex. Early in the season, carbon fixation per RuBisCO peaked near the expected turnover rate (kcat) for a C4 plant, but then declined. The effective absorbance cross sections of PSII varied seasonally, reflecting significant regulation of antenna performance across the season.
Environmental and biotic controls on bryophyte productivity along forest to peatland ecotones
Authors: Bauer Ilka E. , Tirlea Diana , Bhatti Jagtar S. , Errington Ruth C.
Published: July 2007

Bryophyte growth and production can be critical measurements in quantifying carbon input into peatlands. For any species, total biomass produced in a given year is determined by three main factors: abundance of the species, bulk density, and annual (length) increment. We examined the relationship of these parameters to environmental factors (water table depth, tree canopy cover) and biotic interactions (presence of other species) in seven common peatland bryophytes. Correlations suggest that bulk density changed in response to environmental variation in Sphagnum angustifolium (C. Jens. ex Russ.) C. Jens. in Tolf, Sphagnum fuscum (Schimp.) Klinggr., and Aulacomnium palustre (Hedw.) Schwaegr., and it remained constant in Pleurozium schreberi (Brid.) Mitt., Hylocomium splendens (Hedw.) Schimp. in B.S.G., Tomenthypnum nitens (Hedw.) Loeske, and Hamatocaulis vernicosus (Mitt.) Hedenäs. Length increment was dependent on water table depth in S. angustifolium, P. schreberi, and Hamatocaulis vernicosus, and changed with canopy cover in H. splendens at one of two sites examined. Overall, our results suggest that (i) in some species, changes in bulk density are likely to be an important component of changes in productivity in response to environmental variation; (ii) local vigour tends to increase with abundance, but may not do so in all cases; and (iii) phenomena such as biotic interactions and environmental extremes may lead to non-linearity of productivity responses to environmental change.
Pollen polymorphism inThymus capitatus(Lamiaceae)
Authors: Karabournioti Sophia , Eleftheriou Eleftherios P. , Thrasyvoulou Andreas , Fasseas Costas
Published: July 2007

Polymorphism with respect to size and structural characteristics occurs in pollen grains of several species. Pollen grains of Thymus capitatus (L.) Hoffmans & Link. from three different areas of Greece were collected, and their palynological characteristics were measured. Using light and scanning electron microscopy, a quantification of pollen polymorphism of T. capitatus was achieved by measuring the size and the characteristics of exine sculpture. The measurements were repeated during 3 successive years, and statistical analyses with one-way ANOVA and Duncan’s multiple range test were applied. Results revealed differences in the exine pattern between the locations; also, three palynological characteristics (surface, perimeter, and equatorial diameter) differed statistically. The results clearly indicate that pollen grains of T. capitatus are polymorphic between the sampling areas. The polymorphism has been related to environmental parameters and mainly with water availability. Average rainfall seems to be the main factor contributing to the morphological variation of pollen grains by affecting their size and exine sculpture.