bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterizing anatomical variability in breast CT images
Authors: Metheany Kathrine G. , Abbey Craig K. , Packard Nathan , Boone John M.
Published: October 2008

Previous work [Burgess et al., Med. Phys. 28, 419–437 (2001)] has shown that anatomical noise in projection mammography results in a power spectrum well modeled over a range of frequencies by a power law, and the exponent of this power law plays a critical role in determining the size at which a growing lesion reaches the threshold for detection. In this study, the authors evaluated the power‐law model for breast computed tomography (bCT) images, which can be thought of as thin sections through a three‐dimensional (3D) volume. Under the assumption of a 3D power law describing the distribution of attenuation coefficients in the breast parenchyma, the authors derived the relationship between the power‐law exponents of bCT and projection images and found it to be . They evaluated this relationship on clinical images by comparing bCT images from a set of 43 patients to Burgess’ findings in mammography. They were able to make a direct comparison for 6 of these patients who had both a bCT exam and a digitized film‐screen mammogram. They also evaluated segmented bCT images to investigate the extent to which the bCT power‐law exponent can be explained by a binary model of attenuation coefficients based on the different attenuation of glandular and adipose tissue. The power‐law model was found to be a good fit for bCT data over frequencies from , where anatomical variability dominates the spectrum. The average exponent for bCT images was 1.86. This value is close to the theoretical prediction using Burgess’ published data for projection mammography and for the limited set of mammography data available from the authors’ patient sample. Exponents from the segmented bCT images (average value: 2.06) were systematically slightly higher than bCT images, with substantial correlation between the two .
Technical Note: On Cerrobend shielding for electron beams
Authors: Wojcicka Jadwiga B. , Yankelevich Rafael , Werner Barry Leonard , Lasher Donette E.
Published: October 2008

The purpose of this study is to investigate (1) the depth at which the measurement of the block transmission factor should be made, and (2) the level of the transmission of 18 and electron beams through conventional Cerrobend. We measured the block transmission in water phantom as ionization profiles across the beam and as ionization distributions along the central axis of the beam for 18 and electron beams, for cone sizes ranging from . In our analysis, we separated the bremsstrahlung component produced in the Cerrobend block from the component originating in the head in the transmitted dose under the standard Cerrobend block. The block transmission for both beam energies and cone sizes was maximum on the central axis of the beam at depths between 0.4 and . For the beam, the maximum transmission was 6.2% for the cone, and 7.4% for the cone. For the beam, it was 9.5% for the cone, and 11.3% for the cone. For the beam and cone, it takes 2.95 and of Cerrobend to reduce the maximum block transmission to 5% and 10%, respectively. The maximum dose under a blocked electron beam occurs on the central axis closer to the surface than it does for the open beam, and the block transmission factor should be defined at this shallower depth. To decrease the block transmission factor to the level of 5% on the central axis, electron beams with energy and greater require additional shielding.
Small SRS photon field profile dosimetry performed using a PinPoint air ion chamber, a diamond detector, a novel silicon‐diode array (DOSI), and polymer gel dosimetry. Analysis and intercomparison
Authors: Pappas E. , Maris T. G. , Zacharopoulou F. , Papadakis A. , Manolopoulos S. , Green S. , Wojnecki C.
Published: October 2008

Small photon fields are increasingly used in modern radiotherapy and especially in IMRT and SRS/SRT treatments. The uncertainties related to small field profile measurements can introduce significant systematic errors to the overall treatment process. These measurements are challenging mainly due to the absence of charged particle equilibrium conditions, detector size and composition effects, and positioning problems. In this work four different dosimetric methods have been used to measure the profiles of three small circular fields having diameters of 7.5, 15.0, and : a small sensitive volume air ion chamber, a diamond detector, a novel silicon‐diode array (DOSI), and vinyl‐pyrrolidone based polymer gel dosimeter. The results of this work support the validity of previous findings, suggesting that (a) air ion chambers are not suitable for small field dosimetry since they result in penumbra broadening and require significant corrections due to severe charged particle transport alterations; (b) diamond detectors provide high resolution and rather accurate small field profile measurements, as long as positioning problems can be addressed and the necessary dose rate corrections are correctly applied; and (c) the novel silicon‐diode array (DOSI) used in this study seems to be adequate for small field profile measurements overcoming positioning problems. Polymer gel data were assumed as reference data to which the other measurement data were compared both qualitatively and quantitatively using the gamma‐index concept. Polymer gels are both phantom and dosimeter, hence there are no beam perturbation effects. In addition, polymer gels are tissue equivalent and can provide high‐spatial density and high‐spatial resolution measurements without positioning problems, which makes them useful for small field dosimetry measurements. This work emphasizes the need to perform beam profile measurements of small fields (for acceptance, commissioning, treatment planning systems data feed, and periodic quality assurance purposes) using more than one dosimetric method. The authors believe this to be a safe way towards the reduction of the overall uncertainty related to SRS/SRT treatments.
Reference dosimetry condition and beam quality correction factor for CyberKnife beam
Authors: Kawachi Toru , Saitoh Hidetoshi , Inoue Mitsuhiro , Katayose Tetsurou , Myojoyama Atsushi , Hatano Kazuo
Published: October 2008

This article is intended to improve the certainty of the absorbed dose determination for reference dosimetry in CyberKnife beams. The CyberKnife beams do not satisfy some conditions of the standard reference dosimetry protocols because of its unique treatment head structure and beam collimating system. Under the present state of affairs, the reference dosimetry has not been performed under uniform conditions and the beam quality correction factorfor an ordinarylinear accelerator has been temporally substituted for theof the CyberKnife in many sites. Therefore, the reference conditions andas a function of the beam quality index in a new way are required. The dose flatness and the error of dosimeter reading caused by radiation fields and detector size were analyzed to determine the reference conditions. Owing to the absence of beam flattening filter, the dose flatness of the CyberKnife beam was inferior to that of an ordinarylinear accelerator. And if the absorbed dose is measured with an ionization chamber which has cavity length of 2.4, 1.0 andin reference dosimetry, the dose at the beam axis for a field ofcollimator was underestimated 1.5%, 0.4%, and 0.2% on a calculation. Therefore, the maximum field shaped with acollimator and ionization chamber which has a cavity length ofor shorter were recommended as the conditions of reference dosimetry. Furthermore, to determine thefor the CyberKnife, the realistic energy spectrum of photons and electrons in water was simulated with the BEAMnrc. The absence of beam flattening filter also caused softer photon energy spectrum than that of an ordinarylinear accelerator. Consequently, thefor ionization chambers of a suitable size were determined and tabulated as a function of measurable beam quality indexes in the CyberKnife beam.
RADIATION Protection and Dosimetry: An Introduction to Health Physics
Authors: Broga Dean
Published: October 2008

RADIATION Protection and Dosimetry: An Introduction to Health Physics Stabin Michael G. Springer Science+Business Media, LLC, New York, NY, 2008. 384 pp. Price: $89.95 (hardcover) ISBN 978‐0‐387‐49982‐6.
Anniversary Paper: Past and current issues, and trends in brachytherapy physics
Authors: Thomadsen Bruce R. , Williamson Jeffrey F. , Rivard Mark J. , Meigooni Ali S.
Published: October 2008

Brachytherapy began at the turn of the 20th century, contemporary with external‐beam radiotherapy. Physicists and physicians together developed the field. There has not been a period since the beginning that has not witnessed innovations and progress in brachytherapy. At the time of this article, the pace of change in the field has never been more rapid, particularly in image‐guided brachytherapy and the development of unconventional sources and treatment techniques.
Rotational micro‐CT using a clinical C‐arm angiography gantry
Authors: Patel V. , Hoffmann K. R. , Ionita C. N. , Keleshis C. , Bednarek D. R. , Rudin S.
Published: October 2008

Rotational angiography (RA) gantries are used routinely to acquire sequences of projection images of patients from which 3D renderings of vascular structures are generated using Feldkamp cone‐beam reconstruction algorithms. However, these systems have limited resolution . Micro‐computed tomography (micro‐CT) systems have better resolution but to date have relied either on rotating object imaging or small bore geometry for small animal imaging, and thus are not used for clinical imaging. The authors report here the development and use of a 3D rotational micro‐angiography (RMA) system created by mounting a micro‐angiographic fluoroscope (MAF) [, resolution , field of view ] on a standard clinical FPD‐based RA gantry (Infinix, Model RTP12303J‐G9E, Toshiba Medical Systems Corp., Tustin, CA). RA image sequences are obtained using the MAF and reconstructed. To eliminate artifacts due to image truncation, lower‐dose (compared to MAF acquisition) full‐FOV (FFOV) FPD RA sequences (, ) were also obtained to complete the missing data. The RA gantry was calibrated using a helical bead phantom. To ensure high‐quality high‐resolution reconstruction, the high‐resolution images from the MAF were aligned spatially with the lower‐dose FPD images, and the pixel values in the FPD image data were scaled to match those of the MAF. Images of a rabbit with a coronary stent placed in an artery in the Circle of Willis were obtained and reconstructed. The MAF images appear well aligned with the FPD images (average correlation coefficient before and after alignment: 0.65 and 0.97, respectively) Greater details without any visible truncation artifacts are seen in 3D RMA (MAF‐FPD) images than in those of the FPD alone. The FWHM of line profiles of stent struts ( diameter) are approximately and for the 3D RMA and FPD data, respectively. In addition, for the dual‐acquisition 3D RMA, FFOV FPD data need not be of the highest quality, and thus may be acquired at lower dose compared to a standard FPD acquisition. These results indicate that this system could provide the basis for high resolution images of regions of interest in patients with a reduction in the integral dose compared to the standard FPD approach.
Is cortical root colonization required for carbon transfer to arbuscular mycorrhizal fungi? Evidence from colonization phenotypes and spore production in the reduced mycorrhizal colonization (rmc) mutant of tomato
Authors: Manjarrez Maria , Smith F. Andrew , Marschner Petra , Smith Sally E.
Published: October 2008

For the first time, the phenotypes formed in the reduced mycorrhizal colonization (rmc) Solanum lycopersicum  L. (tomato) mutant with different arbuscular mycorrhizal (AM) fungi were used to explore the potential of different fungal structures to support development of external fungal mycelium and spores. The life cycle of AM fungi with rmc was followed for up to 24 weeks. Results showed that production of external mycelium was slight and transitory for those fungi that did not penetrate the roots of rmc (Pen–) ( Glomus intraradices DAOM181602 and Glomus etunicatum ). For fungi that penetrated the root epidermis and hypodermis (Coi–, Glomus coronatum and Scutellospora calospora ) the mycelium produced varied in size, but was always smaller than with the wild-type 76R. Spores were formed by these fungi with 76R but not with rmc. The only fungus forming a Myc+ phenotype with rmc, G. intraradices WFVAM23, produced as much mycelium with rmc as with 76R. We observed lipid accumulation in hyphae and vesicles in both plant genotypes with this fungus. Mature spores were formed with 76R. However, with rmc, spores remained small and (presumably) immature for up to 24 weeks. We conclude that significant carbon transfer from plant to fungus can occur in Coi– interactions with rmc in which no cortical colonization occurs. We speculate that both carbon transfer and root signals are required for mature spores to be produced.
Ecology of the 2004 morel harvest in the Rocky Mountain Forest District of British Columbia
Authors: Winder Richard S. , Keefer Michael E.
Published: October 2008

In the Rocky Mountain Forest District of British Columbia, a dramatic series of fires occurred during 2003, setting the stage for an abundant morel crop in the following year. During 2004, the abundance of post-fire morels ( Morchella spp.) was measured and the plant community associated with morel production was characterized. Morel production averaged 6473 ± 2721 morels·ha–1in five burnt forests that were surveyed. Production ranged from 1702·ha–1at Plumbob Mountain to a significantly higher 16827·ha–1in the Kootenay National Park, where the highest level of duff consumption (71%) was also observed. Several plant species had high importance in morel habitat, and were also associated with above-average morel abundance: Chamerion angustifolium (L.) Holub, Arnica cordifolia Hook., Erythronium grandiflorum Pursh, Spiraea betulifolia Pallas subsp. lucida (Dougl. ex Greene) Taylor and MacBryde, Menziesia ferruginea Sm., Rosa acicularis Lindl. subsp. sayi (Schwein.) W.H. Lewis, Pinus contorta Dougl. ex Loud. var. latifolia Engelm., Abies lasiocarpa (Hook.) Nutt., and Picea glauca (Moench) Voss × engelmannii (Torr. & Gray ex Hook.) Brayshaw. Compositae and Vaccinium spp. were important species when considered as groups. Grass species, including Calamagrostis rubescens Buckl., were more proximate to morel-free plots. The characteristics of morel habitats observed in this study may be useful in future management of the resource, through conservation of habitat, management of prescribed burning, and postponement of salvage logging in potentially highly productive areas.
Effects of zucchini yellow mosaic virus infection on the subcellular distribution of glutathione and its precursors in a highly tolerantCucurbita pepocultivar
Authors: Zechmann Bernd , Müller Maria
Published: October 2008

Glutathione (γ-glutamyl-cysteinyl-glycine) is an antioxidant that plays important protective roles during pathogen attack. Glutathione synthesis is a highly compartment-specific pathway and relies on the supply of its precursors cysteine, glutamate, and glycine. To study the importance of glutathione in the development of tolerance and resistance, glutathione and its precursors were quantified with cytohistochemical methods in a highly tolerant cultivar (‘Quine’) of Cucurbita pepo L. during zucchini yellow mosaic virus (ZYMV) infection. Glutathione concentrations were strongly increased in almost all cell compartments of younger leaves (up to 247% in peroxisomes), older leaves (up to 73% in the cytosol), and roots (up to 104% in nuclei) during ZYMV infection. In addition, glutathione precursor concentrations were generally unchanged or increased in all cell compartments of younger leaves and roots, indicating that glutathione synthesis in these organs was not limited by low levels of glutathione precursors. The lower increase of glutathione in older leaves could be caused by strongly decreased levels of glycine in plastids (42%) and the cytosol (53%) during ZYMV infection, as they are the main centers for glutathione synthesis. Nevertheless, as the increase in glutathione was in general much higher than that observed in a highly susceptible cultivar in previous studies, we can conclude that elevated glutathione concentrations can be strongly correlated with the development of tolerance during ZYMV infection.
Soluble carbohydrate content of shoots of Arctic wetland plants that are consumed by lesser snow geese
Authors: Jefferies Robert L. , Edwards Kate A.
Published: October 2008

We recorded seasonal changes in the total amounts of soluble carbohydrates in shoots of salt- and fresh-water coastal plants at La Pérouse Bay, northern Manitoba, to determine whether adult snow geese and their goslings selected forage rich in soluble carbohydrates during the breeding season. The selection of forage plants in spring and summer by adults and goslings was strongly linked to the presence of high amounts of soluble carbohydrates in tissues: on the order of 100 mg·g–1dry mass. When the content fell as a result of shoot development or leaf senescence, the geese switched to alternative sources of forage. The extent to which individual shoots rich in soluble carbohydrates of the primary freshwater forage species are grazed depends on the local density of breeding geese at the study site, which has fallen in the last decade as a result of the earlier destruction of much of the coastal vegetation by foraging geese.
Resistance-related metabolites in wheat against Fusarium graminearum and the virulence factor deoxynivalenol (DON)
Authors: Paranidharan V. , Abu-Nada Y. , Hamzehzarghani H. , Kushalappa A. C. , Mamer O. , Dion Y. , Rioux S. , Comeau A. , Choiniere L.
Published: October 2008

Inoculation with the virulence factor deoxynivalenol (DON) can induce disease symptoms in wheat ( Triticum aestivum L.) spikelets, even though it is not needed for the initial invasion by Fusarium graminearum Schwabe, thus the mechanism of plant defense against both the pathogen and DON, was investigated. Wheat cultivars that are resistant (‘Sumai3’) or susceptible (‘Roblin’) to fusarium head blight (FHB) were inoculated with F. graminearum, DON, or water. Inoculated spikelets were harvested 48 h after inoculation, the metabolites were extracted in methanol–water and chloroform, then derivatized and analyzed by gas chromatography – mass spectrometry. The metabolite peaks were deconvoluted and identified by manually matching the mass spectra with those in the NIST and GMD libraries. The peaks were aligned, and abundances were measured. A total of 117 metabolites were tentatively identified, including several antimicrobial metabolites and signal molecules or their precursors. Out of these 117 metabolites, 15 and 18 were identified as possible resistance-related (RR) metabolites, following F. graminearum (RRIF) and DON (RRID) inoculations, respectively, with 4 metabolites common to both. Canonical discriminant analysis of marginally significant metabolites (105) identified those with constitutive and induced resistance functions. The metabolites with high canonical loading to the canonical vectors were used to explain these functions. The putative roles of these RR metabolites in plant defense, their metabolic pathways, and their potential application for screening of wheat breeding lines for resistance to FHB are discussed.
Endosporium, a new endoconidial genus allied to the Myriangiales
Authors: Tsuneda A. , Davey M. L. , Hambleton S. , Currah R. S.
Published: October 2008

A new endoconidial genus, Endosporium gen. nov., is reported from Alberta, Canada. Two species are described: Endosporium populi-tremuloidis Tsuneda sp. nov. (type species) isolated from a heavily colonized bud of Populus tremuloides Michx., and Endosporium aviarium Tsuneda sp. nov. isolated from the skin of Bombycilla garrulus (L.) (Bohemian waxwing) and a twig of Populus balsamifera L. This genus is morphologically similar to Phaeotheca in forming black, slow-growing colonies (conidiomata) containing numerous, conidiogenous, cellular clumps, but different in that (i) colonies possess aerial, determinate hyphae on the surface; (ii) mature colonies eventually collapse to release a mixture of conidiogenous cellular clumps, endoconidia, and blastic conidia in slimy liquid; and (iii) endoconidia are hyaline. Phylogenetic analyses of nuclear rDNA SSU, LSU, and ITS sequences indicate that Endosporium is phylogenetically distant from other endoconidial taxa, including Phaeotheca, and is most closely related to the Myriangiales (Dothideomycetes). Similarities in stroma and conidioma development as well as ecology between the two taxa suggest that Endosporium can be accommodated within this order, making it the first endoconidial and first black meristematic genus reported in the Myriangiales.
Phylogeny and biogeography of Apiaceae tribe Oenantheae inferred from nuclear rDNA ITS and cpDNApsbI–5′trnK(UUU)sequences, with emphasis on the North American Endemics clade
Authors: Downie Stephen R. , Katz-Downie Deborah S. , Sun Feng-Jie , Lee Chang-Shook
Published: October 2008

Intergeneric phylogenetic relationships within Apiaceae tribe Oenantheae were investigated using sequence data from the chloroplast DNA psbI–5′trnK(UUU)and nuclear ribosomal DNA internal transcribed spacer regions. One hundred and thirty-one accessions were examined, representing all 17 genera of the tribe and approximately one-half of its species. The cpDNA region includes four intergenic spacers and the rps16 intron and these noncoding loci were analyzed separately to assess their relative utility for resolving relationships. Separate maximum parsimony analyses of the entire psbI–5′trnK(UUU)and ITS regions, each with and without scored indels, yielded concordant trees. Phylogenies derived from maximum parsimony, Bayesian, or maximum likelihood analyses of combined chloroplast and nuclear DNA sequences for 82 accessions were highly resolved, well supported, and consistent. Among the five noncoding loci examined, the trnQ(UUG)–5′rps16 and 3′rps16–5′trnK(UUU)intergenic spacers are the most variable, with the latter contributing the greatest total number of parsimony informative characters relative to its size. The North American genera Atrema , Cynosciadium , Daucosma , Limnosciadium , Neogoezia , Oxypolis , Ptilimnium , and Trepocarpus ally with the western hemispheric and Australasian genus Lilaeopsis in a strongly supported North American Endemics clade that is a sister group to a clade composed primarily of Old World taxa ( Berula sensu lato, Cryptotaenia , Helosciadium , and Sium ). Oxypolis and Ptilimnium are not monophyletic, with the rachis-leaved members of each comprising a clade separate from their compound-leaved congeners. Dispersal-vicariance analysis suggests that the ancestors of the North American Endemics clade probably originated in Canada and the USA or in a broader ancestral area including Mexico and South America.
Assigning morphological variants of Fucus (Fucales, Phaeophyceae) in Canadian waters to recognized species using DNA barcoding
Authors: Kucera Hana , Saunders Gary W.
Published: October 2008

The intertidal brown algal genus Fucus (Phaeophyceae) consists of individuals with a generally dichotomously branched habit. Morphological variability within species, combined with morphological similarity between species, renders field identification difficult. In light of recent taxonomic revisions, which reduced 10 taxa traditionally recognized in Canada to four species, we tested the utility of the DNA barcode (mitochondrial cytochrome oxidase 1, 5′) for assigning individuals to these species. We sequenced the DNA barcode for 125 specimens representing all morphologies recognized. We confirmed our results by sequencing the internal transcribed spacer region for 66 specimens. This is the first study to establish that the DNA barcode successfully assigns different morphologies of brown algae to known species as well as other single-gene molecular markers currently used. Furthermore, the results uncovered substantial phenotypic plasticity in Pacific Fucus distichus , from moss-like fragments embedded in estuarine mud, strap-like morphs on exposed rocky coasts, to “spiralis”-like morphs in the upper intertidal whereas phenotypic expression for this species was more restricted in the Atlantic.
Genetic background affects genetically modified ethylene sensing in birch–insect interaction
Authors: Alatalo Ira , Haviola Sanna , Saloniemi Irma
Published: October 2008

Several studies suggest that ethylene is involved in the responses and resistance of plants against herbivores and pathogens, but the role of ethylene seems to vary depending on the system studied. Here we extend the studies of introduced Arabidopsis thaliana (L.) Heynh. ethylene receptor gene (etr1-1) to a new type of interaction: a woody plant, Betula pendula Roth (silver birch) and its herbivore, Epirrita autumnata (Borkhausen) (autumnal moth). We studied constitutive insect resistance of two wild-type birch genotypes, V and J, which were very different hosts for E. autumnata. On the J background, genetically modified ethylene insensitivity decreased the performance of E. autumnata, measured as leaf damage, larval mass, or pupal mass. However, hardly any changes were detectable in the V background, which is an inferior wild-type genotype for autumnal moth performance, except increased leaf damage caused by E. autumnata in ethylene-insensitive trees. Ethylene insensitivity caused clear side effects on birch phenology and morphology, especially in the J background. In this background, ethylene modification mainly acted via accelerating phenology, but this was hardly detectable in the V genotype. Also, the number of long shoots increased only in the modified J background. Taken together, it seems that the effects of ethylene on several birch traits relevant for E. autumnata and birch morphology depend on the birch genetic background.
Effects of temporal heterogeneity of watering on size of an annual forb, Perilla frutescens (Lamiaceae), depend on soil nutrient levels
Authors: Hagiwara Yousuke , Kachi Naoki , Suzuki Jun-Ichirou
Published: October 2008

Temporal heterogeneity of watering affects plant growth. When the same total amount of water is supplied, frequent watering leads to greater plant size than infrequent watering. However, the effects of a given watering regime can differ when nutrient levels vary. An experiment was designed to test the hypothesis that the effects of temporal heterogeneity of watering on plant growth also vary as a function of nutrient levels. Perilla frutescens (L.) Britton was grown using different combinations of nutrient levels and watering frequencies, with total water held constant across the treatments. The effects on plant size were analysed after 36 d. Under nutrient-rich conditions, frequent watering resulted in significantly larger plants than infrequent watering. However, under nutrient-poor conditions, no significant difference was detected between the different watering frequencies. The temporal heterogeneity of watering thus appears to have different effects on plant growth at different nutrient levels. Therefore, the watering heterogeneity should be examined with nutrients as unity, because the watering heterogeneity and nutrients affect plant growth in an interactive manner.
Interactions between reserve mobilization and regulation of nitrate uptake during regrowth of Lolium perenne L.: putative roles of amino acids and carbohydrates
Authors: Louahlia S. , Laine P. , MacDuff J. H. , Ourry A. , Humphreys M. , Boucaud J.
Published: October 2008

In most forage grass and legume species the recovery of leaf growth following severe defoliation depends on mobilization of carbon and nitrogen reserves from the remaining tissues. Unusually, Lolium perenne L. is able to compensate for low levels of available N storage compounds by rapid up-regulation of mineral N uptake. To investigate the physiological basis of this behaviour, perennial ryegrass plants were exposed to a 10 ​d period of optimal mineral N (high-N plants) or zero N (low-N plants) supply before defoliation. N deprivation decreased total N and amino acid concentrations in roots, and increased root water soluble carbohydrate concentrations. Compared with high-N plants (control), fructans and fructose concentrations in roots of low-N plants were 74% and 49% higher, respectively. Low-N plants had higher rates of nitrate uptake following defoliation, and lower amino acid concentrations in the roots (mainly as asparagine and glutamine); a causal role was suggested by the inhibition of nitrate uptake by external root supply of amino acids to low-N plants or by a stimulation of N uptake of high-N plants by sucrose supply to the roots. The results suggest that down-regulation of nitrate uptake following defoliation of plants with high levels of N reserves, may be effected through an increased cycling of amino acids within the plant and by a shortage of carbohydrates. Results are discussed in relation to the proteolytic activities and mobilization of C and N reserves to leaf meristem.
Mire vegetation gradient established as a result of interaction with a water reservoir
Authors: Horn Petr , Bastl Marek
Published: October 2008

In 1958, 85% of the peat-bog complex Kyselovský les, in the Czech Republic, was flooded with water from the Lipno reservoir. A new vegetation pattern has spontaneously developed in the newly established shoreline and replaced the original peat-bog vegetation dominated by bog pine ( Pinus rotundata Link) forest. This vegetation pattern consists of zonal strips with relatively sharp borders. This zonation is a mosaic of sedge fens, reed canary grass ( Phalaris arundinacea  L.) beds, tussock cottongrass ( Eriophorum vaginatum L.) stands, and a community dominated by ericaceous shrubs. The study focused on the vegetation development of this zonal vegetation. Measurements of the water table level, groundwater pH, and conductivity, together with terrain microtopography, were done to estimate the ways in which the water reservoir influences the mire vegetation. The most important factor is lake water fluctuation, which explained most of the vegetation gradient variability. Lake water fluctuations were represented by lake water levels, which directly flooded a certain part of the gradient from 1990 to 2006 for a known number of days.
Orchid–bird interactions: a case study from Angraecum (Vandeae, Angraecinae) and Zosterops (white-eyes, Zosteropidae) on Reunion Island
Authors: Micheneau Claire , Fournel Jacques , Humeau Laurence , Pailler Thierry
Published: October 2008

Although angraecoid orchids are famous for their spectacular flowers, pollinated by hawkmoths in Madagascar, two species of Angraecum endemic to the Mascarenes (sect. Hadrangis ) have atypical unscented and short-spurred flowers that are pollinated by birds. We focused on the pollination and reproductive success of Angraecum bracteosum Balf.f. & S.Moore, a member of sect. Hadrangis. We investigated the breeding system by performing a set of hand-pollination experiments and by observing natural pollinators using video-captures. Pollinator efficiency (pollen removal and deposition) and reproductive success (fruit set) were quantified once a week in two natural island populations during three consecutive flowering seasons (2003–2005). The orchid is self-compatible but requires pollinator services to achieve reproduction. The two white-eye song-bird species (Zosteropidae) that occur on Reunion, Zosterops borbonicus Boddaert and Zosterops olivaceus  L., were recorded as pollinators. However, while pollination events were rare and occasional following flower visits by Z. borbonicus, foraging of Z. oliveaceus resulted in a high frequency of successful pollinations. White-eyes typically perched on inflorescences, and probed most of the “fresh-looking” flowers for nectar. This study documents a probable case of bird-pollination specialization within Angraecum section Hadrangis, and sheds light on the role played by pollinators during the radiation of section Hadrangis in the Mascarene Archipelago.
Examining the molecular interaction between potato (Solanum tuberosum) and Colorado potato beetleLeptinotarsa decemlineata
Authors: Lawrence Susan D. , Novak Nicole G. , Ju Chelsea J.-T. , Cooke Janice E.K.
Published: October 2008

Colorado potato beetle (CPB) is a devastating herbivorous pest of solanaceous plants. Despite the economic impact, little is known about the molecular interaction of CPB with these plants. Using an 11 421 expressed sequence tag (EST) potato microarray, we identified 320 genes differentially expressed in potato leaves in response to CPB herbivory. Amongst these were genes putatively encoding proteinase inhibitors along with enzymes of terpenoid, alkaloid, and phenylpropanoid biosynthetic pathways, suggesting the defensive chemistries that constitute potato’s defense against CPB herbivory. Several genes, such as those encoding proteinase inhibitors, represent mechanisms implicated in other plant–herbivory interactions, and could correspond with general defensive chemistry strategies. In other cases, products of the differentially expressed genes may represent taxa-specific defensive chemistry. For example, the presumed alkaloid products of a putative tropinone reductase I are specific to a subset of the Solanaceae. Two herbivory-induced genes, not specific to potato, are implicated in the synthesis of volatiles known to attract CPB predators. Comparison of continuous herbivore attack versus recovery from CPB attack indicates that fewer genes involved in defensive chemistry are induced after continuous feeding than after feeding and recovery, suggesting the plant’s ability to mount a full defense response is enhanced under light versus heavy attack.
Effect of soil moisture and temperature during fallow on survival of contrasting isolates of arbuscular mycorrhizal fungi
Authors: Lekberg Y. , Koide R. T.
Published: October 2008

Many arbuscular mycorrhizal (AM) fungal species have worldwide distributions. However, it is not clear whether such species have adapted to local conditions. We compared the responses of mesic temperate and semi-arid tropical isolates of Glomus mosseae and Glomus etunicatum to extremes of temperature and moisture in a pot experiment. Treatments (warm–moist, warm–dry, freeze/thaw–moist, freeze/thaw–dry) were applied to whole soil mycorrhizal inoculum, and their effects were evaluated as both the change in viability of extraradical hyphae and mycorrhizal colonization of bait plants. Moist soil decreased hyphal viability compared with dry soil, irrespective of temperature, but mycorrhizal colonization of bait plants was lower in moist soil only when warm. Frost-heave could have physically ruptured hyphae in the freezing–moist soil without an effect on spores, but parasitism and (or) respiratory depletion of carbon reserves may have reduced survival of all propagules in the warm–moist soil. Hyphae of semi-arid tropical isolates survived all treatments better than hyphae of mesic temperate isolates, but these differences were not reflected in mycorrhizal colonization of bait plants. We found no evidence that these isolates have adapted to local conditions of moisture and temperature. Instead, wide environmental tolerances seem to be present within both populations of these AM fungal species.
Intra- and inter-specific density affects plant growth responses to arbuscular mycorrhizas
Authors: Schroeder-Moreno Michelle S. , Janos David P.
Published: October 2008

Arbuscular mycorrhizas can alter competitive interactions between plants that markedly differ in their dependence upon mycorrhizas, but little is known about how mycorrhizas affect intra- and inter-specific competition between similarly dependent plant species. We conducted competition experiments in pots between all pairs of the similarly facultatively mycotrophic crop species, chili ( Capsicum annuum L.), maize ( Zea mays L.), and zucchini ( Cucurbita pepo L.). We used a two-species yield-density model to analyze the separate effects of mycorrhizal inoculation, intra-, and inter-specific density on biomass responses. Mycorrhizas reduced the growth of all three plant species. Intraspecific competition increased the negative effect of mycorrhizas, as did interspecific competition at low intraspecific density. At high intraspecific density, however, interspecific competition improved plant responsiveness to mycorrhizas. Enhancement of plant benefit from mycorrhizas at high interspecific density of competing, weakly mycorrhiza-dependent species may help to explain the evolutionary maintenance of their associations with mycorrhizal fungi, and may be a key to understanding intercrop combinations that exceed the monoculture yields of component species.
Intercalary growth causes geometric length expansion in Methuselah’s beard lichen (Usnea longissima)
Authors: Rolstad Jørund , Rolstad Erlend
Published: October 2008

In sharp contrast to many slow-growing lichens, some epiphytic pendulous and foliose lichens display striking biomass accumulation in favorable habitats. Whereas lichen growth rates have received considerable attention, comparatively few detailed studies of growth patterns have been carried out. Generally, most lichens seem to grow apically, with only pseudomeristomatic tissue confined to lobe margins and branch tips. However, some species appear to retain the capacity to expand throughout the thallus, thereby increasing their growth potential. Such intercalary growth processes have proved difficult to confirm in the field for two- and three-dimensionally growing folious and fruticose forms. Using transplants of the conspicuous, one-dimensionally growing Usnea longissima Ach., we document that intercalary growth actually does occur, with thalli expanding geometrically in length with a doubling time of less than a year under favorable conditions.
Description of a novel organ in the gametophyte of the fernSchizaea pusillaand its contribution to overall plant architecture
Authors: Davidson Carla , Prusinkiewicz Przemyslaw , von Aderkas Patrick
Published: October 2008

Plant architecture is determined by cell division and growth, thus simulation models describing these processes are ideal for determining how local development produces the overall plant form. Because fern gametophytes are structurally simple, they are ideal for investigating the effects of cellular growth and division on plant form. In this work we examine the gametophytic development of Schizaea pusilla Pursh., a small, bog-adapted fern whose gametophyte forms as a mass of single-celled filaments. Using light and scanning electron microscopy we made detailed observations of gametophyte development to generate data for a simulation mechanical model of S. pusilla gametophyte development. To examine how plant architecture is an emergent property of cell division, we constructed a simulation model expressed using the formalism of L-systems. While developing a model of growth in this fern we discovered a previously undescribed structure that contributes to the architecture of this plant, which we term knots. We document the development of knots and demonstrate how they contribute to the overall plant architecture.
Substrate effects on distribution, biomass allocation, and morphology of forest understory plants
Authors: Six Laura J. , Halpern Charles B.
Published: October 2008

Relationships between rooting substrate and the distribution and performance of forest plants are inadequately understood. We tested whether understory species in a dense coniferous forest were associated with coarse woody debris (CWD) or forest floor. In addition, for three species with differing substrate associations ( Vaccinium parvifolium Smith, Tiarella trifoliata L., and Maianthemum dilatatum (Wood) Nels. and Macbr., we excavated individuals rooted in CWD and forest floor, and compared biomass allocation and plant morphological traits. Substrate samples were also tested for moisture content. Of 29 species tested, 18 (62%) showed positive associations with forest floor and 6 (21%) with CWD. Forest floor is a more predictable and stable substrate; in these forests it also supports lower moss cover that can inhibit seedling establishment. As expected, plants rooted in forest floor (which was drier) allocated greater biomass to belowground structures. Root-system traits, however, did not suggest plasticity in response to resource availability. Instead, the physical structure of logs may constrain root systems in CWD. In addition, total plant biomass did not differ between substrates suggesting that under low light, species may be incapable of responding to differences in belowground resources. Alternatively, substrate associations may develop earlier in the life histories of these plants via differential germination and survival.
Early Devonian putative gyracanthid acanthodians from eastern CanadaInternational Geoscience Programme (IGCP) Contribution 491, Middle Palaeozoic Vertebrate Biogeography, Palaeogeography, and Climate.
Authors: Burrow Carole J. , Turner Susan , Desbiens Sylvain , Miller Randall F.
Published: October 2008

In 1890, Traquair assigned isolated fin spines from the Early Devonian of eastern Canada to a new gyracanthid acanthodian Gyracanthus incurvus , based on the similarity of the distinctive oblique ridges on the spines to the ornament on the large robust fin spines of Gyracanthus spp. from the British Carboniferous Coal Measures. Other similarly ornamented spines from the Early Devonian of Germany were tentatively assigned in 1933 by Gross to the same genus as a new species Gyracanthus? convexus . Based on examination of the type material, as well as newly collected specimens from Emsian sandstones and mudstones of the Gaspé Peninsula, Quebec and the Atholville beds, New Brunswick, we erect a new genus Ankylacanthus gen. nov. for these two species. Spines of the new genus are distinguished by being laterally flattened and thin-walled, with a single row of denticles along one side of the posterior groove, and having thin spine ridges ornamented with low smooth nodes. Other Early to Middle Devonian specimens in South America, Saudi Arabia, and Iran are also tentatively referred to the new genus, which seems to have had an early (Lochkovian–Pragian) cross-north Gondwanan distribution, transferring into Laurentia and spanning Emsian–Eifelian times.
Shock brecciation around the Kidd Creek deposit, Abitibi belt, Canada
Authors: Pitcairn I. K. , Arndt N. T.
Published: October 2008

The Kidd–Munro assemblage, Abitibi belt, Canada, is an ultramafic–mafic–felsic volcanic sequence that contains the giant Kidd Creek volcanic-hosted massive sulfide (VMS) deposit. The Kidd basin, 1.6 km northeast of the deposit, contains pervasively brecciated pillowed and massive basalts. The breccia is distinctly different from most breccias in volcanic rocks, which form through volcanic processes or during later deformation or alteration. The Kidd Creek breccia occurs pervasively through otherwise undeformed pillow interiors and margins, and also in localized corridors of particularly intense brecciation. Clasts are angular, up to 4 cm wide, hosted in a very fine-grained matrix, and commonly show jig-saw fit texture. The chemical compositions of the breccia fragments and matrix are generally similar, although the matrix is slightly enriched in high field-strength elements (HFSE) and heavy rare-earth elements (HREE) and depleted in some mobile elements, such as Rb and Ba. The breccia contains altered basaltic clasts and fragments of in-filled amygdales and is crosscut by late-stage quartz–carbonate–sulfide veins. The observations imply that the breccia was formed in-situ, with minimal transport of material, and developed after solidification of the volcanic rocks. In-situ breccias, such as these, are known to form proximal to major fault zones, but no such structure occurs in the vicinity of the Kidd Basin. We suggest the brecciation was caused by the propagation of shock waves from explosive volcanic eruption, perhaps related to the emplacement of felsic volcanic rocks observed in the Kidd Creek Mine. The breccia was subject to enhanced hydrothermal fluid flow, perhaps linked to the formation of the ore deposit.
Holocene tephras in lake cores from northern British Columbia, Canada
Authors: Lakeman Thomas R. , Clague John J. , Menounos Brian , Osborn Gerald D. , Jensen Britta J.L. , Froese Duane G.
Published: October 2008

Sediment cores recovered from alpine and subalpine lakes up to 250 km apart in northern British Columbia contain five previously unrecognized tephras. Two black phonolitic tephras, each 5–10 mm thick, occur within 2–4 cm of each other in basal sediments from seven lakes in the Finlay River – Dease Lake area. The upper and lower Finlay tephras are slightly older than 10 220 – 10 560 cal year B.P. and likely originate from two closely spaced eruptions of one or two large volcanoes in the northern Cordilleran volcanic province. The Finlay tephras occur at the transition between deglacial sediments and organic-rich postglacial mud in the lake cores and, therefore, closely delimit the termination of the Fraser Glaciation in northern British Columbia. Sediments in Bob Quinn Lake, which lies on the east edge of the northern Coast Mountains, contain two black tephras that differ in age and composition from the Finlay tephras. The lower Bob Quinn tephra is 3–4 mm thick, basaltic in composition, and is derived from an eruption in the Iskut River volcanic field about 9400 cal years ago. The upper Bob Quinn tephra is 12 mm thick, trachytic in composition, and probably 7000–8000 cal years old. A fifth tephra occurs as a cryptotephra near the top of two cores from the Finlay River area and is correlated to the east lobe of the White River tephra (ca. 1150 cal year B.P.). Although present throughout southern Yukon, the White River tephra has not previously been documented this far south in British Columbia. The tephras are valuable new isochrons for future paleoenvironmental studies in northern British Columbia.
Estimation of Selection Differentials from Fish Scales: A Step Towards Evaluating Genetic Alteration of Fish Size in Exploited Populations
Authors: Miller Loren M. , Kapuscinski Anne R.
Published: October 2008

We developed a model to predict genetic response to selection imposed by a size-selective fishery. Use of our model provides estimates of selection as a function of heritability and overall selection differential imposed against a size-related trait, length of a scale radius from the focus to a given annulus (radius n). Selection differentials were estimated using data from the walleye (Stizostedion vitreum) fishery in Red Lakes, Minnesota. Overall selection differentials, incorporating selection differentials estimated by age and sex, and weighted by the contribution to spawning, were negative for the 1955 spawning population and positive for that of 1958. Directions of selection differentials, estimated by age and sex, generally corresponded to expected directions of selection based on the shape of the gillnet selectivity curve for walleye, suggesting that scale radii are useful for estimating selection against size traits. Results indicated that selective effects of gear may be surprisingly complex and population characteristics must be well understood before changes in fishery management are considered. We suggest that measurement of overall selection differentials alone may provide a useful management tool for indicating genetic risks of selective fisheries.