bluuebunny/crossref_metadata_2025 huggingface dataset:
High-Resolution Crystal Structure of an Engineered Human β
2
-Adrenergic G Protein–Coupled Receptor
Authors: Cherezov Vadim , Rosenbaum Daniel M. , Hanson Michael A. , Rasmussen Søren G. F. , Thian Foon Sun , Kobilka Tong Sun , Choi Hee-Jung , Kuhn Peter , Weis William I. , Kobilka Brian K. , Stevens Raymond C.
Published: October 2007

Heterotrimeric guanine nucleotide–binding protein (G protein)–coupled receptors constitute the largest family of eukaryotic signal transduction proteins that communicate across the membrane. We report the crystal structure of a human β
2
-adrenergic receptor–T4 lysozyme fusion protein bound to the partial inverse agonist carazolol at 2.4 angstrom resolution. The structure provides a high-resolution view of a human G protein–coupled receptor bound to a diffusible ligand. Ligand-binding site accessibility is enabled by the second extracellular loop, which is held out of the binding cavity by a pair of closely spaced disulfide bridges and a short helical segment within the loop. Cholesterol, a necessary component for crystallization, mediates an intriguing parallel association of receptor molecules in the crystal lattice. Although the location of carazolol in the β
2
-adrenergic receptor is very similar to that of retinal in rhodopsin, structural differences in the ligand-binding site and other regions highlight the challenges in using rhodopsin as a template model for this large receptor family.
THE RUSTS OF ERIOGONUM, CHORIZANTHE, AND OXYTHECA
Authors: Savile D. B. O.
Published: October 2007

Uromyces intricatus is broken into six varieties. Var. umbellati and var. major attack montane and lowland species of Eriogonum subgen. Eueriogonum in much of western North America, and the former probably attacks Oxytheca. Vars. intricatus (Oregon, California), parvifolii (California), nivei (interior British Columbia to Arizona), and pluriporosus (mainly Montana, Wyoming, and Colorado) attack various species or species groups in Eriogonum subgen. Oregonium, the variation being partly geographic and partly due to host specialization. Var. intricatus attacks Chorizanthe spp. and Eriogonum subgen. Ganysma in California. This variety has met and intergraded with var. pluriporosus in the past but the link is now broken. Uromyces bisbyi, a microcyclic derivative of var. parvifolii, is described on Eriogonum parvifolium in California. The implications on the evolution of Eriogonum and the problem of realistic nomenclature of rusts derived from both host and geographic isolation are discussed. A table clarifies the nomenclature of reported host plants.
Evaluation of two methods for assessing ascospore productivity of the apple scab pathogen, Venturia inaequalis
Authors: Heye C. C. , Andrews J. H. , Nordheim E. V.
Published: October 2007

The standard water bubbler and a modified tower aspirator for quantifying ascospore productivity were compared. Samples, each consisting of 50 discs, were cut randomly from scab-infected McIntosh apple leaf litter in the spring and 18 samples were processed by each method. The square roots of hemocytometer counts adjusted for unit area or gram dry weight of leaf samples were found to be normally distributed. More spores were harvested from the same amount of leaf material with the bubbler than with the tower. The coefficient of variation for spore yields expressed on a per area or a per gram dry weight basis was smaller for the tower method than for the bubbler, although the values were not significantly different. Where detection of low ascospore productivity is not essential, the tower method is preferable in terms of ease, speed of operation, and the potential for electronic enumeration of harvested ascospores.
Algicidal properties of the pesticide cosolvent Aerotex 3470: growth, ATP synthesis, and ultrastructure
Authors: Moody R. P. , Weinberger P. , Greenhalgh R. , Massalski A.
Published: October 2007

The algicidal properties of Aerotex 3470, a pesticide cosolvent in several fenitrothion formulations, have been investigated under controlled laboratory conditions. Aerotex (1–100 ppm) inhibited the growth of three unicellular freshwater algae (Chlamydomonas reinhardii, Chlorella pyrenoidosa, and Scenedesmus obtusiusculus) on agar plates and in liquid culture. Prolongation of the lag phase was directly related to Aerotex concentration. Algal cultures exposed for 1 h to Aerotex (1–10 ppm) had significantly reduced ATP levels. In all cases (agar, liquid culture, and ATP bioassays), Chlamydomonas and Chlorella were more sensitive to Aerotex than Scenedesmus.Electron microscopy demonstrated gross ultrastructural changes in Chlamydomonas treated for 1 h with Aerotex (5 ppm), including swollen mitochondria, disorganization of thylakoids, and crenulation of the cell membrane. Similar membrane damage was caused by 1-methylnaphthalene (5 ppm), a constituent of Aerotex.
Fusion of protoplasts from carrot cell cultures and the green alga Stigeoclonium
Authors: Fowke Larry C. , Marchant Harvey J. , Gresshoff Peter M.
Published: October 2007

Protoplasts from will carrot (Daucus carota) cell cultures were fused with protoplasts of the filamentous green alga Stigeoclonium sp. using polyethylene glycol. Following fusion of the algal and higher plant plasma membranes, intact Stigeoclonium chloroplasts, nuclei, and centrioles were observed within the carrot cytoplasm. Other algal organelles were not distinguishable in the fusion products.
Tetragoniomyces gen.nov. and Tetragoniomycetaceae fam.nov. (Tremellales)
Authors: Oberwinkler F. , Bandoni R. J.
Published: October 2007

The general structure of Tremella uliginosa Karst. is discussed. Basidia of the species are thick walled, deciduous, and germinate directly, i.e., without spore production. Dikaryotic hyphae grow directly from the basidium, or alternatively, a pair of germ tubes conjugate outside the basidium to initiate the dikaryon. Because of its distinctive basidial structure and function, the species is placed in a new genus, Tetragoniomyces gen.nov., and family, Tetragoniomycetaceae fam.nov.
The permeability of phi thickenings in apple (Pyrus malus) and geranium (Pelargonium hortorum) roots to an apoplastic fluorescent dye tracer
Authors: Peterson Carol A. , Emanuel Mary E. , Weerdenburg Carol A.
Published: October 2007

The permeability properties of the phi thickenings in apple (Pyrus malus L.) and geranium (Pelargonium hortorum L. H. Bailey) roots were tested by treating them with a fabric brightener dye, Tinopal CBS-X (disodium-4,4′-bis(2-sulfostyryl)biphenyl). The dye moved apoplastically in the roots of both species and did not penetrate the endodermal layers. In constrast, the dye penetrated the phi thickenings in both types of roots, indicating that phi thickenings do not function as barriers to the apoplastic transport of relatively small molecules.
Chromosome counts in Agalinis and related taxa (Scrophulariaceae)
Authors: Canne Judith M.
Published: October 2007

Chromosome counts were determined for 19 species of Agalinis, 1 species of Tomanthera, and 3 species of Aureolaria. Twelve species of Agalinis were counted at n = 14 and 6 species at n = 13. One species was recorded at 2n = 32. First reports at n = 14 are given for Agalinis divaricata, A. filicaulis, A. filifolia, A. heterophylla, A. neoscotica, A. paupercula, and A. plukenetii. First reports at n = 13 are presented for Agalinis edwardsiana, A. oligophylla, A. pulchella, A. strictifolia, and Tomanthera densiflora. Agalinis tenella was newly counted at 2n = 26 and Agalinis communis at 2n = 32. Aureolaria flava was counted at 2n = 24 and A. virginica at 2n = 26. Aureolaria pedicularia was recorded at 2n = 28.
The effects of drought and subsequent rehydration on the structure and vitality of Zea mays seedling roots
Authors: Stasovski Elida , Peterson Carol A.
Published: October 2007

Drought was induced in Turface and vermiculite-grown seedlings of Zea mays L. by withholding water. Despite a 34-day drought period, the roots of stressed plants increased in dry weight by continued elongation of existing roots and initiation of new roots. A differential response to desiccation, with respect to structure and cell vitality, was observed along the root axes. In apical regions (terminal 20 mm) of seminal roots, all cell layers typically remained alive. In midlength regions (half way between the apex and base), the epidermis died in both control and treatment plants. The cortex of control roots displayed some distortion, but most of the cells were alive; the cortex of stressed roots displayed severe collapse and death of the majority of these cells. In basal regions (20 mm distal to the kernel), cells of the outer cortex were sclerified and less susceptible to collapse. Cells of stelar tissues retained their normal shapes and vitality. Upon rehydration, the root systems of stressed plants resumed growth by elongation of existing seminal, adventitious, and lateral roots and, in some cases, also by emergence of previously dormant lateral root primordia. The root systems' capacity for recovery diminished with increasing stress. Key words: drought, roots, Zea mays L., exodermis, hypodermis.
Fungal development and host cell responses to the rust fungus Puccinia substriata var. indica in seedling and mature leaves of susceptible and resistant pearl millet
Authors: Taylor J. , Mims C. W.
Published: October 2007

The rust fungus Puccinia substriata var. indica established a compatible relationship with host cells, characterized by large numbers of haustoria and an extensive system of intercellular hyphae, in seedling leaves of the susceptible pearl millet cultivar Tift 23DB. At some infection sites, however, necrotic host cells and papillae formed by plant cells adjacent to infection hyphae or haustorial mother cells were noted. In seedling leaves of the moderately resistant cultivar 86-8770, the initial interaction between host cells and the pathogen was quite variable and included successful haustorium formation as well as papilla deposition. Necrosis of host cells apparently developed as a gradual disorganization of the cytoplasm of invaded and surrounding host cells and occurred at all infection sites by 2 days postinoculation. In seedling leaves of the highly resistant cultivar Tift 85DB, haustoria were established at early stages of development, followed by a rapid necrosis response at 1 day postinoculation. Host cell disintegration was noted both before and after abnormalities in haustoria were observed. In mature leaves of all three cultivars, wall deposits were quite extensive at 12 h postinoculation. In addition, necrotic plant cells appeared rapidly in both susceptible and resistant cultivars. Both of these factors may have contributed to the increased resistance to fungal colonization observed in mature leaves. Key words: Puccinia substriata var. indica, pearl millet rust, host resistance, ultrastructure.
Compsopogon cf. coeruleus, a benthic red alga (Rhodophyta) new to the Laurentian Great Lakes
Authors: Manny Bruce A. , Edsall Thomas A. , Wujek Daniel E.
Published: October 2007

We found Compsopogon cf. coeruleus for the first time in the Laurentian Great Lakes, growing on limestone rocks at a depth of 21 m on Six Fathom Bank in central Lake Huron. It is the first freshwater red alga to be found in the Great Lakes and the only red alga ever found on an offshore reef in the Great Lakes. However, because this alga usually inhabits water 10–28 °C and has not survived freezing winter temperatures elsewhere, it may not be a permanent member of the flora. Key words: benthic, Compsopogon, freshwater red algae, Great Lakes, Lake Huron.
Frankia spores of strain HFPCgI4 as inoculum for seedlings of Casuarina glauca
Authors: Mansour Samira R. , Torrey John G.
Published: October 2007

Spore suspensions of Frankia strain HFPCgI4 originally isolated from root nodules of Casuarina glauca were studied with respect to their capacity to germinate in vitro in chemically defined media and added root exudates. Spore germination in general was low and prolonged but could be increased by chemical additions to the basal medium and increased further (doubled percentages) by adding suitable dilutions of root exudates from C. glauca seedlings. Spores inoculated directly on seedling roots at 108 spores/mL caused seedling root hair deformation in C. glauca and some root nodulation (35%). Spore inoculation under axenic conditions elicited limited root hair deformation and no nodulation. Evidence is provided showing that Frankia spores of isolate HFPCgI4 serve as effective agents in root hair infection when applied in nonsterile water culture conditions. Seedling root exudates may facilitate the infection process by stimulating Frankia spore germination. Key words: Frankia, nodulation, root hair infection, root exudate, spores.
Branch architecture of sagebrush and bitterbrush: use of a branch complex to describe and compare patterns of growth
Authors: Bilbrough C. J. , Richards J. H.
Published: October 2007

The concept of the modularity of plant growth form was incorporated with the fates of buds and used as a framework to describe the typical branch-level developmental morphology of sagebrush (Artemisia tridentata ssp. vaseyana (Rydb.) Beetle) and bitterbrush (Purshia tridentata (Pursh) D.C.). Typical branches included one 2-year-old long shoot and all 1-year-old long shoots originating from that twig. Growth patterns were examined by position along each long shoot within the experimental branches. Shoot fates were recorded for each node and biomass production was estimated. Both species had specific locations where vegetative long shoot production was higher than any other location within the experimental branches. Sagebrush had an overall linear (excurrent) growth form, with the leader long shoot much larger than lateral long shoots. Sagebrush produced many lateral long shoots and few short shoots. In contrast, bitterbrush had a branched (decurrent) growth form, with few long shoots and many short shoots. The leader rarely grew and was no larger than laterals. Knowledge of the location, frequency, and size of vegetative long shoot production within a branch complex provides an understanding of the repeated structure of plants. The branch-level approach provides the information necessary before the effects of environmental factors on growth patterns can be determined. Key words: Artemisia tridentata ssp. vaseyana (Rybd.) Beetle, branch architecture, bud fates, developmental morphology, Purshia tridentata (Pursh) D.C., shrub.
A cadmium-tolerant strain of Neocosmospora vasinfecta shows reduced cadmium influx
Authors: Budd K.
Published: October 2007

Neocosmospora vasinfecta was grown in a defined liquid medium and its growth responses to CdSO4 were measured. The specific growth rate of mycelium not previously exposed to cadmium was reduced to 50% by 51 μM cadmium. The growth response to concentrations of cadmium above 50 μM was complex, showing declining and then recovery phases. Inoculum taken from a culture grown to the recovery phase in presence of 100 μM cadmium was cadmium tolerant; a cadmium level of 420 μM was required to reduce its specific growth rate by 50%. Tolerance was not lost by growth in the absence of cadmium. The tolerant mycelium showed markedly reduced net uptake of cadmium as compared with the normal (cadmium sensitive) mycelium. This reduction was due to a decrease in the unidirectional influx of cadmium, with little or no change in efflux. Cadmium toxicity in the normal mycelium was strongly antagonized by calcium but only weakly by manganese or zinc. Calcium also inhibited the uptake of cadmium. Key words: cadmium, calcium, Neocosmospora, tolerance, toxicity, transport.
Effect of triazole-type plant growth regulators on sunflower and safflower seed viability
Authors: Kar C. , Gupta K.
Published: October 2007

Pretreatment of sunflower and safflower seeds with triazole-type plant growth regulators (triazoles) diminished the rate of germination and reduced seedling growth. However, if seeds were aged at 90% relative humidity (accelerated ageing), triazoles significantly reduced the deleterious effects of accelerated ageing on germination percentage and field emergence. Seedling vigour was also greater in seedlings raised from triazole-treated seeds than from untreated seeds after accelerated aging. The activities of enzymes like dehydrogenase declined at a faster rate during accelerated ageing in untreated control than in triazole-treated seeds. Triazoles also slowed down the degradation of ribonucleic acid. The rate of change of soluble carbohydrates and amino acids was low in triazole-treated seeds compared with untreated control seeds. A positive correlation was evident between increase in membrane permeability and loss of seed viability. Membrane permeability and level of malondialdehyde, a peroxidation product of unsaturated fatty acids, gradually increased in storage at 90% relative humidity, but in seeds pretreated with triazoles these changes were minimal. Key words: triazoles, accelerated ageing, sunflower and safflower seed viability.
Pollen size of Betula in northern Alaska and the interpretation of late Quaternary vegetation records
Authors: Edwards Mary E. , Dawe Janice C. , Armbruster W. Scott
Published: October 2007

It is commonly asserted in paleoecological studies that shrub birch tends to have smaller pollen than tree birch, but this is poorly documented for Alaskan taxa. We measured freshly dehisced pollen from 55 plants in four northern Alaskan taxa, Betula resinifera (tree birch), Betula glandulosa (shrub birch), Betula nana ssp. exilis (dwarf birch), and Betula resinifera × glandulosa (hybrid). No significant differences existed between mean pollen sizes of any taxa. Betula glandulosa showed significant size variation among sites. Increase in birch-pollen size with time observed in some late Quaternary fossil records from northern Alaska cannot be safely attributed to a change from shrub to tree-dominated vegetation. Alternative explanations for temporal trends in pollen size are (i) evolution of populations, (ii) an environmental effect on pollen size, and (iii) local extinction of a previously widespread taxon. Key words: Alaska, Beringia, Betula, late Quaternary, pollen size.
The transition from germ tubes to vegetative growth in uredospores of Melampsora lini
Authors: Boasson R. , Shaw M.
Published: October 2007

The transition from uredospore germ tubes to vegetative hyphae marks the initiation of mycelial colonies of Melampsora lini growing in axenic culture. It is promoted by heat shock (31 °C for 2 h) and is arbitrarily defined as having occurred when mitotic divisions of the two original uredospore nuclei have produced more than four nuclei. The percentage of germinating spores in which it occurs (percentage initiation) does not increase beyond 48 h after seeding and is higher (about 9 vs. 5%) at a low (18 spores/mm2) than at a higher (90 spores/mm2) inoculum density. The number of nuclei in a mycelial colony arising from a single uredospore increases exponentially with a mean doubling time of 2.40 days. Neither the percentage initiation nor the rate of increase in number of nuclei (= mycelial growth) are affected by the proximity of neighbouring spores at spore densities of the order of 18 spores/mm2. Approximately 10% of the initiated colonies exhibit a growth rate that renders them visible to the naked eye after 5 weeks. Key words: rust fungus, axenic culture, vegetative growth, single spore colonies.
Transient expression of foreign chimeric genes in the gymnosperm hybrid larch following electroporation
Authors: Charest Pierre J. , Devantier Yvonne , Ward Christine , Jones Catherine , Schaffer Ulriche , Klimaszewska Krystyna K.
Published: October 2007

A transient gene expression system using electroporation and naked plasmid DNA has been developed for hybrid larch (Larix × eurolepis). The β-glucuronidase, neomycin phosphotransferase II, and chloramphenicol acetyltransferase genes were used effectively, but the latter was found to be the most useful. Electroporation conditions were comparable with protocols developed for other conifer and angiosperm species. Of the parameters tested the optimum conditions were 300 V, 150 μF, and 300 μg/mL pCaMVCN DNA. The 35S promoter of cauliflower mosaic virus yielded a stronger level of transient expression than the nopaline synthase promoter, which is consistent with other studies. A construct with the wound-inducible promoter of the potato proteinase IIK gene and the chloramphenicol acetyl transferase reporter coding sequence did not yield to any transient gene expression, even after induction with acetylsalicylic acid and exposure to ultraviolet radiation. Key words: larch, Larix × eurolepis, electroporation, transient gene expression.
The spindle pole body cycle, meiosis, and basidial cytology of the smut fungus Microbotryum violaceum
Authors: Berbee Mary L. , Bauer Robert , Oberwinkler F.
Published: October 2007

Freeze-substituted basidia of the smut fungus Microbotryum violaceum (Ustilaginales, Basidiomycotina) were examined electron microscopically with particular attention to the meiotic spindle pole body cycle and cytoplasmic characters of phylogenetic significance. Prophase basidia contained a subapical cluster of vesicles and tubules. During prophase, the spindle pole body consisted of two globular elements connected by a middle piece. The spindle pole body had an electron-opaque layer near the nucleus, and each globular element was bisected by an electron-opaque disk. The meiosis I spindle extended between two monoglobular, disc-containing spindle pole bodies. During interphase I and II, septa lacking pores divided the basidium between daughter nuclei. In interphase I, a putative new spindle pole body appeared between the nuclear envelope and the monoglobular spindle pole body residual from the first division. In meiosis II, a spindle was again established between two monoglobular spindle pole bodies, each of which again contained an electron-opaque disc. The cytoplasmic characters of M. violaceum are compared with those of Ustilago maydis and Sphacelotheca polygoni-serrulati. Key words: Microbotryum violaceum, basidiomycete, Ustilaginales, spindle pole body, freeze-substitution, ultrastructure.
Importance of hardwood competition to American chestnut survival, growth, and blight development in forest clearcuts
Authors: Griffin Gary J. , Smith H. Clay , Dietz Albert , Elkins John R.
Published: October 2007

Ten years after clear-cutting forest stands in Virginia and West Virginia, competing hardwoods around American chestnut trees were either periodically cut (managed) or not cut (control or unmanaged). Blight epidemics occurred in all clear-cut plots prior to their establishment in 1984. For the control plots, the number of chestnut sprout clusters (group of stems sprouting from a single stump) with blighted live stems had decreased by 1989, but between 1985 and 1988 there was a general increase in blighted chestnut stems for the managed clearcut plots. The number of apparent superficial cankers increased in two of three managed plots between 1986 and 1989. Survival of chestnut clusters was high in managed plots between 1985 and 1989, but decreased in one control plot to zero by 1988. Mean diameters at breast height of measurable chestnut stems (> 0.8 cm) declined or remained constant in control plots, but generally increased in managed plots after initial declines. Similar but greater responses were observed in a plantation of American chestnut. Unmanaged clearcuts with a high survival of chestnut clusters had low stand basal areas for competing hardwoods, and vice versa. A mesic site favored American chestnut growth and apparent superficial cankers in the absence of competing hardwoods. Key words: chestnut blight, hypovirulence, biocontrol, forest competition.
Modélisation de la croissance de la tige feuillée
Authors: Cusset Gérard
Published: October 2007

A model is proposed, which simulates the growth of an axis and its series of leaves, during a long period of growth. Biological validations of the equations and of the parameters are proposed along with remarks on the concept of organ category. Key words: modelling, growth, stem, leaf, sigmoid curves. [Journal translation]
Defense responses of Hevea brasiliensis to elicitors from root rot fungi
Authors: Nicole M. , Toppan A. , Geiger J. P. , Roby D. , Nandris D. , Rio B.
Published: October 2007

Elicitation of root defense responses of rubber tree (Hevea brasiliensis) to Rigidoporus lignosus has been performed by injection of fungal cell wall extracts into the root system of 1-month-old seedlings. A time course study showed that tissue lignification is induced at 3, 8, 15, and 45 days after elicitor treatment, as observed under a light microscope. The ethanolsoluble elicitor fractions stimulated cinnamyl-alcohol dehydrogenase activity, involved in lignin synthesis, as well as callose deposits 15 days and 30 days after elicitor treatment. A differential phellogen activity was observed 15 days after injection of roots with fungal extracts not treated with pronase. Stimulation of chitinase activity in leaves, cell hyperplasia, and suberization of root cell walls did not succeed. These data show that some defense mechanisms of tree roots can be triggered by elicitors from root-rotting fungi and result in the stengthening of structural barriers in host tissues. Key words: root rot diseases, elicitation, lignification, cambium stimulation, callose.
The role of auxin in the removal of dormancy callose and resumption of phloem activity in Vitis vinifera
Authors: Aloni Roni , Raviv Ayala , Peterson Carol A.
Published: October 2007

During winter the phloem of Vitis vinifera L. is dormant and is characterized by heavy deposits of callose on the sieve plates and lateral sieve areas of the sieve tubes. After bud break, the maturing leaves stimulate a nonpolar breakdown of this dormancy callose along the branch axis in the internodes located both above and below the leaves. However, the pattern of callose degradation in the radial direction is polar. It proceeds in a centrifugal direction so that the sieve tubes near the cambium become free of callose first and those adjacent to the periderm last. The effect of the leaves on the removal of dormancy callose can be replaced by auxin. Application of naphthaleneacetic acid to either the top or basal ends of excised dormant branches resulted in the removal of callose from sieve tubes, usually in less than a week. The fluorescent dye fluorescein was used to test phloem reactivation. Both acropetal and basipetal fluorescein movement occurred in sieve tubes in branches that were pretreated for 1 week with auxin, while much less movement of fluorescein occurred in the control branches, which remained dormant. Fluorescein translocation was observed in sieve tubes that had a reduced amount of callose and were wider than 20 μm, but was not detected in the narrow sieve tubes (diameters less than 15 μm) located next to the cambium. The possible roles of auxin, ethylene, and cytokinin in controlling callose levels in the sieve tubes are discussed. Key words: auxin, callose, fluorescein, Vitis vinifera, phloem, dormancy.
The distribution of nine Avena species in Spain and Morocco
Authors: Leggett J. M. , Ladizinsky G. , Hagberg P. , Obanni M.
Published: October 2007

Wild taxa of crop plants have been valuable sources of genes for cultivar improvement in several species. Genes for yield, resistance to pests and diseases, protein quality and quantity, maturity and other characteristics have been transferred from wild species of Avena to the cultivated oat crop (A. sativa L.). In an attempt to preserve some of the genetic variability in the wild species and taxa of Avena, two collecting missions were organised in 1985 and 1988. During the 1985 expedition 49 accessions were collected on mainland Spain and the Canary Islands, and 74 accessions were collected in Morocco. In 1988, a further 64 accessions were collected in Morocco. These accessions included representatives from 10 of the 14 known biological species of Avena and 16 of the 30 generally accepted taxonomic entities. These collections have increased the size of the available gene pool and extended the known geographical distribution of some of the species. Key words: Avena, distribution, germ plasm, genetic resources.
×Dryostichum singulare (Dryopteridaceae), a new fern nothogenus from Ontario
Authors: Wagner Jr. Warren H. , Wagner Florence S. , Reznicek Anton A. , Werth Charles R.
Published: October 2007

A previously unknown fern, here named ×Dryostichum singulare nothogen. et nothosp.nov. W. H. Wagner, has been discovered in several localities in the Georgian Bay region of Ontario, Canada. The plants are found in shaded northern hardwood forests on dolomitic outcrops. First thought to be a bizarre mutation, evidence is presented here that it is a recurring natural hybrid between Dryopteris goldiana and Polystichum lonchitis. Chromosome and spore studies indicate that the hybrid is sterile and has abortive spores; the chromosome number is 2n = 82 with no pairing at meiotic metaphase. Key words: fern, ×Dryostichum, Dryopteris, Polystichum, hybrid, Ontario.
Abundance, vegetation, and environment of four patch types in a northern mixed prairie
Authors: Umbanhowar Jr. Charles E.
Published: October 2007

The importance of concurrent disturbances to the maintenance of plant species diversity in grasslands has been emphasized by several authors, but there are few studies comparing different disturbances at the same site. In this study the size, abundance, vegetation, and environment of thatching ant mounds, earthen mammal mounds, bison wallows, and openings in dry marshes are compared in a northern mixed prairie in north central South Dakota. Patch size and abundance varied considerably between patch types. Ant and earthen mammal mounds were the smallest but most abundant patch types. Bison wallows and dry marshes were larger and occurred less frequently than ant and earthen mounds. Different patch types occupied a similar amount of area. Ordination of patch vegetation revealed marked between-type compositional differences; ant and earthen mounds were dominated by vegetatively reproducing perennials, while annuals occurred more abundantly in bison wallows and dry marshes. Many species were restricted to either wallows or marshes. Levels of nitrate, phosphorus, soil organic matter, and other environmental factors varied significantly between patch types. Different patch types supported different groups of species, and patch vegetation was a product of mechanism of patch creation, patch environment, and location. Key words: ant mounds, disturbance, earthen mounds, northern mixed prairie, patches, potholes, wallows.
Genetic variability in the canker pathogen fungus,Gremmeniella abietina. 2. Fine-scale investigation of the population genetic structure
Authors: Wang Xiao-Ru , Szmidt Alfred E. , Ennos Richard A. , Hansson Per
Published: October 2007

Genetic variation at 32 polymorphic random amplified polymorphic DNA loci was analysed in the ascomycete canker pathogen fungus Gremmeniella abietina (Lagerb.) Morelet collected from one plantation of Pinus contorta Dougl. ex Loud, in northern Sweden. The genetic variability maintained in the G. abietina population was high. Many different multilocus genotypes were found on each tree and in each sampling site within the plantation. The clonal fraction of the population was small, and identical genotypes were found either on the same tree or branch or on trees in the same sampling site. The finding of very few widely distributed clones suggests that the effective dispersal of asexual spores is limited to a few metres and resulted in small clusters of clones in local sites. Analysis of molecular variance revealed that 45.3% of the total variation was attributable to differences among isolates within trees, 22.5% to trees within sites and 32.3% to sampling sites differences. Allele frequencies at most of the loci varied significantly among the sampling sites and average total genetic diversity over the 32 loci was 0.27 indicating high population subdivision. The factors that could have contributed to the observed population structure were discussed. Key words: Gremmeniella abietina, genotype and clone distribution, population subdivision, RAPD.
Population genetic structure of yellow starthistle (Centaurea solstitialis), a colonizing weed in the western United States
Authors: Sun Mei
Published: October 2007

Yellow starthistle (Centaurea solstitialis L.), a diploid annual native to the Mediterranean region, has rapidly colonized a variety of disturbed habitats in the western United States since its accidental introduction in the mid-19th century. Population genetic attributes were investigated in association with the species' colonizing success. Allozyme electrophoretic surveys were conducted for a total of 22 populations from California, Washington, and Idaho, including the southern and northern extremes of its distribution in the Pacific states. High levels of allozyme variation exist within populations, on average 43% of loci were polymorphic, with 2.88 alleles, a heterozygosity of 0.38, and gene diversity of 0.35 per polymorphic locus. At the species level, 56% of loci were polymorphic, with 2.85 alleles per locus, and the total gene diversity was 0.172. With the exception of a marginal population San Diego, the level of genetic diversity was similarly high in all regions. Lack of interpopulation genetic divergence (GST = 0.095) suggests that majority of the colonial populations were founded by a large number of genotypes and that high levels of gene flow may exist between local populations (Nm = 2.38). Information on genetic structure of the weed populations may aid our understanding of the species' colonizing ability in North America and is important for predicting the effectiveness of biological control program. Key words: allozyme variation, Centaurea solstitialis, population genetics, weed colonization, yellow starthistle.
Periphyton community structure and dynamics in a subarctic lake
Authors: Maltais Marie-Josée , Vincent Warwick F.
Published: October 2007

Periphyton species composition was analysed at 20 stations around an island in a large (1239 km2) oligotrophic lake in subarctic Quebec (Lac à l'Eau Claire; latitude 56°10′N, longitude 74°30′W) to describe the mature communities colonizing the upper littoral region and to evaluate periphyton abundance and distribution relative to the physical environment. Four major communities could be clearly distinguished in the field by their macroscopic features, specifically colour (black, brown, and green) and growth form (filamentous or encrusted), as well as by their standing stock (cover and areal Chl a concentration) and photosynthetic characteristics. (1) Black crust—This community was dominated by the cyanobacterium Gloeocapsa, with highest percent cover in shallow waters (≤ 0.25 m) protected from wave action by offshore boulder barriers. Photosynthesis under full sunlight was low per unit biomass (0.7 μg C∙(μg Chl a)−1∙h−1). (2) Brown film—This community was dominated by Calothrix, with Gloeocapsa and Phormidium as subdominants. Maximum abundance was at 0.5 m, with photosynthetic rates that were similar to the black community. (3) Green crust—This community was dominated by the mucilaginous chlorophyte Gloeocystis, with Oscillatoria as subdominant, and colonized shallow depths (≤ 0.25 m) in the shaded underlayer of rocks. It had slow, light-limited photosynthetic rates (0.1 μg C∙(μg Chl a)−1∙h−1). (4) Green filaments—This community was dominated by Ulothrix zonata, with associated chlorophytes and diatoms, and was a rapidly growing assemblage characterized by the highest diversity, species richness, and productivity per unit biomass (3.5 μg C∙(μg Chl a)−1∙h−1). It occurred on gravel beds at depths < 0.5 m and was restricted to the well-illuminated south-facing shores of the island. Communities 1, 2, and 3 had similar maximum standing stocks throughout the period of sampling (mean of 1.3 μg Chl a∙cm−2), whereas the Ulothrix community rose from 1.9 μg Chl a∙cm−2 in late July to 5.5 μg Chl a∙cm−2 by mid-August. The overall rich biodiversity of the Lac à l'Eau Claire periphyton (> 200 taxa recorded) may reflect the diversity of microenvironments and intermediate disturbance in the upper littoral zone. Key words: cyanobacteria, chlorophytes, diatoms, epilithon, periphyton, photosynthesis.
Seed weight, intraspecific competition, and plant performance in Abutilon theophrasti
Authors: Zhang Jianhua , Hamill Allan S.
Published: October 2007

Seed weight of Abutilon theophrasti Medic, varies among populations and with the light conditions of the parent plants. In this study, the impacts of seed weight variation on seed germination and plant growth were investigated. Variations in seed weight did not result in any significant difference in the germination ability of seeds. The enhanced germination associated with large seeds produced by plants in shaded conditions found in previous studies were more likely the result of interpopulational variation or difference in maternal environments. The leaf chlorophyll content of young seedlings and the total leaf area of plants at harvest tended to increase with increasing original seed weight of the plants. Although the aboveground biomass of a plant was not affected by its original seed weight, the performance of the plant depended significantly on the total original seed weight of the neighbouring plants. Key words: seed weight, germination, competition, Thiessen polygon, Abutilon theophrasti.
NON-ADIABATIC GRAVITATIONAL COLLAPSE WITH ANISOTROPIC CORE
Authors: THOMAS V. O. , RATANPAL B. S.
Published: October 2007

The non-adiabatic gravitational collapse of a spherical distribution of matter accompanied by radial heat flux has been studied on the background of a pseudo-spheroidal space–time. The spherical distribution is divided into two regions: a core consisting of anisotropic pressure distribution and an envelope consisting of isotropic pressure distribution. Various aspects of the collapse have been studied using both analytic and numerical methods.
Protein kinases, TNF-α, and proteasome contribute in the inhibition of fructose intestinal transport by sepsis in vivo
Authors: García-Herrera Josefina , Marca M. Carmen , Brot-Laroche Edith , Guillén Natalia , Acin Sergio , Navarro M. Angeles , Osada Jesús , Rodríguez-Yoldi M. Jesús
Published: October 2007

Lipopolysaccharide (LPS) endotoxin is a causative agent of sepsis. The aim of this study was to examine LPS effects on intestinal fructose absorption and to decipher mechanisms. Sepsis was induced by intravenous injection of LPS in rabbits. The ultrastructural study and DNA fragmentation patterns were identical in the intestine of LPS and sham animals. LPS treatment reduced fructose absorption altering both mucosal-to-serosal transepithelial fluxes and uptake into brush border membrane vesicles (BBMVs). Cytochalasin B was ineffective on fructose uptake, indicating that GLUT5, but not GLUT2, transport activity was targeted. GLUT5 protein levels in BBMvs were lower in LPS than in sham-injected rabbits. Thus lower fructose transport resulted from lower levels of GLUT5 protein. LPS treatment decreased GLUT5 levels by proteasome-dependent degradation. Specific inhibitors of PKC, PKA, and MAP kinases (p38MAPK, JNK, MEK1/2) protected fructose uptake from adverse LPS effect. Moreover, a TNF-α antagonist blocked LPS action on fructose uptake. We conclude that intestinal fructose transport inhibition by LPS is associated with diminished GLUT5 numbers in the brush border membrane of enterocytes triggered by activation of several interrelated signaling cascades and proteasome degradation.
The extracellular calcium-sensing receptor (CaSR) on human esophagus and evidence of expression of the CaSR on the esophageal epithelial cell line (HET-1A)
Authors: Justinich Christopher J. , Mak Nanette , Pacheco Ivan , Mulder Dan , Wells Ron W. , Blennerhassett Michael G. , MacLeod R. John
Published: October 2007

Gastrointestinal reflux disease and eosinophilic esophagitis are characterized by basal cell hyperplasia. The extracellular calcium-sensing receptor (CaSR), a G protein-coupled receptor, which may be activated by divalent agonists, is expressed throughout the gastrointestinal system. The CaSR may regulate proliferation or differentiation, depending on cell type and tissue. The current experiments demonstrate the expression of the CaSR on a human esophageal epithelial cell line (HET-1A) and the location and expression of the CaSR in the human esophagus. CaSR immunoreactivity was seen in the basal layer of normal human esophagus. CaSR expression was confirmed in HET-1A cells by RT-PCR, immunocytochemistry, and Western blot analysis. CaSR stimulation by extracellular calcium or agonists, such as spermine or Mg2+, caused ERK1 and 2 activation, intracellular calcium concentration ([Ca2+]i) mobilization (as assessed by microspecfluorometry using Fluo-4), and secretion of the multifunctional cytokine IL-8 (CX-CL8). HET-1A cells transiently transfected with small interfering (si)RNA duplex against the CaSR manifested attenuated responses to Ca2+stimulation of phospho- (p)ERK1 and 2, [Ca2+]imobilization, and IL-8 secretion, whereas responses to acetylcholine (ACh) remained sustained. An inhibitor of phosphatidylinositol-specific phospholipase C (PI-PLC) (U73122) blocked CaSR-stimulated [Ca2+]irelease. We conclude that the CaSR is present on basal cells of the human esophagus and is present in a functional manner on the esophageal epithelial cell line, HET-1A.
NADPH oxidase plays a crucial role in the activation of pancreatic stellate cells
Authors: Masamune Atsushi , Watanabe Takashi , Kikuta Kazuhiro , Satoh Kennichi , Shimosegawa Tooru
Published: October 2007

Activated pancreatic stellate cells (PSCs) play an important role in pancreatic fibrosis and inflammation, where oxidative stress is implicated in the pathogenesis. NADPH oxidase might be a source of reactive oxygen species (ROS) in the injured pancreas. This study aimed to clarify the expression and regulation of cell functions by NADPH oxidase in PSCs. PSCs were isolated from rat and human pancreas tissues. Expression of NADPH oxidase was assessed by reverse transcription-PCR and immunostaining. Intracellular ROS production was assessed using 2′,7′-dichlorofluorescin diacetate. The effects of diphenylene iodonium (DPI) and apocynin, inhibitors of NADPH oxidase, on key parameters of PSC activation were evaluated in vitro. In vivo, DPI (at 1 mg·kg body wt−1·day−1) was administered in drinking water to 10-wk-old male Wistar Bonn/Kobori rats for 10 wk and to rats with chronic pancreatitis induced by dibutyltin dichloride (DBTC). PSCs expressed key components of NADPH oxidase (p22phox, p47phox, NOX1, gp91phox/NOX2, NOX4, and NOX activator 1). PDGF-BB, IL-1β, and angiotensin II induced ROS production, which was abolished by DPI and apocynin. DPI inhibited PDGF-induced proliferation, IL-1β-induced chemokine production, and expression of α-smooth muscle actin and collagen. DPI inhibited transformation of freshly isolated cells to a myofibroblast-like phenotype. In addition, DPI inhibited the development of pancreatic fibrosis in Wistar Bonn/Kobori rats and in rats with DBTC-induced chronic pancreatitis. In conclusion, PSCs express NADPH oxidase to generate ROS, which mediates key cell functions and activation of PSCs. NADPH oxidase might be a potential target for the treatment of pancreatic fibrosis.
Blockade of NKG2D signaling prevents the development of murine CD4+T cell-mediated colitis
Authors: Ito Y. , Kanai T. , Totsuka T. , Okamoto R. , Tsuchiya K. , Nemoto Y. , Yoshioka A. , Tomita T. , Nagaishi T. , Sakamoto N. , Sakanishi T. , Okumura K. , Yagita H. , Watanabe M.
Published: October 2007

It has been recently demonstrated that NKG2D is an activating costimulatory receptor on natural killer (NK) cells, natural killer T (NKT) cells, activated CD8+T cells, and γδ T cells, which respond to cellular stress, such as inflammation, transformation, and infection. Here we show that intestinal inflammation in colitic SCID mice induced by adoptive transfer of CD4+CD45RBhighT cells is characterized by significant increase of CD4+NKG2D+T cells and constitutive expression of NKG2D ligands, such as H60, Mult-1, and Rae-1, by lamina propria CD11c+dendritic cells. Furthermore, treatment with nondepleting and neutralizing anti-NKG2D MAb after transfer of CD4+CD45RBhighT cells into SCID mice significantly suppressed wasting disease with colitis, abrogated leukocyte infiltration, and reduced production of IFN-γ by lamina propria CD4+T cells. These findings demonstrate that NKG2D signaling pathway is critically involved in CD4+T cell-mediated disease progression and suggest a new therapeutic target for inflammatory bowel diseases.
Novel role of the vitamin D receptor in maintaining the integrity of the intestinal mucosal barrier
Authors: Kong Juan , Zhang Zhongyi , Musch Mark W. , Ning Gang , Sun Jun , Hart John , Bissonnette Marc , Li Yan Chun
Published: October 2007

Emerging evidence supports a pathological link between vitamin D deficiency and the risk of inflammatory bowel disease (IBD). To explore the mechanism we used the dextran sulfate sodium (DSS)-induced colitis model to investigate the role of the vitamin D receptor (VDR) in mucosal barrier homeostasis. While VDR+/+ mice were mostly resistant to 2.5% DSS, VDR−/− mice developed severe diarrhea, rectal bleeding, and marked body weight loss, leading to death in 2 wk. Histological examination revealed extensive ulceration and impaired wound healing in the colonic epithelium of DSS-treated VDR−/− mice. Severe ulceration in VDR−/− mice was preceded by a greater loss of intestinal transepithelial electric resistance (TER) compared with VDR+/+ mice. Confocal and electron microscopy (EM) revealed severe disruption in epithelial junctions in VDR−/− mice after 3-day DSS treatment. Therefore, VDR−/− mice were much more susceptible to DSS-induced mucosal injury than VDR+/+ mice. In cell cultures, 1,25-dihydroxy-vitamin D3 [1,25(OH)2D3] markedly enhanced tight junctions formed by Caco-2 monolayers by increasing junction protein expression and TER and preserved the structural integrity of tight junctions in the presence of DSS. VDR knockdown with small interfering (si)RNA reduced the junction proteins and TER in Caco-2 monolayers. 1,25(OH)2D3 can also stimulate epithelial cell migration in vitro. These observations suggest that VDR plays a critical role in mucosal barrier homeostasis by preserving the integrity of junction complexes and the healing capacity of the colonic epithelium. Therefore, vitamin D deficiency may compromise the mucosal barrier, leading to increased susceptibility to mucosal damage and increased risk of IBD.