Phylogeography of native ploidy levels and invasive tetraploids of Solidago gigantea

Ploidy level is an important aspect of the genetic makeup of a plant, and can strongly influence ecological characteristics such as invasiveness. We used a phylogeographical approach to elucidate the history of polyploidization and colonization success of diploid and tetraploid Solidago gigantea Aiton (Asteraceae) within its native range in North America. We were also able to identify the probable source material of the haplotype lineages invasive in Europe and Asia, where only tetraploid plants occur. To do this, we sequenced 1275 bp of chloroplast intergenic spacer DNA in 268 individuals from 57 populations. In addition, we performed a crossing experiment, which supported the hypothesis that chloroplast inheritance in this species is maternal. The phylogeographical analysis showed a complex pattern of 20 haplotypes of diploid and tetraploid plants. In North America, we found significant differentiation among regions, private haplotypes, and isolation by distance. Ploidy levels were more differentiated in the northern regions than in the South. The haplotype network was shallow and included one tetraploid-only, star-shaped cluster of haplotypes that were particularly successful colonizers. Post-glacial migration of diploid S. gigantea occurred mainly northwards east of the Appalachian Mountains, and to a lesser degree also southward. Our data suggest that tetraploids have formed several times in North America. Haplotype number and diversity were lower in European populations than in the native range, and we found evidence that four haplotypes were introduced to Europe from two source areas, New England and the Southern Appalachian Mountains.     

Genetic Diversity and Antibiotic Resistance Patterns in a Campylobacter Population Isolated from Poultry Farms in Switzerland

The diversity and genetic interrelation of Campylobacter jejuni and C. coli isolated from Swiss poultry were assessed by three independent typing methods. Samples were derived prior to slaughter from 100 randomly selected flocks (five birds per flock) raised on three different farm types. The observed flock prevalence was 54% in total, with 50% for conventional and 69% for free-range farms. Birds held on farms with a confined roaming area had the lowest prevalence of 37%. Campylobacter isolates were characterized by amplified fragment length polymorphism (AFLP), restriction fragment length polymorphism of flaA PCR fragments (flaA-RFLP), and disk diffusion testing for eight antimicrobial agents that are commonly used in veterinary or human medicine in Switzerland. Analysis of the genotypic results indicates that the Campylobacter population in Swiss poultry is genetically highly diverse. Nevertheless, occasionally, isolates with identical or nearly identical characteristics were isolated from different farms or farm types in different locations. Genetic typing by AFLP and flaA-RFLP was found to be complementary. The majority of isolates (67%) were susceptible to all tested antibiotics; however, single, double, and triple resistances were observed in 7%, 23%, and 2% of the strains, respectively. There was no correlation between genotype and antibiotic resistance. Surprisingly, sulfonamide resistance was frequently found together with streptomycin resistance. Our findings illustrate the results of common genetic exchange in the studied bacterial population.     

From the linden flower to linden honey--volatile constituents of linden nectar, the extract of bee-stomach and ripe honey

Honey is produced by honeybees (Apis mellifera), which collect nectar from flowers, digest it in their bodies, and deposit it in honeycombs, where it develops into ripe honey. We studied the evolution of the volatile constituents from the nectar of linden blossoms (Tilia cordata) to honey via the 'intermediate' honeybee. The sampling of the contents of the honey stomach or honey sack of the bee is unique. Extracts were prepared from nectar, from the liquid of the honey stomach, and from ripe honey. The chemistry is extremely complex, and compounds spanning from monoterpenes (hydrocarbons, ethers, aldehydes, acids, and bifunctional derivatives), isoprenoids, aromatic compounds (phenylpropanoids, phenols), and products degraded from fatty acids to alkaloids, were identified. Some compounds definitely stem from the plants, whereas other interesting constituents can be attributed to animal origin. Two derivatives of decanoic acid, 9-oxodec-2-enoic acid (12) and 9-hydroxydec-2-enoic acid, identified in the honey are known to be constituents of the so-called 'Queen's pheromone'. Two metabolites of these acids were identified in the extract of the honey stomach: 8-oxononanal (10), a new natural product, and 8-oxononanol (11). There structures were confirmed by synthesis. Nectar and honey stomach contain many aldehydes, which, due to the highly oxidative atmosphere in the honeycomb, are found as corresponding acids in the honey. Two acids were newly identified as 4-isopropenylcyclohexa-1,3-diene-1-carboxylic acid (14) and 4-(1-hydroxy-1-methylethyl)-cyclohexa-1,3-diene-1-carboxylic acid (15).     

Pollen distribution at elevations above 1000 m inSwitzerland

In Switzerland the concentration of allergenic pollendecreases with increasing elevation of the samplingsite of the Swiss pollen measuring network. The aim ofthis study was, to compare the pollen concentrationsof five different localities in the Swiss Alps and inthe Jura mountains, to get an idea of the differencesin the pollen abundance in altitudes above 1000 m. Theinvestigated localities are: La Chaux-de-Fonds(1040 m), Wiesen (1420 m), Davos (1600 m), Samedan(1705 m) and Gütsch (2287 m). These pollen sumswere compared to the Swiss plateau (Basel 273 m).Basel, La Chaux-de-Fonds and Wiesen show clearlyhigher pollen values than Davos, Samedan andGütsch. Pollen concentrations of Corylus,Alnus glutinosa-type and Fraxinus arereduced with increasing altitude and are only a smallproblem for allergies above 1000 m. Betulapollen are also reduced in the higher localities, butthere still occur many days with high pollenconcentrations. Especially Betula pollen frommedium range transport can play an important role forallergies in higher localities. The total grass pollensum does not decrease up to an altitude of 1500 m. Thegrass pollen concentration depends more on factorslike composition of the local grassland, land use andwind situation.Pollen concentrations at higher elevations isinfluenced by the local vegetation, a reduced pollenproduction, land use, topography, exposition, windvelocity and wind direction. These factors modify thepollen concentration considerably. Due to the complextopography of the Prealps and Alps, it is thereforenot possible to propose a general rule of pollenreduction with increasing altitude.     

Diffusion of carbon dioxide through lipid bilayer membranes. Effects of carbonic anhydrase, bicarbonate, and unstirred layers

Diffusion of (14)C-labeled CO(2) was measured through lipid bilayer membranes composed of egg lecithin and cholesterol (1:1 mol ratio) dissolved in n-decane. The results indicate that CO(2), but not HCO(3-), crosses the membrane and that different steps in the transport process are rate limiting under different conditions. In one series of experiments we studied one-way fluxes between identical solutions at constant pCO(2) but differing [HCO(3-)] and pH. In the absence of carbonic anhydrase (CA) the diffusion of CO(2) through the aqueous unstirred layers is rate limiting because the uncatalyzed hydration-dehydration of CO(2) is too slow to permit the high [HCO(3-)] to facilitate tracer diffusion through the unstirred layers. Addition of CA (ca. 1 mg/ml) to both bathing solutions causes a 10-100-fold stimulation of the CO(2) flux, which is proportional to [HCO(3-)] over the pH range 7-8. In the presence of CA the hydration- dehydration reaction is so fast that CO(2) transport across the entire system is rate limited by diffusion of HCO(3-) through unstirred layers. However, in the presence of CA when the ratio [HCO(3-) + CO(3=)]:[CO(2)] more than 1,000 (pH 9-10) the CO(2) flux reaches a maximum value. Under these conditions the diffusion of CO(2) through the membrane becomes rate limiting, which allows us to estimate a permeability coefficient of the membrane to CO(2) of 0.35 cm s(-1). In a second series of experiments we studied the effects of CA and buffer concentration on the net flux of CO(2). CA stimulates the net CO(2) flux in well buffered, but no in unbuffered, solutions. The buffer provides a proton source on the upstream side of the membrane and proton sink on the downstream side, thus allowing HCO(3-) to facilitate the net transport of CO(2) through the unstirred layers.     

Monocarboxylic acid permeation through lipid bilayer membranes

Summary The membrane permeability coefficients for the homologous monocarboxylic acids, formic through hexanoic, as well as benzoic and salicylic, were determined for egg phosphatidylcholine-decane planar bilayer membranes. The permeabilities of formic, acetic and propionic acid were also determined for solvent-free phosphatidylethanolamine bilayers. Permeability coefficients were calculated from tracer fluxes measured under otherwise symmetrical conditions, and precautions were taken to ensure that the values were not underestimated due to unstirred layer effects. The relation between the nonionic (HA) permeability (P ^m ) and the hexadecane/water partition coefficient (K _p ) was: log ^m =0.90 log K_p+0.87 (correlation coefficient=0.996). Formic acid was excluded from the analysis because its permeability was sixfold higher than predicted by the other acids. The permeabilities for solvent-free membranes were similar to those for decanecontaining membranes. The exceptionally high permeability of formic acid and the high correlation of the other permeabilities to the hexadecane/water partition coefficient is a pattern that conforms with other nonelectrolyte permeabilities through bilayers. Similarly, the mean incremental free energy change per methylene group (G-CH₂-) was –764 cal mol^–1, similar to other homologous solutes in other membrane systems. However, much less negative G values (–120, to –400 cal mol^–1) were previously reported for fatty acids permeating bilayers and biological membranes. These values are due primarily to unstirred layer effects, metabolism and binding to membranes and other cell components.     

CDC2/SPDY transiently associates with endoplasmic reticulum exit sites during oocyte maturation

Background  

Fibronectin 1 (FN1), a glycoprotein component of the extracellular matrix, exerts different functions during reproductive processes such as fertilisation, gastrulation and implantation. FN1 expression has been described to increase significantly from the morula towards the early blastocyst stage, suggesting that FN1 may also be involved in early blastocyst formation. By alternative splicing at 3 defined regions, different FN1 isoforms are generated, each with a unique biological function. The analysis of the alternative FN1 splicing on the one hand and the search for candidate FN1 receptors on the other hand during early bovine embryo development may reveal more about its function during bovine preimplantation embryo development.     

Differential and reversible responses of common fen meadow species to abandonment

Abstract. We studied the effects of abandonment on two common fen plant species. In mown and a chronosequence of abandoned fen meadows spanning 35 yr, we measured fitness traits of the sedge Carex davalliana and the forb Succisa pratensis. Cessation of mowing had little effect on fitness traits and seed production of C. davalliana, but seedling density decreased more than threefold. Population density of S. pratensis decreased with increasing community biomass, but was not affected by the cessation of mowing. However, flowering frequency increased threefold and seed production was 20% higher in fallow meadows. Consequently, seedling density of S. pratensis increased nearly threefold after abandonment. However, these changes were not dependent on the age of the fallow. In a common garden and germination experiment, we found no differences in either species between plants from fallows and mown fen meadows, except for the height of the flowering stalk of S. pratensis. The combined results from the common garden experiment and the field studies indicate that changes in fitness traits observed in fallows were mostly phenotypic and likely to be reversible. If other species react in similar ways, there is a high potential for re‐establishing traditional fen meadow communities from fallows by mowing.     

AgTHR4, a new selection marker for transformation of the filamentous fungusAshbya gossypii,maps in a four-gene cluster that is conserved betweenA. gossypii andSaccharomyces cerevisiae

Single-read sequence analysis of the termini of eight randomly picked clones ofAshbya gossypii genomic DNA revealed seven sequences with homology toSaccharomyces cerevisiae genes (15% to 69% on the amino acid level). One of these sequences appeared to code for the carboxy-terminus of threonine synthase, the product of theS. cerevisiae THR4 gene (52.4% identity over 82 amino acids). We cloned and sequenced the complete putativeAgTHR4 gene ofA. gossypii. It comprises 512 codons, two less than theS. cerevisiae THR4 gene. Overall identity at the amino acid sequence level is 67.4%. A continuous stretch of 32 amino acids displaying complete identity between these two fungal threonine synthases presumably contains the pyridoxal phosphate attachment site. Disruption of theA. gossypii gene led to threonine auxotrophy, which could be complemented by transformation with replicating plasmids carrying theAgTHR4 gene and variousS. cerevisiae ARS elements. Using these plasmids only very weak complementation of aS. cerevisiae thr4 mutation was observed. Investigation of sequences adjacent to theAgTHR4 gene identified three additional ORFs. Surprisingly, the order and orientation of these four ORFs is conserved inA. gossypii andS. cerevisiae.