The physiological basis of seed dormancy in Avena fatua. II. On the involvement of alternative respiration in the stimulation of germination by sodium azide

Chromatography on DEAE-cellulose of an extract from etiolated leaves of sorghum ( Sorghum vulgare Pers. cv. INRA 450), a C₄ plant, gave only one form of phosphoenol pyruvate carboxylase with functional and regulatory properties of a C₃ type plant enzyme. Greening of the leaves resulted in a significant increase in activity. This increase was due to the appearance of a new form of the enzyme, which eluted at lower ionic strength and exhibited new properties. This form was glucose-6-P activated and showed a sigmoidal curve response to the concentration of the substrate phosphoerralpyruvate. These kinetic properties are typical of a C₄ plant enzyme.     

Occurrence and characteristics of agglutination of Vibrio cholerae by serum from the eastern oyster, Crassostrea virginica.

Cell-free hemolymph (serum) of the eastern oyster, Crassostrea virginica, agglutinated Vibrio cholerae, including all O1 serovars and biovars. Seventy-nine other strains of bacteria, including 14 genera and 26 species, were not agglutinated. The A, B, and C factors of O1 antigen were not involved in agglutination. Bacterial agglutinating (BA) activity was demonstrated for oysters inhabiting different environments of the U.S. Atlantic and Gulf coasts. Oyster serum BA titers showed high individual variation. The serum component(s) involved in BA was inhibited by 80 degrees C heat, pronase, EDTA, mucin, and fetuin treatments. N-Acetylneuraminic acid (10 mg/ml) weakly inhibited BA activity. Ligands of V. cholerae were sensitive to neuraminidase and resistant to 80 degrees C and pronase. High salinities (24 and 30%) enhanced BA. Cross-adsorption tests with V. cholerae and human O+ erythrocytes indicated that BA and hemagglutinating activities may involve different serum components. These results imply that the ecology of V. cholerae in C. virginica is influenced by agglutinating activity of oyster serum.     

Live imaging and genetic analysis of mouse notochord formation reveals regional morphogenetic mechanisms

The node and notochord have been extensively studied as signaling centers in the vertebrate embryo. The morphogenesis of these tissues, particularly in mouse, is not well understood. Using time-lapse live imaging and cell lineage tracking, we show the notochord has distinct morphogenetic origins along the anterior-posterior axis. The anterior head process notochord arises independently of the node by condensation of dispersed cells. The trunk notochord is derived from the node and forms by convergent extension. The tail notochord forms by node-derived progenitors that actively migrate toward the posterior. We also reveal distinct genetic regulation within these different regions. We show that Foxa2 compensates for and genetically interacts with Noto in the trunk notochord, and that Noto has an evolutionarily conserved role in regulating axial versus paraxial cell fate. Therefore, we propose three distinct regions within the mouse notochord, each with unique morphogenetic origins.     

Response of hatchling wood turtles (Glyptemys insculpta) to an aquatic thermal gradient

Effective thermoregulation and the ability to select preferred temperature is an important factor influencing fitness in hatchling and juvenile turtles. Six-month-old Glyptemys insculpta acclimated to 20 °C selected the warmest temperature available and avoided the coldest temperature available in a gradient of 12–27 °C. Turtles visited fewer chambers and switched chambers in the gradient tank less frequently when the gradient was present than during control tests. Mean selection of chambers differed between control and gradient tests across all temperatures except at 21 °C, the temperature closest to the acclimation and control temperature (20 °C).     

Conservation genetics of a peripherally isolated population of the wood turtle (<Emphasis Type="Italic">Glyptemys insculpta</Emphasis>) in Iowa

The North American wood turtle, Glyptemys insculpta, is a semi-aquatic species that is considered rare, threatened, or endangered over much of its range. In this study, a particularly vulnerable peripheral isolate population in Iowa has been monitored over a period of 7 years. Population census size, estimated from mark-recapture data, and age structure determined from morphology are compared with genetic variation assessed using microsatellites. For reference, the genetics and demographics of this peripheral isolate are compared to data from a more dense population nearer the core of the species range in West Virginia. Geneflow between the Iowa population and a nearby population in Minnesota also is assessed. Genetic data indicate that the Iowa population is isolated, unique, and diverse. Although the Iowa population has lower allelic richness, lower heterozygosity, and smaller genetic effective population size than does the West Virginia population, the difference is not dramatic despite its lower population size, position at the periphery of the species range, and biogeographic history. The Iowa population is not inbred, and there is no genetic signature of a recent population bottleneck. However, interpretations of recent population dynamics based on genetic data may be unduly encouraging in long-lived species such as G. insculpta. Field data suggest a nearly complete lack of recruitment in Iowa. A number of environmental and anthropogenic factors, including recent increases in summer flooding during egg incubation, may have a more negative impact on the Iowa population than on the West Virginia population.     

Geographical variation in antibiotic resistance profiles of Escherichia coli isolated from swine, poultry, beef and dairy cattle farm water retention ponds in Florida

AIMS: The aim of this study was to assess geographical variation in multiple antibiotic resistance (MAR) profiles of livestock Escherichia coli as well as to evaluate the ability of MAR profiles to differentiate sources of faecal pollution. METHODS AND RESULTS: More than 2000 E. coli isolates were collected from water retention ponds and manure of swine, poultry, beef and dairy farms in south, central and north Florida, and analysed for MAR using nine antibiotics. There were significant differences in antibiotic resistance of E. coli by season and livestock type for more than one antibiotic, but regional differences were significant only for ampicillin. Over the three regions, discriminant analysis using MAR profiles correctly classified 27% of swine, 49% of poultry, 56% of beef and 51% of dairy isolates. CONCLUSIONS: Regional variations in MAR combined with moderate discrimination success suggest that MAR profiles of E. coli may only be marginally successful in identifying sources of faecal pollution. SIGNIFICANCE AND IMPACT OF THE STUDY: This study demonstrates the existence of regional and seasonal differences in MAR profiles as well as the limited ability of MAR profiles to discriminate among livestock sources.     

Sedentary life style of Neotropical sedge wrens promotes song imitation

To what extent has the style of song development among songbirds coevolved with other life history strategies? Among Cistothorus wrens in North America, it seems that sedentary or site-faithful habits of marsh wrens, C. palustris, favour song imitation, but seminomadic habits of sedge wrens, C. platensis, favour song improvisation, whereby each male generates a large but unique song repertoire. In this study, we tested whether more sedentary populations of sedge wrens in the Neotropics would imitate songs. At our primary study site near Cartago, Costa Rica, breeding birds were colour-banded during 1995 and 1996, and follow-up surveys revealed that the birds remained at this site the year round. Extensive tape recording and analysis of songs showed that males had large song repertoires (200-300+ songs), and that many songs were shared among neighbouring males. In addition, males only 27 km distant, at La Pastora, used different songs. Furthermore, matched countersinging, in which two males answer each other with identical song types, was recorded near Brasilia, in Brazil. The sharing of songs among permanent neighbours, microgeographical variation in song, and matched countersinging can be achieved only through song imitation, thus revealing a striking difference in the style of song development among different populations of the sedge wren. In the Neotropics, having predictable neighbours throughout life appears to have favoured song imitation, so that individuals can interact using a common, learned code typical of the local population; among more mobile populations in North America, however, individuals improvise large repertoires of species-typical songs, thereby enabling singing males to communicate with any individual, no matter what the population of origin. Strategies of song development must correlate with life history features, and further surveys are needed to make sense of the great diversity of singing behaviours among songbirds. Copyright 1999 The Association for the Study of Animal Behaviour.     

Enhanced Broth Media for Selective Growth of Vibrio vulnificus

Rapid detection of Vibrio vulnificus can be enhanced by optimizing the components of enrichment broth. PNC (5% peptone, 1% NaCl, and 0.08% cellobiose [pH 8.0]) enhanced the growth of V. vulnificus compared to alkaline peptone broth. PNCC (PNC with 1.0 to 4.1 U of colistin methanesulfonate per ml) increased the growth of low levels of V. vulnificus while suppressing non-target bacteria.