Conductance Ratios and Cellular Identity

Recent experimental evidence suggests that coordinated expression of ion channels plays a role in constraining neuronal electrical activity. In particular, each neuronal cell type of the crustacean stomatogastric ganglion exhibits a unique set of positive linear correlations between ionic membrane conductances. These data suggest a causal relationship between expressed conductance correlations and features of cellular identity, namely electrical activity type. To test this idea, we used an existing database of conductance-based model neurons. We partitioned this database based on various measures of intrinsic activity, to approximate distinctions between biological cell types. We then tested individual conductance pairs for linear dependence to identify correlations. Contrary to experimental evidence, in which all conductance correlations are positive, 32% of correlations seen in this database were negative relationships. In addition, 80% of correlations seen here involved at least one calcium conductance, which have been difficult to measure experimentally. Similar to experimental results, each activity type investigated had a unique combination of correlated conductances. Finally, we found that populations of models that conform to a specific conductance correlation have a higher likelihood of exhibiting a particular feature of electrical activity. We conclude that regulating conductance ratios can support proper electrical activity of a wide range of cell types, particularly when the identity of the cell is well-defined by one or two features of its activity. Furthermore, we predict that previously unseen negative correlations and correlations involving calcium conductances are biologically plausible.     

Plant intraspecific functional trait variation is related to within‐habitat heterogeneity and genetic diversity in Trifolium montanum L.

Intraspecific trait variation (ITV), based on available genetic diversity, is one of the major means plant populations can respond to environmental variability. The study of functional trait variation and diversity has become popular in ecological research, for example, as a proxy for plant performance influencing fitness. Up to now, it is unclear which aspects of intraspecific functional trait variation (iFD_CV) can be attributed to the environment or genetics under natural conditions. Here, we examined 260 individuals from 13 locations of the rare (semi‐)dry calcareous grassland species Trifolium montanum L. in terms of iFD_CV, within‐habitat heterogeneity, and genetic diversity. The iFD_CV was assessed by measuring functional traits (releasing height, biomass, leaf area, specific leaf area, leaf dry matter content, F_v/F_m, performance index, stomatal pore surface, and stomatal pore area index). Abiotic within‐habitat heterogeneity was derived from altitude, slope exposure, slope, leaf area index, soil depth, and further soil factors. Based on microsatellites, we calculated expected heterozygosity (H_e) because it best‐explained, among other indices, iFD_CV. We performed multiple linear regression models quantifying relationships among iFD_CV, abiotic within‐habitat heterogeneity and genetic diversity, and also between separate functional traits and abiotic within‐habitat heterogeneity or genetic diversity. We found that abiotic within‐habitat heterogeneity influenced iFD_CV twice as strong compared to genetic diversity. Both aspects together explained 77% of variation in iFD_CV ( = .77, F_{2, 10} = 21.66, p < .001). The majority of functional traits (releasing height, biomass, specific leaf area, leaf dry matter content, F_v/F_m, and performance index) were related to abiotic habitat conditions indicating responses to environmental heterogeneity. In contrast, only morphology‐related functional traits (releasing height, biomass, and leaf area) were related to genetics. Our results suggest that both within‐habitat heterogeneity and genetic diversity affect iFD_CV and are thus crucial to consider when aiming to understand or predict changes of plant species performance under changing environmental conditions.     

Nanoplanktonic coccolithophorids (Prymnesiophyceae, Haptophyceae) from the Weddell Sea, Antarctica

The examination of whole mounts prepared for transmission electron microscopy has resulted in the finding of thirteen taxa of nanoplanktonic coccolithophorids from the Weddell Sea, Antarctica. The material was collected as part of the AMERIEZ programme, March 1986. Cold-water adapted nanoplanktonic coccolithophorids have previously been shown to constitute a recurrent plankton element at subarctic and arctic localities. Three of the Weddell Sea species, Wigwamma annulifera, W. arctica , and Papposphaera sagittifera , are conspecific with northern hemisphere material, while two species, Calciarcus alaskensis and Turrisphaera arctica , are possibly identical with previously described arctidsubarctic material. Six taxa new to science have been described from the Weddell Sea, Wigwamma antarctica, W. triradiata, Trigonaspis melvillea, Pappomonas weddellensis, Papposphaera obpyramidalis , and P. simplicissima . The cooccurrence of identical forms at the two poles, and the fact that the species described are allocated to "arctic" genera, indicate a geologically relatively recent exchange of biological material between the poles.     

Growth of Escherichia coli in the presence of trimethoprim-sulfamethoxazole facilitates detection of Shiga-like toxin producing strains by colony blot assay

Abstract Subinhibitory concentrations of trimethoprim-sulfamethoxazole increased the total yield of Shiga-like toxin (SLT), produced by Shigella dysenteria 1 and by enterophathogenic and enterohemorrhagic strains of Escherichia coli . Stimulation of SLT synthesis by trimethoprim-sulfamethoxazole was demonstrated by an increase in cytotoxic activity for HeLa cells and the diameter of the zone formed around bacterial colonies probed with monoclonal antibodies to SLT. Thus, supplementation of culture media with trimetroprimsulfamethoxazol will facilitate SLT purification and detection of SLT-producing bacteria.     

Zur Ultrastruktur der intrazellulären Symbionten im Embryo der KleinzikadeEuscelis plebejus Fall. (Homoptera,Cicadina)

Summary Two types of bacterial symbionts (a- and t-types) were present intracellularly in embryos of the leafhopperEuscelis plebejus. In the electron microscope, three unit membranes were seen to surround the bacteria; the two inner membranes appeared to originate from the bacteria, the outer — from the host cytoplasm. DNA-structures were not observed in the symbionts. The a-symbionts contained in their cytoplasm crystalloid bodies presumably of protein nature and, during certain stages of embryonic development, tubular membranous bodies. The t-symbionts contained in their cytoplasm chymotrypsin-resistant dense bodies, that probably invade the host cytoplasm.Zusammenfassung Das elektronenmikroskopische Bild der intrazellulären a- und t-Symbionten vonEuscelis plebejus Fall. läßt erkennen, daß die symbiontischen Bakterien von drei Elementarmembranen umgeben sind. Morphologische Gründe sprechen dafür, daß die beiden inneren den Bakterien entstammen, die äußere Hüllmembran aber vom Cytoplasma der Wirtszelle gebildet wird. Bakterien-DNS konnte noch in keinem der beiden Symbiontentypen mit Sicherheit nachgewiesen werden. Die a-Symbionten sind vor Aufnahme in die Mycetocyten reich an tubulären Membrankörpern. Sie enthalten außerdem einen mit Chymotrypsin auflösbaren kristallinen Körper. In den t-Symbionten befinden sich Chymotrypsin-resistente dense bodies, die wahrscheinlich in das Wirtscytoplasma abgegeben werden.

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Mit Unterstützung durch Mittel der Deutschen Forschungsgemeinschaft, die Herrn Prof. Dr.K. Sander zur Verfügung standen.     

Transduction of a Plasmid Carrying the Cohesive End Region from Lactococcus lactis Bacteriophage ΦLC3

Plasmids carrying the cohesive end region from temperate lactococcal bacteriophage ΦLC3 could be packaged in vivo by ΦLC3 and transduced into its host strain, Lactococcus lactis subsp. cremoris NCDO 1201. The transduction frequencies were between 10^-4 and 10^-3 transducing particles per PFU, depending on the size of the phage DNA insert. This transduction system is limited to only certain lactococcal strains. The ΦLC3 cohesive site region (cos) appears to play an important role in plasmid transduction.     

The Influence of Alarm Substance on Feeding in Zebra Danio Fish (Brachydanio rerio)

The effects of alarm substance on feeding behaviour of zebra danio fish (Brachydanio rerio) were tested by offering them high and low densities of enclosed waterfleas (Daphnia magna). Normally the fish attacked high densities of prey, but when exposed to alarm substance they preferred lower and presumably less confusing prey densities — also lowering their feeding rate.     

Isolation of Com1, a New Gene Required to Complete Meiotic Double-Strand Break-Induced Recombination in Saccharomyces Cerevisiae

We have designed a screen to isolate mutants defective during a specific part of meiotic prophase I of the yeast Saccharomyces cerevisiae. Genes required for the repair of meiotic double-strand breaks or for the separation of recombined chromosomes are targets of this mutant hunt. The specificity is achieved by selecting for mutants that produce viable spores when recombination and reductional segregation are prevented by mutations in SPO11 and SPO13 genes, but fail to yield viable spores during a normal Rec(+) meiosis. We have identified and characterized a mutation com1-1, which blocks processing of meiotic double-strand breaks and which interferes with synaptonemal complex formation, homologous pairing and, as a consequence, spore viability after induction of meiotic recombination. The COM1/SAE2 gene was cloned by complementation, and the deletion mutant has a phenotype similar to com1-1. com1/sae2 mutants closely resemble the phenotype of rad50S, as assayed by phase-contrast microscopy for spore formation, physical and genetic analysis of recombination, fluorescence in situ hybridization to quantify homologous pairing and immunofluorescence and electron microscopy to determine the capability to synapse axial elements.