Distance‐dependent seedling mortality and long‐term spacing dynamics in a neotropical forest community

Negative distance dependence (NDisD), or reduced recruitment near adult conspecifics, is thought to explain the astounding diversity of tropical forests. While many studies show greater mortality at near vs. far distances from adults, these studies do not seek to track changes in the peak seedling curve over time, thus limiting our ability to link NDisD to coexistence. Using census data collected over 12 years from central Panama in conjunction with spatial mark‐connection functions, we show evidence for NDisD for many species, and find that the peak seedling curve shifts away from conspecific adults over time. We find wide variation in the strength of NDisD, which was correlated with seed size and canopy position, but other life‐history traits showed no relationship with variation in NDisD mortality. Our results document shifts in peak seedling densities over time, thus providing evidence for the hypothesized spacing mechanism necessary for diversity maintenance in tropical forests.     

Molecular characterization of the <Emphasis Type="Italic">Aspergillus fumigatus NCS-1</Emphasis> homologue,NcsA

Here, we characterize the Aspergillus fumigatus homologue ncsA Neuronal Calcium Sensor. We showed that ncsA is not an essential gene and ?ncsA growth was decreased in the presence of EGTA and SDS. Furthermore, the ?ncsA mutant is more resistant to calcium chloride. NcsA:mRFP localizes to the cytoplasm and its cellular localization is not affected by the cellular response to either calcium chloride or EGTA. The ?ncsA mutant strain is more sensitive to voriconazole, itraconazole, and amphotericin. Polar growth in the ΔncsA mutant was also considerably more affected by lovastatin than in the wild type strain. The Spitzenkörper can be visualized in both strains and although the vacuolar system does not seem to be very different, there is an increase in the staining intensity on the germling surface of the ?ncsA strain. NcsA promotes pmcA and pmcB expression and therefore there is a reduced expression of these ion pumps in the ΔncsA mutant background, and also of other genes involved in the response to calcium in A. fumigatus. The ncsA inactivation mutation is not causing loss of virulence in a low dose murine infection when compared to the corresponding wild type strain.     

Population ecology of the rare carabid beetle Carabus variolosus (Coleoptera: Carabidae) in north-west Germany

The declining European ground beetle Carabus variolosus, an indicator of undisturbed woodland brooks and swamps, is listed in the EU Species and Habitats Directive. Little is known about this flightless and endangered beetle, apart from its distribution range and habitat stenotopy. We present the results of a 2-year mark-release-recapture study on two neighbouring populations in Germany, which investigated basic parameters of population ecology that may be influential in the persistence of the beetle. Extremely small population sizes were the key findings. Since population densities corresponded to those of typical Carabus species, the size of the habitats was most probably the limiting factor. The risk of heavy losses during offspring development and hibernation may be alleviated by the considerable proportion of C. variolosus reproducing in more than 1 year. The fact that we did not recapture any marked specimens from the neighbouring population suggests a very limited dispersal power. The results imply a high vulnerability of the species, provide basic methodological information for an implementation of the EC Directive and for further research, and highlight the necessity to enlarge populated habitats.     

Characterization of single nucleotide polymorphism markers for eelgrass (Zostera marina)

We characterized 37 single nucleotide polymorphism (SNP) makers for eelgrass Zostera marina. SNP markers were developed using existing EST (expressed sequence tag)-libraries to locate polymorphic loci and develop primers from the functional expressed genes that are deposited in The ZOSTERA database (V1.2.1). SNP loci were genotyped using a single-base-extension approach which facilitated high-throughput genotyping with minimal optimization time. These markers show a wide range of variability among 25 eelgrass populations and will be useful for population genetic studies including evaluation of population structure, historical demography, and phylogeography. Potential applications include haplotype inference of physically linked SNPs and identification of genes under selection for temperature and desiccation stress.     

Fluorescent proteins for single‐molecule fluorescence applications

We present single‐molecule fluorescence data of fluorescent proteins GFP, YFP, DsRed, and mCherry, a new derivative of DsRed. Ensemble and single‐molecule fluorescence experiments proved mCherry as an ideally suited fluorophore for single‐molecule applications, demonstrated by high photostability and rare fluorescence‐intensity fluctuations. Although mCherry exhibits the lowest fluorescence quantum yield among the fluorescent proteins investigated, its superior photophysical characteristics suggest mCherry as an ideal alternative in single‐molecule fluorescence experiments. Due to its spectral characteristics and short fluorescence lifetime of 1.46 ns, mCherry complements other existing fluorescent proteins and is recommended for tracking and localization of target molecules with high accuracy, fluorescence resonance energy transfer (FRET), fluorescence lifetime imaging microscopy (FLIM), or multicolor applications. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Real-time imaging of the intracellular glutathione redox potential

Dynamic analysis of redox-based processes in living cells is now restricted by the lack of appropriate redox biosensors. Conventional redox-sensitive GFPs (roGFPs) are limited by undefined specificity and slow response to changes in redox potential. In this study we demonstrate that the fusion of human glutaredoxin-1 (Grx1) to roGFP2 facilitates specific real-time equilibration between the sensor protein and the glutathione redox couple. The Grx1-roGFP2 fusion protein allowed dynamic live imaging of the glutathione redox potential (E(GSH)) in different cellular compartments with high sensitivity and temporal resolution. The biosensor detected nanomolar changes in oxidized glutathione (GSSG) against a backdrop of millimolar reduced glutathione (GSH) on a scale of seconds to minutes. It facilitated the observation of redox changes associated with growth factor availability, cell density, mitochondrial depolarization, respiratory burst activity and immune receptor stimulation.     

Enhanced plating efficiency of trypsin-adapted human embryonic stem cells is reversible and independent of trisomy 12/17

Human embryonic stem cells (hESCs) can be cultured abundantly and indefinitely, but are subject to accumulations of chromosomal aberrations. To preserve their genetic integrity, hESCs are commonly maintained as cell aggregates or clumps during passaging. However, clump passaging hinders large-scale culture and complicates the isolation of single cell clones. To facilitate the isolation of genetically modified clones of hESCs while preserving their genetic integrity, we employed trypsin single-cell passaging for brief periods before returning to clump passaging for long-term maintenance. We observed that accommodation to trypsin passage as single cells is an adaptive process where over three to four passages considerably increases the plating efficiency. However, trypsin passage was associated with abnormalities of chromosomes 12 and 17. Nevertheless, the high plating efficiency of trypsin passaged hESCs is a reversible phenotype, regardless of chromosomal abnormalities, suggesting that epigenetic events are responsible for the switch in phenotype.     

The gross structure of the respiratory complex I: a Lego System

The proton-pumping NADH:ubiquinone oxidoreductase, also called complex I, is the entry point for electrons into the respiratory chains of many bacteria and mitochondria of most eucaryotes. It couples electron transfer with the translocation of protons across the membrane, thus providing the proton motive force essential for energy-consuming processes. Electron microscopy revealed the ‘L’-shaped structure of the bacterial and mitochondrial complex with two arms arranged perpendicular to each other. Recently, we showed that the Escherichia coli complex I takes on another stable conformation with the two arms arranged side by side resulting in a horseshoe-shaped structure. This model reflects the evolution of complex I from pre-existing modules for electron transfer and proton translocation.