Insect communities on experimental mugwort (Artemisia vulgaris L.) plots along an urban gradient

We studied the ability of insect herbivores and their natural enemies to colonize exposed, potted mugwort plants (Artemisia vulgaris L.) along a rural-urban gradient in 1994 in Hamburg (northern Germany). Ectophagous insects, leafmines and galls were monitored weekly from mid-May to mid-September. Endophagous insects were counted by harvesting and dissecting the stems at the end of the growing season. The rural-urban gradient was characterized by a gradient of vegetation-free areas and increasing proportion of ground covered in concrete, tarmac, paving and other impermeable surfaces surrounding the Artemisia plots, i.e. six different zones of increasing isolation. Numbers of insect species (herbivores, parasitoids and predators) decreased along the gradient from 43 to 12. Monophagous herbivores were not more affected than polyphagous herbivores, but parasitoids, especially rare species, were more strongly affected by isolation than predators. Some dominant herbivorous species were very successful colonizers and occurred in inner city sites devoid of all natural vegetation. Sometimes their abundance increased in the inner city to significantly higher densities than in the urban fringe. Isolation appeared to be the main reason for the observed patterns, since area and soil conditions were held constant in the experiment. Microclimate and pollution were considered to play a minor role. Received: 16 January 1997 / Accepted: 26 August 1997     

Analysis of ionic channels by a flash spectrophotometric technique applicable to thylakoid membranes: CF0, the proton channel of the chloroplast ATP synthase,and, for comparison,gramicidin

Summary We previously introduced a flash spectrophotometric method to analyze proton conduction by CF₀ in vesicles derived from thylakoid membranes (H. Lill, S. Engelbrecht, G. Schönknecht & W. Junge, 1986,Eur. J. Biochem. 160:627–634). The unit conductance of CF₀, as revealed by this technique, was orders of magnitude higher than that theoretically expected for a hydrogen-bonded chain. We scrutinized the validity of this method. Small vesicles were derived from thylakoids by EDTA treatment. The intrinsic electric generators in the membrane were stimulated by short flashes of light and the relaxation of the voltage via ionic channels was measured through electrochromic absorption changes of intrinsic pigments. The voltage decay was stimulated by a statistical model. As the vesicle-size distribution had only a minor influence, the simulation required only two fit parameters, the first proportional to the unit conductance of an active channelG, and the second denoting the average number of active channels per vesiclen. This technique was applied to CF₀, the proton channel of the chloroplast ATP synthase, and to gramicidin, serving as a standard. For both channels we found the above two fit parameters physically meaningful. They could be independently varied in predictable wasy, i.e.n by addition of known inhibitors of F₀-type proton channels andG via the temperature. for gramicidin, the unit conductance (2.7 pS) was within the range described in the literature. This established the competence of this method for studies on the mechanism of proton conduction by CF₀, whose conductance so far has not been accessible to other, more conventional approaches. The time-averaged unit conductance of CF₀ was about 1 pS, equivalent to the turnover of 6×10⁵ H⁺/(CF₀·sec) at 100 mV driving force.     

Influence of growth conditions on physicochemical surface characteristics of two gramnegative and two grampositive bacteria

Summary The focus of this work was the investigation of correlations between cultivation parameters and cell surface physicochemistry (hydrophobicity, electrophoretic mobility, isoelectric point) of four strains (Pseudomonas aeruginosa DSM 1253, Escherichia coli 72, Arthrobacter oxydans DSM 420 and Corynebacterium glutamicum DSM 20300).Abbreviations EPM electrophoretic mobility Dedicated to Prof. Dr. Joachim Klein for his 60th birthday     

Studies of congenic MRL-Ipr/Ipr.xid mice

Highly inbred MRL-Ipr/Ipr.xid congenic mice were bred and compared with their + littermates. The xid-bearing congenics developed lymphadenopathy consisting of dull Ly-1+ T cells and impairment of cellular proliferation and IL 2 production in response to the T cell mitogen Con A. Thus, the lpr gene was fully expressed. The xid gene, however, was also expressed as indicated by the failure to respond to immunization with TNP-Ficoll and flow cytometric analysis of splenic B cells. The xid gene was associated with a marked reduction in IgM anti-ssDNA and anti-nDNA of both classes, and serum Ig-bound gp 70. Kidney disease was markedly retarded as was death from the autoimmune process. These studies suggest that the T cell lymphoproliferation and dysfunction characteristic of MRL-Ipr/Ipr mice is not sufficient to induce accelerated autoimmunity; xid is able to markedly slow the process. The xid gene interferes with the development of a B cell subset necessary for maximum autoantibody production, anti-gp 70 production, and the resultant immune complex renal and cardiac disease. The present finding of protection against accelerated autoimmunity in MRL-Ipr/Ipr mice by xid, coupled with previous demonstrations of protection against autoimmunity in other autoimmune mouse strains, suggests that a common approach to the therapy of systemic lupus may be possible.     

Contrasting distributions of bacteriophages and eukaryotic viruses from contaminated coastal sediments

Viruses are ubiquitous, abundant and play an important role in all ecosystems. Here, we advance understanding of coastal sediment viruses by exploring links in the composition and abundance of sediment viromes to environmental stressors and sediment bacterial communities. We collected sediment from contaminated and reference sites in Sydney Harbour and used metagenomics to analyse viral community composition. The proportion of phages at contaminated sites was significantly greater than phages at reference sites, whereas eukaryotic viruses were relatively more abundant at reference sites. We observed shifts in viral and bacterial composition between contaminated and reference sites of a similar magnitude. Models based on sediment characteristics revealed that total organic carbon in the sediments explained most of the environmental stress-related variation in the viral dataset. Our results suggest that the presence of anthropogenic contaminants in coastal sediments could be influencing viral community composition with potential consequences for associated hosts and the environment.     

Effects of BUdR on developmental functions of Dictyostelium discoideum.

The development of Dictyostelium discoideum cells, as measured by spore yield, is somewhat more sensitive to the presence of BUdR during vegetative growth than is growth itself. Observations on the development of control and BUdR-grown cells, their protein labelling patterns and assays of 4 developmentally regulated proteins all reveal a consistent picture. BUdR appears to block spore formation by partially inhibiting several or many different earlier events during development. The relative sensitivity of development compared to growth to inhibition by the drug may be a consequence of the nature of the developmental process rather than of some unique specificity of the inhibitor.     

Orthophosphate-promoted ouabain binding to Na/K pumps of resealed red cell ghosts. Evidence for E*P preferentially binding ouabain.

Modulation of phosphoenzyme forms of the Na/K pump by Na+ and K+ was studied by measuring the rate of Pi-promoted ouabain binding to resealed ghosts made from human red cells. This system permits distinguishing the effects of the ions at intracellular and external binding sites. Internal K+, Ki, inhibited the rate of Pi-promoted ouabain binding, contrary to a prediction based on a current model of the pump. External K+, Ko, failed to inhibit ouabain binding in the absence of Ki. However, Ko enhanced the inhibition by Ki. Nai also inhibited ouabain binding; this inhibition was much less affected by Ko than was inhibition by Ki, suggesting that Ki and Nai affect ouabain binding at different internal sites. Nao inhibited ouabain binding in the absence of Ki or Ko, so Nao and Ko also act at different sites. With Nao present, Ki stimulated ouabain binding. Thus a condition was found in which the predicted stimulation of binding by Ki was observed. The results of this study are interpreted in terms of three phosphoenzyme forms of the pump: E1P, E*P, and E2P. E*P is the form binding ouabain with highest affinity. Ki promotes E*P----E2P, thereby inhibiting ouabain binding. Ko binds only to E2P, therefore Ki is required for inhibition by Ko, and there is little E2P present with no Ki. Nao inhibits binding by stabilizing E1P whereas Nai inhibits by stabilizing E1. The stimulation by Ki with Nao present means that Ki and Nao together favor formation of E*P. Furthermore, Ki and Nao may bind to the pump simultaneously. Ki may play a role in the normal pump cycle, binding at allosteric sites to promote E*P----E2P.