Positive regulation of T cell activation and integrin adhesion by the adapter Fyb/Slap

The molecular adapter Fyb/Slap regulates signaling downstream of the T cell receptor (TCR), but whether it plays a positive or negative role is controversial. We demonstrate that Fyb/Slap-deficient T cells exhibit defective proliferation and cytokine production in response to TCR stimulation. Fyb/Slap is also required in vivo for T cell-dependent immune responses. Functionally, Fyb/Slap has no apparent role in the activation of known TCR signaling pathways, F-actin polymerization, or TCR clustering. Rather, Fyb/Slap regulates TCR-induced integrin clustering and adhesion. Thus, Fyb/Slap is the first molecular adapter to be identified that couples TCR stimulation to the avidity modulation of integrins governing T cell adhesion.     

Detection of radial crossbridge force by lattice spacing changes in intact single muscle fibers

Time-resolved lattice spacing changes were measured (10-millisecond time resolution) by x-ray diffraction of synchrotron radiation in single intact muscle fibers of the frog Rana temporaria undergoing electrically stimulated tension development during application of stretches and releases. Ramp releases, which decreased fiber length at constant speed, caused a lattice expansion. After the ramp, increasing tension during recovery was accompanied by lattice compression. Ramp stretches caused a compression of the lattice. While the fiber was held at a constant length after the stretch, tension decreased and lattice spacing increased. These observations demonstrate the existence of a previously undetected radial component of the force generated by a cycling crossbridge. At sarcomere lengths of 2.05 to 2.2 micrometers, the radial force compresses the myofilament lattice. Hence, the myofilament lattice does not maintain a constant volume during changes in force.     

The trans Golgi network: sorting at the exit site of the Golgi complex

The Golgi complex is a series of membrane compartments through which proteins destined for the plasma membrane, secretory vesicles, and lysosomes move sequentially. A model is proposed whereby these three different classes of proteins are sorted into different vesicles in the last Golgi compartment, the trans Golgi network. This compartment corresponds to a tubular reticulum on the trans side of the Golgi stack, previously called Golgi endoplasmic reticulum lysosomes (GERL).     

Migration of bacterial-feeding nematodes,but not protozoa,to decomposing grass residues

Summary Populations of bacterial-feeding nematodes and protozoa developing in soil amended with dried grass powder or a nutrient solution were monitored in experimental systems designed to prevent migration from surrounding unamended soil. The addition of nutrient solution stimulated both microbial activity, as determined by dehydrogenase activity, and protozoa, but brought about no increase in nematode numbers. Amendment of soil with grass, however, caused an increase in both types of grazer, with the maximum biomass of protozoa (180 g g^-1) exceeding that of bacterial-feeding nematodes (42 g^-1). The decomposing grass was rapidly colonised by rhaditid nematodes, mainly Caenorhabditis sp. Incubating grass-amended soil in the absence of any surrounding soil, to prevent migration, changed the microflora from predominantly bacterial to predominantly fungal, and so could not be used to compare treatments with and without migration. Surrounding the amended soil with sterilised soil prevented migration and caused no detectable change in the microflora. This treatment demonstrated that migration plays an important part in the colonisation of decomposing substrates by nematodes, but that protozoa do not migrate in soil. The nematodes migrated from a volume of unamended soil that was equivalent to eight times the volume of amended soil. The potential effects of the large grazing pressure on the subsequent decomposition of the grass residue are discussed.     

Variations in the rates of nitrification and denitrification during the growth of potatoes (Solanum tuberosum L.) in soil with different carbon inputs and the effect of these inputs on soil nitrogen and plant yield

Summary A potato crop (Solanum tuberosum L. cv. Maris piper) was grown in a soil to which N was added, as NH₄NO₃, with or without added C, as sucrose or straw. Shortly after amendment the soil, in all treatments, contained only relatively low levels of mineral N. However, these levels increased later. The increase, which was greatest in the absence of added C and least with added sucrose, occurred before the emergence of the plant canopy. The addition of C to the soil had no effect on plant yield, measured either as dry matter or total N content. The potential nitrification rate was high early in the season, and decreased significantly as the plants developed. The potential denitrification rate showed two significant peaks in activity, possibly related to plant development, the first to the development of new roots and the second to root senescence. It seems probable that the amount of C released by the potato plants was only about one-quarter of that required for the maximum microbial activity.     

Microbial population dynamics related to temporal variations in nitrification in three arable fields

It seems possible that soil potential nitrification rates (PNRs) are determined by the size and structure of both the eubacterial and nitrifier populations. We have examined this possibility by comparing the structure of the eubacterial community with the subcomponents and dynamics of the ammonium‐oxidizer population, within and between three arable fields. PNRs were significantly different between the three fields and also showed significantly different temporal patterns within each field. The use of eubacterial primers in polymerase chain reaction–denaturing gel gradient electrophoresis (PCR–DGGE) analyses indicated that the bacterial community structure in each field was significantly different from that in the others, and that the bacterial components of these communities changed with time through the season. In contrast, PCR–DGGE analyses specific to ammonium oxidizers suggested that the populations in all three fields were similar in types and did not vary with time. Competitive PCR suggested that there were large and biologically significant differences in the size of the nitrifier population between the three fields, but that within each individual field populations did not change over time. Sequencing identified the ammonium oxidizers in the Nitrosospira spp. cluster. There was also no relation between the size of the nitrifier populations and PNR. Functional expression, as PNR, apparently responded to changes in eubacterial community structure.     

Nematodes as indicators of enhanced microbiological activity in a Scottish organic farming system

Abstract. The presence of spring barley plants increased the numbers of nematodes, particularly of plant-feeders, compared with fallow plots in a Scottish organic farming system. The addition of farmyard manure (FYM) had no detectable effect on nematode populations but poultry manure (PM) caused a considerable increase. The application of PM also altered the types of nematode present and favoured bacterial-feeders and rhabditids in particular. These changes suggest that PM causes shortterm (within a growing season) increases in microbiological activity and nutrient cycling, whereas FYM is more likely to bring about long-term changes.     

Decomposition processes under Bt (Bacillus thuringiensis) maize: Results of a multi-site experiment

The effects of maize expressing the Bacillus thuringiensis Cry1Ab protein (Bt maize) on decomposition processes under three different European climatic conditions were assessed in the field. Farming practices using Bt maize were compared with conventional farming practices using near-isogenic non-Bt maize lines under realistic agricultural practices. The litter-bag method was used to study litter decomposition and nitrogen mineralization dynamics of wheat straw. After 4 months incubation in the field, decomposition and mineralization were mainly influenced by climatic conditions with no negative effect of the Bt toxin on decomposition processes.     

Evaluation of effects of transgenic Bt maize on microarthropods in a European multi-site experiment

The effects of maize expressing the Bacillus thuringiensis Cry1Ab protein (Bt maize) on soil microarthropods were assessed in the field at four European locations (two in Denmark and two in France) that differ in their climatic conditions or soil properties. Each site was considered as a separate experiment, with separate statistical comparison. Effects of farming practices using Bt maize were compared with conventional farming practices using near-isogenic non-Bt maize and also (at some of the sites) other conventional varieties. Furthermore, at one field site (Foulum, Denmark), the effects of Bt crops were studied in both conventional tillage and reduced tillage contexts. At another field site (Askov, Denmark), Bt maize effects were also compared to the effects of the chemical insecticide dimethoate. Moreover, at three of the field sites (all except Narbons, France), the possibility of a localised Bt effect around the rhizosphere compared to the bulk soil was assessed by sampling within and between maize rows. There were some significant negative effects of Bt maize on microarthropods in soils with a high clay content. Significant differences of the same magnitude also occurred between different conventional varieties of maize, but the effect of dimethoate appeared clearly greater than Bt effects. It is thus debatable if the Bt maize effect is an effect of the Bt toxin or just an effect of the maize variety. Based on the results, it can be concluded that the effect of Bt maize on soil microarthropods was small and within the normal variation expected in conventional agricultural systems.