Tolerance breaking by lymphocyte activating factor induced by Escherichia coli O138 lipopolysaccharide from homologous macrophages.

Following an antigenic dose of 10 microgram or a tolerogenic dose of 200 microgram of Escherichia coli O138 lipopolysaccharide (LPS), BALB/c mice were examined on day 14 for percentages of theta-bearing cells. A considerable increase in T cells was noticed in lymphocytes from tolerant draining lymph nodes, and furthermore these cells did not possess receptors for LPS when tested for rosette inhibition. However, when the supernatant from 1 X 10(7) macrophages, pretreated with 150 microgram LPS, was given to tolerant mice on day 7, by day 14 tolerance was found to be broken, anti-LPS IgG was present in circulation and the draining lymph node contained T cells specifically committed to LPS. The change from suppressor to helper T cell activity is discussed in relation to enhancement of the immune response.     

Giant Friedel Oscillations on the Beryllium(0001) Surface

Large-amplitude electron density oscillations were observed on a Be(0001) surface by means of variable-temperature scanning tunneling microscopy. Fourier transforms of the images showed a ring of radius 2kF, where kF is the Fermi wave vector of the Be(0001) surface state. This wavelength was expected from Friedel oscillations caused by electronic screening of surface defects, but the amplitude of the waves for energies near the Fermi energy was anomalously large and inconsistent with the Friedel concept of screening. The enhanced amplitude of the waves must be a many-body effect, either in the electron gas (possibly an incipient charge density wave) or in the response of the lattice (electron-phonon coupling).     

Rise and fall of species occupancy in Cenozoic fossil mollusks

In the time between speciation and extinction, a species' ecological and biogeographic footprint-its occupancy-will vary in response to macroecological drivers and historical contingencies. Despite their importance for understanding macroecological processes, general patterns of long-term species occupancy remain largely unknown. We documented the occupancy histories of Cenozoic marine mollusks from New Zealand. For both genera and species, these show a distinct pattern of increase to relatively short-lived peak occupancy at mid-duration, followed by a decline toward extinction. Thus, species at greatest risk for extinction are those that have already been in decline for a substantial period of time. This pattern of protracted rise and fall stands in contrast to that of incumbency, insofar as species show no general tendency to stay near maximal occupancy once established.     

Single-molecule kinetics of lambda exonuclease reveal base dependence and dynamic disorder

We used a multiplexed approach based on flow-stretched DNA to monitor the enzymatic digestion of lambda-phage DNA by individual bacteriophage lambda exonuclease molecules. Statistical analyses of multiple single-molecule trajectories observed simultaneously reveal that the catalytic rate is dependent on the local base content of the substrate DNA. By relating single-molecule kinetics to the free energies of hydrogen bonding and base stacking, we establish that the melting of a base from the DNA is the rate-limiting step in the catalytic cycle. The catalytic rate also exhibits large fluctuations independent of the sequence, which we attribute to conformational changes of the enzyme-DNA complex.     

Genetic differentiation in populations of Exserohilum turcicum from maize and sorghum in South Africa

Exserohilum turcicum is the causal agent of northern leaf blight, a devastating foliar disease of maize and sorghum. Specificity of E. turcicum to either maize or sorghum has been observed previously, but molecular evidence supporting host specialization is lacking. The aim of this study was to compare the genetic structure of E. turcicum isolates collected from adjacent maize and sorghum fields in Delmas and Greytown in South Africa. In addition, the mode of reproduction of this pathogen was investigated. Isolates from maize (N = 62) and sorghum (N = 64) were screened with 12 microsatellite markers as well as a multiplex mating type PCR assay. No shared haplotypes were observed between isolates from different hosts, although shared haplotypes were detected between isolates from maize from Delmas and Greytown. Population structure and principal coordinate analyses revealed genetic differentiation between E. turcicum isolates from maize and sorghum. Analysis of molecular variance indicated higher among‐population variation when comparing populations from different hosts, than comparing populations from different locations. Lack of shared haplotypes, high proportion of private alleles, greater among‐population variance between hosts than locations and significant pairwise population differentiation indicates genetic separation between isolates from maize and sorghum. The high haplotypic diversity in combination with unequal mating type ratios and significant linkage equilibrium indicates that both sexual and asexual reproduction contributes to the population genetic structure of E. turcicum in South Africa.     

HILL SOILS AND GRASSLANDS IN BRECKNOCKSHIRE: A STUDY OF POTENTIAL LAND USE

The present and potential land use of rough hill pastures in Brecknockshire has been investigated. The interests of the Brecon Beacons National Park, reservoir, Forestry Commission and commonland need not compete, but could be complementary. Areas containing a high proportion of the podzolized soils carry the most nutritious pastures, rich in Agrostis and Vaccinium , and agreement amongst the commoners could ensure they are grazed to the limit of their productivity. In the absence of afforestation, the grazing of superior pastures around the peaks of the Fforest Fawr-Brecon Beacons range is consistent with the interests of both the National Park and reservoir authorities, although the erosion hazard is greater. The S. and E. directed spurs of Drygarn, the N. E. plateau of Mynydd Eppynt and the S. W. flanks of the Black Mountains have similarly productive hill pastures. Areas such as the long back-slopes of the Fforest Fawr-Brecon Beacons range and higher land of Drygarn contain a high proportion of peaty gleyed soils under Molinetum , They provide inferior grazing but support the most productive forests, chiefly of Sitka spruce. By agreement amongst the commoners, where they are known, these areas could be leased to the Forestry Commission for afforestation. However, because common rights are so obscure, prior legislation would probably be necessary. Until their recent destruction, the uplands supported woodland and afforestation of selected areas need not be regarded as incongruous. It would also open up otherwise inaccessible places.     

Seasonality of oocyte development and pigmentation in Atlantic salmon, Salmo salar

This study identifies the presence of a spring drop of flesh pigmentation that coincided with oocyte atresia in Atlantic salmon and outlines the potential influence that additional lighting and feed management strategies can have on these processes.