Distinct pathways of antigen uptake and intracellular routing in CD4 and CD8 T cell activation

The mechanisms that allow antigen-presenting cells (APCs) to selectively present extracellular antigen to CD8+ effector T cells (cross-presentation) or to CD4+ T helper cells are not fully resolved. We demonstrated that APCs use distinct endocytosis mechanisms to simultaneously introduce soluble antigen into separate intracellular compartments, which were dedicated to presentation to CD8+ or CD4+ T cells. Specifically, the mannose receptor supplied an early endosomal compartment distinct from lysosomes, which was committed to cross-presentation. These findings imply that antigen does not require intracellular diversion to access the cross-presentation pathway, because it can enter the pathway already during endocytosis.     

The mRNA of the Arabidopsis gene FT moves from leaf to shoot apex and induces flowering

Day length controls flowering time in many plants. The day-length signal is perceived in the leaf, but how this signal is transduced to the shoot apex, where floral initiation occurs, is not known. In Arabidopsis, the day-length response depends on the induction of the FLOWERING LOCUS T (FT) gene. We show here that local induction of FT in a single Arabidopsis leaf is sufficient to trigger flowering. The FT messenger RNA is transported to the shoot apex, where downstream genes are activated. These data suggest that the FT mRNA is an important component of the elusive "florigen" signal that moves from leaf to shoot apex.     

Organic livestock production as viewed by Swedish farmers and organic initiators

Eleven organic and two conventionalSwedish livestock farmers and two initiators(non-farmers who took part in shaping earlyorganic livestock production in Sweden) wereinterviewed, using a semi-structured method.Respondents were selected through purposive andheterogeneous sampling with regard toconversion year, type of production, and sizeof farm. Conversion of the animal husbandrytook place between 1974 and 2000. All but twohad positive attitudes towards organiclivestock production and saw it as a wayforward for Swedish livestock production,although especially the latecomers did notperceive it as the only alternative. There wasa distinct difference in values between thepioneers, who converted their farms early, andthose converting later. Pioneer farmers sharedthe values of the initiators. They expressed amore ecocentric view emphasizing a systemicapproach, and displayed a more holisticapproach to questions, interpreting them inlarger frameworks. They also had a moreecocentric understanding of animal welfare. Thelater the conversion, the more important theeconomic reason for conversion appeared to be.Those converting later also tended to have amore superficial relationship to organicprinciples. However, the farmers also tended tobe more influenced by organic values the longerthey worked with organic farming.     

Hijacking of host cell IKK signalosomes by the transforming parasite Theileria

Parasites have evolved a plethora of mechanisms to ensure their propagation and evade antagonistic host responses. The intracellular protozoan parasite Theileria is the only eukaryote known to induce uncontrolled host cell proliferation. Survival of Theileria-transformed leukocytes depends strictly on constitutive nuclear factor kappa B (NF-kappaB) activity. We found that this was mediated by recruitment of the multisubunit IkappaB kinase (IKK) into large, activated foci on the parasite surface. IKK signalosome assembly was specific for the transforming schizont stage of the parasite and was down-regulated upon differentiation into the nontransforming merozoite stage. Our findings provide insights into IKK activation and how pathogens subvert host-cell signaling pathways.     

Impact of sulphur and nitrogen deposition on plant species assemblages in natural vegetation

In the present study twelve years of changes in natural plant communities and their relation to S and N deposition are analysed. The Acid-tolerance index (ATI) and Nitrogen-demand index (NDI) based on Ellenberg's indicator values, and the Shannon-Wiener index were employed for characterizing the species assemblages of communities. The deposition at the sites was dramatically higher in the south than in the north of the country. NDI, but not ATI, was significantly correlated to N deposition. Species diversity at each site was quite stable over time. In PCA ordination species diversity, ATI and NDI were almost independent from each other, and were represented by three different principal components. There only NDI was strongly correlated to S and N deposition, while ATI was almost independent of them. Regression analysis suggested that species richness and diversity were weakly correlated to N deposition.     

Nitrogen nutritional status of young maize plants (Zea mays) is not limited by NaCl stress

Maize plants (Zea mays L. cv. Pioneer 3906) were grown in hydroponics with four different NaCl treatments (control, 50, 100, 150 mM NaCl). Nitrogen (N) was supplied as 2 mM Ca(NO₃)₂ in the fully concentrated nutrient solution. Plants of half of the pots were treated with additional 1 mM NH₄NO₃ 2 d after start of the NaCl application. After 23 d, the maize plants were harvested and contents and concentrations of nitrate, reduced N as well as chloride were determined in shoots and roots. With increasing NaCl stress net nitrate uptake and net root‐to‐shoot translocation of total N decreased significantly. Under salt stress, decreased nitrate concentrations in shoots probably caused substrate limitation of nitrate reductase. However, the concentrations of reduced N in shoots were not affected by salt stress and no N deficiency was observed. Additional N application to the 100 and 150 mM NaCl treatments did not improve plant growth. A Cl^?/NO antagonism was only weakly pronounced, probably because of the Cl^? exclusion ability of maize. Thus, although net uptake and net translocation of total N were markedly decreased by NaCl application, the smaller maize plants nevertheless took up enough N to meet their demand pointing to other growth‐limiting factors than N nutrition.     

Freeze-thaw regime effects on carbon and nitrogen dynamics in sub-arctic heath tundra mesocosms

Freeze-thaw fluctuations in soil temperature may be critical events in the annual pattern of nutrient mobilisation that supplies plant growth requirements in some temperate, and most high latitude and high altitude ecosystems. We investigated the effects of two differing freeze-thaw regimes, each of which is realistic of in situ spatial and temporal variation in field conditions, on C and N dynamics in sub-arctic heath tundra mesocosms. In addition, ¹⁵N isotopic label was used to follow the partitioning of a labile N pool between major ecosystem components, both during the freeze-thaw treatments phase, and in a subsequent equilibration phase. A single deep freeze treatment phase enhanced dissolved total and labelled N pools in the soil solution at initial thaw, and resulted in reduced pool sizes at the end of the equilibration phase. By contrast, a multiple freeze-thaw cycling treatment directly enhanced the dissolved labelled N pool, but did not significantly affect dissolved total N. Furthermore, both dissolved labelled N and dissolved total N pools were significantly enhanced in the equilibration period following multiple freeze-thaw, the latter due to a marked increase in soil solution NH₄⁺. Microbial biomass C was not significantly affected by either of the freezing treatments upon final thaw, but was significantly reduced over the combined treatment and equilibration phases of the multiple freeze-thaw regimes. Furthermore, the treatments had no significant effects on total or labelled N within the microbial biomass over either phase. Total mesocosm CO₂ efflux rates remained closely correlated with soil temperature throughout the experiment in both regimes, suggesting that respiratory flushes associated with treatment-induced microbial cell lysis were negligible. Together, these results indicate that moderate freeze-thaw fluctuations may have minimal influences on microbial biomass pools, but nevertheless can have strong contrasting effects on the amounts, forms, and timing of N and organic C supply into the soil solution. Ecosystem losses via N₂O effluxes were of greatest magnitude immediately upon thawing in both treatments, and were of similar total magnitude to inorganic N leachates in throughflow. Herb leaves, total fine roots, and vascular stems accumulated some ¹⁵N label in one or both of the freezing treatments by the end of the experiment. Together, these results indicating very small N losses relative to the magnitudes of internal transfers, suggest tight ecosystem N cycling both during and after freeze-thaw events. Furthermore, our small and subtle effects on microbial and soluble C and N pools relative to previous studies using more severe regimes, suggests that periods of moderate freeze-thaw fluctuations may have only a minor influence on the annual pattern of C and nutrient dynamics in seasonally cold ecosystems.     

Potassium is a potential toxicant for Arabidopsis thaliana under saline conditions

Background and aims : Most physiological and biochemical studies on salt stress are NaCl‐based. However, other ions (e.g., K⁺, Ca²⁺, Mg²⁺, and ${\mathrm{SO}}_4^{2-}$) also contribute to salt stress in special circumstances. In this study, salt stress induced by various salts was investigated for a better understanding of salinity. Methods : Arabidopsis thaliana plants were stepwise acclimated to five iso‐osmotic salts as follows: NaCl, KCl, Na₂SO₄, K₂SO₄, and CaCl₂. Results and Conclusions : Exposure to KCl and K₂SO₄ led to more severe toxicity symptoms, smaller biomass, and lower level of chlorophyll than exposure to NaCl and Na₂SO₄, indicating that Arabidopsis plants are more sensitive to potassium salts. The strongly reduced growth was negatively correlated with the accumulation of soluble sugars observed in KCl‐ and K₂SO₄‐treated plants, suggesting a blockage in the utilization of sugars for growth. We found that exposure to KCl and K₂SO₄ suppressed or even blocked sucrose degradation, thus leading to strong accumulation of sucrose in shoots, which then probably inhibited photosynthesis via feedback inhibition. Moreover, K⁺ was more accumulated in shoots than Na⁺ after corresponding potassium or sodium salt treatments, thus resulting in decreased Ca²⁺ and Mg²⁺ concentrations in response to KCl and K₂SO₄. However, K₂SO₄ caused more severe toxicity symptoms than iso‐osmotic KCl, even when the K⁺ level was lower in K₂SO₄‐treated plants. We found that Na₂SO₄ and K₂SO₄ induced strong accumulation of tricarboxylic acid intermediates, especially fumarate and succinate which might induce oxidative stress. Thus, the severe toxicity symptoms found in K₂SO₄‐treated plants were also attributed to ${\mathrm{SO}}_4^{2-}$ in addition to the massive accumulation of K⁺.     

Distribution of Cd in the vicinity of a metal smelter: Interpolation of soil Cd concentrations with regard to regulative limits

The German soil protection regulation (BBodSchV) requires the investigation and evaluation of sites with known, or suspected contamination. The purpose of this study is the application of geostatistical methods to locate hazardous zones within such a site and to estimate the amount and uncertainty of the contaminant load in these zones. The study site is an area around a metal smelter in the city of Nordenham, Germany, where among other heavy metals, Cd was released to the environment by dust emissions for many decades. In an earlier study soil cores were taken in the area and analyzed for Cd using various extraction methods. After translation of data to results corresponding to a single extraction method using linear regression analysis, Cd concentrations were mapped by ordinary and lognormal kriging. Crossvalidation showed that both methods perform similarly. However, neither ordinary nor lognormal kriging were able to account for the uncertainty of the kriged estimates. We repeated ordinary kriging with a relative variogram having a unit sill. The estimated relative kriging variance was scaled locally. This method considerably improved the estimation of uncertainty. Subsequently, we estimated Cd contents for the land use dependent size of support as specified in the BBodSchV. The kriged Cd estimates as well as their uncertainty were evaluated with regard to limits set by the BBodSchV. Parts of the area which may be declared safe based on merely the kriged estimates, can actually exceed a sanction or test limit by a chance of up to 50 % when uncertainty is also considered. Within the BBodSchV a recommended limit should therefore always be accompanied by a tolerable uncertainty that it may be exceeded on a given support (e.g. 5 %).     

Effects of long-term soil warming and fertilisation on microarthropod abundances in three sub-arctic ecosystems

Soil microarthropod responses to long-term soil warming and increased fertilisation by addition of NKP or litter were assessed in three subarctic ecosystems. The experiment was carried out at three different field sites, where temperature and fertilisation manipulations had been running for 3–5 years (glade), 11 years (fellfield), and 12 years (heath) at the time of sampling. In the glade soil, warming led to decreases in Collembola and Gamasida, and increases in Oribatida, although effects were inconsistent between years. Actinedida densities were increased by fertilization, while Acaridida had higher densities in the treatment with both fertilisation and warming. In the fellfield, we found increased densities of Oribatida, Gamasida and Actinedida in the fertilised treatments, and some increases in Oribatida and decreases in Collembola and Gamasida in warming treatments. In the heath, there were increased densities of Collembola, Oribatida and Actinedida in the fertilised treatments, but we found no strong effects of warming. We suggest that the responses found in this study comply with the assumption that soil microarthropods are bottom-up controlled, and the observed changes are probably linked to changes in food availability more than direct climatic influences.