Long-term Radiocesium Behavior in Spruce and Oak Forests

This paper summarizes the data obtained during a period of 3 years in 'in situ' (distribution of the Chernobyl radiocesium fallout in a Belgian Ardenne spruce stand) and in controlled conditions (spruces growing in contaminated lysimeters and in nutrient media). Experiments in controlled conditions show that deposited radiocesium (thermogenetated aerosols) is washed out very quickly; the short ecological half-lives are confirmed by the post-Chernobyl observations in the NPP contaminated zone. Moreover, field observations reveal that spruce contamination levels remain more or less stable, with seasonal variations (translocation of cesium-137 during the spring and storage in the wood trunk and in the old needles during the winter). Studies conducted on throughfall water pointed out a high seasonally significant correlation between K and cesium-137. Studies of the cycles of stable K and Cs in needles and throughfall water sampled monthly for a year, confirm that radiocesium movements in trees are closely related to the potassium cycle and to the tree physiological status. Five years after the accident, forests seem to be at a steady state without any significant decontamination, throughfall losses being compensated by root absorption. On the other hand, field experiments conducted on spruce litter show that in Belgium, litter decomposition is a very slow process: K and Cs losses are quite negligible after 400 days. These results emphasize the radiological role of the litter. The relative distribution of deposited radioactivity in the different compartments of the forest ecosystem is given, the soil compartment being the main reservoir of radioactivity (particularly the upper Of and OAh organic soil horizons). Soil-tree transfer factors obtained in lysimeters contaminated by cesium-137 (calculated on the soil solution basis) range from 4 to 40 depending on the soil solution concentration of the different soil layers exploited by the root system. Cesium exchangeable fractions (CaCl2 and NH4Ac) represent up to 15% of the total soil activity. In our spruce forest soils (brown acid), a geochemical barrier is present (OAh horizon) where radiocesium presents a quite complete fixation

Transmembrane protein sorting driven by membrane curvature

The intricate structure of prokaryotic and eukaryotic cells depends on the ability to target proteins to specific cellular locations. In most cases, we have a poor understanding of the underlying mechanisms. A typical example is the assembly of bacterial chemoreceptors at cell poles. Here we show that the classical chemoreceptor TlpA of Bacillus subtilis does not localize according to the consensus stochastic nucleation mechanism but accumulates at strongly curved membrane areas generated during cell division. This preference was confirmed by accumulation at non-septal curved membranes. Localization appears to be an intrinsic property of the protein complex and does not rely on chemoreceptor clustering, as was previously shown for Escherichia coli. By constructing specific amino-acid substitutions, we demonstrate that the preference for strongly curved membranes arises from the curved shape of chemoreceptor trimer of dimers. These findings demonstrate that the intrinsic shape of transmembrane proteins can determine their cellular localization

European Nuclear Thermodynamic Database Validated and Applicable in Severe Accident Codes: ENTHALPY Project

International audienc

European Nuclear Thermodynamic Database Validated and Applicable in Severe Accident Codes: ENTHALPY Project

International audienc