Entre la dosimétrie physique et la dosimétrie biologique, la dosimétrie d'effets : SOS Chromotest

Ce papier porte sur les études menées pour qualifier le SOS Chromotest, un test de génotoxicité mis au point à l’Institut Pasteur (Paris), en tant que "dosimètre d’effets" pour les rayonnements ionisants. La "dosimétrie d’effets" est définie comme toute méthode de mesure capable de caractériser et de dénombrer directement ou indirectement les lésions physico-chimiques primitives produites par les rayonnements sur les macromolécules du milieu vivant, principalement l’ADN, puisque la majorité des effets biologiques en découle. La justification de l’étude se trouve dans la nécessité, pour toute application impliquant l’évaluation des dommages, de disposer d’une dosimétrie intégrant les mécanismes d’action des rayonnements plus complètement que ne le fait la dosimétrie physique, y compris la microdosimétrie. On rapporte les travaux préliminaires faits sur le SOS Chromotest dans ce but. L’étude, dont les résultats présentés sont encourageants, a porté sur les qualités métrologiques intrinsèques du test (précision, répétabilité, sensibilité,...) et sur son aptitude à répondre spécifiquement à l'action de différents types de rayonnements

Sublethal effects of sediment-associated uranium on Chironomus riparius (Diptera: Chironomidae) larvae

In aquatic ecosystems, sediments constitute a reservoir for many of the most persistent chemicals that are introduced into surface waters. Sediments provide a habitat for various benthic macroinvertebrates, which could be exposed to sediment-associated chemicals both directly and via food intake. These organisms play an important role on the structure and the functioning of aquatic ecosystems. Among the non-biologically essential metals, data concerning uranium (U) fate and effects on freshwater benthic macroinvertebrates are sparse. The present study aimed at estimating effects of a chronic U exposure on Chironomus riparius larvae. To achieve this goal, a 10-d laboratory bioassay was performed exposing, via the sediment, first instar larvae to a gradient of U concentrations (0, 2.97, 6.07, 11.44, 23.84 μg U/g dry wt). Significant negative effects on mortality, development time and growth were detected at 6.07, 6.07 and 2.97 μg U/g dry wt, respectively. The results underlined a possible impact of U at the population level at environmentally occurring U concentrations. This study confirmed the need for more research on the role of U on benthic macroinvertebrate

Alterations in water and electrolyte absorption in the rat colon following neutron irradiation: Influence of neutron component and irradiation dose

Purpose: To study the absorptive function of rat colon following whole-body exposure to neutron irradiation, either to the same total dose with varying proportion of neutrons or to the same neutron proportion with an increasing irradiation dose. Materials and methods: Different proportions of neutron irradiation were produced from the reactor SILENE using a fissile solution of uranium nitrate (8, 47 and 87% neutron). Water and electrolyte fluxes were measured in the rat in vivo under anaesthesia by insertion into the descending colon of an agarose gel cylinder simulating the faeces. Functional studies were completed by histological analyses. In the first set of experiments, rats received 3.8 Gy with various neutron percentages and were studied from 1 to 14 days after exposure. In the second set of experiments, rats were exposed to increasing doses of irradiation (1-4 Gy) with a high neutron percentage (87%n) and were studied at 4 days after exposure. Results and conclusions: The absorptive capacity of rat colon was diminished by irradiation at 3-5 days, with a nadir at 4 days. The results demonstrate that an increase in the neutron proportion is associated with an amplification of the effects. Furthermore, a delay in the re-establishment of normal absorption was observed with the high neutron proportion (87%n). A dose-dependent reduction of water absorption by rat colon was also observed following neutron irradiation (87%n), with a 50% reduction at 3 Gy. Comparison of this dose-effect curve with the curve obtained following gamma 60Co-irradiation indicates an RBE of 2.2 for absorptive colonic function in rat calculated at 4 days after exposure

Dysfonctionnements radio-induits du transport colique chez le rat

L'un des symptômes majeurs d'une irradiation corporelle totale ou abdominale est l'apparition de diarrhées, dont les causes sont encore mal connues, et qui mettent en jeu le pronostique vital de l'individu irradié. Cette étude vise à mettre en évidence l'atteinte de la régulation du transport intestinal d'eau et d'électrolytes par les rayonnements ionisants. On observe une diminution de la capacité du système nerveux entérique à influencer le transport colique 3 jours après irradiation, corrélée à une diminution de la réponse épithéliale à un neurotransmetteur : la sérotonine. Les diarrhées radio-induites résulteraient d'une atteinte structurelle de l'épithélium mais également des processus de régulation du transport intestinal

Light-Induced Acclimation of the Arabidopsis chlorina1 Mutant to Singlet Oxygen.

International audienceSinglet oxygen (O-1(2)) is a reactive oxygen species that can function as a stress signal in plant leaves leading to programmed cell death. In microalgae, O-1(2)-induced transcriptomic changes result in acclimation to O-1(2). Here, using a chlorophyll b-less Arabidopsis thaliana mutant (chlorina1 [ch1]), we show that this phenomenon can also occur in vascular plants. The ch1 mutant is highly photosensitive due to a selective increase in the release of O-1(2) by photosystem II. Under photooxidative stress conditions, the gene expression profile of ch1 mutant leaves very much resembled the gene responses to O-1(2) reported in the Arabidopsis mutant flu. Preexposure of ch1 plants to moderately elevated light intensities eliminated photooxidative damage without suppressing O-1(2) formation, indicating acclimation to O-1(2). Substantial differences in gene expression were observed between acclimation and high-light stress: A number of transcription factors were selectively induced by acclimation, and contrasting effects were observed for the jasmonate pathway. Jasmonate biosynthesis was strongly induced in ch1 mutant plants under high-light stress and was noticeably repressed under acclimation conditions, suggesting the involvement of this hormone in O-1(2)-induced cell death. This was confirmed by the decreased tolerance to photooxidative damage of jasmonate-treated ch1 plants and by the increased tolerance of the jasmonate-deficient mutant delayed-dehiscence2

Défenses chimiques et morphologiques des feuilles de Quercus pubescens après 10 ans de sécheresse amplifiée et récurrente

International audienceClimate change in the Mediterranean region will lead to an increase indrought episodes marked by a longer drought period and a decrease insummer precipitation of about 30 by the end of the XXI centuryIn this context, it is important to anticipate the strategies of adaptation offorest to cope with future scenarios of amplified water deficitFor this purpose, we characterized the morphological and chemical traits ofDowny oak leaves Quercus pubescens L after 10 years of amplified andrecurrent drought simulated in natura at O 3 HP AnaEE site), includingnumerous chemical defense