L'évolution parallèle des Juraphyllitidae euroboréaux et téthysiens au Pliensbachien: le rôle des contraintes internes et externes

Au Pliensbachien, un trend morphologique se developpe chez les Tragophyllocerassimpliquant un mécanisme hétérochronique (paedomorphose par néoténie) pour I'acquisition d'une morphologie suboxycône. Ce changement morphologique majeurest concomitant avecl'ingression de ces formes dans les mers de plateforme euroboréale ob la compétition inter-taxons est forte. Cette option morphofonctionnelle et évolutive, canalisée essentiellement par des contraintes externes étant amorcée, le genre va I'exploiter dans la mesure de ses possibilités (potentialités intrinsèques) en perfectionnant son oxycônie. Au contraire dans les mers téthysiennes, les Juraphyllites ne montrent pas d'évolution pour la morphologie de la coquille; celle-ci reste subplatycône durant tout le Lias moyen et il n'y a pas de changements environnementaux majeurs (milieux tamponnés). En outre la prolifération d'ornementations plus grossières, aussi bien chez les Juraphyllites que chez les Tragopbylloceras, correspond probablement à une meilleure exploitation des biomes d'Europe du NW et de la Téthys à une période bien précise qui est le Carixien moyen. Ce développement d'ornementation similaire chez des taxons partageant un héritage évolutif commun mais séparés paléogéographiquement, évoque le rôle prépondérant des contraintes internes. Ainsi l'évolution des Juraphyllites des Tragophyllocerasau Lias moyen paraît donc ètre un exemple de parallèlisme au sens strict du terme.□Évolution, hétérochronies, Juraphyllitidae, Lias, ontogenèse, Paléogéographie. A morphological trend in the Pliensbachian Tragophyllocerns involves a heterochronic process (paedomorphosis by neoteny) to acquire a suboxycone morphology. This major morphological change is concomitant with the ‘ingression’ of Tragophylloceras in the Euroboreal platform seas, where competition between taxa was strong. This functional-morphological and evolutionary option is mainly canalized by extrinsic constraints. Exploring these possibilities, Tragophylloceras then exploits and improves the oxycone option. By contrast, in the Tethyan seas, Juraphyllites shows no change in shell coiling; it stays subplatycone during all the Pliensbachian. There is no major environmental change. Moreover, the proliferation of coarser ornamentation in Juraphyllitesand Tragophylloceras probably corresponds to a better exploitation of the Euroboreal and Tethyan marine habitats during the Middle Carixian. The development of similar ornamentation in palaeogeographically separate taxa with a common evolutionary origin is mainly canalized by intrinsic constraints. The evolution of Juraphyllites and Tragophylloceras appears to be a good example of parallelism sensu stricto. □ Evolution, heterochrony, Juraphyllitidae, Lios, ontogeny, palaeogeography.     

Tchernobyl : le vrai, le probable et le faux

The Japanese earthquake and tsunami drew attention worldwide to nuclear power plant accidents and associated health risks. Since Chernobyl 25 years ago, several studies were published and we now have precise information concerning the long-term health of the population living near nuclear power plants and also in different European countries. The authors hope to bring some answers to the key questions from the public concerning radioactive units used and their significance, the evaluation of the number of radio-induced cancers within the different countries of Europe, other eventual health effects and the problem of possible congenital anomalies. Finally, French public perception on nuclear risk is examined and the feedback of the Japanese experience is evoked.     

Explorations adrénergiques et dopaminergiques en médecine nucléaire. Présentation des résultats des enquêtes espagnole et française

We present a data analysis concerning a questionnaire on adrenergic and dopaminergic explorations in nuclear medicine practice. This article is the fruit of collaboration between Spanish and French investigators.     

Modulation des Réactions de Défense du Palmier a Huile Contre le Fusarium oxysporum f. sp. elaeidis (Schlecht) Toovey: Applications: Prémunition et Stimulation Chimique

Defence reactions of palm trees to Fusarium oxysporum f. sp. elaeidis (Schlecht) Toovey Cross protection and stimulation of inhibitory substances In palm tree genetic characters of tolerance to Fusarium oxysporum f. sp. elaeidis are correlated with synthesis of fungal inhibitors in infected tissues. Individual variation of synthesis level is also observed among plants of a same line. Defence reactions are triggered by pre-inoculation of an avirulent strain of Fusarium oxysporum. Similar results are obtained by application of analogs of fungal elicitors like arachidonic acid. Quite the contrary, treatment of plants with a competitive inhibitor of PAL downs natural barriers and in a same way the effects of cross protection and arachidonic treatment. Seven phenolic compounds, mainly benzoic acid derivatives, inhibit in vitro the growth of pathogen like spores germination. The variability of the host reaction and its stimulation by elicitors could be used to improve the resistance.     

Préparation des Antigenes des Mycoplasmes (MLO) Pathogènes de la Flavescence Dorée, à Partir de Tissus Végétaux

Antigen preparation from plant tissues of pathogenic mycoplasms (MLO) causing flavescence doree disease Extraction and purification of plant yellow's pathogen mycoplasms (MLO) from plant tissues is a difficult problem. It concerns indeed non cultivable, heterogeneous and fragile organisms which are localized in the fibrous and resistant phloem tissue. In a work directed by an infectivity test by leafhopper injection, our laboratory investigated the best host plant and the best extraction method for this type of pathogen. Broad bean, Vicia faba gave better extracts than Vitis vinifera. Stems are better than petioles or lamina. The best results were obtained with the top region of the stem, at the level where symptoms are apparent on young plants. The most efficient mincing method is achieved with razorblades moved alternatively by the rapid vertical movement of an electric knife. The extraction medium already published (Caudwell and Kuszala 1986) has to be modified for plants by various additional components, histidine buffer, antioxidizers (glutathion 0.2 mg per ml) and polymers 0.5 to 1 p 100 PVP or Polyclar, 1–2 p 100 PEG). 1 g of plant infected tissue is minced in 4 ml of medium. The extracts are filtered through a 100 mesh nylon cloth. After this stage the purification method goes parallel to that used for leafhopper extracts (Caudwell and Kuszala 1986). It is possible to obtain 4 × 10⁶ infectious units from 1 g of broad bean stem (for calculation, see C 1986). It is possible to obtain 4 × 10⁶ infectious units from 1 g of broad bean stem (for calculation, see Caudwell 1977). The possibility to extract MLO, either from infectious leafhoppers or from diseased plants enabled cross immunological assays involving antigens from one host and antibodies directed towards the other host antigens. The first step was the successful ISEM visualization of ttie MLOs (Caudwell et al. 1982), the second is the immunoenzymatic MLO-detection (Boudon et al. 1986).