Étude polarographique de la mobilisation du fer de la ferritine

Polarographic study of the mobilization of ferritin ironPolarographic study allows to propose a model for mobilization of ferritin iron: an equilibrium exists between iron core and small quantities of iron outside the protein.These iron atoms would be lying on electron acceptor sites including SH groups. The number of sites is dependent on iron content of ferritin.Therefore, the iron could be removed by the action of reducing agents such as xanthine oxidase or ascorbic acid, and then chelated by a complexing agent.     

Modulation de la Réponse du Xyléme selon la Nature de l'Agression Vasculaire

Modulation of the xylem response to different types of vascular aggressions The evolution of cells lining the vessels in the stem xylem of carnation was compared in sham-stressed (s. e.), V. dabliae-infected (i V. d.) and P. cinerescens-infected (i P. c.) plants. All experimental stresses triggered ultrastructural changes leading to the appearance of new cell types. In parallel, vacuolar polyphenols were metabolized and dense-core vesicles appeared. These were early and independant phenomena. In all cases the reactions of carnation xylem were stronger against Verticillium than against Phialophora. Differences in vascular gummosis were disclosed whatever the criterion used (speed of installation, relative importance of the phenomenon, level of structural complexity, dynamics of appearance of the different structures). The possible relations between cell structures and gummous secretions were investigated by means of comparison of an efficient defence system (i V. d.) with a deficient one (i P. c.). All the criteria selected for analysis confirm that faced with a specific parasite the host response was disrupted. In other words, the biosynthetic pathways normally used by the plant after a fungal aggression were blocked, slowed or diverted. The differences in the responses of carnation to Verticillium and Phialophora give a picture of parasite specificity in agreement with the model recently proposed by de Wit (1981) for tomato/Cladosporium fulvum.     

Interaction du photopériodisme et des effets de la zéatine, du saccharose et de ľeau dans la floraison du Chenopodium polyspermum

Interaction of photoperiodism and zeatin, sucrose and water effects on the flowering of Chenopodium polyspermum Root removal in Chenopodium polyspermum, a quatitative short-day plant, enhances flowering under non-inductive conditions. Presence of roots may be mimicked by zeatin applications on buds. Induction of flowering by short days may be counteracted by applications of zeatin, and appearance of flowers depends on the balance between number of inductive short days and zeatin quantity applied. Sucrose added in the culture medium or applied on buds acts as zeatin. Applications of water on buds may also delay flowering. These results show the plurifactorial regulation of the floral development of this plant. The relations between the non-specificity of the induction and the specificity of the morphogenetic response are discussed.     

Influence de la cure chirurgicale de la varicocele sur la qualite du sperme

The aim of this study was to assess the efficacy of surgical varicocèle repair in terms of sperm quality. We have performed a retrospective study including 62 patients. All of them underwent clinical evaluation. A sperm analysis has been done before and after surgical repair. Before sugery, the spermogram was normal in only 11.3%. Oligospermia was found in 62.1 % of cases while 6.5% of patients had azoospermia. Abnormalities like microcephalia were encountered in 36.8% of cases. All patients underwent surgical varicocele repair. They were followed up every three months up to 18 months. A significant improvement of sperm count was found in 18 cases, with a pregnancy rate of 6.45%. Alterations of sperm quality was most severe in older patients. We think that as far as natural history of varicocele is not well established, the duration of its evolution is well correlated with the severity of sperm alterations. So, need for precocious diagnosis in order to lessen the risk of infertility.     

Les Spatangus du Miocène et du Pliocène de l’Ouest de la France

Numerous fragments of spatangoid echinoids have been discovered in the Pliocene deposits of Challans, in Vendée (western France). In spite of the fragmentary data of the samples, a reconstitution of a complete test could be realized using the different fragments and their symetrization. The general shape of the test, and its architectural and ornemental characters allow establishing the presence of the genus Spatangus in western France during the end of Neogene. It allows to precise the biogeography of the genus Spatangus and of the morphological group S. (S.) purpureus on the Atlantic coast after the Messinian crisis. The Pliocene species is compared to the Miocene Spatangus (Phymapatagus) brittanus, abundant in Anjou, Brittany and Touraine. This older species was refered to the subgenus Phymapatagus according to the presumed lack of primary tubercles on its posterior interambulacrum. The discovery of well-preserved specimens, with primary tubercles on every parts of the test, in the Middle Miocene of Brittany allows to refute this subgeneric distinction and to refer the species brittanus to the subgenus Spatangus (Spatangus). The presence of this subgenus in western France is finally confirmed from Middle Miocene to Pliocene.     

Utilisation des isotopes stables pour l’identification de l’origine du carbone dans la datation du charbon de bois du Paléolithique

Recent years have brought many results of radiocarbon dating the earliest periods of the Upper Palaeolithic that can bring light on the origins of figurative art by Sapiens or Neanderthals. These dates are often close to the limit of the field of radiocarbon dating; because they require measurements of the lowest amounts of radiocarbon, controls are particularly essential. Here we examine the case of the dating of charcoal, whose identification after decontamination is difficult. We suggest a method that does not require additional manipulation to determine whether carbon comes exclusively from charcoal: using the proportion of stable carbon isotopes 13C/12C which is often regarded as a signature (δ13C).     

Etude de L'influence de la Concentration Saline et du Rapport Sodium/Calcium du Milieu Nutritif sur la Sensibilite de la Tomate a la Fusariose Vasculaire

Resume Les auteurs étudient chez la tomate l'influence de la concentration saline et du rapport Na/Ca du milieu nutritif sur le développement de la fusariose vasculaire. A concentration saline élevée (50,4 meq/l), les plantes fanent tardivement mais brusquement et sans jaunissement préalable. La colonisation des tiges parF. oxysporum f. sp.lycopersici est tardive et faible; cependant à rapport Na/Ca élevé, elle augmente rapidement. Il n'y a pas d'acides aminés détectables dans la sève des plantes de 14 jours mais la teneur en N inorganique est toujours supérieure à 2.8 μg/ml. A concentration saline faible (2.5 meq/l), les feuilles jaunissent progressivement et précocement. La colonisation du xylème est précoce et dense; l'influence du rapport Na/Ca est faible. Les acides aminés sont présents dans la sève en quantités relativement importantes et d'autant plus que le Na/Ca cro?t. Ces résultats de l'évolution de la maladie sont discutés en relation avec la composition chimique des tissus et de la sève et la localisation histochimique du Na et du Ca.

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Summary The influence of the salt concentration and of the Na/Ca ratio of the nutrient solution on the development of the fusarial wilt of the tomato has been studied. At high salt concentration (50.4 meq/l), plants wilt lately but suddenly without yellowing. The stem colonization byF. oxysporum f. sp.lycopersici is poor and late; however at higher Na/Ca it increases rapidly. There are no amino acids detectable in xylem sap of 14 days old plants but the content of inorganic N is always higher than 2.8μg/ml. At low salt concentration (2.5 meq/l), the yellowing of the leaves begins early and progressively. The xylem colonization by the parasite is dense and precocious; the influence of the Na/Ca is weak. The amino-acids are relatively abundant in xylem sap and their content increases with the increase of the Na/Ca ratio. These results of the development of the disease are discussed in relation to the chemical composition of the tissues and the xylem sap and the histochemical localization of Na and Ca.

     

Variation du taux d'acide abscissique chez deux variétés de poiriers, la Passe-Crassane et la Doyenne du Comice, en fonction de l'induction de la parthénocarpie par l'acide gibbérellique

The content of abscisic acid in the developing fruits of two cultivars of pear (Pyrus communis L.) was determined by UV spectrophotometry and by a colorimetric method based on the possibility of the lactone corresponding to abscisic acid to give a purple colour when sodium hydroxide is added. The young fruits were harvested either from trees treated with gibberellic acid (GA₃), for the purpose of inducing parthenocarpy, or from untreated trees. High levels of abscisic acid were associated with abortion and abscission of young fruits (June drop). There was little difference between fruits of GA₃-treated and untreated trees of the cultivar Passe-Crassane. In the other cultivar, ‘Doyenne du Comice’, the level of abscisic acid in the fruits of GA₃-treated trees was about twice as high as in control fruits and seemed to be directly related to the number of fruits per tree.     

Evolution de la temperature de l'oxygene dissous et de la transparence dans la baie Nord du lac Tanganika

Resume Nous décrivons dans ce travail l'évolution de la température de l'oxygène dissous et de la transparence dans le bassin N. du lac Tanganika.La température de l'eau ne subit des fluctuations intéressantes au cours de l'année que dans les 100 premiers mètres de la surface. Les eaux du Tanganika offrent une temperature élevée jusqu' à ses plus grandes profondeurs; à 1.400 m. la température de l'eau est encore de 23.35° C. La température des eaux superficielles dépend de l'insolation journalière et les variations saisonnières n'affectent qu'une épaisseur d'eau d'une centaine de mètres. La couche oxygénée de l'eau est très faible par rapport aux énormes profondeurs du lac. Dans le bassin N. elle varie au cours de l'année entre les extrêmes de 45 m. et de 115 m.; la plupart du temps la limite de l'oxygène dissous se situant à 75–80 m de profondeur.Les eaux superficielles sont fortement oxygénées, leur teneur en oxygène dissous oscille autour de 100% de satuation, jusqu'au thermocline elles sont encore oxygénées à 80–90%.Le thermocline est toujours plus haut que la limite de l'oxygène dissous et ne présente absolument pas une barrière biologique comme c'est le cas dans la plupart des lacs des régions tempérées.La transparence des eaux du lac Tanganika est considérable, elle atteint souvent 20 m; la moyenne au cours de l'année se situant aux environs de 15 m.

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Summary The author describes the temperature, oxygen and transparency conditions in the Northern basin of Lake Tanganyika.The fluctuations in the temperature of the waters in the course of the year is of interest only down to a depth of 100 m.The temperature of water in Lake Tanganyika is high even in the greatest depths; at 1.400 m depth the temperature of the water is still 23.35° C. The temperature of surface water depends on the daily solar radiation. The influence of seasonal variations is felt only down to a depth of about one hundred meters.The oxygenated layer of water is very thin in comparison with the very great depth of the lake. In the northern basin, this layer varies in thickness between 45 and 115 m, the limit of dissolved oxygen being at a depth of about 75 m most of the time.The oxygen concentration in superficial waters is very high and nearly reaches the saturation point. Down to the thermoclinal point, the concentration is still 80–90 % The thermocline is always higher than the limit of dissolved oxygen, it does not at all constitute a biological barrier as it does in most lakes in temperate climates. The waters of Lake Tanganyika are very transparent, their transparency often reaches the depth of 20 m, the average for the year being 15 m.

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Centre de Recherches du Tanganika (Uvira) Institut pour la Recherche Scientifique en Afrique Centrale I.R.S.A.C.