Etude sur la végétation des dunes et des landes de la bretagne

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Etude de la reponse à un stress hydrique de quelques varietés de riz pluvial et de riz irrigué

Résumé La transpiration de plants de riz cultivés sur sol en chambre de culture, est suivie en continu pendant une séquence déssèchement-irrigation. Les cycles jouraliers de transpiration sont présentés avant et pendant le stress hydrique. Quatre variétés montrent une augmentation de la transpiration nocturne qui disparait lors du stress hydrique. Il apparait que la régulation stomatique est indépendante du potentiel hydrique du sol jusqu'à une valeur seuil au-delà de laquelle la baisse de transpiration est proportionnelle à la baisse du potentiel hydrique. Cette valuer seuil est plus basse pour les variétés de type irrigué.

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Water stress response for some cultivars of upland- and lowland riceI. Effects on transpiration

Summary The transpiration of rice seedlings grown on soil in a growth chamber was observed during a soil drying/rewetting sequence. The diurnal cycles of transpiration are shown before and during the water stress period. Four cultivars showed an increase of transpiration during the night. This increase disappeared during the water stress period. The stomatal regulation appeared not to depend on the soil water potential until a certain value. Below this soil-water threshold, the decrease of transpiration was proportion to the decrease of water potential. This threshold value is lower for the rain-fed cultivars than for the irrigated cultivars.

     

Résistance et viabilité des gamètes d'Omble de fontaine,Salvelinus fontinalis, à différents pH

Résumé Afin d'étudier les effets de l'acidité lors de la fécondation chez l'Omble de fontaine, la motilité des spermatozoïdes, l'absorption d'eau par les oeufs et la survie de ceux-ci ont été déterminées à différents pH. Les poissons fournissant les gamètes utilisés pour ces tests provenaient de lacs acides ou non acides.Pour les valeurs de pH inférieures à 5,0, la proportion de spermatozoïdes motiles diminue rapidement et devient nulle à pH 3,0. A pH 4,0, cette proportion est plus élevée dans une solution d'acide sulfurique, qui est totalement dissocié, que dans une solution d'acide acétique, faiblement dissocié. Dans cette dernière, la quantité d'ions H⁺ neutralises par le sperme est environ cinq fois plus élevée que dans la solution d'acide sulfurique.La pression osmotique du milieu de fécondation ainsi que l'origine des géniteurs, provenant de lacs acides ou non, affectent également la résistance des spermatozoïdes.L'absorption d'eau par les oeufs est diminuée à pH 5,2 ou 4,5 selon l'origine des géniteurs. La survie des oeufs est peu affectée pour des pH de 4,5 et plus, mais est réduite à pH 4,0.L'ensemble des résultats permet d'avancer qu'un pH de 4,5 représente la limite inférieure compatible avec une bonne fécondation chez l'Omble de fontaine; cette limite semble cependant susceptible d'être modifiée par la présence d'acides faibles dans le milieu et par l'origine des géniteurs.

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Variations in acidity were shown to have pronounced effects on the gametes of Salvelinus fontinalis collected from populations living in acid or circum-neutral lakes.Spermatozoa motility was reduced at pH less than 5.0 and ceased at pH 3.0. Within this range, motility was greater in the presence of strongly dissociated acid (H₂SO₄) than in a weakly dissociated one (CH₃COOH). In the latter solution, at pH 4, sperm neutralized 5 times as many H⁺ as in the former. Differences in spermatozoa motility were observed depending upon the origin of the gametes and the osmotic pressure of the medium.Egg survival was reduced at pH 4. Water absorption by eggs decreased below pH 5.2 or 4.5 for eggs collected from circumneutral or acid lakes, respectively.These results suggest that pH 4.5 represents the lower limit for successful fertilization of eggs of brook trout, the precise point depending upon the types of acid present and the origin of the parental stock.

     

Contribution à la connaissance de la végétation rupicole des hautes vallées de l'ubaye et de l'ubayette. (Alpes cottiennes)

Summary The study of the saxatile vegetation of the alpine zone in the Upper Ubaye Valley shows a very sharp demarcation from a phytogeographical point of view.The saxatile groupings on limestone show septentrional affinities. It is interesting to note that the associations described have at least as much relationship to the Swiss Alp groups as to those of The Maritime Alps in fact closer.In our opinion, the explanation is not to be found in very different climatical or ecological considerations but in the presence of important barrier-mountains which have deprived the Upper Ubaye Valley of alien postglacial immigrants.There endemism is apparent but less important than in the neighbouring zone of The Maritime Alps; here it concerns surviving endemic species proceeding from an old native preglacial or interglacial element.These characters are to be found more in the northern areas of Queyras, Embrunais and Briançonnais, regions which have an incontestable relationship with our district.     

Utilisation de la membrane vitelline de l'oeuf de poule en culture organotypique I. Technique et possibilités

• 1.1. This paper describes a technique which uses the vitelline membrane (chorion) of the chicken egg as a substratum and as an exchange membrane for organotypic cultures.
• 2.2. The vitelline membrane serves as an intermediary between the nutrient medium and the explants. It serves as a support for the latter, permitting them to adhere closely to it and spread on its surface. The nutritive substances of the medium diffuse across this membrane under conditions which assure the explants of a progressive nutrition corresponding to their requirements.
• 3.3. This technique, derived from the standard method of Et. Wolff and K. Haffen, is particularly suitable for fragments of organs or for explants which do not have their own envelopes. The vitelline membrane acts as their limiting membrane. In addition it permits the explants to spread out on the medium and to remain thin, assuring them of better nutrition and a better oxygen supply.
• 4.4. The technique is advantageous also for the development of young embryonic rudiments and for experiments involving the reassociation of organs following the dissociation of their constituent tissues.
• 5.5. It has been used successfully for associations between chick embryo tissues and mammalian tumors. Cancer cells of mouse sarcoma and those of human tumor strains spread and multiply under the excellent conditions inside the sac, where they are associated with tissues of the mesonephros. Their dispersion and their proliferation are considerably augmented.
• 6.6. Finally, the vitelline membrane has been used as a filter between mesonephric tissues and colonies of cancer cells. The latter proliferate actively, which demonstrates that substances favorable to cancerous growth are elaborated by the mesonephros and that they can cross a membrane by dialysis.
     

Etude autoradiographique des effets de la 5-fluorodéoxyuridine,de l'actinomycine et de la puromycine chez Acetabularia mediterranea

In Acetabularia it has been shown by autoradiography using H³-uridine that RNA synthesis or RNA turnover continues in the dark; although it diminishes with time, this metabolic activity persists for 10 days.In the dark FUDR has been observed to inhibit the incorporation of H³-uridine into the cytoplasm of nucleated fragments while causing simultaneous accumulation of this isotope in the nucleus. Actinomycin D inhibits the synthesis of a particular RNA in the nucleolus, both in the light and in the dark.The effects of FUDR and actinomycin in the light suggest that a cytoplasmic RNA may be synthesized independently of nuclear control. A special type of protein synthesis which can be inhibited by puromycin occurs only in the light.The relationship that may exist between these different syntheses of RNA and protein are discussed.     

Contribution à la connaissance des Copépodes de la Région Parisienne

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