La signification du cystide des Bryozoaires et la croissance de la colonie

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Cell proliferation and differentiation kinetics during spermatogenesis in Hydra carnea

Spermatogenesis inHydra carnea was investigated. The cell proliferation and differentiation kinetics of intermediates in the spermatogenesis pathway were determined, using quantitative determinations of cell abundance, pulse and continuous labelling with3H-thymidine and nuclear DNA measurements. Testes develop in the ectoderm of male hydra as a result of interstitial cell proliferation. Gonial stem cells and proliferating spermatogonia have cell cycles of 28 h and 22 h, respectively. Stem cells undergo four, five or six cell divisions prior to meiosis which includes a premeiotic S+G2 phase of 20 h followed by a long meiotic prophase (22 h). Spermatid differentiation requires 12–29 h. When they first appear, testes contain only proliferating spermatogonia; meiotic and postmeiotic cells appear after 2 and 3 days, respectively and release of mature sperm begins after 4 days. Mature testes produce about 27,000 sperm per day over a period of 4–6 days: about 220 gonial stem cells per testis are required to support this level of sperm differentiation. Further results indicate that somatic (e.g. nematocyte) differentiation does not occur in testes although it continues normally in ectodermal tissue outside testes. Our results support the hypothesis that spermatogenesis is controlled locally in regions of the ectoderm where testes develop

Les Endoproctes et la classe des Bryozoaires

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MICROSTRUCTURES DIAGRAM OF MAGNETRON SPUTTERED ALN DEPOSITS : AMORPHOUS AND NANOSTRUCTURED FILMS

International audienceIn order to get homogeneous nanostructured Aluminum Nitride deposits, thin films were grown at room temperature on [001] Si substrates by radio frequency magnetron reactive sputtering. The deposits were analysed by Transmission Electron Microscopy, energy dispersive X-ray spectroscopy and Auger electron spectroscopy. Their microstructure and chemical composition were studied versus the plasma working pressure and the radio frequency power. Systematic analysis of cross views of the films allowed the authors to draw a microstructure/process parameters map. Four microstructural types were distinguished according to the decrease of the deposition rate. One is the well-known columnar microstructure. The second one is made of interrupted columns or fibrous grains. The third one is made of nano-sized particles (size of the particles ranges from 1.7 to 8 nm). The fourth and last microstructure is amorphous. The "deposit morphology-process parameters" correlation is commented on

Sultana (Vitis vinifera L.) canes and their exposure to light

During three seasons, each of a number of Sultana vines were provided with three types of cane. These cane types differed, during the two seasons covering shoot development and fruit ripening, in their position within the vine canopy, and hence in exposure to solar radiation. On each vine, two canes (S) were placed outside and two canes (B) below the main body of the canopy formed in the main by the four T-canes.In all the yield components determined mainly by bud development, i.e. % bud burst, % fruitful/burst nodes and bunches/node the B-canes were inferior to the Sand T-canes, which did not differ significantly from each other. In one season, time of bud burst did not differ, but in the other season the buds of the S-canes burst first and the buds of the B-canes last. In the season when yield itself was measured, S-canes yielded about 20% more than T-canes and about 50% more than B-canes, despite the absence of any differences in yield components related to berry development, i.e. mean berry weight and concentration of sugar. There were no high-yielding B-canes, but some low-yielding S- and T-canes.It is concluded that individual shoots on the same vine respond directly to their aerial environment, and that proper cane selection or the choice of a training system allowing full exposure of the developing prospective canes can increase the productivity of Sultana vines.Die Tragruten der Sorte Sultana (Vitis vinifera L.) und ihre BesonnungIn einem dreijährigen Freilandversuch wurden an einer Anzahl von Rebstöcken der Sorte Sultana drei Typen von Tragruten herangezogen. Diese Rutentypen nahmen vom Beginn ihrer Entwicklung als Triebe bis zur Traubenreife unterschiedliche Stellungen innerhalb des Blattwerkes ein und wurden demnach unterschiedlich besonnt. An jedem Rebstock befanden sich zwei Ruten (S) außerhalb und zwei Ruten (B) unterhalb des hauptsächlich durch die vier T-Ruten gebildeten Blattwerkes. In jenen Ertragsfaktoren, die hauptsächlich durch die Knospenentwicklung bestimmt werden, nämlich in % Knospenaustrieb, % fruchtbare je ausgetriebene Knospen und in der Anzahl der Gescheine je Knospe waren die B-Ruten den S- und T-Ruten unterlegen. Unterschiede zwischen den beiden letzteren waren statistisch nicht gesichert. In einem der beiden Jahre wurden keine Unterschiede im Zeitpunkt des Knospenaustriebes gefunden, aber im anderen Jahre trieben im Durchschnitt die S-Knospen zuerst und die B-Knospen zuletzt.In dem Jahr, in dem der Traubenertrag gemessen wurde, lag dieser bei den SRuten um 20% höher als bei den T-Ruten und um etwa 50% höher als bei den B-Ruten. Dabei waren keine Unterschiede in der Beerenentwicklung, nämlich im Einzelbeerengewicht und in der Zuckerkonzentration des Saftes, festzustellen. Es gab keine B-Ruten mit großen, aber einige S- und T-Ruten mit kleinen Erträgen.Diese Ergebnisse zeigen, daß die einzelnen Triebe einer Rebe direkt auf ihre oberirdische Umwelt reagieren und daß man die Produktivität der Sorte Sultana durch Erziehungsarten, die eine volle Besonnung der nächstjährigen Tragruten ermöglichen, und durch entsprechende Wahl der Tragruten verbessern kann