Rides septales à organisation de type tétracoralliaire chez Trachypsammia (Tabulata, Permien)

Précédemment décrite chez Kerforneidictyum et Palaeacis I'organisation des rides septales suivant un schema de type tetracoralliaire est reconnue chez Trachypsammia monoseptata (Permien de Timor) où n'avait été signalé qu'un fort “Medianseptum”. II détermine un plan de symétrie bilatérale dans le calice; la ride cardinale forte est en position dorsale ou interne, la ride antipode également bien développée en position ventrale ou externe souvent plus courte, les rides considérées comme alaires sont identifiables au moins dam leur partie proximale. L'ensemble des rides clairement observables sont les rides majeures (protorides et métarides), les rides mineures sont à peine ébauchées. T. monoseptata pourrait représenter un stade calicinal jeune de T. dendroides. Trachypsammia dendroides (Permien de Timor) posséde un plan de symétrie bilatérale net. la ride cardinale est plus forte et plus longue que les autres rides, la ride antipode plus courte, les rides alaires sont identifiables en coupe transversale. rides majeures el mineures sont bien differenciées; le nombre total de rides est souvent de 32. Chez T. xizangensis (Permien du Tibet), seule une symétrie bilatérale a été observée en coupe. Pas de donnees pour T. mrditerranea (Permien de Sicile). Les affinités systéinatiques très étroites mises en évidence entre Polaeacis et Trachypsammia par les caractéres microstructuraux sont confirmées par Ie dispositif septal, ces Tabulés constituent-ils un groupe particulier? La question est posée A rugosan pattern of the septal ridges, formerly described in Kerforneidictyum and Palaeacis is pointed out in Trachypsammia monoseptata (Permian of Timor) for which only the ‘Medianseptum’ had been observed. T. monoseptata exhibits a strong cardinal ridge in dorsal or internal position. just opposite a shorter counter ridge, thus creating a plane of bilateral symmetry. The ridges assumed to be alar can be identified by their proximal ends being in contact with the ‘Medianseptum’. The major ridges (proto and metaridges) are obvious, the minor ones show only their very proximal ends. T. monoseptuta could be a calicinal young stage of T. dendroides. T. dendroides (Permian of Timor) shows a plane of bilateral symmetry, the cardinal ridge is stronger and longer than the others, the counter shorter, the alar ridges can be identified in transverse section. major and minor ridges are well developed; the number of ridges is often 32. In T.xizangensis (Permian of Tibet) only the bilateral symmetry is known, while there are no data for T mediterranea (Permian of Sicily). The systematic affinities between Palaeacis and Trachiypsammia pointed out on the basis of microstructural data are also supported by the septal ridges pattern. Do Palaeacis, Trochypsammia and others form a special division of Tabulate corals? That is the question     

Effects of temperature and elevated CO2 on cell division in shoot meristems: differential responses of two natural populations of Dactylis glomerata L.

The aim was to establish whether temperature and/or elevated [CO₂] (-700 μmol mol^?1) affects the cell doubling time (cdt) in the different zones of the shoot apex of two natural populations of Dactylis glomerata originating in Portugal (38° S3′ N) and in Sweden (63° 09′ N). In the Portuguese population at ambient [CO₂], only the pith rib meristem (PRM) exhibited a significant shortening of cdts from 10 to 30 °C. Elevated [CO₂] resulted in a significant shortening of cdt, particularly in the PRM where cdt was reduced 4-8- and 6-1-fold at 10 and 20 °C, respectively, but only 2-fold at 30 °C. In the Swedish population at ambient [CO₂], there were no consistent temperature-dependent alterations to cdt and this population was less responsive to elevated [CO₂] than the Portuguese population. Nevertheless, elevated [CO₂] resulted in a significant shortening of the cdt for some of the zones; the maximum reduction occurred in the PRM at 30 °C. We concluded that in the shoot apex of the Portuguese population, and most notably in the PRM, 10 and 20 °C were non-optimal temperatures for cell division, whilst the Swedish population was relatively buffered against temperature change. Elevated [CO₂] resulted in substantially greater reductions in cdts in the shoot meristem of the Portuguese population than in that of the Swedish population.     

Changes in Lipid Composition during Callus Differentiation in Cultures of Oilseed Rape (Brassica napus L.)

The lipid composition of different callus cultures of Brassicanapus varied according to their state of differentiation. Photomixotrophiccallus was characterized by the ability to synthesize relativelyhigh levels of triacylglycerol (TAG) which was rich in oleate.Glycosyldiacylglycerols were also detected. In contrast, heterotrophiccallus was found to possess high proportions of membraneousphospholipids which were rich in palmitate, linoleate, and linolenate.Moreover, the lipid content was considerably less than thatof photomixotrophic callus. Caulogenesis was achieved in bothtypes of callus strains and the lipid composition of the regeneratedleaves contained a much higher proportion of chloroplast glycosyldiacylglycerolsand thus resembled more those of the parent plant. Some callientered a senescent phase whereby there was considerable degradationof the constituent membrane lipids. Senescent callus also exhibiteda high proportion of polyploid nuclei. In this study we havebeen able to cause large changes in the morphology of calluscultures. These morphological changes were accompanied by significantalterations in the quality and quantity of acyl lipids. In photomixotrophiccells the lipid changes resembled those seen for developingseed tissues where high rates of TAG deposition are accompaniedby an altered fatty acid pattern. Thus, the selection of differentcallus types should be of use for investigations of the regulationof lipid biosynthesis under controlled culture conditions.