Comptes Rendus de l'Académie des Sciences - Series III - Sciences de la Vie最新文献

The objective of this work is to characterise the variations of the quality of the glass eels recruitment during a season of migration, from November till March and before and after the transition from marine to continental environment. The emaciation state measured from the ratio DNA/Dry weight and percentage of body water is analysed from a sampling of glass-eels collected at sea and in estuary, in the South of the Bay of Biscay during the migration period 1999/2000. The length and the mass are taken into account, they decrease during the season while the individuals are more and more pigmented. However, our work shows that groups of glass eels arriving on the coasts of the Bay of Biscay are homogeneous from the point of view of their energetic and hydride reserves with a high individual variability within these groups. Also no significant difference in losses of water and energetic reserve were observed among the individuals migrating at the beginning and during tide stream. Fluctuations of the biochemical indication and the percentage of water between the glass eels caught in sea and in estuary show that the transition between maritime and continental environment is not a mobilising event of a lot of energy for glass eels. Differences were only observed in December.

In order to test whether mutations giving rise to color vision deficiencies are more frequently inherited from older fathers, an exhaustive screening of births in the Namur region has allowed to isolate a sample of 225 descending sons of maternal grandfathers who were older than 45 years at their daughter’s birth. The incidence of color vision defects was compared between this set of cases and three control groups totalling 959 boys from independent families. While these comparisons were not conclusive, we propose new hypotheses concerning the population dynamics of color vision deficiencies. Neomutations in X-linked pigment genes may be a marker of the overall genetic load borne by the X chromosome. Selection against such loaded X chromosomes may occur in the second generation, either in the course of embryogenesis, or during female gametogenesis. The future assessment of these novel hypotheses relies on the arbitration of molecular genetics.

Carbon isotope discrimination (Δ) has been proposed as a good criterion for transpiration efficiency and grain yield improvement. Its measurement, however, remains very expensive. Ash content (m_a) has been proposed as an alternative criterion for Δ in bread wheat and barley. The aims of this study were (i) to analyse the relationships between Δ and mineral composition in different durum wheat plant parts and (ii) to compare the variation of these traits between landraces and improved varieties from different geographic origins. For this purpose, Δ, m_a, and composition in four minerals (K, Mg, P and Si) were assessed in flag leaves and awns at anthesis, and in mature grains of ten durum wheat genotypes grown under rainfed Mediterranean conditions. The three plant parts differed significantly for the measured traits. Significant correlations were noted between Δ and m_a in the flag leaf and in the grain. Silicon content in flag leaves and potassium content in awns were also positively related to Δ of the considered plant part. The coefficient of correlation between Δ and m_a was generally higher than that observed between individual mineral content and Δ, suggesting that m_a is the better alternative criterion for Δ. In addition, grain yield was related to grain Δ and both m_a and potassium content in awns. Harvest index was correlated with Δ and m_a of grain and flag leaf. These results emphasised that m_a values in flag leaf and grain represent the efficiency of carbon partitioning to the grain. Improved varieties showed higher Δ and m_a values than landraces. Differences between Middle-East and West Mediterranean genotypes for the measured traits were also presented and discussed.

A detailed pollen analysis has been conducted in a new sedimentary sequence taken at Les Ételles (700 m), in the hill vegetation belt in the Chaîne des Hurtières (Northern French Alps). The Lateglacial history of the vegetation has been supported by 10 AMS datings. Variations in relative abundance of main pollen taxa were compared with variations in ð ¹⁸O in Swiss lacustrine sediments and with the GRIP ice-core record. Those highlight how the vegetation reacted to minor climatic oscillations. The Lateglacial spread of Quercus, Alnus and Corylus in the region is confirmed, thus allowing a new interpretation of some Lateglacial sedimentary sequences at an adjacent region (Bas-Dauphiné).

Three pectin methyltransferases (PMT5, PMT7, PMT18; EC 2.1.1.6.x) were solubilized from the endo-membrane complex of flax cells, with 0.05 % Triton X-100. After a 3 step-chromatography procedure, PMT7 and PMT5 were purified to apparent homogeneity. PMT5 and PMT7 differed regarding their optimum pH (5 or 7), the methyl acceptor (low or highly methylesterified pectin), their focusing pH range (6–7 or 8–9) and relative molecular mass (40 ± 5 or 110 ± 10 kDa). SDS-PAGE of PMT5 and PMT7 did not reveal bands at 40 or 110 kDa but only a silver stained band of about 18 kDa. Two independent methods (photo labelling and enzymatic activity) showed that this silver-stained band corresponded to a methyltransferase with affinity for pectins. This polypeptide was of the same size as the enzyme designed PMT18 (18 ± 3 kDa; pI 4–4.5) recovered during size exclusion chromatography of either PMT7 or PMT5, suggesting that PMT18 bears the catalytic site of PMT5 and PMT7.

Protein interactions within a multimolecular complex can result in information and energy transfer between proteins. This can lead in turn to the emergence of novel functions of some proteins of the complex. Various examples of this situation can be found in the scientific literature. This is probably the case for prion protein, chloroplast phosphoribulokinase bound to glyceraldehyde phosphate dehydrogenase, Ras system, and pancreatic lipase bound to biomembranes, to cite but a few. Any enzyme reaction, or enzyme reaction network, carries Shannon entropy and information. On contrary to genome entropy, the entropy of enzyme reactions and metabolic sequences is sensitive to ‘external’ signals, such as substrate, effector and proton concentrations. Complex structural organization of the cell is associated with a higher entropy content, and one can calculate the gain of entropy and information due to integration and complexity. One may conclude from this brief analysis that the informational content of a living cell is much larger than that of its genome.

The concept of multistationarity has become essential for understanding cell differentiation. For this reason theoretical biologists have more and more frequently to determine the steady values, often multiple, of systems of non-linear differential equations. It is well known that iteration processes of current use converge or not towards a fixed point depending on the absolute value of the slope of the iteration function in the vicinity of the considered fixed point. A number of methods have been developed to obtain or accelerate convergence. As biologists, we do not pretend to review these works. Rather, we propose here a simple algorithm which permits to converge at will towards a chosen type of steady state. Others and we have used this procedure extensively for years for the analysis of complex biological systems. A compact program (using Mathematica) is available.

The present study is the first comprehensive phylogeny of the class of the Phaeophyceae. For 67 species representing all orders of the class, the sequences of the 3’-end of the small and the 5ˈ-end of the large subunit nrRNA genes were aligned and analysed. A further analysis based on sequences of the 3’-end of the small and of the complete sequences of the 28S gene of the large subunits was also performed, but for only eight taxa. In both analyses, Tribonema marinum (Xanthophyceae) was used as outgroup. The analyses showed the Dictyotales as diverging first, followed by the Sphacelariales, then the Syringodermatales. Most of the orders currently accepted were confirmed as monophyletic groups but the Laminariales and Tilopteridales remained polyphyletic. The relationships of the remaining orders to each other were not resolved with the present data set. Ascoseira, included for the first time in a molecular study, appeared as a separate lineage without any clear relationship with other algae possessing conceptacles (Splachnidium and Fucales). Algae with stellate plastids, never studied in a global context, were polyphyletic; this result is consistent with their plastid ultrastructure and is discussed in detail. As further result of the present study, the South African genus Bifurcariopsis appeared as the sister taxon of the North Atlantic genus Himanthalia, and Xiphophora appeared as the sister taxon of Hormosira rather than as a member of the Fucaceae; the taxonomic position of these genera is discussed.

The methodology used by previous authors to resolve the relationships of the elopomorphan taxa is criticized. The morphological characters that have been proposed to support the monophyly of the Elopomorpha are reviewed and it is shown that most of them are weak. A new hypothesis of relationships is proposed on the basis of nucleotidic sequences of ribosomal RNA 18S, 16S and 12S. In order to really test all the possible relationships, the monophyly of the Elopomorpha was not considered a priori. The tree was rooted on Amia calva and Lepisosteus osseus and the ingroup taxa sampling was subsequently increased. The obtained topology shows that the Elopomorpha is a non-monophyletic taxon. Elopiforms, anguilliforms, albuliforms and notacanthiforms are considered here as four monophyletic, incertae sedis taxa among basal teleosts.

Pollen and macro-remains were analysed in a sixth site (La Gouille 1 800 m) of the Chaîne des Hurtières (northern French Alps). Nine A.M.S. dates support the chronology. Thus, the establishment of the vegetation belt of a massif can be modelled in the northern French Alps. Betula invaded sub-Alpine grasslands as early as 10 000 ¹⁴C BP. Around 9 600 ¹⁴C BP shrublands with Corylus, Alnus and Sorbus were established before the spread of Abies at the site approximately 8 200 ¹⁴C BP. A decrease in Abies prior to 8 100 ¹⁴C BP occurred during the Venediger climatic oscillation. At around 2 940 ¹⁴C BP, a strong regression of Abies due to human action is noted with the expansion of Alnus viridis. Recently, a second Abies retraction led to the present sparce P. cembra and Alnus viridis vegetation cover.