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31.
Sophie Arnaud-Haond Marianna Migliaccio Elena Diaz-Almela Sara Teixeira Mirjiam Susanne van de Vliet Filipe Alberto Gabriele Procaccini Carlos M. Duarte Ester A. Serrão 《Journal of Biogeography》2007,34(6):963-976
Aim The seagrass, Posidonia oceanica is a clonal angiosperm endemic to the Mediterranean Sea. Previous studies have suggested that clonal growth is far greater than sexual recruitment and thus leads to low clonal diversity within meadows. However, recently developed microsatellite markers indicate that there are many different genotypes, and therefore many distinct clones present. The low resolution of markers used in the past limited our ability to estimate clonality and assess the individual level. New high‐resolution dinucleotide microsatellites now allow genetically distinct individuals to be identified, enabling more reliable estimation of population genetic parameters across the Mediterranean Basin. We investigated the biogeography and dispersal of P. oceanica at various spatial scales in order to assess the influence of different evolutionary factors shaping the distribution of genetic diversity in this species. Location The Mediterranean. Methods We used seven hypervariable microsatellite markers, in addition to the five previously existing markers, to describe the spatial distribution of genetic variability in 34 meadows spread throughout the Mediterranean, on the basis of an average of 35.6 (± 6.3) ramets sampled. Results At the scale of the Mediterranean Sea as a whole, a strong east–west cleavage was detected (amova) . These results are in line with those obtained using previous markers. The new results showed the presence of a putative secondary contact zone at the Siculo‐Tunisian Strait, which exhibited high allelic richness and shared alleles absent from the eastern and western basins. F statistics (pairwise θ ranges between 0.09 and 0.71) revealed high genetic structure between meadows, both at a small scale (about 2 to 200 km) and at a medium scale within the eastern and western basins, independent of geographical distance. At the intrameadow scale, significant spatial autocorrelation in six out of 15 locations revealed that dispersal can be restricted to the scale of a few metres. Main conclusions A stochastic pattern of effective migration due to low population size, turnover and seed survival is the most likely explanation for this pattern of highly restricted gene flow, despite the importance of an a priori seed dispersal potential. The east–west cleavage probably represents the outline of vicariance caused by the last Pleistocene ice age and maintained to this day by low gene flow. These results emphasize the diversity of evolutionary processes shaping the genetic structure at different spatial scales. 相似文献
32.
B. Friebe M. C. Cermeño F. J. Zeller 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1987,73(3):337-342
Summary C-banding patterns and nucleolar activity were analyzed in Dasypyrum villosum, its added chromosomes to hexaploid wheat and the hexaploid amphiploid Triticum dicoccum-D. villosum. Two different populations of the allogamous species D. villosum (2n= 14, VV) from Greece and Italy were analyzed showing a similar polymorphism for C-banding pattern. Six of the seven addition lines were identified by their characteristic C-banding pattern. No polymorphism between both members of each added alien chromosome was found. Furthermore, nucleolar activity and competition were studied by using silver staining procedure. In D. villosum only one chromosome pair, A, was found to be responsible for organizing nucleoli. The results obtained in the amphiploid and in the addition lines demonstrate that nucleolar activity is restricted to SAT-chromosomes 1B and 6B of wheat, while those of D. villosum remain inactive. 相似文献
33.
Marcelo Oliva Moreno 《Systematic parasitology》1987,10(2):129-133
Choricotyle anisotremi n. sp. is described from the gills and on the inner surface of the operculum of Anisotremus scapularis (Pomadasyidae) from the Chilean coast. Distinct characteristics of the new species are: presence of an oval accessory sclerite on the inner quadrant of the clamp adjacent to the accessory sucker; 12 genital hooks; short and stout peduncles, the last pair of which are closely apposed; a lobed seminal receptacle; and a fan-like posthaptor without a terminal lappet. 相似文献
34.
M H Boyer B Cami J P Chambost M Magnan J Cattanéo 《European journal of biochemistry》1987,162(2):311-316
35.
The interaction of fibrinogen with the mannose-specific lectins concanavalin A (ConA), its acetyl derivative (Ac-ConA) and Lens culinaris agglutinin (LcH) was studied. Both ConA and LcH interact specifically with individual fibrinogen B beta and gamma chains and with denatured fragments D and E. However, analysis of the binding data shows that four moles of Ac-ConA are bound per mole of fibrinogen with two sets of binding sites (Kd1 = 2.4 microM and Kd2 = 16.6 microM; n1 = n2 = 2) while only two moles of LcH are bound per mole of fibrinogen (Kd = 2.6 microM). Ultracentrifugation studies are also in agreement with the presence in the fibrinogen molecule of two and four binding sites for LcH and Ac-ConA, respectively. No aggregates of fibrinogen formed through LcH or Ac-ConA linkages are observed. The use of a crosslinking reagent and ultracentrifugal analysis of the lectin-fibrinogen fragments D1 and E complexes indicated that ConA, as well as Ac-ConA, interact with both fragments D and E while LcH interacts only with fragment D. Furthermore, the binding of ConA to both D and E domains in the intact fibrinogen molecule is clearly demonstrated by using a bifunctional reagent. The bivalent character of ConA tetramers may be misinterpreted as a lack of accessibility of the lectin to two of the four carbohydrate chains of fibrinogen. The differential binding of LcH and ConA to the carbohydrate chains of fibrinogen can be related to a different exposure of the oligosaccharide in D and E fragments and domains and to the different requirements of both lectins for their binding to glycoproteins. 相似文献
36.
A novel group of very long chain polyenoic fatty acids in dipolyunsaturated phosphatidylcholines from vertebrate retina 总被引:10,自引:0,他引:10
M I Avelda?o 《The Journal of biological chemistry》1987,262(3):1172-1179
Dipolyunsaturated phosphatidylcholines from bovine retina contain a whole series of unusual fatty acids. Methyl esters from these acids are very strongly retained on polar and nonpolar gas-liquid chromatography stationary phases. On thin layers of silica-AgNO3, they separate as tetra-, penta-, and hexaenoic fatty acid methyl esters. After hydrogenation, the three polyunsaturated fractions give the same series of saturated methyl esters, having 20 (or 22)-36 carbon atoms. High pressure liquid chromatography, as well as gas-liquid chromatography, indicates that the new components of the three fractions are even-carbon homologs of well known polyenoic fatty acids of the n-6 and n-3 families, since they behave as series of 20-36-carbon tetraenoic (n-6), pentaenoic (n-3 and n-6), and hexaenoic (n-3) fatty acids. Their occurrence in phospholipid molecules also having docosahexaenoate (22:6) explains the separation of major dipolyunsaturated phosphatidylcholines from retina into dodecaenoic, undecaenoic, and decaenoic fractions after argentation thin layer chromatography. Using high pressure liquid chromatography, the latter are resolved into individual species having 10-12 double bonds and 42-58 carbon atoms. The unusual PCs are thus endowed not only with the highest degree of unsaturation, but with the longest hydrocarbon chains yet reported for vertebrate glycerophospholipids. It is shown that phosphatidylcholines containing the novel fatty acids are highly concentrated in photoreceptor membranes and that they occur in the retina of vertebrates so distant in evolution as fish, birds, and various mammals. 相似文献
37.
Alvaro García-Tejedor A. Raul Castaño Federico Morán Francisco Montero 《Journal of molecular evolution》1987,26(4):294-300
Summary The most relevant properties of hypercycles were previously studied mainly from a theoretical point of view. We have developed a Monte Carlo method simulating hypercyclic organization to obtain information about the dynamics of this prebiotic organization. Nucleation, growth, and selective properties have been tested and the results obtained are in good agreement with those of the theoretical predictions. The influence of hypercyclic organization of the error threshold has also been studied. As a consequence of the emergence of a hypercycle, the value of this threshold decreases. The amount of this decrease depends on the population size. Moreover, for some interval of quality factor values, either the hypercycle organization or an error catastrophe can be produced, depending on the initial conditions. The influence of these phenomena on both the dynamic behavior and evolutionary advantages of the hypercycle, as well as their decisive roles on genome size, are discussed.Presented at the FEBS Symposium on Genome Organization and Evolution, held in Crete, Greece, September 1–5, 1986 相似文献
38.
(1-14C)-labeled (n-6) eicosatetraenoate, (n-3) docosapentaenoate and (n-3) docosahexaenoate (20:4, 22:5 and 22:6, respectively) are efficiently taken up and actively esterified into the lipids of bovine retina after 2 h incubation. Photoreceptor membranes, mitochondria, microsomes and postmicrosomal supernatants, which display significant differences in phospholipid and fatty acid compositions, are isolated after such incubations to study the labeling of lipids. The lipid classes preferentially labeled with the acids (1) largely differ among and within subcellular fractions, while (2) some common features in the treatment of the three polyenes are observed in each fraction. In all of them, the three acids are actively incorporated in phosphatidylcholine; ethanolamine glycerophospholipid, phosphatidylserine (PS) and phosphatidylinositol (PI) are highly labeled with 22:6, 22:5 and 20:4 respectively; within ethanolamine glycerophospholipid, the three label phosphatidylethanolamine in preference to plasmenylethanolamine. Most of the 14C esterified in mitochondria is in phospholipids. The endoplasmic reticulum produces in addition highly labeled triacylglycerols, also found in cytosol. High levels of 14C-labeled diacylglycerols are observed exclusively in photoreceptor membranes, where the specific radioactivity of PI is very high. The total amounts of 14C incorporated (1) are in general similar within a given fraction for the three polyenes, but (2) largely differ among fractions. The labeling of the highly unsaturated phospholipids of photoreceptor membranes is the lowest, while the postmicrosomal supernatant (whose lipids are relatively the poorest in polyenoic fatty acids) contains most of the labeled lipids isolated from retinas under these conditions. The results indicate that polyunsaturated species of retina phospholipids undergo an active synthesis and turnover, as well as an intense intracellular traffic among membranes. 相似文献
39.
The effect on fibrinogen coagulation and fibrinolysis of the mannose-specific lectins concanavalin A, its acetyl derivative and Lens culinaris agglutinin was studied. Concanavalin A and acetyl-concanavalin A, which bind to the four carbohydrate chains of fibrinogen, and L. culinaris agglutinin, which only binds to the carbohydrate present in fibrinogen D domains, has the same effect on the coagulation rate: an inhibition at low lectin concentrations and an increase at high concentrations. On the other hand, L. culinaris agglutinin does not alter fibrin crosslinking while acetyl-concanavalin A produces a slight inhibition of both gamma-gamma and alpha-polymer formation. However, this effect is very small when compared with the clear inhibitory effect produced by concanavalin A. Concanavalin A and acetyl-concanavalin A have an inhibitory effect on the rate of fibrin clot lysis proportional to the lectin concentration. Nearly 100% inhibition was obtained when two lectin-binding sites were occupied by either concanavalin A or acetyl-concanavalin A. However, L. culinaris agglutinin has a clearly weaker effect and more than 50% inhibition was not observed. The comparative study of the effect of the three lectins on fibrinolysis as well as on the formation of fibrinogen aggregates suggests that the inhibitory effect of concanavalin A and acetyl-concanavalin A is primarily due to their binding to the carbohydrate chains of fibrinogen E domain. 相似文献
40.
The labeling of molecular species of phosphatidylcholine (PC) has been studied in bovine retinas incubated for 2 h with (1-14C)-labeled (n-6) eicosatetraenoate (n-3) docosapentaenoate and (n-3) docosahexaenoate (20:4, 22:5 and 22:6, respectively) and in four subcellular fractions isolated after such incubations. Of the total radioactivity incorporated in PC, the following percentages of the above fatty acids, respectively, are found in its dipolyunsaturated species: 58, 56 and 53% in rod outer segments; 29, 41 and 49% in mitochondria; 24, 28 and 39% in microsomes; 12, 14 and 16% in postmicrosomal supernatants; 28, 36 and 58% in entire retinas. The remainder percentages are in tetra-, penta- and hexaenoic species of PC, respectively. The levels of pentaenoic species in the PCs of all fractions are similar, while tetraenes are lowest and hexaenes highest in photoreceptor membranes. Dipolyunsaturated species are highly concentrated in photoreceptor membranes, but are minor components of mitochondrial, microsomal and cytosolic PC. The specific radioactivities of tetraenoic, pentaenoic and hexaenoic PCs are decreasingly lower in the following order: postmicrosomal supernatants, microsomes, mitochondria, photoreceptor membranes. In contrast, the specific radioactivities of dipolyunsaturated PCs are higher in mitochondria and microsomes than in the other fractions, especially with 22:5 and 22:6. It is suggested that mitochondria as well as the endoplasmic reticulum could play a role in the synthesis and further modifications of dipolyunsaturated PCs before being supplied to photoreceptor membranes. 相似文献