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  • 1
    ISSN: 1432-1017
    Keywords: Key words Membrane microtubes ; Membrane elasticity ; Phospholipid translocation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Observations over extended times of a lipid microtube (tether) formed from a lecithin vesicle have shown that under constant external loads the tether exhibits a continuous slow growth. It is considered that this growth is a consequence of the net transbilayer movement of phospholipid molecules in a direction which relieves the membrane strain resulting from the elastic deformation of the vesicle. The elastic deformation mode responsible for this effect is identified as the relative expansion of the two membrane layers reflecting the non-local contribution to membrane bending. An equation for the consequent rate of transbilayer movement of phospholipid molecules is derived. The dynamic behavior of the system is modeled by including frictional contributions due to interlayer slip and Stokes drag on the glass bead used to form the tether. The general numerical solution reveals a complex dependence of the tether growth rate on the system parameters and a continuous increase in the rate of tether growth at long times. Closed form expressions approximating the system behavior are derived and the conditions under which they can be applied are specified. Modeling the mechanically-driven lipid transport as a simple, stochastic, thermal process, allows the rate of lipid translocation to be related to the equilibrium transbilayer exchange rate of phospholipid molecules. Consideration of experimental results shows that the time constant for mechanically-driven translocation is shorter than the time for diffusion-driven translocation by approximately two orders of magnitude, indicating that lipid translocation is not a simple diffusive process.
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  • 2
    ISSN: 1432-2242
    Keywords: Key words Disease resistance ; Hordeum vulgare ; Marker-assisted selection ; Molecular markers ; PCR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  The genetic structure of the rym5 locus was studied in a population comprising 391 doubled-haploid lines that were evaluated for resistance to two strains of Barley Yellow Mosaic Virus (BaYMV-1, 2) and to Barley Mild Mosaic Virus (BaMMV). The absence of recombinants that are able to differentiate between the reaction to these different bymoviruses provides evidence that rym5 is a complex locus, which is either composed of several closely linked genes or of an allelic series of a single gene. For marker-assisted introgression of this locus into adapted barley germplasm, a CAPS (cleaved amplified polymorphic sequence) and a microsatellite marker were developed that flank the gene at distances of 0.8 and 1.3% recombination, respectively.
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  • 3
    ISSN: 1432-2242
    Keywords: Key words Genotyping ; Microsatellites ; Potato ; Tomato
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  The potential of microsatellite markers for use in genetical studies in potato (Solanum tuberosum) was evaluated. Database searches revealed that microsatellite sequences were present in the non-coding regions of 24 potato genes. Twenty-two sets of primers were designed and products successfully amplified using 19 primer pairs. These were tested against a panel of 18 tetraploid potato cultivars. Four pairs of primers designed to amplify microsatellites from tomato were also used. Seven (including 2 of the tomato sequences) failed to reveal any variation in the accessions tested. Sixteen primer pairs did reveal polymorphism, detecting between 2 and 19 alleles at each locus. Of these, 3 gave rise to complex band patterns, suggesting that multiple polymorphic loci were being amplified using a single primer pair. Heterozygosity values ranged from 0.408 to 0.921. Phenetic analysis of the derived information allowed a dendrogram to be constructed depicting the relationships between the 18 potato cultivars. The potential of microsatellite markers for genetic analysis and satutory applications in potato is discussed in the context of these results. Furthermore, the potential of ‘cross-species amplification’ is highlighted as an additional source of microsatellite markers for genetic research in potato.
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  • 4
    ISSN: 1432-2242
    Keywords: Genotyping ; Microsatellites ; Potato ; Tomato
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The potential of microsatellite markers for use in genetical studies in potato (Solanum tuberosum) was evaluated. Database searches revealed that microsatellite sequences were present in the non-coding regions of 24 potato genes. Twenty-two sets of primers were designed and products successfully amplified using 19 primer pairs. These were tested against a panel of 18 tetraploid potato cultivars. Four pairs of primers designed to amplify microsatellites from tomato were also used. Seven (including 2 of the tomato sequences) failed to reveal any variation in the accessions tested. Sixteen primer pairs did reveal polymorphism, detecting between 2 and 19 alleles at each locus. Of these, 3 gave rise to complex band patterns, suggesting that multiple polymorphic loci were being amplified using a single primer pair. Heterozygosity values ranged from 0.408 to 0.921. Phenetic analysis of the derived information allowed a dendrogram to be constructed depicting the relationships between the 18 potato cultivars. The potential of microsatellite markers for genetic analysis and satutory applications in potato is discussed in the context of these results. Furthermore, the potential of ‘crossspecies amplification’ is highlighted as an additional source of microsatellite markers for genetic research in potato.
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  • 5
    ISSN: 1432-2242
    Keywords: Key words AFLPs ; Diversity ; Genetic differentiation ; Camellia sinensis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract AFLP markers were successfully employed to detect diversity and genetic differentiation among Indian and Kenyan populations of tea (Camellia sinensis (L.) O. Kuntze). Shannon's index of diversity was used to partition the total phenotypic variation into between and within population components. On average, most of the diversity was detected within populations, with 79% of the variation being within and 21% being between populations of Indian and Kenyan tea. A dendrogram constructed on the basis of band sharing distinctly separated the three populations of tea into China type (sinensis), Assam type (assamica) and Cambod type (assamica ssp. lasiocalyx) in a manner consistent with the present taxonomy of tea, the known pedigree of some of the genotypes and their geographical origin. Principal coordinate (PCO) analysis grouped Assam genotypes both from India and Kenya supporting the suggestion that the Kenyan clones have been derived from collections made in this region. The China types were more dispersed on the PCO plot which is a reflection of wider genetic variation. As would be expected, clones collected from the same region exhibited less overall genetic variation. AFLP analysis discriminated all of the tested genotypes from India and Kenya, even those which cannot be distinguished on the basis of morphological and phenotypic traits.
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  • 6
    ISSN: 1432-2277
    Keywords: Liver transplantation, hepatic failure ; Hepatic failure, liver transplantation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract This paper reports the clinical syndrome of fulminant hepatic failure (FHF) following liver transplantation. FHF was defined as the sudden onset of liver failure [encephalopathy and prolonged International Normalised Ratio (INR)] without arterial thrombosis in the setting of a liver allograft. FHf post-transplant was seen in 8/154 (5.2%) adult patients undergoing transplantation. These eight patients developed a clinical syndrome characterised by: (a) a rapid rise in ALT levels to above 1000 U/l (mean maximum 1600 U/l), (b) a sudden increase in the INR to above 5 (mean maximum 5.6), (c) the development of high fever, (d) the persistence of thrombocytopenia (mean nadir 40×109/dl), (e) a progressive rise in the bilirubin (mean maximum 400 μmol/l) and (f) the development of hepatic encephalopathy. In seven cases this syndrome occurred following good initial graft function at day 6 post (mean)-transplant. In one case the above syndrome developed immediately after liver transplantation. Four of the eight patients developed multiorgan failure associated with systemic acidosis (mean pH 6.84). All of these patients died (mean day 11). Four patients developed systemic alkalosis. Two of these four patients underwent successful retransplantation (on days 12 and 13) and remain alive at a mean of 11 months post-transplant. Six of the eight patients received OKT3 therapy without any apparent affect on clinical outcome. Compared to a control group of patients (n=28), 2/8 versus 2/28 had a positive crossmatch with donor lymphocytes (P=NS), 1/8 versus 7/28 were ABO-non-identical (P=NS), 3/8 versus 10/21 had total MHC mismatches (P=NS) and 5/7 versus 6/16 had UW ischemic times above 10 h (P=NS). No patients had main hepatic artery thrombosis on angiography although four patients had evidence of intrahepatic microthrombi or arterial necrosis at autopsy. In all cases the histology showed massive haemorrhagic necrosis. Three cases had evidence of veno-occlusive lesions whilst foam cell arteriopathy was seen in two cases. Immunofluorescence was performed in three cases. In two cases there was evidence of immunoglobulin, complement and fibrin deposition in blood vessels. In conclusion, we describe an uncommon clinical syndrome occurring post liver transplant. This syndrome represents humorally mediated allograft rejection but there seems to be no relationship with tissue matching (antibody, ABO, MHC) or donor ischaemic times. If recognised earlier in the absence of multiorgan failure, urgent retransplantation seems to be the only effective therapy.
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  • 7
    ISSN: 1432-2242
    Keywords: Barley ; QTLs ; Linkage ; Yield ; Markers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Quantitative trait loci (QTLs) have been revealed for characters in a segregating population from a spring barley cross between genotypes adapted to North-West Europe. Transgressive segregation was found for all the characters, which was confirmed by the regular detection of positive and negative QTLs from both parents. A QTL for all the agronomic, yield and grain characters measured except thousand grain weight was found in the region of the denso dwarfing gene locus. There were considerable differences between the location of QTLs found in the present study and those found in previous studies of North American germ plasm, revealing the diversity between the two gene pools. Thirty-one QTLs were detected in more than one environment for the 13 characters studied, although many more were detected in just one environment. Whilst biometrical analyses suggested the presence of epistasis in the genetic control of some characters, there was little evidence of interactions between the QTLs apart from those associated with yield. QTLs of large effect sometimes masked the presence of QTLs of smaller effect.
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  • 8
    ISSN: 1432-2242
    Keywords: Lens ; RAPD ; Cluster analysis ; Diversity ; Phylogeny
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract RAPD markers were used to distinguish between six different Lens taxa, representing cultivated lentil and its wild relatives. Twenty-four arbitrary sequence 10-mer primers were identified which revealed robust and easily interpretable amplification-product profiles. These generated a total of 88 polymorphic bands in 54 accessions and were used to partition variation within and among Lens taxa. The data showed that, of the taxa examined, ssp. orientalis is most similar to cultivated lentil. L. ervoides was the most divergent wild taxon followed by L. nigricans. The genetic similarity between the latter two species was of the same magnitude as between ssp. orientalis and cultivated lentil. In addition, species-diagnostic amplification products specific to L. odemensis, L. ervoides and L. nigricans were identified. These results correspond well with previous isozyme and RFLP studies. RAPDs, however, appear to provide a greater degree of resolution at a sub-species level. The level of variation detected within cultivated lentils suggests that RAPD markers may be an appropriate technology for the construction of genetic linkage maps between closely related Lens accessions.
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  • 9
    ISSN: 1432-2242
    Keywords: Key words Barley ; Genetic relationships ; Molecular analysis ; RFLP ; AFLP ; RAPD ; SSR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  RFLPs, AFLPs, RAPDs and SSRs were used to determine the genetic relationships among 18 cultivated barley accessions and the results compared to pedigree relationships where these were available. All of the approaches were able to uniquely fingerprint each of the accessions. The four assays differed in the amount of polymorphism detected. For example, all 13 SSR primers were polymorphic, with an average of 5.7 alleles per primer set, while nearly 54% of the fragments generated using AFLPs were monomorphic. The highest diversity index was observed for AFLPs (0.937) and the lowest for RFLP (0.322). Principal co-ordinate analysis (PCoA) clearly separated the spring types from the winter types using RFLP and AFLP data with the two-row winter types forming an intermediate group. Only a small group of spring types clustered together using SSR data with the two-row and six-row winter varieties more widely dispersed. Direct comparisons between genetic similarity (GS) estimates revealed by each of the assays were measured by a number of approaches. Spearman rank correlation ranked over 70% of the pairwise comparisons between AFLPs and RFLPs in the same order. SSRs had the lowest values when compared to the other three assays. These results are discussed in terms of the choice of appropriate technology for different aspects of germplasm evaluation.
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  • 10
    ISSN: 1432-2242
    Keywords: Key words Potato ; Solanum tuberosum ; Nematode resistance ; Globodera pallida ; Linkage in autotetraploids ; Quantitative trait locus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Seventy eight clones from the cross between SCRI clone 12601ab1 and cv Stirling were used to explore the possibility of genetical linkage analysis in tetraploid potato (Solanum tuberosum subsp. tuberosum). Clone 12601ab1 had quantitative resistance to Globodera pallida Pa2/3 derived from S. tuberosum subsp. andigena. The strategy adopted involved identifying single- (simplex) and double- (duplex) dose AFLP markers in the parents from segregation ratios that could be unambiguously identified in their offspring, detecting linkage between a marker and a putative quantitative trait locus (QTL) for resistance, and placing the QTL on the linkage map of markers. The numbers of scorable segregating markers were 162 simplex ones present only in 12601ab1, 87 present in Stirling, and 32 present in both; and 72 duplex markers present only in 12601ab1 and 45 present in Stirling. The total map length was 990.9 cM in 12601ab1 and 484.6 cM in Stirling. A QTL with a resistance allele present in double dose (QQqq) in 12601ab1 was inferred from the associations between resistance scores (square root of female counts) and two duplex markers linked in coupling, which, in turn, were linked in coupling to four simplex markers also associated with resistance, but to a lesser degree. The largest marker class difference was the one for the duplex marker P61M34=15. It accounted for 27.8% of the phenotypic variance in resistance scores, or approximately 30% of the genotypic variance. Subsequently, this duplex marker was found to be linked in coupling with a duplex SSR allele Stm3016=a, whose locus was shown to be on chromosome IV in a diploid reference mapping population. The other QTLs for resistance segregating in the progeny were not identified for one or more of the following reasons: the markers did not cover the whole of the genome, there were unfavourable repulsion linkages between the QTLs and markers, or the gene effects were not large enough to be detected in an experiment of the size conducted. It is concluded that prospects appear good for detecting QTLs and using marker-assisted selection in a tetraploid potato breeding programme, provided that, in future, the population size is increased to over 250 and more SSR markers are used to complement the AFLPs; the same is likely to be true for other autotetraploid crops.
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