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排序方式: 共有195条查询结果,搜索用时 15 毫秒
51.
Christian Knig Patrick Weigelt Amanda Taylor Anke Stein Wayne Dawson Franz Essl Jan Pergl Petr Pyek Mark van Kleunen Marten Winter Cyrille Chatelain Jan J. Wieringa Pavel Krestov Holger Kreft 《Ecography》2021,44(1):44-55
Island disharmony refers to the biased representation of higher taxa on islands compared to their mainland source regions and represents a central concept in island biology. Here, we develop a generalizable framework for approximating these source regions and conduct the first global assessment of island disharmony and its underlying drivers. We compiled vascular plant species lists for 178 oceanic islands and 735 mainland regions. Using mainland data only, we modelled species turnover as a function of environmental and geographic distance and predicted the proportion of shared species between each island and mainland region. We then quantified the over‐ or under‐representation of families on individual islands (representational disharmony) by contrasting the observed number of species against a null model of random colonization from the mainland source pool, and analysed the effects of six family‐level functional traits on the resulting measure. Furthermore, we aggregated the values of representational disharmony per island to characterize overall taxonomic bias of a given flora (compositional disharmony), and analysed this second measure as a function of four island biogeographical variables. Our results indicate considerable variation in representational disharmony both within and among plant families. Examples of generally over‐represented families include Urticaceae, Convolvulaceae and almost all pteridophyte families. Other families such as Asteraceae and Orchidaceae were generally under‐represented, with local peaks of over‐representation in known radiation hotspots. Abiotic pollination and a lack of dispersal specialization were most strongly associated with an insular over‐representation of families, whereas other family‐level traits showed minor effects. With respect to compositional disharmony, large, high‐elevation islands tended to have the most disharmonic floras. Our results provide important insights into the taxon‐ and island‐specific drivers of disharmony. The proposed framework allows overcoming the limitations of previous approaches and provides a quantitative basis for incorporating functional and phylogenetic approaches into future studies of island disharmony. 相似文献
52.
Detection and characterization of point mutations in the choroideremia candidate gene by PCR-SSCP analysis and direct DNA sequencing 下载免费PDF全文
J. A. J. M. van den Hurk T. J. R. van de Pol C. M. Molloy F. Brunsmann K. Rüther E. Zrenner A. J. L. G. Pinckers I. H. Pawlowitzki E. M. Bleeker-Wagemakers B. Wieringa H. -H. Ropers F. P. M. Cremers 《American journal of human genetics》1992,50(6):1195-1202
By making use of positional cloning strategies we recently isolated a candidate gene for choroideremia (CHM), which is transcribed in retina, choroid, and/or retinal pigment epithelium. The gene contains an open reading frame that is structurally altered in 10 CHM patients with sizable deletions and in a female patient with a balanced translocation involving the Xq21 band. Employing PCR-SSCP analysis and direct DNA sequencing we have now detected and characterized different point mutations in five patients with CHM. Each of these mutations introduces a termination codon into the open reading frame of the CHM candidate gene, thereby predicting a distinct truncated protein product. Together these findings provide convincing evidence for the candidate gene being identical with the choroideremia gene. 相似文献
53.
Jan W. P Kuiper Helma Pluk Frank Oerlemans Frank N van Leeuwen Frank de Lange Jack Fransen B Wieringa 《PLoS biology》2008,6(3)
Phagocytosis requires locally coordinated cytoskeletal rearrangements driven by actin polymerization and myosin motor activity. How this actomyosin dynamics is dependent upon systems that provide access to ATP at phagosome microdomains has not been determined. We analyzed the role of brain-type creatine kinase (CK-B), an enzyme involved in high-energy phosphoryl transfer. We demonstrate that endogenous CK-B in macrophages is mobilized from the cytosolic pool and coaccumulates with F-actin at nascent phagosomes. Live cell imaging with XFP-tagged CK-B and β-actin revealed the transient and specific nature of this partitioning process. Overexpression of a catalytic dead CK-B or CK-specific cyclocreatine inhibition caused a significant reduction of actin accumulation in the phagocytic cup area, and reduced complement receptor–mediated, but not Fc-γR–mediated, ingestion capacity of macrophages. Finally, we found that inhibition of CK-B affected phagocytosis already at the stage of particle adhesion, most likely via effects on actin polymerization behavior. We propose that CK-B activity in macrophages contributes to complement-induced F-actin assembly events in early phagocytosis by providing local ATP supply. 相似文献
54.
55.
G. W. Wieringa 《Antonie van Leeuwenhoek》1963,29(1):84-88
The pectinase produced during the anaerobic retting of flax appeared to have a pH optimum between 5.4 and 5.6. Continuous neutralization during the fermentation, however, induced the production of a pectinase with a pH optimum of 7.1.The majority of the pectin splitting bacteria in the acid and in the neutral retting liquors belonged to the speciesClostridium pectinovorum.Pure culture studies withCl. pectinovorum at fixed pH levels showed that the pectinase produced is adapted to the pH of the environment. No differences in pH dependency could be established between the hemicellulases from the acid and the neutral retting liquor.Although a pH of 6.5 is far from optimal for the hemicellulase, the actual hemicellulolytic activity in the neutral pH retting method is greater than the activity of the normal, acid retting liquor. This fact supports the theory that hemicellulase is responsible for losses in fibre quality and quantity in the neutral pH retting method. 相似文献
56.
Labella John J.; Daood Monica J.; Koretsky A. P.; Roman Brian B.; Sieck Gary C.; Wieringa Be; Watchko Jon F. 《Journal of applied physiology》1998,84(4):1166-1173
Creatine kinase(CK) provides ATP buffering in skeletal muscle and is expressed as1) cytosolic myofibrillar CK (M-CK)and 2) sarcomeric mitochondrial CK(ScCKmit) isoforms that differ in their subcellular localization. Wecompared the isometric contractile and fatigue properties of1) control CK-sufficient (Ctl),2) M-CK-deficient (M-CK[/]), and3) combined M-CK/ScCKmit-deficientnull mutant (CK[/]) diaphragm (Dia) todetermine the effect of the absence of M-CK activity on Dia performancein vitro. Baseline contractile properties were comparable across groupsexcept for specific force, which was ~16% lower inCK[/] Dia compared withM-CK[/] and Ctl Dia. During repetitiveactivation (40 Hz, duty cycle), force declined in all threegroups. This decline was significantly greater inCK[/] Dia compared with Ctl and M-CK[/] Dia. The pattern of forcedecline did not differ between M-CK[/] andCtl Dia. We conclude that Dia isometric muscle function is notabsolutely dependent on the presence of M-CK, whereas the completeabsence of CK acutely impairs isometric force generation duringrepetitive activation. 相似文献
57.
58.
Laverman AM Meile C Van Cappellen P Wieringa EB 《Applied and environmental microbiology》2007,73(1):40-47
Denitrifying activity in a sediment from the freshwater part of a polluted estuary in northwest Europe was quantified using two independent approaches. High-resolution N(2)O microprofiles were recorded in sediment cores to which acetylene was added to the overlying water and injected laterally into the sediment. The vertical distribution of the rate of denitrification supported by nitrate uptake from the overlying water was then derived from the time series N(2)O concentration profiles. The rates obtained for the core incubations were compared to the rates predicted by a forward reactive transport model, which included rate expression for denitrification calibrated with potential rate measurements obtained in flowthrough reactors containing undisturbed, 1-cm-thick sediment slices. The two approaches yielded comparable rate profiles, with a near-surface, 2- to 3-mm narrow zone of denitrification and maximum in situ rates on the order of 200 to 300 nmol cm(-3) h(-1). The maximum in situ rates were about twofold lower than the maximum potential rate for the 0- to 1-cm depth interval of the sediment, indicating that in situ denitrification was nitrate limited. The experimentally and model-derived rates of denitrification implied that there was nitrate uptake by the sediment at a rate that was on the order of 50 (+/- 10) nmol cm(-2) h(-1), which agreed well with direct nitrate flux measurements for core incubations. Reactive transport model calculations showed that benthic uptake of nitrate at the site is particularly sensitive to the nitrate concentration in the overlying water and the maximum potential rate of denitrification in the sediment. 相似文献
59.
Borst JW Willemse M Slijkhuis R van der Krogt G Laptenok SP Jalink K Wieringa B Fransen JA 《PloS one》2010,5(11):e13862
Recently, we described that ATP induces changes in YFP/CFP fluorescence intensities of Fluorescence Resonance Energy Transfer (FRET) sensors based on CFP-YFP. To get insight into this phenomenon, we employed fluorescence lifetime spectroscopy to analyze the influence of ATP on these fluorescent proteins in more detail. Using different donor and acceptor pairs we found that ATP only affected the CFP-YFP based versions. Subsequent analysis of purified monomers of the used proteins showed that ATP has a direct effect on the fluorescence lifetime properties of CFP. Since the fluorescence lifetime analysis of CFP is rather complicated by the existence of different lifetimes, we tested a variant of CFP, i.e. Cerulean, as a monomer and in our FRET constructs. Surprisingly, this CFP variant shows no ATP concentration dependent changes in the fluorescence lifetime. The most important difference between CFP and Cerulean is a histidine residue at position 148. Indeed, changing this histidine in CFP into an aspartic acid results in identical fluorescence properties as observed for the Cerulean fluorescent based FRET sensor. We therefore conclude that the changes in fluorescence lifetime of CFP are affected specifically by possible electrostatic interactions of the negative charge of ATP with the positively charged histidine at position 148. Clearly, further physicochemical characterization is needed to explain the sensitivity of CFP fluorescence properties to changes in environmental (i.e. ATP concentrations) conditions. 相似文献
60.