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31.
von Balthazar M Pedersen KR Crane PR Stampanoni M Friis EM 《American journal of botany》2007,94(12):2041-2053
A charcoalified fossil flower, Potomacanthus lobatus gen. et sp. nov., is described from the Early Cretaceous (Early to Middle Albian) Puddledock locality, Virginia, USA. Internal floral structure was studied using nondestructive synchrotron-radiation x-ray tomographic microscopy (SRXTM). The flower is bisexual and trimerous. The perianth consists of two whorls of tepals. The androecium has two whorls of fertile stamens. Anthers open by two distally hinged valves. The gynoecium consists of a single carpel that is plicate in the style and ascidiate in the ovary and contains a single pendant ovule. The fossil flower shares many similarities with flowers of extant Lauraceae and is unlike flowers of other families of Laurales. However, the fossil flower also differs in detail from all extant or fossil Lauraceae, particularly in configuration of the androecium. The new taxon, together with previously described but more fragmentary material from the Puddledock locality, provides the earliest fossil record of plants more closely related to Lauraceae than to any other extant family. It reveals several derived morphological characters that are potential synapomorphies among extant representatives of the family Lauraceae and contributes to the growing evidence for an early diversification of Laurales before the end of the Early Cretaceous. 相似文献
32.
Genome sequencing and analysis of the versatile cell factory Aspergillus niger CBS 513.88 总被引:1,自引:0,他引:1
Pel HJ de Winde JH Archer DB Dyer PS Hofmann G Schaap PJ Turner G de Vries RP Albang R Albermann K Andersen MR Bendtsen JD Benen JA van den Berg M Breestraat S Caddick MX Contreras R Cornell M Coutinho PM Danchin EG Debets AJ Dekker P van Dijck PW van Dijk A Dijkhuizen L Driessen AJ d'Enfert C Geysens S Goosen C Groot GS de Groot PW Guillemette T Henrissat B Herweijer M van den Hombergh JP van den Hondel CA van der Heijden RT van der Kaaij RM Klis FM Kools HJ Kubicek CP van Kuyk PA Lauber J 《Nature biotechnology》2007,25(2):221-231
33.
Zeidler R Albermann K Lang S 《Apoptosis : an international journal on programmed cell death》2007,12(11):1927-1943
Cigarette smoking is associated with a plethora of different diseases. Nicotine is the addictive component of cigarette but
also acts onto cells of the non-neuronal system, including immune effector cells. Although nicotine itself is usually not
referred to as a carcinogen, there is ongoing debate whether nicotine functions as a ‘tumor enhancer.' By binding to nicotinic
acetylcholine receptors, nicotine deregulates essential biological processes like angiogenesis, apoptosis, and cell-mediated
immunity. Apoptosis plays critical roles in a wide variety of physiologic processes during fetal development and in adult
tissue and is also a fundamental aspect of the biology of malignant diseases. This review provides an overlook how nicotine
influences apoptotic processes and is thus directly involved in the etiology of pathological conditions like cancer and obstructive
diseases. 相似文献
34.
van den Berg MA Albang R Albermann K Badger JH Daran JM Driessen AJ Garcia-Estrada C Fedorova ND Harris DM Heijne WH Joardar V Kiel JA Kovalchuk A Martín JF Nierman WC Nijland JG Pronk JT Roubos JA van der Klei IJ van Peij NN Veenhuis M von Döhren H Wagner C Wortman J Bovenberg RA 《Nature biotechnology》2008,26(10):1161-1168
35.
Recent palaeobotanical studies have greatly increased the quantity and quality of information available about the structure and relationships of Cretaceous angiosperms. Discoveries of extremely well preserved Cretaceous flowers have been especially informative and, combined with results from phylogenetic analyses of extant angiosperms (based mainly on molecular sequence data), have greatly clarified important aspects of early angiosperm diversification. Nevertheless, many questions still persist. The phylogenetic origin of the group itself remains as enigmatic as ever and, in some cases, newly introduced techniques from molecular biology have given confusing results. In particular, relationships between the five groups of extant seed plants remain uncertain, and it has sometimes proved difficult to reconcile estimates of the time of divergence between extant lineages made using a 'molecular clock' with the fossil record. One result, however, is becoming increasingly clear: a great deal of angiosperm diversity is extinct. Some groups of angiosperms were evidently more diverse in the past than they are today. In other cases, fossils defy assignment to extant groups at the family level or below. This raises the possibility that evolutionary conclusions based solely upon extant taxa that are merely relics of groups that were once much more diverse might be misled by the effects of extinction. It also introduces the possibility that some early enigmatic fossils might represent lineages that diverged from the main line of angiosperm evolution below the most recent common ancestor of all extant taxa. These, and other questions, are among those that need to be addressed by future palaeobotanical research. 相似文献
36.
37.
Most studies on photosynthetic production of aquatic macrophytes have been made on detached leaves and algal thalli. This may have given the false impression that production is often saturated by light and that inorganic carbon and nutrients are more important limiting factors. However, studies on the more relevant ecological scale of macrophyte communities lead to a completely different perception because community production is light limited due to intense self‐shading. Relatively high irradiances are needed for photosynthesis to balance respiratory costs and not even maximum irradiances at noon during summer saturate photosynthetic production. The fundamental importance of light is confirmed by the close coupling to community light absorptance of both maximum production in high‐light environments and efficiency of light use in low‐light environments. The upper boundaries of light‐limited and light‐saturated production are distinctly and linearly related to community absorptance. Moreover, higher diversity in the community has a positive and stabilizing influence on light absorptance and production because different species supplement each other temporally and spatially. Close predictions of actual production rates in macroalgal communities throughout the year are possible solely from determinations of incident and absorbed irradiance. Along with the increasing regulating role of light from leaves or thalli to entire communities the importance of temperature, inorganic carbon and other resources decreases. Thus, ten‐fold rise of CO2 relative to atmospheric saturation does not enhance maximum production in dense communities of efficient HCO3?‐users and only doubles production of pure CO2‐users. A challenge therefore exists establishing the importance of light for photosynthetic production of macrophytes from individuals to communities and re‐evaluating the postulated main importance of inorganic carbon and temperature in the scenarios of globally rising CO2 and temperature. 相似文献
38.
We investigate conditions under which a model with stochastic demography or population structure converges to the coalescent with a linear change in timescale. We argue that this is a necessary condition for the existence of a meaningful effective population size. We find that such a linear timescale change is obtained when demographic fluctuations and coalescence events occur on different timescales. Simple models of population structure and randomly fluctuating population size are used to exemplify the ideas and provide an intuitive feel for the meaning of the conditions. 相似文献
39.
Portelius E Westman-Brinkmalm A Zetterberg H Blennow K 《Journal of proteome research》2006,5(4):1010-1016
Early pathogenic events in Alzheimer's disease (AD) involve increased production and/or reduced clearance of beta-amyloid (Abeta), especially the 42 amino acid fragment Abeta1-42. The Abeta1-42 peptide is generated through cleavage of the amyloid precursor protein by beta- and gamma-secretase and is catabolised by a variety of proteolytic enzymes such as insulin-degrading enzyme and neprilysin. Here, we describe a method that employs immunoprecipitation combined with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry to determine the pattern of C-terminally truncated Abeta peptides in cerebrospinal fluid (CSF). Using antibodies coupled to magnetic beads, we have detected 18 C-terminally and 2 N-terminally truncated Abeta peptides in CSF. By determining the identity and profile of the truncated Abeta peptides, more insight may be gained about differences in the metabolism and structural properties of Abeta in AD. Finally, the Abeta fragment signatures may prove useful as a diagnostic test for AD. 相似文献
40.
Blomqvist ME Reynolds C Katzov H Feuk L Andreasen N Bogdanovic N Blennow K Brookes AJ Prince JA 《Human genetics》2006,119(1-2):29-37
Most genetic sequence variants that contribute to variability in complex human traits will have small effects that are not
readily detectable with population samples typically used in genetic association studies. A potentially valuable tool in the
gene discovery process is meta-analysis of the accumulated published data, but in order to be valid these require a sample
of studies representative of the true genetic effect and thus hypothetically should include some positive and an abundance
of negative reports. A survey of the literature on association studies for Alzheimer disease (AD) from January 2004–April
2005, identified 138 studies, 86 of which reported positive findings other than for apolipoprotein E (APOE), strongly indicative of publication bias. We report here an analysis of 62 genetic markers, tested for association with
AD risk as well as for possible effects upon quantitative indices of AD severity (mini-mental state examination scores, age-at-onset,
and cerebrospinal fluid (CSF) β-amyloid (Aβ) and CSF tau proteins). Within this set, only modest signals were present that,
with the exception of APOE are easily lost when corrections for multiple hypotheses are applied. In isolation, results are thus broadly negative. Genes
studied encompass both novel candidates as well as several recently claimed to be associated with AD (e.g. urokinase plasminogen
activator (PLAU) and acetyl-coenzyme A acetyltransferase 1 (ACAT1)). By reporting these data we hope to encourage the publication of gene compendia to guide further studies and aid future
meta-analyses aimed at resolving the involvement of genes in complex human traits. 相似文献