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991.
Leif Kullman 《Journal of Ecology》1998,86(3):421-428
1 Macroscopic remains of the fairly thermophilous tree species Alnus glutinosa , Tilia cordata and Betula pendula were recovered in subalpine and adjacent boreal environments far above and beyond their present-day distributional limits. This establishes that the early Holocene tree flora of the Scandes Mountains in northern Sweden was indeed richer than it is today.
2 Dates ranged between c . 8600 and 7000 radiocarbon years bp . These are much earlier than previous estimates by conventional pollen stratigraphical analyses of the arrival of these species at their maximum geographical limits. This highlights problems in using only pollen data for vegetation reconstruction, and suggests re-evaluation of earlier records.
3 The results, together with similar macrofossils for Picea abies and Larix sibirica in northern Sweden, suggest that many tree species spread rapidly and became established at their most extended range limits during the early Holocene. Abundances have subsequently varied in accordance with the ecology of individual species as well as with climatic change.
4 Palaeoclimatic inferences may suggest a strongly continental climate, i.e. warmer and drier summers and possibly fairly cold winters between 8600 and 7000 bp relative to the present. Some change towards a more oceanic climate regime with less pronounced seasonal contrasts may have occurred towards the end of the period. 相似文献
2 Dates ranged between c . 8600 and 7000 radiocarbon years bp . These are much earlier than previous estimates by conventional pollen stratigraphical analyses of the arrival of these species at their maximum geographical limits. This highlights problems in using only pollen data for vegetation reconstruction, and suggests re-evaluation of earlier records.
3 The results, together with similar macrofossils for Picea abies and Larix sibirica in northern Sweden, suggest that many tree species spread rapidly and became established at their most extended range limits during the early Holocene. Abundances have subsequently varied in accordance with the ecology of individual species as well as with climatic change.
4 Palaeoclimatic inferences may suggest a strongly continental climate, i.e. warmer and drier summers and possibly fairly cold winters between 8600 and 7000 bp relative to the present. Some change towards a more oceanic climate regime with less pronounced seasonal contrasts may have occurred towards the end of the period. 相似文献
992.
Denys N. Wheatley Leif Rasmussen Arno Tiedtke 《BioEssays : news and reviews in molecular, cellular and developmental biology》1994,16(5):367-372
Tetrahymena has been used as a model cell system in many studies of morphogenesis, conjugation, gene mapping, cell division and growth kinetics. In this article, we consider some advances which have resulted from the successful development of a chemically defined medium (CDM), and how subsequent work has extended the contribution that this organism has made to our understanding of different aspects of growth, nutrition, cell cycle control, cytokinesis and intercellular signalling. Finally, we discuss the considerable potential that has arisen for the biotechnological exploitation of this big and rapidly growing eukaryotic cell. 相似文献
993.
Upon laser flash photolysis of β-carotene in chloroform instantaneous bleaching of β-carotene and concomitant formation of near infrared absorbing species are observed. One species, absorbing with maximum at 920 nm, is formed during the laser pulse (10 ns) and is practically gone in one millisecond, the decay showing a bi-exponential behaviour. The second species, absorbing with maximum at 1000 nm, is formed from the species absorbing at 920 nm by first order kinetics with a rate constant of 4.9·104 s-1 at 20°C. This second species decays by second order kinetics and is gone within a few milliseconds. An additional slow bleaching of β-carotene and formation of the species absorbing at 920 nm is observed. This slow bleaching/formation of transient absorption is probably due to processes involving free radicals generated during the instantaneous bleaching. The species absorbing at 920 nm is suggested to be either (i) a free radical adduct formed from β-carotene and chloroform or (ii) β-carotene after abstraction of a hydrogen atom. The species absorbing at 1000 nm is most likely the radical cation. Formation and decay of the near infrared absorbing species and bleaching of β-carotene are independent of whether oxygen is present or absent in the solutions. 相似文献
994.
995.
Alon Abraham Majed Alabdali Mohammad Qrimli Hana Albulaihe Ari Breiner Carolina Barnett Hans D. Katzberg Leif E. Lovblom Bruce A. Perkins Vera Bril 《PloS one》2015,10(10)
IntroductionChronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is one of several chronic treatable acquired demyelinating neuropathies.ObjectivesTo explore the association between the degree of demyelination in CIDP, and treatment responsiveness.MethodsA retrospective chart review of CIDP subjects assessed between 1997 and 2013 was performed to compare treatment responsiveness using different sets of criteria.Results99 CIDP patients were included, 34 with diabetes mellitus (DM). Treatment responsiveness was higher in CIDP-DM fulfilling 1 or more EFNS/PNS criteria, (63% vs. 31%, p = 0.03), and in CIDP+DM fulfilling 2 or more criteria (89% vs. 36%, p = 0.01). Nonetheless, treatment responsiveness in CIDP+DM had the highest odds ratio (3.73, p = 0.01). Similar results were also shown in simplified uniform study criteria, with 10% cut off values for CIDP-DM, compared to 30% for CIDP+DM.ConclusionIn CIDP+DM, higher degrees of demyelination are associated with treatment responsiveness, implying the need to adjust current criteria in these patients. 相似文献
996.
997.
Dongfeng Chen Duo Zuo Cheng Luan Min Liu Manli Na Liang Ran Yingyu Sun Annette Persson Elisabet Englund Leif G. Salford Erik Renstr?m Xiaolong Fan Enming Zhang 《PloS one》2014,9(1)
Increased PDGFRA signaling is an essential pathogenic factor in many subtypes of gliomas. In this context the cell surface expression of PDGFRA is an important determinant of ligand sensing in the glioma microenvironment. However, the regulation of spatial distribution of PDGFRA in glioma cells remains poorly characterized. Here, we report that cell surface PDGFRA expression in gliomas is negatively regulated by an ERK-dependent mechanism, resulting in reduced proliferation of glioma cells. Glioma tumor tissues and their corresponding cell lines were isolated from 14 patients and analyzed by single-cell imaging and flow cytometry. In both cell lines and their corresponding tumor samples, glioma cell proliferation correlated with the extent of surface expression of PDGFRA. High levels of surface PDGFRA also correlated to high tubulin expression in glioma tumor tissue in vivo. In glioma cell lines, surface PDGFRA declined following treatment with inhibitors of tubulin, actin and dynamin. Screening of a panel of small molecule compounds identified the MEK inhibitor U0126 as a potent inhibitor of surface PDGFRA expression. Importantly, U0126 inhibited surface expression in a reversible, dose- and time-dependent manner, without affecting general PDGFRA expression. Treatment with U0126 resulted in reduced co-localization between PDGFRA and intracellular trafficking molecules e.g. clathrin, RAB11 and early endosomal antigen-1, in parallel with enhanced co-localization between PDGFRA and the Golgi cisternae maker, Giantin, suggesting a deviation of PDGFRA from the endosomal trafficking and recycling compartment, to the Golgi network. Furthermore, U0126 treatment in glioma cells induced an initial inhibition of ERK1/2 phosphorylation, followed by up-regulated ERK1/2 phosphorylation concomitant with diminished surface expression of PDGFRA. Finally, down-regulation of surface PDGFRA expression by U0126 is concordant with reduced glioma cell proliferation. These findings suggest that manipulation of spatial expression of PDGFRA can potentially be used to combat gliomas. 相似文献
998.
999.
Katrin Schmidt Lorena Martinez-Gamboa Susan Meier Christian Witt Christian Meisel Leif G Hanitsch Mike O Becker Doerte Huscher Gerd R Burmester Gabriela Riemekasten 《Arthritis research & therapy》2009,11(4):R111
Introduction
Interstitial lung disease (ILD) is a frequent manifestation of systemic sclerosis (SSc), and cytokines can contribute to the disease pathology. The aim of the current study was to identify specific changes in cytokine levels that may serve as disease markers and possible targets for therapy. 相似文献1000.