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41.
David M. Newbery Sarah Schwan George B. Chuyong Xander M. van der Burgt 《Trees - Structure and Function》2009,23(2):219-234
Buttressing is a trait special to tropical trees but explanations for its occurrence remain inconclusive. The two main hypotheses
are that they provide structural support and/or promote nutrient acquisition. Studies of the first are common but the second
has received much less attention. Architectural measurements were made on adult and juvenile trees of the ectomycorrhizal
species Microberlinia bisulcata, in Korup (Cameroon). Buttressing on this species is highly distinctive with strong lateral extension of surface roots of
the juveniles leading to a mature buttress system of a shallow spreading form on adults. This contrasts with more vertical
buttresses, closer to the stem, found on many other tropical tree species. No clear relationship between main buttress and
large branch distribution was found. Whilst this does not argue against the essential structural role of buttresses for these
very large tropical trees, the form on M. bisulcata does suggest a likely second role, that of aiding nutrient acquisition. At the Korup site, with its deep sandy soils of very
low phosphorus status, and where most nutrient cycling takes place in a thin surface layer of fine roots and mycorrhizas,
it appears that buttress form could develop from soil-surface root exploration for nutrients by juvenile trees. It may accordingly
allow M. bisulcata to attain the higher greater competitive ability, faster growth rate, and maximum tree size that it does compared with other
co-occurring tree species. For sites across the tropics in general, the degree of shallowness and spatial extension of buttresses
of the dominant species is hypothesized to increase with decreasing nutrient availability. 相似文献
42.
Natalia Shirokova Chifei Kang Miguel Fernandez-Tenorio Wei Wang Qiongling Wang Xander?H.T. Wehrens Ernst Niggli 《Biophysical journal》2014,107(12):2815-2827
Cellular oxidative stress, associated with a variety of common cardiac diseases, is well recognized to affect the function of several key proteins involved in Ca2+ signaling and excitation-contraction coupling, which are known to be exquisitely sensitive to reactive oxygen species. These include the Ca2+ release channels of the sarcoplasmic reticulum (ryanodine receptors or RyR2s) and the Ca2+/calmodulin-dependent protein kinase II (CaMKII). Oxidation of RyR2s was found to increase the open probability of the channel, whereas CaMKII can be activated independent of Ca2+ through oxidation. Here, we investigated how oxidative stress affects RyR2 function and SR Ca2+ signaling in situ, by analyzing Ca2+ sparks in permeabilized mouse cardiomyocytes under a broad range of oxidative conditions. The results show that with increasing oxidative stress Ca2+ spark duration is prolonged. In addition, long and very long-lasting (up to hundreds of milliseconds) localized Ca2+ release events started to appear, eventually leading to sarcoplasmic reticulum (SR) Ca2+ depletion. These changes of release duration could be prevented by the CaMKII inhibitor KN93 and did not occur in mice lacking the CaMKII-specific S2814 phosphorylation site on RyR2. The appearance of long-lasting Ca2+ release events was paralleled by an increase of RyR2 oxidation, but also by RyR-S2814 phosphorylation, and by CaMKII oxidation. Our results suggest that in a strongly oxidative environment oxidation-dependent activation of CaMKII leads to RyR2 phosphorylation and thereby contributes to the massive prolongation of SR Ca2+ release events. 相似文献
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44.
Subtractive phage display selection for screening and identification of peptide sequences with potential use in serodiagnosis of paracoccidioidomycosis caused by Paracoccidioides brasiliensis 下载免费PDF全文
45.
David M. Newbery Christophe J. Praz Xander M. van der Burgt Julian M. Norghauer George B. Chuyong 《Plant Ecology》2010,206(1):151-172
In groves of ectomycorrhizal caesalpiniaceous species in the Atlantic coastal forest of Central Africa the dominant tree Microberlinia bisulcata, which is shade-intolerant as a seedling but highly light-responding as a sapling, shows very limited regeneration. M. bisulcata saplings were mapped in an 82.5-ha plot at Korup and found to be located significantly far (>40 m) away from adults, a result
confirmed by direct testing in a second 56-ha plot. Sapling growth over 6 years, the distribution of newly emerging seedlings
around adults, recruitment of saplings in a large opening and the outward extent of seedlings at the grove edge were also
investigated. Two processes appear to have been operating: (1) a very strong and consistent restriction of the very numerous
seedlings establishing after masting close to adults, and (2) a strong but highly spatially variable promotion of distant
survivors by increased light from the deaths of large trees of species other than M. bisulcata (which itself has very low mortality rate). This leads to an apparent escape-from-adults effect. To maintain saplings in
the shade between multiple short periods of release ectomycorrhizal connections to other co-occurring caesalp species may
enable a rachet-type mechanism. The recorded sapling dynamics currently contribute an essential part of the long-term cycling
of the groves. M. bisulcata is an interesting example of an important group of tropical trees, particularly in Africa, which are both highly light-demanding
when young yet capable also of forming very large forest emergents. To more comprehensively explain tropical tree responses,
the case is made for adding a new dimension to the trade-off concept of early tree light-response versus adult longevity. 相似文献
46.
Solid-state nanopores have received increasing interest over recent years because of their potential for genomic screening and sequencing. In particular, small nanopores (2-5 nm in diameter) allow the detection of local structure along biological molecules, such as proteins bound to DNA or possibly the secondary structure of RNA molecules. In a typical experiment, individual molecules are translocated through a single nanopore, thereby causing a small deviation in the ionic conductance. A correct interpretation of these conductance changes is essential for our understanding of the process of translocation, and for further sophistication of this technique. Here, we present translocation measurements of double-stranded DNA through nanopores down to the diameter of the DNA itself (1.8-7 nm at the narrowest constriction). In contrast to previous findings on such small nanopores, we find that single molecules interacting with these pores can cause three distinct levels of conductance blockades. We attribute the smallest conductance blockades to molecules that briefly skim the nanopore entrance without translocating, the intermediate level of conductance blockade to regular head-to-tail translocations, and the largest conductance blockades to obstruction of the nanopore entrance by one or multiple (duplex) DNA strands. Our measurements are an important step toward understanding the conductance blockade of biomolecules in such small nanopores, which will be essential for future applications involving solid-state nanopores. 相似文献
47.
Maluf ML Takahachi G Svidzinski TI Xander P Apitz-Castro R Bersani-Amado CA Cuman RK 《Revista iberoamericana de micología》2008,25(3):163-166
The natural compound ajoene (4,5,9- trithiadodeca-1,6,11-triene 9-oxide) is capable of controlling infection by Paracoccidioides brasiliensis in experimental models. Swiss mice were inoculated with 5.0 x 10e6 cells of the fungus Paracoccidioides brasiliensis Pb18 by intraperitoneal route and treated with ajoene. In weeks 2, 6, 10 and 13 of treatment, levels of anti-Pb antibodies were measured by the ELISA test and the animals were put down and their lungs, livers and spleens removed for histopathological analysis and determination of the number of viable fungus. The results show that experimental murine paracoccidioidomycosis was well established and that ajoene was capable of controlling the evolution of the disease, as it significantly reduced the levels of antibodies from the 10th week of treatment. 相似文献
48.
Popi AF Godoy LC Xander P Lopes JD Mariano M 《Microbes and infection / Institut Pasteur》2008,10(7):817-824
Protective immunity in paracoccidioidomycosis is mainly mediated by cellular immunity. The role of B cells in this disease, in particular B-1 cells, is poorly understood. The aim of this study was to characterize the participation of B-1 cells in resistance or susceptibility of BALB/c and BALB/Xid mice to P. brasiliensis (Pb) pulmonary infection. BALB/Xid, which lacks B-1 cells, exhibited higher resistance to infection when compared with BALB/c mice. However, adoptive transfer of B-1 cells to BALB/Xid mice drastically increased the susceptibility of these animals to Pb infection. The fungal burden in BALB/c and B-1-reconstituted BALB/Xid was significantly higher as compared to BALB/Xid strain. Compact, well-organized granulomas were observed in the lungs of BALB/Xid mice, whereas large lesions with necrotic center with a plethora of fungi developed in BALB/c mice. It was also shown that B-1 cells impair phagocytosis of Pb by macrophages in vitro via secretion of IL-10, which was increased upon stimulation with a purified Pb antigen, gp43. Finally, in vivo blockade of IL-10 led to a better control of infection by the highly susceptible B10.A mouse. These findings suggest that B-1 cells play a major role in resistance/susceptibility to Pb infection in murine models, most likely via production of IL-10. 相似文献
49.
Sameer Ather Jonathan L. Respress Na Li Xander H.T. Wehrens 《生物化学与生物物理学报:疾病的分子基础》2013,1832(12):2425-2431
Sarcoplasmic reticulum (SR) Ca2 + release plays an essential role in mediating cardiac myocyte contraction. Depolarization of the plasma membrane results in influx of Ca2 + through l-type Ca2 + channels (LTCCs) that in turn triggers efflux of Ca2 + from the SR through ryanodine receptor type-2 channels (RyR2). This process known as Ca2 +-induced Ca2 +release (CICR) occurs within the dyadic region, where the adjacent transverse (T)-tubules and SR membranes allow RyR2 clusters to release SR Ca2 + following Ca2 + influx through adjacent LTCCs. SR Ca2 + released during systole binds to troponin-C and initiates actin–myosin cross-bridging, leading to muscle contraction. During diastole, the cytosolic Ca2 + concentration is restored by the resequestration of Ca2 + into the SR by SR/ER Ca2 +-ATPase (SERCA2a) and by the extrusion of Ca2 + via the Na+/Ca2 +-exchanger (NCX1). This whole process, entitled excitation–contraction (EC) coupling, is highly coordinated and determines the force of contraction, providing a link between the electrical and mechanical activities of cardiac muscle. In response to heart failure (HF), the heart undergoes maladaptive changes that result in depressed intracellular Ca2 + cycling and decreased SR Ca2 + concentrations. As a result, the amplitude of CICR is reduced resulting in less force production during EC coupling. In this review, we discuss the specific proteins that alter the regulation of Ca2 + during HF. In particular, we will focus on defects in RyR2-mediated SR Ca2 + release. This article is part of a Special Issue entitled: Heart failure pathogenesis and emerging diagnostic and therapeutic interventions. 相似文献
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