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991.
Morgan-Kiss RM Chan LK Modla S Weber TS Warner M Czymmek KJ Hanson TE 《Photosynthesis research》2009,99(1):11-21
Green sulfur bacteria (GSB) rely on the chlorosome, a light-harvesting apparatus comprised almost entirely of self-organizing
arrays of bacteriochlorophyll (BChl) molecules, to harvest light energy and pass it to the reaction center. In Chlorobaculum tepidum, over 97% of the total BChl is made up of a mixture of four BChl c homologs in the chlorosome that differ in the number and identity of alkyl side chains attached to the chlorin ring. C. tepidum has been reported to vary the distribution of BChl c homologs with growth light intensity, with the highest degree of BChl c alkylation observed under low-light conditions. Here, we provide evidence that this functional response at the level of the
chlorosome can be induced not only by light intensity, but also by temperature and a mutation that prevents phototrophic thiosulfate
oxidation. Furthermore, we show that in conjunction with these functional adjustments, the fraction of cellular volume occupied
by chlorosomes was altered in response to environmental conditions that perturb the balance between energy absorbed by the
light-harvesting apparatus and energy utilized by downstream metabolic reactions. 相似文献
992.
While one-to-one specificity between reef-dwelling hosts and symbiotic dinoflagellates of the genus Symbiodinium may occur, detailed examination of some hosts reveals that they contain multiple symbiont types. Individuals of the foraminifer
Amphisorus hemprichii living in Papua New Guinea contained mixed communities of Symbiodinium dominated by symbiont types in clades C and F. Moreover, the types showed a distinct pattern in their distribution across
the radius of the foraminifer, with clade F Symbiodinium more prevalent in the center of the host cell. The mixed community of symbionts and their pattern of distribution within
the foraminifer is likely the result of processes happening both inside the foraminifer and in its external environment. Persistent
mixed symbiont communities in foraminifera may be stabilized through benefits conferred by maintaining multiple symbiont lineages
for symbiont shuffling. Alternatively they may be stabilized through a heterogeneous internal host environment, partitioning
of symbiont functional roles or limitation of symbiont reproduction by the host. Six factors generally determine the presence
of any particular symbiont type within a foraminifer: mode of transmission, availability from the environment, recognition
by the host, regulation by the host, competition between lineages, and fitness of the holobiont.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
993.
Ricardo Brando Francielli Weber Santos Renata Oliveira Silvane Souza Roman Cristina Wayne Nogueira 《Journal of trace elements in medicine and biology》2009,23(4):324-333
The involvement of non-enzymatic antioxidant defenses in the protective effect of diphenyl diselenide (PhSe)2 on testicular damage caused by cadmium in mice was investigated. Mice received a single dose of CdCl2 (5 mg/kg, intraperitoneally). Thirty minutes after the CdCl2 injection, they received a single oral dose of (PhSe)2 (400 μmol/kg). Twenty-four hours after CdCl2 administration, blood samples were collected and mice were killed and had their testes dissected. Parameters in plasma (aspartate (AST) and alanine (ALT) aminotransferases and lactato dehydrogenase (LDH) activities as well as creatinine levels) were determined. The activity of δ-aminolevulinate dehydratase (δ-ALA-D), the levels of thiobarbituric acid-reactive substances (TBARS), ascorbic acid and nonprotein thiols (NPSH) and histological analysis were determined in collected samples. Results demonstrated that (PhSe)2 protected against toxicity induced by CdCl2 on δ-ALA-D activity, ascorbic acid and NPSH levels. (PhSe)2 protected against the increase in plasma AST, ALT and LDH activities caused by CdCl2. Testes of mice exposed to CdCl2 showed marked histopathological alterations that were ameliorated by administration of (PhSe)2. (PhSe)2 protected against toxicity induced by CdCl2 in testes of mice. Ascorbic acid and NPSH, non-enzymatic antioxidant defenses, are involved in the protective effect of (PhSe)2 against testicular damage caused by CdCl2 in mice. 相似文献
994.
Anuradha Seshadri Badrinath Dubey Michael H. W. Weber Umesh Varshney 《Molecular microbiology》2009,72(3):795-808
Ribosomal RNA (rRNA) contains a number of modified nucleosides in functionally important regions including the intersubunit bridge regions. As the activity of ribosome recycling factor (RRF) in separating the large and the small subunits of the ribosome involves disruption of intersubunit bridges, we investigated the impact of rRNA methylations on ribosome recycling. We show that deficiency of rRNA methylations, especially at positions 1518 and 1519 of 16S rRNA near the interface with the 50S subunit and in the vicinity of the IF3 binding site, adversely affects the efficiency of RRF-mediated ribosome recycling. In addition, we show that a compromise in the RRF activity affords increased initiation with a mutant tRNAfMet wherein the three consecutive G-C base pairs (29 GGG31 :39 CCC41 ), a highly conserved feature of the initiator tRNAs, were mutated to those found in the elongator tRNAMet (29 UCA31 :39 ψGA41 ). This observation has allowed us to uncover a new role of RRF as a factor that contributes to fidelity of initiator tRNA selection on the ribosome. We discuss these and earlier findings to propose that RRF plays a crucial role during all the steps of protein synthesis. 相似文献
995.
Maria Grandoch Maider López de Jesús Paschal A. Oude Weernink Artur-Aron Weber Karl H. Jakobs Martina Schmidt 《Cellular signalling》2009,21(4):609-621
Signaling by the B cell antigen receptor (BCR) is essential for B lymphocyte homeostasis and immune function. In immature B cells, ligation of the BCR promotes growth arrest and apoptosis, and BCR-driven balancing between pro-apoptotic extracellular signal-regulated kinase 1 and 2 (ERK1/2) and anti-apoptotic phosphoinositide 3-kinase-dependent Akt seems to define the final cellular apoptotic response. Dysfunction of these late BCR signaling events can lead to the development of immunological diseases. Here we report on novel cyclic AMP-dependent mechanisms of BCR-induced growth arrest and apoptosis in the immature B lymphoma cell line WEHI-231. BCR signaling to ERK1/2 and Akt requires cyclic AMP-regulated Epac, the latter acting as a guanine nucleotide exchange factor for Rap1 and H-Ras independent of protein kinase A. Importantly, activation of endogenously expressed Epac by a specific cyclic AMP analog enhanced the induction of growth arrest (reduced DNA synthesis) and apoptosis (nuclear condensation, annexin V binding, caspase-3 cleavage and poly-ADP-ribose polymerase processing) by the BCR. Our data indicate that cyclic AMP-dependent Epac signals to ERK1/2 and Akt upon activation of Rap1 and H-Ras, and is involved in BCR-induced growth arrest and apoptosis in WEHI-231 cells. 相似文献
996.
The thermal dissipation probe was described in the early 1930s for the demonstration of a volume and mass flow of sap in the
conductive elements of the xylem in trees. It was subsequently developed further and is now widely used in physiological ecology
including measurements in the field. Thermal dissipation demonstrates the occurrence of sap flow and allows determination
of its velocity. Here we report simultaneous continuous measurements of sap flow using the thermal dissipation technique and
of transpiration by infrared gas analysis for diurnal and annual cycles in a deciduous and an evergreen oak tree, Quercus robur L. and Quercus turneri Willd., respectively, in a deciduous and an evergreen conifer, Larix decidua Mill. and Pinus griffithii McClell., respectively, and the host/mistletoe consortium of the deciduous linden Tilia mandschurica Rupr. & Max. and the evergreen Viscum album L. We show (1) that in diurnal cycles sap flow closely follows dynamic changes of the rate of transpiration elicited by daily
fluctuations of weather parameters (sunshine, cloudiness, air temperature and humidity), (2) that in annual cycles sap flow
reflects autumnal yellowing and shedding of leaves of the deciduous trees. We report for the first time comparative measurements
of sap flow towards mistletoe shoots and host branches in a parasite/host consortium. This demonstrates (3) that mistletoes
maintain considerably larger sap flow rates in their xylem conduits than the adjacent host branches dragging the transpiration
stream of their host towards their own shoots. We also show (4) that even after the deciduous host has shed its leaves and
itself does not transpire any more the evergreen mistletoe towards its shoots can maintain the persistence of a continuous
sap flow via the stem and branches of the host as long as frost does not prevent that. The work presented underlines the contention
that transpiration is the driving force for sap flow with continuous files of water in the xylem. It shows for the first time
that mistletoes direct the flow of water through host roots and stems towards its own shoots by not only performing stronger
transpiration as it is known from the literature but also by maintaining larger sap flow rates in the xylem conduits of its
stems. 相似文献
997.
Following important donor funding in Tanzania since the 1990s to support community based natural resource management, several cooperation agencies have implemented projects aiming at developing innovative conservation strategies combining protected and sustainable use areas. Based on data gathered in the Katavi Rukwa Lukwati and Ugalla core areas of Western Tanzania, this paper compares and analyses how projects developed their strategy and objectives to address conflicts between local population and conservation agents, and how this led to changes in conservation practices. The projects managed to achieve their objectives in conservation and poverty reduction at various degrees. Enhanced conflict resolution capacity involving private stakeholders, conservation agents and local communities, as well as improved collaboration between projects, helped to solve part of the conflicts. This was the case with the negotiation of rights of access for beekeepers to Rukwa game reserve. However, enduring sector based approaches continue to hinder opportunities for developing multiple use approaches. Contrasted results of the projects can be explained by factors inherent to projects’ planning and management, but also by factors that are beyond projects’ influence such as the historical and contemporary context in terms of governance of natural resources and more globally, of power relationships between the state, private organisations and the communities. 相似文献
998.
Ian K. Dawson Ard Lengkeek John C. Weber Ramni Jamnadass 《Biodiversity and Conservation》2009,18(4):969-986
Tree species in agroforestry ecosystems contribute to the livelihoods of rural communities and play an important role in the conservation of biodiversity. Unless agroforestry landscapes are productive, however, farmers will not maintain or enhance the range and quality of tree species in them, and both income opportunities and biodiversity will be lost. Productivity depends on both tree species diversity and genetic (intra-specific) variation, but research on the latter has until recently not received the recognition it deserves. Worse, when knowledge on tree genetic variation in agroforestry systems has become available, it has not generally been linked in any systematic way with management, indicating a disjunction between research and field-level practice. In this essay, we attempt to bridge this gap by considering three questions: why is genetic diversity important in tree species? What is our current state of knowledge about intra-specific variation in trees in agroforestry systems? And, finally, what practical interventions are possible to support the conservation of this diversity in agricultural landscapes, while enhancing farmers’ livelihoods? A wide genetic base in agroforestry trees is essential to prevent inbreeding depression and allow adaptation to changing environmental conditions and to altering markets for tree products. Recent evidence shows, however, that many species are subject to poor germplasm collection practice, occur at low densities in farmland, and are found in highly aggregated distributions, all of which observations raise concerns about productivity and sustainability. A range of germplasm-access based interventions is necessary to improve current management, including the enhancement of community seed- and seedling-exchange networks, and the development of locally based tree domestication activities. Equally necessary, but more difficult to address, is the development of markets that support genetic diversity in tropical tree species; we discuss approaches by which this may be undertaken. 相似文献
999.
Johanna Weigert Markus Neumeier Josef Wanninger Franziska Schober Daniela Sporrer Markus Weber Andrea Schramm Sylvia Wurm Fabian Stögbauer Michael Filarsky Andreas Schäffler Charalampos Aslanidis Jürgen Schölmerich Christa Buechler 《Cytokine》2009,45(2):86-91
Adiponectin is an adipocyte-derived protein with atheroprotective and immunoregulatory function. Adiponectin and activin A reduce foam cell formation and adiponectin activates the p38 MAPK pathway that is well described to induce activin A. Therefore, it was analyzed whether adiponectin alters activin A in primary human monocytes. Adiponectin dose- and time-dependently induced activin A in the supernatant, and the maximal amount was observed after 12 h of incubation. Adiponectin-stimulated release of activin A was blocked by a p38 MAPK inhibitor. Metformin and pioglitazone are drugs frequently used to treat diabetic patients and metformin slightly reduced monocytic activin A release whereas pioglitazone had no effect. Type 2 diabetes is associated with elevated inflammatory systemic cytokines but activin A serum levels were similar in slim probands, overweight controls and type 2 diabetic patients. Furthermore, activin A did not correlate to systemic adiponectin, body mass index, waist to hip ratio or C-reactive protein. These findings indicate that adiponectin upregulates monocytic activin A release via the p38 MAPK pathway, and this may in part explain the immunoregulatory and antiatherosclerotic effects of this adipokine. 相似文献
1000.