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71.
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Phloem flow and sugar transport in Ricinus communis L. is inhibited under anoxic conditions of shoot or roots 下载免费PDF全文
ANDREAS D. PEUKE ARTHUR GESSLER SUSAN TRUMBORE CAREL W. WINDT NATALIA HOMAN EDO GERKEMA HENK VAN AS 《Plant, cell & environment》2015,38(3):433-447
Anoxic conditions should hamper the transport of sugar in the phloem, as this is an active process. The canopy is a carbohydrate source and the roots are carbohydrate sinks. By fumigating the shoot with N2 or flooding the rhizosphere, anoxic conditions in the source or sink, respectively, were induced. Volume flow, velocity, conducting area and stationary water of the phloem were assessed by non‐invasive magnetic resonance imaging (MRI) flowmetry. Carbohydrates and δ13C in leaves, roots and phloem saps were determined. Following flooding, volume flow and conducting area of the phloem declined and sugar concentrations in leaves and in phloem saps slightly increased. Oligosaccharides appeared in phloem saps and after 3 d, carbon transport was reduced to 77%. Additionally, the xylem flow declined and showed finally no daily rhythm. Anoxia of the shoot resulted within minutes in a reduction of volume flow, conductive area and sucrose in the phloem sap decreased. Sugar transport dropped to below 40% by the end of the N2 treatment. However, volume flow and phloem sap sugar tended to recover during the N2 treatment. Both anoxia treatments hampered sugar transport. The flow velocity remained about constant, although phloem sap sugar concentration changed during treatments. Apparently, stored starch was remobilized under anoxia. 相似文献
73.
Gomes AC Miranda I Silva RM Moura GR Thomas B Akoulitchev A Santos MA 《Genome biology》2007,8(10):R206
Background
Genetic code alterations have been reported in mitochondrial, prokaryotic, and eukaryotic cytoplasmic translation systems, but their evolution and how organisms cope and survive such dramatic genetic events are not understood. 相似文献74.
Gingival epithelial cells are part of the first line of host defense against infection. Toll-like receptors (TLRs) serve important immune and nonimmune functions. We investigated how interferon gamma (INF-γ) and interleukin 13 (IL-13) are involved in the TLR4 ligand-induced regulation of interleukin-8 (IL-8) effects on gingival epithelial cells. We used immunohistochemistry to localize TLR4 in ten healthy and ten periodontitis tissue specimens. Gingival epithelial cells then were primed with Th1 cytokine (INF-γ) or Th2 cytokine (IL-13) before stimulation with Escherichia coli-derived lipopolysaccharide (LPS) and enzyme-linked immunosorbent assay (ELISA) was performed to detect the level of IL-8 secretion in cell culture supernatants. Although both healthy and periodontitis gingival tissue samples expressed TLR4, the periodontitis samples showed more intense expression on gingival epithelial cells. Gingival epithelial cell cultures were primed with either INF-γ or IL-13 before stimulation with TLR4 ligand. Supernatants from co-stimulated epithelial cells exhibited IL-8 production in opposite directions, i.e., as one stimulates the release, the other reduces the release. INF-γ significantly increased TLR4 function, whereas IL-13 significantly decreased TLR4 function, i.e., production of IL-8. Pathogen associated molecular pattern-LPS, shared by many different periodonto-pathogenic bacteria, activates the gingival epithelial cells in a TLR-dependent manner. Diminished or increased TLR function in gingival epithelial cells under the influence of different Th cell types may protect or be harmful due to the altered TLR signaling. 相似文献
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One of the most conspicuous and widely analyzed patterns in ecology is the latitudinal gradient in species richness. Over the 200 years since its recognition, several hypotheses have accumulated in order to account for spatial variations in diversity. Geographic variations in seasonality have been repeatedly proposed as a determinant of community richness. However, the geographic structure of community seasonality has not yet been analyzed. In the present work we evaluated three hypotheses that account for variations in the temporal structuring of communities: first, environmental seasonality determines community seasonality; second, community richness determines its degree of structuring; and third, the presence of an increase in species segregation with latitude, reflected in a pattern of species negative co‐occurrence. The hypotheses were evaluated using path analysis on 29 amphibian communities from South America, connecting latitude, environmental conditions, diversity, seasonality, and coexistence structure – nestedness and negative co‐occurrence – within communities. Latitude positively affects community seasonality through an increase in temperature seasonality, but a weak negative direct effect suggests that other variables not considered in the model – such as the strength of biotic interactions – could also be involved. Both latitude and diversity (directly and indirectly) determine an increase in negative co‐occurrence and nestedness. This suggests that groups of species that are mutually nested in time are internally segregated. Further, the strength of this structure is determined by community diversity and latitude. Temporal structuring of a community is associated with latitude and diversity, pointing to the existence of a systematic change in community organization far beyond, but probably interrelated, with the recognized latitudinal trend in richness. The available information and analysis supported the three hypotheses evaluated. 相似文献
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Anja S. Knaupp Shani Keleher Li Yang Weiwen Dai Stephen P. Bottomley Mary C. Pearce 《PloS one》2013,8(1)
α1-Antitrypsin, the archetypal member of the serpin superfamily, is a metastable protein prone to polymerization when exposed to stressors such as elevated temperature, low denaturant concentrations or through the presence of deleterious mutations which, in a physiological context, are often associated with disease. Experimental evidence suggests that α1-Antitrypsin can polymerize via several alternative mechanisms in vitro. In these polymerization mechanisms different parts of the molecule are proposed to undergo conformational change. Both strand 5 and helix I are proposed to adopt different conformations when forming the various polymers, and possess a number of highly conserved residues however their role in the folding and misfolding of α1-Antitrypsin has never been examined. We have therefore created a range of α1Antitypsin variants in order to explore the role of these conserved residues in serpin folding, misfolding, stability and function. Our data suggest that key residues in helix I mediate efficient folding from the folding intermediate and residues in strand 5A ensure native state stability in order to prevent misfolding. Additionally, our data indicate that helix I is involved in the inhibitory process and that both structural elements undergo differing conformational rearrangements during unfolding and misfolding. These findings suggest that the ability of α1-Antitrypsin to adopt different types of polymers under different denaturing conditions may be due to subtle conformational differences in the transiently populated structures adopted prior to the I and M* states. 相似文献
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JOSÉ ARTURO ALCÁNTARA‐RODRÍGUEZ JORGE CIROS‐PÉREZ ELIZABETH ORTEGA‐MAYAGOITIA CARMEN R. SERRANIA‐SOTO ELÍAS PIEDRA‐IBARRA 《Freshwater Biology》2012,57(4):728-740
1. Salinity is a strong selective force for many aquatic organisms, affecting both ecological and evolutionary processes. Most of our knowledge on the effects of salinity on rotifers in the Brachionus plicatilis species complex is based mainly on populations from waterbodies that experience broad environmental changes both seasonally and annually. We tested the hypothesis that, despite the supposedly high potential for gene flow among rotifers inhabiting neighbouring environments, constant salinity has promoted local adaptation, genetic population divergence and even cryptic speciation in B. plicatilis complex populations from three deep maar lakes of distinct salinities [1.1, 6.5 and 9.0 g L?1 total dissolved solids (TDS)] in Central Mexico. 2. To look for local adaptation, we performed common garden experiments to test the effect of different salinities on population density and intrinsic growth rate (r). Then, we evaluated the genetic divergence by sequencing the cytochrome c oxidase subunit I (COI) gene and performed reproductive trials to assess the potential gene flow among the three populations and with other closely related B. plicatilis complex species. 3. We confirmed that the rotifer populations have phenotypic plasticity in tolerance of salinity, but only rotifers from the least saline lake are adapted to low salinity. Among the populations, sequence divergence at COI was very low (just a single haplotype was found), suggesting a persistent founder effect from a relatively recent single colonisation event and a subsequent dispersal from one lake to the others, and a very restricted immigration rate. In the phylogenetic analysis, rotifers from this area of Mexico clustered in the same clade with the middle‐sized species Brachionus ibericus and B. sp. ‘Almenara’. Mexican rotifers showed successful recognition, copulation and formation of hybrids among them, but interpopulation breeding with the Spanish B. ibericus and B. sp. ‘Almenara’ was unsuccessful. 4. We conclude that the B. plicatilis complex populations from these three lakes belong to a new biological species not yet described (presently named B. sp. ‘Mexico’). To our knowledge, this is the first report of local adaptation of a natural B. plicatilis complex population living in freshwater conditions (1.1 g L?1 TDS). 相似文献
80.