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61.
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
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Background
Benchmarking algorithms in structural bioinformatics often involves the construction of datasets of proteins with given sequence and structural properties. The SCOP database is a manually curated structural classification which groups together proteins on the basis of structural similarity. The ASTRAL compendium provides non redundant subsets of SCOP domains on the basis of sequence similarity such that no two domains in a given subset share more than a defined degree of sequence similarity. Taken together these two resources provide a 'ground truth' for assessing structural bioinformatics algorithms. We present a small and easy to use API written in python to enable construction of datasets from these resources. 相似文献65.
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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Cadmium toxicity in Nostoc UAM208: protection by calcium 总被引:1,自引:0,他引:1
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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