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Institution

University of Fribourg

EducationFribourg, Freiburg, Switzerland
About: University of Fribourg is a education organization based out in Fribourg, Freiburg, Switzerland. It is known for research contribution in the topics: Population & Glacier. The organization has 6040 authors who have published 14975 publications receiving 542500 citations. The organization is also known as: UNIFR & Universität Freiburg.


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Journal ArticleDOI
TL;DR: The existing techniques to measure and compute the fractal dimension df are critically discussed based on the cases of organic/inorganic particles and proteins, pointing out the most recent literature findings and the limitations of the current understanding.

127 citations

Journal ArticleDOI
TL;DR: Analysis of leaf lipid composition during the Arabidopsis thaliana-Pseudomonas syringae interaction found that accumulation of the phytosterol stigmasterol is a significant plant metabolic process that occurs upon bacterial leaf infection.
Abstract: Upon inoculation with pathogenic microbes, plants induce an array of metabolic changes that potentially contribute to induced resistance or even enhance susceptibility. When analysing leaf lipid composition during the Arabidopsis thaliana-Pseudomonas syringae interaction, we found that accumulation of the phytosterol stigmasterol is a significant plant metabolic process that occurs upon bacterial leaf infection. Stigmasterol is synthesized from beta-sitosterol by the cytochrome P450 CYP710A1 via C22 desaturation. Arabidopsis cyp710A1 mutant lines impaired in pathogen-inducible expression of the C22 desaturase and concomitant stigmasterol accumulation are more resistant to both avirulent and virulent P. syringae strains than wild-type plants, and exogenous application of stigmasterol attenuates this resistance phenotype. These data indicate that induced sterol desaturation in wild-type plants favours pathogen multiplication and plant susceptibility. Stigmasterol formation is triggered through perception of pathogen-associated molecular patterns such as flagellin and lipopolysaccharides, and through production of reactive oxygen species, but does not depend on the salicylic acid, jasmonic acid or ethylene defence pathways. Isolated microsomal and plasma membrane preparations exhibited a similar increase in the stigmasterol/beta-sitosterol ratio as whole-leaf extracts after leaf inoculation with P. syringae, indicating that the stigmasterol produced is incorporated into plant membranes. The increased contents of stigmasterol in leaves after pathogen attack do not influence salicylic acid-mediated defence signalling but attenuate pathogen-induced expression of the defence regulator flavin-dependent monooxygenase 1. P. syringae thus promotes plant disease susceptibility through stimulation of sterol C22 desaturation in leaves, which increases the stigmasterol to beta-sitosterol ratio in plant membranes.

127 citations

Journal ArticleDOI
TL;DR: Endogenous calcium binding ratios in dendrites of cultured hippocampal neurons were estimated according to the single compartment model for transients in intracellular Ca2+ concentration, and there was no significant difference in κS between the groups classified according to firing patterns.
Abstract: Endogenous calcium binding ratios (κS) in dendrites of cultured hippocampal neurons were estimated according to the single compartment model for transients in intracellular Ca2+ concentration ([Ca2+]). In addition, the electrophysiological characteristics of neurons were classified by their autaptic currents and intrinsic firing patterns. These data were analysed in order to determine whether a correlation between Ca2+ buffers and electrophysiological type exists. Ca2+ binding ratios of endogenous buffers were estimated by eliciting [Ca2+] transients with short depolarizations, while cells were loaded with fura-2. Two types of estimates could be obtained: one termed κS(τ), based on analysing time constants (τ) of [Ca2+] transients, and another termed κS(dCa), derived from an analysis of initial amplitudes of [Ca2+] transients. Values for κS(τ) and κS(dCa) were estimated as 57 ± 10 (mean ±s.d., n = 10) and 60 ± 14 (n = 10), respectively, in excitatory neurons, and 130 ± 50 (n = 11) and 150 ± 70 (n = 11), respectively, in inhibitory neurons. The κS values of excitatory and inhibitory cells were significantly different from each other, regardless of the measurement method (Student's t test, P < 0.01). However, there was no significant difference in κS between the groups classified according to firing patterns. Although κS(τ) values were well matched to those of κS(dCa) in most excitatory cells, the two values did not agree in three out of the fourteen inhibitory cells investigated. In these cells, the first few [Ca2+] transients after obtaining the whole cell configuration displayed a double exponential decay, suggesting that buffers with slow binding kinetics, such as parvalbumin, are involved. This hypothesis is further explored in an accompanying paper. Spatial and temporal fine tuning of the intracellular Ca2+ level ([Ca2+]i) allows Ca2+ to serve a multitude of cellular functions as a second messenger. The spatio-temporal extent of the [Ca2+]i increase upon perturbation from its resting levels is largely determined by calcium influx channels, extrusion mechanisms, and calcium buffers. Within a given calcium flux system, calcium buffers have profound effects on the amplitude of [Ca2+] transients, the diffusional range, and the relaxation time constant of these signals. Lumped Ca2+ intracellular buffer capacity can be quantified by measuring the differential increment of Ca2+ bound buffer divided by the free calcium increase (the calcium binding ratio, κ) using the single compartment model (Neher & Augustine, 1992; Helmchen et al. 1996). Such measurements have been described for chromaffin cells (Neher & Augustine, 1992), somata of cerebellar Purkinje neurons (Fierro & Llano, 1996), dendrites of pyramidal neurons in cerebral cortex (Helmchen et al. 1996), and motoneurons (Lips & Keller, 1998). Considerable differences in endogenous calcium binding ratios (κS), as estimated in these different types of neurons, prompted us to survey κS in hippocampal neurons and to attempt a correlation between this quantity and their electrophysiological characteristics. Hippocampal neurons cultured in low density offer an excellent model system, in which inhibitory and excitatory cells can be readily identified based on the type of autaptic current (Bekkers & Stevens, 1991), thereby allowing unambiguous comparison of Ca2+ dynamics between inhibitory and excitatory cells.

127 citations

Journal ArticleDOI
TL;DR: A new technique based on a sandwich of two scattering cells aimed to overcome the problem of nonergodicity in DWS of solidlike systems is presented, obtaining quantitative information about the microscopic dynamics all the way from an aggregating suspension to the final gel, thereby covering the whole sol-gel transition.
Abstract: Diffusing-wave spectroscopy (DWS) was used to follow the sol-gel transition of concentrated colloidal suspensions. We present a new technique based on a sandwich of two scattering cells aimed to overcome the problem of nonergodicity in DWS of solidlike systems. Using this technique we obtain quantitative information about the microscopic dynamics all the way from an aggregating suspension to the final gel, thereby covering the whole sol-gel transition. At the gel point a dramatic change of the particle dynamics from diffusion to a subdiffusive arrested motion is observed. A critical-power-law behavior is found for the time evolution of the maximum mean square displacement delta(2) probed by a single particle in the gel.

127 citations

Journal ArticleDOI
TL;DR: A nanoscale turbine wheel is an apt description of the structure of the enantiomerically pure helicate, which precipitates as PF6 salt on mixing dissolved AgPF6 with the ligand L2 (a bis-bidentate ligand comprising two condensed α-pinene/bipyridine units linked by a xylylene bridge).
Abstract: A nanoscale turbine wheel is an apt description of the structure of the enantiomerically pure helicate [Ag6 (L2)6 ]6+ (1), which precipitates as PF6 salt on mixing dissolved AgPF6 with the ligand L2 (a bis-bidentate ligand comprising two condensed α-pinene/bipyridine units linked by a xylylene bridge). The helicate has an outer diameter of about 3 nm and an inner diameter of 0.84 nm, and is a potential model for the study of stereospecific recognition processes.

127 citations


Authors

Showing all 6204 results

NameH-indexPapersCitations
Jens Nielsen1491752104005
Sw. Banerjee1461906124364
Hans Peter Beck143113491858
Patrice Nordmann12779067031
Abraham Z. Snyder12532991997
Csaba Szabó12395861791
Robert Edwards12177574552
Laurent Poirel11762153680
Thomas Münzel116105557716
David G. Amaral11230249094
F. Blanc107151458418
Markus Stoffel10262050796
Vincenzo Balzani10147645722
Enrico Bertini9986538167
Sandeep Kumar94156338652
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Performance
Metrics
No. of papers from the Institution in previous years
YearPapers
202367
2022348
20211,110
20201,112
2019966
2018924