A molecular mechanosensor for real-time visualization of appressorium membrane tension in Magnaporthe oryzae

The rice blast fungus Magnaporthe oryzae uses a pressurized infection cell called an appressorium to drive a rigid penetration peg through the leaf cuticle. The vast internal pressure of an appressorium is very challenging to investigate, leaving our understanding of the cellular mechanics of plant infection incomplete. Here, using fluorescence lifetime imaging of a membrane-targeting molecular mechanoprobe, we quantify changes in membrane tension in M. oryzae. We show that extreme pressure in the appressorium leads to large-scale spatial heterogeneities in membrane mechanics, much greater than those observed in any cell type previously. By contrast, non-pathogenic melanin-deficient mutants, exhibit low spatially homogeneous membrane tension. The sensor kinase ∆sln1 mutant displays significantly higher membrane tension during inflation of the appressorium, providing evidence that Sln1 controls turgor throughout plant infection. This non-invasive, live cell imaging technique therefore provides new insight into the enormous invasive forces deployed by pathogenic fungi to invade their hosts, offering the potential for new disease intervention strategies

Formation and structure of ionomer complexes from grafted polyelectrolytes

We discuss the structure and formation of Ionomer Complexes formed upon mixing a grafted block copolymer (poly(acrylic acid)-b-poly(acrylate methoxy poly(ethylene oxide)), PAA21-b-PAPEO14) with a linear polyelectrolyte (poly(N-methyl 2-vinyl pyridinium iodide), P2MVPI), called grafted block ionomer complexes (GBICs), and a chemically identical grafted copolymer (poly(acrylic acid)-co-poly(acrylate methoxy poly(ethylene oxide)), PAA28-co-PAPEO22) with a linear polyelectrolyte, called grafted ionomer complexes (GICs). Light scattering measurements show that GBICs are much bigger (~70–100 nm) and GICs are much smaller or comparable in size (6–22 nm) to regular complex coacervate core micelles (C3Ms). The mechanism of GICs formation is different from the formation of regular C3Ms and GBICs, and their size depends on the length of the homopolyelectrolyte. The sizes of GBICs and GICs slightly decrease with temperature increasing from 20 to 65 °C. This effect is stronger for GBICs than for GICs, is reversible for GICs and GBIC-PAPEO14/P2MVPI228, and shows some hysteresis for GBIC-PAPEO14/P2MVPI43. Self-consistent field (SCF) calculations for assembly of a grafted block copolymer (having clearly separated charged and grafted blocks) with an oppositely charged linear polyelectrolyte of length comparable to the charged copolymer block predict formation of relatively small spherical micelles (~6 nm), with a composition close to complete charge neutralization. The formation of micellar assemblies is suppressed if charged and grafted monomers are evenly distributed along the backbone, i.e., in case of a grafted copolymer. The very large difference between the sizes found experimentally for GBICs and the sizes predicted from SCF calculations supports the view that there is some secondary association mechanism. A possible mechanism is discussed

Synthesis and characterization of PY2- and TPA-appended diphenylglycoluril receptors and their bis-Cu-I complexes

Contains fulltext : 35327.pdf (postprint version ) (Open Access

Solvent developments for liquid-liquid extraction of carboxylic acids in perspective

The growing desire to produce organic acids through fermentative routes, as a starting point for bio-based plastics, has revived the scientific attention on carboxylic acid removal from aqueous streams. One of the main technologies to recover carboxylic acids from diluted aqueous streams is liquid-liquid extraction (LLX). In this review, solvent developments for LLX of carboxylic acids are reviewed. In the past decades, a significant number of research papers have appeared, describing completely new solvents such as ionic liquids, as well as improvements of the traditional state-of-the-art solvent systems comprising of amines and organophosphorous extractants in diluents. The state-of-the-art technology for acid extractions has long been using trioctylamine (TOA) — or Alamine 336, a commercial mixture of trialkyl amines — as the complexating agent. However, with dropping acid concentrations, the economic feasibility of the TOA-based processes is compromised. This review discusses three main categories of solvents, i.e. composite solvents containing nitrogen-based extractants, phosphorous-based extractants and ionic liquids, and includes a discussion on solvent property models that may aid solvent selection. Furthermore, regeneration strategies are discussed, aiming to provide direction towards regenerations that do not further dilute streams that are already diluted before the LLX process. The main conclusion with respect to solvent regeneration when back-extraction is applied, is that solvent-swing strategies should be applied that maximize the ratio between the acid distribution coefficient in the forward extraction and the distribution coefficient in the back-extraction at minimal energy cost. This appears to be through evaporation of part of the diluent after the primary extraction

Thermally-activated delayed failure in heterogeneous solids : An experimental model system

Many pervasive construction materials, including wood, paper, plastics and concrete, exhibit creep when subjected to stresses below the yield stress. This can lead to catastrophic failure at prolonged, moderate loads. Remarkably, the creep response of these dissimilar materials shares at least two important features: First, the average time-to-failure decreases exponentially with the applied stress. This suggests that a stress-enhanced, thermally-activated process governs the creep. Secondly, the variability of the time-to-failure between samples is huge, which is usually attributed to their stochastic microstructures. Owing to the strong molecular bonds between the constituents of typical construction materials, they creep slowly, and the time-to-failure under typical loading conditions can be very long, which is experimentally challenging. Therefore, we consider an experimental model system for studying the thermally-activated, delayed failure. Weakly attractive colloidal particles in suspension form a sample-spanning network with the low-frequency mechanical response of an elastic solid. This material is a statistically homogeneous, hierarchically structured solid, with two distinct length-scales: that of the particles and that of the filaments. The interaction potential between the particles is controlled in this system, so that the thermally-activated remodeling of the material operates on experimental time-scales. The creep response of the colloidal gel is investigated in simple shear, using a stress-controlled rheometer. For each constant shear stress, the shear strain is measured as a function of time. After an initial elastic deformation, the material deforms slowly at an essentially constant rate. After a time-delay, the material fails abruptly. This delay time decreases exponentially with the applied stress. Moreover, if the gel is made anisotropic by applying a high rate pre-shear, the delay time is reduced, and two regimes appear with different exponential factors. It is hypothesized that the initial creep is governed by a distributed, stochastic failure process, which preserves the statistical homogeneity of the sample. This slow process is followed by avalanching critical crack growth and failure. The time-to-failure is dominated by the initial process, which can be model using mean-field theory, by virtue of the assumed statistical homogeneity. In this model, the stress-enhanced dissociation dynamics of individual particle bonds are related to the stochastic fracture of strands, which, in turn, are govern the delay time of the macroscopic failure.</p