A Model Analysis of Mechanisms for Radial Microtubular Patterns at Root Hair Initiation Sites

Plant cells have two main modes of growth generating anisotropic structures. Diffuse growth where whole cell walls extend in specific directions, guided by anisotropically positioned cellulose fibers, and tip growth, with inhomogeneous addition of new cell wall material at the tip of the structure. Cells are known to regulate these processes via molecular signals and the cytoskeleton. Mechanical stress has been proposed to provide an input to the positioning of the cellulose fibers via cortical microtubules in diffuse growth. In particular, a stress feedback model predicts a circumferential pattern of fibers surrounding apical tissues and growing primordia, guided by the anisotropic curvature in such tissues. In contrast, during the initiation of tip growing root hairs, a star-like radial pattern has recently been observed. Here, we use detailed finite element models to analyze how a change in mechanical properties at the root hair initiation site can lead to star-like stress patterns in order to understand whether a stress-based feedback model can also explain the microtubule patterns seen during root hair initiation. We show that two independent mechanisms, individually or combined, can be sufficient to generate radial patterns. In the first, new material is added locally at the position of the root hair. In the second, increased tension in the initiation area provides a mechanism. Finally, we describe how a molecular model of Rho-of-plant (ROP) GTPases activation driven by auxin can position a patch of activated ROP protein basally along a 2D root epidermal cell plasma membrane, paving the way for models where mechanical and molecular mechanisms cooperate in the initial placement and outgrowth of root hairs.This work was funded by the Knut and Alice Wallenberg Foundation via grant ShapeSystems (KAW 2012.0050) to MG and HJ, the Swedish Research Council (VR2013-4632) to HJ, and the Gatsby Charitable Foundation (GAT3395/PR4) to HJ

Construction, gene delivery, and expression of DNA tethered nanoparticles

PURPOSE: Layered nanoparticles have the potential to deliver any number of substances to cells both in vitro and in vivo. The purpose of this study was to develop and test a relatively simple alternative to custom synthesized nanoparticles for use in multiple biological systems, with special focus on the eye. METHODS: The biotin-labeled transcriptionally active PCR products (TAP) were conjugated to gold, semiconductor nanocrystals, and magnetic nanoparticles (MNP) coated with streptavidin. The process of nanoparticle construction was monitored with gel electrophoresis. Fluorescence microscopy followed by image analysis was used to examine gene expression levels from DNA alone and tethered MNP in human hepatoma derived Huh-7 cells. Adult retinal endothelial cells from both dog (ADREC) and human (HREC) sources were transfected with nanoparticles and reporter gene expression evaluated with confocal and fluorescent microscopy. Transmission electron microscopy was used to quantify the concentration of nanoparticles in a stock solution. Nanoparticles were evaluated for transfection efficiency, determined by fluorescence microscopy cell counts. Cells treated with MNP were evaluated for increased reactive oxygen species (ROS) and necrosis with flow cytometry. RESULTS: Both 5' and 3' biotin-labeled TAP bound equally to MNP and there were no differences in functionality between the two tethering orientations. Free DNA was easily removed by the use of magnetic columns. These particles were also able to deliver genes to a human hepatoma cell line, Huh-7, but transfection efficiency was greater than TAP. The semiconductor nanocrystals and MNP had the highest transfection efficiencies. The MNP did not induce ROS formation or necrosis after 48 h of incubation. CONCLUSIONS: Once transfected, the MNP had reporter gene expression levels equivalent to TAP. The nanoparticles, however, had better transfection efficiencies than TAP. The magnetic nanoparticles were the most easily purified of all the nanoparticles tested. This strategy for bioconjugating TAP to nanoparticles is valuable because nanoparticle composition can be changed and the system optimized quickly. Since endothelial cells take up MNP, this strategy could be used to target neovascularization as occurs in proliferative retinopathies. Multiple cell types were used to test this technology and in each the nanoparticles were capable of transfection. In adult endothelial cells the MNP appeared innocuous, even at the highest doses tested with respect to ROS and necrosis. This technology has the potential to be used as more than just a vector for gene transfer, because each layer has the potential to perform its own unique function and then degrade to expose the next functional layer

Highlights from the Pierre Auger Observatory

The Pierre Auger Observatory is the world's largest cosmic ray observatory. Our current exposure reaches nearly 40,000 km$^2$ str and provides us with an unprecedented quality data set. The performance and stability of the detectors and their enhancements are described. Data analyses have led to a number of major breakthroughs. Among these we discuss the energy spectrum and the searches for large-scale anisotropies. We present analyses of our X$_{max}$ data and show how it can be interpreted in terms of mass composition. We also describe some new analyses that extract mass sensitive parameters from the 100% duty cycle SD data. A coherent interpretation of all these recent results opens new directions. The consequences regarding the cosmic ray composition and the properties of UHECR sources are briefly discussed.Comment: 9 pages, 12 figures, talk given at the 33rd International Cosmic Ray Conference, Rio de Janeiro 201

The Pierre Auger Observatory III: Other Astrophysical Observations

Astrophysical observations of ultra-high-energy cosmic rays with the Pierre Auger ObservatoryComment: Contributions to the 32nd International Cosmic Ray Conference, Beijing, China, August 201

Update on the correlation of the highest energy cosmic rays with nearby extragalactic matter

Data collected by the Pierre Auger Observatory through 31 August 2007 showed evidence for anisotropy in the arrival directions of cosmic rays above the Greisen-Zatsepin-Kuz'min energy threshold, \nobreak{$6\times 10^{19}$eV}. The anisotropy was measured by the fraction of arrival directions that are less than $3.1^\circ$ from the position of an active galactic nucleus within 75 Mpc (using the V\'eron-Cetty and V\'eron $12^{\rm th}$ catalog). An updated measurement of this fraction is reported here using the arrival directions of cosmic rays recorded above the same energy threshold through 31 December 2009. The number of arrival directions has increased from 27 to 69, allowing a more precise measurement. The correlating fraction is $(38^{+7}_{-6})$, compared with $21$ expected for isotropic cosmic rays. This is down from the early estimate of $(69^{+11}_{-13})$. The enlarged set of arrival directions is examined also in relation to other populations of nearby extragalactic objects: galaxies in the 2 Microns All Sky Survey and active galactic nuclei detected in hard X-rays by the Swift Burst Alert Telescope. A celestial region around the position of the radiogalaxy Cen A has the largest excess of arrival directions relative to isotropic expectations. The 2-point autocorrelation function is shown for the enlarged set of arrival directions and compared to the isotropic expectation.Comment: Accepted for publication in Astroparticle Physics on 31 August 201

Atmospheric effects on extensive air showers observed with the Surface Detector of the Pierre Auger Observatory

Atmospheric parameters, such as pressure (P), temperature (T) and density, affect the development of extensive air showers initiated by energetic cosmic rays. We have studied the impact of atmospheric variations on extensive air showers by means of the surface detector of the Pierre Auger Observatory. The rate of events shows a ~10% seasonal modulation and ~2% diurnal one. We find that the observed behaviour is explained by a model including the effects associated with the variations of pressure and density. The former affects the longitudinal development of air showers while the latter influences the Moliere radius and hence the lateral distribution of the shower particles. The model is validated with full simulations of extensive air showers using atmospheric profiles measured at the site of the Pierre Auger Observatory.Comment: 24 pages, 9 figures, accepted for publication in Astroparticle Physic

A search for point sources of EeV photons

Measurements of air showers made using the hybrid technique developed with the fluorescence and surface detectors of the Pierre Auger Observatory allow a sensitive search for point sources of EeV photons anywhere in the exposed sky. A multivariate analysis reduces the background of hadronic cosmic rays. The search is sensitive to a declination band from -85{\deg} to +20{\deg}, in an energy range from 10^17.3 eV to 10^18.5 eV. No photon point source has been detected. An upper limit on the photon flux has been derived for every direction. The mean value of the energy flux limit that results from this, assuming a photon spectral index of -2, is 0.06 eV cm^-2 s^-1, and no celestial direction exceeds 0.25 eV cm^-2 s^-1. These upper limits constrain scenarios in which EeV cosmic ray protons are emitted by non-transient sources in the Galaxy.Comment: 28 pages, 10 figures, accepted for publication in The Astrophysical Journa

Europeanisation should meet international constructivism: the Nordic Plus group and the internalisation of political conditionality by France and the United Kingdom

This article is a plausibility probe for the significance of international constructivist ‘mediating factors’ to explain variation in Europeanisation outcomes. It applies a most similar systems design (or Mill's method of difference) to show that the UK has internalised political conditionality to a larger extent than France at least partially because it has been the object of stronger socialisation pressures within the ‘Nordic Plus’ group. The article contributes to the literature on Europeanisation and development cooperation in two important ways. First, it enlarges its scope of analysis, both geographically (beyond new European Union member states) and thematically (beyond simple measures of aid quality and/or quantity). Second, it emphasises the importance of international (versus domestic) mediating factors. The empirical analysis focusses on three cases of aid sanctions in response to human rights abuses and democratic setbacks: Zimbabwe 2002, Madagascar 2009 and Mozambique 2009