Plant peroxidases : biochemistry and physiology

Resistant (Reba B50) and susceptible (Acala 44) cotton plants were investigated for intratissular growth of bacterial populations and peroxidase (POx) activity, after infection of cotyledons with races 18 or 20 from #Xanthomonas (#Axonopodis$) campestris$ pv. #malvacearum$. Considerable multiplication of the bacterial population was noticed in the compatible interaction (Acala 44 / Xcm race 18) ; it was much lower during the incompatible interaction when race 18 was infiltrated into cotyledons of Reba B50. An intermediate level of bacterial growth was obtained when Reba B50 was infiltrated with race known to overcome resistance of this line. High increase in POx activity occurred into the infected cotyledons during incompatible interaction, while the increase was much lower when the interactions were compatible. On leaves, a similar and significant difference in enzyme activity was also observed indicating that the "peroxidase response" was systemically induced in entire resistant plants. Five isoperoxidases were evidenced by IEF in both lines, whether they were infected or not. But only two of them accounted for the increase in activity in infected resistant cotyledons. Microscopy revealed that POx activity, detected at the infection sites two hours after infiltration of the resistant line was mainly located in cell walls and the middle lamella bordering intercellular spaces. Our data indicate that bacterial infection of cotton plants enhanced the activity of two of the preexistent isoperoxidases in resistant plants and suggest that stimulation of POx activity is associated with resistance mechanisms. (Résumé d'auteur

Flavonoids accumulate in cell walls, middle lamellae and callose-rich papillae during an incompatible interaction between Xanthomonas campestris pv. malvacearum and cotton

Interactions between cotton cotyledons and #Xanthomonas campestris pv. #malvacearum were examined. During an incompatible interaction, fluorescence microscopy revealed that flavonoid compounds accumulated within 10 h after inoculation. Electron micrographs showed ultrastructural modifications of cells that exhibited an intense fluorescence suggesting the presence of flavonoids. Phenol-like molecules were produced by cells of infection sites and were found in paramural areas within papillae enriched with callose and in host cell walls and middle lamellae. Histochemistry showed that peroxidase activity and terpenoids were detected in the infected resistant plants, 4 and 48 h after inoculation, respectively. In contrast, no changes in the deposits of lignin, suberin, and catechin were seen in either the infected susceptible or resistant lines. We suggest that early flavonoid accumulation is associated with the hypersensitive reaction of cotton cotyledons to #X. campestris pv. #malvacearum. The activity of wall-bound peroxidases may play a role in the incorporation of flavonoids in cell walls and paramural papillae. (Résumé d'auteur

The effect of oxygen stoichiometry on electrical transport and magnetic properties of La0.9Te0.1MnOy

The effect of the variation of oxygen content on structural, magnetic and transport properties in the electron-doped manganites La0.9Te0.1MnOy has been investigated. All samples show a rhombohedral structure with the space group . The Curie temperature decreases and the paramagnetic-ferromagnetic (PM-FM) transition becomes broader with the reduction of oxygen content. The resistivity of the annealed samples increases slightly with a small reduction of oxygen content. Further reduction in the oxygen content, the resistivity maximum increases by six orders of magnitude compared with that of the as-prepared sample, and the r(T) curves of samples with y = 2.86 and y = 2.83 display the semiconducting behavior () in both high-temperature PM phase and low-temperature FM phase, which is considered to be related to the appearance of superexchange ferromagnetism (SFM) and the localization of carriers. The results are discussed in terms of the combined effects of the increase in the Mn2+/(Mn2++Mn3+) ratio, the partial destruction of double exchange (DE) interaction, and the localization of carriers due to the introduction of oxygen vacancies in the Mn-O-Mn network.Comment: 20 pages, 8 figure

Observing Supermassive Black Holes across cosmic time: from phenomenology to physics

In the last decade, a combination of high sensitivity, high spatial resolution observations and of coordinated multi-wavelength surveys has revolutionized our view of extra-galactic black hole (BH) astrophysics. We now know that supermassive black holes reside in the nuclei of almost every galaxy, grow over cosmological times by accreting matter, interact and merge with each other, and in the process liberate enormous amounts of energy that influence dramatically the evolution of the surrounding gas and stars, providing a powerful self-regulatory mechanism for galaxy formation. The different energetic phenomena associated to growing black holes and Active Galactic Nuclei (AGN), their cosmological evolution and the observational techniques used to unveil them, are the subject of this chapter. In particular, I will focus my attention on the connection between the theory of high-energy astrophysical processes giving rise to the observed emission in AGN, the observable imprints they leave at different wavelengths, and the methods used to uncover them in a statistically robust way. I will show how such a combined effort of theorists and observers have led us to unveil most of the SMBH growth over a large fraction of the age of the Universe, but that nagging uncertainties remain, preventing us from fully understating the exact role of black holes in the complex process of galaxy and large-scale structure formation, assembly and evolution.Comment: 46 pages, 21 figures. This review article appears as a chapter in the book: "Astrophysical Black Holes", Haardt, F., Gorini, V., Moschella, U and Treves A. (Eds), 2015, Springer International Publishing AG, Cha

Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector

A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results

Jet size dependence of single jet suppression in lead-lead collisions at sqrt(s(NN)) = 2.76 TeV with the ATLAS detector at the LHC

Measurements of inclusive jet suppression in heavy ion collisions at the LHC provide direct sensitivity to the physics of jet quenching. In a sample of lead-lead collisions at sqrt(s) = 2.76 TeV corresponding to an integrated luminosity of approximately 7 inverse microbarns, ATLAS has measured jets with a calorimeter over the pseudorapidity interval |eta| < 2.1 and over the transverse momentum range 38 < pT < 210 GeV. Jets were reconstructed using the anti-kt algorithm with values for the distance parameter that determines the nominal jet radius of R = 0.2, 0.3, 0.4 and 0.5. The centrality dependence of the jet yield is characterized by the jet "central-to-peripheral ratio," Rcp. Jet production is found to be suppressed by approximately a factor of two in the 10% most central collisions relative to peripheral collisions. Rcp varies smoothly with centrality as characterized by the number of participating nucleons. The observed suppression is only weakly dependent on jet radius and transverse momentum. These results provide the first direct measurement of inclusive jet suppression in heavy ion collisions and complement previous measurements of dijet transverse energy imbalance at the LHC.Comment: 15 pages plus author list (30 pages total), 8 figures, 2 tables, submitted to Physics Letters B. All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2011-02

The International Pulsar Timing Array: First data release

International audienceThe highly stable spin of neutron stars can be exploited for a variety of (astro)physical investigations. In particular, arrays of pulsars with rotational periods of the order of milliseconds can be used to detect correlated signals such as those caused by gravitational waves. Three such 'pulsar timing arrays' (PTAs) have been set up around the world over the past decades and collectively form the 'International' PTA (IPTA). In this paper, we describe the first joint analysis of the data from the three regional PTAs, i.e. of the first IPTA data set. We describe the available PTA data, the approach presently followed for its combination and suggest improvements for future PTA research. Particular attention is paid to subtle details (such as underestimation of measurement uncertainty and long-period noise) that have often been ignored but which become important in this unprecedentedly large and inhomogeneous data set. We identify and describe in detail several factors that complicate IPTA research and provide recommendations for future pulsar timing efforts. The first IPTA data release presented here (and available on-line) is used to demonstrate the IPTA's potential of improving upon gravitational-wave limit