Etudes des déterminants moléculaires impliqués dans la capacité de transmission d'Alternaria brassicicola aux semences d'Arabidopsis thaliana

Seed transmission is one on the most efficient way for fungal pathogens to survive and ensure their dispersal. On the other hand, contaminated seeds are compromised on their germination and survival capacities. Hence, we aimed at identifying molecular mechanisms involved in the transmission abilities of seed-borne fungi using the model pathosystem based on Alternaria brassicicola and Arabidopsis thaliana. We analyzed the response of A. brassicicola to various in vitro and in vivo conditions: stress induced by Brassicaceous defenses metabolites (camalexin, brassinin and isothiocyanates), stress related to a water deficiency (desiccation, sorbitol and PEG) and stress occurring during seed colonization through siliques. Concerning the first type of stress, we showed that indolic phytoalexins probably target mitochondria as revealed by altered respiration and mitochondrial membrane potential after short time exposures. Our analyses also revealed that the fungal response to water stress involved hydrophilins-like and eisosomal proteins. We showed that the expression of most of these proteins was dependent of at least one of the three protein kinases AbSch9, AbNik1 and AbHog1. Finally, our in planta analysis revealed an unexpected possible role of chromatin remodeling mechanisms in the regulation of fungal genes expression during seed transmission

Reorientation Transition in Single-Domain (Ga,Mn)As

We demonstrate that the interplay of in-plane biaxial and uniaxial anisotropy fields in (Ga,Mn)As results in a magnetization reorientation transition and an anisotropic AC susceptibility which is fully consistent with a simple single domain model. The uniaxial and biaxial anisotropy constants vary respectively as the square and fourth power of the spontaneous magnetization across the whole temperature range up to T_C. The weakening of the anisotropy at the transition may be of technological importance for applications involving thermally-assisted magnetization switching.Comment: 4 pages, 4 figure

DC-transport properties of ferromagnetic (Ga,Mn)As semiconductors

We study the dc transport properties of (Ga,Mn)As diluted magnetic semiconductors with Mn concentration varying from 1.5% to 8%. Both diagonal and Hall components of the conductivity tensor are strongly sensitive to the magnetic state of these semiconductors. Transport data obtained at low temperatures are discussed theoretically within a model of band-hole quasiparticles with a finite spectral width due to elastic scattering from Mn and compensating defects. The theoretical results are in good agreement with measured anomalous Hall effect and anisotropic longitudinal magnetoresistance data. This quantitative understanding of dc magneto-transport effects in (Ga,Mn)As is unparalleled in itinerant ferromagnetic systems.Comment: 3 pages, 3 figure

Search For Hole Mediated Ferromagnetism In Cubic (Ga,Mn)N

Results of magnetisation measurements on p-type zincblende-(Ga,Mn)N are reported. In addition to a small high temperature ferromagnetic signal, we detect ferromagnetic correlation among the remaining Mn ions, which we assign to the onset of hole-mediated ferromagnetism in (Ga,Mn)N.Comment: 2 pages, 1 figure, proc. ICPS 27, Flagstaff '0