Étude des relations source/puits de carbone dans la symbiose endomycorhizienne à arbuscules

Tableau d'honneur de la Faculté des études supérieures et postdoctorales, 2002-2003Les relations source/puits de carbone (C) dans la symbiose mycorhizienne à arbuscules (MA) ont été examinées sous différents aspects. Une première partie éco-physiologique rapporte l’existence d’échanges de C entre espèces végétales en conditions naturelles via des champignons MA répondant à la phénologie différente des plantes impliquées. Deux études physiologiques basées sur le système de «split-root» ont montré que la force de puits de C des champignons MA est dépendante de l’espèce fongique, de la souche fongique, ainsi que de l’hôte végétal. Enfin, une étude écologique se positionnant dans un contexte de perturbation naturelle (verglas) endommageant le houppier d’arbres matures a révélé qu’une mauvaise reprise de croissance post-traumatique peut être associée à des taux de mycorhization racinaire plus élevés que ceux d’arbres à bonne reprise de croissance. En résumé, les besoins en C des champignons MA varient en fonction des espèces impliquées dans la symbiose et du stade phénologique de chacune d’elles.Different aspects of the carbon (C) source-sink relationships in the arbuscular mycorrhizal (AM) symbiosis were investigated. In an initial ecophysiological-based study carried under natural conditions, the existence of AM fungal mediated C exchanges between plant species with different phenology was reported. Two physiological studies based on a split-root system showed the C sink strength of AM fungi to be fungal species, fungal strain and plant species dependent. Finally, an ecological study carried out subsequently to the ice storm of 1998 (natural disturbance) which severely damaged mature tree crowns revealed that poor post-traumatic crown regrowth was associated with higher mycorrhizal colonization levels than in good regrowth trees. In conclusion, the C demand of AM fungi varies with the species involved in the symbiosis and with the phenological stage and health of the phytobiont

Suppression of arbuscular mycorrhizal colonization and nodulation in split‐root systems of alfalfa after pre‐inoculation and treatment with Nod factors

Roots of legumes establish symbiosis with arbuscular mycorrhizal fungi (AMF) and nodule‐inducing rhizobia. The existing nodules systemically suppress subsequent nodule formation in other parts of the root, a phenomenon termed autoregulation. Similarly, mycorrhizal roots reduce further AMF colonization on other parts of the root system. In this work, split‐ root systems of alfalfa (Medicago sativa) were used to study the autoregulation of symbiosis with Sinorhizobium meliloti and the mycorrhizal fungus Glomus mosseae. It is shown that nodulation systemically influences AMF root colonization and vice versa. Nodules on one half of the split‐root system suppressed subsequent AMF colonization on the other half. Conversely, root systems pre‐colonized on one side by AMF exhibited reduced nodule formation on the other side. An inhibition effect was also observed with Nod factors (lipo‐chito‐oligosaccharides). NodSm‐IV(C16:2, S) purified from S. meliloti systemically suppressed both nodule formation and AMF colonization. The application of Nod factors, however, did not influence the allocation of 14C within the split‐root system, excluding competition for carbohydrates as the regulatory mechanism. These results indicate a systemic regulatory mechanism in the rhizobial and the arbuscular mycorrhizal association, which is similar in both symbiose

Boron Laser Doping through High Quality Al2O3 Passivation Layer for Localized B-BSF PERL Solar Cells

AbstractA new doping process is investigated by using Excimer Laser Annealing (ELA) on various Atomic Layer Deposition (ALD)-Al2O3/PECVD-SiNx(B) passivation stack. In a first part the passivation quality of dielectric stacks is investigated on lowly doped p-type Si substrate. Similar passivation level is highlighted with Boron containing SiNx as compared to un-doped SiNx layer when a thin interfacial Al2O3 layer is first deposited on silicon.In a second part laser doping of the silicon substrate is highlighted by sheet resistance (Rsh) decrease. Pulse energy and pulse number influence the diffusion of Boron and Aluminum atoms from the dielectric stack into the silicon. Electro Chemical Voltage (ECV) profiles confirmed p+ region formation. XPS analysis confirmed the presence of both doping atoms in the p+ region. It is suggested that Al is rather bonded to N and O than to Si atoms while B plays a major role in the doping mechanism of the Si lattice

Ebola: should we consider influenza vaccination?

International audienc

Effect of vitamin C on prevention of complex regional pain syndrome type I in foot and ankle surgery

BACKGROUND: The public health cost impact of complex regional pain syndrome type I (CRPS I) is considerable in both emergency and scheduled orthopaedic surgery. We proposed to assess the effectiveness of vitamin C in prevention of CRPS I in foot and ankle surgery. METHODS: We carried out a "before-after" quasi-experimental study comparing two chronologically successive groups without (Group I: July 2002-June 2003) and with (Group II: July 2003-June 2004) preventive 1g daily vitamin C treatment. All patients having surgery on the foot or ankle were enrolled, with the exception of diabetic foot cases. Several factors were analysed: sex, age, type of pathology, history of CRPS I, psychological context, tourniquet time, and cast immobilisation time. RESULTS: 420 feet (392 patients) were included in the study: 185 in Group I, 235 in Group II. CRPS I occurred in 18 cases in Group I (9.6%) and 4 cases in Group II (1.7%) (p<10(-4)), with history of CRPS I as a significantly correlated factor (relative risk=10.4). The psychological context (anxio-depressive state) showed a (sub-significant) tendency to increase the risk of CRPS I (relative risk=2.6). CONCLUSION: Vitamin C has been shown to be effective in preventing CRPS I secondary to wrist fracture, but few data are available with respect to foot and ankle cases. The present study demonstrates the effectiveness of vitamin C in preventing CRPS I of the foot and ankle-a frequent complication in our control group (9.6%). The authors recommend preventive management by vitamin C