Conséquences esthétiques du traitement de la classe II : étude comparative Distal Active Concept (DAC)/Forces Extra-Buccales (FEB)

Les thérapeutiques orthodontiques fréquemment utilisées dans le passé tendaient à corriger les malocclusions de classe II en freinant la croissance squelettique par l’utilisation de tractions extra-orales ; la démarche actuelle réduit l’emploi de tractions sur le maxillaire et s’oriente vers une stimulation de la croissance mandibulaire. Cette différence d’approche thérapeutique se répercute-t-elle sur l’esthétique faciale ? Pour évaluer les conséquences esthétiques sur le profil, nous avons réalisé une étude portant sur 64 patients en denture adolescente présentant une malocclusion de classe II, division 1 n’ayant subi aucune extraction et aucun traitement orthodontique préalable. Deux groupes d’adolescents ont été différenciés : l’un de 33 patients traités par Distal Active Concept (DAC), l’autre de 31 patients traités par Forces Extra-Buccales (FEB) sur multi-attache. Nous avons comparé, par des mesures céphalométriques, les profils obtenus après les deux types de traitements. Les résultats obtenus au niveau des tissus cutanés de l’étage inférieur de la face montrent un développement sagittal cutané significativement plus important pour le groupe d’enfants traité par DAC

nod Genes and Nod signals and the evolution of the rhizobium legume symbiosis.

The establishment of the nitrogen-fixing symbiosis between rhizobia and legumes requires an exchange of signals between the two partners. In response to flavonoids excreted by the host plant, rhizobia synthesize Nod factors (NFs) which elicit, at very low concentrations and in a specific manner, various symbiotic responses on the roots of the legume hosts. NFs from several rhizobial species have been characterized. They all are lipo-chitooligosaccharides, consisting of a backbone of generally four or five glucosamine residues N-acylated at the non-reducing end, and carrying various O-substituents. The N-acyl chain and the other substituents are important determinants of the rhizobial host specificity. A number of nodulation genes which specify the synthesis of NFs have been identified. All rhizobia, in spite of their diversity, possess conserved nodABC genes responsible for the synthesis of the N-acylated oligosaccharide core of NFs, which suggests that these genes are of a monophyletic origin. Other genes, the host specific nod genes, specify the substitutions of NFs. The central role of NFs and nod genes in the Rhizobium-legume symbiosis suggests that these factors could be used as molecular markers to study the evolution of this symbiosis. We have studied a number of NFs which are N-acylated by α,β-unsaturated fatty acids. We found that the ability to synthesize such NFs does not correlate with taxonomic position of the rhizobia. However, all rhizobia that produce NFs such nodulate plants belonging to related tribes of legumes, the Trifolieae, Vicieae, and Galegeae, all of them being members of the so-called galegoid group. This suggests that the ability to recognize the NFs with α,β-unsaturated fatty acids is limited to this group of legumes, and thus might have appeared only once in the course of legume evolution, in the galegoid phylum

A Diffusible Factor from Arbuscular Mycorrhizal Fungi Induces Symbiosis-Specific MtENOD11 Expression in Roots of Medicago truncatula

Using dual cultures of arbuscular mycorrhizal (AM) fungi and Medicago truncatula separated by a physical barrier, we demonstrate that hyphae from germinating spores produce a diffusible factor that is perceived by roots in the absence of direct physical contact. This AM factor elicits expression of the Nod factor-inducible gene MtENOD11, visualized using a pMtENOD11-gusA reporter. Transgene induction occurs primarily in the root cortex, with expression stretching from the zone of root hair emergence to the region of mature root hairs. All AM fungi tested (Gigaspora rosea, Gigaspora gigantea, Gigaspora margarita, and Glomus intraradices) elicit a similar response, whereas pathogenic fungi such as Phythophthora medicaginis, Phoma medicaginis var pinodella and Fusarium solani f.sp. phaseoli do not, suggesting that the observed root response is specific to AM fungi. Finally, pMtENOD11-gusA induction in response to the diffusible AM fungal factor is also observed with all three M. truncatula Nod(−)/Myc(−) mutants (dmi1, dmi2, and dmi3), whereas the same mutants are blocked in their response to Nod factor. This positive response of the Nod(−)/Myc(−) mutants to the diffusible AM fungal factor and the different cellular localization of pMtENOD11-gusA expression in response to Nod factor versus AM factor suggest that signal transduction occurs via different pathways and that expression of MtENOD11 is differently regulated by the two diffusible factors