Le comportement mécanique d’un sol constitue un des facteurs prépondérants affectant la croissance et le développement racinaire. L’augmentation de la résistance mécanique d’un sol affecte l’architecture du système racinaire, la croissance axiale et radiale des racines, et l’orientation de la croissance. Bien que ces réponses soient décrites sur diverses espèces végétales dans la littérature, leur mise en place et les mécanismes de signalisation sous-jacents restent à ce jour méconnus. L’objectif principal de cette thèse est d’étudier la mise en place des réponses des racines primaires d’Arabidopsis thaliana à des variations de contraintes mécaniques de son substrat. La littérature fait état jusqu’ici de deux voies de signalisation mécanique possibles, l’une impliquant une mécanoperception au niveau de la coiffe racinaire, et l’autre faisant intervenir entres autres l’activation de canaux mécano-sensibles au niveau de l’apex racinaire. Pour étudier leur implication respective, nous avons caractérisé les réponses à une augmentation des contraintes mécaniques de racines primaires issues de la lignée Arabidopsis thaliana sauvage et de lignées mutantes affectées au niveau de l’organisation de la coiffe (fez-2, smb-3, brn1-1 brn2-1) ou au niveau de canaux ioniques mécanosensibles (mca1-null, mslΔ5). Nous avons développé un système expérimental original basé sur le suivi de croissance et d’orientation des racines dans des milieux de culture à base de Phytagel. Ces milieux de culture permettent de mimer d’une part une augmentation à long terme et simultanée des contraintes mécaniques axiales, radiales et des frottements et d’autre part une augmentation à court terme des contraintes mécaniques axiales. Tout d’abord, nous avons observé que la mise en place des réponses de croissance des racines primaires d’Arabidopsis thaliana à ces augmentations de contraintes mécaniques reposait sur une interaction entre des processus mécaniques (flambement) et biologiques (régulations de la zone de croissance). Ensuite, nous avons mis en évidence que la coiffe racinaire participait à la mise en place des réponses des racines d’Arabidopsis thaliana face à une augmentation des contraintes mécaniques. Nos résultats suggèrent que la coiffe pourrait constituer un siège de la mécanoperception. Par ailleurs, nos résultats sur les lignées mca1-null et mslΔ5 suggèrent que les canaux ioniques MCA1 et MSLs participeraient également à la mise en place des réponses racinaires à l’augmentation des contraintes mécaniques. / Root growth and development are highly modulated by soil mechanical properties such as texture, structure and bulk density. Increases in soil penetration resistance affect root system architecture, root cell production and elongation, root diameter, and root tip orientation. Although root responses to changes in mechanical stresses are well described in several plant species, their establishment and the signaling pathways underlying these responses remains misunderstood. The main objective of this thesis is to study the establishment of Arabidopsis thaliana primary root responses to changes in mechanical stresses. So far, studies reported two distinct putative mechanical signaling pathways involving either (i) the root cap as a main mechanosensing site or (ii) the activity of stretch-activated ion channels localized on the cell plasma membranes along the root apex. According to previous studies, we studied the implication of the root cap and of the stretch-activated channels of the MCA and MSL families in the root responses to increases in mechanical stresses. We developed an original experimental set-up based on the monitoring of growth and orientation of Arabidopsis thaliana primary roots in one-layer and two-layer Phytagel based growth media. The one-layer growth media mimicked a long-term increase in frictions and in radial and axial mechanical stresses whereas the two-layer growth media mimicked a short-term increase in axial mechanical stresses. We characterized penetration abilities, growth rate and tip orientation of Arabidopsis thaliana wild type roots (Col-0) and mutant roots showing defects in root cap organization (fez-2, smb-3, brn1-1 brn2-1) or in stretch-activated ion channels activity (mca1-null, mslΔ5) in one-layer and two-layer media. Firstly, we observed that the establishment of root growth responses to increases in mechanical stresses involved both mechanical (buckling) and biological (growth zone modulations) mechanisms. Then, our experiments demonstrated that alterations in root cap organization led to altered root growth responses to increases in mechanical stresses. Our results suggest that the root cap acts as a mechanosensing site. Moreover, the results obtained with the mca1-null and mslΔ5 Arabidopsis lines suggest that the MCA1 and MSLs ion channels also participate in the establishment of root responses to increases in mechanical stresses.

Made available in DSpace on 2016-07-18T17:51:14Z (GMT). No. of bitstreams: 1 Joice Yuri Minamiguchi.pdf: 940892 bytes, checksum: 640b533bbf1ddeb7da432aa4e6083c07 (MD5) Previous issue date: 2013-03-12 / Sweet potato culture has a high potential for human and animal feeding; and for this last purpose the branches can be used as hay. Is a high yield root, rich in nutrients which occupy marginal crop lands. The propagation is highly vegetative using branches or shoots from roots, what can affect it by disseminating pathogens. The main objective of this work was to evaluate the effect of gelling agents and a systemic disinfectant in sweet potato tissue culture. Two experiments were done; one with different doses of gelling agents (Agar and Phytagel®) and another with a response curve of isothiazolinones (Kathon®CG). Shoots and roots Length and dry weight, their development rates; biochemical parameters as proline accumulation and Superoxide Dismutase were evaluated. Sweet potato did not respond to different gelling agents, and the recommendation is to use the low cost effective. Kathon®CG reduced the growth in the different concentrations. The return to the medium without Kathon®CG improved the plantlet growth. / A cultura da Ipomoea batatas (L.) é de imenso potencial alimentar, tanto para seres humanos quanto para animais. É uma raiz de alto rendimento e rico em nutrientes, que ainda ocupa áreas marginais da agricultura. A propagação é vegetativa utilizando-se ramas ou brotações de raízes para plantio. Porém, estes métodos podem afetar a propagação desta espécie, uma vez que pode disseminar doenças. O objetivo deste trabalho foi avaliar gelificantes e um desinfetante sistêmico na cultura de tecido de batata-doce. Para isso dois experimentos foram montados, um comparando três doses de cada um dos gelificantes (agar e Phytagel®) e outro uma curva de doses de isotiazolinonas (Kathon®CG). Foram avaliados parâmetros de desenvolvimento como altura e massa seca dos explantes, e as taxas de desenvolvimento de cada um, além parâmetros bioquímicos, como acúmulo de prolina e atividade da superóxido dismutase. A batata-doce não respondeu positivamente aos diferentes gelificantes, recomendando-se então o de menor custo. O Kathon®CG provocou redução no crescimento dos explantes em qualquer dose. O retorno ao meio sem o Kathon®CG promoveu incremento no crescimento das plantas sob condições experimentais oferecidas. Batata-doce não se comporta como espécie acumuladora de prolina.