Olivier Catrice

Nitric oxide (NO) is involved in various plant-microbe interactions. In the symbiosis between the soil bacterium Sinorhizobium meliloti and the model legume Medicago truncatula NO is required for an optimal establishment of the interaction but is also a signal for nodule senescence. Little is known about the molecular mechanisms responsible for NO effects in the legume-rhizobium interaction. Here we investigate the contribution of the bacterial NO response to the modulation of a plant protein post-translational modification in nitrogen fixing nodules. We made use of different bacterial mutants to finely modulate NO levels inside M. truncatula root nodules and examine the consequence on tyrosine nitration of the plant Glutamine synthetase (GS), a protein responsible for assimilation of the ammonia released by nitrogen fixation. Our results reveal that S. meliloti possesses several proteins which limit inactivation of plant enzyme activity via NO-mediated post-translational modifications. This is the first demonstration that rhizobia can impact the course of nitrogen fixation by modulating the activity of a plant protein.

FM-dyes are widely used to study endocytosis, vesicle trafficking and organelle organization in living eukaryotic cells. The increasing use of FM-dyes in plant cells has provoked much debate with regard to their suitability as endocytosis markers, which organelles they stain and the precise pathways they follow through the vesicle trafficking network. A primary aim of this article is to assess critically the current status of this debate in plant cells. For this purpose, background information on the important characteristics of the FM-dyes, and of optimal dye concentrations, conditions of dye storage, and staining and imaging protocols, are provided. Particular emphasis is placed on using the FM-dyes in double labelling experiments to identity specific organelles. In this way, staining of the Golgi with FM4-64 has been demonstrated for the first time.

Le cycle dans le contexte du développement. Régulation de la prolifération : une machinerie moléculaire de base commune aux eucaryotes. La biologie cellulaire de la prolifération : spécificités de la cellule végétale. Prolifération cellulaire et Cycle des organites intracellulaires : un dialogue fonctionnel. Durée d’un cycle cellulaire : de quelques heures à quelques jours… Analyser et suivre le cycle cellulaire. Endoréplication et définitions afférentes. Endoréplication fondamentale Endoréplication et biotechnologie. Endoréplication partielle progressive chez une plante monocotylédone. Conclusion