Histo-cytological changes in Pelargonium apices during the cryopreservation process: Effect of the osmotic agent chosen for the preculture step

International audienceApex cryopreservation studies were undertaken to guarantee the safe, long-term conservation of a Pelargonium collection. Plant regrowth was obtained with a modified encapsulation-dehydration process. Choosing P. x peltatum 'Balcon Lilas' as a model, the main objective was to determine if sucrose is specific in conferring dehydration tolerance to apices. In the preculture medium sucrose was replaced by glucose, glucose with 3% sucrose, or sorbitol at similar osmolarities. None of the osmotic agents tested produced a level of tolerance to desiccation as high as that of sucrose. A high concentration of glucose was toxic and did not induce a dehydration tolerance. A histo-cytological study was performed on apices precultured with the various osmotic agents. Starch accumulation was only observed in most of the apex cells following sucrose preculture, not with the other osmotica. Other important differences concerned nucleus aspect, nucleolus presence, cell plasmolysis and cytoplasm constitutio

In situ hybridization of a radioactive RNA probe on resin-embedded legume root-nodule sections: a tool for observing gene expression in the rhizosphere?

In this work we performed in situ hybridization of a carbonic anhydrase RNA $^{35}$S-labeled probe on nodule sections previously embedded in a methacrylate resin. The results were more precise and reproducible than those obtained on paraffin-embedded nodules. Thanks to the small thickness of the sections and the good preservation of tissue during sectioning, the specific localization of the carbonic anhydrase gene expression in the inner cortex of the nodule could be described quite precisely. It is argued that these results are consistent with the hypothesis of osmoregulation of the symbiotic nitrogen fixation. Moreover, the quality of these results with a radioactive probe makes it possible to consider using ISH for such rhizospheric applications as localizing and quantifying a microbial invasion of the endorhizosphere or the rhizoplan by using bacterial- or fungal-specific RNA probes, and counting the number of radioactive dots per cell. However, major artifacts observed with a digoxegin RNA cold probe makes it necessary to recommend the use of a radioactive RNA probe for these prospects.Hybridation in situ d'une sonde ARN radioactive sur des coupes de nodosités de légumineuses incluses dans une résine méthacrylique : un outil pour observer l'expression génique dans la rhizosphère ? Dans ce travail, nous avons réalisé une hybridation in situ d'une sonde ARN d'anhydrase carbonique marquée au $^{35}$S, sur des coupes de nodosités préalablement incluses dans une résine méthacrylique. Grâce à la faible épaisseur des coupes et la bonne conservation des tissus durant la coupe, la localisation spécifique de l'expression du gène d'anhydrase carbonique dans le cortex interne des nodosités a pu être décrite très précisément. Il est argumenté que cette localisation est en accord avec l'hypothèse d'osmorégulation de la fixation symbiotique d'azote. De plus, la qualité de ces résultats avec une sonde radioactive suggère qu'il serait possible d'utiliser l'hybridation in situ pour des applications telles que la localisation et la quantification d'une invasion microbienne de l'endorhizosphère ou du rhizoplan en utilisant des sondes ARN spécifiques de champignons ou de bactéries, et en comptant le nombre de signaux radioactifs par cellule. Il est recommandé d'utiliser un marquage radioactif des sondes, en raison des artefacts observés dans ce travail avec une sonde ARN marquée à la digoxygénine

Shaping the shoot: the relative contribution of cell number and cell shape to variations in internode length between parent and hybrid apple trees

UMR DAP, équipe AFEF, Correspondance: [email protected] Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699International audienceGenetic control of plant size and shape is a promising perspective, particularly in fruit trees, in order to select desirable genotypes. A recent study on architectural traits in an apple progeny showed that internode length was a highly heritable character. However, few studies have been devoted to internode cellular patterning in dicotyledonous stems, and the interplay between the two elementary cell processes that contribute to their length, i.e. cell division and elongation, is not fully understood. The present study aimed at unravelling their contributions in the genetic variation of internode length in a selection of F(1) and parent genotypes of apple tree, by exploring the number of cells and cell shape within mature internodes belonging to the main axes. The results highlighted that both the variables were homogeneous in samples collected either along a sagital line or along the pith width, and suggest that cell lengthening was homogeneous during internode development. They allowed the total number of cells to be estimated on the internode scale and opened up new perspectives for simplifying tissue sampling procedures for further investigations. Differences in internode length were observed between the genotypes, in particular between the parents, and partly resulted from a compensation between cell number and cell length. However, genetic variations in internode length primarily involved the number of cells, while cell length was more secondary. These results argue for an interplay between cellular and organismal control of internode shape that may involve the rib meristem