Approche au niveau ultrastructural du fonctionnement des ectomycorhizes de truffe

National audienc

Characterization of the spinule wall of the truffle ectomycorrhizae by ultrastructural cytochemistry

International audienc

Functional alterations of root meristematic cells of Arabidopsis thaliana induced by a simulated microgravity environment

Environmental gravity modulates plant growth and development, and these processes are influenced by the balance between cell proliferation and differentiation in meristems. Meristematic cells are characterized by the coordination between cell proliferation and cell growth, that is, by the accurate regulation of cell cycle progression and the optimal production of biomass for the viability of daughter cells after division. Thus, cell growth is correlated with the rate of ribosome biogenesis and protein synthesis. We investigated the effects of simulated microgravity on cellular functions of the root meristem in a sequential study. Seedlings were grown in a clinostat, a device producing simulated microgravity, for periods between 3 and 10 days. In a complementary study, seedlings were grown in a Random Positioning Machine (RPM) and sampled sequentially after similar periods of growth. Under these conditions, the cell proliferation rate and the regulation of cell cycle progression showed significant alterations, accompanied by a reduction of cell growth. However, the overall size of the root meristem did not change. Analysis of cell cycle phases by flow cytometry showed changes in their proportion and duration, and the expression of the cyclin B1 gene, a marker of entry in mitosis, was decreased, indicating altered cell cycle regulation. With respect to cell growth, the rate of ribosome biogenesis was reduced under simulated microgravity, as shown by morphological and morphometric nucleolar changes and variations in the levels of the nucleolar protein nucleolin. Furthermore, in a nucleolin mutant characterized by disorganized nucleolar structure, the microgravity treatment intensified disorganization. These results show that, regardless of the simulated microgravity device used, a great disruption of meristematic competence was the first response to the environmental alteration detected at early developmental stages. However, longer periods of exposure to simulated microgravity do not produce an intensification of the cellular damages or a detectable developmental alteration in seedlings analyzed at further stages of their growth. This suggests that the secondary response to the gravity alteration is a process of adaptation, whose mechanism is still unknown, which eventually results in viable adult plants

Exploration of plant growth and development using the European Modular Cultivation System facility on the International Space Station

Plant Biol.ISI Document Delivery No.: AE5RITimes Cited: 1Cited Reference Count: 35Kittang, A. -I. Iversen, T. -H. Fossum, K. R. Mazars, C. Carnero-Diaz, E. Boucheron-Dubuisson, E. Le Disquet, I. Legue, V. Herranz, R. Pereda-Loth, V. Medina, F. J.French Space Agency (CNES); Norwegian Research Council; Spanish National Plan for Research, Development and Innovation; ELIPS Programme of the European Space Agency (ESA); ESAWe thank Prof. John Z. Kiss (University of Mississippi, USA), Prof. Gerald Perbal (University P. and M. Curie, France) and Dr. Imara Y. Perera (North Carolina State University, USA) for their contribution to some parts of this article. Experimental work reported in this paper and performed in the authors' laboratories was supported by the French Space Agency (CNES), the Norwegian Research Council, the Spanish National Plan for Research, Development and Innovation (different grants) and the ELIPS Programme of the European Space Agency (ESA). Specifically, the activities related to the 'Arabidopsis Topical team' were supported by an ESA grant.Wiley-blackwellHobokenSpace experiments provide a unique opportunity to advance our knowledge of how plants respond to the space environment, and specifically to the absence of gravity. The European Modular Cultivation System (EMCS) has been designed as a dedicated facility to improve and standardise plant growth in the International Space Station (ISS). The EMCS is equipped with two centrifuges to perform experiments in microgravity and with variable gravity levels up to 2.0g. Seven experiments have been performed since the EMCS was operational on the ISS. The objectives of these experiments aimed to elucidate phototropic responses (experiments TROPI-1 and -2), root gravitropic sensing (GRAVI-1), circumnutation (MULTIGEN-1), cell wall dynamics and gravity resistance (Cell wall/Resist wall), proteomic identification of signalling players (GENARA-A) and mechanism of InsP(3) signalling (Plant signalling). The role of light in cell proliferation and plant development in the absence of gravity is being analysed in an on-going experiment (Seedling growth). Based on the lessons learned from the acquired experience, three preselected ISS experiments have been merged and implemented as a single project (Plant development) to study early phases of seedling development. A Topical Team initiated by European Space Agency (ESA), involving experienced scientists on Arabidopsis space research experiments, aims at establishing a coordinated, long-term scientific strategy to understand the role of gravity in Arabidopsis growth and development using already existing or planned new hardware