title: Functional alterations of root meristematic cells of Arabidopsis thaliana induced by a simulated microgravity environment.
abstract: 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 10days. 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.
authors: Université Pierre et Marie Curie - Paris 6, Sorbonne Universités, Institut de Systématique, Évolution, Biodiversité, ISYEB - UMR 7205 - CNRS, MNHN, UPMC, EPHE, 57 rue Cuvier, CP50, 75005 Paris, France. Electronic address: elodie.boucheron_dubuisson@upmc.fr.
authors: Elodie
authors: E
authors: Boucheron-Dubuisson
authors: Centro de Investigaciones Biológicas (CSIC), Ramiro de Maeztu 9, E-28040 Madrid, Spain. Electronic address: chabel@cib.csic.es.
authors: Ana I
authors: AI
authors: Manzano
authors: Université Pierre et Marie Curie - Paris 6, Sorbonne Universités, Institut de Systématique, Évolution, Biodiversité, ISYEB - UMR 7205 - CNRS, MNHN, UPMC, EPHE, 57 rue Cuvier, CP50, 75005 Paris, France. Electronic address: isabel.le_disquet@upmc.fr.
authors: Isabel
authors: I
authors: Le Disquet
authors: Centro de Investigaciones Biológicas (CSIC), Ramiro de Maeztu 9, E-28040 Madrid, Spain. Electronic address: isabelmatia@hotmail.com.
authors: Isabel
authors: I
authors: Matía
authors: Laboratoire Génome et Développement des Plantes, CNRS, UMR 5096, Université de Perpignan via Domitia, 66860 Perpignan, France. Electronic address: saez@univ-perp.fr.
authors: Julio
authors: J
authors: Sáez-Vasquez
authors: DESC (Dutch Experiment Support Center), Dept. Oral and Maxillofacial Surgery/Oral Pathology, VU University Medical Center & Academic Centre for Dentistry Amsterdam (ACTA), Gustav Mahlerlaan 3004, 1081 LA Amsterdam, The Netherlands; ESA-ESTEC, TEC-MMG, Keplerlaan 1, NL-2200 AG, Noordwijk, The Netherlands. Electronic address: j.vanloon@vumc.nl.
authors: Jack J W A
authors: JJ
authors: van Loon
authors: Centro de Investigaciones Biológicas (CSIC), Ramiro de Maeztu 9, E-28040 Madrid, Spain. Electronic address: rherranz@cib.csic.es.
authors: Raúl
authors: R
authors: Herranz
authors: Université Pierre et Marie Curie - Paris 6, Sorbonne Universités, Institut de Systématique, Évolution, Biodiversité, ISYEB - UMR 7205 - CNRS, MNHN, UPMC, EPHE, 57 rue Cuvier, CP50, 75005 Paris, France. Electronic address: eugenie.carnero_diaz@upmc.fr.
authors: Eugénie
authors: E
authors: Carnero-Diaz
authors: Centro de Investigaciones Biológicas (CSIC), Ramiro de Maeztu 9, E-28040 Madrid, Spain. Electronic address: fjmedina@cib.csic.es.
authors: F Javier
authors: FJ
authors: Medina
mesh_terms: D017360:Arabidopsis / Q000166:cytology* / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000378:metabolism; D002453:Cell Cycle; D002466:Cell Nucleolus / Q000378:metabolism / Q000648:ultrastructure; D049109:Cell Proliferation; D056744:Cyclin B1 / Q000378:metabolism; D004777:Environment; D005434:Flow Cytometry; D018506:Gene Expression Regulation, Plant; D018519:Meristem / Q000033:anatomy & histology / Q000166:cytology* / Q000502:physiology*; D009929:Organ Size; D001678:Organelle Biogenesis; D012270:Ribosomes / Q000378:metabolism / Q000648:ultrastructure; D018474:Weightlessness Simulation
chemical_list: D029681:Arabidopsis Proteins; D056744:Cyclin B1
keywords: Cell cycle; Cell proliferation; Flow cytometry; Gravity; Nucleolus; Ribosome biogenesis