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Reproduction et développement des plantes à fleurs

École normale supérieure de Lyon, UMR 5667 CNRS–Inra–ENS–université Lyon-1, 46, allée d’Italie, 69364 Lyon cedex 7, France
Comptes Rendus de l'Académie des Sciences - Series III - Sciences de la Vie 01/2001; 324(6):517-521. DOI: 10.1016/S0764-4469(01)01320-8

ABSTRACT Why mark the centenary of the independant discovery of double fertilization by Sergius Nawashin (1898) and Léon Guignard (1899), when biology has progressed so much since the beginning of the XXth century? This discovery still constitutes one of the key references in plant biology: double fertilization is unique to flowering plants among all living organisms. This meeting is also the occasion to associate angiosperm fertilization with developmental biology because of the localization of this event in the flower. Very important and significant progress has been made in elucidating flower development during the last ten years. And today it is possible to understand the diversity of floral structure present in the angiosperms in the context of a underlying mechanism of flower development inherited from their common ancestor. This special issue also allows a survey of these two broad scientific fields, plant reproduction and plant development (flower and embryo). It might also attract new, talented young scientists.RésuméPourquoi marquer un centenaire comme la découverte de la double fécondation chez les angiospermes 〚1〛, alors que la biologie a fait d’énormes progrès depuis le début du XXe siècle ? Cette découverte réalisée indépendamment par le russe Sergius Nawashin (1898) et le français Léon Guignard (1899) constitue toujours une des références clés en biologie de la reproduction des plantes à fleurs : elle singularise leur type de fécondation par rapport à celui de tous les autres êtres vivants. Par ailleurs, il nous a semblé particulièrement intéressant d’associer fécondation et développement, d’autant que cet évènement a pour siège la fleur. En effet, des progrès très significatifs ont été réalisés au cours de la dernière décennie dans la compréhension de son développement. Et, à la très grande diversité des fleurs observée chez les angiospermes, on peut désormais opposer le mode unitaire de leur développement. Ce numéro spécial permet de faire un bilan sur quelques aspects de ces deux vastes champs disciplinaires et, je l’espère, suscitera de nouvelles vocations.

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    ABSTRACT: The double fertilization of flowering plants is a complex process, encompassing multiple steps. From its discovery more than a century ago, many useful descriptive approaches have been employed to better unveil specific steps/mechanisms. More recently, the development of an in vitro assay developed in our laboratory, has allowed a better understanding of this phenomenon. However, in vitro methods may show some limitations. The search for complementary strategies, especially with the search of mutants affected in the fertilization step allowed one to elucidate this critical and unique phenomenon in living organisms. Genes involved in pollen tube guidance or pollen discharge in synergids have been identified, as well as genes exhibiting differential expression in sperm, egg and central cells before and after fertilization. A calcium wave proved to correspond to the first cellular event seen after cytoplasmic fusion in the fertilized egg cell or zygote, which develops into a multi-cellular organism with an elaborate body plan. The development of the fertilized central cell into a nourishing tissue (endosperm) starts with the formation of the coenocyte, a multinuclear single cell unique in the plant kingdom, cellularization occurring later on. The balance of the paternal and maternal genomes, which is under the control of the FIS polycomb group complex, was found to be of the utmost importance for the successful development of the seed.
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