716 C.Dumas.P.Rogowsky/C.R.Biologies 331(2008)715-725 la cellule centrale avant ou apres fecondation.Une vague de calcium est le premier venement cellulaire documente apres fusion cpar le comppolycomb Fmrcnciale pour lesu d developpement de la grine.Pcrc s331(0 SAS.All rights reserved. Keywords:Gamete:Egg cell:Fertilization:Zygolelembryo;Endosperm:Angiosperms Mors-cles:Gamete:Oosphere:Fecondation:Zygote/embryon:Albumen:Angiospermes 1.Introduction tomogamy),wind (anemogamy)and,more rarely. Awye pblishedpecal of h -A progam es occu des science g or at the n Ci cell Mo ble fertilization process in plants.Thes neer authors he ee differ t pr cesses such as adhesion of the pollen independently observed for the first time the occurrence grain to pistil prior to water uptake,enzyme (e.g. of a double fertilization in two different plant species. cytochrome oxidase,cellulase.phosphorylase,ri- Turk's cap lily (Lilium martagon)and the perennial herb bonuclease,acid phosphatase,...)release and ac Fritillaria tenella.At that time no one was using model tivation,and the preparation of pollen tube (PT) s important discover formation.In thi s tube a second mitotic division b the on in plan ng to 0n0 que vehicle nd the establishment of a new ration.from the to their target cells within the so-caled"ule to the embryo included within the seed.The beg in (a terminology that is somehow misleading in re of embrvology research during the 20th century led to lation to animal or algae terminology).Ovules in many novel aspects in developmental biology.notably angiosperms are matemal organs containing the fe in plants.Sev ral books have been published on thi e monograph by Masheswari re ref related to em evolut ut ha eds of ve prevent self-fertilization.The mos 2.Fertilization in angiosperms:a multi-step cated and widespread of these mechanisms is self phenomenon incompatibility (SI).a process leading to the rejec tion of self-pollen by the pistil.SI is controlled by Fertilization in flowering plants (angiosperms)is a a single multiallelic locus,the S-locus (S standing very complex process as compared with animal or algae for self-incompat inty)and several plant systems systems.It consists of three successive phases (Fig.1): ave been carefully ana edfor this aspect.e.g. Papaver (I- Pollination that c to th tra of a hird p叫 of fe tophyte or pollen grain.from the male org the anther.to the receptive female organ,the stigma in angiosperms.Here.the first sperm nucleus fuses surface of the pistil.Note that since plants are ses- with the egg nucleus (at the origin of the zygotic sile organisms,sexual partners just meet by chance. embryo),while the second sperm nucleus fuses sometimes with the aid of animals like insects (en- with the two polar nuclei of the central cell of the716 C. Dumas, P. Rogowsky / C. R. Biologies 331 (2008) 715–725 la cellule centrale avant ou après fécondation. Une vague de calcium est le premier évènement cellulaire documenté après fusion cytoplasmique dans l’oosphère fécondé ou zygote, qui se développe en un organisme pluricellulaire avec un plan d’organisation très élaboré. Le développement de la cellule centrale en tissu nourricier, l’albumen, commence par la formation d’un cénocyte, une cellule multi-nucléée unique aux plantes, qui sera suivie par une cellularisation. La balance entre les génomes paternel et maternel, contrôlée par le complexe polycomb FIS, a une importance cruciale pour le succès du développement de la graine. Pour citer cet article : C. Dumas, P. Rogowsky, C. R. Biologies 331 (2008). © 2008 Académie des sciences. Published by Elsevier Masson SAS. All rights reserved. Keywords: Gamete; Egg cell; Fertilization; Zygote/embryo; Endosperm; Angiosperms Mots-clés : Gamète ; Oosphère ; Fécondation ; Zygote/embryon ; Albumen ; Angiospermes 1. Introduction A few years ago, we published a special issue of the Comptes rendus de l’Académie des sciences [1] to cel￾ebrate the centenary of the independent discovery by Sergius Nawashin [2] and Léon Guignard [3] of the dou￾ble fertilization process in plants. These pioneer authors independently observed for the first time the occurrence of a double fertilization in two different plant species, Turk’s cap lily (Lilium martagon) and the perennial herb Fritillaria tenella. At that time no one was using model plants or model systems. Yet, this important discovery still corresponds to one of the key hallmarks in plant biology. Indeed, the double fertilization is unique to flowering plants among living organisms and permits the establishment of a new generation, from the zygote to the embryo included within the seed. The beginning of embryology research during the 20th century led to many novel aspects in developmental biology, notably in plants. Several books have been published on this topic [4], of which the monograph by Masheswari re￾mains the historical reference in plant embryology [5]. In this paper, we summarize key features related to fer￾tilization and the earliest developmental aspects of em￾bryo tissues within the seeds of flowering plants. 2. Fertilization in angiosperms: a multi-step phenomenon Fertilization in flowering plants (angiosperms) is a very complex process as compared with animal or algae systems. It consists of three successive phases (Fig. 1): – Pollination that corresponds to the transfer of a male nucleus containing unit, called male game￾tophyte or pollen grain, from the male organ, the anther, to the receptive female organ, the stigma surface of the pistil. Note that since plants are ses￾sile organisms, sexual partners just meet by chance, sometimes with the aid of animals like insects (en￾tomogamy), wind (anemogamy) and, more rarely, water (hydrogamy). – A progamic phase that includes all processes occur￾ring from the landing of pollen grains on the recep￾tive stigma to the time that the sperm cell reaches the egg cell. More precisely, this phase includes different processes such as adhesion of the pollen grain to pistil prior to water uptake, enzyme (e.g., cytochrome oxidase, cellulase, phosphorylase, ri￾bonuclease, acid phosphatase, . . . ) release and ac￾tivation, and the preparation of pollen tube (PT) formation. In this tube, a second mitotic division often occurs leading to the formation of two sperm cells. Here, the PT acts as a sort of vehicle (sperm cells are not motile) carrying the two sperm cells to their target cells within the so-called “ovule” (a terminology that is somehow misleading in re￾lation to animal or algae terminology). Ovules in angiosperms are maternal organs containing the fe￾male gametophyte, the embryo sac (a complex hap￾loid and pluricellular structure containing two fe￾male gametes), the egg cell and the central cell (Fig. 1). During the course of evolution, about half of the angiosperm species have acquired specific recognition mechanisms, which strongly limit or even prevent self-fertilization. The most sophisti￾cated and widespread of these mechanisms is self￾incompatibility (SI), a process leading to the rejec￾tion of self-pollen by the pistil. SI is controlled by a single multiallelic locus, the S-locus (S standing for self-incompatibility) and several plant systems have been carefully analyzed for this aspect, e.g., Brassica or Papaver [7–9]. – The third phase, referred to as syngamy, is the last and decisive phase of fertilization, which corre￾sponds to the unique double nuclear fusion event in angiosperms. Here, the first sperm nucleus fuses with the egg nucleus (at the origin of the zygotic embryo), while the second sperm nucleus fuses with the two polar nuclei of the central cell of the