Double fertilization in Gnetum gnemon (Gnetaceae): its bearing on the evolution of sexual reproduction within the Gnetales and the anthophyte clade

The fertilization process in Gnetum is critical to our understanding of the evolution of sexual reproduction within the Gnetales, a monophyletic group of nonflowering seed plants that are the closest living relatives to flowering plants. Although much is known about the fertilization process in Ephe...

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Published inAmerican journal of botany Vol. 83; no. 6
Main Authors Carmichael, J.S. (University of North Dakota, Grand Forks, ND.), Friedman, W.E
Format Journal Article
LanguageEnglish
Published 01.06.1996
Subjects
ANGIOSPERMAS
ANGIOSPERME
DESARROLLO BIOLOGICO
DEVELOPPEMENT BIOLOGIQUE
ESTRUCTURA CELULAR
ETAPAS DE DESARROLLO DE LA PLANTA
EVOLUCION
EVOLUTION
FECONDATION
FECUNDACION
GAMETE
GAMETOS
GNETUM GNEMON
MORFOGENESIS
MORPHOGENESE
OVULE
OVULO
POLINIZACION
POLLINISATION
REPRODUCCION SEXUAL
REPRODUCTION SEXUEE
SEXE
SEXO
STADE DE DEVELOPPEMENT VEGETAL
STRUCTURE CELLULAIRE
TUBE DU POLLEN
TUBOS POLINICOS
ULTRAESTRUCTURA
ULTRASTRUCTURE
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Summary:The fertilization process in Gnetum is critical to our understanding of the evolution of sexual reproduction within the Gnetales, a monophyletic group of nonflowering seed plants that are the closest living relatives to flowering plants. Although much is known about the fertilization process in Ephedra, which is basal within the Gnetales, little is known about sexual reproduction in the derived sister groups Gnetum and Welwitschia. Ovules of Gnetum gnemon were collected at various stages after hand pollination and processed for light, fluorescence, and electron microscopy. Approximately 5 d after pollination, pollen tubes reach sexually mature female gametophytes, which are coenocytic. At that time, a binucleate sperm cell is found within each pollen tube, Within 7 d of pollination, double fertilization events occur when each of two sperm nuclei released from a pollen tube fuses with a separate, undifferentiated female nucleus within the free nuclear female gametophyte, which lacks differentiated egg cells. The products of double fertilization are two viable zygotes; endosperm is not formed. The lack of differentiated egg cells in Gnetum gnemon is unparalleled among land plants and the documentation of a regularly occurring process of double fertilization is congruent with the hypothesis that a rudimentary process of double fertilization evolved in a common ancestor of angiosperms and Gnetales
Bibliography:F50
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9736096
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ISSN:0002-9122
1537-2197
DOI:10.1002/j.1537-2197.1996.tb12766.x