Some reflections on double fertilization, from its discovery to the present

Abstract

Contents Summary 000 Introduction 000 Discovery of double fertilization 000 Seed development without double fertilization 000 A case for double fertilization in gymnosperms 000 Structural and cytological perspectives on double fertilization 000 In vitro double fertilization 000 Genetic and molecular perspectives 000 Concluding comments 000 Acknowledgements 000 References 000 Summary The fusion of one sperm with the egg cell to form the embryo and of the other sperm with the polar fusion nucleus to give rise to the endosperm (‘double fertilization’) was discovered by Nawaschin in 1898 in the liliaceous plants, Lilium martagon and Fritillaria tenella. The occurrence of two fusion events analogous to double fertilization has recently been described in some gymnosperm species although the product of the second fusion is a transient embryo, rather than the endosperm as in angiosperms. Recent investigations in angiosperms describe the cell biology and nuclear cytology of double fertilization and the successful in vitro demonstration of the two fusion events using isolated egg cells, central cells, and sperm cells and the development of the fusion products into the embryo and endosperm. Molecular and genetic studies on the component elements of double fertilization have focused on the identification of mutants of Arabidopsis thaliana that display developmental patterns in the seed that result in autonomous endosperm development and even partial embryogenesis in the absence of fertilization. Characterization of the genes and their protein products has provided evidence for a predominant effect of maternal gametophytic genes and of silencing of paternal genes during double fertilization.

Isolation of gametes from <i>Brachypodium distachyon</i>

“…Fertilization and subsequent events in angiosperms, such as embryogenesis and endosperm development, occur in the embryo sac deeply embedded in ovular tissue (Guignard 1899;Nawaschin 1898;Raghavan 2003;Russell 1992). Since investigations into the molecular mechanisms of fertilization and embryogenesis have been impeded by the difficulties in directly researching the biology of the embedded female gametophyte, zygote and early embryo, studies for these mechanisms have been conducted predominantly through analyses of Arabidopsis mutants or transformants coupled with live imaging (reviewed in Berger 2011;Denninger et al 2014;Hamamura et al 2012Hamamura et al , 2014Maruyama et al 2015).…”

Formation of triploid plants via possible polyspermy

“…The egg and central cells fused with each sperm cell develop into an embryo, which transmits genetic material from the parents to the next generation, and into an endosperm, which nourishes the developing embryo/seedling, respectively. [23][24][25][26] It has been indicated that polyspermy block functions in the egg cell [27][28][29][30] and the central cell 30 to promote faithful double fertilization 31 . In addition, Ca 2C -dependent egg activation occurs in plants as well as animals, [32][33][34] and it has been postulated that the increased Ca 2C level triggers the polyspermy block of fertilized egg cells via Ca…”

Multinucleate storage cells in Douglas-fir (Pseudotsuga menziesii (Mirbel) Franco) and the effect of seed parasitism by the chalcid Megastigmus spermotrophus Wachtl

“…In gymnosperms, this occurs after meiosis; in angiosperms, it is after double fertilization. Although they differ in the initial events that bring about syncytial development (Raghavan, 2003), the outcome is similar: the initial cell increases in size while nuclei continue to divide in the absence of any cell wall formation. During this period, these cells can reach high ploidy levels.…”