Polyspermy barriers in plants: from preventing to promoting fertilization |
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Authors: | Melissa Spielman Rod J Scott |
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Institution: | (1) Department of Biology and Biochemistry, University of Bath, Claverton Down, Bath, BA2 7AY, UK |
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Abstract: | Barriers to polyspermy (fertilization of a female gamete by more than one sperm) are essential to successful reproduction
in a wide range of organisms including mammals, echinoderms, fish, molluscs, and algae. In animals and fucoid algae, polyspermy
results in early death of the zygote due to transmission of extra centrioles from the sperm and consequent disruptions to
the mitotic spindle. Accordingly, a variety of mechanisms have evolved to prevent penetration of an egg by more than one sperm,
or more than one sperm nucleus from fusing with an egg nucleus. The evolution of internal fertilization has also provided
an opportunity to limit the number of sperm that gain access to each egg, as occurs in the mammalian female reproductive tract.
Polyspermy and polyspermy barriers in plants have received much less attention. Plants lack centrioles and therefore, polyspermy
would not be expected to cause lethal aberrant spindle organization. However, we find evidence from cytological, genetic and
in vitro fertilization studies for polyspermy barriers in plants. Angiosperms, like mammals, are internally fertilized, and
exert a high level of control over the number of sperm that have access to each female gamete. In particular, regulation of
pollen tube growth ensures that in general only two sperm enter each embryo sac, where one fertilizes the egg and the other
the central cell. Despite this 1:1 ratio of sperm to gametes within the embryo sac, angiosperms still require a mechanism
to ensure that each female gamete is fertilized by one and only one sperm. Here, we present evidence suggesting that a polyspermy
block on the egg may be part of the mechanism that promotes faithful double fertilization. |
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Keywords: | Polyspermy block Double fertilization Heterofertilization Angiosperm |
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