In botany , apomixis was defined by Hans Winkler as replacement of the normal sexual reproduction by asexual reproduction , without fertilization. This definition notably does not mention meiosis. Thus "normal asexual reproduction " of plants, such as propagation from cuttings or leaves, has never been considered to be apomixis, but replacement of the seed by a plantlet or replacement of the flower by bulbils were categorized as types of apomixis. Apomictically produced offspring are genetically identical to the parent plant.
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Apomixis and adventitious polyembryony have been reported for several species of Bombacoideae, including Eriotheca pubescens, a tree species of the Neotropical savanna Cerrado areas in Brazil.
However, the origin of polyembryonic seeds and their importance for the reproduction of the species remained to be shown. Here, we analyzed the early embryology of this species to establish the apomictic origin of extranumerary embryos.
We also observed the geographic distribution of polyembryony in E. Moreover, we tested if polyembryonic apomictic embryos would develop normally into seedlings. In the observed seed primordia, after a relatively long quiescent period, the zygote developed into a sexual embryo concurrently with adventitious apomictic embryos which developed from nucellus cells.
Adventitious embryos develop faster than sexual ones and are morphologically similar, so that 44 days after anthesis it was virtually impossible to distinguish and trace the fate of the sexual embryo.
Polyembryony is widely distributed in populations some km distant, and only one strictly monoembryonic individual was observed during the study. The number of embryos per seed varied between fruits and individuals but was significantly higher in seeds from cross-pollinations than from selfs, although fruit and seed set after crosses were much lower than after selfs.
Embryo development into seedlings depended on their weight at germination, but polyembryonic seeds germinated and produced up to seven seedlings per seed in greenhouse conditions.
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Similar articles Does polyembryony reduce seed germination and seedling development in Eriotheca pubescens Malvaceae: Bombacoideae? Mendes-Rodrigues C, et al. Am J Bot. Epub Sep PMID: Pollen and stomata morphometrics and polyploidy in Eriotheca Malvaceae-Bombacoideae. Marinho RC, et al. Plant Biol Stuttg. Epub Dec Polyembryony in Melastomataceae from Brazilian Cerrado: multiple embryos in a small world.
Epub Feb 6. Apomixis in plant reproduction: a novel perspective on an old dilemma. Barcaccia G, Albertini E. Barcaccia G, et al. Plant Reprod. Epub Jul Genetic heterogeneity of seeds]. Batygina TB, et al. PMID: Review.
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Polyembryony and Apomixis in Eriotheca Pubescens (Malvaceae - Bombacoideae)