Polyembryony and Apomixis in Eriotheca pubescens (Malvaceae - Bombacoideae)

Abstract

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. pubescens, and tested if apomixis was related to the source of pollen (self or cross) and population density. 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 400 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. Adventitious embryony and apomictic seedlings would explain the mostly clonal populations suggested by molecular studies.

Biologia reprodutiva de Miconia angelana (Melastomataceae), endêmica da Serra da Canastra, Minas Gerais

“…Mas de maneira geral a espécie é autocompatível e não apomítica. A possibilidade de apomixia via pseudogamia, como ocorre em outras plantas lenhosas de cerrado (Costa et al 2004, Mendes-Rodrigues et al 2005, não pode ser afastada. No entanto, a frequência de tubos polínicos e fertilizações nos pistilos resultantes de autoplonização espontânea indicam que a contaminação natural dos pistilos em infl orescências ensacadas é sufi ciente para explicar a frutifi cação obtida neste tratamento.…”

Polyembryony increases embryo and seedling mortality but also enhances seed individual survival in Handroanthus species (Bignoniaceae)

“…Morphological anomalies, brood competition inside the seed and seedling competition during establishment may affect the turnover of embryos into seedlings (Hotchkiss et al, 2008;Mu et al, 2010;Uma Shaanker and Ganeshaiah, 1997). Brood competition would be due to the limited amount of resources allocated to each seed and may be evinced by the reduction of mean embryo mass with the increase on embryo number per seed (Mendes-Rodrigues et al, 2005). Anomalies on size and morphology of cotyledons are related with competition for space and, although they may not affect the turnover of these embryos into seedlings, in more severe cases they do impair seedling establishment (Mendes-da-Glória et al, 2001).…”

“…Reported for at least 115 flowering plant families and very common and widespread among the Angiosperms (Carman, 1997), polyembryony has been studied and described for temperate weeds (Asker and Jerling, 1992;Naumova, 1992), and for some families of tropical woody species as Bignoniaceae (Costa et al, 2004), Malvaceae (Mendes-Rodrigues et al, 2005) and Melastomataceae (Goldenberg and Shepherd, 1998; Abbreviations: MENS, mean embryo number per seed; MSNS, mean seedling number per seed; PSP, polyembryonic seed percentage; EC, embryonic class.…”

Polyembryony in Maize: A Complex, Elusive, and Potentially Agronomical Useful Trait

“…Gupta in 1996 [81] reported in guggul (Commiphora wightii) the occurrence of apomixis not pseudogamous (development of an embryo only from maternal chromosomes after activation of the egg by a sperm: sperm penetrates the egg, causes division, but there is no effective fertilization), nucellar PE and autonomous endosperm formation suggesting that plants have reproductive and survival strategies in the absence of male plants, but in the presence of males, sexual reproduction can occur. Moreover, in 2005, Mendes-Rodriguez [82] studied Eriotheca pubescens, which presents apomixis and adventitia polyembryony, found that in seeds, the zygote became a sexual embryo simultaneously with apomictic adventitious embryos that developed from nucellus cells. The adventitious embryo developed more rapidly than sexual ones, but they are morphologically similar so that 44 days after anthesis it was impossible to distinguish the sexual from the apomictic embryos.…”