Polyploidy and polyembryony in Anemopaegma (Bignonieae, Bignoniaceae)

Abstract

Polyploidy is a key process in plant evolution, with the asexual formation of embryos representing a way through which polyploids can escape sterility. The association between polyploidy and polyembryony is known to occur in Bignoniaceae. In this study, we investigate polyembryony in four polyploid species of Anemopaegma: A. acutifolium, A. arvense, A. glaucum and A. scabriusculum as well as in one diploid species, A. album. Polyembryony was observed only in polyploid species. We used seed dissection and germination tests to compare the number of polyembryonic seeds. We tested how the pollen source influences the number of polyembryonic seeds and the number of embryos per seed and tested the correlation between the number of viable seeds per fruit and mean number of embryos per seed. The number of polyembryonic seeds observed by seed dissection was higher than the number of polyembryonic seeds determined by the germination test, with the number of embryos produced per seed being higher than the number of seedlings. The dissection of seeds of A. glaucum indicated that a higher number of polyembryonic seeds and a higher number of embryos were present in seeds from cross-pollination than in seeds from self-pollination. On the other hand, germination tests indicated that a higher number of polyembryonic seeds were present in fruits from self-pollination than from cross-pollination. The mean number of embryos per seed was not influenced by the number of viable seeds per fruit in fruits from open pollination. These results indicate a positive relationship between polyembryony and polyploidy in Anemopaegma.

Self-sterility in the hexaploid Handroanthus serratifolius (Bignoniaceae), the national flower of Brazil

“…In species with LSI, the simultaneous abortion of pistils from self-pollination treatment is expected (Bittencourt et al 2003). If we consider the self-compatible neopolyploid species of Bignoniaceae as presenting strong inbreeding depression, the similar fruit-set between self-and cross-pollinations in apomictic plants (Bittencourt & Semir 2005;Bittencourt & Moraes 2010;Firetti-Leggieri et al 2013;Sampaio et al 2013a) would be justified only by the development of adventitious embryos, and we would have to assume that inbreeding depression does not affect endosperm development, which is unlikely. Histological studies of post-pollination events of apomictic self-compatible neopolyploid species of Bignoniaceae do not show endosperm malformations that could be caused by inbreeding depression (Bittencourt & Moraes 2010;Sampaio et al 2013a), although a slight delay in endosperm development, which is commonly associated with the action of the LSI, has been reported in Anemopaegma acutifolium (Sampaio et al 2013a).…”

“…If the studied plants were sporophytic apomicts, high proportions of polyembryonic seeds (> 20%) were expected. However, a low proportion of polyembryonic seeds (< 5%) can be attributed to some exceptions in the sexual process or to other types of apomixis (Mendes-Rodrigues et al 2012, Firetti-Leggieri et al 2013Sampaio et al 2013b). One investigation of the proportion of polyembryonic seeds in a population of Handroanthus serratifolius showed little variation among individuals (Mendes-Rodrigues et al 2012).…”

“…Eighty percent of the studied species present self-sterility, which is often characterized as a result of late-acting self-incompatibility (LSI) mechanisms (Gibbs & Bianchi 1993;Bittencourt et al 2003;Bittencourt & Semir 2005;Gandolphi & Bittencourt 2010). To date, all neopolyploid Bignoniaceae species have been found to be self-compatible (Gobatto-Rodrigues & Stort 1992;Bittencourt & Semir 2005;Bittencourt & Moraes 2010;Firetti-Leggieri et al 2013;Sampaio et al 2013a), although not all self-compatible species are neopolyploids (Dutra & Machado 2001;Yanagizawa & Maimoni-Rodella 2007;Qu et al 2007). Therefore, self-fertility in Bignoniaceae could be caused by various factors, of which polyploidy appears to be one of the most important.…”

“…Studies of the breeding systems of the neopolyploid species of Anemopaegma and Handroanthus have shown self-fertility and polyembryony (Bittencourt & Semir 2005;Bittencourt & Moraes 2010;Mendes-Rodrigues et al 2012;Firetti-Leggieri et al 2013;Sampaio et al 2013a). Histological analyses have shown that the supernumerary embryos found in polyembryonic seeds arise from somatic tissues of the ovule in Handroanthus ochraceus (Cham.)…”

“…(Sampaio et al 2013b), indicating the occurrence of sporophytic apomixis. On the basis of those findings, high frequencies of polyembryonic seeds have been used as evidence of sporophytic apomixis in Bignoniaceae (Mendes-Rodrigues et al 2012, Firetti-Leggieri et al 2013Sampaio et al 2013b). …”