Self-fertility and polyembryony in South American yellow trumpet trees (Handroanthus chrysotrichus and H. ochraceus, Bignoniaceae): a histological study of postpollination events

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Sporophytic apomixis in polyploid Anemopaegma species (Bignoniaceae) from central Brazil

Apomixis and polyploidy have been important in the evolution of the angiosperms, and sporophytic apomixis has been associated with polyembryony and polyploidy in tropical floras. We studied the occurrence of polyembryony in populations of tetraploid Anemopaegma acutifolium, A.arvense and A.glaucum from the Brazilian cerrados, and histological features of sexual and apomictic processes were investigated in A.acutifolium. All populations and species were polyembryonic (68.9-98.4% of seeds). Normal double fertilization occurred in most ovules, with exceptions being that 3% of ovules were penetrated but not fertilized and in 4% of ovules both synergids were penetrated. The penetration of both synergids suggests a continuous attraction of pollen tubes and polyspermy. Adventitious embryo precursor cells (AEPs) arose from nucellar and integumental cells of the ovule in pollinated and unpollinated A.acutifolium, indicating sporophytic apomixis. However, further embryo and endosperm development required pollination and fertilization. This pseudogamy also allows concurrent sexual embryo development. Similar polyembryony rates and polyploidy indicated that A.arvense and A.glaucum are also apomictic, forming an agamic complex similar to that observed for some species of confamilial, but not closely related Handroanthus. The co-occurrence of apomixis and polyploidy in different groups of Bignoniaceae indicates homoplasious origin of these agamic complexes. © 2013 The Linnean Society of London.

Mating in the pseudogamic apomictic Anemopaegma acutifolium DC: Another case of pseudo-self-compatibility in Bignoniaceae?

Self-compatibility in apomictic pseudogamic species is considered fundamental to assure reproduction by seeds in extreme situations, making apomictic species more advantageous than sexual ones in these scenarios. Anemopaegma acutifolium is a polyploidy, apomictic sporophytic species with no endosperm development in ovules of unpollinated pistils, which indicates obligate pseudogamy. Thus, the aim of the present work is to study the breeding system and post-pollination events to test if there is similar pseudogamous development irrespective of pollination treatment. We analysed fruit and seed set obtained in controlled experimental pollinations, as well as embryo number per seed, and the progress of ovule penetration, fertilisation and early endosperm development between self- and cross-pollinated pistils. We found that the species is self-fertile and that spontaneous selfing fruit set is also possible, although emasculated flowers never form fruits. Selfed pistils were as efficient as crossed ones for all parameters analysed, except for a delay in endosperm development observed in the former that may be an effect of the late-acting self-incompatibility. Therefore, the avoidance of selfed pistil abortion seems to be promoted by the presence of adventitious embryos and a normal endosperm. We conclude that A. acutifolium shows apomixis-related pseudo-self-compatibility, as in other self-fertile apomictic species of Bignoniaceae, which confer reproductive assurance and increases fruit-set and persistence ability in fast-changing tropical habitats. © 2012 German Botanical Society and The Royal Botanical Society of the Netherlands.