ABSTRACT In diploid late-acting self-incompatible (LSI) species of Bignoniaceae, self-pollinated pistils show a marked delay in ovule penetration by pollen tubes, followed by delayed, but otherwise normal, initial stages of endosperm development and subsequent pistil abscission. Most polyploid species of Bignoniaceae are apomictic and set selfed fruits with viable polyembryonic seeds carrying adventitious embryos. Handroanthus serratifolius is a polyploid species with sporophytic apomictic individuals that produce polyembryonic seeds after either self- or cross-pollination, and other LSI individuals that produce exclusively monoembryionic seeds. Our aim was to determine whether self-sterility events in the latter are similar to those observed in other diploid LSI species of Bignoniaceae. No conspicuous differences in the progress of ovule penetration, fertilization and early stages of endosperm development were observed between selfed and crossed pistils, which contrasts with the marked delay observed in these events after self-pollination in diploid LSI species of the family. Adventitious embryo precursor cells (AEPs) were observed in some ovules, but they apparently do not develop into embryos. We believe that the AEPs in these plants represent a ‘potential’ for sporophytic apomixis, which would explain the similar behaviour of post-pollination events in selfed vs. crossed pistils despite their inability to set fruits after selfing.

Os óvulos de Tabebuia pulcherrima são anátropos, unitégmicos e tenuinucelados. Os nucelos apresentam estrutura trizonada. O tegumento é iniciado por divisões periclinais na camada dérmica (zona I), ao redor da base do arquespório. Em seguida, células derivadas da camada subdérmica (zona II) tomam parte na constituição do tegumento, empurrando as células de origem dérmica para a região micropilar. A célula arquespórica diferencia-se diretamente em megasporócito, sofre meiose e origina uma tétrade linear de megásporos. A célula-mãe do megásporo madura é alongada, com núcleo central e vacuoma bipolar apresentando conteúdo fibro-granular. As camadas celulares mais internas do tegumento diferenciam-se em endotélio rico em amiloplastos. Padrões de deposição de calose na tétrade e da seleção do megásporo funcional, bem como o valor taxonômico de alguns caracteres são discutidos.

The ovule of Tabebuia pulcherrima is anatropous, unitegmic and tenuinucellate. The nucellus shows a trizonate structural organization. The integument is initiated by periclinal divisions in the dermal layer (zone I), around the base of the archesporium. Subsequently, cells derived from the subdermal layer (zone II) start to push the dermal cells, so that they shift toward the micropylar region. The archesporial cell differentiates directly into the megaspore mother cell, undergoes meiosis, and originates a linear tetrad of megaspores. The mature embryo sac mother cell is elongated, possess a conspicuous central nucleus, and a characteristic bipolar vacuome with fibrous-granulated content. The inner cell layers of the integument differentiate into an amyloplast-rich endothelium. Patterns of callose deposition in the tetrad and selection of the functional megaspore, as well as the taxonomic value of some characters are discussed.