Ovule and female gametophyte development in the Bromeliaceae: an embryological study of Pitcairnia encholirioides

Abstract

Pitcairnia encholirioides L.B.Sm. is an endangered species endemic to the Brazilian Atlantic Forest. This species exhibits limited flowering, late seed germination, and preference for clonal growth. Because little is known about its life cycle and female gametophyte development, the ovule development, gynosporogenesis, and gynogametogenesis were analysed to advance knowledge of the species’ life cycle and structural alterations during ovule and female gametophyte development. Also, identification of embryological characters contributing to systematics of Pitcairnioideae is relevant. The ovules are anatropous, bitegmic, and crassinucellate, the gynosporogenesis is monosporic, and the female gametophyte is a Polygonum type. Different patterns in development of the integuments, nucellus, chalazal appendage, and micropylar channel indicate the potential of these characters for subfamily systematics. In the filiform apparatus, a range of glycan-directed monoclonal antibodies was used; the filiform exhibited a biphasic structure. While only arabinogalactan proteins (AGPs) occurred in the translucent matrix, mannans were the most prevalent glycan in the denser matrix. These phases may have distinct mechanical or signalling properties, as they showed different cell wall component distributions. The distinct spatial distribution between AGPs and other glycans showed that the filiform apparatus is heterogeneous and has a common polymer assemblage for both synergids.