Ovule development, megasporogenesis, and megagametogenesis of Fouquieria fasciculata (Willd. ex Roem. & Schult.) Nash (Fouquieriaceae)

Abstract

Background: Fouquieriaceae is a small family that consists of a single genus, Fouquieria, with eleven species occurring mostly in arid and semiarid regions of Mexico and the southwestern United States. The development of the ovule and the female gametophyte has been poorly characterized in species of the family; thus, it is proposed to carry out a detailed study on the development of the ovule, megasporogenesis and megagametogenesis in Fouquieria fasciculata. Questions: How are the developmental patterns of the ovule and the female gametophyte in Fouquieria fasciculata? Study species: Fouquieria fasciculata (Willd. ex Roem. & Schult.) Nash (Fouquieriaceae). Methods: Embryology, morphology and histochemical tests of floral buds and flowers at pre-anthesis of Fouquieria fasciculata were examined using light microscopy and scanning electron microscopy. Results: The ovules of Fouquieria fasciculata are anatropous, bitegmic and tenuinucellate, and the micropyle is formed by the inner integument. The innermost layer cells of the inner integument form an integumentary tapetum or endothelium. The cells of integumentary tapetum are characterized by very conspicuous wall thickenings on the inner tangential side, and are radially elongated surrounding the nucellus. The pattern of development of the female gametophyte is monosporic Polygonum-type, and the formation of a lateral haustorium was observed. Conclusions: This investigation describes in detail the development of the ovule and the female gametophyte ofFouquieria fasciculata. Our results show interesting features, such as the differentiation of an integumentary tapetum, a monosporic Polygonum-type pattern of development and the formation of lateral haustorial arm in the female gametophyte.