Botanical Journal of the Linnean Society, 2003, 142, 73–81. With 24 figures © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society, 2003, 142, 73–81 73 Blackwell Science, LtdOxford, UKBOJBotanical Journal of the Linnean Society0024-4074The Linnean Society of London, 2003 142 7381 Original Article M. T. AMELA GARCÍA ET AL. MEGAGAMETOPHYTE DEVELOPMENT OF PASSIFLORA CAERULEA *Corresponding author. E-mail: amela@bg.fcen.uba.ar Development and ultrastructure of the megagametophyte in Passiflora caerulea L. (Passifloraceae) M. T. AMELA GARCÍA 1,2 *, B. G. GALATI 2 and A. M. ANTON 1 1 Instituto Multidisciplinario de Biología Vegetal, Universidad Nacional de Córdoba, Argentina 2 Departamento de Ciencias Biológicas, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Argentina Received July 2002; accepted for publication November 2002 Megasporogenesis and megagametogenesis of Passiflora caerulea L. were studied using light and transmission elec- tron microscopy. The archesporial tissue is generally formed by one cell. The megaspore mother cell gives rise to a linear tetrad of megaspores. The chalazal megaspore is the functional one, and originates a Polygonum-type female gametophyte. The antipodals are ephemeral. Abundant starch is found in the nucellar cells, specially the ones adja- cent to the megagametophyte. The two synergids show ultrastructural differences, involving the filiform apparatus, the nucleolus and the endoplasmic reticulum; these differences suggest a functional differentiation, probably related to the reception of the pollen tube. This is the first report in angiosperms of substantial morphological differences between the two synergids. © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society, 2003, 142, 73–81. ADDITIONAL KEYWORDS: female gametophyte – fertilization – megagametogenesis – megasporogenesis – synergids. INTRODUCTION Ultrastructural studies of the megagametophyte of angiosperms have been undertaken on quite diverse genera (Willemse & van Went, 1984; Raghavan, 1997), but mainly on members of the Poaceae, Solanaceae and Asteraceae. Many families still lack investigation. Little information is available on megasporogenesis and megagametogenesis of Passiflora spp. Several authors have studied these processes in some species of the genus (Kratzer, 1918; Raju, 1956; Padhye & Deshpande, 1960; Singh, 1962), but all these approaches have involved only light microscopy. The ontogeny of the megagametophyte of P. caerulea L. has not yet been studied. This is the first relevant light microscopy study on P. caerulea and the first ultrastructural description in any species belonging to the Passifloraceae. MATERIAL AND METHODS The material was collected from a natural population of P. caerulea in Ciudad Universitaria (Capital Fed- eral), Argentina. Megagametophyte development was studied under light microscopy, and the mature mega- gametophyte with transmission electron microscopy. LIGHT MICROSCOPY (LM) Pistils at different stages of development were fixed in FAA, dehydrated, embedded in paraffin wax, serially sectioned with a Minot microtome and stained with a safranin-fast green combination (D’Ambrogio, 1986). The material was observed and drawn with a Wild M20 microscope. The photographs were taken with a digital camera on a Nikon Labophot AFX-II microscope. TRANSMISSION ELECTRON MICROSCOPY (TEM) Mature ovules were pre-fixed in 2.5% glutaraldehyde in phosphate buffer (pH 7.2) for 24 h and then post- fixed in OsO 4 at 2∞C in the same buffer for 3 h; they Downloaded from https://academic.oup.com/botlinnean/article-abstract/142/1/73/2433523 by guest on 11 June 2020