title: Developmental and ultrastructural characters of the pollen grains and tapetum in species of Nymphaea subgenus Hydrocallis.
abstract: Variations in pollen characters and tapetum behavior were recently acknowledged in the early-divergent family Nymphaeaceae and even within the genus Nymphaea, which probably is not monophyletic; some traits such as infratectum and tapetum type are also a matter of different interpretations. In this study, developmental characters of the pollen grains and tapetum in Nymphaea subgenus Hydrocallis are provided for the first time. Observations were made in N. amazonum, N. gardneriana, and N. prolifera using light, scanning, and transmission electron microscopy. Tapetum is of the secretory type and produces orbicules. At microspore and pollen grain stages, the distal and proximal walls differ considerably. This result supports the operculate condition of the aperture in Hydrocallis, and such aperture might be plesiomorphic for Nymphaeoideae. The infratectum is intermediate, composed of inter-columellae granular elements, robust columellae consisting of agglomerated granules, complete columellae, and fused columellae. Narrow microchannels are present and persist until the mature pollen grain stage. The membranous granular layer is often present in the pollen grains of Nymphaeaceae. In N. gardneriana, this layer is most probably a component of the intine because it is lost after acetolysis. Orbicules in the Nymphaeaceae are characterized as spherical or subspherical, with a smooth sporopolleninic wall that surrounds an electron-lucent core and with individual orbicules that usually merge to give irregular aggregations. The aperture, pollen wall ultrastructure, and the tapetum of the studied species are discussed in an evolutionary and systematic context, and these characters are also compared with those of other angiosperm lineages.
authors.affiliation: Instituto de Botánica del Nordeste (Consejo Nacional de Investigaciones Científicas y Técnicas, Universidad Nacional del Nordeste), Facultad de Ciencias Agrarias, Av. Sargento Cabral 2131, C.P 3400, Corrientes, Argentina. lmelisa.zini@yahoo.com.ar.
authors.forename: Lucía Melisa
authors.initials: LM
authors.lastname: Zini
authors.affiliation: Cátedra de Botánica General, Departamento de Recursos Naturales y Ambiente, Facultad de Agronomía, Universidad de Buenos Aires, Buenos Aires, Argentina.
authors.forename: Beatriz Gloria
authors.initials: BG
authors.lastname: Galati
authors.affiliation: Cátedra de Botánica General, Departamento de Recursos Naturales y Ambiente, Facultad de Agronomía, Universidad de Buenos Aires, Buenos Aires, Argentina.
authors.forename: Gabriela
authors.initials: G
authors.lastname: Zarlavsky
authors.affiliation: Instituto de Botánica del Nordeste (Consejo Nacional de Investigaciones Científicas y Técnicas, Universidad Nacional del Nordeste), Facultad de Ciencias Agrarias, Av. Sargento Cabral 2131, C.P 3400, Corrientes, Argentina.
authors.forename: María Silvia
authors.initials: MS
authors.lastname: Ferrucci
mesh_terms: D046529:Microscopy, Electron, Transmission; D030721:Nymphaea / Q000254:growth & development / Q000648:ultrastructure*; D011058:Pollen / Q000254:growth & development / Q000648:ultrastructure*
keywords: Exine; Membranous granular layer; Orbicules; Pollen; Tapetum type