Sonia Rosenfeldt

Pollen ontogeny in Magnolia liliflora Desr.

Pollen ontogeny contributes significantly to the evolutionary analysis and the understanding of the reproductive biology of seed plants. Although much research on basal angiosperms is being carried out there are still many important features about which little is known in these taxa, such as the sporophytic structures related to pollen development and morphology. In this study, pollen development of Magnolia liliflora was analyzed by optical microscopy and transmission electron microscopy. The aim of this paper was to supply data that will help characterize basal angiosperms. Microsporogenesis is of the successive type, so that tetrads are decussate or isobilateral. The callosic walls form by the centripetal growth of furrows. The secretory tapetum develops orbicules, which start to form in the microspore tetrad stage. Pollen grains are shed at the bicellular stage. The exine wall has a granular infratectum. Ultrastructural changes observed in the cytoplasm of microspores and tapetal cells are related to the development of the pollen grain wall and orbicules. Centrifugal cell plates are more usual for the successive type of microsporogenesis. The presence of the successive type of microsporogenesis with callosic walls formed by the centripetal growth of furrows could reflect the fact that the successive type in Magnoliaceae is derived from the simultaneous type. The granular infratectum of the ectexine and the presence of orbicules could indicate that this species is one of the most evolved of the genus.

The structure of the stigma and the style of Oxalis spp. (Oxalidaceae)1

Abstract The anatomy of the stigma and style of three species of Oxalis (O. articulata, O. hispidula, and O. paludosa), belonging to different sections (Articulatae, Ionoxalis, and Corniculatae) was studied using light, scanning, and transmission electron microscopy. The stigma morphology of each of the different flower morphs of the three species (longistylous, medistylous, and brevistylous flowers) was compared in this work. The stigma is dry and has multicellular and multiseriate papillae. The morphology of the papillae does not differ between flower morphs. According to the Ca2+ concentration in pre-anthesis, anthesis, and post-anthesis, we hypothesize that the stigmas of the different morphs are equally receptive. Oxalis style is solid type. The cytoplasm of the transmitting tissue cells is dense with few vacuoles and abundant organelles. The transmitting tissue cells have large amounts of intercellular substance, mainly at the corners. This substance has moderate electron density in the species O. articulata and O. hispidula and shows some laxer areas in O. paludosa. The transmitting cell wall of the two first species has wall ingrowths like fingers with low electron density that protrude into the cytoplasm. The ultrastructural characteristics of the transmitting cells allow to characterize three of the sections of the genus.

Megasporogenesis and Megagametophyte Development in Ten Species of Oxalis

Ovule morphology, megasporogenesis and megagametogenesis of ten species of Oxalis were examined. The ovule is anatropous, bitegmic and the integuments form a zig-zag micropyle. The type of female gametophyte development is variable in the studied species. The majority of them have a monosporic Polygonum-type female gametophyte. Two of the studied species show binucleate dyad members, so they have a bisporic Allium-type female gametophyte. Only O. articulata follows tetrasporic Adoxa-type development of the megagametophyte. This is the first report of a tetrasporic female gametophyte in Oxalidaceae. The endosperm is nuclear, and development of the embryo corresponds to the Solanad type.

Autofluorescence and Ultrastructure in the Myxomycete Diachea leucopodia (Physarales)

Autofluorescence is reported for the first time in Myxomycete fruiting bodies. Ultrastructure of stalked sporangia of Diachea leucopodia (Didymiaceae, Physarales) was studied using scanning and transmission electron microscopy, energy-dispersive X-ray microanalysis, and fluorescence microscopy. External and internal properties of the peridium that surround the spores and capillitium exhibit autofluorescence. The stalk is composed of calcareous granules and energy-dispersive X-ray microanalysis demonstrates that the elemental composition of the peridium, capillitium, and stalk has varying concentrations of calcium.

Embryological studies in Melia azedarach L.1,2

Abstract Previous studies described the lateral flowers of Melia azedarach cymules as staminate, and the terminal one as perfect. This paper shows that all the flowers of the inflorescence present both gynoecium and androecium but only the terminal ones produce fruits. Both types of flowers are successful in developing megagametophytes and viable pollen. All flowers are fertilized but ovules of the lateral flowers of cymules degenerate after fertilization. The lateral flowers mature later than the apical ones. Therefore, it could be apical dominance by terminal flowers that prevents development of seeds from lateral ones as a possible energy saving. However, when the apical flower fails in its development after fertilization, lateral flowers can form seeds and fruits. This ensures good seed production in this species and that is what makes it a highly invasive species.