Beatriz G. Galati

Embryology of Helianthus annuus (Asteraceae)

Abortion of sunflower fruits during different phases of their development could be due to abnormalities in the reproductive process. We report a comparative study of the sporogenesis, gametogenesis and the development of the related sporophytic structures in three commercial hybrids, DK 4050, CF 17 and P30, and a line, HA 89. The anther wall consists of epidermis, endothecium, one middle layer and a plasmodial tapetum with binucleate cells before integrating. A peritapetal membrane with orbicules encloses the pollen grains, which are triporate, angulaperturate and shed at tri cellular stage. HA 89 also presents tetraporate pollen grains. The ovule is tenuinucellate, unitegmic and anatropous. The young female gametophyte consists of six cells and eight nuclei. Antipodals, which vary in number and in the number of nuclei in each cell, usually have thick walls between themselves and the central cell. Differences among the genotypes studied may explain the contradictions found on previous accounts.

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.

Embryology of Macroptilium arenarium (Leguminosae)

Macroptilium arenarium (Bacigalupo) S.I.Drewes & R.A.Palacios produces two floral morphs, aerial chasmogamous flowers and cleistogamous flowers in geophyte racemes. A comparative study of the sporogenesis, gametogenesis and the development of the related sporophytic structures in both floral morphs is reported. The anther is tetrasporangiate, its wall consists of epidermis, endothecium, one or two middle layers and an uninucleate secretory tapetum. The mature endothecium presents fibrilar thickenings that are more developed in cleistogamous flowers. Pollen grains are tricolporate, angulaperturate, and are shed at bicellular stage. The ovule is crassinucelate, bitegmic and anacampylotropous. Megaspore tetrads with linear arrangement have been observed in chasmogamous flowers, whereas only megaspore dyads have been found in cleistogamous flowers. In both floral morphs the chalazal megaspore develops into an embryo sac of Polygonum type. Apomixis is considered as a possible replacement for sexual reproduction in cleistogamous flowers.

Morphological and ultrastructural studies of floral nectaries in Rhamnaceaea,b

Abstract Morphology, anatomy, and ultrastructure of nectaries of 12 species belonging to five tribes of Rhamnaceae (Pomaderreae, Colletieae, Paliureae, and Gouanieae of the Ziziphoids clade and Rhamneae of the Rhamnoids clade) were studied by light and electron microscopy. Four types of nectaries were observed in this study. Species of the tribes Rhamneae, Gouanieae, Paliureae, and Cryptandra tomentosa Lindl. of the Pomaderreae tribe have annular nectaries. Siegfriedia darwinioides C.A. Gardner and Stenanthemum humile Benth. (Pomaderreae) have revolute nectaries, as do Colletia paradoxa (Spreng.) Escalante and Colletia spinosissima J.F. Gmel. (Colletieae). Retanilla patagonica (Speg.) Tortosa and Kentrothamnus weddellianus (Miers) M.C. Johnst. (Colletieae) have indistinct and adpressed nectaries, respectively. Nectar secretion occurs through modified nectary stomata in all species. Differences in the ultrastructure, mode of nectar secretion, and position of the nectaries are discussed. According to the organelles found in the nectary cells of all the species studied, granulocrine secretion is most likely to occur. Further research on these structures in additional species of this family could help to establish nectary homologies.

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.

Pollen Development and Morphology in four Species of Pterocactus (Cactaceae)

We report a detailed study of the development and morphology of pollen in four species of the genus Pterocactus (Cactaceae), carried out by using LM and SEM. The anther is tetrasporangiate, its wall consists of epidermis, endothecium, one middle layer and a binucleate secretory tapetum. Microspore tetrads are tetrahedrical and pollen grains are shed at bicellular stage. Pollen grains are pantoporate, with a perforate tectum and supratectate spinules.

A comparative ultrastructural study of the pollen of Linum burkartii and L. usitatissimum (Linaceae)1,2

Abstract We report a detailed study of the pollen wall structure in Linum burkartii and L. usitatissimum (Linaceae). This study was carried out using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Results confirm that the exine of the species studied is formed by: the ectexine constituted by clavae, gemmae, and a loose basal layer, a thin endexine and a fibrilar intine. These observations constitute the first report on the ultrastructure of pollen in the Linaceae that characterizes the species here studied and expands the palynological knowledge of this family.

Embryological studies on Trichloris (Poaceae, Chloridoideae)

Geraldina Alicia RICHARD*, María Carolina CERINO, Beatriz Gloria GALATI, Eliana De Luján EXNER, José Francisco PENSIERO Department of Plant Biology, Faculty of Agricultural Sciences, National University of the Littoral (Universidad Nacional del Litoral, in Spanish), Esperanza, Argentina National Council of Scientific and Technical Research, Buenos Aires, Argentina Department of Natural Resources and Environment, Faculty of Agriculture, National University of Buenos Aires (Universidad Nacional de Buenos Aires, in Spanish), Buenos Aires, Argentina

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.