A combined light and scanning electron microscopy study

The uppermost Eocene Florissant Formation, Rocky Mountains, Colorado, has yielded numerous insect, vertebrate and plant fossils. Three previous comprehensive palynological studies investigated sections of lacustrine deposits of the Florissant Formation and documented the response of plant communities to volcanic eruptive phases but overall found little change in plant composition throughout the investigated sections. These studies reported up to 150 pollen and spore phenotypes. In the present paper, we used a taxonomic approach to the investigation of dispersed pollen and spores of the Florissant Formation. Sediment samples from the shale units containing macrofossils were investigated using light microscopy (LM) and scanning electron microscopy (SEM). The general picture of the palynoflora is in agreement with previous studies. However, the combined LM and SEM investigation provides important complementary information to previous LM studies. While a fairly large amount of previous pollen determinations could be confirmed, the purported taxonomic affinities of several pollen phenotypes need to be revised. For example, pollen referred to as Podocarpus or Podocarpidites sp. belongs to the Pinaceae Cathaya, Malus/Pyrus actually belongs to Dryadoideae, pollen of the form genus Boehlensipollis referred to as Proteaceae/Sapindaceae/Elaeagnaceae or Cardiospermum belongs to Sapindaceae but not to Cardiospermum, and pollen of Persicarioipollis sp. B with previously assumed affinities to Polygonaceae actually belongs to Thymelaeaceae. Pandaniidites and one type of Malvacipollis cannot be linked with Pandanaceae and Malvaceae. A few taxa are new records for Florissant (Ebenaceae: Diospyros; Mernispermaceae; Trochodendraceae: Tetracentron). In general, SEM investigations complement the LM palynological studies and improve the identification of dispersed pollen and spores and enable integration of data from dispersed fossil pollen into a wide range of comparative morphological, taxonomic, evolutionary, biogeographic and phylogenetic studies.     

The transfer of Fragilaria obtusa Hustedt to the genus Staurosira Ehrenberg (Bacillariophyceae)

The ultra‐structure of the frustule of the rarely recorded diatom Fragilaria obtusa Hustedt was studied in detail using sand samples from Laranjal Bay (Lagoa dos Patos Rio Grande do Sul State, Brazil). F. obtusa is transferred to the genus Staurosira Ehrenberg as Staurosira obtusa (Hustedt) Garcia. The taxon is characterized by striae composed of elliptical areolae that are occluded by an internal velum, apical pore field formed by several rows of rimmed pores, girdle bands free of ornamentation, wide valvocopulae, and absence of rimoportulae. This is the first record of S. obtusa from an epipsammic habitat.     

A method for the sequential study of synaptonemal complexes by light and electron microscopy

Summary A method is described for the sequential study of synaptonemal complexes by light and electron microscopy. The method is easy, permits one to determine the geometry of chromosome pairing, and should become a routine procedure in the diagnosis of human male subfertility. It should also be useful to establish the risk of recurrence of chromosome aberrations in the progeny of carriers of chromosome rearrangements.This paper is dedicated to the memory of Prof. Gerónimo Forteza Bover, the pioneer of human genetics in Spain, an excellant teacher and a good friend     

The crater defect in boar spermatozoa: A correlative study with transmission electron microscopy,scanning electron microscopy,and light microscopy

Nuclear vacuoles resembling the “crater defect” described in bull spermatozoa were observed in 14 boars. Both the incidence of the defect and semen quality were monitored with phase contrast microscopy over a three-month period. The percentages of cratered spermatozoa varied widely both among boars and in ejaculates from the same boar taken on different days. The presence of cratered spermatozoa at a level of 5% or more appeared to be associated with low semen quality. The defect was studied with scanning and transmission electron microscopy and was found to consist of nuclear invaginations, about 0.5 μm in diameter, containing some scanty amorphous electron-dense material. In boars showing a high incidence of spermatozoa with crater defects, abnormalities of the acrosome and perforatorium were common.     

Sequential study of synaptonemal complexes in mouse spermatocytes by light and electron microscopy

Synaptonemal complex (SC) studies in male mice from the beginning of meiosis to its completion (7–40 days of age) indicate: (1) the existence of a leptotene stage with fragmented and completely unpaired axial elements; (2) that synapsis begins at several different initiation points of the axial elements, resulting in X-shaped and Y-shaped configurations; (3) that interlocking of axial elements at zygotene is a normal phenomenon; and (4) that zygotene (presynaptic) and diplotene (postsynaptic) configurations are different from each other. This investigation received financial support from the special Programme of Research, Development and Research Training in Human Reproduction, World Health Organization.     

A light and electron microscopic study of the quadriflagellate green algaSpermatozopsis exsultans

The green flagellateSpermatozopsis exsultans Korshikov has been studied in culture by light and electron microscopy. The organism is naked, bears four flagella and is conspicuously spirally twisted. The ultrastructure and location of cell organelles (except the flagellar apparatus) has been investigated in detail using an absolute configuration analysis. With the exception of a doubling of the flagella and of the secondary cytoskeletal microtubule system,S. exsultans has the exact same complement of organelles occupying the same relative positions as has been described forS. similis. The two species are therefore correctly placed in the same genus. The usefulness of absolute orientations of cell organelles for green algal taxonomy and phylogeny is stressed.Dedicated to Prof.M. Mix on the occasion of her 60th birthday.     

A new method for studying human oocytes by light and electron microscopy

Since ovarian follicles appear to be randomly oriented with respect to the plane of the section, the method of sectioning and examining follicles at their maximum diameter described here allows direct comparison between oocyte populations of women and small differences can be detected. Re-sectioning for EM allows selected follicles of interest to be examined at a higher resolution.     

Karyotyping chromosomes by electron microscopy. II. A method for the sequential examination of spread and banded metaphases by light and electron microscopy

Summary In an attempt to improve the resolving power of the conventional methods used to karyotype chromosomes, a procedure is presented here which allows the sequential study of selected R-banded metaphases by light and electron microscopy. Small sub-bands, not visible by light microscopy, could be clearly identified.     

New characters in the Gnathostomulid mouth parts revealed by scanning electron microscopy

An analysis with SEM of the mouth parts of 16 species belonging to 10 genera of Gnathostomulida resulted in the following new characters and conclusions: 1) At least in the genus Haplognathia, jaw teeth that are visible by conventional light microscopy are composed of the same aggregated needle-like denticles that are found, often in large numbers, on the basal plates of many filospermoid species. 2) Other new ultrastructural tooth features include the tricuspid basal plate teeth in Problognathia minima, tripartite teeth in Austrognathia and Austrognatharia, and the clear separation, in the Gnathostomula basal plate, of a mediodorsal set of teeth from a more extensive rostroventral set. 3) Three rows of teeth, as typical for Gnathostomulidae and Austrognathiidae, are also present in the filospermoid Haplognathia filum. 4) The wide range of geographic variation in Haplognathia ruberrima is confirmed by significant differences in jaw teeth between specimens from Belize and Bermuda. 5) A compartmentalized involucrum is present in Labidgonathia longicollis. 6) A pair of lamellae addentales, until now only known from Valvognathia pogonostoma, was found in Tenuignathia rikerae, Problognathia minima, and probably also Labidognathia rikerae. 7) In all gnathostomulids, the lamella symphysis is composed of identical rods that are considered homologous with those in the mouth parts of Rotifera and Micrognathozoa.     

Assembly of Octopus dofleini hemocyanin. A study of the kinetics by sedimentation, light scattering and electron microscopy

The kinetics of association of Octopus dofleini hemocyanin subunits to form the native decameric molecule have been studied with a combination of sedimentation, light scattering and electron microscopy. The reaction, initiated by addition of magnesium, is relatively slow, requiring hours to reach completion, with monomer and decamer as predominant molecular species throughout. Analysis of the light-scattering data, including stopped-flow studies, reveals an initial lag period in the reaction, followed by a second-order process that is rate limiting. The lag period depends on both protein and magnesium ion concentration. Electron microscope studies reveal intermediates in the process, and support a model of assembly in which nucleation begins at the dimer level. Theoretical models for the process are compared.     

Morphology of the cyst of Giardia microti by light and electron microscopy

Cysts of Giardia microti, isolated from feces and intestinal contents of Microtus ochrogaster, were examined by light and electron microscopy. These cysts differed morphologically from cysts of other G. duodenalis morphological types in that these cysts often contained two apparently differentiated trophozoites with mature ventral discs. Cysts more closely resembling those reported for G. lamblia and G. muris were in greater abundance in preparations made from intestinal contents and were interpreted as immature cysts. "Multiple fission" cysts, reported in G. muris and G. microti by earlier workers, were not observed; however, endosymbiotic bacteria were found in the cysts of G. microti and may have been responsible for reports of multiple fission in the cysts of Giardia.     

A light and electron microscopical study of the green flagellateSpermatozopsis similis spec. nova

The green flagellateSpermatozopsis similis spec. nova has been studied in culture by light and electron microscopy. The flagellate bears two flagella, is naked and has a characteristic crescent and spirally twisted cell shape. The two flagella are of subequal length, each with a prominent hair-point. Each cell contains two contractile vacuoles, a single chloroplast with an anterior eyespot but lacking a pyrenoid, an anteriorly located nucleus, a single dictyosome associated with the posterior end of the nucleus, a single mitochondrion posterior to the nucleus and associated with a small microbody, some conspicuous vacuoles, and a greater number of secondary cytoskeletal microtubules which probably are responsible for maintaining the peculiar shape of this species. SinceS. similis in culture is only biflagellate, it cannot be accommodated within the quadriflagellate, but otherwise very similar speciesS. exsultans. Spermatozopsis similis is compared with other green flagellates and is shown to share common ultrastructural characters withChlamydomonas-type green algae.     

Characterization of a modular, cell-surface protein and identification of a new gene family in the diatom Thalassiosira pseudonana

We report the characterization of a cell-surface protein isolated from copper-stressed cells of the centric diatom Thalassiosira pseudonana Hasle and Heimdal (CCMP 1335). This protein has an apparent molecular weight of 100kDa and is highly acidic. The 100kDa protein (p100) sequence is comprised almost entirely of a novel domain termed TpRCR for T. pseudonana repetitive cysteine-rich domain, that is repeated 8 times and that contains conserved aromatic, acidic, and potential metal-binding amino acids. The analysis of the T. pseudonana genome suggests that p100 belongs to a large family of modular proteins that consist of a variable number of TpRCR domain repeats. Based on cell surface biotinylation and antibody data, p100 appears to migrate more rapidly with SDS-PAGE when extracted from cells exposed to high levels of copper; however, the discovery of a large family of TpRCR domain-containing proteins leaves open the possibility that the antibody may be cross-reacting with members of this protein family that are responding differently to copper. The response of the gene encoding p100 at the mRNA level during synchronized progression through the normal cell cycle is similar to previously characterized genes in T. pseudonana encoding cell wall proteins called silaffins.