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Wall Ultrastructure (wall + ultrastructure)

Distribution by Scientific Domains
Earth and Environmental Science66%
Life Sciences33%

Selected Abstracts

Wall ultrastructure of an Ediacaran acritarch from the Officer Basin, Australia

LETHAIA, Issue 2 2007
SEBASTIAN WILLMAN
Well-preserved organic-walled microfossils referred to as acritarchs occur abundantly in Ediacaran deposits in the Officer Basin in Australia. The assemblages are taxonomically diverse, change over short stratigraphical intervals and are largely facies independent across marine basins. Affinities of this informal group of fossils to modern biota are poorly recognized or unknown, with the exception of only a few taxa. Morphological studies by use of transmitted light microscopy, geochemical analyses and other lines of evidence, suggest that some Precambrian acritarchs are related to algae (including prasinophytes, chlorophytes, and perhaps also dinoflagellates). Limitations in magnification and resolution using transmitted light microscopy may be relevant when assessing relationships to modern taxa. Scanning electron microscopy reveals details of morphology, microstructure and wall surface microelements, whereas transmission electron microscopy provides high-resolution images of the cell wall ultrastructure. In the light of previous ultrastructural studies it can be concluded that the division of acritarchs into leiospheres (unornamented) and acanthomorphs (ornamented) is entirely artificial and has no phylogenetic meaning. Examination of Gyalosphaeridium pulchrum using transmission electron microscopy reveals a vesicle wall with four distinct layers. This multilayered wall ultrastructure is broadly shared by a range of morphologically diverse acritarchs as well as some extant microalgae. The chemically resistant biopolymers forming the comparatively thick cell, together with the overall morphology support the interpretation of the microfossil as being in the resting stage in the life cycle. The set of features, morphological and ultrastructural, suggests closer relationship to green algae than dinoflagellates. [source]

Morphology and wall ultrastructure of leiosphaeric and acanthomorphic acritarchs from the Ediacaran of Australia

GEOBIOLOGY, Issue 1 2009
S. WILLMANArticle first published online: 18 DEC 200
ABSTRACT Acritarchs are a group of organic-walled microfossils with unknown biological affinities. The wall ultrastructure of the unornamented, smooth Leiosphaeridia sp. and the acanthomorphic Gyalosphaeridium pulchrum from the Ediacaran Dey Dey Mudstone in the Officer Basin, South Australia, was studied by use of transmission and scanning electron microscopy, and transmitted light microscopy. The study of the ultrastructure reveals a complexity in the cell wall not seen in prokaryotes. Wall ultrastructures range from single-layered to three- or four-layered and from homogeneous to porous. Acritarchs with different wall ultrastructures may be different organisms, but may also reflect different stages in a life cycle. In this paper I review previous ultrastructure studies and discuss possible algal and metazoan affinities for the specimens studied herein. [source]

Wall ultrastructure of an Ediacaran acritarch from the Officer Basin, Australia

LETHAIA, Issue 2 2007
SEBASTIAN WILLMAN
Well-preserved organic-walled microfossils referred to as acritarchs occur abundantly in Ediacaran deposits in the Officer Basin in Australia. The assemblages are taxonomically diverse, change over short stratigraphical intervals and are largely facies independent across marine basins. Affinities of this informal group of fossils to modern biota are poorly recognized or unknown, with the exception of only a few taxa. Morphological studies by use of transmitted light microscopy, geochemical analyses and other lines of evidence, suggest that some Precambrian acritarchs are related to algae (including prasinophytes, chlorophytes, and perhaps also dinoflagellates). Limitations in magnification and resolution using transmitted light microscopy may be relevant when assessing relationships to modern taxa. Scanning electron microscopy reveals details of morphology, microstructure and wall surface microelements, whereas transmission electron microscopy provides high-resolution images of the cell wall ultrastructure. In the light of previous ultrastructural studies it can be concluded that the division of acritarchs into leiospheres (unornamented) and acanthomorphs (ornamented) is entirely artificial and has no phylogenetic meaning. Examination of Gyalosphaeridium pulchrum using transmission electron microscopy reveals a vesicle wall with four distinct layers. This multilayered wall ultrastructure is broadly shared by a range of morphologically diverse acritarchs as well as some extant microalgae. The chemically resistant biopolymers forming the comparatively thick cell, together with the overall morphology support the interpretation of the microfossil as being in the resting stage in the life cycle. The set of features, morphological and ultrastructural, suggests closer relationship to green algae than dinoflagellates. [source]

A host-vector system for molecular study of the intracellular growth of Mycobacterium tuberculosis in phagocytic cells

MICROBIOLOGY AND IMMUNOLOGY, Issue 10 2009
Mari Nomoto
ABSTRACT The mechanisms by which Mycobacterium tuberculosis survives and persists in phagocytic cells remain poorly understood. To study the question, a convenient and safe host-vector system is indispensable. In this study it has been shown that, in contrast with M. smegmatis strain mc2155 which has been widely used for molecular analysis, M. smegmatis strain J15cs is able to survive even at day 6 post-infection in a murine macrophage cell line, J774. The survivability of J15cs was found to depend on the culture medium used for the bacteria prior to infection. Bacteria precultured on nutrient agar medium showed a high survivability and a characteristic cell wall ultrastructure. A plasmid vector, pYT923hyg, was developed from an Escherichia coli - mycobacterium shuttle vector pYT923 (previously constructed in our laboratory) to obtain three drug resistant genes (amp-, hyg- and km-resistant gene) and cloning sites in the km resistant gene. The vector pYT923hyg exerted no influence on in vitro growth of J15cs and intracellular survival in J774 cells, and was stably retained in J15cs after serial subculturing (three subcultures) in Luria-Bertani broth and at day 5 post-infection into J774 cells. Furthermore, using this system, the possibility of a relationship between some seemingly essential genes of M. tuberculosis and intracellular growth was demonstrated. In this study, M. smegmatis strain J15cs and pYT923hyg were found to be capable of serving as an appropriate host-vector system for molecular study of the intracellular growth of M. tuberculosis in phagocytic cells; this system may be useful as a screening tool for M. tuberculosis genes. [source]

Gametophyte morphology and ultrastructure of the extremely deep shade fern, Trichomanes speciosum

NEW PHYTOLOGIST, Issue 1 2001
Kittima Makgomol
Summary ,,The extent to which macro- and micromorphological features might contribute to tolerance of extremely deep shade by Trichomanes speciosum, a member of the filmy ferns (Hymenophyllaceae), is reported here. ,,Confocal laser scanning, transmission and scanning electron microscopy were used to study the ultrastructure of gametophytes and sporophyte leaves. ,,Gametophyte filament cells contain numerous small, spherical or ovoid chloroplasts, whereas sporophyte leaf cells have fewer, slightly larger, disc-shaped chloroplasts. The chloroplast grana of gametophytic cells have fewer thylakoids than sporophyte cells, although grana are not numerous in either. Gametophyte filament cell walls resemble those of sporophyte leaf cells, with two or more layers of electron-opaque material and covered in a thin cuticle. Gemma cell wall ultrastructure does not differ from that of gametophyte filament cells; rhizoid cell walls are thick and several-layered. ,,Neither gametophyte filaments nor sporophyte leaves have chloroplasts of the extreme forms reported for deep shade fern or angiosperm leaves. The success of the fern is attributed to a low metabolic rate and inability of other species to cope with extreme low light. [source]

Morphology and wall ultrastructure of leiosphaeric and acanthomorphic acritarchs from the Ediacaran of Australia

GEOBIOLOGY, Issue 1 2009
S. WILLMANArticle first published online: 18 DEC 200
ABSTRACT Acritarchs are a group of organic-walled microfossils with unknown biological affinities. The wall ultrastructure of the unornamented, smooth Leiosphaeridia sp. and the acanthomorphic Gyalosphaeridium pulchrum from the Ediacaran Dey Dey Mudstone in the Officer Basin, South Australia, was studied by use of transmission and scanning electron microscopy, and transmitted light microscopy. The study of the ultrastructure reveals a complexity in the cell wall not seen in prokaryotes. Wall ultrastructures range from single-layered to three- or four-layered and from homogeneous to porous. Acritarchs with different wall ultrastructures may be different organisms, but may also reflect different stages in a life cycle. In this paper I review previous ultrastructure studies and discuss possible algal and metazoan affinities for the specimens studied herein. [source]