School of Botany - Theses
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ItemA taxonomic study of the genus Nostoc in Antarctica(University of Melbourne, 1981)This thesis provides written descriptions and illustrations of Antarctic specimens of Nostoc from both field and cultured material. The aims of the project were to provide the first detailed morphological descriptions of Nostoc from Antarctica and to assess the three different taxonomic approaches currently in use for this genus and for blue-green algae in general. Eight samples of field material are shown to consist of colonies of just two distinctly different structures. Clonal cultures obtained from all of these are described in detail using defined, standardized culture conditions. Five morphologically distinct strains have been recognized from these eight samples. Additionally two distinct strains, previously isolated from field material of unrecorded morphology, have been incorporated into the study. Detailed observations on the morphology and life-cycles displayed by cultures have been made over a 12 week period. Seven genetically distinct strains are distinguished, essentially by plant-mass appearance, although microscopic characters are of importance in some. Two basic types of life-cycle are elucidated, one of which differs from those previously described in the literature. A key is presented which allows the identification of Nostoc strains in culture using these characters. An attempt is made to identify the isolates, and the field material from which they were derived, using three taxonomic approaches. The classical system (Geitler, 1932) is useful only on the field material which is assigned either to N. commune Vauch. or as being close to N. sphaericum Vauch. and N. fuscescens Fritsch. The revised classical system proposed by Drouet (1978) identifies all field and culture material as N. commune (Vauch.) Drouet. Some close correlations are made between cultured strains and those examined in culture by Kantz and Bold (1969). It is concluded that none of these three taxonomic approaches is without its problems and shortcomings and presently no correlation can be made between them. A programme for future work is suggested which might be able to overcome these difficulties and which would lead to an even greater understanding of the important Antarctic genus, Nostoc.
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ItemAspects of the biology and ultrastructure of prorocentrum spp. (pyrrhophyta)( 1987)Ultrastructural characteristics were evaluated as taxonomic determinants for several species of dinoflagellates in the Prorocentrales (Pyrrhophyta). Five species of Prorocentrum from several localities were examined using the techniques of light and electron microscopy. The organisms were described and identified by light microscopy, and certain internal features of Prorocentrum spp. cells were described using transmission electron microscopy. Specifically, the.ultrastructure of the nucleus, cytoplasm, vesicles, pusules, trichocysts, mitochondria, chloroplasts, pyrenoids, cortex (cell wall) and flagellar apparatus was examined in these organisms. The structure of the cortex in P. gracile was also examined by the technique of freeze fracture/deep etch. Most organelles were found to vary little between taxa. The ultrastructure of a few organelles, namely the pyrenoids and some features. of the cortex, varied considerably between species and are therefore considered taxonomically more useful than others. The morphology of the chondriome (mitochondrial complement) of P. minimum was established using the technique of serial sectioning. It was found to consist of a major reticulated mitochondrion and several smaller satellite mitochondria. During cytokinesis, the major portion of the chondriome is split by the cleavage furrow and approximately half of the chondriome is passed to each daughter cell. The significance of this structure and the division mechanism is discussed (Chapter Three). Aspects of the processes of mitosis (karyokinesis) and cell division (cytokinesis) are described in P. gracile and P. minimum. Both species were found to have a closed mitosis, the nuclear membrane being strongly associated with the chromosomes, and microtubules traversing channels through the nucleus, as observed for other members of this group. Kinetochore-like structures may occur in these organisms. A cell of P. gracile undergoing division is also illustrated (Chapter Four).