School of Botany - Theses
Permanent URI for this collection
Search Results
1 - 4 of 4
-
ItemA molecular and taxonomic appraisal of selected tribes and genera of the Rhodomelaceae (Ceramiales: Rhodophyta)( 2001-07)The largest of the 80 families in the division Rhodophyta is the Rhodomelaceae. A great many genera and species are restricted to Australasia, which is the major centre of diversity and distribution. Perhaps as a consequence, the Rhodomelaceae has remained relatively unstudied compared with most other red algal families even at the morphological/anatomical level. Within the confines of a PhD program it would not be possible to study all of the 125 genera credited to the Rhodomelaceae. The focus of this thesis has, therefore, been narrowed down to selected tribes and genera, all of which have a strong Australasian component. Anatomical and molecular analyses have been undertaken on members of the tribes Amansieae, Pleurostichidieae, Streblocladieae and Sonderelleae and the genus Halydictyon. The results of these analyses have led to the description of two new genera, three new species, and one new tribe as well as the resurrection of two genera and the recombination of ten species. The taxonomic position and validity of the studies tribes and genera has also been established.
-
ItemA cladistic and biogeographic analysis of Philotheca (Rutaceae) and allied genera( 2001)This thesis considers the relationships, classification and historical biogeography of the related Australian endemic flowering plant genera Philotheca, Eriostemon and Crowea (family Rutaceae, tribe Boronieae). It focuses mostly on relationships within and between these genera, but also considers the relationships of these groups to other members of the tribe Boronieae, particularly the small genera Geleznowia and Drummondita. It includes a brief appraisal of the species-level taxonomy of Philotheca, Eriostemon and Crowea, a survey of morphological characters, a survey of leaf phenolic compounds, and a series of cladistic and biogeographic analyses. The appraisal of species-level taxonomy identified terminal taxa suitable for use in cladistic analyses, and has resulted in the recognition of one new species (Philotheca sporadica) and three new subspecies (P. myoporoides subsp. brevipedunculata, subsp. euroensis, and subsp. obovatifolia, as well as a recommendation to reinstate one species (Eriostemon banksii, which was previously reduced to subspecific status under E. australasius). The survey of morphological variation identified 108 morphological characters, 99 of which are potentially useful in the assessment of relationships, and nine that are unique to single terminal taxa. The survey of leaf phenolics was based on two-dimensional paper chromatography, and the chromatographic properties and distributions of 26 compounds are reported. Twenty-three of these compounds are potentially useful in the assessment of relationships, and three are unique to single terminal taxa. Assessment of the higher-level relationships of Philotheca, Eriostemon and Crowea (to each other and to other taxa of Boronieae) was based on reappraisal, and re-analysis, of a previous phylogenetic analysis (Armstrong 1991). This reappraisal was based on a limited set of morphological characters, and used genera, sections within genera, and some species as terminal taxa. In general higher-level relationships of the three genera were either poorly resolved or poorly supported. A close relationship of Drummondita to Philotheca sect. Philotheca was supported, but a close relationship of Geleznowia to this group (as has recently been proposed) was not. A series of subsequent analyses of relationships within Philotheca, Drummondita, Eriostemon and Crowea employed a larger set of morphological and phenolic characters (in various combinations), and used species, subspecies and varieties as terminal taxa. Character state transformations were polarised using Crowea as an outgroup to Philotheca, Drummondita and Eriostemon, and vice versa. This assignment of ingroup/outgroup relationships was based on an a posteriori decision, given the lack of a well-supported higher-level phylogeny for the group. These subsequent analyses provided good support for the monophyly of each of Crowea, Philotheca sect. Erionema, P. sect. Corynonema, P. sect. Cyanochlamys, Eriostemon, Drummondita, and a group comprising both Drummondita and P. sect. Philotheca. Philotheca sect. Philotheca was only supported as monophyletic in some analyses. Relationships among these groups were not unequivocally resolved, but the monophyly of Philotheca, as currently circumscribed, was not supported. The biogeographic analyses used the method of subtree analysis and considered the historical relationships of areas in south-western and eastern Australia. The pattern or area relationships was not unequivocally resolved, with some areas showing multiple relationships. The results of these analyses are compared with those from other studies on Australian biogeography. A general historical scenario for the differentiation of taxa and areas is discussed.
-
ItemHyperaccumulation of metals in Australian native plants( 2000)The central aim of this thesis was to study the accumulation of metals in Australian native plants. Firstly, this involved searching for new hyperaccumulators on serpentine outcrops in the Wellington region of Victoria and serpentine areas between Rockhampton and Marlborough in central Queensland. A new hyperaccumulator of Mn was found in central Queensland, Austromyrtus bidwillii. This is the first Australian native plant to be reported to hyperaccumulate Mn. Manganese accumulated throughout the above-ground parts of this dry rainforest tree, reaching concentrations up to 19,200 µg g-1 and 26,500 µg g-1 in leaves and young bark, respectively. Concentrations of Ni, Cr, Co, Mn, Mg and Fe in the other species sampled were generally either lower than or similar to the concentrations reported to be typical for serpentine vegetation throughout the world (96 species were sampled from Victoria and 138 species from central Queensland). The aim of the second part of this thesis was to examine possible mechanisms involved in detoxification of metal ions and storage of metal complexes in two known hyperaccumulators of Ni from Australia, Hybanthus floribundus and Stackhousia tryonii, and the hyperaccumulator of Mn identified in the surveys described above. This involved identifying and quantifying organic acids present in leaf extracts and determining whether there were sufficient concentrations of these compounds to sequester the metal. In leaves of Austromyrtus bidwillii, a number of organic acids (oxalic, malic, malonic and succinic acids) were present in relatively high concentrations compared with normal plants and the total concentration of organic acids exceeded the concentration of cations (Mn, Mg and Ca). Purification of the Mn rich extracts of leaves by size exclusion chromatography showed that these organic acids could be associated with the Mn. In both Stackhousia tryonii and Hybanthus floribundus, citric acid was the dominant organic acid present in leaf extracts, but it was present in concentrations that are considered as normal for plant leaves. The effect of treating plants with Ni on citric acid content in leaves and roots of Hybanthus floribundus was investigated. Ni treatment had no significant effect on citric acid content in leaves, but a strong and significant correlation was found between Ni and citric acid content in roots. Citric acid was present in sufficient concentrations in both leaves and roots to complex the Ni in most treated plants, except for those treated with the highest dose of Ni. Similarly, in field samples that contained very high concentrations of Ni (collected from Widgiemooltha, W A), there was insufficient citric acid to complex a significant portion of the Ni. The cellular and sub-cellular distribution of Ni in the two Ni hyperaccumulators was investigated using x-ray microanalysis. In leaves of Hybanthus floribundus, Ni was predominantly localised in the vacuoles of epidermal cells, averaging 128 lnmol kg- l of embedded tissue. Ni was also detected on the outside of the cell walls throughout the leaf cross sections, suggesting that apoplastic compartmentation is also involved in Ni tolerance and accumulation in this species. In leaves of Stackhousia tryonii, Ni was predominantly localised in the cuticle on the surface of the leaf and was also present in epidermal vacuoles. In both species, there was no indication that Ni was associated with phosphates or phytochelatins, as concentrations of P and S were insufficient to suggest an involvement in sequestration of Ni. Thirdly, a protocol for the micropropagation of Hybanthus floribundus was developed, as the germination requirements of seed of this species are unknown and propagation from cuttings is slow and has low efficiency. Large quantities of plants were successfully grown in culture from sterilised pieces of stem or leaf tissue. Importantly, cloned plants retained their ability to hyperaccumulate Ni. Micropropagation provides many opportunities for studying metal tolerance and hyperaccumulation of Ni in this species in the future. Moreover, the protocol presented in this thesis may be used for cultivation of Hybanthus floribundus for rehabilitation of mine sites or perhaps for phytoextraction. Finally, the ability of Hybanthus floribundus ssp. floribundus growing on non-metalliferous soil in Bendigo, Victoria, to hyperaccumulate Ni was investigated. Plants hyperaccumulated Ni when grown on Ni-enriched potting mix, with no adverse effect on growth or nutrient status. This finding suggests that hyperaccumulation of Ni in this species may not be restricted to the populations that grow on serpentine in Western Australia.
-
ItemThe infection process of Fusarium oxysporum f. sp. vasinfectum in Australian cotton and associated cotton defence mechanisms( 2007)Fusarium oxysporum f. sp. vasinfectum (Fov) was first identified in Australia in 1993, and has since become one of the most significant threats to the country’s thriving cotton industry. The interaction between a unique Australian biotype of Fov and cotton hosts with varying susceptibilities to Fusarium wilt was studied. This research described the infection process and associated host defence mechanisms of two commercial cotton varieties after inoculation with Fov, and quantified their subsequent accumulation of antimicrobial terpenoids. A rapid, reliable glasshouse bioassay that correlated with field resistance was developed for the study of Fusarium wilt of cotton. Detailed observations of the infection process obtained through light microscopy were used to formulate the disease cycle of Australian Fusarium wilt cotton. Using pathogen growth assays, varietal differences in root exudates and vascular tissues in the cotton hosts were documented. Root diffusate from the most susceptible cotton variety to Fusarium wilt, Siokra 1-4, contained a lipophilic compound that promoted the germination of Fov microconidia. On the other hand, a lipophilic compound present in diffusate from the least susceptible variety, Sicot 189, inhibited the growth of Fov germ tubes. A bioassay using inoculated whole plants showed that Fov colonisation of the vascular tissues of Sicot 189 was restricted after 3 days. The basis for this inhibition was investigated further using light and transmission electron microscopy. Infection induced the reorganisation of contact cells in host vascular tissue, including an increase in cytoplasmic content and the partitioning of vacuoles, which was concurrent with the accumulation of materials in adjacent vessel lumens, via pits. Histochemical analysis indicated these globular materials secreted into the vessels were terpenoids. These structural and terpenoid responses in Siokra 1-4 and Sicot 189 were similar, however, they were more intense and rapid in the latter, less susceptible variety. The responses in Sicot 189 also corresponded to the time period that pathogen inhibition was observed. Thus, a correlation was demonstrated between the rapid and intense induction of both structural and biochemical responses with decreased susceptibility to Fusarium wilt. Detailed HPLC analysis of vascular tissues confirmed that terpenoids accumulated more rapidly and at higher concentrations in the less susceptible cotton variety. These findings provided strong evidence for the involvement of antimicrobial terpenoids in the determination of Fusarium wilt susceptibility of Australian cotton varieties. This work represents the most complete survey to date of the interaction of Australian biotypes of Fov with cotton. These insights can contribute to future cotton breeding efforts and cultural management of Fusarium wilt in the field. Thus, each part of this study has advanced complementary facets of our understanding of Fov, and has provided a framework from which future studies on phytoalexins and other putative cotton defences can be studied.