The aim of this thesis was to investigate the regulation and role of invertases in plant carbohydrate metabolism. In the first part of this thesis a molecular approach was adopted and the expression of five invertase genes were examined in different organs and in leaves of different ages in the model plant species Arabidopsis thaliana (L. ). Of the five genes examined two encoded apoplastic invertases (ATßFRUCT 1 and ATßFRUCT 2), two encoded soluble invertases with a probable vacuolar localisation (ATßFRUCT 3 and 4) while the fifth encoded an invertase with an unknown subcellular localisation (ATßFRUCT 5). Generally, Northern hybridisation assays were sufficiently sensitive for the detection of invertase gene expression in A. thaliana, however, in order to examine the expression of rare ATßFRUCT 1 and ATßFRUCT 2 mRNA the reverse transcriptase polymerase chain reaction (RT-PCR) was the method of choice. The development of an RT-PCR internal standard enabled these data to be semi-quantitative in nature. Expression analysis revealed that each of the five invertase genes were differentially regulated in A. thaliana. However, high levels of invertase gene expression were associated with tissues typically considered sinks for carbohydrate. Examination of these tissues also revealed a relationship between invertase activity and the ratio of sucrose to hexoses. Previous work has shown that certain environmental stimuli can influence invertase activity and gene expression. In this thesis the infection of A. thaliana leaves with the biotrophic pathogen Albugo candida resulted in the localised stimulation of cell-wall associated invertase activity. Examination revealed that the majority of this increase was attributable to the stimulation of the host apoplastic invertase gene, ATßFRUCT 1. Furthermore, expression of this gene was also elevated in response to mechanical leaf wounding. The high expression of ATßFRUCT 1 in sink tissues and in response to pathogenesis and wounding suggested that this gene plays an important role in establishing a supply of hexoses to tissues under a wide range of conditions. In the second part of this thesis transgenic tomato plants (prepared by Zeneca Plant Science) with a range of leaf vacuolar invertase activities were examined. There was a linear relationship between vacuolar invertase activity and the amount of leaf hexose. In plants with no detectable leaf vacuolar invertase activity there was an accumulation of sucrose. This suggests that hexoses generated in the leaves of tomato plants are the product of sucrose cycling through the vacuole. The implications of such cycling are discussed in detail.

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Thesis (Ph.D.)--Boston University / It is now generally recognized that insulin facilitates the transfer of certain sugars through cytostructural barriers. If the transfer of a utilizable sugar into the cell is affected by a rate-limiting reaction, then all subsequent enzymatic reactions of this sugar in the cell would be dependent upon this reaction. This study has involved an investigation of factors which regulate the transfer of sugar into muscle cells. [TRUNCATED]

Suspensions of C. perfringens, when grown on a peptone-free, semi-defined medium, have been shown to remain resistant to autolysis for extended periods of time. The stability of these suspensions has been compared with that of cells grown on complex media. Extracts of cells grown on this semi-defined medium were found to contain all of the enzymes of the Embden-Meyerhof pathway of glycolysis, in addition to lactic acid dehydrogenase and the pyruvate-clastic system, but no evidence of glucose-6-phosphate dehydrogenase activity could be demonstrated. Evidence has been presented for the implication of the Embden-Meyerhof pathway as the major pathway of glucose degradation by this organism. Resting suspensions of C. perfringens were shown to transport radioactive glucose and mannose, but not other carbohydrates by a common mechanism and accumulate glucose to concentrations several hundred times those found in the external medium. The transport system was found to be an enzymatic, energy-dependent, temperature-sensitive, and highly specific mechanism which was saturated at high substrate concentrations. The carbohydrate was found to be accumulated as an equilibrium mixture of phosphorylated hexoses. The phosphorylation mechanism involved in accumulation was demonstrated to be other than the soluble hexo-kinase. / Science, Faculty of / Microbiology and Immunology, Department of / Graduate

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vi, 90 leaves : tables, graphs ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.1979) from the Dept. of Biochemistry, University of Adelaide

xvi, 257 leaves : ill. ; 26 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.1975)--The Dept. of Agricultural Biochemistry and Soil Science, University of Adelaide

Typescript (photocopy) / x, 210 leaves, [2] leaves of col. plates : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Botany, 1982