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Title: The regulation of mitochondrial function during early seedling development in cucumber (Cucumis sativus L.)
Author: Hill, Steven Arthur
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1990
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This thesis is concerned with the following areas: first, the nature of the developmental modulations in mitochondrial function, and the role of coarse control, at the level of protein synthesis, in bringing them about; and secondly, the importance of mitochondrial reactions in the regulation of cellular metabolism. Changes in respiratory physiology in developing cotyledons have been characterised and correlated with changing metabolic phases. During lipid mobilisation, carbon is diverted away from the decarboxylating reactions of the TCA cycle, whereas the capacity exists for full cycle operation in the photosynthetic phase. Mitochondrial glycine oxidation, necessary for the maintenance of the photorespiratory cycle, is induced during photosynthetic development. The non-phosphorylating pathway of electron transport, via the alternative oxidase, is present, and the access of substrates to this pathway appears to be regulated such that high rates of succinate and glycine oxidation can occur simultaneously. These changes are brought about, at least in part, by protein synthesis. The steps regulating succinate oxidation by isolated cotyledon mitochondria have been determined using the quantitative techniques of metabolic control theory. During lipid mobilisation, succinate metabolism is regulated by the adenine nucleotide translocator and the processes of succinate uptake into the mitochondria. A mitochondrial r^ole in the integration of biosynthesis and degradation is proposed in the light of these results. In the photosynthetic phase, the regulation of succinate oxidation is by the steps of the respiratory chain. There is evidence to suggest that variation in succinate oxidation rates during development is a result of the synthesis of specific proteins. Studies into the pathway of pyruvate metabolism in developing cotyledons indicate that carbon may be diverted into the TCA cycle during chloroplast biogenesis, through pyruvate production by the mitochondrially located NAD-malic enzyme. It is suggested that this mitochondrial route of carbon entry would enable TCA cycle flux to be regulated by the demand for intermediates required for biosynthetic pathways, rather than the rate of sucrose production from lipid. Evidence is presented for the more conventional route of carbon entry into the TCA cycle from cytosolic pyruvate during the photosynthetic phase. Results indicate that the developmental modulation of pyruvate metabolism is regulated at the level of protein synthesis. Application of metabolic control theory to in vitro systems capable of hexose production from organic acids, provides further support for the proposed r^ole of mitochondria during lipid mobilisation. The adenine nucleotide translocator and other mitochondrial steps have significant flux control coefficients for hexose production in vitro. The results presented are used as the basis for the development of a hypothesis concerning the importance of mitochondria in the regulation of plant metabolism.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available