It has been suggested that lipid peroxidation is involved in the loss of seed vigour, although many attempts to examine the relationships between lipid peroxidation and seed vigour have proved equivocal. Studies were undertaken on seed lots of cabbage and soya bean to find evidence for peroxidation by the analysis of i) total and polar fatty acid levels; ii) lipid hydroperoxides; iii) volatile products produced on heating dry seeds; and iv) volatile products produced on imbibition. The loss of polyunsaturated fatty acids (PUFAs) detected in the dry seeds was clearly related to germinability in both soya bean and cabbage seeds. Furthermore, an increase in hydroperoxides was observed in both seed types. Although the relationship of the level of hydroperoxides to germinability was less clear than for the decline in the level of PUFAs, these results suggested that the loss of PUFAs was possibly due to evidence the peroxidation of the seed obtained from the heating lipid, indirect of the seeds suggesting that hydroperoxide breakdown may be necessary in order that the changes in PUFAs become apparent. In contrast to the poor relationship observed between germinability and hydroperoxide level, a marked relationship between hydroperoxide level and seed moisture content was observed in the cabbage seeds. This may be significant with regard to the observed relationship between storability and seed moisture content, although no such relationship was seen in the soya beans. Certain volatile compounds derived from dry heated seeds were related to seed vigour in both seed types and evidence suggests that the lipid hydroperoxides were the source of these compounds. Although the total volatiles counts evolved from imbibing cabbage seeds showed no quantitative relationship to seed vigour, one peak was noted which was clearly associated with the vigour of these seeds. The variability in the volatiles evolved from soya beans on imbibition, however, precluded the detection of any possible relationship between these and seed vigour. In both seed types, results suggest that the volatiles derived on imbibition were of a different source to those derived on heating. A marked increase in the level of hydroperoxides was observed in whole cabbage seeds and soya bean axes of low vigour over the first hour of imbibition. This may suggest that an exacerbation of damage on imbibition was associated with low vigour seeds. In contrast to this, in the seeds of high vigour, the increase in hydroperoxide levels was markedly less or rapidly reduced, suggesting the possible activity of repair mechanisms. Ferrous ions were shown to invigorate both seed types, particularly cabbage seeds. It is suggested that the invigorating effect of these compounds was due to the facilitation of repair, including hydroperoxide breakdown and the quenching of any free radicals. / Thesis (M.Sc.)-University of Natal, Durban, 1986.

No description available.

Submitted in fulfilment of the requirements of the Degree of Master of Technology: Biotechnology, Durban University of Technology, 2011. / The depletion of global energy supplies coupled with an ever increasing need for energy and the effects of global warming have warranted the search for alternate renewable sources of fuel such as biodiesel. First generation biofuels are not sustainable enough to meet long term global energy requirements and more recently there has been concern expressed as to the potential negative implication of crop based biofuels in the form of negative energy balances and potentially no greenhouse gas benefit due to land utilisation not being taken into account. Microalgae have shown great promise as a sustainable alternative to first generation biofuels. They have faster growth rates, have greater photosynthetic efficiencies, require minimal nutrients and are capable of growth in saline waters which are unsuitable for agriculture. Microalgae utilise a large fraction of solar energy and have the potential to produce 45 to 220 times higher amounts of triglycerides than terrestrial plants. The use of microalgae for biodiesel production requires strain selection, optimisation and viability testing to ascertain the most appropriate organism for large scale cultivation. This study focuses on bioprospecting for indigenous lipid producing microalgae, screening, selection and optimisation of growth and lipid yields with respect to nutrient limitation. Further we have ascertained the sustainability of a selected species of microalgae in open pond system. Chlorella sp. and Scenedesmus sp. were found to be dominant amongst the isolates. Strains we selected and underwent media selection and growth and lipid optimisation trials. BG11 media was selected as the most appropriate media for the growth of the selected Chlorella and Scenedesmus strains. Little variation in growth was observed for both cultures ten days into cultivation under varying nitrate concentrations. Phosphate optimum was shown to be 0.032g/l for Scenedesmus sp and 0.04g/l for Chlorella sp. Best lipid yield determined during exponential growth was achieved in cultures with 0.3g/L to 0.6g/L nitrate and phosphate as per BG11 medium. pH optimisation showed that cultures may be adapted to growth at higher pH over time. The optimum pH range for growth was determined to be narrow and was found to be between pH 10 and pH 11. Chlorella sp. was shown to be sustainable as a dominant culture in open pond system. Open pond systems however are prone to contamination by other species of microalgae within weeks of inoculation. / National Research Foundation.

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The capacity of pea root plastids for galactolipid synthesis was investigated utilizing radiolabelled acetate and UDP-galactose. Galactolipid biosynthesis was completely dependent on an exogenous supply of UDP-galactose. UDP-galactose stimulated both total lipid biosynthesis from acetate and the proportion of radioactivity accumulated in monogalactosyldiacylglycerol (MGDG). The proportion of MGDG synthesized was saturated at 30$ mu$M UDP-galactose and represented approximately 30% of the total lipid radioactivity after a one hour incubation. However, total lipid biosynthesis continued to increase with concentrations of UDP-galactose up to 75$ mu$M while the proportion of radioactivity in MGDG remained at 30%. MGDG biosynthesis was always accompanied by a corresponding decrease in the amount of diacylglycerol (DAG) accumulated. Digalactosyldiacylglycerol (DGDG) synthesis was not routinely observed in these experiments. These results suggest that the in vitro pathway for MGDG synthesis in the root plastids of pea (an 18:3 plant) is similar to 16:3 plants (FFA's$ to$PA$ to$DAG$ to$MGDG). The endogenous lipids, consistent with the thought of pea as an 18:3 plant, contained 80% C$ sb{18}$ in the fatty acids of MGDG, DGDG, TG and PC. However, in labelled acetate experiments palmitate was the predominately labelled fatty acid in all lipids except PC (where 80% was 18:1). The precursors PA and DAG had ratios of 16:0, 18:0, and 18:1 similar to that of MGDG. 70-80% of the label was associated with the sn-2 position of glycerolipids. The cofactors required for fatty acid synthesis were generally not as required for galactolipid synthesis. The results suggest that galactolipid synthesis relies primarily on endogenous DAG and only partly involves de novo fatty acid synthesis. (Abstract shortened by UMI.)

Pea root plastids were isolated by differential centrifugation and resulting crude plastid fraction was purified by centrifugation through 10%(v/v) Percoll. Marker enzymes indicated that greater than 50% of the plastids were recovered essentially free from mitochondrial and endoplasmic reticulum contamination. The optimum in vitro conditions for glycerolipid biosynthesis from (U-$ sp{14}$C) glycerol-3-phosphate have been determined. Total glycerolipid biosynthesis was approximately 15 nmole/hr/mg protein in the presence of 200 $ mu$M glycerol-3-phosphate, 0.5 mM each of NADH and NADPH, 15 mM KH$ sb2$CO$ sb3$, 0.05 mM CoA, and 2 mM each of ATP and MgCl$ sb2$, 100 mM Bis Tris Propane (pH 7.5) and incubated at the standard temperature of 25$ sp circ$C. ATP, Coenzyme A and a divalent cation are absolutely required for glycerolipid biosynthesis, whereas reduced nucleotides and bicarbonate improve the synthesis to varying degrees. Dihydroxyacetone phosphate had little effect, while dithiothreitol, detergent and Mn$ sp{2+}$ inhibited activity. Under the optimum conditions, isolated pea root plastids mainly synthesized approximately 15% phosphatidic acid, 16% phosphatidylcholine, 13% phosphatidylglycerol, 32% triacylglycerol. Galactolipid synthesis occurred only when UDP-galactose was supplied. Different concentrations of some cofactors resulted in alterations of glycerolipid distribution. Phospholipase A$ sb2$ and Rhizopus lipase digestions of phospholipids and neutral lipids revealed that radioactive fatty acids were preferentially esterified to position sn 2 of each glycerolipid with generally 2-4 times as much radioactivity as position sn 1. Pea root plastids are composed of approximately 62% phospholipid, 24% neutral lipid and 14% glycolipid. Within these classes PG, TAG, and the galactolipids are the major components representing 24, 12, and 12% of the total plastid lipids.

Thesis (M.Sc.) - Carleton University, 2008. / Includes bibliographical references (p. 120-144). Also available in electronic format on the Internet.

Thesis (Ph.D.)--Michigan State University. Dept. of Plant Biology, 2008. / Title from PDF t.p. (viewed on July 16, 2009) Includes bibliographical references (p. 273-293). Also issued in print.

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No description available.