Thesis (doctoral)--Swedish University of Agricultural Sciences, 2003. / Thesis documentation sheet inserted. Appendix includes reproductions of four papers and manuscripts, three co-authored with others. Includes bibliographical references. Abstract also available online.

Thesis (M.S.)--Oregon State University, 2002. / Typescript (photocopy). Includes bibliographical references. Also available on the World Wide Web.

Thesis (M.S.)--Oregon State University, 2002. / Typescript (photocopy). Includes bibliographical references. Also available on the World Wide Web.

published_or_final_version / Dentistry / Doctoral / Doctor of Philosophy

Pepper plants (Capsicum annuum L.) were grown in field and a greenhouse in Arizona to determine the effects of water stress, root temperature, and exogenously applied growth regulators on cytokinin production and the resulting growth. Research showed that vegetative plants were significantly higher in cytokinin activity and growth parameters than fruiting plants. Also, in root-pruned fruiting plants, cytokinin activity was less than that of intact fruiting plants. In vegetative plants, the competition between removed sinks and the rest of the shoot was reduced and, hence, more cytokinin came from the roots to the shoots. Besides, additional carbohydrates were available and recycled to the roots. In respect to temperature effect, elevating temperature from 15 to 30°C had a pronounced effect of increasing the growth rate and cytokinin activity. The measured parameters declined when temperature exceeded 30°C. Temperatures between 25 and 30°C were found to be optimum. Under experimental conditions, growth regulators (Cytex® and Burst®) applied to the soil or foliage had no significant effect on growth rates or cytokinin activity in roots. Also, applying Burst® or kinetin to the nutrient medium had inconsistent and statistically nonsignificant effects on photosynthesis and transpiration.

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This study was undertaken to characterize the nod and sdh operons of Bradyrhizobium japonicum and Sinorhizobium meliloti. Ten putative B. japonicum mutants with altered nod gene induction characteristics were isolated by screening mutants for genistein-independent nod gene expression. The mutants were found to have higher nodY expression than the wild-type in the presence of genistein. The increased sensitivity of all mutants to genistein was more apparent under suboptimal inducer concentration (0.1muM) and/or temperature (15°C). The expression of nodY gene induction was determined for five strains (Bj30050, 53, 56, 57, 58) under different temperature and inducer conditions. These five strains were also found to produce more lipochitooligosaccharide than the wild-type, at both 25°C and 15°C. Three of the ten mutant strains (including Bj30056 and 57) were unable to fix nitrogen with soybeans grown at optimal temperatures. Based on nodY gene expression and symbiotic phenotype the B. japonicum mutants were classified into three groups. / A molecular genetic approach was taken to investigate the regulation of expression of succinate dehydrogenase (SDH) in S. meliloti. The sdhCDAB genes encoding SDH were shown by RT-PCR to be co-transcribed and thus constitute an operon. The transcriptional start site and putative promoter region of the first gene in the operon, sdhC , were identified by 5'-RACE and DNA sequence analysis. Transcriptional lacZ fusions to sdhC indicated that expression of the operon is regulated by carbon source in the growth medium but not by growth phase. The highest expression of the sdh operon was observed in cells grown with acetate, arabinose and glutamate, as sole carbon sources, and the lowest expression was observed in cells grown with glucose and pyruvate as sole carbon sources. / Also presented is the isolation and characterization of the first defined sdh mutant in a rhizobial species. The mutants helped demonstrate that the total lack of SDH activity would be lethal to S. meliloti cells. Symbiotic phenotype of the mutants indicated that SDH is required for N2-fixation.

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.)