No description available.

No description available.

No description available.

E151 (sym15) is characterized as a pleiotropic pea (Pisum sativum L.) mutant. It has been described as having short lateral roots, a short primary root, and a shorter epicotyl than that of the wild type Sparkle. Furthermore, after 4 weeks of growth it was described as a low nodulator since nodulation was rare (Kneen et al., 1994). My main objective is to further characterize the nodulation phenotype of this mutant. Inoculated of the mutant with two separate strains of Rhizobium leguminosarum biovar viciae caused E151 to develop more nodules when infected with 8401 (lacZ) than with 128C53K. These results suggest that E151 exhibits different levels of susceptibility to infection with different strains. Nodule organogenesis was studied by inoculating E151 with a rhizobial strain that constitutively produces ß-galactosidase and then staining cleared whole root sections with the X-Gal substrate. The substrate produced a blue colour and allowed the rhizobial path to be visualized. It was found that nodule organogenesis in the mutant line is delayed at stage C (i.e., IT associated with cortical cell division) and eventually mature nodules form. The rates of N2 fixation (µmol N2/hr)/nodule dry weight (g) were found to be similar between Sparkle and E151 at 14, 21, and 28 days after inoculation. When comparing the nodulation defect of E151 to other pea mutants summarized by Guinel and Geil (2002), it appears that the nodulation phenotype of E151 is unique.

E151 (sym15) is characterized as a pleiotropic pea (Pisum sativum L.) mutant. It has been described as having short lateral roots, a short primary root, and a shorter epicotyl than that of the wild type Sparkle. Furthermore, after 4 weeks of growth it was described as a low nodulator since nodulation was rare (Kneen et al., 1994). My main objective is to further characterize the nodulation phenotype of this mutant. Inoculated of the mutant with two separate strains of Rhizobium leguminosarum biovar viciae caused E151 to develop more nodules when infected with 8401 (lacZ) than with 128C53K. These results suggest that E151 exhibits different levels of susceptibility to infection with different strains. Nodule organogenesis was studied by inoculating E151 with a rhizobial strain that constitutively produces ß-galactosidase and then staining cleared whole root sections with the X-Gal substrate. The substrate produced a blue colour and allowed the rhizobial path to be visualized. It was found that nodule organogenesis in the mutant line is delayed at stage C (i.e., IT associated with cortical cell division) and eventually mature nodules form. The rates of N2 fixation (µmol N2/hr)/nodule dry weight (g) were found to be similar between Sparkle and E151 at 14, 21, and 28 days after inoculation. When comparing the nodulation defect of E151 to other pea mutants summarized by Guinel and Geil (2002), it appears that the nodulation phenotype of E151 is unique.

No description available.

Nitrogen (N) is present in proteins, enzymes, cell structures, purines and pyrimidines in DNA and RNA molecules, photosynthetic pigments, and several other types of molecules in all living organisms. Nonetheless, even though N makes up more than 78% of the atmosphere, it is reported to be the most frequent deficient nutrient in plants. Nitrate (NO3-) and ammonium (NH4+) are the N forms absorbed by plants from soil, but legume crops can establish symbiotic relationships with rhizobia bacteria, and fix N2 from the atmosphere. In soybean, increasing yield and protein content are raising the crop's N requirement; therefore, enhanced N2 fixation is seen as a reliable path to avoid the use of N fertilizers. In this study, the objective was to perform a comprehensive screening in greenhouse and field conditions of soybean genotypes for traits related to N2 fixation. The purpose was to identify among the soybean genotypes different N2 fixation profiles at early and late stages, as well as to investigate their capacity to accumulate above-ground N and supply carry-over N to following crops. The results showed different profiles among the soybean genotypes for early and late N2 fixation capacity, both in greenhouse and field evaluations. Different traits were correlated to either early or late N2 fixation activity. Soybean and winter-rye shoot dry mass were evaluated in the field to assess above-ground N accumulation and carry-over N, respectively. Soybean genotypes were identified with specific capacities to accumulate N in above-ground biomass or supply N to winter-rye. The patterns of N2 fixation identified in this study, as well as the different abilities to accumulate N above-ground or supply N to following crops, could assist in the selection of superior lines with improved N2 fixation capacity.

This study examined the effects of elevated CO2 and its interaction with drought and nitrogen fertilizer on the growth, production and nodulation of the leguminous crop lentil (Lens culinaris Medic) cultivars ILL7979 and ILL6994 (Idlib 3). Plants were grown under ambient and elevated CO2 at full and limited irrigation conditions in both open top chambers, which were later proven to be unreliable because of CO2 leakage, and tightly sealed and ventilated chambers which were reliable. Destructive harvests at anthesis and at maturity were conducted and results from sealed chambers at maturity showed that above ground dry weight was increased by an average of 12% under elevated CO2, but this increase was not statistically significant.

ABSTRACT Stirred yogurt is a cultured dairy product produced by mixed cultures of lactic acid bacteria. It is a semi-viscous liquid whose rheological properties are major quality determinants. These are influenced by several manufacturing factors such as heat treatment of the yogurt milk. Improvement of the properties of stirred yogurt made under different manufacturing conditions was the key focus in this research. The research included an investigation of the key factors involved in the development of nodulation which is an unsightly defect, as consumers expect stirred yogurt to have a smooth consistency. This research consisted of three main experimental parts: 1. Effect of different heat treatments on the properties of stirred yogurt; 2. Factors involved in nodulation in stirred yogurt; and 3. The physical and chemical nature of nodules. The types and levels of heat treatment have a major influence on the properties of stirred yogurt. In this study, yogurt milk was treated at pasteurization and UHT conditions. The milk heated at pasteurization, 80-95oC, and UHT, 130-145oC, conditions had similar levels of whey protein denaturation, approximately 85-99%, while the milk treated at low temperature for a long time, 65oC for 4 hr, had a significantly lower level of denaturation (~55%). Yogurt made from milk pasteurized at 85oC for 30 min and 92oC for 7 min and UHT treated milk at 130-145oC for 5 s had similar hardness and viscosity while yogurt made from milk treated at 65oC for 4 hr had significantly lower hardness and viscosity than corresponding yogurts from high heat treatments. In addition, the water-holding capacity and syneresis of yogurts made from either pasteurized or UHT milk were not significantly different. Yogurt (made from either pasteurized or UHT-treated milk) enriched with non-dairy ingredients, gelatin, inulin and sugar, showed higher hardness, viscosity, water-holding capacity than yogurt made with only dairy ingredients. These yogurts also showed no syneresis. This can be largely attributed to the gelatin which improves the texture, binds additional water and prevents syneresis. The formation of nodules in yogurt has been reported to be influenced by several factors. In this study, the heat treatment of the yogurt milk, the types and levels of sugar added, and the type of starter cultures were found to significantly influence the level of nodulation in the stirred yogurts. Severe pasteurization heat treatments, at temperatures < 100ºC, caused more nodules than mild heat treatments at temperatures in this range. The type of heat treatment was also important, with yogurt made from UHT-treated milk showing much less nodulation than yogurt made from pasteurized. This was observed when the levels of whey protein denaturation in the pasteurized and UHT milk were similar, indicating that the extent of whey protein denaturation alone is not a major factor in the development of nodules. Sucrose added either before or after heat treatment of yogurt milk also affected the extent of nodulation. Increasing the amount of added sucrose from 0 to 6.5% caused correspondingly higher numbers of nodules. In addition, there was a positive synergistic effect between heat treatment and sugar addition on nodulation; the highest numbers of nodules appeared when the yogurt milk was severely heated and sugar was added at the highest level, 6.5%. Addition of lactose or fructose instead of sucrose did not promote nodule formation while glucose caused nodulation in a similar manner to sucrose. The use of different starter cultures affected the numbers of nodules; yogurts made with the culture ABT 10 had much less nodulation than those made with ABT5 and ABT6, even under heating conditions and sugar addition conducive to nodule development. The amount of exopolysaccharide (EPS) produced by the starter cultures, ABT5 and ABT10, did not correlate with the extent of nodulation in the yogurt. Disturbance during yogurt fermentation by changing the temperature (from 37 to 42 or 45 to 42oC) when the gel was forming increased the numbers of nodules while refrigerated storage of yogurt and altering the pH during heat treatment (from pH 6.46 to 6.90) did not affect the number of nodules. Ultrasonication of the yogurt milk caused a reduction in the numbers of nodules in the yogurt. This was attributed to disruption of clumps of starter culture bacteria, thus preventing excessive localised build-up of acid around the bacterial clumps which could form the nucleus of nodules. The major conclusions from this study are that heat treatment of the yogurt milk and the level and type of added sugar are important factors affecting the extent of nodulation of stirred yogurt. Other factors such as the type of starter culture bacteria and their degree of clumping are also significant. Optimisation of these factors would allow yogurt manufacturers to minimise nodulation in stirred yogurt.

Bacteria perform biological nitrogen fixation (BNF) which leads to conversion of N2 to ammonia. One of the best studied models of BNF is the symbiotic association of Sinorhizobium meliloti - Medicago sativa (alfalfa). Since alfalfa is a major source of animal feed and the fourth largest crop grown in the USA, enhanced understanding of this symbiosis can have implications for increasing crop yields, reducing environmental contamination and food costs. Studies discussed here focus on two symbiotically important bacterial traits, type IVb pili and chemotaxis. Chapter 2 characterizes S. meliloti type IVb pili encoded by flp-1 and establishes their role in nodulation. Bundle-forming pili were visualized in wild-type cells, while cells lacking pilA1, the pilin-encoding gene, showed an absence of pili. Competitive nodulation assays with alfalfa concluded that cells lacking pili had a significant nodulation defect. Regulation of pilA1 expression via a quorum sensing regulator, ExpR, was confirmed. Chapter 3 describes the role of the flp-2 cluster in establishing symbiosis. PilA2 is a pilin subunit encoded from flp-2. The pilA2 deletion strain was defective in nodulation by 31% as compared to the wild type. A non-significant change in nodulation was seen in pilA1pilA2 strain. Thus, both flp-1 and flp-2 have a significant role in establishing symbiosis. Chapter 4 focuses on the deviations of S. meliloti chemotaxis from the enterobacterial paradigm. Transcriptional fusions showed that S. meliloti chemoreceptors (MCPs) are class III genes and regulated by FlbT. Quantitative immunoblots determined the cellular amounts of chemoreceptors. Chemoreceptors were grouped in three classes; high, low, and extremely-low abundance, similar to the high and low abundance chemoreceptors of Escherichia coli. Importantly, the MCP:CheA ratio in an S. meliloti cell was observed to be 37:1, similar to that in Bacillus subtilis of 24:1, but quite different from that in E. coli of 3.4:1. In conclusion, our data indicates that soil bacteria may have optimized their chemotaxis system based on their milieu, which is different from enteric bacteria. These studies have enhanced our understanding of two symbiotically important processes in S. meliloti, and pave the way for future manipulations of the system to increase symbiosis and reduce our dependence on synthetic fertilizers. / Ph. D.