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<p> The experiments described in this thesis were performed to study the: 1. Role of nitrate in the induction of nitrate reductase. 2. Effect of nitrate on the in vivo regulation of nitrate reductase. 3. Role of atrazine on the regulation of nitrate reductase.</p> <p> The nitrate reductase assay system was improved up to 10 fold over that previously used (28). This improvement included the addition of oxalacetic acid and malic dehydrogenase to the system, thereby oxidizing all the NADH at the end of the reaction. NADH, which was a required co-factor in the assay system, interfered with the nitrite colour formation.</p> <p> When the induction kinetics of the enzyme are followed in root tip sections (0 -10 mm) of corn, a 25 minute lag period followed by a period of rapid nitrate reductase synthesis is seen. Neither the lag period nor the rate of increase in enzyme activity is affected by the concentration of the inducer used (1.0, 10.0 or 25.0 mM nitrate), However, with concentrations of nitrate from 0.1 mM to 10.0 mM, there is an increase in the final level of nitrate reductase. Nitrate levels between 10.0 mM to 100.0 mM did not alter this maximally induced level of enzyme.</p> <p> In mature root sections (25-35 mm from the tip), a longer lag time and a slower rate of increase in enzyme activity is seen. The system is not saturated with nitrate concentrations up to 100.0 mM.</p> <p> Cycloheximide, a protein synthesis inhibitor, was added to the roots after the enzyme had been maximally induced. This allowed one to study the in vivo turnover of the enzyme. Nitrate did not alter the in vivo turnover of nitrate reductase in corn roots.</p> <p> Atrazine is a herbicide that has been reported to increase nitrate reductase levels in corn (34). When used in the experiments described here, it was found to be ineffective in altering the nitrate reductase activity of the roots and leaves of corn.</p> / Thesis / Master of Science (MSc)

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Solanaceous crops such as peppers and more commonly tomatoes have been linked to Salmonella outbreaks that have occurred in the United States. The source of contamination for some of these outbreaks was traced back to the preharvest environment. Sources of contamination at the preharvest level of production often include irrigation water, soil, and the use of biological soil amendments of animal origin (BSAAO). This dissertation aims to (i) determine how factors such as the use of BSAAO's, Salmonella strain, soil type, and irrigation influence the survival of Salmonella in agricultural soils and (ii) determine the risk of Salmonella internalization in to transplanted solanaceous crops (tomatoes and bell peppers) and identify factors that influence internalization through the roots such as mode of contamination, soil contamination level, and root damage. Sandy loam (SL) and clay loam (CL) soils both unamended and amended with poultry litter (PL), irrigated either daily or weekly were inoculated with one of twelve strains of Salmonella enterica and monitored for growth and survival until no longer detected. Tomato plants were transplanted into one of three contamination treatments: contaminated soil (A) or irrigation water administered either once (B, single exposure event) or for 7 d following transplantation (C, repeated exposure event). Plants were sampled 1, 2, 3, 7 and 90 d post-transplantation for Salmonella internalization. Pepper plant roots were left intact, damaged, or removed and placed in inoculated water (6.2 log CFU/ml). Pepper plants in the soil contamination study, were transplanted into soil inoculated with Salmonella at different contamination levels (High, Mid, and Low). Samples were collected 1, 2, 3, and 7d post-transplant. Plants were surface sanitized and enumerated for Salmonella internalization by plant section. Strains in soils treated with PL survived significantly (P<0.05) longer (56 and 112 days for SL and CL respectively), than Salmonella strains in unamended soils. In PL amended SL and CL soils, most strains grew significantly (P<0.05) within the first week following inoculation and ranged from 84 to 210 days in the point it was last detected. Strains survival increased significantly (P<0.05) in soil irrigated weekly compared to soils irrigated daily, weekly irrigation increased survival by 140 to 224 and 42 to 168 days in SL and CL soils respectively depending on the strain. Root sections in the tomato plants of treatment A had significantly (P<0.05) higher recovery of Salmonella internalization compared to the other treatments. No tomato fruit sampled were positive for Salmonella internalization. Pepper plants with damaged roots had significantly higher (P<0.05) Salmonella internalization in the stem than plants with intact roots, while plants with no root stalk had significantly higher (P<0.05) Salmonella internalization in the stem and leaves of plants with intact and damaged roots. Pepper plants exposed to high concentrations of Salmonella had significantly more internalization occur in the roots than plants exposed to mid and low concentrations of Salmonella. Due to the results of these studies assessing the risk of using PL and irrigation regime should be considered in the Salmonella growth and survival in agricultural soils. Though it is unlikely, steps should be considered to limit Salmonella contamination of soil and irrigation water and root damage to prevent the internalization of Salmonella in tomato and bell pepper plants through intervention measures such as composting, water treatment, and effective transplanting techniques. / Doctor of Philosophy / Produce such as tomatoes and peppers has commonly been associated with Salmonella outbreaks in the United States. Fresh produce may be contaminated during the growing period by irrigation water, soil, or manure contaminated with Salmonella. This dissertation aims to (i) determine how factors such as poultry litter, Salmonella strain, soil type, and irrigation affects the survival of Salmonella in agricultural soils and (ii) identify the capability of Salmonella uptake through the roots of tomato and bell pepper plants, and identify factors that facilitate the uptake of Salmonella such as how the plant is contaminated, the Salmonella population level in the soil, and root damage. Sandy loam and clay loam soils untreated and treated with poultry litter, irrigated daily or weekly, were contaminated with one of twelve strains of Salmonella and tested for Salmonella levels until it was no longer detected in the soils. Tomato plants were planted into one of three treatments: Salmonella contaminated soil (A) or irrigated with Salmonella contaminated water once after planting (B, single exposure event) or for 7 days following planting (C, repeated exposure event). Tomato plants were tested for Salmonella uptake within the first week or 90 days following planting. The roots of pepper plants were either left intact, damaged, or removed and placed into Salmonella contaminated water. Pepper plants in the Salmonella contaminated soil study were planted into soil containing one of three different Salmonella contamination levels (high, mid and low). Plants were tested for Salmonella uptake within the first week following planting. Factors such as the use of poultry litter and irrigation influenced the growth and presence of Salmonella in both soil types. The uptake of Salmonella of tomato plants in contaminated soil was observed in the roots more than the roots of plants irrigated with contaminated irrigation water. No tomatoes tested were found positive for Salmonella internalizing. The uptake of Salmonella in the stems and leaves of pepper plants was highly dependent on root damage and the presence of the roots. Pepper plants that were exposed to high levels of Salmonella in the soil had more instances of Salmonella uptake than plants with lower levels of Salmonella in the soil. Based on these results, the use of poultry litter and irrigation should be considered in the potential risk of Salmonella contamination during the growing stage of produce. Though the uptake of Salmonella in tomato and pepper plants is unlikely, precautions should be taken to limit the potential contamination of soil and irrigation water with Salmonella and prevent root damage from occurring to prevent possible uptake of Salmonella.

The law of one price (LOP) plays an important role as a building block in theories of international trade and exchange rate determination. It also serves as a measure of integration for international commodity markets. The LOP states that in competitive markets after adjustment for transportation costs and trade barriers, identical commodities sold in different countries should sell for the same price when their prices are defined in a common currency. The existing economic literature provides a vast body of theoretical and empirical investigations of the validity of the LOP. In general, previous evidence is mixed and there is no unanimous LOP support or refutation. The effects of exchange rate changes on agricultural outputs have been extensively studied, but the issue of the impacts on traded non-farm produced inputs has not been explored as much. This study investigates the impact of the exchange rate ($CN/$US) on the relative prices in U.S. and Canadian agricultural markets for five major farm outputs and four non-farm produced inputs, which are traded between these two closely integrated economies. Adherence to the LOP is evaluated by examining the pass-through effects of exchange rate changes on these prices using quarterly data. The sample covers the period of 1975 - 1999, when there were substantial exchange rate movements. Regression and cointegration techniques are utilized to estimate whether and at what rate exchange rate changes are transmitted to prices. The empirical results give rise to supportive evidence in favor of the LOP for the five farm outputs. The evidence is somewhat weaker for three of the four non-farm produced inputs, and the LOP is violated for one input. / Master of Science

Studies were conducted to explore the interactions among rye grass, chlorophenols and microorganisms. The objectives were to examine some of the processes by which plants affect the fate of subsurface organic contaminants. The research was divided into three studies: interactions between live grasses and 2,4-dichlorophenol (DCP), 2,4,6-trichlorophenol (TCP), and pentachlorophenol (PCP); physico-chemical interactions between the three chlorophenols and root tissue; and effect of root exudates on biodegradation of TCP. To study the interactions between plants and organic contaminants, rye grass plants were grown in solutions containing DCP, TCP or PCP for one to three weeks. The grass removed substantial amounts of the chlorophenols throughout the incubation time. The majority of each chlorophenol removed from solution could not be recovered by non-destructive solvent extraction. The removal of the chlorophenols from solution and the unrecoverability of the removed compound followed different kinetics, indicating that the two are different processes. Both contaminant removal and unrecoverability were closely related to root surface area but not to transpiration. A qualitative model was developed to describe the uptake of organic contaminants by plants. The data demonstrate the importance of physico-chemical interactions between contaminants and roots and suggest that maximization of root surface area should be one consideration when selecting a plant species for phytoremediation. To study the physico-chemical interactions between plant roots and organic contaminants, the distribution of DCP, TCP and PCP within a three phase system was examined. The three phases were severed grass roots, water and an organic solvent, either hexane or ethyl acetate. The chlorophenol mass that partitioned into the solvent phase was inversely correlated with root mass and root surface area index. Partition coefficients calculated with respect to the organic liquid phase were inversely correlated with root mass and root surface area index. A similar partitioning experiment was conducted using PCP placed in a solution containing only the dissolved organic material released by roots. These resulting partition coefficients decreased with increasing organic carbon concentration. It appeared that the organic compounds released into solution by the roots affected the movement of the chlorophenol into the organic liquid phase. It is proposed that the presence of roots simultaneously promoted retention of the chlorphenols in the aqueous phase and provided a sorption site. The effect of grass root exudates and glucose on the lag time associated with 2,4,6-trichlorophenol (TCP) degradation by an unacclimated microbial inoculant and an acclimated microbial inoculant was investigated. The presence of an alternate organic carbon source reduced lag time for both the acclimated microbial inoculant and the inoculant that had not been previously exposed to chlorinated phenols. The lag time for acclimation of microbes to TCP mineralization was affected by the ratio of the alternate organic carbon source concentration to the biomass concentration. It is proposed that the presence of a readily available, alternate organic carbon source affected lag time through promotion of microbial population growth and provision of a preferred source of carbon and energy. The results indicate that rye grass may directly, through partitioning and uptake, and indirectly, through soil microbes, affect the fate of chlorophenols in the subsurface environment. / Ph. D.