Nutrient accumulation in vegetable crops is declining. New varieties, selected for high yield, may be subject to a dilution effect of nutrient concentration. Alternatively, soil fertility may be to blame. Here, we investigate how nitrogen fertilization can enhance or suppress calcium and potassium content in two lettuce varieties already known to accumulate high or low amounts of these nutrients. Effects of varying the ammonium:nitrate ratio and effects of calcium carbonate buffering on plant growth by mass and on uptake and accumulation of potassium and calcium in two lettuce (Lactuca sativa L.) cultivars, Two Star and Red Deer Tongue, were investigated in three greenhouse hydroponic experiments in which ammonium supplied none, 6%, 12%, 25%, 50%, 75% or all of the nitrogen. Ammonium, supplied as the sole nitrogen source (15 mM), was toxic under buffered or unbuffered conditions. It limited growth and concentrations of potassium and calcium in lettuce leaves. Proportions of ammonium-N greater than 50% of total N nutrition severely curtailed growth and nutrient accumulation for both cultivars. For both cultivars, optima for all three variables occurred in treatments that contained less than 50% NH4+-N in the total N supply. Application of calcium carbonate buffer did not result in improved maxima for growth and shoot potassium or shoot calcium concentrations compared to the best responses in unbuffered solutions. However, supplying calcium carbonate buffer did raise the minima for growth and shoot potassium and shoot calcium concentration. Both cultivars in buffered solutions compared to unbuffered solutions had significantly greater values for growth and for shoot potassium or shoot calcium concentration in treatments that contained 50% ammonium-N or greater in the total N supply. Although buffering relieved symptoms of ammonium toxicity, it did not eliminate symptoms, confirming the work of other researchers that ammonium toxicity is not due solely to acidification of the root-zone and that buffering has an effect on the capacity of plants to tolerate ammonium nutrition. Supplying nitrogen with ammonium:nitrate ratios in which nitrate predominates enhances yield and accumulation of calcium and potassium in lettuce. Two Star, the modern variety, is more ammonium-sensitive than Red Deer Tongue, the heirloom variety, if calcium carbonate buffering is not provided.

M.S.

Oxidative stress-inducing chemical contamination in the environment is a significant concern for public health. The depletion of antioxidants by these chemicals results in oxidative stress which may cause detrimental effects in many cell types. For example, multiple stress responses may be activated in bacteria and several disorders including neurodegenerative disorders may occur in mammalian organisms. Oxidative chemicals also have negative effects on engineered water systems as an oxidative stress response in bacteria has been implicated to cause process failure in wastewater treatment facilities. Therefore, it is essential to monitor oxidative chemical contamination in water environments to provide early warning of potential negative effects. Whole-cell biosensors that indicate bacterial stress responses to oxidative toxic agents can be powerful tools in environmental monitoring. An oxidative stress response found in many Gram-negative heterotrophic bacteria called the glutathione-gated potassium efflux (GGKE) mechanism is a good biological indicator to be used in a biosensor designed to detect the presence of oxidative chemicals in water. The authors of this study propose the development of a GGKE biosensor using an environmental strain of Pseudomonas aeruginosa. The abundance of the global antioxidant glutathione, the gating compound in GGKE, in various cell types suggests that there may be connections between the responses of the different cell types to oxidative stress. In this study, specific oxidative stress responses in two distantly related cell types were studied: the GGKE mechanism in Gram-negative heterotrophic bacteria, and mitochondrial dysfunction in rat brain cells. Furthermore, the use of an octanol-based emulsification method for the immobilization of P. aeruginosa in calcium alginate microbeads was evaluated for long-term mechanical stability, viability, and GGKE response of the immobilized cells. The immobilization of cells is an important factor in the design of a whole-cell biosensor, and must yield viable and active cells over time. This study showed that the dose-dependent responses of GGKE in Pseudomonas aeruginosa cells and of mitochondrial dysfunction in a mixed culture of rat brain cells to a model oxidative electrophilic chemical, N-ethylmaleimide, correspond well to each other. We also showed that both responses are accompanied by the depletion of intracellular glutathione, which precedes the GGKE response in P. aeruginosa as well as mitochondrial damage in rat brain cells. Thus, this study suggests that bacterial responses to oxidative stress involving glutathione, such as GGKE, could potentially be used as an early warning to predict the presence of bioavailable oxidative chemicals that can induce oxidative stress in eukaryotic systems. Although further research is needed, this suggests that bacterial stress response biosensors may be used to predict oxidative stress responses in mammalian brain cells. The octanol-based emulsification method produced P. aeruginosa encapsulated alginate microbeads with an average diameter of 200 μm. The microbeads were mechanically stable in solutions containing up to 20 mg/L K+ for 15 days. LIVE/DEAD® and specific oxygen uptake rate (SOUR) analyses showed that the microbead-immobilized cells recovered their membrane integrity within 5 days but not their net respiration potential. The microbead immobilized cells had no net GGKE potential in response to 50 mg/L N-ethylmaleimide after 14 days whereas water-based alginate bead (2mm) immobilized cells did, albeit at a reduced level to planktonic cells. Confirmation experiments revealed that octanol impeded cellular activities of the immobilized cells. Overall, this study showed that the octanol-based emulsification method is not suitable for the immobilization of P. aeruginosa for use in the GGKE biosensor and other microscale immobilization methods should be evaluated. / Master of Science

Dans le présent travail, l’efficacité d’une solution d’acétate de potassium électro-activée combinée à un traitement thermique modéré sur la conservation des haricots en conserve a été démontrée. L’électro-activation d’une solution d’acétate de potassium 0,0625M pendant 60 min à une intensité de 200 mA a permis d’obtenir un pH de 3,8 et un potentiel redox de +989 mV. Combinée à un traitement thermique de 95°C pendant 10 min, cette solution électro-activée, utilisée à titre de saumure des haricots verts en conserve, a détruit complètement les spores et les bactéries de Clostridium sporogenes. L’efficacité de l’effet barrière est donc prouvée. Comparativement au traitement standard, la texture des haricots est largement améliorée; il est jusqu’à six fois plus ferme et croustillant. L’absence de sodium et de chlore dans la solution électro-activée fait d’elle un produit de l’avenir. Ce nouveau procédé permet une importante économie de temps et d’argent.

Dry matter production must be predicted to utilize nitrogen recommendation models for winter wheat at growth stage 30. Four methods of dry matter estimation were evaluated for their ability to predict dry matter production. The pasture probe, height, and rising plate methods did not have adequate prediction ability. The drop plate method predicted dry matter with an r² of prediction of 0.82 for all sites combined. The predictive ability for an individual site was lower. The combined model on an individual site caused a wide range of errors. Consequently, the four methods are not recommended for estimating dry matter. The changes in percent nitrogen and dry matter near growth stage 30 were measured. Dry matter increased significantly, but percent nitrogen did not vary significantly. The number of clipped samples necessary to estimate the dry matter for the five ha field studied was four samples. The number of samples needed for larger fields will depend on the variability of the dry matter in the field and on the variation inherent to the sampling technique. Adequate potassium nutrition is required for high yields of winter wheat. Current soil test levels were evaluated and found to adequately describe the crop’s need for potassium. The influence of preplant and growth stage 25 applied potassium on yield and lodging was evaluated. On the medium to high potassium test soils used, the timing of the application did not affect yields or lodging. Ethephon reduced lodging better than potassium. / Master of Science

The influence of solution pH, DOC concentration, the relative molecular weight distribution of DOC, and the source of DOC were investigated for their effects on the removal of complexed Fe(II) by alum coagulation and/or KMn04 and H20 2 oxidation. The differentiation between particulate, colloidal, and soluble iron species was achieved through the use of 0.2 urn filters and 100K ultrafilters. Results from oxidation and ultrafiltration studies indicated incomplete complexation of the Fe(II) by DOC in solution. Following the addition of either oxidant, uncomplexed Fe(II) was oxidized to Fe (III) which was either complexed by high molecular weight DOC or formed colloidal iron oxides, both of which were efficiently removed by alum coagulation. Alum coagulation alone, however, was ineffective for removing Fe(II) in the presence of DOC. Results revealed the formation of particulate iron species to be a function of DOC source. The formation of colloidal iron was dependent upon DOC concentration and DOC source. The adsorption of DOC by iron oxides was observed to accompany the formation of colloidal iron species. / Master of Science

To improve the process stability of wastewater treatment plants, the construction of a whole-cell bacterial biosensor is explored to harness the natural stress response of the bacterial cells. The stress response selected in this work is the glutathione-gated potassium efflux (GGKE) system, which responds to electrophilic stress by effluxing potassium from the interior to the exterior of the cell. Thus, the bulk potassium in solution can be monitored as an indicator of bacterial stress. By utilizing this stress response in a biosensor, the efflux of potassium can be correlated to the stress response of the immobilized culture, providing an early warning system for electrophilic shock. This type of shock is a causative factor in many process upset events in wastewater treatment plants, so the application of the sensor would be an early warning device for such plants. The research conducted here focused on the biological element of the biosensor under development. Three immobilization matrices were explored to determine the cell viability and potassium efflux potential from immobilized cells: a calcium alginate, a photopolymer, and a thermally reversible gel. The calcium alginate was unstable, and dissolved after five days, such that the long-term impact of immobilization on the cells could not be determined in the matrix. The photopolymer resulted in very low actvity and viability of immobilized cellsOf the three matrices tested, indicating that the composition of the polymer was toxic to the cells. Of the matrices tested, the thermally-reversible gel showed the best response for further study, in that the matrix did not inhibit cell activity or potassium efflux. / Master of Science

Ph. D.

Two experiments were conducted to study the effects of a high dietary potassium intake on magnesium metabolism. In experiment 1, eight 3-day balance trials were conducted with 12 crossbred wether lambs. Rations containing equal amounts of magnesium, calcium and sodium and 0.6 or 4.9% potassium were fed. Apparent absorption of magnesium was greatly depressed (P < .05) while apparent absorption of sodium and potassium were generally increased by the addition of 100 gm. of potassium bicarbonate to the ration. There was a trend for higher apparent absorption of calcium by the high-potassium fed lambs. Although blood serum calcium, sodium or potassium showed no distinct trends, there was a trend toward lowered serum magnesium levels after 14 days of potassium supplementation, which disappeared after 27 days. In experiment 2, six paired yearling wethers were fed two rations identical in ingredient composition to those used in experiment 1. All wethers received an intravenous dose of radioactive magnesium²⁸ and magnitude of fecal and urinary magnesium²⁸ excretion was determined and magnesium turnover rates calculated. The high-potassium fed wethers tended to secrete smaller amounts of magnesium²⁸ in the urine and slightly greater amounts in the feces. The high-potassium fed wethers had lower magnesium turnover rates indicating that high potassium levels interfere with magnesium absorption rather than drastically increase the excretion into the intestine. / Master of Science

A study was conducted to determine the feasibility of utilizing potassium sorbate as a fungistatlc agent in country ham processing. The study was divided into three phases: the first utilized 60 and 90 day old cured country (long cut) ham; the second used country ham slices; and the third phase utilized 70 day old country cured (packer style cut) hams. Samples were incubated at various temperatures and relative humidities to determine the extent of protection offered by sorbate against fungal growth. Intensity of fungal growth was determined subjectively through periodic visible evaluations and were quantitated by culture plating methods. A UV spectrophotometric technique was utilized to determine the concentrations of sorbic acid deposited on ham surfaces or slices by various methods of application. Of the different methods of application that were tested, the 5% (W/V) 1 minute spray offered the lowest effective level for inhibition of fungal growth. The 5% l minute spray significantly lowered initial mold and yeast colony counts and protected the hams for 30 to 60 days under conditions conducive to fungal outgrowth (21.1±5°C and 70±5% relative humidity). An analogous 10% spray provided a slightly greater measure of mold inhibition than the 5% treatment under identical conditions. / Master of Science