<p>Adoption of conservation tillage systems is known to result in increased soil K stratification. Yet, there have been few investigations into the optimization of K management in these tillage systems, particularly regarding the placement and timing of K-based fertilizer applications. Additionally, there are many unknowns regarding the influence of tillage timing with/ without K fertilizer application. Increased availability of fertilizers containing both macro- and micro-nutrients, such as Aspire™ (which includes both K and B), has coincided with new questions about potential micronutrient deficiencies in maize (<i>Zea mays</i> L.) production. Previous research has investigated the influence of K and B individually; however, few university studies utilize multi-nutrient fertilizer sources. These knowledge gaps prompted a series of field investigations into the impacts of alternative tillage/ placement of Aspire™ on maize growth and development. Because K stratification is thought to potentially limit K availability to maize, tillage/fertilizer placement treatments involving no till (NT), fall strip-till (FST), spring strip-till (SST), and fall chisel (FC) were compared with at least two application rates of Aspire™ (ranging from 0 to 108 kg K ha^-1) from 2016 to 2019 on Indiana soils with moderate exchangeable K concentrations. Maize was grown in rotation with unfertilized soybean (<i>Glycine max </i>L) planted after strip-till.</p><p>Although tillage systems, other than no-till, were intended to decrease stratification, little change in vertical stratification for in-row samples was observed in the strip-till systems when Aspire™ was band applied at the time of strip-till (indicating fertilizer application was limited to the top several centimeters of soil). Few interactions were evident in maize response between tillage/placement and Aspire™ applications; however, superior V6-stage growth/nutrition responses to Aspire™ application occurred in fall tillage systems (FST or FC). The latter was especially true when comparing the two strip-till timings (FST and SST) at three rates. In addition to early season plant nutritional benefits, plant stature also benefited from Aspire™ across tillage/ placement systems (e.g., ~20% increase in height at V8, plus a leaf area index (LAI) gain at V14 of ~10%) reflecting on the potential to increase the source capacity of fertilized maize plants. By R1, there was little synergism between treatments in the tested parameters, indicating little difference among the tillage/ placement methods (and strip-till timing), and few immediate consequences from 50% rate reduction for Aspire™ in the strip-till systems. Although grain yield increases of 4-8% were common when Aspire™ was applied, yield component analysis showed little interaction between tillage/placement and Aspire™. Grain yields were shown to be more highly correlated and had significant relationships to earleaf K at R1, and less so with minor changes in B concentrations at R1.</p><p>Aspire™ application at the full and 50% rate commonly benefited plant nutrition and grain yield, but little synergism between Aspire™ application and tillage/ placement system was evident. Although rate reduction did not show immediate consequences to plant nutrition in either strip-till timing, longer-term research is necessary to better understand future consequences from this management practice. The lack of differences in response to strip-till timing (fall vs. spring) shows the potential for flexible timing when optimum tillage conditions are present. This research confirmed the importance of K fertilization to maize performance, but the efficient management of K requires further inquiry.</p>

Capillary ion analysis (CIA) is a form of capillary electrophoresis which uses the differential electrophoretic mobility of ions to perform a separation of an ionic mixture. Application of this technique for direct detection of potassium concentrations in human vitreous humor was the purpose of this investigation. CIA was performed using a Waters Quanta 4000 Capillary Electrophoresis System with a 745 Data Module using a 75 μm x 60 cm capillary and a run electrolyte of 67.7 mg hydroxyisobutyric acid (HIBA), 52.8 mg 18-crown-6-ether and 64 μL UV-CAT-1 reagent (4-ethylbenzylamine in a volume of 100 mL water (18 Mohm) with a voltage of 20 kV using ultraviolet absorption detection at 214 nm. Migration times were: ammonium ion, 2.86 min; potassium, 3.24 min; calcium, 3.84 min; sodium, 3.98 min; barium (internal standard), 4.68 min; and lithium, 4.79 min. Correlation coefficients (r) between peak area ratios and concentration ranges of 2.5-144 mmole/L (100-1000 ppm) were from 0.9855 to 0.9999. Coefficients of variation (CV) ranged from 1.45 to 13.8% between days and from 1.38 to 9.43% within-day. Application of this methodology to twenty-five vitreous humor specimens from forensic cases was compared to analysis by ion-specific electrode for potassium concentration. Comparison of CIA to ion-specific electrode analysis of vitreous humor potassium concentrations revealed a correlation coefficient of 0.9642. CIA is applicable to forensic analysis of potassium concentration in forensic vitreous humor specimens. Quantitation of numerous cation concentrations is possible by direct CIA of vitreous humor.

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<p> Potassium levels in serum are used in the diagnosis of diseases involving cardiac arrhythmias, neuromuscular weakness, and chronic kidney diseases. These illnesses are becoming more prevalent, therefore, developing new potassium quantification methods would aid in advancing preventative care. Current methods of quantifying potassium mainly rely on the use of glass ion-selective electrodes which are costly, fragile, and requires frequent maintenance and recalibration. For faster and more accessible quantification of potassium, we are developing low cost, portable, and easy to fabricate electrochemical tape-and-paper-based devices. Our sensor bypasses the inconveniences of ion-selective electrodes and could ultimately serve as a point-of-care device to allow for regular monitoring or even home-use. Our sensing method relies on Prussian blue immobilized on the surface of electrodes as a potassium recognition element. Potassium ions intercalate into the Prussian blue lattice and subsequently changes the electrochemical characteristics of Prussian blue such as the redox peak potentials. These devices are highly robust, feature a limit of detection of 1.3 mM potassium and the response is linear to at least 100 mM, which contains the clinically relevant ranges required for diagnostics. Quantification was developed using cyclic voltammetry, demonstrated in Chapter 3. We observed changes in Prussian blue redox peak potentials at different concentrations of potassium and followed the expected Nernstian response. We investigated multiple methods of immobilizing Prussian blue onto the electrode surfaces to investigate stability and reproducibility in Chapter 4. Adsorption, <em>in-situ</em> synthesis, and carbon paste incorporation of Prussian blue was tested. Prussian blue-carbon paste devices had reproducibility issues and featured broad reduction peaks. <em>In-situ</em> synthesis of Prussian blue directly onto the surface of the electrodes also featured broad reduction peaks but the Prussian blue response was reproducible. The issue with <em>in-situ</em> synthesis was the stability of the Prussian blue layer, which was susceptible to degradation after repeated use of the device, which is required for evaluating the performance of the device. Although adsorption using Prussian blue in water had some reproducibility issues as well, this method led to the most stable Prussian blue layer, had distinct reduction peaks, and was simple to perform. Various solvents were used to dissolve Prussian blue in Chapter 5 to investigate methods of increasing device reproducibility when using adsorption. A few organic solvents were able to dissolve Prussian blue to form a stable solution with the goal of forming a more uniform Prussian blue layer and potentially improving consistency of the layer immobilization. While these alternative solvents were able to dissolve Prussian blue, they also damaged the graphite electrodes on the devices, which altered the electrochemical responses of the devices to the point where potassium quantification was no longer possible. Due to incompatibility between these alternative solvents and the devices, adsorption of Prussian blue in water continued to be used. Different modes of adsorption were explored and was optimized in Chapter 6. By altering the adsorption setup and allowing the Prussian blue particles to settle evenly onto a level electrode surface, device reproductivity increased substantially. To understand the applicability of the devices in real samples, interferent studies were performed in Chapter 7. Other cations such as Na+, Li+, Ca2+, Mg2+, and Ba2+ were not observed to enter the Prussian blue lattice in the cyclic voltammograms. Monovalent cations that share the same charge as K+ but have smaller ionic radius, Na+ and Li+, were able to decrease K+ sensitivity. Divalent cations that had a smaller ionic radius than K+ did not alter sensitivity. The exception was Ba2+, which also decreased K+ sensitivity. These results suggested that both ionic radius and charge of a species were important factors in impacting K+ intercalation into the Prussian blue lattice. Other interferents such as sulfates, phosphates, carbonates, urea, and lactic found in serum and sweat samples were tested. The presence of these interferents decreased the current intensity of the reduction peak of Prussian blue, which resulted in less definition in the peaks. For the future of this project, the effects of interferents found in serum and sweat must be investigated further. Additionally, reproducibility of the devices could be improved further if less harsh organic solvents are tested for adsorption, square wave voltammetry could be used for quantification to evaluate the viability of alternative voltametric techniques, and Prussian blue analogues could be implemented into the devices for quantification of other cations. </p>

Les cotransporteurs cation-Cl (CCCs) appartiennent à une grande famille de protéines qui comprend neuf isoformes : CCCl à CCC7, qui permettent le mouvement du Cl" avec celui d'un Na+ et/ou K+ à travers la membrane cellulaire, CCC9, qui agit comme un transporteur de polyamine (PA) - glutamate, et CCC8, dont on en connaît pas la fonction. Les CCCs font aussi partie d'une famille plus large de protéines qui sont regroupées sous le nom de « amino acid - polyamine - orgcmocation carriers (APC) ». À l'exception de CCC9, cependant, les protéines impliquées dans le transport des PAs n'ont été isolées que chez les unicellulaires et ne font pas nécessairement partie de la famille des APC. Dans cette étude, nous avons trouvé que CCC8 joue vraisemblablement le rôle de transporteur de polyamines chez des espèces plus complexes puisque son expression dans les cellules HEK-293 augmente l'influx de spermidine à la surface cellulaire et puisque cette protéine est ubiquitaire chez les mammifères. Nous avons aussi observé que l'influx de spermidine dirigé par les cellules exprimant CCC8 est inhibé par la pentamidine, le methyl-glyoxal-bis-guanylhydrazone, le furosémide et la paraquat, et que cet influx est aussi associé avec celui certains ions comme le Na+ et le Cl". Ainsi, un groupe de substrats qui sont transportés par CCC8 a été découvert pour la première fois suite à ce travail tout comme l'identification d'un nouveau système de transport de polyamines dans les cellules animales. Ces résultats ont un intérêt majeur puisque les polyamines intracellulaires jouent un rôle clé dans la prolifération cellulaire.

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