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El objetivo de este trabajo fue estudiar el efecto de la fertilización con nitrógeno (N) y azufre (S) sobre el rendimiento y calidad nutricional en el forraje y grano de trigo doble propósito. El Experimento I, conducido a campo sobre parcelas experimentales bajo un diseño en bloques completos y aleatorizados (n=4). Los niveles empleados en los tratamientos fueron 0 y 60 kg N ha-1 y 0 y 20 kg S ha-1 aplicados como UAN y tiosulfato de amonio. Fue sembrado trigo var. ACA 304 el 13/03/2009 y se realizaron dos cortes de forraje, el primero cuando el cultivo logró una altura de 30 cm (02/06/2009), y el último al alcanzar el estado de primer entrenudo hueco visible (28/07/2009). El forraje fue secado y procesado para: fibra detergente neutro y ácido (FDN, FDA), lignina detergente ácido (LDA), digestibilidad in vitro de la materia seca (DIVMS), proteína bruta (PB) y azufre (S). El rendimiento del grano fue corregido al 12% de humedad. Además se registró el peso de 1000 granos y determinó el contenido de PB y S. Experimento II y III fueron conducidos en invernadero sobre macetas, utilizándose trigo variedad ACA 304, bajo un diseño completamente aleatorizado (n=4). Los tratamientos emplearon los siguientes niveles: 0, 30, 60 y 90 kg N ha-1 y 0, 15 y 30 kg S ha-1, aplicados en inicios de macollaje con UAN y sulfato de potasio como fuente nutritiva. Para el Experimento II la siembra se efectuó el 02/07/2009, registrándose cada 3 días altura de planta para posteriormente estimar la tasa de crecimiento del cultivo. El rendimiento de MS se determinó por corte al momento de aparición del primer entre nudo hueco visible (21/09/2009). En el Experimento III, la siembra fue el 25/03/2010 efectuándose un solo corte a inicios de la elongación del ápice caulinar (06/08/2010). Las muestras fueron secadas y procesadas para MS, digestibilidad in vitro (DIVMS), macro y micro-nutrientes: N, P, S, K, Ca, Mg, Cu, Mn, Mo, y Zn. La totalidad de los datos fueron analizados por estadística descriptiva, ANOVA y correlaciones. Durante el Experimento I, la precipitación anual fue de 370 mm, correspondiendo el 57% al ciclo del cultivo. Esto afectó sensiblemente la respuesta del cultivo a la fertilización con N y S. El primer corte produjo 1447 kg MS ha-1, mientras que para el segundo el rendimiento cayó un 73%. Aun los bajos niveles de producción los tratamientos que tuvieron aplicación de S incrementaron su producción un 11%. Por su parte, el forraje cosechado exportó alrededor de 70 kg N ha-1 y 4 kg S ha-1. Sólo fue observado un efecto altamente significativo en el agregado de S sobre la concentración de S y DIVMS en el forraje, con un incremento de 10 y 6,6%, respectivamente, sobre los tratamientos sin adición de S. El rendimiento de grano no fue afectado por la fertilizacón. Sin embargo tuvo un incremento de 14% en aquellos tratamientos que recibieron S. El estrés hídrico afectó el llenado de grano, aumentando consecuentemente la proporción de PB en el grano. En el Experimento II el rendimiento de MS se incrementó con cada nivel de N aplicado, mientras que el S no mostró efectos significativos. La altura de planta y la tasa de crecimiento no fueron afectadas por la fertilización, sin embargo, los mayores niveles de N empleado mostraron los registros más altos. En el Experimento III la DIVMS mostró interacción NxS. Sólo se observó efecto significativo del N en aquellas macetas que no fueron fertilizadas con S. Rendimiento de MS y concentración de N respondieron positiva y significativamente a N. Sólo la concentración de S se incrementó con la adición del mismo elemento. MS osciló entre 1,55 y 3,61 g por maceta y exhibió una respuesta lineal hasta 50 kg N ha-1. El agregado de S redujo consistentemente la concentración Mo, atribuible a la competencia iónica por los sitios de absorción en el sistema radical. En forma análoga puede explicarse el decremento de K por su competencia con el anión sulfato. Las relaciones N:S y K/(Ca+Mg) fueron superiores en la mayoría de los casos a los valores críticos de 12 y 2,2, respectivamente. En este último caso, el forraje mantuvo un elevado riesgo de contraer tetania en animales a pastoreo. Los efectos opuestos de la fertilización N-S sobre la calidad del forraje ameritan ampliar el estudio en otros suelos de la zona. Aun en condiciones de baja respuesta a la fertilización se observó un impacto positivo, aunque no relevante, de N y S sobre la calidad del forraje de trigo. Esto sugiere que bajo situaciones de precipitación normal se obtendrían respuestas positivas tanto en el rendimiento como en la calidad del forraje y grano de trigo. / The aim of this study was to evaluate the effect of nitrogen (N) and sulfur (S) fertilization on the yield and nutritional value of the forage and grain of dual purpose wheat (Triticum aestivum L). Experiment I was conducted in experimental plots in a randomized complete blocks design (n = 4). The treatment levels used were 0 and 60 kg N ha-1 and 0 and 20 kg S ha-1 applied as UAN and ammonium thiosulfate. Wheat (cv. ACA 304) was sown on 13/03/2009. Two cuts were performed, the first one when the crop reached 30 cm height (02/06/2009), and the second one when the first hollow stem was observed (28/07/2009). Forage was dried and processed for: neutral and acid detergent fiber (NDF, ADF), acid detergent lignin (ADL), in vitro dry matter digestibility (IVDMD), crude protein (CP) and sulfur (S) content. Grain yield was adjusted to 12% moisture. The weight of 1000 grains was recorded, and grains were also analyzed for CP and S content. Experiment II and III were conducted in a greenhouse. Wheat was planted in pots using the variety ACA 304 in a completely randomized design (n = 4). Fertilization levels assigned to treatments were: 0, 30, 60 and 90 kg N ha-1 and 0, 15 and 30 kg S ha-1, applied as UAN and potassium sulfate at early tillering. For Experiment II sowing was on 02/07/2009, recording plant height every 3 days to estimate growth rate. At first hollow stem stage (21/09/2009), the DM yield was determined by clipping at surface level. Experiment III, wheat was planted on 25/03/2010. The whole biomass was cut at early elongation of the shoot apex (06/08/2010). The samples were dried and processed for DM, IVDMD, macro and microelement contents of N, P, S, K, Ca, Mg, Cu, Mn, Mo, and Zn. All the data were analyzed by descriptive statistics, ANOVA and correlations. In Experiment I, the annual precipitation was 370 mm, 57% of that corresponding to the crop cycle. This fact appeared to have affected crop response to fertilization with N and S. The first cut was 1447 kg DM ha-1, while the second the yield decreased by 73%. Despite of overall low DM yield, S application increased production by 11%. Besides that, the harvested forage exported about 70 kg N ha-1 and 4 kg S ha-1. It was only observed a highly significant effect of S addition on the S content and forage IVDMD, with increases of 10 and 6.6% respectively, contrasted with treatments without S addition. Grain yield was not affected by the fertilization treatments. However, it increased 14% in those treatments receiving S. Water stress affected grain filling, thus increasing the proportion of CP in the grain. In Experiment II DM yield increased with each level of N applied, while the S showed no significant effect. Plant height and growth rate were not affected by fertilization. However, the highest levels of N applied showed also the highest growth rates. In Experiment III an interaction NxS in IVDMD was detected. Significant effects were only observed in those pots fertilized with N, but without S. A positive and significant response in DM yield and N concentration to N fertilization was detected. An increase in S concentration was detected only when this element was added. DM yield ranged between 1.55 and 3.61 g per pot and exhibited a linear response up to 50 kg N ha-1. The addition of S consistently reduced Mo concentration, probably due to ionic competition for absorption sites in the root system. By analogy, this would explain the decrease of K concentration due to its competence with the sulfate anion. Relations N:S and K / (Ca + Mg) were higher in most cases than the critical values of 12 and 2.2, respectively. In the latter case, the feed had an elevated risk of tetany in grazing animals. The variable effects of N and S fertilization on wheat forage quality justify expanding this study to other soil types of the area. Even the low general response to fertilization, it was observed, a positive although not significant N and S effect on forage quality of wheat pasture. This suggests that under better rainfall conditions positive responses in both yield and quality of forage and grain of wheat could be expected.

Iron-sulfur clusters are simple inorganic cofactors that are ubiquitous in living systems. The assembly of iron sulfur clusters is an essential process and must be carefully controlled in order to limit the release of toxic free iron or sulfide. Thus far there are three known protein systems for iron sulfur cluster assembly including the <i>nif, suf,</i> and <i>isc</i> systems. The <i>nif</i> system makes iron-sulfur clusters for nitrogenase production, while both the <i>suf</i> and <i>isc</i> systems provide iron-sulfur clusters for general cellular use. In <i>Azotobacter vinelandii</i> the isc operon contains eight genes which are transcribed together as a single operon: <i>iscR iscS iscU iscA hscB hscA fdx iscX</i>. The two central <i>isc</i> players include IscS, a cysteine desulfurase, and IscU the proposed site of iron-sulfur cluster assembly. Using <i>A. vinelandii</i> as a model organism, we have sought to better understand the mechanism of <i>in vivo isc</i> cluster assembly. In order test the scaffold hypothesis, we constructed strains that allowed for quick and rapid isolation of IscU. The purification of IscU with a bound [2Fe-2S] cluster strongly supports the model that IscU serves as the site of cluster synthesis <i>in vivo</i>. Additionally, using this same genetic system we isolated an IscU39DA variant with an oxygen stable bound [2Fe-2S] cluster. The IscU39^DA scaffold came in tight α₂β₂ complex with IscS and was not separated by high salt, size exclusion, or reducing conditions. On the other hand, wild-type IscU also associated with IscS in a α₂β₂ complex, but readily dissociated upon increased salt concentration. The tight association of IscU39^DA and IscS was found to occur regardless of the presence of a bound [Fe-S] cluster. We conclude that the IscU Asp-39 residue is essential for mediating the dissociation of IscU and IscS. In addition to studying IscS and IscU, we were interested to further understand how the isc system is regulated in response to external factors. Previous work has demonstrated that IscR controls expression of the isc operon in <i>Escherichia coli</i>. When IscR is holo this protein represses <i>isc</i> expression, while in its apo-form it allows <i>isc</i> expression. In <i>A. vinelandii</i> we found that ∆<i>iscR</i> strains exhibit in a 5 – 7 fold elevation of isc expression. Additionally, ∆<i>iscR</> strains reveal a small growth phenotype on plates, and a tendency to form spontaneous suppressor mutations allowing reversion to wild-type growth. Loss of apo-IscR function was found to cause a more severe effect on growth than the loss of holo-IscR function, suggesting IscR has cellular roles in addition to the regulation of the <i>isc</i> operon. / Ph. D.

Plants are surrounded by various threats from the environment such as pathogens, abiotic stresses, and animal attacks. Nutrient content and distribution are essential for plant growth and development as well as plant immunity. Pathogens extract nutrients from host plants to benefit their own growth and reproduction. Sulfate, amino acids, and phosphate are indispensable elements for plant growth, plant nutrition, and plant resistance/susceptibility to disease. However, the role of these nutrients in plant-oomycete interactions is an unexplored area. We developed a hydroponic system to precisely control the nutrients applied to plants. We used Arabidopsis thaliana and Nicotiana benthamiana (N. b) as model plants. Hyaloperonospora arabidopsidis as well as two Phytophthora species, Phytophothora capsici (P. cap) and Phytophothora nicotianae (P. nic) were used as model oomycete pathogens. Hpa is an obligate biotrophic pathogen that obtains nutrients directly from the host plant without causing cell death, while P. cap and P. nic are hemibiotrophic pathogens that display a biotrophic phase followed by a necrotrophic phase where they feed on dead cells. Genomic evidence suggests that these pathogens might obtain nutrients including sulfur in different forms from the host (organic and inorganic respectively). We have optimized the hydroponic system and used Taqman PCR assays and sporangiophore counts to assay the influence of sulfur nutrients on Hpa and P. cap infections. We found that (1) sulfur transporter and metabolism genes play essential roles in plant-oomycete interactions; (2) sulfur is critical components for HR responses against Hpa; (3) low sulfur induces pathogenesis related genes as a systemic acquired response. RNA-seq analysis on Phytophthora-infected Arabidopsis suggested that sulfur transport, assimilation, and metabolism play an important role in plant-oomycete interactions. A second project used RNA-seq analysis on P. nic infected N. b, to identify potential nutrition-related-plant genes that are necessary for full pathogen virulence. RNAi knockdowns of N. b AAP6 (amino acid permease 6) and PHT4 (phosphate transporter 4) genes showed an inhibition of oomycete colonization. These experiments together advance the study on the interplay between nutrient assimilation/metabolism in host plants and oomycete infection which will provide insight into the mechanisms how pathogens intercept nutrients from host. In the long-term, this research could reveal new traits applicable for disease resistance to promote crop and food production. / Doctor of Philosophy / Plants are surrounded by diverse threats from the environment such as pathogens, abiotic stresses, and animal attacks. Oomycetes are the most destructive group of pathogens, triggering severe food security issues. Phytophthora is an oomycete genus causing serious economic loss. Traditional disease control managements including pesticides, crop rotation and culture practices, are not time- or financially- efficient due to the difficulty in managing oomycete spread and oomycete resistance to chemicals. Thus, new plant genes for resistance to oomycete diseases would have a major impact. Plant nutrients are critically important for plant fitness in every aspect of plant growth and plant immunity. Cellular regulatory networks for sulfur, amino acids, and phosphate assimilation and metabolism networks connect to every aspect of plant activity such as functioning enzymes, formation of chlorophyll, synthesis of proteins, and plant immunity. These nutrients are part of the plant defense system but also can be beneficial nutrients fed to the invading pathogens. Studying how nutrients are involved in the responses to oomycete invasions will provide information to introduce resistance strategies into crops. We utilized oomycete pathogens with different lifestyles to study the interactions and found that some sulfate transporter genes, an amino acid transporter and a phosphate transporter might be manipulated by oomycete to obtain nutrients. Sufficient nutrition is a critical factor for successfully triggering plant immunity but also could be reprogrammed by pathogens for successful infection and development. Our studies gave useful information to understand which plant nutrient genes are important during plant–oomycete interactions. These findings could be useful in identifying or engineering new plant genes to control plant diseases.

It appears impossible to nitrate cellulose in a medium of liquid sulfur dioxide either ~~th ruming nitric acid, a mixture of fuming nitric acid and sulfuric acid t a mixture of fuming nitric acid and phosphorus pentoxide, a mixture of fuming nitric acid, phosphorus pentox1de ana chlorine gas, or with nitrogen tetroxide. This is attributed to the fact that in each case the primary reaction ist hat of the formation of the compound N23209. / Ph. D.

An investigation of the literature showed that as the diameter of a hydrocyclone was decreased, smaller particles could be effectively separated on the basis of specific gravity. Consequently, a laboratory scale study was conducted to determine the possibility of removing pyritic sulfur from fine coal using a 1.0" diameter hydrocyclone. A 1.0" diameter hydrocyclone was constructed from stainless steel. The hydrocyclone was fabricated with easily interchangable parts that permitted rapid variations in the inlet diameter, apex discharge diameter, vortex finder diameter, vortex finder position, and cone angle. The feed pressure to the hydrocyclone could also be varied. A recirculating system was used. Synthetic material was used in place of actual coal during this investigation. The synthetic material, made from casting resin and barium sulfate, duplicated the coal with respect to particle size, shape, and specific gravity distribution. The synthetic coal had the advantage of not degrading during the course of the experiment. Three coals were simulated for the purposes of this experiment. Pocahontas 113 coal served as the "light" coal, the Hagy seam was selected as the "medium" coal, and coal from the Cortes area of New Mexico was chosen as the "heavy" coal. By optimizing the 1.0" diameter hydrocyc1one for these three coals, it would be possible to extend the results of the investigation to any coal. The results of the investigation showed that the 1.0" diameter hydrocyclone was an effective device for removing pyritic sulfur from 65 x 200 mesh coal. The results for the minus 200 mesh size fraction were not good. A smaller diameter hydrocyclone would be necessary in order to effectively process the minus 200 mesh size fraction. / Ph. D.

It is not known whether biosynthesis of [Fe-S] clusters occurs through a spontaneous self-assembly process or an enzymatic process. However, in the <I>Azotobacter</I> <I>vinelandii</I> nitrogenase system, it has been proposed that NifS and NifU are involved in the mobilization of sulfur and iron necessary for nitrogenase-specific [Fe-S] cluster assembly. The NifS protein has been shown to have cysteine desulfurase activity and can be used to supply sulfur for the <I>in</I> <I>vitro</I> catalytic formation of [Fe-S] clusters. The activity of the NifU protein has not yet been established, but NifU could have functions complementary to NifS by mobilizing iron or serving as an intermediate site necessary for nitrogenase-specific [Fe-S] cluster assembly. A second iron-binding site within NifU was predicted to serve these functions because two identical [2Fe-2S] clusters that had previously been identified within the homodimeric NifU are tightly bound, and the NifU primary sequence is rich in cysteine residues. In this dissertation, I examined the possibility that NifU might mobilize iron or serve as an intermediate site for [Fe-S] cluster assembly, as well as the possibility that NifU could work in concert with NifS. Primary sequence comparisons, amino acid substitution experiments, and biophysical characterization of recombinantly-produced NifU fragments were used to show that NifU has a modular structure. One module is contained in approximately the C-terminal half of NifU and provides the binding site for the [2Fe-2S] cluster previously identified (the permanent [2Fe-2S] cluster). Cysteine residues Cys¹³⁷, Cys¹³⁹, Cys¹⁷⁵, and Cys¹⁷⁵ serve as ligands to the [2Fe-2S] cluster. Another module (referred to as NifU-1) is contained in approximately the N-terminal third of NifU and provides a second iron-binding site (rubredoxin-like Fe(III)-binding site). Cysteine residues Cys³⁵, Cys⁶², Cys¹⁰⁶>, and a putative non-cysteine ligand of unknown origin provide coordination to the iron at this site. The significance of these iron-binding sites was also accessed by showing that cysteine residues involved in providing the rubredoxin-like Fe(III)-binding site and those that provide the [2Fe-2S] cluster binding site are all required for the full physiological function of NifU. The two other cysteine residues contained within NifU, Cys²⁷² and Cys²⁷⁵, are neither necessary for binding iron at either site nor are they required for the full physiological function of NifU. These results provide the basis for a model where iron bound at the rubredoxin-like sites within NifU-1 (one iron per monomer) is proposed to be destined for [Fe-S] cluster formation. It was possible to find in vitro evidence supporting this idea. First, it was demonstrated that NifU and NifS are able to form a transient complex. Second, in the presence of NifS as well as L-cysteine and a reducing agent, the Fe(III) contained at the rubredoxin-like sites within the NifU-1 or NifU homodimer can rearrange to form a transient [2Fe-2S] cluster between the two subunits. Finally, a mutant form of NifU-1 was isolated that appears to be trapped in the [2Fe-2S] cluster-containing form, and this [2Fe-2S] cluster (the transient [2Fe-2S] cluster) can be released from the polypeptide matrix upon reduction with dithionite. Previous work has shown that the permanent [2Fe-2S] clusters of as-isolated NifU are in the oxidized form but can be reduced chemically. The transient [2Fe-2S] cluster formed between rubredoxin-like sites, in contrast, is reductively labile. If the transient cluster serves as an intermediate [Fe-S] cluster to be destined for [Fe-S] cluster assembly, I propose that the permanent [2Fe-2S] clusters could have redox roles participating in either one or all of the following events. The permanent [2Fe-2S] clusters could have a redox function in the acquisition of iron for initial binding at the mononuclear sites. They could also provide reducing equivalents for releasing the transient [2Fe-2S] cluster. In addition, upon releasing the transient [2Fe-2S] cluster, the permanent [2Fe-2S] clusters could provide the appropriate oxidation state of the irons to be destined to nitrogenase metallocluster core formation. Finally, because proteins homologous to NifU and NifS are widely distributed in nature, it is suggested that the mechanism for NifU and NifS in the formation of nitrogenase-specific [Fe-S] clusters could represent a general mechanism for [Fe-S] cluster synthesis in other systems. / Ph. D.

1. A systematic study of the reduction of organic sulfur compounds by different metals in liquid ammonia is reported for the first time. 2. A metal with a high half-cell potential favors a greater extent of reduction than a lower potential metal. 3. The greater the concentration of ammonium ion as a proton donor, the greater will be the evolution of hydrogen, and the lower will be the extent of reduction. 4. A mechanism for the reduction of organic sulfur compounds by metals in ammonia is presented. 5. A new procedure for the quantitative removal and determination of hydrogen sulfide in mercaptans was developed. 6. A new synthesis for allyl mercaptan was found. 7. The formation of a resin believed to be a thiophene polymer of the formula (C₄H₄S)_x is reported. / M.S.

Gallium antimonide (GaSb) is a promising low-bandgap binary substrate for the fabrication of various infrared-based optoelectronic devices, particularly thermophotovoltaics (TPV). In order to make GaSb-based technologies like TPV more widely available, non-epitaxial dop- ing methods for GaSb must be pursued. Ion implantation is relatively unexplored for GaSb, and can offer advantages over the more common method of zinc diffusion, including higher flexibility with regards to substrate type and control over the resulting doping profile. Pre- vious work has shown beryllium (Be+) implantation to be a suitable method for fabricating a diode in an n-type GaSb substrate, opening the possibility for other ions to be considered for implanting into both n-type and p-type substrates. This work identifies sulfur (S+) as another species to investigate for this purpose. To do so, material and electrical characterization was done on S+ and beryllium implanted GaSb films grown onto a semi-insulating gallium arsenide (GaAs) substrate. X-ray Diffraction spectroscopy (XRD) and Atomic Force Microscopy (AFM) indicate that the post-implant anneal of 600 for 10 s repaired the implant damage in the bulk material, but left behind a damaged surface layer composed of coalesced vacancies. While the beryllium implant resulted in moderate doping concentrations corresponding to an activation percentage near 15 %, Hall Effect data showed that implanting S+ ions induced a strongly p-type behavior, with hole concentrations above 1 × 19 cm^3 and sheet hole densities 3.5 times higher than the total implanted dose. This strong p-type behavior is attributed to the remaining lattice damage caused by the implant, which induces a large density of acceptor-like defect states near the valence band edge. This technique was used on an unintentionally-doped p-type GaSb substrate to create a + /p junction. The implant process succeeded in producing a potential barrier similar to that of a hole-majority camel diode with a thin delta-doped region suitable for collecting diffused carriers from the p-type substrate. A post-fabrication etching process had the effect of strongly increasing the short circuit current density to as high as 41.8 mA/cm^2 and the open circuit voltage as high as 0.21 V by simultaneously removing a high carrier recombination surface layer. This etching process resulted in a broadband spectral response, giving internal quantum efficiencies greater than 90 %. / Doctor of Philosophy / Thermophotovoltaics (TPV) is a technology that converts light and other forms of electromagnetic energy into electrical power, much like a typical solar panel. However, instead of sunlight, the energy source used in a TPV system is a terrestrial heat source at a temperature range of 1250–1750 ◦C, whose radiation is primarily infrared (IR). The IR-absorbing qualities and commercial availability of the compound semiconductor gallium antimonide (GaSb) have made it a key component in the development of absorber devices for TPV-related systems. GaSb-based devices have most often been fabricated using epitaxy, a method in which layer(s) of material are ‘grown’ in a layer-by-layer fashion atop a substrate GaSb wafer to induce an interface between negatively-charged (n-type) and positively-charged (p-type) regions. In order to improve upon the scalability of TPV production, device fabrication methods for GaSb that avoid the use of epitaxy are sought after as a lower-cost alternative. In this work, sulfur ion implantation is examined as one of these methods, in which elemental sulfur ions are injected at a high energy into a p-type GaSb substrate. The implanted ions then alter the charge characteristics at the surface of the material, producing an electric field from which a photovoltaic (PV) device can be fabricated. The results of this study showed that by implanting sulfur ions, an extremely p-type (p++) layer was formed at the surface of the GaSb substrate, which was attributed to residual damage induced by the implant process. The resulting interface between the p++ surface and the moderately p-type GaSb substrate was found to induce an electric field suitable for a PV device. Removing the excess surface damage away from the device’s metal contacts resulted in an improvement in the output electrical currents, with measured values being significantly higher than that of other devices made using more common non-epitaxial fabrication methods. The success of this work demonstrates the advantages of using a p-type GaSb substrate in place of an n-type substrate, and could help diversify the types of TPV-related devices that can be produced.