Apesar do ambiente epifítico ser caracterizado como bastante desfavorável para o desenvolvimento de vegetais devido à falta intermitente de água e escassez de nutrientes, uma grande diversidade de bromélias o ocupam com sucesso. Uma série de características adaptativas, tanto morfológicas, anatômicas e fisiológicas, está presente nessas plantas e as capacitam a utilizar com grande eficiência os recursos disponíveis de maneira escassa e temporária. O enfoque deste trabalho foi direcionado à compreensão das estratégias adotadas pela bromélia epífita com tanque Vriesea gigantea para a utilização da ureia, uma fonte de nitrogênio não usual para a maioria das plantas terrestres. Em decorrência da frequente associação com anfíbios em ambiente natural, a ureia é um recurso disponibilizado ocasionalmente e durante um curto período na água do tanque. Foram isolados 2 cDNAs completos de aquaporinas potencialmente envolvidos no transporte de ureia: VgPIP1,5 e VgTIP2, que codificam proteínas de membranas plasmática e de tonoplasto, respectivamente. Ambos os genes tiveram expressão mais acentuada nas bases foliares e foram pouco afetados pelo regime de luz. Além disso, a expressão desses genes foi estimulada na presença de ureia, o que não foi observado para em relação às fontes inorgânicas amônio e nitrato. A assimilação de ureia pareceu ser, em grande parte, dependente de hidrólise prévia em NH4+ e CO2, reação essa catalisada pela urease. Foi demonstrado que ambos os produtos dessa reação são incorporados rapidamente, formando aminoácidos (principalmente via GDH, GS/GOGAT e subseqüentes transaminases) e esqueletos carbônicos Infelizmente, a incorporação direta de ureia via reação inversa da arginase não foi confirmada, embora esse resultado possa estar relacionado a limitações metodológicas para a análise de arginina. Ainda assim, evidências sugerem que, se não pela arginase, outras vias alternativas de assimilação direta de ureia possam estar envolvidas. Além da sua importância da urease na hidrólise citossólica de ureia, foi demonstrada, de forma inédita em plantas, a presença dessa enzima nas frações de membranas e parede celular de V. gigantea. É muito provável que, além da capacidade de secreção da urease para a região do tanque, a presença dessa enzima em regiões próximas à superfície celular torne mais rápido e eficiente o processo de assimilação de ureia pelas células. Embora seja caracterizada como um recurso de disponibilidade ocasional e de curta duração e por ser alvo de intensa competição interespecífica, a ureia ainda assim é a fonte de N preferencial para Vriesea gigantea. É provável que um dos motivos que levou essa espécie a utilizar preferencialmente a ureia seja a vantagem de se obter, simultaneamente, tanto carbono quanto nitrogênio, ambos presentes em quantidades limitantes no seu habitat natural. / Although the growth conditions in epiphytic habitats are unfavourable for plant growth due to water and nutrient limitations, a great diversity of bromeliads successfully occupy this environment. These plants have evolved a variety of morphological, anatomical and physiological adaptations allowing them a highly efficient use of available resources. The main objective of the present work was to elucidate the strategies of the epiphytic tank bromeliad Vriesea gigantea to utilize urea, a nitrogen source generally considered to be uncommon for most terrestrial plants. Although in natural environments urea is frequently excreted by amphibians that are associated with the tank of these plants, the availability of this nitrogen source is nevertheless short-lived and unpredictable. Two complete cDNA sequences encoding plasma membrane and tonoplast aquaporin proteins, which are potentially involved in urea transport, were isolated from leaf tissues of Vriesea gigantea: VgPIP1,5 and VgTIP2, respectively. Both genes were mainly expressed in the leaf bases and were not affected by light conditions. Moreover, the expression of these aquaporins was stimulated in the presence of urea in the culture medium, while no effect was observed with ammonium and nitrate as nitrogen source. Urea assimilation is thought to be strongly dependent on precedent hydrolysis of urea to NH4+ and CO2 mediated by urease. Both products of this reaction were quickly assimilated and incorporated into amino acids (mainly via GDH, GS/GOGAT and subsequent transaminases) and carbon skeletons. On the contrary, the direct incorporation of urea via a reverse reaction of arginase could not be confirmed due to the methodological limitation of analyzing double-labelled (13C-,15N-) arginine. However, there is strong evidence suggesting that arginase or other alternative assimilation pathways may be involved in urea assimilation. Despite the importance of urease in the cytosolic hydrolysis of urea, the present work demonstrates for the first time that this enzyme is present in both, membrane and cell wall fractions of V. gigantea. Consequently, besides the capacity of this plant to excrete urease into the tank water, the close association of this enzyme to urea uptake regions could further increase the rate and efficiency of urea assimilation by plant cells. Although urea is characterized as an occasional and only short-lived nutrient source, which is furthermore subject to intense interspecific competition, urea can be considered to be a preferential nitrogen source for Vriesea gigantea. One reason for the preferential use of urea could be the advantage of simultaneously gaining carbon and nitrogen, two limiting resources in the natural habitat of epiphytic bromeliads.

Ruminants have a unique ability to acquire protein from non-protein nitrogen (NPN) sources, and to recycle nitrogen back into the rumen, instead of excreting all of it via the urine, faeces and milk. However, a high concentration of blood urea nitrogen (BUN) has a negative influence on conception. Additionally, a high dietary nitrogen intake poses a challenge to the environment in the form of ammonia emissions, eutrophication and bad odours. This calls for strategies to reduce the environmental impact of livestock production. Variation exists in the ability of cattle to recirculate nitrogen between as well as within cattle breeds. The purpose of this study was to investigate the effects of BUN concentration on reproductive performance in beef heifers under different management systems in South Africa. Serum samples from 369 Bonsmara heifers were taken in November and December 2010 to determine the BUN concentrations prior to the onset of the breeding season. Heifers were from five herds with different levels of protein supplementation during the weeks before the commencement of the breeding season. Body mass, age, body condition score (BCS) and reproductive tract score (RTS) were recorded at the same time as BUN concentration. Trans-rectal ultrasound and/or-palpation was performed four to eight weeks after the three-month breeding season to detect and estimate the stage of pregnancy. Days to pregnancy (DTP) was defined as the number of days from the start of the breeding season until a heifer was successfully mated. Logistic regression and Cox proportional hazards survival analysis were performed to estimate the effect of BUN concentration on subsequent pregnancy and DTP respectively, while stratifying by herd and adjusting for potential confounders. The correlations between BUN concentration, BCS and RTS were estimated using Spearman’s rho. Pearson correlations were used for the normally distributed variables of age and body mass. BUN concentration was not a significant predictor of pregnancy status but was a significant (P = 0.007) and independent predictor of DTP in heavily and some moderately supplemented herds. As BUN concentration increased, DTP also increased [hazard ratio (HR) = 0.827; 95% CI: 0.721 – 0.949; P = 0.007], while the chance of becoming pregnant decreased, although this was not statistically significant [odds ratio (OR) = 0.882; 95% CI: 0.772 – 1.007; P = 0.063]. Bonsmara heifers with higher BUN concentration, which suggests a better ability to recirculate nitrogen, might be at a disadvantage when the production system includes high levels of RDP supplementation because of this negative impact on reproductive performance. It is proposed that production systems be adapted to avoid selection against animals with an improved ability to recirculate nitrogen. / Dissertation (MMedVet)--University of Pretoria, 2013. / gm2014 / Production Animal Studies / Unrestricted

Doctor of Philosophy / Department of Chemistry / Mark D. Hollingsworth / Urea inclusion compounds (UICs) are classic examples of nanoporous, host:guest materials in which the linear channels of the honeycomb structure of the urea host can include various types of long-chain compounds (the guests). By using synchrotron X-ray radiation sources, a deeper understanding of these materials is made possible through detailed structural studies. In particular, this dissertation describes a series of structural phase transitions that occur upon cooling two related UICs containing alkanedione guest molecules. UICs may be classified as either commensurate or incommensurate structures, depending on whether the repeat lengths of the host (c[subscript h]) and guest (c[subscript g]) along the channel axis are related by a small whole number ratio. Crystals of 2,8-nonanedione/urea and 2,11-dodecanedione/urea, which are incommensurate structures at room temperature, undergo "lock-in" phase transitions below room temperature to generate commensurate structures in which the guest repeat lengths are elongated. Upon nucleation and growth of these elongated, commensurate phases, other molecules in the same channels are compressed to give successively shorter guest repeat lengths. Further lock-in phase transitions give a multitude of commensurate and incommensurate phases during cooling. The crystal structures of two of these commensurate phases have been determined using synchrotron sources. The "self-compression" observed in these 1-D crystals serves as a paradigm for understanding solid-state reactions in three-dimensional crystals.

This study considered the use of urea eutectics as fast release solid dosage carrier forms for the acaricide N-methylbis (2,4-xylyliminomethyl) methylamine (AmitrazTM). Wettol D2 and Arkopal N090 were chosen as the wetting agent and dispersants respectively. Their optimum levels were determined as the surfactant concentrations that yielded a minimum in the dispersion viscosity of a concentrated (30% m/m) Amitraz suspension. The optimum dosage levels were found to be ca. 2% Arkopal N090 and ca. 1% Wettol D2. Eutectic phase diagrams were obtained using the melting-cooling method. The components were ground together into a fine powder and heated in a glass tube immersed in a silicon oil bath. The liquid was allowed to cool down and solidify at ambient conditions. The time-dependant temperature change of the sample was tracked with a thermocouple. The data was captured in real time on a personal computer and analysed using an Excel spreadsheet programme. The melt-cast method was used to prepare eutectic mixtures. They were characterised using DSC, DTA, XRD and Light Microscopy. The XRD peaks showed the presence of the two separate crystal structures for the eutectic mixture constituents. The urea – CaBr2.2H2O combination was initially considered as carrier for Amitraz. However, this eutectic system was found to be too hygroscopic. Small additions of PEG 6000 improved the tablet strength but decreased the dissolution rate. Urea and acetamide formed a eutectic at ± 46oC with a composition of ca. 40 % m/m urea. Unfortunately acetamide is a suspected carcinogen. Therefore the urea - 1,3-dimethylurea was selected as Amitraz carrier system instead. The eutectic mixture comprised 40% m/m urea and 60% m/m 1,3-dimethylurea, which melt at ± 56oC. The melt-press method was used to prepare Amitraz containing pellets measuring 5 mm thick and 33 mm ö and weighing about 5,0 g. It was possible to suspend Amitraz powder in the eutectic melt mixture provided it remained in powder form. However, when liquefied (by melting), phase separation occurred. Thus the temperature of the eutectic mixture should be kept below the 80oC melting point of Amitraz. The dissolution tests were performed in a 10-liter Pyrex glass beaker with normal tap water (± 25oC). The time taken for complete dissolution was measured with a stopwatch. These results were confirmed with turbidity tests. Starch-based super disintegrants were used in an attempt to enhance the dissolution rate of the pellets. Explotab® improved the dissolution rate of 30% and 40% m/m Amitraz formulations slightly. The best formulation obtained in this study had the following composition (in m/m): 30% Amitraz; 8% CaCO3; 1 % Wettol D2; 2% Arkopal N090; 10% Explotab® and 49% urea – 1,3-dimethylurea eutectic. Such tablets disintegrated within 6,5 minutes when suspended in water. / Dissertation (MSc (Applied Science))--University of Pretoria, 2007. / Chemical Engineering / MSc / unrestricted

During alcoholic fermentation Saccharomyces cerevisiae metabolizes L-arginine to ornithine and urea. S. cerevisiae can metabolize urea through the action of urea amidolyase, encoded by the DUR1,2 gene; however, DUR1,2 is subject to nitrogen catabolite repression (NCR) in the presence of high quality nitrogen sources during fermentation. Being cytotoxic at high concentrations, urea is exported into wine where it spontaneously reacts with ethanol, and forms the carcinogen ethyl carbamate (EC). Urea degrading yeast strains were created by integrating a linear cassette containing the DUR1,2 gene under the control of the S. cerevisiae PGK1 promoter and terminator signals into the URA3 locus of the Sake yeast strains K7 and K9. The ‘self-cloned’ strains K7EC- and K9EC- produced Sake wine with 68% less EC. The Sake strains K7EC- and K9EC- did not efficiently reduce EC in Chardonnay wine due to the evolutionary adaptation of said strains to the unique nutrients of rice mash; therefore, the functionality of engineered yeasts must be tested in their niche environments as to correctly characterize new strains. S. cerevisiae possesses an NCR controlled high affinity urea permease (DUR3). Urea importing yeast strains were created by integrating a linear cassette containing the DUR3 gene under the control of the PGK1 promoter and terminator signals into the TRP1 locus of the yeast strains K7 (Sake) and 522 (wine). In Chardonnay wine, the urea importing strains K7D3 and 522D3 reduced EC by 7% and 81%, respectively; reduction by these strains was equal to reduction by the urea degrading strains K7EC- and 522EC-. In Sake wine, the urea degrading strains K7EC- and 522EC- reduced EC by 87% and 84% respectively, while the urea importing strains K7D3 and 522D3 were significantly less capable of reducing EC (15% and 12% respectively). In Chardonnay and Sake wine, engineered strains that constitutively co-expressed DUR1,2 and DUR3 did not reduce EC more effectively than strains in which either gene was expressed solely. Uptake of 14C-urea under non-inducing conditions was enhanced in urea importing strains; parental strains failed to incorporate any 14C-urea thus confirming the functionality of the urea permease derived from the integrated DUR3 cassette. / Medicine, Faculty of / Medical Genetics, Department of / Graduate

Tesis para optar al título profesional de Ingeniero Agrónomo y al grado de Magíster en Ciencias Agropecuarias, mención en Producción Animal / En la Estación Experimental Oromo, Departamento de Producción Animal, Facultad de Ciencias Agronómicas de la Universidad de Chile, se llevó a cabo una investigación que tuvo como objetivo cuantificar el efecto de incluir carbohidratos con distinta tasa de degradación en la dieta de vacas lactantes pastoreando una pastura con alto contenido de proteína degradable, sobre parámetros ruminales, sanguíneos y lácteos, así como también determinar el efecto de este tipo de suplementación sobre el uso de la energía metabolizable para sintetizar urea en desmedro de la producción de leche. Se utilizaron 24 vacas Holstein Neozelandés, 4 de las cuales contaban con cánula ruminal y fueron distribuidas en 4 tratamientos con diseño de cuadrado latino 4x4, las 20 vacas restantes fueron dispuestas al azar en 4 grupos de 5 vacas cada uno. Los tratamientos fueron T1: Sin suplementación, T2: 20% maíz y 80% avena, T3: 50% maíz y 50% avena y T4: 80% maíz y 20% avena. La cantidad de suplemento entregado fue de 4 Kg día-1 ajustándose a cada tratamiento en base a T2, de manera que las raciones fuesen isoenergéticas. La pastura base de la dieta presentó un contenido promedio de proteína de 22,3%. El coeficiente “a” de degradabilidad de la materia seca (MS) fue un 81% mayor en la avena respecto al maíz, siendo esta diferencia significativa (P<0,05). La fracción lentamente degradable (coeficiente “b”) fue mayor en el caso del maíz superando a la avena en un 73% (P<0,05). La suma de los coeficientes “a” y “b” fue mayor para el caso del maíz alcanzando un 99,8%. Por su parte la tasa de degradación de la MS (coeficiente “c”) fue mayor en la avena respecto del maíz (P<0,05). En el caso de las mezclas de grano formuladas, la fracción soluble fue mayor en la mezcla 20M80A (P<0,05). La fracción lentamente y potencialmente degradable presentó diferencias significativas (P<0,05) siendo mayor en la mezcla 80M20A. La tasa de degradación de la MS (coeficiente “c”) fue superior para la mezcla 50M50A e inferior y similares en las mezclas 80M20A y 20M80A. En cuanto a la degradabilidad de la MS de la pastura de ballica, la fracción soluble “a” fue de 39,1% en promedio, en tanto que la fracción lentamente degradable “b” y la degradabilidad potencial de la MS fueron de 57,0% y 96,1% en promedio respectivamente. La tasa de degradación fue del orden de 0,064 % h-1. Los coeficientes “a” y “b” de la degradabilidad de la proteína bruta de la pastura de ballica, fueron de 57% y 11% respectivamente. La fracción potencialmente degradable fue en promedio de 71%. Por su parte la tasa de degradación fue de 0,24% h-1 en promedio. El consumo diario de materia seca no presentó diferencias significativas (P>0,05) entre tratamientos, pero si entre periodos (P<0,05) siendo mayor durante los periodos 3 y 4, lo mismo sucedió con el consumo de energía y proteína. 2 Tanto el amoniaco ruminal, plasmático y urea plasmática fueron mayores en el tratamiento sin concentrado (P<0,05), del orden de 19,83, 0,22 y 14,24 mg dL-1 respectivamente. Estos mismos parámetros presentaron diferencias significativas entre periodos (P<0,05) siendo siempre mayores en el periodo 4. La producción de urea en la orina fue de 1,05 g día-1 W-1 en promedio (P>0,05), presentando diferencias significativas entre periodos experimentales, siendo mayor en el periodo 4 (P<0,05). El peso vivo y cambio de peso vivo fueron mayores en el tratamiento 80M20A (537,8 y 1,32 Kg respectivamente), siendo significativo solo el peso vivo (P<0,05). En cuanto a la condición corporal esta no presentó diferencias significativas entre tratamientos (P>0,05). La producción de leche fue mayor en el tratamiento 50M50A (P<0,05), con un contenido graso y proteico mayor en el tratamiento sin concentrado (P<0,05). En cuanto a los periodos estos no presentaron diferencias significativas para las variables nombradas (P>0,05). La urea en leche fue mayor en el tratamiento sin concentrado (0,085 mg dL-1PV-1) (P<0,05), y durante el periodo 4 (P<0,05). Los requerimientos de energía metabolizable para producción de leche, cambio de peso vivo y requerimientos totales no presentaron diferencias significativas entre tratamientos (P>0,05), no así para los requerimientos de energía metabolizable de mantención, siendo menores para el tratamiento sin concentrado (P<0,05). La eficiencia de uso de la energía (EMm*100/EMT) fue mayor en los tratamientos 50M50A y 20M80A (P<0,05). Los requerimientos energéticos de mantención presentaron correlaciones altamente significativas con la concentración de urea en la leche (r=0,4028; P<0,001) y urea en plasma (r=0,4204; P<0,001), pero no con el amoniaco plasmático (r=0,207; P>0,05). La energía (MJ día-1) utilizada para la síntesis de urea láctea no presentó diferencias significativas (P>0,05), en promedio 0,15 MJ día-1. Al expresar dicha energía en términos de producción de leche fueron del orden de 44 g de leche diarios que, en términos porcentuales, no supera el 0,3% de la producción diaria de leche. No se encontraron efectos en los niveles productivos de las vacas atribuibles a una mayor disponibilidad de energía neta a raíz de una menor síntesis de urea por el uso de carbohidratos de distinta tasa de degradación en las dietas de las vacas. / In order to quantify the effects of including different carbohydrate sources having different degradation rates in the diet of lactating cows grazing a pasture rich in highly degradable protein on ruminal parameters, blood and milk urea and ammonia, and also to estimate the effect of supplements on the quantity of metabolizable energy spent on urea synthesis, a research was carried out, at the Oromo Experimental Station, Animal Production Department, Faculty of Agricultural Sciences. Twenty four New Zealand Holstein cows, four of them rumen fistulised were used. Twenty of them were randomly assigned to the following treatments: T1: Not supplemented; T2: 80% corn and 20% oats; T3: 50% corn plus 50% oat and T4: 20% corn plus 80% oats. Four kg animal-1day-1 was offered. Pasture was composed of annual rye grass and white clover with 23% of crude protein. The four fistulised cows were randomly assigned to the treatments in a 4 x 4 Latin square design. The dry matter degradability coefficient “a” of oat was 81% higher than corn (P<0,05). Coefficient “b” was 73% higher in corn than in oat (P<0,05). Potential degradable fraction (a+b) was 98% higher for corn (P<0,05) The constant rate of degradation “c” was higher in oats than corn (P<0,05). The mix of grain (20%C; 80%O) had a higher fraction “a” than the others mix. However the fraction “b” was significantly higher in mix 80%M; 20%C. Constant degradation rate “c” was significantly higher (P<0,05) in the mix 50%C, 50%O) and similar between the others mix. Dry matter degradability of pasture was characterized by a fraction “a” of 39,1%; a fraction “b” of 57% , a potential degradable fraction of 96,1% and a constant rate of degradation “c” of 0,064%/h . The fraction “a” and “b” of pasture crude protein was 57% and 11% respectively and the constant ”c” was 0,24% h-1. No differences were found for dry matter, protein and energy intake (P>0.05) among treatments but it was among periods (P<0.05) being higher during periods 3 and 4. Ruminal, plasma ammonia and plasma urea were higher (P<0,05) for the treatments without supplements (T1) with values of 19.3; 0,22 and 14,24 mg dL-1 respectively. All of these parameters had differences among periods being higher in period 4. Urea excreted in urine was 1,05 g day-1W-1 on average (P>0,05), being greater in period 4 (P<0,05) . Body weight and weight changes were higher in T2 (80%C; 20%O) (P<0,05) with 537,8 kg and 1,32 kg day-1 respectively. Body condition was not affected by treatments. Milk production was higher in T3 (50%C and 50%O) but fat and protein milk content was higher in T1. Urea in milk was higher in T1 with 0,085 mg dL-1 (P<0,05) and during the period 4. Metabolizable energy for milk production, weight changes and total requirements did no differ (P>0,05) among treatments, but energy requirements for maintenance was lower (P>0,05) for T1 (P<0,05) . The efficiency of energy use (EMM*100/EMT) was higher for treatments T2 and T3 (P<0,05). Maintenance energy requirements showed a highly significant correlation with urea en milk (r= 0,4028; P<0,01) and with urea in 4 plasma (0,4204; P<0,01) but not with plasma ammonia (r= 0,207; P<0,05). The energy (MJ d-1) used for milk synthesis. When this energy was expressed in terms of milk production it was 44 g, equivalent to 0,3% of energy deposited as milk. It was not possible to detect the effects of different carbohydrate sources increased the net energy availability for milk production since the synthesis of urea was diminished.

Urea forms crystalline complexes with n-alkanes and their liner derivatives but not with most branched and cyclic hydrocarbons and their derivatives. The compounds are stable enough to be used in separating these types of aliphatic compounds from their branched and cyclic analogs. Linear esters derived from normal saturated acids give adducts as expected. Urea complexation was found to be of great importance in the purification and separation of unsaturated esters of high molecular weight. The object of the present research was to investigate the compositions of urea adducts of various long-chain esters, approaching the class of waxes, to test various methods of determining their compositions, and to determine the suitability of the adduct method for purifying such esters.

Urea formaldehyde (UF) resins are widely used as adhesives for wood-based composites. These thermosetting polymers have advantages of relative low price, fast curing speed, and relative good bonding performance. However, UF resin bonded composites are designed for interior applications due to its weak water resistance. Moreover, traditional prevalent ways for recycling wood-based composites face problems caused by UF resins. In this project, the reuse of cured UF resins was systematically studied. The verification and characterization of crystalline structures in cured UF resins were conducted. The results showed that the crystalline regions were accounted for nearly 14.48% in a typical 1.2 formaldehyde to urea (F/U) molar ratio UF resin. The details of the resin crystalline regions, such as grain sizes and interplanar spacing (d-spacing), were characterized. The crystalline structures, nevertheless, did not affect the UF resin hydrothermal hydrolysis in this study. The reuse of cured UF resin was started with a hydrothermal hydrolysis. Under 140 °C and 2 h of hydrothermal process, 20 mL of 30 w.t. % formaldehyde water solution was able to depolymerize up to 1.7 g of cured UF resin. The hydrolyzed formaldehyde solutions were directly used as normal formaldehyde solutions for UF resin synthesis. The synthesized resin (named as UUF resin) contained about 6 w.t. % of cured UF resin and presented similar chemical structures and bonding performance as normal UF resins. Hybrid resins made of UUF resin and polymeric 4-4 diphenyl methane diisocyanate (pMDI) were prepared. The pMDI was found evenly dispersed in the hybrid resins by using acetone as its solvent. These hybrid resins resulted in faster curing and stronger bonding performance than pure UUF resins. Furthermore, the hybrid resin was used in a new bonding design, which used southern pine wood radial section features. This design generated finger joint like bonding interfaces by hot pressing two resin coated wood radial sections. The bonding strength and bond line stability were enhanced by this design.

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