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Metabolismo do nitrogênio e concentração de nutrientes no cafeeiro irrigado em razão da dose de N; Nitrogen metabolism and nutrient concentration in irrigated coffee plants due to nitrogen fertilization rates.

Paula Neto, Ana
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 29/01/2010 PT
Relevância na Pesquisa
492.6268%
A adubação nitrogenada e sua implicação no metabolismo do cafeeiro ainda não são bem conhecidas nas condições de campo, em cafeicultura altamente tecnificada, com temperatura média de outono-inverno superior a 22 ºC e maior quantidade de horas-luz. O objetivo da presente pesquisa foi avaliar a atividade das enzimas redutase do nitrato (RN), glutamina sintetase (GS) e urease em função da dose de nitrogênio (sem N, 200, 400, 600 e 800 kg ha-1). Avaliou-se também a influência das doses de N (uréia) nas concentrações de N-total, nitrato, amônio, clorofila e carotenóides presentes nas folhas; as flutuações de macro e micronutrientes; bem como a correlação entre a produtividade e doses de N. Objetivou-se também identificar a época do pico da atividade da RN. Os experimentos foram realizados no Oeste baiano e em Piracicaba, SP. As avaliações foram realizadas nas fases fenológicas: vegetação, antese, fruto chumbinho, granação e maturação. A maior atividade da RN ocorreu com o fornecimento de 800 kg ha-1 de N, sem variação nas demais doses, bem como não influenciou a atividade da GS e urease. As concentrações de nitrato e amônio não aumentaram com as doses de N, mas a concentração de aminoácidos foi crescente com a dose do nutriente. A maior atividade da RN verificou-se na fase de vegetação e granação dos frutos...

Análise da concentração de nitrato no líquido cefalorraquidiano e da atividade enzimática das óxido nítrico sintases no hipotálamo de ratos submetidos à sepse experimental; Analysis of nitrate concentration in the cerebrospinal fluid and of the enzymatic activity of nitric oxide synthase in the hypothalamus of rats submitted to experimental sepsis.

Aguila, Fábio Alves
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 21/09/2012 PT
Relevância na Pesquisa
489.2876%
Sepse é definida como uma resposta inflamatória sistêmica frente a um estímulo infeccioso. Na fase inicial da doença ocorre aumento da secreção de vasopressina (AVP) e na fase tardia observamos uma redução, apesar dos elevados níveis de mediadores inflamatórios e agravamento da hipotensão que são estímulos para a secreção do hormônio. O óxido nítrico (NO), produzido pela enzima óxido nítrico sintase (NOS), parece modular a secreção de AVP dependendo do contexto fisiopatológico. Durante sepse experimental nosso grupo demonstrou que as concentrações plasmáticas de nitrato, que servem como índice da produção de NO, se elevam progressivamente durante a evolução da doença, mas não há evidências de que isto ocorra também a nível central. Nosso objetivo foi avaliar temporalmente a concentração de nitrato no líquido cefalorraquidiano (LCR) e a atividade enzimática das NOS no hipotálamo de ratos submetidos à sepse por ligadura e perfuração cecal (CLP). Os procedimentos, aprovados pelo Comitê de Ética no Uso de Animais do Campus de Ribeirão Preto (CEUA-USP, protocolo nº 10.1.294.53.7), foram realizados com ratos Wistar pesando 250 ± 30 gramas, os quais foram divididos em dois grupos: CLP e operação fictícia (OF). Após 0...

Teor de nitrato como indicador complementar da disponibilidade de nitrogênio no solo para o milho; Nitrate concentration as a complementary indicator of soil nitrogen availability to corn

Rambo, Lisandro; Silva, Paulo Regis Ferreira da; Bayer, Cimelio; Argenta, Gilber; Strieder, Mércio Luíz; Silva, Adriano Alves da
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Artigo de Revista Científica Formato: application/pdf
POR
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Avanços na adubação nitrogenada em cobertura em milho poderão ser obtidos com a inclusão de características de solo como indicadores complementares da disponibilidade de N. Os objetivos deste estudo foram avaliar o potencial de uso, o nível crítico e o melhor estádio de desenvolvimento da cultura para determinação do teor de N-NO3 - no solo, visando à predição da disponibilidade de N ao milho, e verificar se a determinação do teor de N-NH4 +, em adição ao teor de N-NO3 -, aumenta a eficiência na avaliação da disponibilidade de N. Para isso, realizou-se um experimento por dois anos agrícolas (2002/03 e 2003/04) em Argissolo Vermelho da Depressão Central do RS, no qual se realizou a simulação de diferentes níveis de disponibilidade de N no solo a partir da utilização de cinco doses de N (0, 50, 100, 200 e 300 kg ha-1), parte na semeadura (20 %) e o restante em cobertura (estádio V3). O experimento seguiu o delineamento de blocos casualizados, com quatro repetições, e nos dois anos agrícolas foram avaliados os teores de N-NO3 -, de N-NH4 + e de N mineral (N-NO3 - + N-NH4 +) no solo (0–30 cm), em diferentes estádios de desenvolvimento (V3, V6, V10 e espigamento), e o rendimento de grãos do milho. Em geral...

Effects of nitrate concentration on larval development of the giant river prawn, Macrobrachium rosenbergii

Mallasen, Margarete; Valenti, Wagner Cotroni; Ismael, Deborah
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 55-69
ENG
Relevância na Pesquisa
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The effect of nitrate concentration on giant river prawn, Macrobrachium rosenbergii, larvae was investigated. Survival rate, weight gain, and larval development were evaluated for different concentrations of nitrate in three experiments. The experiments were divided i n to two phases. In the first phase, larvae from stages I through VIII were analysed, while in the second phase larvae from stage VIII through post-larvae metamorphosis were analysed. Oxygen consumption was also determined for zoea I, II, and VIII exposed to 0, 700, and 1,000 mg/L of nitrate-N. No effect was observed for concentrations up to 180 mg/L NO3-N (experiments I and II), and nitrate levels as 1,000 mg/L NO3-N did not affect survival in the first phase of the third experiment. On the other hand, larval stage index (LSI) and weight gain decreased as nitrate-N concentration increased from 0 to 1,000 mg/L. In the second phase, survival and metamorphosis rate decreased as nitrate concentration increased, according to a linear model. The effect of nitrate levels on weight gain followed a curvilinear pattern. Larval respiration decreased in the water where nitrate was added, but only during stage II. The results demonstrated that nitrate presents extremely low toxicity for giant river prawn larvae...

Denitrification of a landfill leachate with high nitrate concentration in an anoxic rotating biological contactor

Cortez, Susana; Teixeira, P.; Oliveira, Rosário; Mota, M.
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Publicado em /06/2011 ENG
Relevância na Pesquisa
484.2763%
The denitrification performance of a lab-scale anoxic rotating biological contactor (RBC) using landfill leachate with high nitrate concentration was evaluated. Under a carbon to nitrogen ratio (C/N) of 2, the reactor achieved N-NO3 − removal efficiencies above 95% for concentrations up to 100 mg N-NO3 − l−1. The highest observed denitrification rate was 55 mg N-NO3 − l−1 h−1 (15 g N-NO3 − m−2 d−1) at a nitrate concentration of 560 mg N-NO3 − l−1. Although the reactor has revealed a very good performance in terms of denitrification, effluent chemical oxygen demand (COD) concentrations were still high for direct discharge. The results obtained in a subsequent experiment at constant nitrate concentration (220 mg N-NO3 − l−1) and lower C/N ratios (1.2 and 1.5) evidenced that the organic matter present in the leachate was non-biodegradable. A phosphorus concentration of 10 mg P-PO4 3− l−1 promoted autotrophic denitrification, revealing the importance of phosphorus concentration on biological denitrification processes.

Effect of nitrogen source on soil nitrate concentration and yield, and quality of intermediate-day onions

Machado, Rui; Campos, Tiago
Fonte: NutriHORT Publicador: NutriHORT
Tipo: Aula
POR
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588.4345%
The effect of nitrogen source application, broadcast onto the planting bed during the growing phase, on soil nitrate concentration, soil pH, yield, and quality of intermediate-day onions was evaluated in a field experiment in southern Portugal. In addition, the soil potential for providing nitrate-N to the crop along the growing season was also monitored. The field trial consisted of six treatments of different combinations of ammonium nitrate (17% NH4-N + 17% NO3-N) (AN) and ammonium sulphate (20.5 % NH4-N and 60% SO3) (AS) as fertilizers. Soil NO3-N and soil pH were measured at 0, 47, 76, 95, and 124 days after transplanting (DAT). Nitrogen source did not significantly affect the soil nitrate concentration, commercial yield, bulb dry weight, soluble solids or pH. AS-AS application as compared with AN-AN led to a significantly decrease in soil pH. The nitrate release through the mineralization of organic matter began in the first 47 DAT and occurred throughout the growing season. At 0 to 10 cm soil depth from 0 to 47 DAT, nitrate concentration increased by 14.8 mg kg-1. A significant amount of N uptake was provided by the soil, achieving a high commercial yield of 7.52 kg m-2 in the treatment without nitrogen application and 9.05 kg m-2 where N (45kg N/ha) was applied.

Effect of nitrogen source on soil nitrate concentration and yield, and quality of intermediate-day onions

Machado, RMA; Campos, Tiago
Fonte: Nutriort Publicador: Nutriort
Tipo: Aula
POR
Relevância na Pesquisa
589.2876%
Abstract The effect of nitrogen source application, broadcast onto the planting bed during the growing phase, on soil nitrate concentration, soil pH, yield, and quality of intermediate-day onions was evaluated in a field experiment in southern Portugal. In addition, the soil potential for providing nitrate-N to the crop along the growing season was also monitored. The field trial consisted of six treatments of different combinations of ammonium nitrate (17% NH4-N + 17% NO3-N) (AN) and ammonium sulphate (20.5 % NH4-N and 60% SO3) (AS) as fertilizers. Soil NO3-N and soil pH were measured at 0, 47, 76, 95, and 124 days after transplanting (DAT). Nitrogen source did not significantly affect the soil nitrate concentration, commercial yield, bulb dry weight, soluble solids or pH. AS-AS application as compared with AN-AN led to a significantly decrease in soil pH. The nitrate release through the mineralization of organic matter began in the first 47 DAT and occurred throughout the growing season. At 0 to 10 cm soil depth from 0 to 47 DAT, nitrate concentration increased by 14.8 mg kg-1. A significant amount of N uptake was provided by the soil, achieving a high commercial yield of 7.52 kg m-2 in the treatment without nitrogen application and 9.05 kg m-2 where N (45kg N/ha) was applied

The Influence of Nitrogen Fertilization on Growth, Yield and Nitrate and Oxalic Acid Concentration in Purslane (Portulaca oleracea)

Santos, R.V; Machado, RMA; Alves- Pereira, I; Ferreira, Rui
Fonte: Universidade de Évora Publicador: Universidade de Évora
Tipo: Aula
POR
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Abstract Culinary use of purslane (Portulaca oleracea L.) is appreciated across the whole of the Mediterranean, and the interest in this plant has been increasing due to be a source of bio-protectives compounds, such as fatty acids and antioxidants. However, their use may be difficult due to the accumulation of high contents of compounds harmful to human health, such as nitrate and oxalic acid. The main objective of the present study was to evaluate the influence of nitrogen fertilization on growth and yield parameters, and on nitrate and oxalic acid concentration in leaves and stems. Plants of golden-leafed purslane of sativa subspecies were grown in styrofoam boxes with substrate and fertigated 2 times per week along 4 weeks with ammonium-nitrate solution (16.9% NO3--N and 17.6% NH4+-N), for testing 4 nitrogen levels (0, 30, 60 and 90 kg N ha-1). Plant growth, yield, nitrate and oxalic acid concentrations were significantly affected by nitrogen application. The best quantity/quality ratio was achieved in fertilization level of 60 kg N ha-1, in which the yield was 5.1 kg m-2 FW and nitrate concentration was 48.98 and 43.90 mg g-1 DW in leaf and stem, respectively, and oxalic acid concentration was 1.27 and 0.55 mg g-1 DW, in leaf and stem...

Nitrate and ammonium in soil solution in tobacco management systems

Kaiser,Douglas Rodrigo; Reinert,Dalvan José; Reichert,José Miguel; Streck,Carlos Arnoldo; Pellegrini,André
Fonte: Sociedade Brasileira de Ciência do Solo Publicador: Sociedade Brasileira de Ciência do Solo
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2010 EN
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487.11445%
Tobacco farmers of southern Brazil use high levels of fertilizers, without considering soil and environmental attributes, posing great risk to water resources degradation. The objective of this study was to monitor nitrate and ammonium concentrations in the soil solution of an Entisol in and below the root zone of tobacco under conventional tillage (CT), minimum tillage (MT) and no-tillage (NT). The study was conducted in the small-watershed Arroio Lino, in Agudo, State of Rio Grande do Sul, Brazil. A base fertilization of 850 kg ha-1 of 10-18-24 and topdressing of 400 kg ha-1 of 14-0-14 NPK fertilizer were applied. The soil solution was sampled during the crop cycle with a tension lysimeter equipped with a porous ceramic cup. Ammonium and nitrate concentrations were analyzed by the distillation and titration method. Nitrate concentrations, ranging from 8 to 226 mg L-1, were highest after initial fertilization and decreased during the crop cycle. The average nitrate (N-NO3-) concentration in the root zone was 75 in NT, 95 in MT, and 49 mg L-1 in CT. Below the root zone, the average nitrate concentration was 58 under NT, 108 under MT and 36 mg L-1 under CT. The nitrate and ammonium concentrations did not differ significantly in the management systems. However...

Nitrate concentration in lettuce leaves depending on photosynthetic photon flux and nitrate concentration in the nutrient solution

Cometti,Nilton Nélio; Martins,Madlles Q; Bremenkamp,Cintia Aparecida; Nunes,José Arcanjo
Fonte: Associação Brasileira de Horticultura Publicador: Associação Brasileira de Horticultura
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2011 EN
Relevância na Pesquisa
488.89824%
The nitrate accumulation in plant tissues can occur due to low light availability. However, published studies have not linked nitrate accumulation to photosynthetic photon flux (PPF) measured during the growing period. This study aimed to evaluate the effect of the reduction of photosynthetic photon flux and the concentration of nitrate in the nutrient solution on agronomic characteristics and accumulation of nitrate in lettuce grown in hydroponics. The trial design was entirely randomized in a factorial scheme (4 x 2) with three repetitions, and four shading levels: 0, 30, 50, and 80% and two nitrate levels in nutrient solution: 5 and 10 mmol L-1. The dry matter production decreased directly and linearly with the reduction of light. The lowest level in nitrate solution also led to reduction in dry mass yield. The maximum accumulation of nitrate reached 966.3 mg kg-1 fresh mass, with PPF of 118 μmol/m²/s and 140 mg L-1 of N-NO3-1 (below the maximum levels recommended by the European Union), and the minimum of 200 mg kg-1 with PPF of 455 μmol/m²/s and 70 mg L-1 of N-NO3-1 in the nutrient solution. The reduction of nitrate in the nutrient solution from 140 to 70 mg L-1 led to the reduction of nitrate accumulation in shoots...

Note on the effect of high nitrate concentration and light intensity on the growth and uptake rates of Phaeodactylum tricornutum (Bohlin) culture

Schmidt,Gilda
Fonte: Instituto Oceanográfico da Universidade de São Paulo Publicador: Instituto Oceanográfico da Universidade de São Paulo
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/1983 EN
Relevância na Pesquisa
484.22406%
The effect of high nitrate concentration and light intensity on chlorophyll-a synthesis, cell number and nitrate assimilation on P. tJt¿coh,nuutum culture, was determined. Growth and uptake rates were determined as a function of nitrate concentration ranging from 0.40 to 35.40 µg/l. The Ks showed high values, when compared with those obtained with lower nitrate concentration. The percentual variation of Ks was greater than that of Vmax.

Plasma nitrate concentration in infective gastroenteritis and inflammatory bowel disease.

Dykhuizen, R S; Masson, J; McKnight, G; Mowat, A N; Smith, C C; Smith, L M; Benjamin, N
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /09/1996 EN
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489.2876%
BACKGROUND: In subjects on a low nitrate diet, plasma nitrate concentration and urinary nitrate excretion are thought to reflect endogenous nitric oxide (NO) production, and have been reported to increase during infective and inflammatory bowel disease. AIMS: To compare the extent of NO production in patients with infective versus non-infective forms of bowel dysfunction. SUBJECTS: Four groups: 20 healthy, volunteer clerical and laboratory staff, 12 patients with irritable bowel syndrome, 19 patients with inflammatory bowel disease, and 20 patients with infective gastroenteritis. METHODS: The plasma nitrate concentration was determined with a copper coated cadmium column and spectrophotometry. Mean and median plasma nitrate concentrations were calculated and compared within the four groups. Mann-Whitney distribution free rank testing was used to compare the median values. RESULTS: Median plasma nitrate concentrations in the four groups were: controls 32.7 mumol/l; irritable bowel syndrome 35.5 mumol/l; inflammatory bowel disease 35.1 mumol/l; and gastroenteritis 117.9 mumol/l (p < 0.001 gastroenteritis v all other groups). CONCLUSIONS: Plasma nitrate concentration could serve as a discriminant between infective and inflammatory or functional bowel disease in patients presenting with diarrhoea. It is not clear why there is considerable difference in endogenous nitrate synthesis in these two conditions...

Adaptation of cytochrome-b5 reductase activity and methaemoglobinaemia in areas with a high nitrate concentration in drinking-water.

Gupta, S. K.; Gupta, R. C.; Seth, A. K.; Gupta, A. B.; Bassin, J. K.; Gupta, A.
Fonte: World Health Organization Publicador: World Health Organization
Tipo: Artigo de Revista Científica
Publicado em //1999 EN
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487.37336%
An epidemiological investigation was undertaken in India to assess the prevalence of methaemoglobinaemia in areas with high nitrate concentration in drinking-water and the possible association with an adaptation of cytochrome-b5 reductase. Five areas were selected, with average nitrate ion concentrations in drinking-water of 26, 45, 95, 222 and 459 mg/l. These areas were visited and house schedules were prepared in accordance with a statistically designed protocol. A sample of 10% of the total population was selected in each of the areas, matched for age and weight, giving a total of 178 persons in five age groups. For each subject, a detailed history was documented, a medical examination was conducted and blood samples were taken to determine methaemoglobin level and cytochrome-b5 reductase activity. Collected data were subjected to statistical analysis to test for a possible relationship between nitrate concentration, cytochrome-b5 reductase activity and methaemoglobinaemia. High nitrate concentrations caused methaemoglobinaemia in infants and adults. The reserve of cytochrome-b5 reductase activity (i.e. the enzyme activity not currently being used, but which is available when needed; for example, under conditions of increased nitrate ingestion) and its adaptation with increasing water nitrate concentration to reduce methaemoglobin were more pronounced in children and adolescents.

Genetic variation for nitrate concentration in Nicotiana tabacum L.

Ostrem, J. A.; Collins, G. B.
Fonte: Oxford University Press Publicador: Oxford University Press
Tipo: Artigo de Revista Científica Formato: text/html
EN
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496.45008%
Genetic variation for nitrate concentration was examined in replicated field plots of 32 tobacco varieties representing a diverse sample of the Nicotiana tabacum germplasm. Two low, two intermediate, and two high nitrate cultivars were crossed in a diallel mating design without reciprocals. Highly significant general and specific combining ability mean squares were obtained for lamina nitrate concentration indicating that nitrate concentration in N. tabacum is significantly influenced by both additive and nonadditive gene action. Variation in nitrate accumulation was postulated to be due to genotypic differences in 1) structural characteristics modifying light penetration into the canopy, 2) in vivo nitrate reductase activity, and 3) uptake and translocation of nitrate to the lamina. Highly significant positive correlations were found between lamina nitrate concentration, total leaf area, and average area per leaf. Lamina nitrate concentration was not significantly correlated with in vivo nitrate reductase activity. Vascular nitrate concentration appeared to contribute to variation in lamina nitrate concentration. The results of this study indicate that nitrate accumulation in N. tabacum can be attributed to an interaction of genotypic differences in nitrate uptake...

Note on the effect of high nitrate concentration and light intensity on the growth and uptake rates of Phaeovactylum tricornutum (Bohlin) culture

Schmidt, Gilda
Fonte: Universidade de São Paulo. Instituto Oceanográfico Publicador: Universidade de São Paulo. Instituto Oceanográfico
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; ; Formato: application/pdf
Publicado em 01/01/1983 ENG
Relevância na Pesquisa
484.22406%
Foi determinado o efeito dc ama alta concentração de nitrato e alta incensidade luminosa na síntese de clorofila-α, número de células e assimilação nitrato em uma cultura de P. triconotum. As velocidade de crescimento e de assimilação foram determinados em função de concentrações de nitrato variando de 0,40 a 35,40 µg-at/l e intensidade luminosa de 12 KLUX. A Ks e a Vmax apresentaram valores altos, comparativamente com valores obtidos em concentrações mais baixas de nitrato e menor intensidade luminosa. A variação porcentual da Ks foi maior que a variação porcentual da Vmax.; The effect of high nitrate concentration and light intensity on chlorophyll-a synthesis, cell number and nitrate assimilation on P. tJt¿coh,nuutum culture, was determined. Growth and uptake rates were determined as a function of nitrate concentration ranging from 0.40 to 35.40 µg/l. The Ks showed high values, when compared with those obtained with lower nitrate concentration. The percentual variation of Ks was greater than that of Vmax.

Modeling Nitrate Concentration in Ground Water Using Regression and Neural Networks

Ramasamy, Nacha; Krishnan, Palaniappa; Bernard, John C.; Ritter, William F.
Fonte: Department of Food and Resources Economics Publicador: Department of Food and Resources Economics
Tipo: Staff Paper Formato: 419195 bytes; application/pdf
EN_US
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483.2131%
Nitrate concentration in ground water is a major problem in specific agricultural areas. Using regression and neural networks, this study models nitrate concentration in ground water as a function of iron concentration in ground water, season and distance of the well from a poultry house. Results from both techniques are comparable and show that the distance of the well from a poultry house has a significant effect on nitrate concentration in groundwater.

Modeling Nitrate Concentration in Ground Water Using Regression and Neural Networks

Ramasamy, Nacha; Krishnan, Palaniappa; Bernard, John C.; Ritter, William F.
Fonte: Universidade de Delaware Publicador: Universidade de Delaware
Tipo: Relatório Formato: 419193 bytes; application/pdf
EN_US
Relevância na Pesquisa
686.7594%
Nitrate concentration in ground water is a major problem in specific agricultural areas. Using regression and neural networks, this study models nitrate concentration in ground water as a function of iron concentration in ground water, season and distance of the well from a poultry house. Results from both techniques are comparable and show that the distance of the well from a poultry house has a significant effect on nitrate concentration in groundwater.

Nitrate sensing and cell wall modification in Staphylococci

Niemann, Volker
Fonte: Universität Tübingen Publicador: Universität Tübingen
Tipo: Dissertation; info:eu-repo/semantics/doctoralThesis
EN
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479.05234%
This thesis highlights two topics concerning the regulation of energy metabolism and the cell wall biosynthesis in Staphylococci. Most members of this genus are facultative anaerobic microorganisms able to respire on nitrate as final electron acceptor. The completely apathogenic organism Staphylococcus carnosus is used as starter culture in food industry. Dissimilatory nitrate reduction causes desired effects during the ripening process of sausages. First, the nitrate concentration is reduced, and nitrite combines with myoglobin to nitrosomyoglobin to yield the appealing red color of sausages. Secondly, use of starter cultures in food production reduces likewise the risk of food poisoning and food spoilage. The signal transduction system that regulates the anaerobic respiration has to transduce two signals: The absence of oxygen and the presence of nitrate as the final electron acceptor. The two component system NreBC is composed of an oxygen-sensing histidine kinase with its cognate response regulator, which induces gene expression in the absence of oxygen. In Niemann et al we present two X-ray structures of NreA bound to its physiological ligand nitrate as well as to iodide in the binding pocket. Based on the X-ray structure...

Assessment of nitrate contamination of karst springs, Bani Kanana, northern Jordan

Obeidat,Mutewekil M.; Ahmad,Fayez Y.; Hamouri,Nezar A.; Massadeh,Adnan M.; Athamneh,Faisal S.
Fonte: Instituto de Geología, UNAM Publicador: Instituto de Geología, UNAM
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2008 EN
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Contamination of ground-water from point and non-point sources is one of the major problems of water resources in Jordan. Altogether one hundred and six groundwater samples were collected from twenty six karst springs emerging from Umm Rijam aquifer and three wells tapping Amman-Wadi As Sir aquifer, and investigated for NO3- concentrations. Results showed that NO3- concentration in spring water ranged from 8 to 192 mg/L with an average of 33 mg/L. Seventy seven percent of the samples collected from the springs had nitrate concentrations exceeding the threshold value of 20 mg/L of anthropogenic source, and eight percent of the samples collected had nitrate concentrations higher than 50 mg/L, the maximum acceptable nitrate concentration for drinking water. About eighty percent of the sampled springs had nitrate concentrations higher than 20 mg/L. The K-means cluster analysis performed on the collected samples revealed the presence of three major clusters. The data were processed for the possible presence ofdiscordant outliers using the unpublished computer program UDASYS by Verma and Díaz-González. There is a wide spatial variation in the nitrate concentration in spring water. Monitoring the water quality of these springs showed that the lowest concentrations of nitrate were found in the wet season (January...

Effect of irradiance and nitrate levels on the relationship between gross photosynthesis and electron transport rate in the seagrass Cymodocea nodosa

Cabello-Pasini,Alejandro; Abdala-Díaz,Roberto T; Macías-Carranza,Víctor; Figueroa,Félix L
Fonte: Universidad Autónoma de Baja California, Instituto de Investigaciones Oceanológicas Publicador: Universidad Autónoma de Baja California, Instituto de Investigaciones Oceanológicas
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2015 EN
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The relationship between gross photosynthesis (GPS) and electron transport rate (ETR) in marine algae has been shown to vary as a function of irradiance; however, little is known about the effect of nutrients on the this relationship in seagrasses. The objective of this study was to evaluate the effect of nitrate concentration on the GPS (measured as O2 evolution) vs ETR (estimated by fluorescence quenching analysis) relationship of the seagrass Cymodoceanodosa from the Spanish Mediterranean Sea. Carbon levels in the tissue increased 6.5% when nitrate in the culture medium augmented from 0 to 100 µM. Nitrogen in the tissue, however, increased more than 60% when nitrate concentration in the medium reached 100 µM. Chlorophyll a + b levels increased approximately 30%, while absorptance augmented 15% when nitrate increased from 0 to 100 µM. In general, maximum oxygenic photosynthesis and maximum ETR values increased when nitrate in the medium increased. The relationship between GPS and ETR did not show a linear response at low nitrate levels and high irradiances. In contrast, a linear relationship was observed at nitrate levels above 50 µM, even at high irradiances. The results from this study suggest that the lack of correlation between ETR and GPS is the result of low nitrogen levels in the tissue of marine macrophytes. They also suggest that seasonal fluctuations in nitrate levels or nitrogen pulses...