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At least 163 records · Page 9Linked to original sources
PubMed1996

Activity of nitrogen fixation and nitrogen assimilation enzymes in soybean plants inoculated with Bradyrhizobium japonicum strains.

In studying the symbiotic associations of 8 Bradyrhizobium japonicum strains with two soybean varieties (NS-10 and NS-21), we determined the activity of nitrogen fixing (nitrogenase, NG) and nitrogen assimilation (glutamine synthetase, GS) and glutamate dehydrogenase (GDH) enzymes and the content of soluble proteins. The number of nodules was not in correlation with dry matter mass and nitrogen content. Dry matter mass and nitrogen content in the nodules of the soybean varieties in association with Bradyrhizobium strains 1, 1a, 2b, 2/1, 1003 and 8k turned out to be significantly higher than mass and nitrogen content of those in association with B. japonicum strains 17z and 2k. The results obtained indicate that the activity of the enzymes NG and GS in plants correlates with nitrogen fixation for both varieties on average, while the activity of GDH enzyme is conditioned by the specificity of variety and the Bradyrhizobium japonicum strains.

Nitrogen Fixation↗
PubMed1978

Interdependence of Nitrogen Nutrition and Photosynthesis in Pisum sativum L: I. Effect of Combined Nitrogen on Symbiotic Nitrogen Fixation and Photosynthesis.

Photosynthesis, primary productivity, N content, and N(2) fixation were determined as a function of applied NH(4) (+) in peas (Pisum sativum L. cv. Alaska) which were inoculated or not inoculated with Rhizobium leguminosarum. Cabon dioxide exchange rate (CER) increased 10-fold, total N content 7-fold, and total dry weight 3-fold in 26-day-old uninoculated plants as applied NH(4) (+) was increased from 0 to 16 millimolar. In inoculated plants of the same age CER and dry weight were maximal at 2 millimolar NH(4) (+), and total N content increased between 0 and 2 millimolar NH(4) (+) but did not change significantly with higher NH(4) (+) applications. Per cent N content of uninoculated plants was significantly lower than that of inoculated plants except at the highest NH(4) (+) concentration (16 millimolar). Symbiotic N(2) fixation by inoculated plants was maximal in peas grown with 2 millimolar NH(4) (+); and apparent relative efficiency of N(2) fixation, calculated from C(2)H(2) reduction and H(2) evolution, was maximal in the 2 to 4 millimolar NH(4) (+) concentration range. The capacity to fix N(2) through the Rhizobium-legume symbiosis significantly enhanced the rate and efficiency of photosynthesis and plant N content when NH(4) (+) concentration in the nutrient solution was below 8 millimolar. Above 8 millimolar NH(4) (+) concentration uninoculated plants had greater CER, N content, and dry weight.

Journal Article↗
PubMed2005

Nitrogen content, 15N natural abundance and biomass of the two pleurocarpous mosses Pleurozium schreberi (Brid.) Mitt. and Scleropodium purum (Hedw.) Limpr. in relation to atmospheric nitrogen deposition.

The suitability of the two pleurocarpous mosses Pleurozium schreberi and Scleropodium purum for assessing spatial variation in nitrogen deposition was investigated. Sampling was carried out at eight sites in the western part of Germany with bulk deposition rates ranging between 6.5 and 18.5 kg N ha(-1) yr(-1). In addition to the effect of deposition on the nitrogen content of the two species, its influence on 15N natural abundance (delta15N values) and on productivity was examined. Annual increases of the mosses were used for all analyses. Significant relationships between bulk N deposition and nitrogen content were obtained for both species; delta15N-values reflected the ratio of NH4-N to NO3-N in deposition. A negative effect of nitrogen input on productivity, i.e. decreasing biomass per area with increasing N deposition due to a reduction of stem density, was particularly evident with P. schreberi. Monitoring of N deposition by means of mosses is considered an important supplement to existing monitoring programs. It makes possible an improved spatial resolution, and thus those areas that receive high loads of nitrogen are more easily discernible.

Air Pollutants↗
PubMed1996

Supplementation with gum arabic fiber increases fecal nitrogen excretion and lowers serum urea nitrogen concentration in chronic renal failure patients consuming a low-protein diet.

In chronic renal failure (CRF), plasma concentrations of the products of protein metabolism are increased. Current dietary management is to prescribe a decrease in protein intake. The use of dietary fiber to increase fecal excretion of retained metabolites in CRF may be a beneficial adjunct to a low-protein diet (LPD). Colonic bacteria ferment dietary fiber, providing them with energy for growth and nitrogen incorporation, in turn, increasing nitrogen excretion in feces. Sixteen CRF patients consuming an LPD were randomly assigned to receive a supplement of a highly fermentable fiber, gum arabic (50 g/d), or a placebo (1 g pectin/d) in a prospective, single-blind, crossover design. Fecal bacterial mass and fecal nitrogen content were significantly increased during supplementation with gum arabic compared with the baseline LPD or supplementation with pectin. Serum urea nitrogen was significantly decreased during supplementation with gum arabic compared with the baseline LPD or supplementation with pectin. Nitrogen balance did not change significantly.

Adult↗
PubMed2002

The role of glutamine synthetase and glutamate dehydrogenase in nitrogen assimilation and possibilities for improvement in the nitrogen utilization of crops.

This short review outlines the central role of glutamine synthetase (GS) in plant nitrogen metabolism and discusses some possibilities for crop improvement. GS functions as the major assimilatory enzyme for ammonia produced from N fixation, and nitrate or ammonia nutrition. It also reassimilates ammonia released as a result of photorespiration and the breakdown of proteins and nitrogen transport compounds. GS is distributed in different subcellular locations (chloroplast and cytoplasm) and in different tissues and organs. This distribution probably changes as a function of the development of the tissue, for example, GS1 appears to play a key role in leaf senescence. The enzyme is the product of multiple genes with complex promoters that ensure the expression of the genes in an organ- and tissue-specific manner and in response to a number of environmental variables affecting the nutritional status of the cell. GS activity is also regulated post-translationally in a manner that involves 14-3-3 proteins and phosphorylation. GS and plant nitrogen metabolism is best viewed as a complex matrix continually changing during the development cycle of plants. Along with GS, a number of other enzymes play key roles in maintaining the balance of carbon and nitrogen. It is proposed that one of these is glutamate dehydrogenase (GDH). There is considerable evidence for a GDH shunt to return the carbon in amino acids back into reactions of carbon metabolism and the tri-carboxylic acid cycle. Results with transgenic plants containing transferred GS genes suggest that there may be ways in which it is possible to improve the efficiency with which crop plants use nitrogen. Marker-assisted breeding may also bring about such improvements.

Ammonia↗
PubMed1982

Pleiotropic deficiency in nitrogen-uptake systems and derepression of nitrogen-catabolic enzymes in npr-1 mutants of Saccharomyces cerevisiae.

The npr-1 mutation has two types of effects in Saccharomyces cerevisiae. On one hand, several nitrogen-catabolic enzymes are derepressed in the presence of ammonia, glutamine, or asparagine, which provoke their repression in a wild-type strain. On the other hand, the activity of several ammonia-sensitive permeases is decreased (from 50-100% depending on the permease considered) in npr-1 cells, independently of the nitrogen source used for growth. Our results favour the idea that the primary effect of the npr-1 mutation is on the permeases, and that the derepression of the enzymes is a consequence of the reduced uptake rate of the repressing nitrogen compounds. Hence, the product of the npr-1 gene appears to be directly involved in the development of the activity of a set of permeases which transport nitrogen compounds and which are regulated by nitrogen effectors.

Amino Acid Transport Systems↗
PubMed1969

Nitrogen fixation by Rhodospirillum rubrum grown in nitrogen-limited continuous culture.

Cell-free extracts of the photosynthetic bacterium Rhodospirillum rubrum were inconsistent in reducing N(2). An internally illuminated fermentor, designed for the continuous culture of this organism on N(2) under nitrogen-limited conditions, produced cells which yielded cell extracts with consistent activity for cell-free N(2) fixation. A nitrogen-limited continuous culture, supplied ammonia rather than N(2), gave cell-free extracts with even more active N(2) fixation. Extracts of cells grown in the fermentor with glutamate nitrogen as the limiting nutrient in continuous culture did not reduce N(2), but whole cells fixed (15)N-enriched N(2). The discovery that cells from ammonia and glutamate nitrogen-limited continuous cultures are capable of N(2) reduction suggests that R. rubrum cells produce the N(2)-reducing enzymes in response to conditions of nitrogen deficiency rather than in response to the presence of N(2). Examination of the effect of the pN(2) on N(2) reduction by cell-free preparations of R. rubrum indicated that the K(N(2)) is approximately 0.071 atm. Cell-free extracts from R. rubrum were tested for their ability to reduce substrates other than N(2).

Ammonia↗
PubMed1985

Microassay for ammonium by determination of ammonia nitrogen in a nitrogen analyzer.

The method described comprises the transformation of ammonium into ammonia, the rapid and gentle liberation of the ammonia followed by the measurement of the nitrogen in a Dohrmann nitrogen analyzer. Untreated biological samples (1-50 microliters) were pipetted onto magnesium oxide tablets at 130 degrees C and the ammonia liberated was transferred by a continuous stream of nitrogen carrier gas into the nitrogen analyzer. There the ammonia was determined by oxidative pyrolysis and subsequent chemiluminescence measurement of the excited NO2. The result could be read in nanograms ammonia nitrogen within 6.5 min. Apart from volatile amines, which are usually negligible in biological samples, the method was specific for ammonia because under the given conditions of volatilization the labile groups of glutamine and asparagine did not interfere. The assay was sensitive in the range of 1.5-150 nmol ammonia and suitable for the routine analysis of small samples.

Ammonia↗
PubMed2001

PtdIns(4,5)P(2) and phospholipase C-independent Ins(1,4,5)P(3) signals induced by a nitrogen source in nitrogen-starved yeast cells.

Addition of ammonium sulphate to nitrogen-depleted yeast cells resulted in a transient increase in Ins(1,4,5)P(3), with a maximum concentration reached after 7-8 min, as determined by radioligand assay and confirmed by chromatography. Surprisingly, the transient increase in Ins(1,4,5)P(3) did not trigger an increase in the concentration of intracellular calcium, as determined in vivo using the aequorin method. Similar Ins(1,4,5)P(3) signals were also observed in wild-type cells treated with the phospholipase C inhibitor 3-nitrocoumarin and in cells deleted for the only phospholipase C-encoding gene in yeast, PLC1. This showed clearly that Ins(1,4,5)P(3) was not generated by phospholipase C-dependent cleavage of PtdIns(4,5)P(2). Apart from a transient increase in Ins(1,4,5)P(3), we observed a transient increase in PtdIns(4,5)P(2) after the addition of a nitrogen source to nitrogen-starved glucose-repressed cells. Inhibition by wortmannin of the phosphatidylinositol 4-kinase, Stt4, which is involved in PtdIns(4,5)P(2) formation, did not affect the Ins(1,4,5)P(3) signal, but significantly delayed the PtdIns(4,5)P(2) signal. Moreover, wortmannin addition inhibited the nitrogen-induced activation of trehalase and the subsequent mobilization of trehalose, suggesting a role for PtdIns(4,5)P(2) in nitrogen activation of the fermentable-growth-medium-induced signalling pathway.

Ammonium Sulfate↗
PubMed1974

Nitrogen metabolism in the isolated perfused rat liver. Nitrogen balance, redox state and rates of proteolysis.

Nitrogen balances were measured in isolated perfused rat livers in the presence and absence of nitrogen donors. In all instances the balance apparently was incomplete. The expression [alanine][alpha-oxoglutarate]/[pyruvate][glutamate] remained fairly constant under the metabolic conditions studied, indicating that it may be at near-equilibrium. The source of the extra nitrogen seems to be derived from increased hepatic proteolysis. The addition of a nitrogen donor to the perfusate arrested proteolysis, as did the addition of pyruvate. The free mitochondrial [NAD(+)]/[NADH] ratio, calculated from the glutamate dehydrogenase and beta-hydroxybutyrate dehydrogenase reactants, showed similar values and exhibited parallel changes under most metabolic situations studied. These results suggest that, under the reported experimental conditions, both dehydrogenases share a common mitochondrial NAD pool. Glutamate dehydrogenase plays an important role in hepatic nitrogen metabolism in vivo.

Alanine↗
PubMed2000

Effect of removal of caecal contents on nitrogen utilisation and nitrogen excretion in caecally ligated chickens fed on a low protein diet supplemented with urea.

1. The effect of washing out the caecal contents on nitrogen utilisation and nitrogen excretion were examined in Single Comb White Leghorn cockerels fed on a 50 g/kg protein diet supplemented with urea. 2. Flushing out the caecal contents with saline in caecally ligated chickens produced a significantly increased nitrogen balance and increased nitrogen utilisation (P<0.05). 3. Washing out the caecal contents significantly decreased uric acid excretion but the treatment had no effect on urea and ammonia excretion. 4. Caecal bacterial contents were significantly decreased by caecal ligation and decreased further by washing out the caecal contents. 5. It is concluded that nitrogen metabolism in chickens is affected by possible changes in caecal fermentation produced by preventing substances from urine and digesta from entering the caeca.

Ammonia↗
PubMed1985

[Effect of type of starch and quantity in rations on apparent and true digestibility of nitrogen and nitrogen balance in sheep].

In a digestibility trial 5 semisynthetic rations were fed in 3 periods to 10 male sheep to examine the effects on N balance, components of faecal nitrogen and N digestibility. The rations contained constant amounts of nitrogen but different contents of cellulose and two different types of starch (untreated and steamflaked). Content and type of starch did not show any noticeable effect neither on excretion of undigested dietary nitrogen nor on true digestibility. There could not be noticed any effects on the apparent N digestibility by changing contents of cellulose or untreated starch. If the rations contained steamflaked corn starch, the animals excreted more faecal nitrogen and therefore showed a lower apparent N digestibility. Especially the water soluble N fraction of the faecal nitrogen was clearly higher. Compensation took place through a lower N excretion with the urine. The reason for increased faecal N excretion may be higher microbial protein synthesis in the rumen. This was accented by the allantoin excretion with the urine.

Animal Feed↗
PubMed1983

Effects of increasing nitrogen intake on nitrogen balance and energy expenditure in nutritionally depleted adult patients receiving parenteral nutrition.

The effects of increasing nitrogen intake were studied in 10 nutritionally depleted patients receiving total parenteral nutrition. After 1 to 2 days on 5% dextrose, the patients received, in random order, intravenous diets containing either a low (180 mg/kg . day) or high (364 mg/kg . day) nitrogen content. Equicaloric amounts of glucose and fat emulsion were given. Total energy intake averaged 33.0 kcal/kg . day corresponding to 1.31 X resting energy expenditure or 1.08 X total energy expenditure. Nitrogen and energy balances were measured daily. Concentrations of glucose, glycerol, fatty acids, triglycerides, urea, insulin and glucagon in plasma, and of beta-hydroxybutyrate in whole blood were measured during the last 2 days of each diet period. An increase in plasma urea was the only change in hormone or substrate concentrations identified. Resting energy expenditure increased approximately 10%, going from 5% dextrose to the low and from the low to the high N diet. Nitrogen balances were 0.21 and 0.61 mg N/kg . day on the low and high N diets. Nitrogen retention of 21% of the increment in intake, three times that seen in normal adult subjects, indicates that the malnourished patients in this study responded in a manner similar to growing organisms. Attainment of markedly positive N balance at, or close to, zero energy balance indicates that lean body mass can be restored without excessive energy intakes which may often be undesirable.

Adaptation, Physiological↗
PubMed1989

Cyclic variations in nitrogen uptake rate of soybean plants: ammonium as a nitrogen source.

When NO3- is the sole nitrogen source in flowing solution culture, the net rate of nitrogen uptake by nonnodulated soybean (Glycine max L. Merr. cv Ransom) plants cycles between maxima and minima with a periodicity of oscillation that corresponds with the interval of leaf emergence. Since soybean plants accumulate similar quantities of nitrogen when either NH4+ or NO3- is the sole source in solution culture controlled at pH 6.0, an experiment was conducted to determine if the oscillations in net rate of nitrogen uptake also occur when NH4+ is the nitrogen source. During a 21-day period of vegetative development, net uptake of NH4+ was measured daily by ion chromatography as depletion of NH4+ from a replenished nutrient solution containing 1.0 millimolar NH4+. The net rate of NH4+ uptake oscillated with a periodicity that was similar to the interval of leaf emergence. Instances of negative net rates of uptake indicate that the transition between maxima and minima involved changes in influx and efflux components of net NH4+ uptake.

Biological Transport↗
PubMed1990

Transcriptional regulatory cascade of nitrogen-fixation genes in anoxygenic photosynthetic bacteria: oxygen- and nitrogen-responsive factors.

Many photosynthetic bacteria from aquatic and terrestrial habitats reduce atmospheric dinitrogen to ammonia. The synthesis of proteins required for nitrogen fixation in these microorganisms is repressed by fixed nitrogen or oxygen. Studies on the purple non-sulphur phototroph Rhodobacter capsulatus have helped to clarify this transcriptional control and to define the factors involved in this regulation. The molecular mechanisms by which the nitrogen and oxygen status of the cell are relayed into nif gene expression or repression involve many trans- and cis-acting factors. The roles of these factors in the nif regulatory cascade of R. capsulatus are summarized. Two levels of control are present. The first level of control involves the nitrogen sensing circuitry in which at least four proteins act in a cascade. Upon nitrogen deficiency, genes involved in the second level of control are transcriptionally activated. These genes encode regulatory proteins that subsequently activate transcription of all other nif genes under anaerobic conditions. The R. capsulatus cascade is compared to the nif regulatory cascade in Klebsiella pneumoniae, highlighting both common and unique aspects.

Bacteria↗