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PubMed1980

Intra versus interregional nitrogen gradients in the single breath nitrogen test.

To investigate the genesis of cardiogenic oscillations (C.O.) and the slopes of the single-breath nitrogen test, we studied ten healthy volunteers with a modified test. This test utilized incremental volumes of air from 10% to 100% vital capacity (VC) after a nitrogen washout with oxygen. Subjects exhaled to residual volume, inspired the air volume and completed a full inspiration with oxygen. C.O. and both slopes were positive with low air volumes and negative with a VC of air. The slope of phase IV showed a linear decrease with the increasing inspired air volume, and reached zero with an air volume of 38% VC. AT higher volumes it became progressively more negative. The slope of phase III and C.O. were highly positive with 10% to 50% VC air volume then subsequently decreased. The values for C.O. and the slope of phase III were significantly different (P < 0.001) from those of the slop of phase IV and the apex-base gradients predicted by the model of Milic-Emili et al. These results suggest that intraregional gradients are significantly involved in the genesis of C.O. and the slop of phase III.

Adult↗
PubMed2006

The influence of nitrogen-15 proton-driven spin diffusion on the measurement of nitrogen-15 longitudinal relaxation times.

The effect of nitrogen-15 proton-driven spin diffusion on quantitative (15)N T(1) measurements in solid proteins is investigated, and the impact on the measurement of dynamic parameters is assessed. A simple model of exchange between neighboring nitrogens is used to reproduce the evolution of (15)N spin systems whose longitudinal relaxation rates and exchange rates are compatible with experimental measurements. We show that the induced error in the measured T(1) and its effect on the determination of dynamics parameters is likely to be less than the current experimental error. The use of deuterated protein samples is shown to have a small but sometimes visible effect, and may also considerably slow down or even suppress the exchange of magnetization due to spin diffusion.

Artifacts↗
PubMed2004

Nitrogen-15 NMR studies of nitrogen metabolism in Picea glauca buds.

In vivo (15)N nuclear magnetic resonance (NMR) as well as (15)N solid-state magic angle spinning (MAS) NMR spectroscopy were used to investigate nitrogen metabolism in cultured white spruce (Picea glauca) buds. Long-term as well as short-term experiments were carried out involving the use of inhibitors of the nitrogen pathways such as methionine sulfoximine (MSO), azaserine (AZA) and aminooxyacetate (AOA). Both in vivo and solid-state NMR showed that when MSO blocked glutamine synthetase (GS) no NH(4)(+) is incorporated. When glutamate synthase (GOGAT) is blocked by AZA there is some incorporation into glutamine (Gln), but very little into alpha-amino groups (glutamate, Glu). The transamination inhibitor AOA does not affect the metabolism of (15)NH(4)(+) into Gln and Glu, but blocks the production of arginine (Arg), as would be expected. Proline (Pro) and gamma-aminobutyric acid (GABA), which are produced directly from Glu without a transamination step, were not affected. The solid-state NMR experiments showed that protein synthesis occurred. Collectively, our results show that NH(4)(+) can only be assimilated through the GS/GOGAT pathway in P. glauca buds.

Aminooxyacetic Acid↗
PubMed2001

Chemiluminescence nitrogen detection in ion chromatography for the determination of nitrogen-containing anions.

Chemiluminescence nitrogen detection (CLND) provides equimolar response for nitrogen-containing ions such as nitrate, nitrite, cyanide, ammonium and tetradecyltrimethylammonium. Only azide yields a lower response. Nitrite, azide and nitrate are separated on a Dionex AS11 column using 5 nM NaOH as eluent with a 3 microM (1 ng N) limit of detection. Matrices, such as 1:10 diluted seawater, do not degrade these detection limits. CLND also provides equally sensitive (limit of detection 3 microM, 78 ppb) detection of weak acids such, as cyanide, which yield poor sensitivity with suppressed conductivity detection.

Anions↗
PubMed2003

Importance of atmospherically deposited nitrogen to the annual nitrogen budget of the Neuse River estuary, North Carolina.

Wet deposition of nitrogen, as NH(4)(+), NO(3)(-), and organic N, contributes up to 50% of the total externally supplied or 'new' N flux to the Neuse River Estuary (North Carolina). Excessive nitrogen (N) loading to N-sensitive waters such as the Neuse River Estuary has been linked to changes in microbial and algal community composition and function (harmful algal blooms), hypoxia/anoxia, and fish kills. In a 4-year study from July 1996 to July 2000, the weekly wet deposition of NH(4)(+), NO(3)(-), and dissolved organic N was calculated, based on concentration and precipitation measurements, at 11 sites on a northwest-southeast transect in the watershed. Data from this period indicate that the annual mean total wet atmospherically deposited (AD)-N flux was 11 kg ha(-1) year(-1). Deposition was fairly evenly distributed between nitrate, ammonium, and organics (32%, 32%, and 36%, respectively). Seasonally, the summer (June-August) months contained the highest weekly wet total N deposition; this trend was not driven by precipitation amount. Estimates of watershed N retention and in-stream riverine processing revealed that the AD-N flux contributed an estimated 20% (range of 15-51%) of the total 'new' N flux to the estuary, with direct deposition of N to the estuary surface accounting for 6% of the total 'new' N flux. This study did not measure the dry depositional flux, which may double the contribution of AD-N to the estuary. The AD-N is an important source of 'new' N to the Neuse River Estuary as well as other estuarine and coastal ecosystems downwind of major emission sources. As such, AD-N should be included in effective nutrient mitigation and management efforts for these N-sensitive waters.

Air Pollutants↗
PubMed2002

Defining the spatial impacts of poultry farm ammonia emissions on species composition of adjacent woodland groundflora using Ellenberg Nitrogen Index, nitrous oxide and nitric oxide emissions and foliar nitrogen as marker variables.

The marker variables, Ellenberg Nitrogen Index, nitrous oxide and nitric oxide fluxes and foliar nitrogen, were used to define the impacts of NH3 deposition from nearby livestock buildings on species composition of woodland ground flora, using a woodland site close to a major poultry complex in the UK. The study centred on 2 units in close proximity to each other, containing 350,000 birds, and estimated to emit around 140,000 kg N year(-1) as NH3. Annual mean concentrations of NH3 close to the buildings were very large (60 microg m(-3)) and declined to 3 microg m(-3) at a distance of 650 m from the buildings. Estimated total N deposition ranged from 80 kg N ha(-1) year(-1) at a distance of 30 m to 14 kg N ha(-1) year(-1) at 650 m downwind. Emissions of N2O and NO were 56 and 131 microg N m(-2) h(-1), respectively at 30 m and 13 and 80 microg N m(-2) h(-1), respectively at 250 m downwind of the livestock buildings. Species number in woodland ground flora downwind of the buildings remained fairly constant for a distance of 200 m from the units then increased considerably, doubling at a distance of 650 m. Within the first 200 m downwind, trends in plant species composition were hard to discern because of variations in tree canopy composition and cover. The mean Ellenberg N Index ranged from 6.0 immediately downwind of the livestock buildings to 4.8 at 650 m downwind. The mean abundance weighted Ellenberg N Index also declined with distance from the buildings. Tissue N concentrations in trees, herbs and mosses were all large, reflecting the substantial ammonia emissions at this site. Tissue N content of ectohydric mosses ranged from approximately 4% at 30 m downwind to 1.6% at 650 m downwind. An assessment of the relative merits of the three marker variables concludes, that while Ellenberg Index and trace gas fluxes of N2O and NO give broad indications of impacts of ammonia emissions on woodland vegetation, the application of a critical foliar N content for ectohydric mosses is the most useful method for providing spatial information which could be of value to policy developers and planners.

Agriculture↗
PubMed1999

Oxygen and nitrogen are pro-carcinogens. Damage to DNA by reactive oxygen, chlorine and nitrogen species: measurement, mechanism and the effects of nutrition.

Humans are exposed to many carcinogens, but the most significant may be the reactive species derived from metabolism of oxygen and nitrogen. Nitric oxide seems unlikely to damage DNA directly, but nitrous acid produces deamination and peroxynitrite leads to both deamination and nitration. Scavenging of reactive nitrogen species generated in the stomach may be an important role of flavonoids, flavonoids and other plant-derived phenolic compounds. Different reactive oxygen species produce different patterns of damage to DNA bases, e.g., such patterns have been used to implicate hydroxyl radical as the ultimate agent in H(2)O(2)-induced DNA damage. Levels of steady-state DNA damage in vivo are consistent with the concept that such damage is a major contributor to the age-related development of cancer and so such damage can be used as a biomarker to study the effects of diet or dietary supplements on risk of cancer development, provided that reliable assays are available. Methodological questions addressed in this article include the validity of measuring 8-hydroxydeoxyguanosine (8OHdG) in cellular DNA or in urine as a biomarker of DNA damage, the extent of artifact formation during analysis of oxidative DNA damage by gas chromatography-mass spectrometry and the levels of oxidative damage in mitochondrial DNA.

Antioxidants↗
PubMed1988

Flavodoxin from Anabaena 7120: uniform nitrogen-15 enrichment and hydrogen-1, nitrogen-15, and phosphorus-31 NMR investigations of the flavin mononucleotide binding site in the reduced and oxidized states.

Interactions between flavin mononucleotide (FMN) and apoprotein have been investigated in the reduced and oxidized states of the flavodoxin isolated from Anabaena 7120 (Mr approximately 21,000). 1H, 15N, and 31P NMR have been used to characterize the FMN-protein interactions in both redox states. These are compared with those seen in other flavodoxins. Uniformly enriched [15N]flavodoxin (greater than 95% isotopic purity) was isolated from Anabaena 7120 grown on K15NO3 as the sole nitrogen source. 15N insensitive nucleus enhanced by polarization transfer (INEPT) and nuclear Overhauser effect (NOE) studies of this sample provided information regarding protein structure and dynamics. A 1H-detected 15N experiment allowed the correlation of nitrogen resonances to those of their attached protons. Over 90% of the expected N-H cross peaks could be resolved in this experiment.

Binding Sites↗
PubMed2004

Crystal structure of the C-terminal domain of the two-component system transmitter protein nitrogen regulator II (NRII; NtrB), regulator of nitrogen assimilation in Escherichia coli.

The kinase/phosphatase nitrogen regulator II (NRII, NtrB) is a member of the transmitter protein family of conserved two-component signal transduction systems. The kinase activity of NRII brings about the phosphorylation of the transcription factor nitrogen regulator I (NRI, NtrC), causing the activation of Ntr gene transcription. The phosphatase activity of NRII results in the inactivation of NRI-P. The activities of NRII are regulated by the signal transduction protein encoded by glnB, PII protein, which upon binding to NRII inhibits the kinase and activates the phosphatase activity. The C-terminal ATP-binding domain of NRII is required for both the kinase and phosphatase activities and contains the PII binding site. Here, we present the crystal structure of the C-terminal domain of a mutant form of NRII, NRII-Y302N, at 1.6 A resolution and compare this structure to the analogous domains of other two-component system transmitter proteins. While the C-terminal domain of NRII shares the general tertiary structure seen in CheA, PhoQ, and EnvZ transmitter proteins, it contains a distinct beta-hairpin projection that is absent in these related proteins. This projection is near the site of a well-characterized mutation that reduces the binding of PII and near other less-characterized mutations that affect the phosphatase activity of NRII. Sequence alignment suggests that the beta-hairpin projection is present in NRII proteins from various organisms, and absent in other transmitter proteins from Escherichia coliK-12. This unique structural element in the NRII C-terminal domain may play a role in binding PII or in intramolecular signal transduction.

Adenosine Triphosphate↗
PubMed2026

Natural variation in BRN1 enhances nitrogen sensitivity to improve rice nitrogen use efficiency.

Green Revolution rice varieties deliver high yields but require excessive nitrogen (N) fertilizer and show diminished N responsiveness, severely reducing nitrogen-use efficiency (NUE). To dissect the molecular basis of low N sensitivity in modern cultivars, we conducted a genome-wide association study (GWAS) for biomass response to N (BRN), a trait tightly linked to N sensitivity, using a diverse rice germplasm panel. We identified BRN1 as a key regulator of N-dependent biomass accumulation that regulates NLP3, a master transcription factor governing nitrate signaling. Under elevated N supply, the strigolactone signaling repressor D53 accumulates substantially and interacts with BRN1 to repress NLP3 transcription, thereby reducing rice N response. Notably, the high-response BRN1H allele encodes a more stable protein that alleviates D53-mediated suppression. Introgression of this allele into modern cultivars significantly enhanced N sensitivity and grain yield under both low and high N conditions. Our findings establish a D53-BRN1-NLP3 regulatory module controlling rice NUE, providing a target for rice breeding to sustain high productivity with improved resource sustainability.

Oryza↗
PubMed1991

Urinary excretion of nitrogenous and non-nitrogenous compounds in the chronic ethanol-fed rat.

1. The metabolic consequences of chronic ethanol feeding was investigated by assay of urinary metabolites. Male Wistar rats were fed a liquid diet containing 35% of total energy as ethanol or isovolumetric, isocaloric and isonitrogenous amounts of the same diet in which ethanol was substituted by isocaloric glucose (controls). 2. At 6 weeks the entire skeletal muscle mass was reduced by approximately 20%. The urinary excretion of nitrogen, urea and uric acid increased by between 23 and 128%. Urinary creatinine excretion was not significantly altered. 3. Urinary excretion of magnesium was significantly increased by 43%. Urinary excretion of sodium, potassium, calcium and phosphate was increased slightly (i.e. 5-22%), but this change was not statistically significant. 4. Proton n.m.r. spectroscopic analysis showed that ethanol feeding reduced the urinary excretion of citrate and 2-oxoglutarate (by approximately 50%), suggesting decreased citric acid cycle activity. There was an increased excretion of alanine (44%), but excretion of succinate and acetate was not significantly altered. Ethanol in the urine of ethanol-fed rats comprised approximately 2% of total ethanol intake and less than 1% of total energy intake. 5. Lactose was detectable in urine of ethanol-fed rats, but not in control rats, reflecting the reported decreased intestinal lactase activity and increased gut permeability in alcoholics. Urinary galactose excretion decreased by 41%, but relatively large increases in lactate excretion (50%) did not achieve statistical significance. 6. It was concluded that chronic ethanol feeding causes disturbances in whole-body nitrogen homoeostasis and alterations in intermediary metabolism.

Alanine↗
PubMed2002

Rumen fermentation and nitrogen balance of lambs fed diets containing plant extracts rich in tannins and saponins, and associated emissions of nitrogen and methane.

Tannins were added to experimental diets at levels of 1 and 2 g/kg DM (hydrolysable tannins; Castanea sativa wood extract) and saponins at 2 and 30 mg/kg DM (sarsaponin; Yucca schidigera extract). These levels were far below thresholds expected to be adverse in ruminants. Effects were measured in lambs by comparison with unsupplemented control diets calculated to be either deficient (10%) or adequate in protein. The diets consisted of hay, concentrate (1:1) and extra wheat starch with increasing body weight. Ruminal pH, VFA concentration, protozoa count and apparent digestibilities of organic matter and fibre did not differ among treatments. The low tannin dose significantly decreased bacteria count compared to the high saponin dose. Saponin supplementation and the high tannin dose showed some potential to reduce ruminal ammonia concentration. This was associated with weak trends towards lower urine N excretion (only tannins) and ammonia emission from manure. Methane release was increased by the low tannin dose compared to the unsupplemented control. Diet effects on heat production were not systematic. In conclusion, the extracts rich in tannins or saponins gave only slight indications for either increased body nitrogen retention or reduced nitrogen emission. However, effects might have been larger with more pronounced dietary protein deficit.

Animal Feed↗
PubMed1998

Linear model of nitrogen balance and examination of the nature of true metabolisable energy and its nitrogen corrected form.

1. The nature of nitrogen (N) corrected true metabolisable energy (TMEN) was derived using a linear model of N balance, constructed from the relationship between excreted and ingested N. 2. TME was described in terms of a regression line, formed from 'fed' points relating energy voided to energy ingested (GE), as GE - (afed + bGE) + afast. On assignment of theoretical excreta and ingested energy components, a deviation from conceptual metabolisable energy (MEc), equal to the difference between afed and afast, was established and attributed to metabolic urinary energy (UmE). 3. The N balance model is based on the form of relationship between N excreted and N ingested (NI) that exhibits a linear deviation at 'initial' rates of N ingestion. The model postulates the following: The deviation is the result of a sparing effect of ingested N on the N component of UmE, viz. metabolic urinary N (UmN); The magnitude of UmN, through 'initial' values of fed N, is described by an intercept component, aNp, and a slope quantity, -(bNr - bNna) NI, where bNna and bNr are respectively the slopes of N excretion through 'initial' and 'subsequent' rates of ingested food N; The magnitude of the deviation from zero nitrogen balance (ZNB) through 'initial' and 'subsequent' rates of ingested N is the sum of the previous terms and aNm - (1 - bNr) NI, where aNm is the intercept component representing maintenance losses of N at fasting and (1-bNr) NI is the quantity of fed N retained to replace maintenance N loss. 4. Application of the appropriate energetic forms of UmN and aNm, viz. Et aNp - Et (bNr - bNna) NI and EuaNm, to the expression for obtaining TME, demonstrated that TME exceeded MEc by the quantities Et (bNr - bNna) NI and Et aNp, for test food intakes resulting in 'initial' and 'subsequent' rates of food N, respectively. 5. Application of appropriate energetic components of the model to simulate correction of TME to ZNB, demonstrated TMEZNB to be a biased quantity, deviating from MEc by the amount -Eu (1 - bNr) NI or expressed as an excreta energy slope component, [formula: see text] where Eu is an appropriate energy coefficient. An alternative perspective is that ZNB correction removes the energetic form of UmN as a source of bias, but introduces one related to EuaNm. Its nature may be perceived by regarding TME as a function of a regression line relating energy excreted (EE) to energy ingested that has been corrected for UmN energetic bias and is pivoting on a fulcrum vertically aligned with the position of ZNB on the GE (x) axis. The regression line rotates anti-clockwise in response to ZNB correction by an amount equal to the magnitude of EuaNm measured on the EE (y) axis from the point of interception. 6. The study identified processes that may be employed to remove bias and improve precision of TME.

Animals↗
PubMedDate not supplied

The effects of different sources of nitrogen supplementation on the post ruminal flows of organic matter and different nitrogenous constituents in steers.

Friesian steers, virtually protozoa free, were equipped with simple rumen and abomasal cannulas. They were given diets consisting of approximately equal proportions of ground, pelleted alkali treated straw and a rolled barley, tapioca mixture supplemented with urea + casein (UC), soybean meal (SBM), 'normal' white fishmeal (NDF) or white fishmeal designated as being of 'low' rumen degradability (LDF). The diets were isoenergetic (the protein sources replacing part of the tapioca) and they were given in amounts to supply sufficient metabolizable energy (ME) to support an average growth rate of 0.5 kg/d. Rumen degradable nitrogen (RDN): ME values were estimated to be 2.08, 1.40, 1.90 and 1.66 for diets UC, SBM, NDF and LDF respectively. RNA, alpha-epsilon-diaminopimelic acid and 35S (added as sulphate) were used as bacterial markers. Chromic oxide and polyethylene glycol (PEG) were given as flow markers and flows (g/24 h) at the abomasum of organic matter (OM) and nitrogenous constituents were calculated. Rumen volumes and ruminal liquid fractional outflow rates were measured using PEG. Samples of mixed rumen bacteria separated from strained rumen digesta from animals receiving diet UC contained significantly less DAP-N (0.322 g/kg DM) than those from animals receiving diets SBM, NDF or LDF (0.530 g/kg DM). Mean rumen volume (approximately 15 l) and liquid fractional outflow rates (approximately 0.105/h) were similar on all diets but there was appreciable variation between animals. The proportion of OM intake digested in the rumen was similar on all diets. The proportional contribution of bacterial-N to the total non-ammonia-N passing the abomasum based on mean values derived from DAP and 35S as markers was 0.57, 0.47, 0.39 and 0.31 for diets UC, SBM, NDF and LDF respectively. Corresponding values based on RNA were 0.71, 0.50, 0.48 and 0.35 respectively. Bacterial-N (RNA) flows at the abomasum were 31, 25, 26 and 20 g/d for diets UC, SBM, NDF and LDF respectively. Corresponding values for 35S and DAP were 26, 24, 21 and 18 g/d respectively. Values derived from RNA flows were consistently and significantly higher (P less than 0.01) than those based on DAP or 35S. Mean estimated efficiencies of bacterial protein synthesis (g bacterial-N/kg OM truly digested) were 15, 15, 14 and 12 for diets UC, SBM, NDF and LDF respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Abomasum↗
PubMed1979

An analysis of temporal patterns in urinary nitrogen excretion of young adults receiving constant diets at two nitrogen intakes for 8 to 11 weeks.

The temporal pattern of daily urinary nitrogen (UN) excretion was investigated in 21 young adult men and women who participated in two metabolic studies involving constant diets and lasting 8 to 11 weeks. For one group (16 subjects), nitrogen (N) intake was about 280 mg N/kg per day (mixed animal and plant protein sources) for 8 weeks; for the second group (five subjects), N intake was about 90 mg N/kg per day (egg protein) for 11 weeks. Two mathematical models were examined to determine how well they described the variations in UN. The first modeled only random variability while the second added a component of serial correlation (correlation between successive daily observations). After correcting the UN data for linear trend, to minimize effects of possible alterations in body composition, only two of the 21 subjects showed significant serial correlation of daily UN. Moreover, it is shown that any serial correlation undetectable in these data would not be of practical importance in estimating UN levels in short-term dietary experiments. It is concluded that the interpretation of metabolic N balance measurements involving constant N intakes over relatively short dietary periods in not complicated by cyclic, time-dependent variations in UN.

Adolescent↗
PubMed2006

Transpiration, and nitrogen uptake and flow in two maize (Zea mays L.) inbred lines as affected by nitrogen supply.

BACKGROUND AND AIMS: The influence of two nitrogen (N) levels on growth, water relations, and N uptake and flow was investigated in two different inbred lines of maize (N-efficient Zi330 and N-inefficient Chen94-11) to analyse the differences in N uptake and cycling within a plant. METHODS: Xylem sap from different leaves of the inbred lines cultured in quartz sand was collected by application of pressure to the root system. Plant transpiration was measured on a daily basis by weighing five pots of each of the treatments. KEY RESULTS: N-efficient Zi330 had a higher relative growth rate and water-use efficiency at both high (4 mm) and low (0.08 mm) N levels. At a high N level, the amount of N taken up was similar for the two inbred lines; the amount of N transported in the xylem and retranslocated in the phloem was slight greater in Chen94-11 than in Zi330. At a low N level, however, the total amount of N taken up, transported in the xylem and retranslocated in the phloem of Zi330 was 2.2, 2.7 and 2.7 times more, respectively, than that of Chen94-11. Independent of inbred line and N level, the amounts of N transported in the xylem and cycled in the phloem were far more than that taken up by roots at the same time. Low N supply shifted NO(3)(-1) reduction towards the roots. The major nitrogenous compound in the xylem sap was NO(3)(-1), when plants grew at the high N level, while amino acid-N was predominant when plants grew at the low N level. CONCLUSIONS: The N-efficient maize inbred line Zi330 had a higher ability to take up N and cycle N within the plant than N-inefficient Chen94-11 when grown under N-deficiency.

Nitrogen↗
PubMed2007

Effect of nitrogen form and root-zone pH on growth and nitrogen uptake of tea (Camellia sinensis) plants.

BACKGROUND AND AIMS: Tea (Camellia sinensis) is considered to be acid tolerant and prefers ammonium nutrition, but the interaction between root zone acidity and N form is not properly understood. The present study was performed to characterize their interaction with respect to growth and mineral nutrition. METHODS: Tea plants were hydroponically cultured with NH4+, NO3- and NH(4+) + NO3-, at pH 4.0, 5.0 and 6.0, which were maintained by pH stat systems. KEY RESULTS: Plants supplied with NO3- showed yellowish leaves resembling nitrogen deficiency and grew much slower than those receiving NH4+ or NH(4+) + NO3- irrespective of root-zone pH. Absorption of NH4+ was 2- to 3.4-fold faster than NO3- when supplied separately, and 6- to 16-fold faster when supplied simultaneously. Nitrate-grown plants had significantly reduced glutamine synthetase activity, and lower concentrations of total N, free amino acids and glucose in the roots, but higher concentrations of cations and carboxylates (mainly oxalate) than those grown with NH4+ or NH(4+) + NO3-. Biomass production was largest at pH 5.0 regardless of N form, and was drastically reduced by a combination of high root-zone pH and NO3-. Low root-zone pH reduced root growth only in NO(3-)-fed plants. Absorption of N followed a similar pattern as root-zone pH changed, showing highest uptake rates at pH 5.0. The concentrations of total N, free amino acids, sugars and the activity of GS were generally not influenced by pH, whereas the concentrations of cations and carboxylates were generally increased with increasing root-zone pH. CONCLUSIONS: Tea plants are well-adapted to NH(4+)-rich environments by exhibiting a high capacity for NH4+ assimilation in their roots, reflected in strongly increased key enzyme activities and improved carbohydrate status. The poor plant growth with NO3- was largely associated with inefficient absorption of this N source. Decreased growth caused by inappropriate external pH corresponded well with the declining absorption of nitrogen.

Amino Acids↗
PubMed1985

Quantitative aspects of glycine and alanine nitrogen metabolism in postabsorptive young men: effects of level of nitrogen and dispensable amino acid intake.

The nutritionally indispensable amino acids (IAA) alone do not maintain body nitrogen (N) balance; a source of "nonspecific" nitrogen from dispensable amino acids (DAA), such as from glycine and alanine or other N compounds, is required. However, the in vivo regulation of the metabolism of these amino acids in humans with varying nutritional states has received little study. Hence, the effects of N intake and the IAA:DAA ratio on kinetic aspects of whole-body alanine and glycine metabolism were examined in eight healthy young adult male subjects. They received an L-amino acid diet supplying N equivalent to about 1.5 g and 0.6 g protein (N X 6.25) per kilogram body weight per day. All were studies at each N level with the IAA:DAA ratio (wt/wt) of 1:1 and 1:0, each for a 7-d diet period. Constant primed, intravenous infusions of L-[1-13C]leucine together with either L-[15N]alanine (four subjects) or [15N]glycine (four subjects) were given to each subject at the end of the diet period, after an overnight fast, to determine rates of de novo whole-body alanine and glycine N synthesis. The rate of alanine synthesis was similar (P greater than 0.05) for all four diets. Glycine de novo N synthesis declined (P less than 0.01) with removal of dietary DAA, especially at the lower intake, where the mean rates [micromoles/(kilogram X hour)] were 59 and 20 for 1:1 and 1:0 ratios, respectively. The possible significance of reduced rates of glycine N synthesis for maintenance of protein nutritional status in the healthy adult is discussed.

Adult↗