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PubMed1994

Poplar Bark Storage Protein and a Related Wound-Induced Gene Are Differentially Induced by Nitrogen.

Poplars (Populus deltoides Bartr. ex Marsh) accumulate a 32-kD bark storage protein (BSP) in phloem parenchyma and xylem ray cells during autumn and winter. Accumulation of poplar BSP is associated with short-day (SD) photoperiods. Poplar BSP shares sequence similarity with the product of the wound-inducible poplar gene win4. The influence of nitrogen availability and photoperiod on the levels of BSP, BSP mRNA, and win4 mRNA was investigated. In long-day (LD) plants BSP, BSP mRNA, and win4 mRNA levels were correlated with the amount of NH4NO3 provided to the plant. BSP mRNA and BSP were detected only in bark, whereas win4 mRNA was detected only in leaves. In LD plants treated with NH4NO3, BSP mRNA levels were significantly greater than those of win4. In nitrogen-deficient plants exposed to SD conditions, the accumulation of BSP mRNA and BSP was delayed for 2 weeks. This delay was eliminated by further SD exposure, and after 6 weeks of SD treatment similar levels of BSP and BSP mRNA were detected in the bark of SD plants regardless of the level of NH4NO3 treatment. win4 mRNA levels declined to undetectable levels in young leaves of SD plants but increased in mature leaves. These results indicate that BSP accumulation in both LD and SD plants is influenced by nitrogen availability. Although both BSP and win4 appear to be involved in nitrogen storage, our data suggest that BSP is probably the primary protein involved in both seasonal and short-term nitrogen storage in poplar. These results also suggest that nitrogen cycling and storage in poplar could involve a two-component system. In this system the win4 gene product may modulate accumulation and mobilization of leaf nitrogen, whereas BSP is involved in seasonal and short-term nitrogen storage during periods of excess nitrogen availability.

Journal Article↗
PubMed1970

Effect of Nitrogen Deficiency upon Translocation of C in Sugarcane.

Withholding nitrogen decreased the percentages of nitrogen and chlorophyll in the blades; reduced the total fixation of radioactive carbon dioxide at 15, 37, and 178 seconds; and changed the relative composition of fixation products. Translocation of radioactive photosynthate from the fed part down the attached blade and into the stalk was less in the plants deprived of nitrogen than in the control plants supplied with nitrogen. Both the percentage of total activity translocated and the velocity of transport were decreased by nitrogen deficiency. During a translocation period of 90 minutes the minus nitrogen blade retained more (14)C-sucrose than the control in the fed part and the blade below the fed part, but it sent less (14)C-sucrose to the sheath of the fed leaf. Thus translocation decreased with nitrogen deficiency not for lack of sucrose but for some other reason. Although withholding nitrogen decreased translocation of labeled carbon in and from attached blades, there was no effect upon transport in detached blades. The effect of nitrogen deficiency upon translocation may be indirect and secondary to the effect upon growth of the plant as a whole.

Journal Article↗
PubMed1982

Dark Stomatal Movement in Sunflowers in Response to Illumination under Nitrogen.

Experiments were performed on intact sunflowers (Helianthus annuus) placed in a specially designed experimental chamber which allows instantaneous modifications of the atmospheric composition without changing any other conditions. After one night in normal conditions, the plant was illuminated under pure nitrogen atmosphere; the opening stomatal movement, measured as a transpiration rate variation, was inhibited. After an anoxia time period not exceeding one hour, the light was turned off and normal air restored. The stomatal movement was no longer inhibited, and a transient increase in the transpiration rate, referred to here as the postillumination transpiration peak (PITP), was observed.The quantity of transpired water during the PITP can be related to the total incident light energy supplied during the light-nitrogen period. Furthermore, the addition of a dark-nitrogen period between the light-nitrogen and dark-air periods caused the PITP to decrease. The PITP is almost suppressed after a 20-minute dark-nitrogen period.It is shown that the PITP does not result from a hydropassive mechanism but is metabolically controlled. Moreover, it seems that the PITP is not due to a CO(2)-suppression effect during the light-nitrogen period.The results are interpreted in terms of stomatal mechanism. The metabolites leading to PITP originate from the reducing equivalents created during the light-nitrogen period. They could be synthesized at the beginning of the PITP period (darkness under normal air) or during the dark-nitrogen plus CO(2) period between the light-nitrogen and PITP periods. The results obtained are related to the first steps of classical photoactive stomatal opening.

Journal Article↗
PubMed1984

Carbohydrate Metabolism in Leaf Meristems of Tall Fescue : II. Relationship to Leaf Elongation Rates Modified by Nitrogen Fertilization.

Our objective was to examine alterations in carbohydrate status of leaf meristems that are associated with nitrogen-induced changes in leaf elongation rates of tall fescue (Festuca arundinacea Schreb.). Dark respiration rates, concentrations of nonstructural carbohydrates, and soluble proteins were measured in leaf intercalary meristems and adjacent segments of elongating leaves. The two genotypes used differed by 43% in leaf elongation rate. Application of high nitrogen (336 kilograms per hectare) resulted in 140% higher leaf elongation rate when compared to plants receiving low nitrogen (22 kilograms per hectare). Leaf meristems of plants receiving high and low nitrogen had dark respiration rates of 5.4 and 2.9 microliters O(2) consumed per milligram structural dry weight per hour, respectively. Concentrations of soluble proteins were lower while concentrations of fructan tended to be slightly higher in leaf meristems of low-nitrogen plants when compared to high-nitrogen plants. Concentrations of reducing sugars, nonreducing sugars, and takadiastase-soluble carbohydrate of leaf meristems were not affected by nitrogen treatment. Total nonstructural carbohydrates of leaf meristems averaged 44 and 39% of dry weight for low- and high-nitrogen plants, respectively. Within the leaf meristem, approximately 74 and 34% of the pool of total nonstructural carbohydrate could be consumed per day in high- and low-nitrogen plants, respectively, assuming no carbohydrate import to the meristem occurred. Plants were able to maintain high concentrations of nonstructural carbohydrates in leaf meristems despite a 3-fold range in leaf elongation rates, suggesting that carbohydrate synthesis and transport to leaf intercalary meristems may not limit leaf growth of these genotypes.

Journal Article↗
PubMed1986

Analysis of the Symbiotic Performance of Bradyrhizobium japonicum USDA 110 and Its Derivative I-110 and Discovery of a New Mannitol-Utilizing, Nitrogen-Fixing USDA 110 Derivative.

Previously, Bradyrhizobium japonicum USDA 110 was shown to contain colony morphology variants which differed in nitrogen-fixing ability. Mannitol-utilizing derivatives L1-110 and L2-110 have been shown to be devoid of symbiotic nitrogen fixation ability, and non-mannitol-utilizing derivatives I-110 and S-110 have been shown to be efficient at nitrogen fixation. The objectives of this study were to determine the effect of media carbon sources on the symbiotic N(2)-fixing ability of strain USDA 110 and to compare the effectiveness of strain USDA 110 and derivative I-110. Based on acetylene reduction activity and the nitrogen content of 41-day-old soybean plants, neither derivative I-110 nor cultures of USDA 110 grown in media favoring non-mannitol-using derivatives had symbiotic nitrogen fixation that was statistically superior to that of cultures of USDA 110 grown in media favoring mannitol-using derivatives. In another experiment 200 individual nodules formed by strain USDA 110 grown in yeast extract gluconate were screened for colony morphology of occupying variant(s) and acetylene reduction activity. Nodules occupied by mannitol-using derivatives (large colony type on 0.1% yeast extract-0.05% K(2)HPO(4)-0.08% MgSO(4) . 7H(2)O-0.02% NaCl-0.001% FeCl(3) . 6H(2)O [pH 6.7] with 1% mannitol [YEM] plates) had a mean acetylene reduction activity equal to that of nodules occupied by non-mannitol-using derivatives (small colony type on YEM plates). A total of 20 large colonial derivatives and 10 small colonial derivatives (I-110-like) were isolated and purified by repeated culture in YEM and YEG (same as YEM except 1% gluconate instead of 1% mannitol) media, respectively, followed by dilution in solutions containing 0.05% Tween 40. After 25 days of growth, soybean plants inoculated with the large colony isolates had mean whole-plant acetylene reduction activity, whole-plant dry weight, and whole-plant nitrogen contents equal to or better than those of plants inoculated with either the small colony isolates (I-110-like) or the I-110 (non-mannitol-using) derivative. Hence, the existence of a mannitol-utilizing derivative that fixes nitrogen in a culture of strain USDA 110 obtained from the U.S. Department of Agriculture, Beltsville, Md., was established. This new USDA 110 derivative was designated as MN-110 because it was a mannitol-utilizing nitrogen-fixing USDA 110 derivative. This derivative was morphologically indistinguishable from the non-nitrogen-fixing derivative L2-110 found in cultures obtained earlier from the U.S. Department of Agriculture, Beltsville. DNA-DNA homology and restriction enzyme analyses indicated that MN-110 is genetically related to other USDA 110 derivatives that have been characterized previously.

Journal Article↗
PubMed1994

Utilization of dissolved nitrogen by heterotrophic bacterioplankton: a comparison of three ecosystems.

The contributions of different organic and inorganic nitrogen and organic carbon sources to heterotrophic bacterioplankton in batch cultures of oceanic, estuarine, and eutrophic riverine environments were compared. The importance of the studied compounds was surprisingly similar among the three ecosystems. Dissolved combined amino acids (DCAA) were most significant, sustaining from 10 to 45% of the bacterial carbon demands and from 42 to 112% of the bacterial nitrogen demands. Dissolved free amino acids (DFAA) supplied 2 to 7% of the carbon and 6 to 24% of the nitrogen incorporated into the bacterial biomass, while dissolved DNA (D-DNA) sustained less than 5 and 12% of the carbon and nitrogen requirements, respectively. Ammonium was the second most important source of nitrogen, meeting from 13 to 45% of the bacterial demand in the oceanic and estuarine cultures and up to 270% of the demand in riverine cultures. Nitrate was taken up in the oceanic cultures (uptake equaled up to 46% of the nitrogen demand) but was released in the two others. Assimilation of DCAA, DFAA, and D-DNA combined supplied 43% of the carbon demand of the bacteria in the oceanic cultures, while approximately 25% of the carbon requirements were met by the three substrates at the two other sites. Assimilation of nitrogen from DCAA, DFAA, D-DNA, NH(4), and NO(3), on the other hand, exceeded production of particulate organic nitrogen in one culture at 27 h and in all cultures over the entire incubation period (50 h). These results suggest that the studied nutrient sources may fully support the nitrogen needs but only partially support the carbon needs of microbial communities of geographically different ecosystems. Furthermore, a comparison of the initial concentrations of the different substrates indicated that relative pool sizes of the substrates seemed to influence which substrates were primarily being utilized by the bacteria.

Journal Article↗
PubMed1987

Glutathione and related enzymes in rat brain tumor cell resistance to 1,3-bis(2-chloroethyl)-1-nitrosourea and nitrogen mustard.

Reduced glutathione (GSH) and activities of several glutathione-related enzymes were measured in two 9L rat brain tumor cell lines with differing sensitivities to both 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and nitrogen mustard. GSH, measured by a specific high-performance liquid chromatographic method, was found to be approximately twice as high in 9L cells sensitive to BCNU but resistant to nitrogen mustard. The nitrogen mustard resistant cell line was also found to have 2.5-fold more bulk glutathione transferase activity and approximately 3-fold more gamma-glutamyl transpeptidase activity. Glutathione reductase activity, protein thiol, and total protein content were similar in the two cell lines. Pretreatment of 9L cells with 50 microM buthionine sulfoximine for 24 h to deplete GSH only slightly potentiated BCNU cytotoxicity in a clonogenic assay whereas that of nitrogen mustard was markedly potentiated in both cell lines. Similarly, buthionine sulfoximine pretreatment had little effect on the induction of sister chromatid exchanges by BCNU, but significantly increased the number of sister chromatid exchanges induced by nitrogen mustard in both cell lines. Depleting GSH also had no significant effect on the cytotoxicity of 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea and 1-(2-chloroethyl)-3-(trans-4-methylcyclohexyl)-1-nitrosourea to 9L cells. Pretreatment of 9L cells with 1 mM GSH significantly protected against nitrogen mustard cytotoxicity. Moreover, nitrogen mustard incubated with GSH and glutathione transferase was 4-fold less cytotoxic than nitrogen mustard incubated with GSH alone. Incubation of BCNU with GSH alone or with glutathione transferase had no effect on BCNU cytotoxicity. These results indicate that elevated GSH and glutathione transferase activity is one mechanism of cellular resistance to nitrogen mustard in the 9L cell line, but it does not correlate with resistance to BCNU or other clinically important nitrosoureas.

Animals↗
PubMed1988

Nitrogen isotopic fractionation and 18O exchange in relation to the mechanism of denitrification of nitrite by Pseudomonas stutzeri.

Two types of mechanisms for the enzymatic reduction of NO2- to N2O have been proposed. In one, two NO2- ions are reduced in parallel, with the nitrogen-nitrogen bond formed from reduced intermediates. In the second, the two NO2- ions enter the reaction sequentially, with the nitrogen of at least one of the two having a valence of 3+ when the nitrogen-nitrogen bond is formed. Our objective was to distinguish between these two types of mechanism. Toward that end, the exchange of 18O from H2O to NO2- and the overall nitrogen isotopic fractionation factor (beta obs) were measured. The rate of exchange of oxygen from H2O to NO2-, resulting from a protonation-dehydration step preceding reductive events in both mechanisms, was less than 10% of the rate of denitrification at both low and high [NO2-]. The value of beta obs was 1.010 +/- 0.001 and 1.020 +/- 0.001 at low and high [NO2-], respectively. Expressions for beta obs, as a function of the measured rate of entry of oxygen from H2O into NO2-, were derived for both types of mechanism. The measured dependence of beta obs on substrate concentration, as constrained by the 18O exchange data, is inconsistent with the first type of mechanism, but consistent with the second type. Thus, by combining nitrogen isotopic fractionation and 18O exchange data, we rule out any mechanism in Pseudomonas stutzeri in which NO2- ions are reduced in parallel, with the nitrogen-nitrogen bond being formed from reduced intermediates.

Mathematics↗
PubMed1997

Comparison of nitrogen mustard, cytarabine and dacarbazine as pleural sclerosing agents in rabbits.

We have previously shown that the intrapleural injection of mitozantrone but not bleomycin resulted in pleural fibrosis. Mechlorethamine hydrochloride (nitrogen mustard) was used extensively in the past to control malignant effusions, with relatively good success. The objective of this study was to determine if the intrapleural injection of nitrogen mustard would produce pleural sclerosis in our experimental model in rabbits. We therefore evaluated sclerosing capabilities of nitrogen mustard as well as those of cytarabine and dacarbazine. Nitrogen mustard (0.4 and 0.8 mg x kg(-1)), cytarabine (3, 6 and 20 mg x kg(-1)) and dacarbazine (4, 8 and 20 mg x kg(-1)) were instilled intrapleurally into anaesthetized rabbits. Twenty eight days after the instillation, the animals were killed, and the pleural spaces were assessed grossly for evidence of pleurodesis and microscopically for evidence of fibrosis and inflammation. The intrapleural injection of 0.8 mg x kg(-1) nitrogen mustard was effective in creating pleural fibrosis, either grossly or microscopically. The mean degree (scale 0-4) of gross pleurodesis in the rabbits that received 0.8 mg x kg(-1) nitrogen mustard was 3.2+/-1.0 and the mean degree of microscopic pleural fibrosis was 3.5+/-0.8. The intrapleural injection of 0.4 mg x kg(-1) nitrogen mustard and the different doses of cytarabine (3, 6 and 20 mg x kg(-1)) and dacarbazine (4, 8 and 20 mg x kg(-1)) were ineffective in producing pleurodesis. From this study, we conclude that the intrapleural injection of 0.8 mg x kg(-1) of nitrogen mustard produces clinically significant pleurodesis in rabbits. Consideration should be given to future clinical studies utilizing 0.6-0.8 mg x kg(-1) nitrogen mustard intrapleurally for the treatment of malignant pleural effusion.

Animals↗
PubMedDate not supplied

[Effect of nitrogen source on growth of Arthrobacter simplex and its biosynthesis of cholinesterase].

The effect of organic and inorganic forms of nitrogen on biomass accumulation and cholinesterase synthesis was studied with Arthrobacter simplex var. cholinesterasus. The culture assimilates nitrogen of ammonium compounds better than other forms of inorganic nitrogen; the best nitrogen source for biosynthesis of cholinesterase is ammonium phosphate. Nitrogen of nitrates is not assimilated. The amount of biomass is almost twice as high on the medium with peptone, casein or casein hydrolysate as on the medium with mineral nitrogen, while the activity of cholinesterase on these nitrogen sources decreases 1.5--2.0 times. Yeast extract as a nitrogen source increases biomass accumulation by a factor of 2.5 and does not supress synthesis of cholinesterase. The concentration of the enzyme synthesized per unit biomass on the medium with yeast extract is the same as on the medium containing ammonium phosphate. The effect of amino acids and amides, i.e. beta-alanine, proline, amides of aspartic and glutamic acids, and their mixtures, is similar to the action of yeast extract: they stimulate biomass accumulation and do not inhibit synthesis of the enzyme. Other amino acids supress synthesis of cholinesterase. The amount of accumulated biomass in the presence of glutamic acid is twice as high as in the case of any other amino acid, and three times as high as on the medium containing ammonium phosphate. Similar action of glutamic acid is manifested when it is used in mixtures with other amino acids. On the medium containing glutamic acid as a sole source of nitrogen, an increase in biomass production is accompanied with a decrease in biosynthesis of the enzyme by 50%. Repression of the biosynthesis is less if glutamic acid is added in mixtures with proline, beta-alanine and asparagine.

Arthrobacter↗
PubMed1986

[The effect of cellulose on endogenous nitrogen excretion in rats, evaluated using N-15 technics].

Metabolic faecal nitrogen excretion was assessed in 8 young rats (90-100 g body weight) following an oral application of 75 mg 15N-glycine (95 atom-% 15N). Four rats received an experimental diet containing 12% cellulose, while a control diet containing 4% cellulose was fed to the remaining 4 animals. The high cellulose content induced a highly significant reduction of the N balance due to a greatly increased urinary N excretion. The metabolic faecal nitrogen was determined by measuring 15N excretion in faeces and urine from day 5 (3) to day 8 following 15N glycine administration. During this time interval 15N elimination follows an exponential curve. Increasing the dietary cellulose content from 4 to 12% produced a rise in metabolic faecal nitrogen from 13.9 to 15.7 mg/day and in total faecal nitrogen from 21.3 to 24.4 mg/day. From these values a mean true protein digestibility of 98% was calculated for both groups of rats, regardless of the difference in dietary cellulose content. The fraction of endogenous faecal nitrogen which is of bacterial origin was determined through the analysis of 2, 6-diamino-pimelic acid (DAP). The added cellulose in the experimental diet caused a rise in faecal DAP from 0.302 to 0.402 mg/day corresponding to an increase of bacterial nitrogen from 5.2 to 6.4 mg/day. Accordingly the observed rise in endogenous faecal nitrogen is largely due to increased bacterial nitrogen.

Animals↗
PubMed1997

Amino acid losses and nitrogen balance during slow diurnal hemodialysis in critically ill patients with renal failure.

OBJECTIVE: The effects of slow diurnal hemodialysis (slow HD) on amino acid losses and nitrogen balance were studied. DESIGN: Slow HD was conducted for 10 h during the day at the dialysate flow rate of 30 ml/min. The patients received total parenteral nutrition including 40 g of amino acids (6.08 g of nitrogen). The amino acid concentrations in plasma and dialysate were determined and the daily nitrogen balance was calculated from the urea nitrogen appearance. PATIENTS: Six critically ill patients with renal failure were entered into the study. RESULTS: Slow HD eliminated 48.5 +/- 4.4 mmol (6.2 +/- 0.6 g) of amino acids, representing 16% of the daily amino acid load. The estimated nitrogen balance was -2.3 +/- 1.3 g/day. Amino acid nitrogen lost in the dialysate was 1.0 +/- 0.1 g, contributing 43% of the daily negative nitrogen balance. CONCLUSION: The amount of amino acid losses during slow HD should be taken into consideration when designing nutritional schedules for maintaining positive nitrogen balance in critically ill patients.

Aged↗
PubMed2005

Off-season uptake of nitrogen in temperate heath vegetation.

In this field study we show that temperate coastal heath vegetation has a significant off-season uptake potential for nitrogen, both in the form of ammonium and as glycine, throughout winter. We injected 15N-ammonium and 15N 2x(13C)-glycine into the soil twice during winter and once at spring. The winter temperatures were similar to those of an average winter in the northern temperate region of Europe, with only few days of soil temperatures below zero or above 5 degrees C. The vegetation, consisting of the evergreen dwarf shrub Calluna vulgaris, the deciduous dwarf shrub Salix arenaria, and the graminoids Carex arenaria and Deschampsia flexuosa, showed high root uptake of both forms of nitrogen, both 1 day after labelling and after a month, in species specific temporal patterns. Plant uptake of 13C was not significant, providing no further evidence of intact uptake of glycine. Translocation of the labelled nitrogen to shoots was generally evident after 1 month and increased as spring approached, with different translocation strategies in the three plant functional types. Furthermore, only the graminoids showed shoot growth during winter. Increasing plant nitrogen concentration from fall to spring at temperate heaths may, hence, be due to nitrogen uptake. Our results suggest that the potential for nitrogen uptake in plants at winter is of the same order of magnitude as at summer. Hence, winter nitrogen uptake in ecosystems in the temperate/boreal region should be considered when making annual nitrogen budgets of heath ecosystems, and the view of plant nutrient uptake as low in this climatic region during winter should be revised.

Biological Transport, Active↗
PubMed1989

Biological nitrogen fixation under primordial Martian partial pressures of dinitrogen.

Early Earth and early Mars were similar enough such that past geochemical and climatic conditions on Mars may have also been favorable for the origin of life. However, one of the most striking differences between the two planets was the low partial pressure of dinitrogen (pN2) on early Mars (18 mb). On Earth, nitrogen is a key biological element and in many ecosystems the low availability of fixed nitrogen compounds is the main factor limiting growth. Biological fixation of dinitrogen on Earth is a crucial source of fixed nitrogen. Could the low availability of dinitrogen in the primordial Martian atmosphere have prevented the existence, or evolution of Martian microbiota? Azotobacter vinelandii and Azomonas agilis were grown in nitrogen free synthetic medium under various partial pressures of dinitrogen ranging from 780-0 mb (total atmosphere=1 bar). Below 400 mb the biomass, cell number, and growth rate decreased with decreasing pN2. Both microorganisms were capable of growth at a pN2 as low as 5 mb, but no growth was observed at a pN2 < or = 1 mb. The data appear to indicate that biological nitrogen fixation could have occurred on primordial Mars (pN2=18 mb) making it possible for a biotic system to have played a role in the Martian nitrogen cycle. It is possible that nitrogen may have played a key role in the early evolution of life on Mars, and that later a lack of available nitrogen on that planet (currently, pN2=0.2 mb) may have been involved in its subsequent extinction.

Atmosphere↗
PubMed1986

Effect of energy intake on nitrogen metabolism in nondialyzed patients with chronic renal failure.

Dietary energy requirements were evaluated during 16 studies that were carried out in six clinically stable nondialyzed chronically uremic patients who lived in a clinical research center and were fed diets providing 45, 35, 25 or 15 kcal/kg/day. Each diet was fed for 23.7 +/- 5.7 SD days and provided about 0.55 to 0.60 g protein/kg/day. Nitrogen balance after equilibration and adjusted for changes in body urea nitrogen, and change in body weight each correlated directly with energy intake. Correcting for estimated unmeasured nitrogen losses of about 0.58 g/day, nitrogen balance was negative in one of four patients fed 45 kcal/kg/day, one of five patients receiving 35 kcal/kg/day, three of five patients ingesting 25 kcal/kg/day and both patients fed 15 kcal/kg/day. The urea nitrogen appearance (UNA), the UNA divided by nitrogen intake, and several plasma amino acids, determined after an overnight fast, each correlated inversely with dietary energy intake. Resting energy expenditure measured by indirect calorimetry did not differ from normal and averaged 0.012 +/- 0.0033 kcal/kg/min with the different diets. These observations suggest that although some clinically stable nondialyzed chronically uremic patients ingesting 0.55 to 0.60 g protein/kg/day may maintain nitrogen balance with energy intakes below 30 kcal/kg/day, a dietary intake providing approximately 35 kcal/kg/day may be more likely to maintain neutral or positive nitrogen balance, maintain or increase body mass, and reduce net urea generation.

Amino Acids↗
PubMed2004

Using the natural 15N abundance to assess the main nitrogen inputs into the sand dune area of the north-western Negev Desert (Israel).

The variation of the natural 15N abundance is often used to evaluate the origin of nitrogen or the pathways of N input into ecosystems. We tried to use this approach to assess the main input pathways of nitrogen into the sand dune area of the north-western Negev Desert (Israel). The following two pathways are the main sources for nitrogen input into the system: i. Biological fixation of atmospheric nitrogen by cyanobacteria present in biological crusts and by N2-fixing vascular plants (e.g. the shrub Retama raetam); ii. Atmospheric input of nitrogen by wet deposition with rainfall, dry deposition of dust containing N compounds, and gaseous deposition. Samples were taken from selected environmental compartments such as biological crusts, sand underneath these crusts (down to a depth of 90 cm), N2-fixing and non-N2-fixing plants, atmospheric bulk deposition as well as soil from arable land north of the sandy area in three field campaigns in March 1998, 1999 and 2000. The delta15N values measured were in the following ranges: grass -2.5/1000 to +1.5/1000; R. reatam: +0.5/1000 to +4.5/1000; non-N2-fixing shrubs +1/1000 to +7/1000; sand beneath the biological crusts +4/1000 to +20/1000 (soil depth 2-90 cm); and arable land to the north up to 10/1000. Thus, the natural 15N abundance of the different N pools varies significantly. Accordingly, it should be feasible to assess different input pathways from the various 15N abundances of nitrogen. For example, the biological N fixation rates of the Fabaceae shrub R. reatam from the 15N abundances measured were calculated to be 46-86% of biomass N derived from the atmosphere. The biological crusts themselves generally show slight negative 15N values (-3/1000 to -0.5/1000), which can be explained by biological N fixation. However, areas with a high share of lichens, which are unable to fix atmospheric nitrogen, show very negative values down to -10/1000. The atmospheric N bulk deposition, which amounts to 1.9-3.8 kg N/hayr, has a 15N abundance between 4.4/1000 and 11.6/1000 and is likely to be caused by dust from the arable land to the north. Thus, it cannot be responsible for the very negative values of lichens measured either. There must be an additional N input from the atmosphere with negative delta15N values, e.g. gaseous N forms (NOx, NH3). To explain these conflicting findings, detailed information is still needed on the wet, particulate and gaseous atmospheric deposition of nitrogen.

Desert Climate↗
PubMed1999

Genetics of nitrogen regulation in Methanococcus maripaludis.

We have used genetic methods in Methanococcus maripaludis to study nitrogen metabolism and its regulation. We present evidence for a "nitrogen regulon" in Methanococcus and Methanobacterium species containing genes of nitrogen metabolism that are regulated coordinately at the transcriptional level via a common repressor binding site sequence, or operator. The implied mechanism for regulation resembles the general bacterial paradigm for repression, but contrasts with well-known mechanisms of nitrogen regulation in bacteria, which occur by activation. Genes in the nitrogen regulons include those for nitrogen fixation, glutamine synthetase, (methyl)ammonia transport, the regulatory protein GlnB, and ammonia-dependent NAD synthetase, as well as a gene of unknown function. We also studied the function of two novel GlnB homologues that are encoded within the nif gene cluster of diazotrophic methanogens. The phenotype resulting from a glnB null mutation in M. maripaludis provides direct evidence that glnB-like genes are involved in "ammonia switch-off," the post-transcriptional inhibition of nitrogen fixation upon addition of ammonia. Finally, we show that the gene nifX is not required for nitrogen fixation, in agreement with findings in several bacteria. These studies illustrate the utility of genetic methods in M. maripaludis and show the enhanced perspective that studies in the Archaea can bring to known biological systems.

Amino Acid Sequence↗
PubMed2002

Regulatory response of Methanococcus maripaludis to alanine, an intermediate nitrogen source.

In the methanogenic archaeon Methanococcus maripaludis, growth with ammonia results in conditions of nitrogen excess. Complete repression of nitrogen fixation (nif) gene transcription occurs, and glutamine synthetase (glnA) gene transcription falls to a basal constitutive level. In addition, ammonia completely switches off nitrogenase enzyme activity. In contrast, growth with dinitrogen as the sole nitrogen source results in nitrogen starvation, full expression of nif and glnA, and high activity of nitrogenase. Here we report that a third nitrogen source, alanine, results in an intermediate regulatory response. Growth with alanine resulted in intermediate transcription of nif and glnA, and addition of alanine to a nitrogen-fixing (diazotrophic) culture caused partial switch-off of nitrogenase. This uniformity of response occurred despite differences in regulatory mechanisms. Nitrogenase switch-off requires the nitrogen sensor homologs NifI(1) and NifI(2), while transcriptional regulation of nif and glnA relies on a different, unknown sensor mechanism. In addition, although nif and glnA transcription are governed by a common repressor, the numbers and arrangements of repressor binding sites differ. Thus, the nif promoter region contains two operators situated downstream of the transcription start site, while the glnA promoter region contains only one operator just upstream of two closely spaced transcription start sites. In a previous study of nif expression using ammonia, we were able to detect a role only for the first nif operator in repression. Here we show that nif repression by alanine requires the second operator as well. In contrast, in the case of glnA the single operator was sufficient for repression by ammonia or alanine. These results suggest a uniform cellular response to nitrogen that is mediated by a different mechanism in each case.

Alanine↗