Inhibition Of NO3 Research Articles

Uncovering the Differential Growth of Microcystis aeruginosa Cultivated under Nitrate and Ammonium from a Photophysiological Perspective

Cyanobacteria have a relatively high affinity for NH4+, yet a NO3–-rich environment is comparatively conducive to their proliferation. To date, little information is available on why NO3–-N favors cyanobacterial biomass accumulation. This study investigated the dependence of biomass, nitrogen assimilation characteristics, and photophysiological performance of Microcystis aeruginosa on the forms of nitrogen supply, including NO3–-N-only, NH4+-N-only, and NO3–-N + NH4+-N. The results indicated that despite the retarded growth of M. aeruginosa, cells supplied with NO3–-N-only maintained a simultaneous promotion in the growth rate, nitrogen assimilation efficiency, and photosynthetic capacity, resulting in high biomass production. Cells supplied with NH4+-N-only and NO3–-N + NH4+-N were able to rapidly assimilate nitrogen during initial cell proliferation, showing a preferential use of NH4+-N and the inhibition of NO3– uptake by NH4+. However, growth repression occurred as cultivation time was prolonged when NH4+-N was excessively supplied, mainly due to PSII photodamage, intracellular redox imbalance, and increased electron energy accumulation. Thus, cells supplied with NH4+-N-only had to reduce light energy capture, increase photoprotection, and consume excess electrons to mitigate the damage. These findings are critical for improving our understanding of the role of different nitrogen forms in the regulation of cyanobacterial photophysiological performance and growth.

Elevated Carbon Dioxide and Chronic Warming Together Decrease Nitrogen Uptake Rate, Net Translocation, and Assimilation in Tomato.

The response of plant N relations to the combination of elevated CO2 (eCO2) and warming are poorly understood. To study this, tomato (Solanum lycopersicum) plants were grown at 400 or 700 ppm CO2 and 33/28 or 38/33 °C (day/night), and their soil was labeled with 15NO3− or 15NH4+. Plant dry mass, root N-uptake rate, root-to-shoot net N translocation, whole-plant N assimilation, and root resource availability (%C, %N, total nonstructural carbohydrates) were measured. Relative to eCO2 or warming alone, eCO2 + warming decreased growth, NO3− and NH4+-uptake rates, root-to-shoot net N translocation, and whole-plant N assimilation. Decreased N assimilation with eCO2 + warming was driven mostly by inhibition of NO3− assimilation, and was not associated with root resource limitations or damage to N-assimilatory proteins. Previously, we showed in tomato that eCO2 + warming decreases the concentration of N-uptake and -assimilatory proteins in roots, and dramatically increases leaf angle, which decreases whole-plant light capture and, hence, photosynthesis and growth. Thus, decreases in N uptake and assimilation with eCO2 + warming in tomato are likely due to reduced plant N demand.

Effect of Silver Nanoparticles on Denitrification and Functional Gene Abundances of Sediment in Dagu River Estuary and Northwest of Jiaozhou Bay

The influence of silver nanoparticles (AgNPs) on the denitrification performance, enzyme activity, and functional gene relative abundances of sediment was investigated based on the methods of laboratory simulation incubation in the Dagu River estuary and bay area in the northwest of Jiaozhou Bay. The different dosages of AgNPs (i.e., 0, 135, and 1350 mg·L-1 in final concentration) was added to the incubation system containing surface sediments and in-situ bottom water. During six days' incubation, the concentrations of NO3- and NO2-, NO3-, and NO2- reductases activity, and relative abundances of narG and nirS genes were measured to explore the effects of AgNPs on denitrification and its mechanism. The results showed that AgNPs significantly inhibited NO3- and NO2- reductive capacity, NO3- and NO2- reductase activity, and narG and nirS gene relative abundances, which led to aggravated accumulation of NO2-. The inhibition of NO2- reductase was significantly greater than that of NO3- reductase, and the inhibition of the nirS gene was significantly higher than that of the narG gene. The inhibition of NO3- reduction was mainly ascribed to the inhibition of functional genes, but the inhibition of NO2- reduction was mainly due to the inhibition of reductase activity. The inhibition of NO3- and NO2- reductive capacity, NO3- reductase activity, and narG and nirS gene relative abundances in the northwest of Jiaozhou Bay was significantly higher than that in the Dagu River estuary.

Aluminium-inhibited NO3- uptake is related to Al-increased H2O2 content and Al-decreased plasma membrane ATPase activity in the root tips of Al-sensitive black soybean.

In this study, Al-sensitive black soybean (Glycine max (L.) Merr.) specimens were treated in Hoagland solutions containing 50-400µM Al for 1-4 days. The measurement for NO3- uptake showed that the NO3- uptake decreased gradually as the Al concentration and treatment time increased, suggesting that Al stress significantly reduced the NO3- uptake by soybean. Under 100-µM Al stress for 4 days, the plasma membrane (PM) ATPase activity (inorganic phosphate (Pi) release), H+ pump activity, phosphorylation of PM ATPase and its interaction with 14-3-3 protein in soybean root tips were all smaller than those in the root tips of control plants. The addition of 150µM Mg2+ in Al treatment solutions significantly alleviated the Al inhibition of NO3- uptake in soybean. The presence of Mg2+ in a 100-µM Al solution pronouncedly enhanced PM ATPase activity, H+ pump activity, phosphorylation of PM ATPase and its interaction with 14-3-3 protein in soybean root tips. The application of 2mM ascorbic acid (AsA, an H2O2 scavenger) in Al treatment solutions significantly decreased Al-inhibited NO3- uptake in soybean. The cotreatment of soybeans with 2mM AsA and 100µM Al significantly reduced H2O2 accumulation and increased the PM ATPase activity, H+ pump activity, phosphorylation of PM H+-ATPase and its interaction with 14-3-3 protein in soybean root tips. The evidence suggested that Al-inhibited NO3- uptake is related to Al-increased H2O2 content and Al-decreased phosphorylation of PM ATPase and its interaction with 14-3-3 protein as well as PM ATPase activity in the root tips of soybean.

Acute dietary nitrate consumption improves glucose tolerance

Insulin resistance is characterized by low nitric oxide (NO) bioavailability. Consistent with this observation, insulin sensitivity is improved with stimulation of NO generating pathways. Consumption of dietary nitrate (e.g. beet juice) has been purported to increase NO formation, mediated in part through the reduction of nitrate (NO3−) to nitrite (NO2−) by oral bacteria, and subsequent NO2− reduction to NO in blood. We hypothesized that acute dietary nitrate consumption would improve glucose tolerance. Accordingly, in 8 sedentary adults (23 ± 0 years, body mass index: 26.0 ± 0.8 kg/m2 (mean ± SE)) we determined the blood glucose response to oral consumption of 500 ml organic beet juice, supplemented with 25 g of sucrose (estimated carbohydrate load ~ 75g), with and without prior use of an antibacterial mouthwash to inhibit NO3− reduction to NO2−. In the absence of inhibition of oral bacteria NO3− reductase activity, peak blood glucose concentration (106 ± 4 vs. 118 ± 6 mg/dL; P = 0.04) and the area under the blood glucose response curve (93 ± 4%; P = 0.07) were decreased. These preliminary data suggest dietary nitrate consumption may promote glucose tolerance, and this effect may be attenuated following inhibition of NO3− conversion to NO2−.Support: America Diabetes Association 1‐09‐RA‐09

Effect of ammonium on nitrate utilization by Emiliania huxleyi, a coccolithophore from the oceanic northeastern Pacific

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 186:67-74 (1999) - doi:10.3354/meps186067 Effect of ammonium on nitrate utilization by Emiliania huxleyi, a coccolithophore from the oceanic northeastern Pacific Diana E. Varela*, Paul J. Harrison Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada *E-mail: varela@unixg.ubc.ca ABSTRACT: Explanations for the high nitrate (NO3-), low phytoplankton biomass of the subarctic NE Pacific have mainly centered on iron limitation and grazing pressure. Although ammonium (NH4+) has been proven to inhibit NO3- uptake by phytoplankton in numerous laboratory and field studies, this hypothesis has not been experimentally tested for the subarctic Pacific. The effect of increasing NH4+ concentrations on NO3- uptake by Emiliania huxleyi, a coccolithophore isolated from Ocean Station Papa in the subarctic NE Pacific, is examined. The effect of diel periodicity on NO3- uptake and other physiological parameters for E. huxleyi during a 14:10 h light:dark cycle are also reported. About 84% of the total daily NO3- was taken up during the light period. Cell division occurred only during the last part of the dark period. Chlorophyll a, nitrogen, and carbon quotas and cell volume increased during the light period and decreased during the dark. The presence of NH4+ inhibited NO3- uptake in E. huxleyi. Nitrate uptake rates were reduced to half the maximum value at 0.24 µM NH4+, and maximum realized inhibition was ~100% at 2.2 µM NH4+. If this laboratory result is extrapolated to field conditions, the inhibition of NO3- uptake rates for the small size class of phytoplankton would be predicted to be 38 to 70% for the range of ambient NH4+ concentrations found in the oceanic NE Pacific. KEY WORDS: Nitrate uptake · Ammonium inhibition · Diel periodicity · Emiliania huxleyi · Ocean station Papa · northeastern Pacific · HNLC Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 186. Publication date: September 17, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

Nitric oxide production in experimental gram-negative infection: studies with cytokine receptor-deficient mice.

Overproduction of nitric oxide (NO) upon expression of inducible NO synthase (iNOS) may be responsible for refractory hypotension in septic shock. Whereas high levels of NOS activity have been documented in experimental models of endotoxemia or intravenous challenge with Escherichia coil, much less is known concerning tissue models of Gram-negative infection. We examined NO production (measured as the accumulation of plasma NO3- + NO2-) in a murine model of Gram-negative peritonitis. Plasma NO3- + NO2- increased progressively from 25 microM to peak levels of 50-150 microM 24 h after intraperitoneal challenge with E. coli 0111:B4, similar to values reported for septic shock patients. Treatment of infected mice with NG-monomethyl-L-arginine, an inhibitor of NOS activity, resulted in the efficient inhibition of NO3- + NO2- production. In order to evaluate the roles of interferon-gamma (IFN-gamma) and tumor necrosis factor (TNF-alpha) in the induction of NO synthesis in murine peritonitis, mice deficient in the respective cytokine receptors were studied. In control in vitro experiments, macrophages from IFN-gammaR- or TNFR55-deficient mice, while failing to respond to IFN-gamma or TNF-alpha, respectively, produced high levels of NO under appropriate stimulation. When challenged intraperitoneally with E. coli, IFN-gammaR- or TNFR55-deficient mice exhibited similar levels of bacteremia and NO production as their wild-type controls. These data thus suggest that enhanced NO production during focal Gram-negative infection may occur in the absence of signaling through either IFN-gammaR or TNFR55.

Effects of genetic modification of nitrate reductase expression on 15NO3- uptake and reduction in Nicotiana plants

The physiological consequences for NO3– utilization by the plant of underexpression and overexpression of nitrate reductase (NR) were investigated in nine transformants of Nicotiana tabacum and Nicotiana plumbaginifolia. The in vitro NR activities (NRAs) in both roots and leaves of low- and high-NR tobacco transformants ranged from 5–10% to 150–200%, respectively, of those measured in wild-type plants. The level of NR expression markedly affected the NO3– reduction efficiency in detached leaves and intact plants. In both species, 15NO3– reduction ranged from 15–45% of 15NO3– uptake in the low-NR plants, to 40–80% in the wild-type, and up to 95% in high-NR plants. In the high-NR genotypes, however, total 15NO3– assimilation was not significantly increased when compared with that in wild-type plants, because the higher 15NO3– reduction efficiency was offset by lower 15NO3– uptake by the roots. The inhibition of NO3– uptake appeared to be the result of negative feedback regulation of NO3– influx, and is interpreted as an adjustment of NO3– uptake to prevent excessive amino acid synthesis. In genotypes underexpressing NR, the low 15NO3– reduction efficiency also was generally associated with a decrease in net 15NO3– uptake as compared with the wild type. Thus, underexpression of NR resulted in an inhibition of reduced 15N synthesis in the plant, although the effect was much less pronounced than that expected from the very low NRAs. The restricted NO3– uptake in low-NR plants emphasizes the point that the products of NO3– assimilation are not the only factors responsible for down-regulation of the NO3– uptake system.

Kinetics of nitrate uptake by Citrus seedlings and inhibitory effects of salinity

Nitrate absorption by roots of both Troyer citrange (hybrid of Citrus sinensis×Poncirustrifoliata) and Cleopatra mandarin (C.reshni) seedlings was studied. The ion depletion in the external nutrient solutions was used to estimate NO3− net uptake. In both rootstocks the kinetics of nitrate uptake showed a biphasic pattern in response to increasing external NO3− concentrations up to 10 mol m−3. The low concentration transport system followed Michaelis-Menten kinetics reaching saturation at 0.5 mol m−3 NO3− in both rootstocks. The apparent Kms of nitrate uptake were 282 and 281 mmol m−3 respectively, for Troyer citrange and Cleopatra mandarin. A linear system was also found at higher external NO3− concentrations (between 1–10 mol m−3). Double reciprocal plots showed that Cl− inhibited NO3− uptake competitively in the low concentration system. In contrast, the high concentration system was insensitive to external Cl−, but was inhibited when plants were pretreated with salt solutions. Net NO3− uptake in both systems was severely affected by Cl− ions more in Troyer citrange than in Cleopatra mandarin. Since Cl− accumulation in tissues was higher in Troyer citrange than in Cleopatra mandarin, a relationship between the ability to absorb Cl− and the inhibition of NO3− uptake is suggested for these plants.

Responses of soybean to ammonium and nitrate supplied in combination to the whole root system or separately in a split‐root system

To address the questions of whether allocation of carbohydrates to roots is influenced by ionic form of nitrogen absorbed and whether allocation of carbohydrates to roots in turn influences proportionality between NH4+ and NO3- uptake from mixed sources, NH4+ and NO3- were supplied separately to halves of a split-root hydroponic system and were supplied in combination to a whole-root system. Dry matter accumulation in the split-root system was 18% less in the NH4(+)-fed axis than in the NO3(-)-fed axis. This, however, does not indicate that partitioning of carbohydrate between the two axes was different. Most of the reduction in dry matter accumulation in the NH4(+)-fed axis can be accounted for by the retransport of CH2O equivalents from the root back to the shoot with amino acids produced by NH4+ assimilation. Uptake of NH4+ or NO3- by the respective halves of the split-root system was proportional to the estimated allocation of carbohydrate to that half. When NH4+ and NO3- were supplied to separate halves of the split-root system, the cumulative NH4+ to NO3- uptake ratio was 0.81. When supplied in combination to the whole-root system, the cumulative NH4+ to NO3- uptake ratio was 1.67. Thus, while the shoot may affect total nitrogen uptake through the export of carbohydrates to roots, the shoot (common for halves of the split-root system) apparently does not exert a direct effect on proportionality of NH4+ and NO3- uptake by roots. For whole roots supplied with both NH4+ and NO3-, the restriction in uptake of NO3- may involve a stimulation of NO3- efflux rather than an inhibition of NO3- influx. While only the net uptake of NH4+ and NO3- was measured by ion chromatography, monitoring at approximately hourly intervals during the first 3 days of treatment revealed irregularly occurring intervals of both depletion (net influx) and enrichment (net efflux) in solutions. In the case of NH4+, numbers of net efflux events were similar (21 to 24 out of 65 sequential sampling intervals) whether NH4+ was supplied with NO3- to whole-root systems or separately to an axis of the split-root system. In the case of NO3-, however, the number of net efflux events increased from 8 when NO3- was supplied to a separate axis of the split-root system to between 19 and 24 when NO3- was supplied with NH4+ to whole-root systems.

Effect of NaCl salinity, nitrogen form, calcium and potassium concentration on nitrogen uptake and kinetics in Triticum aestivum L. cv. Gamtoos

SUMMARYIn wheat plants it was found that salinity stress (50 mM NaCl) and an increase in the exogenous Ca2+ supply (to 5 mM) had a differential influence on N uptake capacity depending on the N source (NO3− or NH4+). In NO3−supplied wheat plants which had not been supplied with supplemental calcium, a salinity of 50 mM NaCl reduced the N uptake rate of the root by 30 %, reduced the Fmax of NO3− uptake by 38 % and the N concentration of the plants by 35 %. In NH4+supplied plants (which were not affected by a change in calcium concentration) a salinity of 50 mM resulted in a reduction in the N concentration by 16 % (only in the root), a reduction in the Fmax of NH4+uptake by 50 %, while the N uptake rate by the plant was reduced by 16 %. In salt‐stressed NO3−supplied wheat, an exogenous Ca24 concentration of 5 mM resulted in a 65 % increase in Vmax of NO3− uptake, a 58% increase in NO3− uptake rate by the shoot per g root and a 61 and 5 % increase in shoot and root N concentration respectively. Increased exogenous concentrations of either Ca2+ or K+ had no effect on NH4+ uptake. Kinetic calculations indicate that the inhibitory activity of NaCl on both NO3− and NH4+ uptake was one of noncompetitive inhibition. When NO3−, but not NH4+, was the N source, Ca2+ at a concentration of 5 mM partially ameliorated the NaCl‐mediated inhibition of NO3− uptake.

Hg2+-induced leakage of electrolytes and inhibition of NO3 ? utilization inNostoc calcicola

The effect of mercury (Hg2+) in the absence and presence of methylmercury (CH3Hg+), cadmium (Cd2+), copper (Cu2+), nickel (Ni2+) and calcium (Ca2+) on Nostoc calcicola Breb. has been studied in terms of electrolyte leakage, NO3 − uptake and in vivo nitrate reductase (NR) activity to discover any possible correlation among such parameters under Hg2+ stress. Leakage of electrolytes from Hg2+-treated cyanobacterial cells was directly proportional to Hg2+ concentrations and exposure time. In comparison to NO3 − uptake, an about 60-fold slower rate of NR activity was observed in the untreated cultures, the former being five times more Hg2+-sensitive. A non-competitive synergistic interaction of Hg2+ with CH3Hg+ or Cd2+ and antagonistic with that of Ni2+ or Ca2+ has been observed for both the processes of NO3 − utilization. The antagonistic interaction of Cu2+ with Hg2+ in terms of NO3 − uptake and synergistic with respect to NR activity, has been attributed to the dual bonding preference of Cu2+ for cellular ligands. These findings suggest that (a) a statistically significant correlation exists among such parameters; (b) Hg2+ predominantly attacks the cyanobacterial cell membrane; (c) Hg2+ inhibits NO3 − utilization; (d) the presence of other cations increases or decreases the inhibitory actions of Hg2+.

Cadmium induced inhibition of nitrate Uptake in Anacystis nidulans: Interaction with other divalent cations.

The effect of Cd2+ (4ppm) and a combination of Cd2+ with the non-inhibitory levels of metals like Ca2+ (150ppm), Zn2+ (2ppm), and Hg2+ (0.04ppm) on the uptake of nitrate by Anacystis nidulans IU 625 (ATCC 27144) was investigated. The NO3- uptake kinetics was studied by monitoring short-term uptake rates at different NO3- levels (1-20mM). The values for Vmax (0.8μmol/μg protein/hr) and half saturation constant for uptake (Km 3.03mM) were obtained employing the double reciprocal plot. A 4ppm level of Cd2+ inhibited 50% of the NO3- uptake rate (at saturating NO3- level) compared to Cd2+-less control. Cd2+ inhibition of NO3- uptake (Km 5.88mM) was alleviated as a result of competitive interaction by either Ca2+ (Km 4.34mM) or Zn2+ (Km 4.08mM). Hg2+ ions, however, interacted synergistically with Cd2+ (Km 12.5mM). There was no change in the uptake capacity (Vmax 0.8μmol/μg protein/hr) for NO3- under various treatments.

ACCUMULATION OF NITRATE AND CHLORIDE BY BURLEY TOBACCO

Experiments were conducted to study the NO3− and Cl− interactions during uptake by burley tobacco (Nicotiana tabacum L., cult Ky 14) and the effects of their interactions on plant composition over long growth periods. Results indicated that NO3− or Cl− inhibited the absorption of the other anion by burley tobacco plants but did not influence the composition of cations. Positive linear relationships were found between NO3− and Cl− levels in solution, and the NO3− and Cl− contents in the plants in the laboratory and greenhouse studies. The inhibition of NO3− by Cl− during accumulation was also evident for tobacco plants grown under field conditions for longer periods. The interaction between NO3− and Cl− appears to be competitive during accumulation by burley tobacco. Competition between NO3− and Cl− during accumulation is proposed to be localized in the leaf cell rather than at the root–media interface.