Comparative effects of sodium nitrate and calcium nitrate on the potato

Summary Comparative trials with sodium nitrate and calcium nitrate on the potato indicate a certain superiority of the former, probably due to a greater utilization of potassium and hence improved carbohydrate metabolism.     

Effect of nitrate on the synthesis and decay of nitrate reductase of Neurospora

1. A method was developed to examine the turnover of nitrate reductase by the use of tungstate. 2. Evidence is presented which suggests that the disappearance of nitrate reductase activity from Neurospora mycelia exposed to non-inducing conditions is due to the disappearance of the enzyme protein(s) from the mycelia, and not merely due to the disappearance of its (their) catalytic power. 3. The presence of NO(3) (-) in the culture medium slows down the rate of degradation of nitrate reductase in Neurospora in vivo.     

Effect of sulfide to nitrate ratios on the simultaneous anaerobic sulfide and nitrate removal

Present investigation deals with the effect of sulfide to nitrate (S/N) molar ratio on the simultaneous anaerobic sulfide and nitrate removal on capacity, stability and selectivity of the process. The volumetric sulfide-sulfur and nitrate-nitrogen removal rates at molar S/N ratio of 5:2 were 4.86 kg (m³ d)⁻¹ and 0.99 kg (m³ d)⁻¹, respectively, which were higher than those at S/N molar ratios of 5:5 and 5:8. Moreover, the fluctuations in the effluent at S/N ratio of 5:2 were less than those at the other two tested ratios. During the operation, the ratio of converted sulfide to converted nitrate tended to approach 5:2. The selectivity for elemental sulfur and dinitrogen was improved when the S/N molar ratio was set at 5:2 rather than 5:5 or 5:8. The process became unstable if the influent sulfide surpassed its critical concentration. The electron balance between reactants was also analyzed for different S/N molar ratios.     

Studies of the uptake of nitrate in barley : v. Estimation of root cytoplasmic nitrate concentration using nitrate reductase activity-implications for nitrate influx

The cytoplasmic NO₃⁻ concentration ([NO₃⁻]_c) was estimated for roots of barley (Hordeum vulgare L. cv Klondike) using a technique based on measurement of in vivo nitrate reductase activity. At zero external NO₃⁻ concentration ([NO₃⁻]_o), [NO₃⁻]_c was estimated to be 0.66 mm for plants previously grown in 100 μm NO₃⁻. It increased linearly with [NO₃⁻]_o between 2 and 20 mm, up to 3.9 mm at 20 mm [NO₃⁻]_o. The values obtained are much lower than previous estimates from compartmental analysis of barley roots. These observations support the suggestion (MY Siddiqi, ADM Glass, TJ Ruth [1991] J Exp Bot 42: 1455-1463) that the nitrate reductase-based technique and compartmental analysis determine [NO₃⁻]_c for two separate pools; an active, nitrate reductase-containing pool (possibly located in the epidermal cells) and a larger, slowly metabolized storage pool (possibly in the cortical cells), respectively. Given the values obtained for [NO₃⁻]_c and cell membrane potentials of −200 to −300 mV (ADM Glass, JE Schaff, LV Kochian [1992] Plant Physiol 99: 456-463), it is very unlikely that passive influx of NO₃⁻ is possible via the high-concentration, low-affinity transport system for NO₃⁻. This conclusion is consistent with the suggestion by Glass et al. that this system is thermodynamically active and capable of transporting NO₃⁻ against its electrochemical potential gradient.     

Ammonium can stimulate nitrate and nitrite reductase in the absence of nitrate in Clematis vitalba

Nitrogen assimilation was studied in the deciduous, perennial climber Clematis vitalba. When solely supplied with NO₃^– in a hydroponic system, growth and N-assimilation characteristics were similar to those reported for a range of other species. When solely supplied with NH₄⁺, however, nitrate reductase (NR) activity dramatically increased in shoot tissue, and particularly leaf tissue, to up to three times the maximum level achieved in NO₃^– supplied plants. NO₃^– was not detected in plant material that had been solely supplied with NH₄⁺, there was no NO₃^– contamination of the hydroponic system, and the NH₄⁺-induced activity did not occur in tobacco or barley grown under similar conditions. Western Blot analysis revealed that the induction of NR activity, either by NO₃^– or NH₄⁺, was matched by NR and nitrite reductase protein synthesis, but this was not the case for the ammonium assimilation enzyme glutamine synthetase. Exposure of leaf disks to N revealed that NO₃^– assimilation was induced in leaves directly by NO₃^– and NH₄⁺ but not glutamine. Our results suggest that the NH₄⁺-induced potential for NO₃^– assimilation occurs when externally sourced NH₄⁺ is assimilated in the absence of any NO₃^– assimilation. These data show that the potential for nitrate assimilation in C. vitalba is induced by a nitrogenous compound in the absence of its substrate and suggest that NO₃^– assimilation in C. vitalba may have a significant role beyond the supply of reduced N for growth.     

The roles of nitrate and ammonium in the regulation of the development of nitrate reductase in Chlamydomonas reinhardii

The regulation of the development of nitrate reductase (NR) activity in Chlamydomonas reinhardii has been compared in a wild-type strain and in a mutant (nit-A) which possesses a modified nitrate reductase enzyme that is non-functional in vivo. The modified enzyme cannot use NAD(P)H as an electron donor for nitrate reduction and it differs from wild-type enzyme in that NR activity is not inactivated in vitro by incubation with NAD(P)H and small quantities of cyanide; it is inactivated when reduced benzyl viologen or flavin mononucleotide is present. After short periods of nitrogen starvation mutant organisms contain much higher levels of terminal-NR activity than do similarly treated wild-type ones. Despite the inability of the mutant to utilize nitrate, no nitrate or nitrite was found in nitrogen-starved cultures; it is therefore concluded that the appearance of NR activity is not a consequence of nitrification. After prolonged nitrogen starvation (22 h) the NR level in the mutant is low. It increases rapidly if nitrate is then added and this increase in activity does not occur in the presence of ammonium, tungstate or cycloheximide. Disappearance of preformed NR activity is stimulated by addition of tungstate and even more by addition of ammonium. The results are interpreted as evidence for a continuous turnover of NR in cells of the mutant with ammonium both stimulating NR breakdown and stopping NR synthesis. Nitrate protects the enzyme from breakdown. Reversible inactivation of NR activity is thought to play an insignificant rôle in the mutant.Abbreviations NR nitrate reductase - BV benzyl viologen     

Biochemical characterization of nitrate and nitrite reduction in the wild-type and a nitrate reductase mutant of soybean

Enzyme activities involved in nitrate assimilation were analyzed from crude leaf extracts of wild-type (cv. Williams) and mutant ( nr₁ ) soybean [ Glycine max (L.) Merr.] plants lacking constitutive nitrate reductase (NR) activity. The nr₁ soybean mutant (formerly LNR-2), had decreased NADH-NR, FMNH₂-NR and cytochrome c reductase activities, all of which were associated with the loss of constitutive NR activity. Measurement of FMNH₂-NR activity, by nitrite determination, was accurate since nitrite reductase could not use FMNH₂ as a reductant source. Nitrite reductase activity was normal in the nr₁ plant type in the presence of reduced methyl viologen. Assuming that constitutive NR is similar in structure to nitrate reductases from other plants, presence of xanthine dehydrogenase activity and loss of cytochrome c reductase activity indicated that the apoprotein and not the molybdenum cofactor had been affected in the constitutive enzyme of the mutant. Constitutive NR from urea-grown wild-type plants had 1) greater ability to use FMNH₂ as an electron donor, 2) a lower pH optimum, and 3) decreased ability to distinguish between NO₃⁻ and HCO₃⁻, compared with inducible NR from NO₃⁻-grown nr₁ plants. The presence in soybean leaves of a nitrate reductase with a pH optimum of 7.5 is contrary to previous reports and indicates that soybean is not an exception among higher plants for this activity.     

Role of oxygen limitation and nitrate metabolism in the nitrate inhibition of nitrogen fixation by pea

The impact of nitrate (5–15 m M , 2 to 7 days) on nitrogenase activity and nodule-oxygen limitation was investigated in nodulated, 21-day-old plants of a near-isogenic nitrate reductase-deficient pea mutant (A3171) and its wild-type parent ( Pisum sativum L. cv. Juneau). Within 2 days, 10 or 15 m M nitrate, but not 5 m M nitrate, inhibited the apparent nitrogenase activity (measured as in situ hydrogen evolution from nodules of intact plants) of wild-type plants; none of these nitrate levels inhibited the apparent nitrogenase activity of A3171 plants. Nodule-oxygen limitation, measured as the ratio of total nitrogenase activity to potential nitrogenase activity, was increased in both wild-type and A3171 plants by all nitrate treatments. By 3 to 4 days the apparent nitrogenase activity of A3171 and wild-type plants supplied with 5 m M nitrate declined to 53 to 69% of control plants not receiving nitrate. By 6 to 7 days the apparent nitrogenase activity of A3171 plants was similar to the control value whereas that of the wild-type plants continued to decline. From 3 to 7 days, no significant differences in nodule-oxygen limitation were observed between the nitrate (5 m M ) and control treatments. The results are interpreted as evidence for separate mechanisms in the initial (O₂ limitation) and longer-term (nitrate metabolism) effects of nitrate on nitrogen fixation by effectively nodulated pea.     

Bacterial nitrate reductases: Molecular and biological aspects of nitrate reduction

Nitrogen is a vital component in living organisms as it participates in the making of essential biomolecules such as proteins, nucleic acids, etc. In the biosphere, nitrogen cycles between the oxidation states +V and -III producing many species that constitute the biogeochemical cycle of nitrogen. All reductive branches of this cycle involve the conversion of nitrate to nitrite, which is catalyzed by the enzyme nitrate reductase. The characterization of nitrate reductases from prokaryotic organisms has allowed us to gain considerable information on the molecular basis of nitrate reduction. Prokaryotic nitrate reductases are mononuclear Mo-containing enzymes sub-grouped as respiratory nitrate reductases, periplasmic nitrate reductases and assimilatory nitrate reductases. We review here the biological and molecular properties of these three enzymes along with their gene organization and expression, which are necessary to understand the biological processes involved in nitrate reduction.     

Differences among maize cultivars in the utilization of soil nitrate and the related losses of nitrate through leaching

In a 2-year field experiment conducted on a Gleyic Luvisol in Stuttgart-Hohenheim one experimental and nine commercial maize cultivars were compared for their ability to utilize soil nitrate and to reduce related losses of nitrate through leaching. Soil nitrate was monitored periodically in CaCl₂ extracts and in suction cup water. Nitrate concentrations in suction water were generally higher than in CaCl₂ extracts. Both methods revealed that all cultivars examined were able to extract nitrate down to a soil depth of at least 120 cm (1988 season) or 150 cm (1987 season). Significant differences among the cultivars existed in nitrate depletion particularly in the subsoil. At harvest, residual nitrate in the upper 150 cm of the profile ranged from 73–110 kg N ha^–1 in 1987 and from 59–119 kg N ha^–1 in 1988. Residual nitrate was closely correlated with nitrate losses by leaching because water infiltration at 120 cm soil depth started 4 weeks after harvest (1987) or immediately after harvest (1988) and continued until early summer of the following year. The calculated amount of nitrate lost by leaching was strongly influenced by the method of calculation. During the winter of 1987/88 nitrate leaching ranged from 57–84 kg N ha^–1 (suction cups) and 40–55 kg N ha^–1 (CaCl₂ extracts), respectively. The corresponding values for the winter of 1988/89 were 47–79 and 20–39 kg N ha^–1, respectively. ei]Section editor: B E Clothier     

Genomic analysis of the nitrate response using a nitrate reductase-null mutant of Arabidopsis

A nitrate reductase (NR)-null mutant of Arabidopsis was constructed that had a deletion of the major NR gene NIA2 and an insertion in the NIA1 NR gene. This mutant had no detectable NR activity and could not use nitrate as the sole nitrogen source. Starch mobilization was not induced by nitrate in this mutant but was induced by ammonium, indicating that nitrate was not the signal for this process. Microarray analysis of gene expression revealed that 595 genes responded to nitrate (5 mm nitrate for 2 h) in both wild-type and mutant plants. This group of genes was overrepresented most significantly in the functional categories of energy, metabolism, and glycolysis and gluconeogenesis. Because the nitrate response of these genes was NR independent, nitrate and not a downstream metabolite served as the signal. The microarray analysis also revealed that shoots can be as responsive to nitrate as roots, yet there was substantial organ specificity to the nitrate response.     

Efficiency of nitrate uptake in spinach: impact of external nitrate concentration and relative growth rate on nitrate influx and efflux

Regulation of nitrate influx and efflux in spinach (Spinacia oleracea L., cv. Subito), was studied in short-term label experiments with 13N- and 15N-nitrate. Nitrate fluxes were examined in relation to the N demand for growth, defined as relative growth rate (RGR) times plant N concentration. Plants were grown at different nitrate concentrations (0.8 and 4 mM), with mineral composition of growth and uptake solutions identical. Nitrate influx, efflux and net nitrate uptake rate (NNUR) were independent of the external nitrate concentration, despite differences in internal nitrate concentration. At both N regimes, NNUR was adequate to meet the N demand for growth. RGR-related signals predominantly determined the nitrate fluxes. At high RGR (0.25 g g-1 day-1), nitrate influx was 20 to 40% lower and nitrate efflux was 50 to 70% lower than at lower RGR (0.17 g g-1 day-1); efflux:influx ratio (E:I) declined from 0.5 at low RGR to 0.2 at higher RGR. Thus, the efficiency of NNUR substantially increased with increasing RGR. Differences in nitrate translocation between morning and afternoon coincided with differences in nitrate efflux, which is in accordance with the suggested regulation of nitrate efflux by the root cytoplasmic nitrate concentration. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of electron donors on nitrate removal by nitrate and nitrite reductases

Effects of artificial electron donors to deliver reducing power on enzymic denitrification were investigated using nitrate reductase and nitrite reductase obtained fromOchrobactrum antropi. The activity of nitrite reductase in the soluble portion was almost the same as that in the precipitated portion of the cell extract. Nitrate removal efficiency was higher with benzyl viologen than with methyl viologen or NADH as an artificial electron donor. The turn-over numbers of nitrate and nitrite reductase were 14.1 and 1.9 μmol of nitrogen reduced/min·mg cell extracts, respectively when benzyl viologen was used as an electron donor.     

Assessing the sources and magnitude of diurnal nitrate variability in the San Joaquin River (California) with an in situ optical nitrate sensor and dual nitrate isotopes

1. We investigated diurnal nitrate (NO₃⁻) concentration variability in the San Joaquin River using an in situ optical NO₃⁻ sensor and discrete sampling during a 5‐day summer period characterized by high algal productivity. Dual NO₃⁻ isotopes (δ¹⁵N_NO3 and δ¹⁸O_NO3) and dissolved oxygen isotopes (δ¹⁸O_DO) were measured over 2 days to assess NO₃⁻ sources and biogeochemical controls over diurnal time‐scales. 2. Concerted temporal patterns of dissolved oxygen (DO) concentrations and δ¹⁸O_DO were consistent with photosynthesis, respiration and atmospheric O₂ exchange, providing evidence of diurnal biological processes independent of river discharge. 3. Surface water NO₃⁻ concentrations varied by up to 22% over a single diurnal cycle and up to 31% over the 5‐day study, but did not reveal concerted diurnal patterns at a frequency comparable to DO concentrations. The decoupling of δ¹⁵N_NO3 and δ¹⁸O_NO3 isotopes suggests that algal assimilation and denitrification are not major processes controlling diurnal NO₃⁻ variability in the San Joaquin River during the study. The lack of a clear explanation for NO₃⁻ variability likely reflects a combination of riverine biological processes and time‐varying physical transport of NO₃⁻ from upstream agricultural drains to the mainstem San Joaquin River. 4. The application of an in situ optical NO₃⁻ sensor along with discrete samples provides a view into the fine temporal structure of hydrochemical data and may allow for greater accuracy in pollution assessment.