External Nitrate Concentration Research Articles

Growth, nodulation and nitrate reductase activity in the aquatic legume Neptunia plena (L.) benth. At different external nitrate concentrations

The effects of different external nitrate concentrations (0 (control), 1, 50, 100, 500, 1000 and 20 000 mmol m −3) on growth, nodulation and nitrate-reductase activity (NRA) of inoculated Neptunia plena (L.) Benth. were examined. Plants given 500 and 1000 mmol m −3 nitrate had greater ( P < 0.05) shoot length, leaf, stem and root dry mass, and carbon and nitrogen contents than the controls and plants given 20 000 mmol m −3 nitrate. Nodule number was not significantly affected by nitrate concentration up to 50 mmol m −3, but 100 mmol m −3 nitrate reduced nodulation by 68% and concentrations above 100 mmol m −3 completely inhibited nodule development. Plants given 100–20000 mmol m −3 nitrate had a greater nitrate content per g leaf, stem and root dry mass (DM) than controls. Nitrate per g root DM did not increase with external nitrate concentration above 500 mmol m −3, but levels in leaf and stem were greater at 20 000 mmol m −3 nitrate than at all other concentrations. NRA per g leaf, stem and root fresh mass (FM) was greater for plants given 500–20000 mmol m −3 than for controls, but there was no significant increase with nitrate concentration above 500 mmol m −3. Substantial proportions of total plant nitrate and NRA were found in both root and shoot over the entire range of external nitrate concentrations given. Findings for N. plena are compared with data obtained previously for terrestrial legumes.

Cyclic variations in nitrogen uptake rate of soybean plants: effects of external nitrate concentration.

Net uptake of NO3- by non-nodulated soybean plants [Glycine max (L.) Merr. cv. Ransom] growing in flowing hydroponic cultures containing 0.5, 1.0 and 10.0 mol m-3 NO3- was measured daily during a 24-d period of vegetative development to determine if amplitude of maximum and minimum rates of net NO3- uptake are responsive to external concentrations of NO3-. Removal of NO3- from the replenished solutions during each 24-h period was determined by ion chromatography. Neither dry matter accumulation nor the periodicity of oscillations in net uptake rate was altered by the external NO3- concentrations. The maxima of the oscillations in net uptake rate, however, increased nearly 3-fold in response to external NO3- concentrations. The maxima and minima, respectively, changed from 4.0 and 0.6 mmol NO3- per gram root dry weight per day at an external solution level of 0.5 mol m-3 NO3- to 15.2 and -2.7 mmol NO3- per gram root dry weight per day at an external solution level of 10.0 mol m-3 NO3-. The negative values for minimum net uptake rate from 10.0 mol m-3 NO3- solutions show that net efflux was occurring and indicate that the magnitude of the efflux component of net uptake was responsive to external concentration of NO3-.

In situ nitrate reductase activity as an indicator of nitrate availability

The effect of external nitrate concentration in the nutrient solution on nitrate reduction by 7-day-old barley seedlings was investigated using anin situ nitrate reductase activity (NRA) assay, performed with or without exogenous nitrate during the incubation. The difference between plus and minus nitrate NRA of the leaves related to plus nitrate NRA decreased with increasing nitrate concentration in the nutrient solution. Furthermore, the root contribution to the whole plant NRA became predominant at low external nitrate levels. It is proposed that plus and minus nitrate NRA should be used together as an indicator of nitrate availability in the medium and of root contribution to whole plant nitrate reduction.

Ammonium thresholds for simultaneous uptake of ammonium and nitrate by oyster-pond algae

Natural microalgal populations and axenic algal isolates from oyster ponds have been grown either in situ or in controlled conditions, in the presence of ammonium and nitrate as nitrogen sources. Both ions were added at various concentrations, up to 50 μg-at. N·l −1; other nutrients were in excess. In one experiment, urea was also added. Uptake of nitrate was followed by measuring disappearance of nitrate from the medium, and by incorporation of 15NO 3; nitrate reductase (NR) activity and the intracellular nitrate pool were also measured. The uptake of nitrate was prevented by the presence of ammonium above a concentration which varied according to species. The ammonium threshold (in units of μg-at. N·l −1) was ≈ 30 for natural populations and the diatom Navicula ostrearia Bory, ≈ 21 for Nitzschia ovalis (sensu Hustedt), and ≈ 44 for Amphora coffeaeformis (sensu Hendey). Nitrate uptake started at a rate which was ≈ 39% of the eventual maximum rate observed for the natural populations, and from 11 to 17% for cultured strains. The initial low rate was maintained until the ambient ammonium concentration had decreased to ≈ 7.5 μg-at. N·l −1, except for A. coffeaeformis which shifted from slow to fast nitrate uptake at 23.5μg-at. N·l −1. The nitrate uptake system then operated at a slightly higher rate than the one for ammonium (ammonium uptake/nitrate uptake = 0.86). Cultures with an initial ammonium concentration lower than the threshold values did not show an initial low rate or a lag phase for uptake of nitrate. NR activity was detectable even in the presence of ≈ 30 μg-at. NH 4-N·l −1 in the external medium. When urea and nitrate were presented simultaneously, urea was not taken up preferentially, as reported elsewhere; uptake was initially at a reduced rate until the external nitrate concentration decreased to 3.7 μg-at. N·l −1. Then the rate of urea uptake increased to a maximum. It is suggested that because oyster-pond algae have evolved in an environment where concentrations of ammonium, nitrate, and organic nitrogen are continuously high, the threshold of inhibition by ammonium of uptake of these compounds is much higher than for similar pelagic and neritic species, so that they are able to assimilate other sources of nitrogen, such as nitrate and urea, simultaneously with ammonium.

The partitioning of nitrate assimilation between root and shoot of higher plants

Abstract The partitioning of nitrate assimilation between root and shoot of higher plant species is indicated by the relative proportions of total plant nitrate reductase activity (NRA) in the two plant parts and the relative concentrations of nitrate and reduced N in the xylem sap. These have been collated here from the literature and temperate and tropical species compared.Both the distribution of NRA and xylem sap nitrate: reduced N indicate that the following four generalizations can be made. Temperate, perennial species growing in low external nitrate concentrations (about 1 mol m−3) carry out most of their nitrate assimilation in the root. As external nitrate concentration increases (in the range found in agricultural soils, 1–20 mol m−3), shoot nitrate assimilation becomes increasingly important. Temperate, annual legume species growing in low external nitrate concentrations carry out most of their nitrate assimilation in the root. Shoot nitrate assimilation increases in importance as external nitrate concentration is increased. Temperate, annual non‐legume species vary greatly in their partitioning of nitrate assimilation between root and shoot when growing in low external nitrate concentrations. Regardless of the proportion carried out in the root at low external nitrate concentrations, nitrate assimilation in the shoot becomes increasingly important as external nitrate concentration is increased. Tropical and subtropical species, annual and perennial, carry out a substantial proportion of their nitrate assimilation in the shoot when growing in low external nitrate concentrations. The partitioning of nitrate assimilation between root and shoot remains constant as external nitrate concentration increases. It is proposed that a greater proportion of nitrate assimilation occurs in the shoot when an increase in the rate of nitrate uptake does not induce an increase in NR level in the root. Thus, a greater proportion of the nitrate taken up remains unassimilated and is passed into the xylem. A constant partitioning of nitrate assimilation between root and shoot is achieved by balancing NR levels in the root with rates of nitrate uptake.The advantages and disadvantages of assimilating nitrate in either the root or shoot are discussed in relation to temperate and tropical habitats.

Characteristics of nitrate uptake into seedlings of pea (Pisum sativum L. cv. Feltham First). Changes in net NO−3 uptake following inoculation with Rhizobium and growth in low nitrate concentrations

Abstract Nitrate uptake into intact pea seedlings (Pisum sativum L. cv. Feltham First) grown in hydroponic culture has been investigated. Following inoculation with Rhizobium leguminosarum a twofold increase in net nitrate uptake was observed. Changes in morphological characteristics following inoculation were found to decrease the effective area available for absorption.There was a two‐fold decrease in net nitrate uptake into intact seedlings grown in the presence of N compared with N free media. In the former case net nitrate uptake appeared to stall at regular intervals. In both cases only the initial rates of nitrate uptake were found to be responsive to the external nitrate concentration. The results are discussed in terms of current models for the regulation of NO−3 uptake by higher plants.

The Distribution of Nitrate Assimilation Between Root and Shoot in Vicia faba L.

Nitrate assimilation was examined in two cultivars (Banner Winter and Herz Freya) of Vicia faba L. supplied with a range of nitrate concentrations. The distribution between root and shoot was assessed. The cultivars showed responses to increased applied nitrate concentration. Total plant dry weight and carbon content remained constant while shoot: root dry weight ratio, total plant nitrogen, total plant leaf area and specific leaf area (SLA) all increased. The proportion of total plant nitrate and nitrate reductase (NR) activity found in the shoot of both cultivars increased with applied nitrate concentrations as did NO3−: Kjeldahl-N ratios of xylem sap. The cultivars differed in that a greater proportion of total plant NR activity occurred in the shoot of cv. Herz Freya at all applied nitrate concentrations, and its xylem sap NO3−: Kjeldahl-N ratio and SLA were consistently greater. It is concluded that the distribution of nitrate assimilation between root and shoot of V. faba varies both with cultivar and with external nitrate concentration.

Nitrate content and nitrate reductase activity in Rumex obtusifolius L. : II. Responses to nitrate starvation and nitrogen fertilization.

The aim of this work was to investigate the effect of nitrogen starvation and subsequent fentilization with nitrate or ammonium on nitrate content and nitrate reductase activity of Rumex obtusifolius L. under natural conditions.When plants were transplanted to nitrate-poor media, endogenous nitrate was reduced within a few days. In parallel, nitrage reductase activities dropped to about 25% of the initial values. As a consequence of nitrate fertilization (1; 10 or 100 mmol KNO3/l substrate), endogenous nitrate content of the plant abruptly increased within one day. In extreme cases, nitrate concentrations of up to 10% of plant dry weight could be observed without being lethal. High external nitrate concentrations caused an inhibition of nitrate reductase within the leaves, while low external concentrations provoked an increase in the enzyme activity of about 450% within one day. Ammonium fertilization (5 mmol (NH4)2SO4/l substrate) also caused an increase in nitrate reductase activity and nitrate content within leaf blades. This observation indicates a rapid nitrification of ammonium in the substrate. When plants were fertilized with ammonium plus nitrate (2.5 mmol (NH4)2SO4+ 5 mmol KNO3/l substrate), an extremely high and long term increase in nitrate reduction could be observed. Due to an intensive enzymatic nitrate turnover, the nitrate content of leaf blades then remained relatively low. Our observations do not point to an inhibition of nitrate reductase activity in leaves of Rumex obtusifolius by ammonium. Despite temporarily high endogenous nitrate concentrations, Rumex obtusifolius may not be termed as a "nitrate storage" plant, since the accumulation of nitrate is a short term process only.

THE EFFECT OF DIFFERENT INORGANIC NITROGEN SOURCES AND PLANT AGE ON THE COMPOSITION OF BLEEDING SAP OF PHASEOLUS VULGARIS

The composition of the bleeding sap N of Phaseolus vulgaris varied with the inorganic nitrogen source fed to the plant but was not changed by a fourfold difference in external nitrate concentration. Highest sap N concentration and fastest growth were observed in ammonium nitrate grown plants. With nitrate grown plants 60 % of the total sap N was inorganic nitrate-N and 40 % organic-N whereas with ammonium nitrate grown plants nitrate contributed 30 % to the total N and organic-N 70 %. Virtually all of the N in the sap of ammonium grown plants was organic-N. Allantoic acid was the major individual reduced N compound in the bleeding sap of plants fed with nitrate, ammonium or ammonium nitrate. During the development of the plant from seedling to mature plant with ripened pods, the concentration of N in the bleeding sap of nitrate grown plants decreased sharply initially and then gradually during pod formation; it increased again when the pods had ripened. Nitrate reductase activity of leaf extracts was correlated with nitrate content of bleeding sap and was not much affected by increases in reduced N compounds in the sap.

Nitrate content and induction of NADH nitrate reductase in cultured rice cells

Abstract The nitrate content of cultured rice cells grown in liquid R-2 medium containing 40 mM nitrate increased rapidly and reached a maximum 6 hr after inoculation. After about 6-hr lag period, NADH nitrate reductase activity increased rapidly to the 24th hr. Promotive effects on the nitrate accumulation and the induction of NADH nitrate reductase were found by the addition of 5 mM ammonium into the medium. Nitrate content increased exponentially as a function of increasing external nitrate concentration between 0 and 80 mM. The NADH nitrate reductase activity also increased from 0 to 40 mM of nitrate media, but leveled off between 40 and 80 mM. A high level of nitrate content was detected in the cells grown in 10 or 40 mM of nitrate medium without sucrose for 48 hr, suggesting that sucrose in the medium may have no effect on the nitrate accumulation in the early growth period.

Nitrate reductase activity as a function of in situ nitrate uptake and environmental factors of euphotic zone profiles

The activity of nitrate reductase in euphotic zone profiles from several oceanic areas has been compared with in situ nitrate uptake rates estimated by the 15N technique. There were marked variations in the ratio of uptake to reduction and these have been related to the available light intensity, nitrate concentration, and the absolute value of nitrate uptake. It is shown that uptakereduction ratios greater than one are not due to dephasing between the two processes and that accumulation of nitrate inside the cells cannot account for the discrepancy. Nitrate uptake depends primarily on the external nitrate concentration, while nitrate reductase activity seems to be controlled by the intracellular nitrate level. The importance of those results as regards the significance of the nitrate reductase assay as an index of nitrate assimilation by marine phytoplankton is discussed.

Nitrate Uptake and Induction of Nitrate Reductase in Excised Corn Roots

The characteristics of nitrate uptake and induction of nitrate reductase were studied in excised roots of corn (Zea mays L.). Upon initial exposure to nitrate, the low initial rate of nitrate uptake gradually increased until a steady uptake rate was achieved in 1 to 2 hours depending on the NO(3) (-) concentration. The pattern was observed over a wide range (0.2-5 mm) of nitrate concentrations and was independent of the accompanying cation.The nitrate uptake pattern as a function of increasing external nitrate concentrations (0.2-50 mm) followed saturation type kinetics. The reciprocal plot of the data was not linear but hyperbolic, indicating that more than one Km for nitrate uptake can be resolved from the data. This suggests the existence of either one carrier system with changing kinetic constants or the existence of dual uptake systems. The pattern of induction of nitrate reductase was coincident with the pattern of nitrate uptake as a function of time and increasing nitrate concentrations. The rate of induction of nitrate reductase was regulated by the rate of nitrate flux.Washing the roots for 2 hours enhances nitrate uptake by 2.5-fold over the nonwashed tissue. The presence of nitrate in the washing solution leads to further (3.5-fold over control) increases in the rate of nitrate uptake supporting the contention that nitrate plays a specific role in the induction of the inducible nitrate carrier independent of the washing effect.

Light‐stimulated Absorption of Nitrate by Wolffia arrhiza

AbstractThe mechanism of the light‐stimulated absorption of nitrate by Wolffia arrhiza was studied. The nitrate‐absorption mechanism in ammonium‐grown plants is stimulated by the presence of nitrate. In a manner similar to the absorption of many other ions, the absorption of nitrate follows a typical biphasic pattern in relation to external nitrate concentration. Mechanism 1 is effective at nitrate concentrations up to 0.5 to 0.75 mM and mechanism 2 becomes operative at higher nitrate levels.Light stimulates the absorption of nitrate independently of the effect of light on the reduction of nitrate. The effects of uncouplers, inhibitors, and light of wavelengths of 700 nm or longer indicate that nitrate absorption by Wolffia cells is reduced when non‐cyclic electron transport is blocked. It is postulated that under this condition, ATP in the chloroplast (produced by cyclic photophosphorylation) may be less readily transported across the chloroplast envelope than when non‐cyclic electron transport is proceeding.

Studies on Metal Complex Species using an Anion Exchange Resin. III. Uranium(VI)-Nitrate Complex and Zinc-Chloride Complex

Abstract 1) The “indifferent electrolyte-adding” method described in previous papers was applied to the uranyl-nitrate and to the zinc-chloride complexes. A sodium nitrate-sodium perchlorate mixed medium was employed in the former, and a sodium chloride-sodium nitrate mixed medium in the latter. 2) The predominant species of the uranyl-nitrate complex adsorbed from sodium nitrate solutions was UO2(NO3)3− at the external nitrate concentration of about 2 m and UO2(NO3)42− at the 4∼6 m concentration. The coexistence of the two species may be presumed at 2∼4 m. 3) The principal zinc-chloride complex adsorbed on the resin from the chloride solution of 0.4∼3 m was simply ZnCl42−, accompanied by a small quantity of ZnCl3− in a low ionic strength. On the other hand, the predominant species in the aqueous phase were ZnCl3− and ZnCl42− for a sodium chloride concentration of 3 m, and Zn2+ and ZnCl+ for a 0.4 m concentration. These results were approximately consistent with those obtained in a hydrochloric acid medium by other investigators.

Studies on Metal Complex Species Using an Anion Exchange Resin. II. On the Adsorption of Silver from Nitrate Solution

Abstract 1) It was found that silver was to some extent adsorbed on a strong base anion exchange resin from nitrate solutions. Its behavior was significantly different from that of alkali metals. 2) The equations derived in the previous paper were applied to a study of silver-nitrate complex. Starting from the same equation, two methods using either NaNO3 + NaClO4 mixed media or the loading of the complex were employed, and the two results were in good agreement. 3) It was presumed that most silver in the resin exists as Ag(NO3)2− in neutral nitrate media where the external nitrate concentrations were about 2∼3 m, although such anionic species may not be considered to exist in an ordinary nitrate solution.

Studies on Metal Complex Species Using an Anion Exchange Resin, I. Derivation of Equations and Application to Mercury (II)-Nitrate Complex

Abstract 1) The equations for determining the composition of a metal complex using an anion exchange resin have been derived by considering the complex formation equilibria in both the resin phase and the solution phase. 2) The method based on these equations was successfully applied to the investigation of mercury (II)-nitrate complex at various external nitrate concentrations by means of the sodium nitrate-sodium perchlorate mixed solution. 3) Mercury (II) adsorbed from a sodium nitrate solution exists in the form of Hg(NO3)3− at the external nitrate concentration of 0.5∼1 m, Hg(NO3)42− at 3∼5 m and a mixture of Hg(NO3)3− and Hg(NO3)42− at the middle of these concentrations, though no anionic complex appears to be present in an ordinary nitrate solution.