Inhibition Of Nitrate Assimilation Research Articles

Review Aktivitas Fotosintesis pada Tanaman Sorgum (Sorghum bicolor) dalam Kondisi Cekaman Kekeringan

Sorghum (Sorghum bicolor L. Moench) is a cereal crop that has the potential to be developed in Indonesia as a food, feed and industrial crop. Sorghum is a C4 plant that has the advantage of efficiency in hot and dry environments. Drought stress is one of the most limiting environmental factors for crop productivity worldwide, and can be caused by water deficits in the soil and in the atmosphere. On the decreasing leaf water status, the rate of CO2 assimilation and the conductance of stomata decreased rapidly. The CO2 concentration mechanism is able to saturate C4 photosynthesis under the relatively low intercellular CO2 concentration. In addition, CO2 photorespiration is likely to be repaired before it exits the bundle sheat cells. The effects of non-stomatal factors include reduced activity of photosynthetic enzymes, inhibition of nitrate assimilation, induction of premature aging, and changes in leaf anatomy. Photosynthesis in C4 plants, including sorghum, involves, others, the PEPC and Rubisco enzymes. Drought can also trigger oxidative stress, which is an environmental condition that has increased Reactive Oxygen Species (ROS) due to an over reduction of the photosynthesis process.

Revisiting Why Plants Become N Deficient Under Elevated CO2: Importance to Meet N Demand Regardless of the Fed-Form.

An increase in plant biomass under elevated CO2 (eCO2) is usually lower than expected. N-deficiency induced by eCO2 is often considered to be a reason for this. Several hypotheses explain the induced N-deficiency: (1) eCO2 inhibits nitrate assimilation, (2) eCO2 lowers nitrate acquisition due to reduced transpiration, or (3) eCO2 reduces plant N concentration with increased biomass. We tested them using C3 (wheat, rice, and potato) and C4 plants (guinea grass, and Amaranthus) grown in chambers at 400 (ambient CO2, aCO2) or 800 (eCO2) μL L−1 CO2. In most species, we could not confirm hypothesis (1) with the measurements of plant nitrate accumulation in each organ. The exception was rice showing a slight inhibition of nitrate assimilation at eCO2, but the biomass was similar between the nitrate and urea-fed plants. Contrary to hypothesis (2), eCO2 did not decrease plant nitrate acquisition despite reduced transpiration because of enhanced nitrate acquisition per unit transpiration in all species. Comparing to aCO2, eCO2 remarkably enhanced water-use efficiency, especially in C3 plants, decreasing water demand for CO2 acquisition. As our results supported hypothesis (3) without any exception, we then examined if lowered N concentration at eCO2 indeed limits the growth using C3 wheat and C4 guinea grass under various levels of nitrate-N supply. While eCO2 significantly increased relative growth rate (RGR) in wheat but not in guinea grass, each species increased RGR with higher N supply and then reached a maximum as no longer N was limited. To achieve the maximum RGR, wheat required a 1.3-fold N supply at eCO2 than aCO2 with 2.2-fold biomass. However, the N requirement by guinea grass was less affected by the eCO2 treatment. The results reveal that accelerated RGR by eCO2 could create a demand for more N, especially in the leaf sheath rather than the leaf blade in wheat, causing N-limitation unless the additional N was supplied. We concluded that eCO2 amplifies N-limitation due to accelerated growth rate rather than inhibited nitrate assimilation or acquisition. Our results suggest that plant growth under higher CO2 will become more dependent on N but less dependent on water to acquire both CO2 and N.

Changes in metabolism, growth and nutrient uptake of Ulva fasciata (Chlorophyta) in response to nitrogen source

The form of inorganic nitrogen (N) determines the biofiltration performance of Ulva, particularly by inhibition of nitrate assimilation in the presence of ammonia. In the current study, Ulva fasciata from a biofilter of fishpond effluent was examined for its biomass production, photosynthetic activity, nutrient uptake and activity of nitrate reductase when supplied with either ammonia or nitrate as the sole nitrogen source. The effects of prior acclimation to either nitrogen source were also studied. Cultivation of Ulva with ammonia resulted in a rapid uptake of this nutrient, whereas photosynthesis, uptake of orthophosphate and C:N ratio were greater in cultures with nitrate. The transfer of Ulva from ammonia to nitrate nutrition increased carbohydrate content in the biomass. Longer culture in nitrate did not influence photosynthetic yields, growth, or N and P uptake rate by the algae, but increased both lipid and P content in biomass. Once transferred from ammonia-rich to nitrate-rich seawater, nitrate uptake by Ulva commenced immediately, although the activity of the enzyme nitrate reductase was first detected only 28 h later. Culture of Ulva in different nitrogen forms, ammonia and nitrate, may determine application of the resulting biomass in different industries, e.g., feeding, bioethanol, biofiltration, etc., considering the rapid production of protein-rich Ulva in the presence of ammonia, while yield is lower in the presence of nitrate but the biomass contains more carbohydrates and removes P from the effluent more rapidly.

Rising atmospheric CO2 concentration inhibits nitrate assimilation in shoots but enhances it in roots of C3 plants.

We have proposed that rising atmospheric CO2 concentrations inhibit malate production in chloroplasts and thus impede assimilation of nitrate into protein in shoots of C3 plants, a phenomenon that will strongly influence primary productivity and food security under the environmental conditions anticipated during the next few decades. Although hundreds of studies support this proposal, several publications in 2018 and 2019 purport to present counterevidence. The following study evaluates these publications as well as presents new data that elevated CO2 enhances root nitrate assimilation in wheat and Arabidopsis while it inhibits shoot nitrate assimilation.

Lower photorespiration in elevated CO2 reduces leaf N concentrations in mature Eucalyptus trees in the field.

Rising atmospheric CO2 concentrations is expected to stimulate photosynthesis and carbohydrate production, while inhibiting photorespiration. By contrast, nitrogen (N) concentrations in leaves generally tend to decline under elevated CO2 (eCO2 ), which may reduce the magnitude of photosynthetic enhancement. We tested two hypotheses as to why leaf N is reduced under eCO2 : (a) A "dilution effect" caused by increased concentration of leaf carbohydrates; and (b) inhibited nitrate assimilation caused by reduced supply of reductant from photorespiration under eCO2 . This second hypothesis is fully tested in the field for the first time here, using tall trees of a mature Eucalyptus forest exposed to Free-Air CO2 Enrichment (EucFACE) for five years. Fully expanded young and mature leaves were both measured for net photosynthesis, photorespiration, total leaf N, nitrate ( ) concentrations, carbohydrates and reductase activity to test these hypotheses. Foliar N concentrations declined by 8% under eCO2 in new leaves, while the fraction and total carbohydrate concentrations remained unchanged by CO2 treatment for either new or mature leaves. Photorespiration decreased 31% under eCO2 supplying less reductant, and in situ reductase activity was concurrently reduced (-34%) in eCO2 , especially in new leaves during summer periods. Hence, assimilation was inhibited in leaves of E.tereticornis and the evidence did not support a significant dilution effect as a contributor to the observed reductions in leaf N concentration. This finding suggests that the reduction of reductase activity due to lower photorespiration in eCO2 can contribute to understanding how eCO2 -induced photosynthetic enhancement may be lower than previously expected. We suggest that large-scale vegetation models simulating effects of eCO2 on N biogeochemistry include both mechanisms, especially where is major N source to the dominant vegetation and where leaf flushing and emergence occur in temperatures that promote high photorespiration rates.

C4 photosynthesis and water stress.

In contrast to C(3) photosynthesis, the response of C(4) photosynthesis to water stress has been less-well studied in spite of the significant contribution of C(4) plants to the global carbon budget and food security. The key feature of C(4) photosynthesis is the operation of a CO(2)-concentrating mechanism in the leaves, which serves to saturate photosynthesis and suppress photorespiration in normal air. This article reviews the current state of understanding about the response of C(4) photosynthesis to water stress, including the interaction with elevated CO(2) concentration. Major gaps in our knowledge in this area are identified and further required research is suggested. Evidence indicates that C(4) photosynthesis is highly sensitive to water stress. With declining leaf water status, CO(2) assimilation rate and stomatal conductance decrease rapidly and photosynthesis goes through three successive phases. The initial, mainly stomatal phase, may or may not be detected as a decline in assimilation rates depending on environmental conditions. This is because the CO(2)-concentrating mechanism is capable of saturating C(4) photosynthesis under relatively low intercellular CO(2) concentrations. In addition, photorespired CO(2) is likely to be refixed before escaping the bundle sheath. This is followed by a mixed stomatal and non-stomatal phase and, finally, a mainly non-stomatal phase. The main non-stomatal factors include reduced activity of photosynthetic enzymes; inhibition of nitrate assimilation, induction of early senescence, and changes to the leaf anatomy and ultrastructure. Results from the literature about CO(2) enrichment indicate that when C(4) plants experience drought in their natural environment, elevated CO(2) concentration alleviates the effect of water stress on plant productivity indirectly via improved soil moisture and plant water status as a result of decreased stomatal conductance and reduced leaf transpiration. It is suggested that there is a limited capacity for photorespiration or the Mehler reaction to act as significant alternative electron sinks under water stress in C(4) photosynthesis. This may explain why C(4) photosynthesis is equally or even more sensitive to water stress than its C(3) counterpart in spite of the greater capacity and water use efficiency of the C(4) photosynthetic pathway.

Nitrate assimilation in plant shoots depends on photorespiration.

Photorespiration, a process that diminishes net photosynthesis by approximately 25% in most plants, has been viewed as the unfavorable consequence of plants having evolved when the atmosphere contained much higher levels of carbon dioxide than it does today. Here we used two independent methods to show that exposure of Arabidopsis and wheat shoots to conditions that inhibited photorespiration also strongly inhibited nitrate assimilation. Thus, nitrate assimilation in both dicotyledonous and monocotyledonous species depends on photorespiration. This previously undescribed role for photorespiration (i) explains several responses of plants to rising carbon dioxide concentrations, including the inability of many plants to sustain rapid growth under elevated levels of carbon dioxide; and (ii) raises concerns about genetic manipulations to diminish photorespiration in crops.

Growth of zooxanthellae in culture with two nitrogen sources

Physiological characteristics of zooxanthellae were examined under nutrient-saturated conditions created by mixing ammonium (15NH4) with nitrate (15NO3) to give 0.88 mM total nitrogen. Growth rate varied with the form of nitrogen provided. Ammonium alone resulted in the lowest C:N and C:chl-a ratios. Although zooxanthellae took up nitrate in the absence of ammonium, ammonium assimilation was 1.3 times higher than nitrate assimilation. Ammonium strongly inhibited nitrate assimilation. While high-ammonium treatments resulted in the highest 14C incorporation into intermediate compounds, high nitrate levels resulted in the highest 14C incorporation into protein, suggesting that the intermediate compounds are produced prior to the subsequent production of protein when ammonium is the dominant N source. The enhanced production of intermediate compounds at the expense of carbon directed to protein synthesis in the presence of ammonium might be analogous to the “host factor” observed in zooxanthellae–host symbioses, since growth rate is depressed due to low production of protein.

Sink‐stimulated photosynthesis and sink‐dependent increase in nitrate uptake: nitrogen and carbon relations of the parasitic association Cuscuta reflexa–Ricinus communis

ABSTRACT Ricinus communis L. was grown under limiting N supply in quartz sand culture, fed with 0.2, 1 or 5 mol m−3 NO3−, or in liquid culture with 0.022, 0.05 or 0.5 mol m−3 NO3−. Some of the plants were infected with Cuscuta reflexa Roxb. As occurred for the host, dry matter production and growth of C. reflexa were severely depressed with decreasing N supply to the host. When parasitized by C. reflexa, the shoot and root dry weight of Ricinus was diminished at all levels of N nutrition, but the total dry weight of host plus parasite was almost the same as that of uninfected Ricinus. In contrast to the situation in Lupinus albus (Jeschke et al. 1994b), infection by Cuscuta resulted in increased tissue N levels in the host and the N content of the system Ricinus plus C. reflexa was the same or even somewhat larger than that of uninfected plants. This indicated a sink‐dependent stimulation of nitrate uptake. As a result of decreased root weights, nitrate uptake g−1 FW was stimulated by 80, 60 or only 40% at 0.2, 1 or 5 mol m−3 nitrate supply. Increased nitrate uptake was reflected, particularly at low N supply, in xylem transport; xylem sap nitrate concentrations were substantially elevated, while those of amino acids were decreased in parasitized plants. This indicated an inhibition of nitrate assimilation in roots of parasitized plants under limiting N supply. Besides these effects on N relations, C. reflexa induced a substantial sink‐dependent stimulation of net photosynthesis in host leaves and a concomitant increase in stomatal opening and transpiration. This stimulation depended on the relative sink size induced by Cuscuta, on nitrogen nutrition and on leaf age, indicating that delayed senescence of leaves contributes to the overall effects of Cuscuta on its host. The Cuscuta‐induced inhibition of nitrate assimilation in the roots and the increase in nitrate uptake suggest that nitrate reduction was shifted towards the leaves in the presence of C. reflexa. The stimulating effects of C. reflexa in the Ricinus‐Cuscuta association are compared with the strongly inhibitory effects occurring in the tripartite association L. albus–Rhizobium–Cuscuta reflexa.

Energy-dependence of the Assimilatory Nitrate Uptake in Azorhizobium caulinodans Strain IRBG 46

Nitrate assimilation by suspensions of Azorhizobium caulinodans strain IRBG 46, as determined by disappearance of nitrate ions from the external medium, displayed the requirement of readily utilizable carbon source. Nitrate uptake was blocked by the uncouplers of oxidative phosphorylation such as 2,4-dinitrophenol, carbonyl cyanide m-chlorophenyl hydrazone and by an inhibitor of ATPase, N, N — dicyclohexyl carbodiimide. The inhibition of nitrate assimilation in the absence of appropriate carbon source was not overcome by the non-physiological terminal electron donor ascorbate plus N-methyl phenazinium methyl sulphate, a substrate combination that allows electron transfer to O2 without the synthesis of ATP. These data suggest that transport of nitrate into the cell is directly dependent on ATP.

Energy-dependence of the Assimilatory Nitrate Uptake in Azotobacter chroococcum

Nitrate assimilation by suspensions of Azotobacter chroococcum, as determined by the disappearance of the ion from the external medium, displayed saturation kinetics, was inhibited by nitrite, and exhibited an affinity for nitrate higher than that of nitrate reductase. This suggests that the entry of nitrate into the cell is mediated by a specific transporter. Nitrate assimilation required a readily utilizable carbon source and aerobic conditions and was blocked by the uncouplers carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) and 2,4-dinitrophenol (DNP) but not by N, N'-dicyclohexylcarbodiimide (DCCD), an inhibitor of ATPases. The inhibition of nitrate assimilation in the absence of an appropriate carbon source was overcome by the non-physiological energy source ascorbate plus N-methylphenazinium methylsulphate (PMS), a substrate combination that allowed respiration. Though an ATP-dependent nitrate uptake mechanism cannot be ruled out, these data suggest that transport of nitrate into the cell is directly dependent on the proton electrochemical gradient across the cytoplasmic membrane.

Nitrate assimilation in Candida nitratophila and other yeasts

Nitrate assimilation has been studied in four species of yeasts; Candida nitratophila, Candida utilis, Hansenula anomala and Rhodotorula glutinis. Ammonium-grown cultures of these organisms did not assimilate nitrate but acquired the capacity to do so after a 3 h period of nitrogenstarvation. Ammonium inhibited nitrate assimilation completely in nitrate-grown cultures of R. glutinis. With Candida spp. ammonium and nitrate were assimilated simultaneously but each was assimilated at a lower rate than when either was supplied alone. Nitrogen-starved cultures of C. nitratophila contained enough nitrate reductase activity to sustain high rates of nitrate assimilation. Results indicate that the high levels of nitrate reductase in nitrate-grown cultures of C. nitratophila do not limit nitrate assimilation. Nitrate assimilation appears to be limited by nitrate uptake and/or the supply of reducing equivalents for nitrate reduction in these cultures.

Nitrate Assimilation in the Basidiomycete Yeast Sporobolomyces roseus

Summary: Ammonium-grown cultures of Sporobolomyces roseus developed the capacity to assimilate nitrate when they were incubated in nitrate or nitrogen-free medium. Cycloheximide, 6-methyl purine and antimycin A inhibited this process. Nitrate assimilation required aerobic energy metabolism and was inhibited completely by ammonium. The rapid inhibition of nitrate assimilation by ammonium was not the result of an inhibition of nitrate reductase (NR) activity. Nitrite also inhibited nitrate assimilation. NR in cell-free extracts of S. roseus was NADPH-specific and its activity was repressed in cultures containing ammonium and derepressed during nitrogen starvation. Nitrate stimulated the appearance of NR in these cultures. Nitrate assimilation was not limited by apparent (potential) NR activity.

Inhibition of Nitrate Assimilation in Roots in the Presence of Ammonium: The Moderating Influence of Potassium

Experiments were conducted to investigate the effect of concentration of NH4+ in nutrient solution on root assimilation of NO3− and to determine whether the NH4+NO3− interaction was modified in the presence of K+. Dark-grown, detopped corn seedlings (cv. Pioneer 3369A) were exposed for 8 h to 0.15 mM Ca(NO3)2 and varying concentrations of (NH4)2SO4 in the absence or presence of 0.15 mM K2SO4. The accelerated phase of NO3− uptake appeared most sensitive to restriction by additions of 0.15 mM (NH4)2SO4. In the absence of K+, the restriction increased only slightly even when solution (NH4)2SO4, was increased from 0.15 mM to 12.5 mM which was accompanied by an increase of NH4+ in the tissue from about 7.0 to 35 μmol g−1 fr. wt. of root. Increasing concentrations of solution NH4+ progressively inhibited net K+ uptake. At the highest solution NH4+ concentrations, there was an initial net efflux of K+ and no net influx occurred during the treatment period. The severity of the NH4)SO4 restriction of NO3− uptake was moderated considerably in the presence of K+ as long as a net influx of K+ occurred. However, net influx of K+ was not associated with alteration of NH4+ uptake, assimilation, or accumulation in the root tissue. The lack of correlation between the severity of restriction of NO3− uptake and endogenous NHJ suggested the restriction resulted from an effect exerted by exogenous NH4+ which tended to saturate at lower solution NHJ concentrations or by inhibitory factors generated during assimilation of NH4+. Several mechanisms were postulated to account for the moderating influence of K+. In all experiments, root NO3− reduction was restricted by the presence of ambient NH4+. The quantitative decreases in reduction tended to be less than decreases in NO3− uptake and therefore, could result from inhibition solely of uptake with subsequent limitation in availability of substrate for the reduction process, but the possibility of a direct effect on reduction could not be excluded.

Assimilatory nitrate uptake in Pseudomonas fluorescens studied using nitrogen-13.

The mechanism of nitrate uptake for assimilation in procaryotes is not known. We used the radioactive isotope, 13N as NO3-, to study this process in a prevalent soil bacterium, Pseudomonas fluorescens. Cultures grown on ammonium sulfate or ammonium nitrate failed to take up labeled nitrate, indicating ammonium repressed synthesis of the assimilatory enzymes. Cultures grown on nitrite or under ammonium limitation had measurable nitrate reductase activity, indicating that the assimilatory enzymes need not be induced by nitrate. In cultures with an active nitrate reductase, the form of 13N internally was ammonium and amino acids; the amino acid labeling pattern indicated that 13NO3- was assimilated via glutamine synthetase and glutamate synthase. Cultures grown on tungstate to inactivate the reductase concentrated NO3- at least sixfold. Chlorate had no effect on nitrate transport or assimilation, nor on reduction in cell-free extracts. Ammonium inhibited nitrate uptake in cells with and without active nitrate reductases, but had no effect on cell-free nitrate reduction, indicating the site of inhibition was nitrate transport into the cytoplasm. Nitrate assimilation in cells grown on nitrate and nitrate uptake into cells grown with tungstate on nitrite both followed Michaelis-Menten kinetics with similar Km values, 7 muM. Both azide and cyanide inhibited nitrate assimilation. Our findings suggest that Pseudomonas fluorescens can take up nitrate via active transport and that nitrate assimilation is both inhibited and repressed by ammonium.

Aerobic inhibition of nitrate assimilation in Escherichia coli.

Growth of Escherichia coli, strain K-10, in synthetic medium with nitrate as a sole source of nitrogen was not found under aerobic conditions, but found in the medium under anaerobic conditions as well as in synthetic medium with ammonium or nitrite under both aerobic and anaerobic conditions. The presence of nitrate reductase activity in cells indicates that the growth inhibition is due to the inhibition of the enzyme by oxygen and not due to its absence. Conditions of preculture, inoculation size, pH, and composition of the nitratesynthetic medium did not affect the inhibition. All the 37 strains of E. coli tested were grown in the nitrate medium only anaerobically, while 18 strains of Klebsiella-Aerobacter among 22 strains tested were grown in the nitrate medium both aerobically and anaerobically.

Inhibition of nitrate and nitrite reduction by 2,4-dinitrophenol in ankistrodesmus

As Kessler (1955, 1959) has shown, nitrite reduction by the green alga, Ankistrodesmus braunii is completely inhibited by 10-3 m 2,4-dinitrophenol. However, although nitrite accumulates in the medium when cultures are supplied with nitrate and dinitrophenol, the reduction of nitrate is not completely insensitive to the inhibitor. Direct measurements show that 2,4-dinitrophenol inhibits nitrate disappearance from the medium by 65–80%. The degree of inhibition increases when the initial nitrate concentration is decreased. It is suggested that inhibition of nitrate assimilation by dinitrophenol is due to inhibition of an active uptake of nitrate by the cells, and that at high nitrate concentrations, a dinitrophenol-insensitive uptake process increases in importance.

CELL DIVISION AND FAT ACCUMULATION IN NITZSCHIA SP. GROWN IN CONTINUOUSLY ILLUMINATED MASS CULTURES.

1. Cell division in Nitzschia sp. was found to be independent upon the nitrogen content of the cells. Rapid cell division as well as its cessation was observed in cells with either high or low nitrogen content. 2. Blocking of cellular division in cells with relatively high nitrogen content at the stationary phase of growth is attributed to the presence of an autotoxin. 3. This autotoxin inhibits nitrate assimilation without affecting carbon assimilation, as a result of which fats accumulate in the diatom cells. 4. Fat-containing cells which are incapable of cell division could restore their full capacity to divide and assimilate nitrate, when the old medium containing the autotoxin is substituted by a fresh nutrient one. During their recovery, these cells consume the accumulated fats.

The inhibition of nitrate assimilation by ammonium in chlorella

Abstract Chlorella vulgaris growing with ammonium nitrate as nitrogen source preferentially assimilates ammonium. Nitrate assimilation ceases completely when ammonium is added and recommences as soon as ammonium has disappeared. Ammonium does not inhibit nitrate reduction by cells unable to assimilate ammonium because they lack a carbon source. Thus the inhibition is not due to ammonium per se but is connected with its assimilation. The inhibition is not thought to result from competition for reduced pyridine nucleotide because nitrate reductase of Chlorella is specific for DPN while glutamic dehydrogenase is specific for TPN. Nitrite addition also inhibits nitrate assimilation completely but ammonium only partially inhibits nitrite assimilation.

The inhibition of nitrate assimilation by ammonium in chlorella

The inhibition of nitrate assimilation by ammonium in chlorella