Regulation of Nitrate Assimilation and Nitrate Respiration in Aerobacter aerogenes

The influence of growth conditions on assimilatory and respiratory nitrate reduction in Aerobacter aerogenes was studied. The level of nitrate reductase activity in cells, growing in minimal medium with nitrate as the sole nitrogen source, was much lower under aerobic than anaerobic conditions. Further, the enzyme of the aerobic cultures was very sensitive to sonic disintegration, as distinct from the enzyme of anaerobic cultures. When a culture of A. aerogenes was shifted from anaerobic growth in minimal medium with nitrate and NH(4) (+) to aerobiosis in the same medium, but without NH(4) (+), the production of nitrite stopped instantaneously and the total activity of nitrate reductase decreased sharply. Moreover, there was a lag in growth of about 3 hr after such a shift. After resumption of growth, the total enzymatic activity increased again slowly and simultaneously became gradually sensitive to sonic disintegration. These findings show that oxygen inactivates the anaerobic nitrate reductase and represses its further formation; only after a de novo synthesis of nitrate reductase with an assimilatory function will growth be resumed. The enzyme in aerobic cultures was not significantly inactivated by air, only by pure oxygen. The formation of the assimilatory enzyme complex was repressed, however, by NH(4) (+), under both aerobic and anaerobic conditions. The results indicate that the formation of the assimilatory enzyme complex and that of the respiratory enzyme complex are regulated differently. We suggest that both complexes have a different composition, but that the nitrate reductase in both cases is the same protein.     

UV-A Inhibition of Alternative Respiration in Pea Leaves and a Unicellular Green Alga Chlamydomonas reinhardtii

Total respiration (v_T) increased after exposure to UV, but a decrease in the capacity of SHAM-sensitive-alternative respiration (V_alt) was accompanied by an increase in residual respiration (v_res). The capacity for CN sensitive-cytochrome c respiration (V_cyt) was not inhibited by UV-A. After 4 h of irradiation of high-CO₂-grown cells of Chlamydomonas reinhardtii with UV-A (2 μW. CM^?2) in the presence of white light (300μE.m^?2.s^?1), the capacity of Vast was reduced from 10 to 4 μmol O₂. mg^?1Chl.h^?1, a 60 % reduction. After a similar exposure to UV-A, the capacity of V_alt in pea leaves was reduced from 13 to 5 μmol O₂.g^?1 fr wt.h^?1. Exposure to UV-C was not inhibitory, but UV-B caused up to 25% inhibition of the V^alt. Twenty to 48 h after exposure to UV-A radiation, the capacity of alternative respiration had recovered. UV-A inhibition of the alternative respiration was consistent with UV-A absorption by quinones, except that UV-A did not inhibit the cyt c pathway of electron transport that also involves the ubiquinones.     

Role of Menaquinone in Nitrate Respiration in Staphylococcus aureus

Two menaquinone-deficient and one aromatic-deficient mutants of Staphylococcus aureus were unable to reduce nitrate to nitrite. Reinitiation of menaquinone synthesis in the aromatic-deficient mutant by growing it with shikimic acid restored its nitrate respiratory activity. The results clearly demonstrate a role for menaquinone in nitrate respiration in Staphylococcus aureus.     

铵态氮和硝态氮营养与大豆幼苗的抗氰呼吸作用

在植物体内,NO云还原成NHI是一个耗能很多的生化过程,每还原一个NO。大约要消耗15个ATP分子（Salsac等1987）。植物直接吸收和利用NHi＋,可以减少能量消耗,所节约的能量可用于植物的生长。因此,从理论上讲,供NHI的植株要比供NOt的植株能够获得更高的生物产量。然而,对于大多数植物,供NOS的植株常具有更大的生长量和产量。对于这种现象,过去人们一直在矿物质和有机物积累的差异（Robin和Salsac1985）、根际的酸化程度（Ruftv等1983,Tolley－Henry和Rapen1986）、NHt有害浓度的积累（Haynes和Goh1978）、对光合作用的…     

Influence of Oxygen on Development of Nitrate Respiration in Bacillus stearothermophilus

A denitrifying mutant of Bacillus stearothermophilus NCA 2184, strain 2184-D, was used to explore the development of nitrate respiration in relation to oxygen respiration. Aerobically grown wild-type cultures could acquire the ability to use nitrate as a result of selection of nitrate-respiring mutants by the presence of nitrate and a reduced oxygen tension. Fluctuation analysis has revealed that the frequency of occurrence of the nitrate-respiring mutant is about 7.5 x 10(-8) per bacterium per generation. Nitrate reductase and nitrite reductase appeared to be induced sequentially in strain 2184-D by the addition of nitrate. The formation of both of these enzymes was repressed by oxygen so that cells grown aerobically with nitrate possessed a low basal level of nitrate reducatase and exhibited no denitrification. The rate of synthesis of nitrate reductase increased quickly after addition of nitrate and removal of oxygen. It then declined to a lower steady-state level. Cells grown anaerobically with nitrate retained approximately 30 to 40% of the respiratory activity of aerobically grown cells. Aeration of anaerobically grown cells in the presence of amino acids increased the respiratory activity to normal aerobic levels. This aeration promoted rapid degradation of the existing nitrate reductase with or without the added amino acids.     

Inhibition of Respiration in Prototheca zopfii by Light

Irradiation of cells of Prototheca zopfii with blue light inhibited the respiratory capacity of the cells. The inhibition of respiration was correlated with a photodestruction of cytochrome c(551), cytochrome b(559), and cytochrome a₃. Cytochrome c(549), cytochrome b(555), and cytochrome b(564) were unaffected by the irradiation treatment. The α-band of reduced cytochrome a was shifted from 599 to 603 nm by irradiation, an effect similar to that observed when methanol was added to nonirradiated cells. The presence of oxygen was required during irradiation for both photoinhibition of respiration and photodestruction of the cytochromes. Cytochrome a₃ was protected against photodestruction by cyanide. Photodestruction of these same cytochromes also occurred when washed mitochondria of P. zopfii were irradiated.     

Trichlorfon-Induced Inhibition of Nitrate and Ammonium Uptake in Cyanobacteria

The possibility that the primary effect of the toxic insecticidetrichlorfon is an inhibition of nitrate uptake in cyanobactenahas been investigated. A drastic reduction in the rate of uptakeis detected 3 h after the addition of the insecticide to batchcultures of nabaena PCC 7119. The dose-response curves indicatea relationship between the degree of inhibition of nitrate uptakeand the reduction of chlorophyll content and growth. Nitratereductase (ferredoxin : nitrate reductase, EC 1.7.99.4 [EC] ) activityis also lowered as a result of insecticide action. When AnabaenaPCC 7119 cells are grown with ammonium as a source of combinednitrogen, trichlorfon reduces the rate of ammonium uptake. Therate of uptake of both nitrate and ammonium is restored uponwashing the cells. Ultrastructural analysis of Anabaena nitrate-growncells shows that trichlorfon does not damage thylakoid membranes,but brings about the accumulation of enlarged cyanophycin granulesand the increase of carboxysome number. Nitrate uptake rateand chlorophyll and phycobiliprotein contents are also reducedby insecticide treatment in the cyanobacteria SynechococcusUAM 211, GloeothecePCC 6501, Plectonema calothricoides, NostocUAM 205 and Chlorogloeopsis PCC 6912. These results are consistentwith the inhibition of nitrate uptake due to weak adsorptionof trichlorfon to the plasmalemma being the main effect of theinsecticide on cyanobacterial metabolism. Key words: Nitrate uptake, cyanobacteria, Anabaena, ammonium uptake, trichlorfon     

Light-stimulated Absorption of Nitrate by Wolffia arrhiza

The 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.     

Dopamine Neurotoxicity: Inhibition of Mitochondrial Respiration

Abstract: Dopamine, due to metabolism by monoamine oxidase or autoxidation, can generate toxic products such as hydrogen peroxide, oxygen-derived radicals, semiquinones, and quinones and thus exert its neurotoxic effects. Intracerebroventricular injection of dopamine into rats pretreated with the monoamine oxidase nonselective inhibitor pargyline caused mortality in a dose-dependent manner with LD₅₀ = 90 µg. Norepinephrine was less effective with LD₅₀ = 141 µg. The iron chelator desferrioxamine completely protected against dopamine-induced mortality. In the absence of pargyline more rats survived, indicating that the products of dopamine enzymatic metabolism are not the main contributors to dopamine-induced toxicity. Biochemical analysis of frontal cortex and striatum from rats that received a lethal dose of dopamine did not show any difference from control rats in lipid and protein peroxidation and glutathione reductase and peroxidase activities. Moreover, dopamine significantly reduced the formation of iron-induced malondialdehyde in vitro, thus suggesting that earlier events in cell damage are involved in dopamine toxicity. Indeed, dopamine inhibited mitochondrial NADH dehydrogenase activity with IC₅₀ = 8 µ M , and that of norepinephrine was twice as much (IC₅₀ = 15 µ M ). Dopamine-induced inhibition of NADH dehydrogenase activity was only partially reversed by desferrioxamine, which had no effect on norepinephrine-induced inhibition. These results suggest that catecholamines can cause toxicity not only by inducing an oxidative stress state but also possibly through direct interaction with the mitochondrial electron transport system. The latter was further supported by the ability of ADP to reverse dopamine-induced inhibition of NADH dehydrogenase activity in a dose-dependent manner.     

Nitrate Absorption by Barley: II. Influence of Nitrate Reductase Activity

The influence of protein synthesis and nitrate reductase activity on nitrate absorption by barley (Hordeum vulgare L.) was investigated. Cycloheximide decreased nitrate absorption. Pretreatment studies showed that cycloheximide affects either energy transfer or nitrate reductase activity or both.     

Inhibition of Nitrate Transporter 1.1-Controlled Nitrate Uptake Reduces Cadmium Uptake in Arabidopsis

Identification of mechanisms that decrease cadmium accumulation in plants is a prerequisite for minimizing dietary uptake of cadmium from contaminated crops. Here, we show that cadmium inhibits nitrate transporter 1.1 (NRT1.1)-mediated nitrate (NO₃⁻) uptake in Arabidopsis (Arabidopsis thaliana) and impairs NO₃⁻ homeostasis in roots. In NO₃⁻-containing medium, loss of NRT1.1 function in nrt1.1 mutants leads to decreased levels of cadmium and several other metals in both roots and shoots and results in better biomass production in the presence of cadmium, whereas in NO₃⁻-free medium, no difference is seen between nrt1.1 mutants and wild-type plants. These results suggest that inhibition of NRT1.1 activity reduces cadmium uptake, thus enhancing cadmium tolerance in an NO₃⁻ uptake-dependent manner. Furthermore, using a treatment rotation system allowing synchronous uptake of NO₃⁻ and nutrient cations and asynchronous uptake of cadmium, the nrt1.1 mutants had similar cadmium levels to wild-type plants but lower levels of nutrient metals, whereas the opposite effect was seen using treatment rotation allowing synchronous uptake of NO₃⁻ and cadmium and asynchronous uptake of nutrient cations. We conclude that, although inhibition of NRT1.1-mediated NO₃⁻ uptake by cadmium might have negative effects on nitrogen nutrition in plants, it has a positive effect on cadmium detoxification by reducing cadmium entry into roots. NRT1.1 may regulate the uptake of cadmium and other cations by a common mechanism.Cadmium is highly toxic to humans (Nicholson et al., 1983), and its primary route of entry into the body is through crops grown in cadmium-contaminated soil (Clemens et al., 2013). A recent survey indicated that vegetables and rice (Oryza sativa) account for approximately 40% and 38%, respectively, of total cadmium exposure in residents of Shanghai, China’s largest city (He et al., 2013). However, cadmium contamination of agricultural soils as a result of rapid industrial development and release of agrochemicals into the environment is an increasingly serious problem. Many strategies have been proposed for remediating cadmium-contaminated soil to prevent cadmium uptake by crops. These strategies include the dig-and-dump method or encapsulation of the contaminated soil, chemical immobilization or extraction of cadmium, and phytoremediation by cadmium-hyperaccumulating plants (Pulford and Watson, 2003). However, the dig-and-dump and chemical methods are expensive, whereas phytoremediation requires several growing seasons to be effective, making it impractical in regions where farmland is limited and food supply insufficient.The shortfalls of these strategies have prompted researchers to develop alternative techniques that are cost-effective and interfere less with crop production. Use of nitrogen fertilizers is one of the most important agronomic practices and it has been suggested that their appropriate use might provide a relatively inexpensive, time-saving, and effective strategy for reducing cadmium entry into, and accumulation in, crops because NO₃⁻ facilitates cadmium uptake in hydroponically grown plants (Sarwar et al., 2010; Luo et al., 2012). However, in a preliminary study, we found that, in plants grown in soil, the effect of the nitrogen form on cadmium accumulation was strongly associated with the pH-buffering capacity of the soil. In soil with a lower pH-buffering capacity, application of ammonium (NH₄⁺) resulted in higher cadmium levels in plants than application of NO₃⁻, probably as a result of soil acidification by NH₄⁺, and the opposite effect was seen when plants were grown in soil with higher pH-buffering capacity (S.K. Fan, S.T. Du, and C.W. Jin, unpublished data). This suggests that management of the use of nitrogen fertilizers to prevent cadmium entry into crops might be difficult because of the wide variation in soil pH-buffering capacity.Because NO₃⁻ facilitates cadmium uptake in hydroponically grown plants as described above, modification of NO₃⁻ uptake pathways in plants might also affect cadmium uptake, in which case modifying these pathways to reduce cadmium entry into crops could circumvent the risks and the difficulties involved in nitrogen fertilizer management. Exposure to cadmium has been shown to reduce NO₃⁻ uptake by roots (Hernández et al., 1997; Gouia et al., 2000; Rizzardo et al., 2012), but this has been assumed to be deleterious to plant growth (Finkemeier et al., 2003; Rizzardo et al., 2012). The process by which NO₃⁻ is taken up across the root plasma membrane is complex, and several nitrate transporters (NRTs) involved in NO₃⁻ uptake from the growth medium have been characterized. In Arabidopsis (Arabidopsis thaliana), NRT1.1 is a dual-affinity transporter involved in both high- and low-affinity uptake, NRT1.2 is involved only in low-affinity NO₃⁻ uptake, whereas NRT2.1, NRT2.2, and NRT2.4 are only involved in high-affinity NO₃⁻ uptake (Wang et al., 2012; Léran et al., 2014). However, the transporter responsible for the cadmium-induced decrease in NO₃⁻ uptake remains unknown. Given the presumed association between NO₃⁻ uptake and cadmium uptake, it is important to identify the molecular mechanism involved in this process, and it is particularly important to determine whether the modulation of relevant NO₃⁻ transporters affects cadmium entry into plants.In this study, we investigated the relationship between NO₃⁻ uptake and cadmium uptake in Arabidopsis roots. To our knowledge, our results reveal a new mechanism for resisting cadmium toxicity: Cadmium reduces NO₃⁻ uptake by inhibiting NRT1.1 activity, which in turn reduces cadmium entry into root cells. As a result, cadmium levels in plants are lower and plant growth is improved. Our findings may provide a strategy for minimizing cadmium accumulation in crops grown in contaminated soil using biotechnological pathways to decrease NO₃⁻ uptake.     

Inhibition of the Development of Induced Respiration and Cyanide-insensitive Respiration in Potato Tuber Slices by Cerulenin and Dimethylaminoethanol

The interdependence of the development of wound-induced respiration and membrane-related phospholipid biosynthesis in potato tuber (Solanum tuberosum var. Russet) slices was established by the use of agents which selectively affect lipid and phospholipid synthesis. Cerulenin, a specific inhibitor of de novo fatty acid synthesis, inhibited the ultimate development of wound-induced respiration and of cyanide resistance only when given in the critical first 10 to 12 hours of slice aging. Similarly, when slices were exposed to the choline analogue dimethylaminoethanol within the first 10 hours, the phospholipid composition of the membrane lipids was drastically altered, the wound-induced respiration in a 24-hr period was substantially curtailed, and the development of cyanide insensitivity was sharply inhibited. These observations indicate that time-restricted membrane-related phospholipid synthesis is prerequisite to the development of wound-induced respiration and concurrent cyanide insensitivity.     

Inhibition of Respiration in Protoplasts from Meristematic Tissues3

Owen, J. H., Hetherington, A. M. and Wellburn, A. R. 1986. Inhibitionof respiration in protoplasts from meristematic tissues by abscisicacid in the presence of calcium ions.—J. exp. Bot. 38:498–505. A study was made of the influences of abscisic acid (ABA) andcalcium ions on mitochondrial respiration in protoplasts fromcells close to the basal intercalary meristem of light-grownbarley (Hordeum vulgare L. cv. Patty) seedlings. This respirationwas inhibited by ABA only when calcium ions were present. Thecalcium channel agonist BAY K8644 caused a significant inhibitionof protoplast dark respiration, similar to that observed usingABA and calcium, presumably because it imitated the action ofABA by increasing calcium influx into protoplasts. These resultssuggest that ABA increases the permeability of the plasmamembraneto calcium and that calcium acts as a second messenger to regulatemitochondrial respiratory activity and thus the very early eventsassociated with plastid and meristematic cell development. Key words: Abscisic acid, calcium, meristematic respiration     

Evidence for Iron-Dependent Nitrate Respiration in the Dissimilatory Iron-Reducing Bacterium Geobacter metallireducens

The dissimilatory iron-reducing bacterium Geobacter metallireducens was found to require iron at a concentration in excess of 50 μM for continuous cultivation on nitrate. Growth yield (~3-fold), cytochrome c content (~7-fold), and nitrate (~4.5-fold) and nitrite (~70-fold) reductase activities were all increased significantly when the growth medium was amended with 500 μM iron.