Impact of Bacterial NO3? Transport on Sediment Biogeochemistry

Experiments demonstrated that Beggiatoa could induce a H₂S-depleted suboxic zone of more than 10 mm in marine sediments and cause a divergence in sediment NO₃⁻ reduction from denitrification to dissimilatory NO₃⁻ reduction to ammonium. pH, O₂, and H₂S profiles indicated that the bacteria oxidized H₂S with NO₃⁻ and transported S⁰ to the sediment surface for aerobic oxidation.     

Inhibition of NO3? and NO2? Reduction by Microbial Fe(III) Reduction: Evidence of a Reaction between NO2? and Cell Surface-Bound Fe2+

A recent study (D. C. Cooper, F. W. Picardal, A. Schimmelmann, and A. J. Coby, Appl. Environ. Microbiol. 69:3517-3525, 2003) has shown that NO₃⁻ and NO₂⁻ (NO_x⁻) reduction by Shewanella putrefaciens 200 is inhibited in the presence of goethite. The hypothetical mechanism offered to explain this finding involved the formation of a Fe(III) (hydr)oxide coating on the cell via the surface-catalyzed, abiotic reaction between Fe²⁺ and NO₂⁻. This coating could then inhibit reduction of NO_x⁻ by physically blocking transport into the cell. Although the data in the previous study were consistent with such an explanation, the hypothesis was largely speculative. In the current work, this hypothesis was tested and its environmental significance explored through a number of experiments. The inhibition of ~3 mM NO₃⁻ reduction was observed during reduction of a variety of Fe(III) (hydr)oxides, including goethite, hematite, and an iron-bearing, natural sediment. Inhibition of oxygen and fumarate reduction was observed following treatment of cells with Fe²⁺ and NO₂⁻, demonstrating that utilization of other soluble electron acceptors could also be inhibited. Previous adsorption of Fe²⁺ onto Paracoccus denitrificans inhibited NO_x⁻ reduction, showing that Fe(II) can reduce rates of soluble electron acceptor utilization by non-iron-reducing bacteria. NO₂⁻ was chemically reduced to N₂O by goethite or cell-sorbed Fe²⁺, but not at appreciable rates by aqueous Fe²⁺. Transmission and scanning electron microscopy showed an electron-dense, Fe-enriched coating on cells treated with Fe²⁺ and NO₂⁻. The formation and effects of such coatings underscore the complexity of the biogeochemical reactions that occur in the subsurface.     

Short-term studies of NO 3 − uptake in Pisum using 13NO 3 −

Influx, efflux and net uptake of NO ₃ ^– was studied in Pisum sativum L. cv. Marma in short-term experiments where ¹³NO ₃ ^– was used to trace influx. The influx rate in N-limited plants was similar both during net uptake at external concentrations of around 50 M, and at low external NO ₃ ^– concentrations (4–6 M) when net uptake was practically zero. Efflux could be inferred from discrepancies between influx and net uptake but was never very high in the N-limited plants during net uptake. Close to the threshold concentration for not NO ₃ ^– uptake, efflux was high and equalled influx. Thus, the threshold concentration can be regarded as a NO ₃ ^– compensation point. The inclusion of NH ₄ ⁺ in the outer medium decreased influx by about 40% but did not significantly affect efflux. The roles of NO ₃ ^– fluxes and nitrate-reductase activity in regulating/limiting NO ₃ ^– utilization are discussed.Abbreviations DW dry weight - FW fresh weight - R_N relative nitrogen addition rate     

Is there NO help for leptin?

Since the initial identification of leptin as the product of the ob gene in 1994, the signaling pathways by which this hormone alters cell physiology have been the subject of extensive investigations. The fact that leptin can induce nitric oxide (NO) production was first demonstrated in studies of the pituitary gland and pancreatic islets. A large number of additional studies further showed that this adipokine stimulates NO synthesis in multiple tissues. This review article discusses the role of leptin in NO production and its pathophysiological consequences. The role of this gaseous messenger in cell physiology depends on the cell type, the concentration of NO and the duration of exposure. It can be either a potent oxidant or a protector of cell integrity against the formation of reactive oxygen species. Leptin plays two opposing roles on arterial pressure. It exerts a hypertensive effect due to sympathetic activation and a vasorelaxant effect due to NO production. This adipokine acts via NO to produce pro-inflammatory factors in cartilage pathology, potentially contributing to an increased risk for osteoarthritis. Another well-documented role of leptin-induced NO, acting either directly or via the hypothalamus, concerns lipid metabolism in muscle and adipose tissue. In adipocytes, the direct and rapid action of leptin is to activate the nitric oxide synthase III, which favors lipolysis. In contrast, in the long-term, leptin reduces lipolysis. However, both in the short-term and in the long-term, glyceroneogenesis and its key enzyme, the cytosolic phosphoenolpyruvatecarboxykinase (PEPCK-C), are down-regulated by the adipokine, thus favoring fatty acid release. Hence, leptin-induced NO production plays a crucial role in fatty acid metabolism in adipose tissue. The resulting effects are to prevent lipid storage and to improve energy expenditure, with possible improvements of the obese state and its associated diseases.     

Can erythrocytes release biologically active NO?

Under physiological conditions, endothelial cells and the endothelial nitric oxide (NO) synthase (eNOS) are the main source of NO in the cardiovascular system. However, several other cell types have also been implicated in the NO-dependent regulation of cell function, including erythrocytes. NO derived from red blood cells has been proposed to regulate erythrocyte membrane fluidity, inhibit platelet activation and induce vasodilation in hypoxic areas, but these proposals are highly controversial. In the current issue of Cell Communication and Signaling, an elegant study by Gambaryan et al., assayed NO production by erythrocytes by monitoring the activation of the platelet intracellular NO receptor, soluble guanylyl cyclase, and its downstream kinase protein kinase G. After systematically testing different combinations of erythrocyte/platelet suspensions, the authors found no evidence for platelet soluble guanylyl cyclase/protein kinase G activation by erythrocytes and conclude that erythrocytes do not release biologically active NO to inhibit platelet activation.     

Just say NO to muscle degeneration?

The devastating muscle degeneration characteristic of Duchenne muscular dystrophy is caused by mutations in the gene encoding dystrophin. The dystrophin complex has two functions: a structural role in maintaining sarcolemmal integrity during contraction and a scaffolding function that recruits signaling proteins such as neuronal nitric oxide synthase to the membrane. New studies indicate that transgenic restoration of nitric oxide (NO) production in the mdx dystrophic mouse improves muscle pathology. Although NO-mediated killing of inflammatory cells might be involved, other mechanisms are also possible. These results point to the therapeutic potential of manipulating the signaling activity of the dystophin complex as a way to ameliorate the progression of muscle degeneration.     

To NO or not to NO: 'where?' is the question

Nitric oxide (NO) is a gaseous radical with unique biological functions essential for the cardiovascular system, host defense and neuro-transmission. For two decades it was thought that NO was able to diffuse freely across relatively long distances and to traverse major parts of the cell, if not multiple cell layers. However, NO has been proven to be extremely reactive: it reacts with other reactive oxygen species, heavy metals, as well as with cysteine and tyrosine residues in proteins. In accordance, it is now widely accepted that once NO is generated, it is very short-lived and diffuses only over a short distance. This urges for the local production of NO and the localization of NO synthases in the proximity of their downstream targets. This review discusses the highly organized localization of NO synthases, with the endothelial isoform (eNOS) as its main focus, since from this synthase most is known about its subcellular localization and regulation.     

Nitrogen Utilization in Lemna: II. Studies of Nitrate Uptake Using 13NO3?

¹³N-labeled nitrate was used to trace short-term nitrate influx into Lemna gibba L. G3 in experiments where disappearance of both radioactivity and total nitrate from the incubation medium was measured continuously and simultaneously. In plants performing net nitrate uptake from an initial nitrate concentration of 40 to 60 micromolar, there was no discrepancy between net uptake and influx, irrespective of the N status of the plants, indicating that concomitant nitrate efflux was low or nil. Plants treated with tungstate to inactivate nitrate reductase were able to take up nitrate following induction of the uptake system by exposure to a low amount of nitrate. Also, in this case, net uptake was equivalent to influx. In tungstate-treated plants preloaded with nitrate, both net uptake and influx were nil. In contrast to these observations, a clear discrepancy between net uptake and influx was observed when the plants were incubated at an initial nitrate concentration of approximately 5 micromolar, where net uptake is low and eventually ceases. It is concluded that plasmalemma nitrate transport is essentially unidirectional in plants performing net uptake at a concentration of 40 to 60 micromolar, and that transport is nil when internal nitrate sinks (vacuole, metabolism) are eliminated. The efflux component becomes increasingly important when the external concentration approaches the threshold value for net nitrate uptake (the nitrate compensation point) where considerable exchange between internal and external nitrate occurs.     

NO3- and ClO3- fluxes in the chl1-5 mutant of Arabidopsis thaliana. Does the CHL1-5 gene encode a low-affinity NO3- transporter?

The CHL1 gene is considered to encode a low-affinity transport system (LATS) for NO3- in Arabidopsis thaliana (Y.-F. Tsay, J.I. Schroeder, K.A. Feldmann, N.M. Crawford [1993] Cell 72: 705-713). However, the anticipated reduced NO3- uptake by the LATS associated with loss of CHL1 gene activity in chl1-5 deletion mutants was evident only when plants were grown on NH4NO3. When KNO3 was the sole N source, NO3- accumulation and short-term tracer influx (using 13NO3- and 15NO3-) in leaves and roots of wild-type and mutant plants were essentially identical. Nevertheless, root uptake of 36CIO3- by the LATS and CIO3- accumulation in roots and shoots of mutant plants were significantly lower than in wild-type plants when grown on KNO3. One explanation for these results is that a second LATS is able to compensate for the chl1-5 deficiency in KNO3-grown plants. Growth on NH4NO3 may down-regulate the second LATS enough that the anticipated difference in NO3- uptake becomes apparent.     

Do bonobos say NO by shaking their head?

Head-shaking gestures are commonly used by African great apes to solicit activities such as play. Here, we report observations of head shaking in four bonobos apparently aimed at preventing the recipient from doing something. This may reflect a primitive precursor of the negatively connoted head-shaking behavior in humans. Further investigations are needed to clarify the preventive function of head shakes and their evolutionary role in the evolution of negation in humans.     

The NO way to increase muscular utrophin expression?

Duchenne muscular dystrophy (DMD), a severe X-linked recessive disorder that results in progressive muscle degeneration, is due to a lack of dystrophin, a membrane cytoskeletal protein. An approach to the search for a treatment is to compensate for dystrophin loss by utrophin, another cytoskeletal protein. During development, in normal as in dystrophic embryos, utrophin is found at the membrane surface of immature skeletal fibres and is progressively replaced by dystrophin. Thus, it is possible to consider utrophin as a 'foetal homologue' of dystrophin. In a previous work, we studied the effect of L-arginine, the substrate of nitric oxide synthetase (NOS), on utrophin expression at the muscle membrane. Using a novel antibody, we confirm here that the immunocytochemical staining was indeed due to an increase in utrophin at the sarcolemma. The result is observed not only on mdx (an animal model of DMD) myotubes in culture but also in mdx mice treated with L-arginine. In addition, we show here the utrophin increase in muscle extracts of mdx mice treated with L-arginine, after electrophoretic separation and western-blotting using this novel antibody, and thus extending the electrophoretic results previously obtained on myotube cultures to muscles of treated mice.     

Can irradiated tumors take NO for an answer?

In a recent issue of Molecular Cell, Li et al. (2007) reported that ionizing radiation stabilizes hypoxia-inducible factor 1alpha (HIF-1alpha) in normoxic tumor tissues through S-nitrosylation by nitric oxide (NO) generated from neighboring activated macrophages.     

Nitric oxide (NO) traffic in endothelial NO synthase. Evidence for a new NO binding site dependent on tetrahydrobiopterin?

Nitric oxide (NO) traffic within the reduced ferrous-nitrosyl complex of endothelial nitric-oxide synthase (eNOS) has been studied by ultrafast time-resolved absorption spectroscopy. In the presence of tetrahydrobiopterin, the rate of NO rebinding to the heme upon photodissociation depends on the NO concentration. The time scale of this process, picoseconds to nanoseconds, precludes a diffusion from the solution toward the protein medium, and altogether the data point at a new NO binding site within the protein. Comparison of the kinetics of pterin-bound and -depleted eNOS points out that the existence of this new site depends on the presence of tetrahydrobiopterin. The new non-heme site may act as a "doorstep" to the heme pocket and control NO escape from eNOS.     

Characteristics of Injury and Recovery of Net NO3? Transport of Barley Seedlings from Treatments of NaCl

The nature of the injury and recovery of nitrate uptake (net uptake) from NaCl stress in young barley (Hordeum vulgare L, var CM 72) seedlings was investigated. Nitrate uptake was inhibited rapidly by NaCl, within 1 minute after exposure to 200 millimolar NaCl. The duration of exposure to saline conditions determined the time of recovery of NO₃⁻ uptake from NaCl stress. Recovery was dependent on the presence of NO₃⁻ and was inhibited by cycloheximide, 6-methylpurine, and cerulenin, respective inhibitors of protein, RNA, and sterol/fatty acid synthesis. These inhibitors also prevented the induction of the NO₃⁻ uptake system in uninduced seedlings. Uninduced seedlings exhibited endogenous NO₃⁻ transport activity that appeared to be constitutive. This constitutive activity was also inhibited by NaCl. Recovery of constitutive NO₃⁻ uptake did not require the presence of NO₃⁻.     

Visualization of NO3?/NO2? Dynamics in Living Cells by Fluorescence Resonance Energy Transfer (FRET) Imaging Employing a Rhizobial Two-component Regulatory System

Nitrate (NO₃⁻) and nitrite (NO₂⁻) are the physiological sources of nitric oxide (NO), a key biological messenger molecule. NO₃⁻/NO₂⁻ exerts a beneficial impact on NO homeostasis and its related cardiovascular functions. To visualize the physiological dynamics of NO₃⁻/NO₂⁻ for assessing the precise roles of these anions, we developed a genetically encoded intermolecular fluorescence resonance energy transfer (FRET)-based indicator, named sNOOOpy (sensor for NO₃⁻/NO₂⁻ in physiology), by employing NO₃⁻/NO₂⁻-induced dissociation of NasST involved in the denitrification system of rhizobia. The in vitro use of sNOOOpy shows high specificity for NO₃⁻ and NO₂⁻, and its FRET signal is changed in response to NO₃⁻/NO₂⁻ in the micromolar range. Furthermore, both an increase and decrease in cellular NO₃⁻ concentration can be detected. sNOOOpy is very simple and potentially applicable to a wide variety of living cells and is expected to provide insights into NO₃⁻/NO₂⁻ dynamics in various organisms, including plants and animals.     

Nitric oxide: NO apoptosis or turning it ON?

Nitric oxide (NO) is known for its diverse activities throughout biology. Among signaling qualities, NO affects cellular decisions of life and death either by turning on apoptotic pathways or by shutting them off. Although copious reports support both notions, the dichotomy of NO actions remains unsolved. Proapoptotic pathways of NO are compatible with established signaling circuits appreciated for mitochondria-dependent roads of death, with some emphasis on the involvement of the tumor suppressor p53 as a target during cell death execution. Antiapoptotic actions of NO are numerous, ranging from an immediate interference with proapoptotic signaling cascades to long-lasting effects based on expression of cell protective proteins with some interest on the ability of NO-redox species to block caspases by S-nitrosylation/S-nitrosation. Summarizing emerging concepts to understand p53 accumulation on the one hand while proposing inhibition of procaspase processing on the other may help to define the pro- versus antiapoptotic roles of NO.     

外源γ-氨基丁酸对Ca(NO3)2胁迫下甜瓜幼苗NO3——N同化的影响

以盐敏感型甜瓜品种‘一品天下208’为试材,用80 mmol·L^-1 Ca(NO₃)₂模拟设施土壤盐渍化,采用深液流水培,研究外源 γ-氨基丁酸(GABA)对Ca(NO₃)₂胁迫下甜瓜幼苗硝态氮(NO₃^--N)同化的影响.结果表明: Ca(NO₃)₂胁迫显著降低了甜瓜幼苗体内硝酸还原酶(NR)、谷氨酰胺合酶(GS)和谷氨酸合酶(GOGAT)活性,增强了谷氨酸脱氢酶(GDH)、谷草转氨酶(GOT)和谷丙转氨酶(GPT)活性,导致铵态氮(NH₄⁺-N)和游离氨基酸含量增加,NO₃^--N和可溶性蛋白质含量下降,植株生长和光合作用受到严重抑制.Ca(NO₃)₂胁迫下,外源喷施GABA有效促进了甜瓜根系对NO₃^--N的吸收及其向地上部的转运,并通过增强NR、GS和GOGAT活性提高了甜瓜幼苗对NH₄⁺的同化力;通过抑制GDH脱氨作用减少了甜瓜幼苗体内NH₄⁺的释放量,从而缓解了盐诱导产生的NH₄⁺-N积累所造成的氨毒害作用;外源喷施GABA也能调节甜瓜组织中氨基酸代谢途径,促进蛋白质的合成.表明外源GABA能增强甜瓜幼苗对NO₃^--N的同化能力,调控氨基酸代谢,进而有效缓解Ca(NO₃)₂胁迫对甜瓜幼苗的盐伤害作用.     

Synthesis and characterization of [Pt(COD)Cl(NO3)] and [Pt(COD)(NO3)2] and the use of [Pt(COD)Clx(NO3)2−x] in the preparation of cis[Pt(PPh3)2Clx(NO3)2−x] (x=0, 1, 2) and [Pt(PPh3)3L](NO3) (L=Cl,NO3)

[Pt(COD)Cl₂] (COD=1,5-cyclooctadiene) is a versatile starting material for the synthesis of Pt(II) compounds. The preparations of the new compounds [Pt(COD)Cl(NO₃)], [Pt(COD)(NO₃)₂] and [Pt(PPh₃)₃(NO₃)](NO₃) and also of the known compounds cis[Pt(PPh₃)₂Cl₂], cis [Pt(PPh₃)₂Cl(NO₃)], cis[Pt(PPh₃)₂(NO₃)₂] and [Pt(PPh₃)₃Cl](NO₃)are reported. The compounds are characterized by elemental analysis, ³¹P{¹H} NMR spectroscopy and IR spectroscopy.