Nitrogen Uptake by Wheat Seedlings,Interactive Effects of Four Nitrogen Sources: NO3?, NO2?, NH4+, and Urea

The net influx (uptake) rates of NO₃⁻, NH₄⁺, NO₂⁻, and urea into roots of wheat (Triticum aestivum cv Yecora Rojo) seedlings from complete nutrient solutions containing all four compounds were monitored simultaneously. Although urea uptake was too slow to monitor, its presence had major inhibitory effects on the uptake of each of the other compounds. Rates of NO₃⁻, NH₄⁺, and NO₂⁻ uptake depended in a complex fashion on the concentration of all four N compounds. Equations were developed which describe the uptake rates of each of the compounds, and of total N, as functions of concentrations of all N sources. Contour plots of the results show the interactions over the range of concentrations employed. The coefficients of these equations provide quantitative values for evaluating primary and interactive effects of each compound on N uptake.     

Comparative estimation of phylogenesis of Vietnam dairy cattle using the Serebrovski?, Hedrick and Rogers methods]

Starch gel electrophoresis has been used to study polymorphism of proteins of blood (Hb, Tf, Al) and milk (alpha S1-Cn, beta-Cn, beta-Lg) in animals of the Holstein-Friesian (n = 140), Leisindian (n = 32) breeds and their hybrids (F1, n = 34); F2, n = 37; F3, n = 31) reared in Vietnam. It has permitted comparatively studying phylogenesis of anew formed dairy cattle using the Serebrovski?+, Hedrick and Rogers methods. This comparative study has yielded similar results.     

Oxides of Nitrogen (NO· and NO2 –) as Cofactors of the Myeloperoxidase System

Myeloperoxidase is the main peroxisomal protein of neutrophils, monocytes, and a subpopulation of tissue macrophages; it plays the key role in protective and inflammatory responses of the organism. This role is mediated by various diffusible radicals formed during oxidative reactions catalyzed by the enzyme heme. Myeloperoxidase and nitric oxide synthase are stored in peroxisomes. Nitric oxide reacts with the heme of myeloperoxidase. Low nitric oxide concentrations increase peroxidase activity through reduction of Compound II to native myeloperoxidase. Conversely, high nitric oxide concentrations inhibit the catalytic activity of myeloperoxidase through formation of inactive nitrosyl–heme complexes. Such effect of nitric oxide on catalytic activity of myeloperoxidase has various consequences for infectious and local inflammatory processes. Another oxide of nitrogen, nitrite, is a good substrate for myeloperoxidase Compound I but slowly reacts with Compound II. Nitrogen dioxide is formed after nitrite oxidation by myeloperoxidase. Formation of nitrogen dioxide is another protective mechanism and nitration of microbial proteins by myeloperoxidase can represent an additional protective response of peroxisomes.     

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.     

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⁻.     

In vitro studies of interactions of NO· donor drugs with superoxide and hydroxyl radicals

Nitric oxide (NO·) is a free radical characterized by a high spontaneous chemical reactivity with many other molecules including the superoxide radical (O₂·^–). This complex interaction may generate a peroxynitrite anion (ONOO^–), which behaves as an important mediator of oxidative stress in many pathological states. In the present study, in vitro experiments were performed to assess directly the O₂·^– and hydroxyl (·OH) radical scavenging effects of various NO· donor drugs, i.e. sodium nitroprusside (SNP), sodium nitrite (NaNO₂), molsidomine and SIN 1, at pH 7.4, 7 or 6. Concentrations of NO· in the incubation medium containing the different NO· donor drugs were measured by the assay based on the reaction of Fe-N-methyl-D-glucamine dithiocarbamate (MGD) with NO· that yields a stable spin-adduct measured by electron paramagnetic resonance (EPR). O₂·^– and ·OH generation was characterized by EPR spin trapping techniques, using the spin trap 5,5-dimethyl-1-pyrroline-1-oxide (DMPO). These free radicals were generated from the enzymatic system xanthine-xanthine oxidase, in phosphate buffer adjusted at pH 7.4, 7 and 6. Under these experimental conditions, SNP exhibited the strongest superoxide scavenging properties, characterized by IC₅₀ values expressed in the µmolar range, which decreased at low pH. Addition of SNP (800 µM) to solution containing MGD and Fe²⁺ (5:1) at pH 7 4 produced a three line EPR spectrum which is identified to [(MGD)₂-Fe²⁺-NO]. In control experiments no EPR signal was observed. We obtained the same results with NaNO₂ and an augmentation of the spin-adduct level was noted with the prolongation of the incubation period. In return, molsidomine (2 mM) did not produce, in our conditions, a detectable production of NO·. NaNO₂ displayed a significant superoxide scavenging effect only at pH 6, whilst neither molsidomine nor SIN 1 had any effect. Therefore, the superoxide scavenging properties of SNP, NaNO₂, and molsidomine appeared to be closely related to their potential for NO· release, which partially depends on the pH conditions. The behaviour of SIN 1 is more complicated, the speed of oxygen diffusion probably acting as a limiting factor in NO· formation in our conditions. The production of NO· was detected in presence of SIN 1. The intensity of the complex is comparable with the signal founded with NaNO₂. By contrast, all molecules exhibited hydroxyl radical scavenging properties, highlighting the capacity of ·OH to react with a wide range of molecules. In conclusion, considering the poor chemical reactivity of O₂·^–, the NO· donor drugs/O₂·^– interactions suggest a special relationship between these two radical species, which, in certain pathological states, could lead to the generation of cytotoxic end-products with strong oxidizing properties.     

Synthesis of new bergenin derivatives as potent inhibitors of inflammatory mediators NO and TNF-α

Bergenin is an isocoumarin natural product which aides in fat loss, healthy weight maintenance, enhancing the lipolytic effects of norepinephrine, inhibiting the formation of interleukin 1α and cyclooxygenases-2. Here we describe the anti-inflammatory activity of new bergenin derivatives 1-15 in the respiratory burst assay. Bergenin was isolated from the crude extract of Mallotus philippenensis after repeated column chromatography and was then subjected to chemical derivatization. The structures of all compounds were elucidated by NMR and mass spectroscopic techniques. Compound 2 was also studied using single crystal X-ray diffraction. Compounds 4, (54.5±2.2%) 5 (47.5±0.5%) 5, and 15 (86.8±1.9%) showed significant (P≤0.005) NO inhibitory activities whereas 6, 7, 11, 12 and 13 displayed moderate inhibitory activities that ranges between 16% and 31%. Furthermore compounds 4 and 15, were discovered as significant (P≤0.005) TNF-α inhibitors with 98% and 96% inhibition, respectively, while compounds 3, 5, 7, 8, 11, and 12 showed low level of TNF-α inhibition (0.4-28%). Compounds 8, 13 and 15 exhibited moderate anti-inflammatory IC(50) activities with 212, 222, and 253 μM, respectively, compared to the standard anti-inflammatory drug indomethacin as well as the parent bergenin compound. No cytotoxic effects could be detected when the compounds were tested on 3T3 cells up to concentrations of 100 μM.     

Reaction of peroxynitrite with carbon dioxide: intermediates and determination of the yield of CO3 •– and NO2 •

CO2 catalyses the isomerization of the biological toxin ONOO- to NO3- via an intermediate, presumably ONOOCO2-, which has an absorption maximum near 650 nm. The reflection spectrum of solid NMe4+ ONOO- exposed to CO2 shows a similar band near 650 nm; this absorption decays over minutes. Stopped-flow experiments in which CO2 solutions were mixed with alkaline ONOO- solutions indicate the formation of at least one intermediate. The initial absorption at 302 nm is less than that of ONOO-, which indicates that reactions take place within the mixing time, and this absorption is dependent (but not linearly) on the ONOO- and CO2 concentrations. We found that reaction of peroxynitrite with carbon dioxide forms some trioxocarbonate(*1-) (CO3*-) and nitrogen dioxide (NO2*) radicals via homolysis of the O-O bond in ONOOCO2-. We determined the extent of radical formation by mixing peroxynitrite, carbon dioxide and nitrogen monoxide. The later reacts with CO3*- and NO2* radicals to form, effectively, three NO2- per homolysis; ONOOCO2- that does not undergo homolysis yields NO3- and CO2. Based on the NO3- and NO2- analyses, the extent of conversion to NO3- is 96 +/- 1% and that of homolysis is 3 +/- 1%, respectively, significantly less than that reported in the literature.     

Alteration in enrichment of NO 3 − and reduced-N in xylem exudate during and after extended plant exposure to15NO 3 −

Summary Distinctly different patterns of¹⁵N enrichment were observed in the nitrate and reduced-N fractions of xylem exudate from soybean plants during and after 5 to 6 days of exposure to¹⁵NO ₃ ^– . Within 1 d after changes in solution NO ₃ ^– label, more than 90% of the exudate NO ₃ ^– originated from the exogenous supply. Alterations in the enrichment of exudate reduced-N were much slower, however, and the enrichment reached only 40% even after 5 d of continuous exposure to¹⁵NO ₃ ^– . Taking into account possible reduction of endogenous NO ₃ ^– and delayed translocation of NO ₃ ^– reduction products, it was concluded that root reduction could have contributed only 30 to 42% of the reduced-N found in the exudate.     

Effects of NO 3 − -N on the growth and salinity tolerance of Tamarix laxa Willd

The influence of NO ₃ ^? -N on growth and osmotic adjustment was studied in Tamarix laxa Willd., a halophyte with salt glands on its twigs. Seedlings of T. laxa Willd. were exposed to 1 mM (control) or 300 mM NaCl, with 0.05, 1 or 10 mM NO ₃ ^? -N for 24 days. The relative growth rate of seedlings at 300 mM NaCl was lower than that of control plants at all NO ₃ ^? -N levels, but the concentrations of organic N and total N in the twigs did not differ between the two NaCl treatments. Increasing NO ₃ ^? supply under 300 mM NaCl improved the growth of T. laxa, indicating that NO ₃ ^? played positive roles in improving salt resistance of the plant. The twigs of T. laxa Willd. accumulated mainly inorganic ions, especially Na⁺ and Cl^?, to lower osmotic potential (Ψs): the contributions of Na⁺ and Cl^? to Ψs were estimated at 31% and 27% respectively, at the highest levels of supply of both NaCl and NO ₃ ^? -N. The estimated contribution of NO ₃ ^? -N to Ψs was as high as 20% in the twigs in these conditions, indicating that NO ₃ ^? was also involved in osmotic adjustment in the twigs. Furthermore, increases in tissue NO ₃ ^? were accompanied by decreases in tissue Cl^? and proline under 300 mM NaCl. The estimated contribution of proline to Ψs declined as with NO ₃ ^? -N supply increased from 1 to 10 mM, while the contributions of nitrate to Ψs were enhanced under 300 mM NaCl. This suggested that higher accumulation of nitrate in the vacuole alleviated the effects of salinity stress on the plant by balancing the osmotic potential. In conclusion, NO ₃ ^? -N played both nutritional and osmotic roles in T. laxa Willd. in saline conditions.     

Hg2+-induced leakage of electrolytes and inhibition of NO3 − utilization inNostoc calcicola

Summary The effect of mercury (Hg²⁺) in the absence and presence of methylmercury (CH₃Hg⁺), cadmium (Cd²⁺), copper (Cu²⁺), nickel (Ni²⁺) and calcium (Ca²⁺) on Nostoc calcicola Bréb. has been studied in terms of electrolyte leakage, NO₃ ^– uptake and in vivo nitrate reductase (NR) activity to discover any possible correlation among such parameters under Hg²⁺ stress. Leakage of electrolytes from Hg²⁺-treated cyanobacterial cells was directly proportional to Hg²⁺ concentrations and exposure time. In comparison to NO₃ ^– uptake, an about 60-fold slower rate of NR activity was observed in the untreated cultures, the former being five times more Hg²⁺-sensitive. A non-competitive synergistic interaction of Hg²⁺ with CH₃Hg⁺ or Cd²⁺ and antagonistic with that of Ni²⁺ or Ca²⁺ has been observed for both the processes of NO₃ ^– utilization. The antagonistic interaction of Cu²⁺ with Hg²⁺ in terms of NO₃ ^– uptake and synergistic with respect to NR activity, has been attributed to the dual bonding preference of Cu²⁺ for cellular ligands. These findings suggest that (a) a statistically significant correlation exists among such parameters; (b) Hg²⁺ predominantly attacks the cyanobacterial cell membrane; (c) Hg²⁺ inhibits NO₃ ^– utilization; (d) the presence of other cations increases or decreases the inhibitory actions of Hg²⁺.     

Effects of NO2 − or NO3 − supply on polyamine accumulation and ethylene production of wheat roots at acidic and neutral pH: implications for root growth

Exposure of plant tissues to nitrite ion or nitrite-derived NO at acidic pH results in the degradation of important macromolecules and may lead to the formation of reactive molecular species. Polyamines as free radical scavengers protect plant tissues against membrane and DNA damage during stress and may contribute to the acclimation processes caused by nitrite as an abiotic stressor at acidic pH. The putrescine content of wheat roots grown under low salt conditions increased only transiently at pH 7.0 when the nutrient solution was replaced by 1mM KNO₂, KNO₃, NaNO₂ or NaNO₃, but the concentration of this diamine remained high after a 24-hour incubation at pH 4.0. The acid stress-induced putrescine accumulation was further enhanced by an external N source, especially by nitrite. The contents of spermine and spermidine in the 24-hour samples were also higher in N-supplied roots at acidic pH. Polyamine contents were not closely correlated with the ethylene production by the intact roots. Nitrite treatment, however, significantly decreased the ethylene release from the root apex, but not from the basal parts at pH 4.0. The peroxidative capacities of the tissues in the soluble fractions were also inhibited by nitrite in the apical zones, which might modify the H₂O₂-coupled oxidative processes. Nitrite ion at acidic pH may react directly with guaiacol-like phenolic compounds and in this way interfere with the lignification process. The low ethylene release by the apical zones in acidic environment may be a symptom of the nitrite-induced inhibition of root extension.     

Role of cytokinin in enhanced productivity of maize supplied with NH4 + and NO3 −

Supplying both N forms (NH₄ ⁺+NO₃ ⁻) to the maize (Zea mays L.) plant can optimize productivity by enhancing reproductive development. However, the physiological factors responsible for this enhancement have not been elucidated, and may include the supply of cytokinin, a growth-regulating substance. Therefore, field and gravel hydroponic studies were conducted to examine the effect of N form (NH₄ ⁺+NO₃ ⁻ versus predominantly NO₃ ⁻) and exogenous cytokinin treatment (six foliar applications of 22 μM 6-benzylaminopurine (BAP) during vegetative growth versus untreated) on productivity and yield of maize. For untreated plants, NH₄ ⁺+NO₃ ⁻ nutrition increased grain yield by 11% and whole shoot N content by 6% compared with predominantly NO₃ ⁻. Cytokinin application to NO₃ ⁻-grown field plants increased grain yield to that of NH₄ ⁺+NO₃ ⁻-grown plants, which was the result of enhanced dry matter partitioning to the grain and decreased kernel abortion. Likewise, hydroponically grown maize supplied with NH₄ ⁺+NO₃ ⁻ doubled anthesis earshoot weight, and enhanced the partitioning of dry matter to the shoot. NH₄ ⁺+NO₃ ⁻ nutrition also increased earshoot N content by 200%, and whole shoot N accumulation by 25%. During vegetative growth, NH₄ ⁺+NO₃ ⁻ plants had higher concentrations of endogenous cytokinins zeatin and zeatin riboside in root tips than NO₃ ⁻-grown plants. Based on these data, we suggest that the enhanced earshoot and grain production of plants supplied with NH₄ ⁺+NO₃ ⁻ may be partly associated with an increased endogenous cytokinin supply.     

The kinetics of NH4 + and NO3 − uptake by Douglas fir from single N-solutions and from solutions containing both NH4 + and NO3 −

The kinetics of NH₄ ⁺ and NO₃ ⁻ uptake in young Douglas fir trees (Pseudotsuga menziesii [Mirb.] Franco) were studied in solutions, containing either one or both N species. Using solutions containing a single N species, the V_max of NH₄ ⁺ uptake was higher than that of NO₃ ⁻ uptake. The K_m of NH₄ ⁺ uptake and K_m of NO₃ ⁻ uptake differed not significantly. When both NH₄ ⁺ and NO₃ ⁻ were present, the V_max for NH₄ ⁺ uptake became slightly higher, and the K_m for NH₄ ⁺ uptake remained in the same order. Under these conditions the NO₃ ⁻ uptake was almost totally inhibited over the whole range of concentrations used (10–1000 μM total N). This inhibition by NH₄ ⁺ occurred during the first two hours after addition. ei]{gnA C}{fnBorstlap}