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.     

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}     

The solid state chemistry of uranium. Part I: The thermal decomposition of U(NO3)4·2tdpo and U(NO3)4·2tppo

The thermal decomposition of U(NO₃)₄·2tdpo (tdpo=tris-(dimethylamino)phosphine oxide) and U(NO₃)₄·2tppo (tppo=triphenyl phosphine oxide have been examined using thermogravimetry and differential scanning calorimetry. Decomposition of the crystals approximates to the general reaction U(NO₃)₄·2L(s) → UO₂(NO₃)₂·2L(s) + gases The general thermal behaviour of the two compounds were found to be different.     

α-Tocopherol Application Modulates the Response of Wheat (Triticum aestivum L.) Seedlings to Elevated Temperatures by Mitigation of Stress Injury and Enhancement of Antioxidants

Wheat seedlings (4 days old) were subjected to varying temperatures of 25, 30, and 35 °C for 7 days in a growth chamber under hydroponic conditions in the absence or presence of α-tocopherol (5 μM). The growth of shoots and roots was inhibited severely at 35 °C. The endogenous α-tocopherol increased in the shoots at 30 °C over the controls but decreased significantly at 35 °C over the previous temperature. The exogenous application of α-tocopherol elevated the endogenous levels in the heat-stressed plants, which were consequently able to maintain significantly greater growth associated with reduction in damage to membranes, cellular oxidizing ability, chlorophyll content, and photochemical efficiency in shoots. The relative leaf water content and stomatal conductance were not affected significantly with the application of tocopherol. The oxidative stress induced by high temperature (35 °C) in terms of malondialdehyde and hydrogen peroxide contents was significantly lower in the presence of α-tocopherol. The enzymatic antioxidants such as superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase showed considerable reduction in their activities at 35 °C compared to those at 30 °C, with greater effects on APX and GR. The nonenzymatic antioxidants like ascorbate, glutathione, and proline increased at 30 °C but decreased appreciably at 35 °C, suggesting impairment in their synthesis at stressful temperatures. α-Tocopherol-treated plants, especially those growing at 35 °C, had improved levels of enzymatic and nonenzymatic antioxidants. These observations provided evidence about the involvement of α-tocopherol in governing heat sensitivity in wheat and suggested manipulation of its endogenous levels to induce heat tolerance in this crop.     

The Effect of Rye Chromosomes on Callus Induction and Regeneration in Callus Cultures of Immature Embryos of Wheat–Rye Substitution Lines,Triticum aestivum L. Cultivar Saratovskaya 29–Secale cereale L. Cultivar Onokhoiskaya

The effect of individual rye chromosomes on the induction of callus and the character of its regenerating capacity was studied with cultured immature embryos of wheat–rye (Triticum aestivum L. cv. Saratovskaya 29–Secale cereale L. cv. Onokhoiskaya) substitution lines. The genotypic diversity of the substitution lines proved to significantly affect variation of parameters characterizing the major types of callus cultures, that is, frequencies of embryogenic calli, which are capable of shoot regeneration, and of morphogenic calli, which produce root structures. Functioning in the genotypic background of common wheat cultivar Saratovskaya 29, chromosomes 2R and 3R of rye cultivar Onokhoiskaya stimulated significantly the induction of embryogenic callus highly capable of shoot regeneration. Rye chromosome 2R present in place of chromosome 2D in the common wheat genome suppressed the induction of callus producing root structures. Rye chromosomes 1R and 6R suppressed the induction of embryogenic callus capable of shoot regeneration.     

Enhancement of rhizosphere citric acid and decrease of NO3−/NH4+ ratio by root interactions facilitate N fixation and transfer

Plant and Soil - Plant growth is often limited by low soil phosphorus (P) availability, soil nitrogen (N) availability may affect plants’ responses to P supply. We studied the growth and...     

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 Ca2+-inactivated Cl− Channel at Work: Selectivity,Blocker Kinetics and Transport Visualization

Removal of extracellular divalent cations activated a Cl⁻ channel in the plasma membrane of Xenopus laevis oocytes. This so-called Ca²⁺-inactivated Cl⁻ channel (CaIC) was present in every oocyte and was investigated using two-electrode whole-cell voltage clamp and single-channel patch-clamp techniques. Beside other Cl⁻ channel inhibitors, anthracene-9-carboxylic acid (9-AC) and 3′azido-3′deoxythymidine (AZT), a nucleoside analogue commonly used as an antiviral drug, blocked at least partly the CalC-mediated currents. Using the Cl⁻-sensitive dye 6-methoxy-N-(sulfopropyl)quinolinium (SPQ) we could visualize the transport of Cl⁻ from the oocyte cytoplasm to the surrounding medium after activation of the CaIC by Ca²⁺ removal. In the absence of external Cl⁻ and Ca²⁺, the emission intensity of SPQ declined continuously, indicating a quenching of fluorescence by the efflux of Cl⁻ in the millimolar range. In the presence of external Ca²⁺, no emission changes could be observed during the same time period. Chelating external Ca²⁺ in absence of Cl⁻ immediately activated Ca²⁺-inactivated Cl⁻ channels leading to subsequent emission decrease of SPQ. Investigations on the selectivity of the CaIC revealed only poor discrimination between different anions. With single-channel measurements, we found an anion selectivity sequence I⁻ > Br⁻ > Cl⁻≫ gluconate as it is also typical for maxi Cl⁻ channels. Contrary to the majority of all other transport systems of the Xenopus oocyte, which show reduced activity due to membrane depolarization or endocytotic removal of the transport protein from the plasma membrane during oocyte maturation, the CaIC remained active in maturated oocytes. Single-channel measurements on maturated oocytes, also known as eggs, showed the presence of Ca²⁺-inactivated Cl⁻ channels. However, this egg CaIC revealed an altered sensitivity to external Ca²⁺ concentrations. All these data confirm and extend our previous observations on the CaIC and give clear evidence that this channel is peculiar among all Cl⁻ channels described up to now. Received: 16 May 1996/Revised: 4 September 1996     

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.     

Effects of clipping and shading on 15NO3− and 15NH4+ recovery by plants in grazed and ungrazed temperate grasslands

Plant and Soil - In natural ecosystems, plants generally promote the acquisition of nitrogen (N) through the input of carbon (C) into the soil. The present study aimed to clarify how changes in C...     

High-Affinity NO− 3-H+ Cotransport in the Fungus Neurospora: Induction and Control by pH and Membrane Voltage

High-affinity nitrate transport was examined in intact hyphae of Neurospora crassa using electrophysiological recordings to characterize the response of the plasma membrane to NO⁻ ₃ challenge and to quantify transport activity. The NO⁻ ₃-associated membrane current was determined using a three electrode voltage clamp to bring membrane voltage under experimental control and to compensate for current dissipation along the longitudinal cell axis. Nitrate transport was evident in hyphae transferred to NO⁻ ₃-free, N-limited medium for 15 hr, and in hyphae grown in the absence of a nitrogen source after a single 2-min exposure to 100 μm NO⁻ ₃. In the latter, induction showed a latency of 40–80 min and rose in scalar fashion with full transport activity measurable approx. 100 min after first exposure to NO⁻ ₃; it was marked by the appearance of a pronounced sensitivity of membrane voltage to extracellular NO⁻ ₃ additions which, after induction, resulted in reversible membrane depolarizations of (+)54–85 mV in the presence of 50 μm NO⁻ ₃; and it was suppressed when NH₄ ⁺ was present during the first, inductive exposure to NO⁻ ₃. Voltage clamp measurements carried out immediately before and following NO⁻ ₃ additions showed that the NO⁻ ₃-evoked depolarizations were the consequence of an inward-directed current that appeared in parallel with the depolarizations across the entire range of accessible voltages (−400 to +100 mV). Measurements of NO⁻ ₃ uptake using NO⁻ ₃-selective macroelectrodes indicated a charge stoichiometry for NO⁻ ₃ transport of 1(+):1(NO⁻ ₃) with common K _m and J _max values around 25 μm and 75 pmol NO⁻ ₃ cm⁻²sec⁻¹, respectively, and combined measurements of pH _o and [NO⁻ ₃] _o showed a net uptake of approx. 1 H⁺ with each NO⁻ ₃ anion. Analysis of the NO⁻ ₃ current demonstrated a pronounced voltage sensitivity within the normal physiological range between −300 and −100 mV as well as interactions between the kinetic parameters of membrane voltage, pH _o and [NO⁻ ₃] _o . Increasing the bathing pH from 5.5 to 8.0 reduced the current and the associated membrane depolarizations 2- to 4-fold. At a constant pH _o of 6.1, driving the membrane voltage from −350 to −150 mV resulted in an approx. 3-fold reduction in the maximum current and a 5-fold rise in the apparent affinity for NO⁻ ₃. By contrast, the same depolarization effected an approx. 20% fall in the K _m for transport as a function in [H⁺] _o . These, and additional results are consistent with a charge-coupling stoichiometry of 2(H⁺) per NO⁻ ₃ anion transported across the membrane, and implicate a carrier cycle in which NO⁻ ₃ binding is kinetically adjacent to the rate-limiting step of membrane charge transit. The data concur with previous studies demonstrating a pronounced voltage-dependence to high-affinity NO⁻ ₃ transport system in Arabidopsis, and underline the importance of voltage as a kinetic factor controlling NO⁻ ₃ transport; finally, they distinguish metabolite repression of NO⁻ ₃ transport induction from its sensitivity to metabolic blockade and competition with the uptake of other substrates that draw on membrane voltage as a kinetic substrate. Received: 17 March 1997/Revised: 20 June 1997     

Specific Features of the Nuclear Genome Recombination in Backcross Progenies of Barley–Wheat Hybrids Hordeum vulgare L. (2n = 14) × Triticum aestivum L. (2n = 42)

The backcross progenies of the barley–wheat hybrids Hordeum vulgare L. (2n = 14) × Triticum aestivum L. (2n= 42) and two alloplasmic lines derived from them were studied using microsatellite markers of barley and wheat. The F₁ hybrids and first backcross plants BC₁ contained the genetic material of both cultivated barley and the cultivars of common wheat involved in developing of these hybrid genotypes. The genomes of BC₃, BC₄, and alloplasmic lines contained no microsatellite markers of the cultivated barley, whereas chromosomes of each homeologous group of common wheat were identified. In chromosomes of backcross progenies BC₃, BC₄, and alloplasmic lines yielded by backcrosses of hybrids and various common wheat cultivars, microsatellite markers of the parental wheat cultivars were shown to undergo recombination.     

Does nitrogen supply affect the response of wheat (Triticum aestivum cv. Hanno) to the combination of elevated CO(2) and O(3)?

Spring wheat (Triticum aestivum cv. Hanno) was grown at ambient (350 micromol mol(-1)) or elevated CO(2) (700 micromol mol(-1)) in charcoal/Purafil-filtered air (CFA <5 nmol mol(-1)) or ozone (CFA +75 nmol mol(-1) 7 h d(-1)) at three levels of N supply (1.5, 4 and 14 mM NO(-3)), to test the hypothesis that the combined impacts of elevated CO(2) and O(3) on plant growth and photosynthetic capacity are affected by nitrogen availability. Shifts in foliar N content reflected the level of N supplied, and the growth stimulation induced by elevated CO(2) was dependent on the level of N supply. At 60 d after transfer (DAT), elevated CO(2) was found to increase total biomass by 44%, 29%, 12% in plants supplied with 14, 4 and 1.5 mM NO(-3), respectively, and there was no evidence of photosynthetic acclimation to elevated CO(2) across N treatments; the maximum in vivo rate of Rubisco carboxylation (V(cmax)) was similar in plants raised at elevated and ambient CO(2). At 60 DAT, ozone exposure was found to suppress plant relative growth rate (RGR) and net photosynthesis (A) in plants supplied with 14 and 4 mM NO(-3). However, O(3) had no effect on the RGR of plants supplied with 1.5 mM NO(-3) and this effect was accompanied by a reduced impact of the pollutant on A. Elevated CO(2) counteracted the detrimental effects of O(3) (i.e. the same ozone concentration that depressed RGR and A at ambient CO(2) resulted in no significant effects when plants were raised at elevated CO(2)) at all levels of N supply and the effect was associated with a decline in O(3) uptake at the leaf level.     

Purification and characterization of (1→3, 1→4)-β-glucan endohydrolases from germinated wheat (Triticum aestivum)

A (13, 14)--glucan 4-glucanohydrolase [(13, 14)--glucanase, EC 3.2.1.73] was purified to homogeneity from extracts of germinated wheat grain. The enzyme, which was identified as an endohydrolase on the basis of oligosaccharide products released from a (13, 14)--glucan substrate, has an apparent pI of 8.2 and an apparent molecular mass of 30 kDa. Western blot analyses with specific monoclonal antibodies indicated that the enzyme is related to (13, 14)--glucanase isoenzyme EI from barley. The complete primary structure of the wheat (13, 14)--glucanase has been deduced from nucleotide sequence analysis of cDNAs isolated from a library prepared using poly(A)⁺ RNA from gibberellic acid-treated wheat aleurone layers. One cDNA, designated LW2, is 1426 nucleotide pairs in length and encodes a 306 amino acid enzyme, together with a NH₂-terminal signal peptide of 28 amino acid residues. The mature polypeptide encoded by this cDNA has a molecular mass of 32085 and a predicted pI of 8.1. The other cDNA, designated LW1, carries a 109 nucleotide pair sequence at its 5 end that is characteristic of plant introns and therefore appears to have been synthesized from an incompletely processed mRNA. Comparison of the coding and 3-untranslated regions of the two cDNAs reveals 31 nucleotide substitutions, but none of these result in amino acid substitutions. Thus, the cDNAs encode enzymes with identical primary structures, but their corresponding mRNAs may have originated from homeologous chromosomes in the hexaploid wheat genome.     

Ester Derivatives of Nucleoside Inhibitors of Reverse Transcriptase: 1. Molecular Transport Systems for 3′-Azido-3′-Deoxythymidine and 2′,3′-Didehydro-3′-Deoxythymidine

The methods of synthesis of the derivatives of nucleoside analogues esterified with various aliphatic, aromatic, and heteroaromatic acids and the construction from them of molecular transport systems that involve lipids, carbohydrates, peptides, and amino acids are discussed. The characteristics of the biological activity of a number of such systems are described.__________Translated from Bioorganicheskaya Khimiya, Vol. 31, No. 4, 2005, pp. 339–356.Original Russian Text Copyright © 2005 by Berezovskaya, Chudinov.