On the relation between the index of the interelectrode gap filling with spark channels and the current of a pulsed multichannel sliding discharge in Ne,Ar, and Xe

Experimental results and model concepts concerning the relation between the index K of the interelectrode gap filling with spark channels and the peak current I _peak of a single-pulse submicrosecond multichannel complete sliding discharge on an alumina ceramic surface are discussed. The spatial structure of an incomplete discharge at the threshold for the surface spark breakdown of gas is considered. The experiments were performed with three gases, Ne, Ar, and Xe, at pressures of 30 and 100 kPa and opposite polarities of the discharge voltage, with two discharge chambers differing in the geometry of the discharge gap and the thickness of the ceramic plate. It is shown that, although the structure of the incomplete discharge at the threshold for spark breakdown varies from diffuse homogeneous to pronounced filamentary, the dependence \(K\left( {\sqrt[6]{{I_{peak} }}} \right)\) for a complete discharge is close to linear and can be qualitatively explained by the earlier proposed semiempirical model of the time evolution of the structure of a multichannel discharge. In particular, the estimated steepness of the dependence \(K\left( {\sqrt[6]{{I_{peak} }}} \right)\) agrees best with the experimental results when the local density of free electrons at the threshold for spark breakdown is 10¹⁶ cm^?3 or higher.     

Experimental and theoretical studies of the optical and electrical characteristics of a high-pressure pulsed discharge in argon

The optical and electrical characteristics of pulsed discharges in pure Ar at pressures of up to 7 atm, at which the discharge becomes unstable, are studied in a simple experimental device with automatic preionization. The gas temperature in the discharge is estimated from the width of the recorded emission spectrum. An analytical model of the vibrational relaxation of Ar ^*₂ (v) is used to better determine the constants of the vibrational-translational relaxation of Ar ^*₂ (v) molecules in their collisions with Ar atoms. The zerodimensional numerical model of a pulsed discharge in Ar is modified. The experimental and calculated results are compared in detail. Good agreement is achieved between the measured and calculated time dependences of the electrode voltage and the intensity of spontaneous emission in the pressure range of 1–6 atm, as well as between the measured and calculated values of the gas temperature at pressures of 3–6 atm. Preliminary results from numerical studies of the possibility of achieving generation are discussed.

     

Determination of the electron density and electric field in the plasma of a low-pressure microwave electrode discharge in hydrogen from the measured spectral line intensities

The parameters of the plasma of a microwave electrode discharge in hydrogen at pressures of 1–8 torr and incident powers of 20–80 W are measured by the so-called “relative intensity” method. The method allows one to determine the electron density and electric field in plasma by measuring the relative intensities of the H_α, H_β, and 763.5-nm Ar line emission and calculating the electron-impact rate constants from the homogeneous Boltzmann equation. The measurements show that there are regions in the discharge where the electron density is higher (a bright electrode sheath) and lower (a spherical region) than the critical density for the frequency 2.45 GHz (n_cr～7×10¹⁰ cm^?3). Inside the spherical region, the electric field varies slightly over the radius and the electron density increases as the discharge boundary is approached. The observed discharge structure can be attributed to the presence of a self-sustained discharge zone (electrode sheath); a non-self-sustained discharge zone (spherical region); and a decaying plasma region, which is separated from the active discharge zone by an electric double layer.     

Effects of negative air ions on oxygen uptake kinetics,recovery and performance in exercise: a randomized,double-blinded study

Limited research has suggested that acute exposure to negatively charged ions may enhance cardio-respiratory function, aerobic metabolism and recovery following exercise. To test the physiological effects of negatively charged air ions, 14 trained males (age: 32?±?7 years; \( \overset{\cdotp }{V}{\mathrm{O}}_{2 \max } \) : 57?±?7 mL min^?1 kg^?1) were exposed for 20 min to either a high-concentration of air ions (ION: 220?±?30?×?10³ ions cm^?3) or normal room conditions (PLA: 0.1?±?0.06?×?10³ ions cm^?3) in an ionization chamber in a double-blinded, randomized order, prior to performing: (1) a bout of severe-intensity cycling exercise for determining the time constant of the phase II \( \overset{\cdotp }{V}{\mathrm{O}}_2 \) response (τ) and the magnitude of the \( \overset{\cdotp }{V}{\mathrm{O}}_2 \) slow component (SC); and (2) a 30-s Wingate test that was preceded by three 30-s Wingate tests to measure plasma [adrenaline] (ADR), [nor-adrenaline] (N-ADR) and blood [lactate] (B_Lac) over 20 min during recovery in the ionization chamber. There was no difference between ION and PLA for the phase II \( \overset{\cdotp }{V}{\mathrm{O}}_2 \) τ (32?±?14 s vs. 32?±?14 s; P?=?0.7) or \( \overset{\cdotp }{V}{\mathrm{O}}_2 \) SC (404?±?214 mL vs 482?±?217 mL; P?=?0.17). No differences between ION and PLA were observed at any time-point for ADR, N-ADR and B_Lac as well as on peak and mean power output during the Wingate tests (all P?>?0.05). A high-concentration of negatively charged air ions had no effect on aerobic metabolism during severe-intensity exercise or on performance or the recovery of the adrenergic and metabolic responses after repeated-sprint exercise in trained athletes.     

Effect of the magnetic field structure on the intensity of electron cyclotron emission from the plasma of the L-2M stellarator

Results are presented from experimental studies of the influence of the stellarator magnetic field structure on the plasma behavior in electron-cyclotron resonance regimes with a high heating power per electron. The magnetic field structure was changed by varying the induction current I _p from ?14 to +14 kA. The plasma electrons were heated at the second harmonic of the electron gyrofrequency by an X-mode microwave beam with a power of P ～ 200 kW, the average plasma density being in the range n _e = (0.5–2) × 10¹³ cm^?3. At I _p = 0, the rotational transform varies from $\rlap{--} \iota $ (0) = 0.2 on the magnetic axis to 0.8 at the plasma boundary. At a positive current of I _p = 13.5 kA, the rotational transform was $\rlap{--} \iota $ (0) = 0.8 on the axis and $\rlap{--} \iota $ (a _p) = 0.9 at the plasma boundary. Experiments with a positive current have shown that the radiative temperature first increases with current. When the current increases to I _p = 11–14 kA, strong modulation appears in the electron cyclotron emission signals received from all the plasma radii, the emission spectrum changes, and the emission intensity decreases. At a negative current of I _p = ?(6.5–13.5) kA, the rotational transform vanishes at r/a _p = 0.4–0.6. In this regime, the number of suprathermal electrons is reduced substantially and the emission intensity decreases at both low and high plasma densities.     

Characterization of uptake and release processes ford- andl-aspartate in primary cultures of astrocytes and cerebellar granule cells

The uptake ofl-andd-aspartate was studied in astrocytes cultured from prefrontal cortex and in granule cells cultured from cerebellum. A high affinity uptake system forl- andd-aspartate was found in both cell types, and the two stereoisomers exhibited essentially the sameK _m - andV _max -values in bouth astrocytes (l-aspartate:K _m 77 μM;V _max 11.8 nmol×min^?1×mg^?1;d-aspartate:K _m 83 μM;V _max 14.0 nmol×min^?1×mg^?1) and granule cells (l-aspartate:K _m 32 μM;V _max 2.8 nmol ×min^?1×mg^?1;d-aspartate:K _m 26 μM;V _max 3.0 nmol×min^?1×mg^?1). To investigate whetherl-glutamate,l-aspartate andd-aspartate use the same uptake system a detailed kenetic analysis was performed. The uptake kinetics of each one of the three amino acids was studied in the presence of the two other amino acids, and no essential differences between the uptake characteristics of the amino acids were found. In addition to the uptake studies the release ofD-aspartate from cerebellar granule cells was investigated and compared withl-glutamate release. A Ca²⁺-dependent, K⁺-induced release was found for both amino acids.     

Backscattering of gyrotron radiation and short-wavelength turbulence during electron cyclotron resonance plasma heating in the L-2M stellarator

Backscattering of gyrotron radiation (θ = π) by short-wavelength density fluctuations (k _⊥ = 30 cm^?1) in the plasma of the L-2M stellarator was studied under conditions of electron cyclotron resonance (ECR) plasma heating at the second harmonic of the electron gyrofrequency (75 GHz). The scattering of the O-wave emerging due to the splitting of the linearly polarized gyrotron radiation into the X- and O-waves was analyzed. The signal obtained after homodyne detection of scattered radiation is a result of interference of the reference signal, the quasi-steady component, and the fast oscillating component. The coefficients of reflection of the quasi-steady component, R ₌ ² (Y), and fast oscillating component, R _～ ² (Y), of scattered radiation are estimated. The growth of the R _～ ² (Y) coefficient from 3.7 × 10^?4 to 5.2 × 10^?4 with increasing ECR heating power from 190 to 430 kW is found to correlate with the decrease in the energy lifetime from 1.9 to 1.46 ms. The relative density of short-wavelength fluctuations is estimated to be 〈n _～ ² 〉/〈n _e ² 〉 = 3 × 10^?7. It is shown that the frequencies of short-wavelength fluctuations are in the range 10–150 kHz. The recorded short-wavelength fluctuations can be interpreted as structural turbulence, the energy of which comprises ～10% of the total fluctuations energy. Simulations of transport processes show that neoclassical heat fluxes are much smaller than anomalous ones. It is suggested that short-wavelength turbulence plays a decisive role in the anomalous heat transport.     

Mechanisms of cell volume regulation in the proximal segment of the Malpighian tubule of Rhodnius neglectus

The cell volume regulation of the lower segment cells of the Malpighian tubule of Rhodnius neglectus in anisosmotic media was evaluated by using videooptic techniques. When the medium osmolality was increased with addition of 100 mm mannitol the cells shrank to a minimum of 16.84±2.62% and subsequently swelled towards their initial volume undergoing a typical regulatory volume increase (RVI). Replacement of either K⁺ or Cl^? or HCO ₃ ^? by Na⁺, gluconate and phosphate, respectively, abolished the RVI response. Furthermore, the substitution of Na⁺ by tetramethylammonium (TMA⁺) in isosmotic conditions led to cellular swelling and death. Addition of either amiloride 10^?4 m, anthracene-9-COOH 5×10^?4 m, furosemide 5×10^?4 m or ethacrynic acid 5×10^?5 m, also abolished RVI. On the other hand, addition of either Ba²⁺ 10^?3 m, SITS 5× 10^?4 m, ouabain 10^?3 m or vanadate 10^?3 m, did not change the RVI response. When the tubules were incubated in hyperosmotic media with EGTA 2 mm or verapamil 10^?6 m, the RVI response was abolished. In contrast, a decrease of NaCl concentration from 129 to 79 mm induced a cell swelling to a maximum of 33.11+1.73%, but the cells maintained swollen, only partially regulating their volume. These results show that the proximal cells of Malpighian tubule of R. neglectus are able to regulate their volume in hyperosmotic but only partially regulating in hyposmotic solutions. The mechanisms in RVI involve Na⁺, K⁺, Cl^?, Ca²⁺ and HCO ₃ ^? transport pathways and a ouabain-insensitive ATPase stimulated by Na⁺. This work was supported by grants from the Fundação de Amparo à Pesquisa do Estado de São Paulo—FAPESP; Conselho Nacional de Desenvolvimento Científico e Tecnológico—CNPq e Financiadora de Projetos e Pesquisas-FINEP.     

Uptake of amino acids by actidione-treated yeast cells

The active uptake ofl-aspartic acid, glycine andl-lysine by actidione-treated cells ofSaccharomyces cerevisiae was found to be inhibited by anaerobic conditions in the absence of a source of energy, only facilitated diffusion persisting. Similarly, metabolic inhibitors (iodoacetamide, sodium fluoride and potassium sorbate) inhibited the uptake very substantially. 2,4-Dinitrophenol and sodium azide appeared to inhibit the movement of the transport carrier itself, while uranyl ions showed a complex interaction pattern, ranging from inhibition at concentrations of 10^?6–10^?4 m, to stimulation at concentrations of 3×10^?4–10^?3 m, to pronounced inhibition at higher concentrations. The uptake was pH-dependent with optima forl-aspartic acid near pH 4, for glycine near pH 5, forl-lysine near pH 6.5.     

Measurements of CO2 and CH4 evasion from UK peatland headwater streams

Peatland headwater streams are consistently supersaturated with respect to gaseous C and are known to degas CO₂ and CH₄ directly to the atmosphere. Using a combination of injection of a purposeful gas tracer (propane) and a soluble tracer (NaCl) we carried out 49 measurements of the gas transfer coefficient on 12 representative stream reaches to quantify the gas transfer rates of CO₂ and CH₄ in headwater (1st–3rd order) streams draining six UK peatlands. These were compared to measured stream reach physical variables, such as discharge and water travel time. Whilst we found that evasion rates were highly variable in space and time, $ {\text{K}}_{{{\text{CO}}_{2} }} $ (gas transfer coefficient of CO₂) was positively related to discharge. Individual study sites showed a high degree of variability in gas transfer rates; at all 49 sites median/mean values for $ {\text{K}}_{{{\text{CO}}_{2} }} $ were 0.087/0.157 and $ {\text{K}}_{{{\text{CH}}_{4} }} $ 0.092/0.176 min^?1. Median/mean instantaneous CO₂ and CH₄ evasion rates were 133/367 and 0.22/1.45 μg C m^?2 s^?1, respectively. Methane evasion rates were therefore more than two orders of magnitude lower than CO₂, with CH₄ invasion (rather than evasion) measured on 37 % of occasions. Our gas flux measurements from peatland headwater streams are higher than values previously used to estimate landscape scale fluxes and emphasise the importance of the evasion flux term in the overall carbon balance.     

Efficient generation of negative hydrogen ions in a low-voltage cesium-hydrogen discharge

The possibility of achieving the high density of negative hydrogen ions \(N_{H^ - } \) in a low-voltage cesium-hydrogen discharge is investigated. The \(N_{H^ - } \) density is determined experimentally from the absorption of laser radiation due to the photodetachment of electrons from H^? ions. The discharge plasma is investigated by the probe technique. The populations of the excited states of Cs atoms are determined from their emission intensities. With an input power of W≈(15–25) W/cm² in the discharge, densities of \(N_{H^ - } \sim (10^{12} - 10^{13} )cm^{ - 3} \) are achieved. The self-consistent calculations of the plasma parameters in the discharge gap agree well with the experimental results. The absorption of laser radiation due to the photoionization of Cs atoms is investigated. It is shown that the role of this absorption mechanism is negligible.     

Ionization fraction of the sputtered metal flux in a hollow cathode magnetron

Results from studies of the parameters of a novel type of plasma source—a hollow cathode magnetron—are presented. The magnetron operates at a gas pressure of 5–20 mTorr, the discharge power being in the range of 0.5–4 kW. At discharge powers exceeding 2 kW, a plasma flow with a density of higher than 10¹¹ cm^?3 and length of up to 30 cm forms at the magnetron output. Using a grid quartz crystal microbalance, the ionized copper flux fraction was measured as a function of the gas pressure, discharge power, and distance from the target. At gas pressures of higher than 15 mTorr, the degree of ionization at a distance of 31 cm exceeds 50%.     

Mechanism for electric breakdown in a chemically nonequilibrium system and the influence of the chain oxidation reaction in an H2-air mixture on the breakdown threshold

A mathematical model is developed and a numerical analysis is performed for an electric breakdown in a hydrogen-air mixture with a low concentration of H₂. It is shown that, at sufficiently low pressures p<10^?2 atm, a small molecular-hydrogen additive (η=5×10^?5–5×10^?3) decreases the reduced field of an electric breakdown in air by a factor of more than 2 because of the appearance of an additional detachment process associated with the chain hydrogen-oxidation reaction. Detailed calculations are performed for the mean number density of negative oxygen ions [O ₂ ^? ]=10³ cm^?3 and the hydrogen concentration in air [H₂]=0.5, 0.05, and 0.005%. It is found that, for [H₂]=0.005%, the breakdown can develop under the action of a geoelectric field of 1.3 V/cm at p?10^?4 atm.     

Greenhouse Gas Emissions, Nitrate Leaching, and Biomass Yields from Production of Miscanthus × giganteus in Illinois, USA

Understanding the effects of nitrogen (N) fertilization on Miscanthus × giganteus greenhouse gas emissions, nitrate leaching, and biomass production is an important consideration when using this grass as a biomass feedstock. The objective of this study was to determine the effect of three N fertilization rates (0, 60, and 120?kg?N?ha^?1 using urea as the N source) on nitrous oxide (N₂O) and carbon dioxide (CO₂) emissions, nitrogen leaching, and the biomass yields and N content of M. × giganteus planted in July 2008, and evaluated from 2009 through early 2011 in Urbana, Illinois, USA. While there was no biomass yield response to N fertilization rates in 2009 and 2010, the amount of N in the harvested biomass in 2010 was significantly greater at the 60 and 120?kg?N?ha^?1?N rates. There was no significant CO₂ emission response to N rates in 2009 or 2010. Similarly, N fertilization did not increase cumulative N₂O emissions in 2009, but cumulative N₂O emissions did increase in 2010 with N fertilization. During 2009, nitrate (NO ₃ ^? ) leaching at the 50-cm soil depth was not related to fertilization rate, but there was a significant increase in NO ₃ ^? leaching between the 0 and 120?kg?N?ha^?1 treatments in 2010 (8.9 and 28.9?kg?NO₃?CN?ha^?1?year^?1, respectively). Overall, N fertilization of M. × giganteus led to N₂O releases, increased fluxes of inorganic N (primarily NO ₃ ^? ) through the soil profile; and increased harvested N without a significant increase in biomass production.     

Dark induction of nitrate reductase in the halophilic alga Dunaliella salina

The effect of nitrogen starvation on the NO₃-dependent induction of nitrate reductase (NR) and nitrite reductases (NIR) has been investigated in the halophilic alga Dunaliella salina. When D. salina cells previously grown in a medium with NH ₄ ⁺ as the only nitrogen source (NH ₄ ⁺ -cells) were transferred into NO ₃ ^? medium, NR was induced in the light. In contrast, when cells previously grown in N-free medium were transferred into a medium containing NO ₃ ^? , NR was induced in light or in darkness. Nitrate-dependent NR induction, in darkness, in D. salina cells previously grown at a photon flux density of 500 umol · m^?2 s^?1 was observed after 4 h preculture in N-free medium, whilst in cells grown at 100 umol · m^?2 s^?1 NR induction was observed after 7–8 h. An inhibitor of mRNA synthesis (6-methylpurine) did not inhibit NO ₃ ^? -induced NR synthesis when the cells, previously grown in NH ₄ ⁺ medium, were transferred into NO ₃ ^? medium (at time 0 h) after 4-h-N starvation. However, when 6-methylpurine was added simultaneously with the transfer of the cells from NH ₄ ⁺ to NO ₃ ^? medium (at time 0 h), NO ₃ ^? induced NR synthesis was completely inhibited. The activity of NIR decreased in N-starved cells and the addition of NO ₃ ^? to those cells greatly stimulated NIR activity in the light. The ability to induce NR in darkness was observed when glutamine synthetase activity reached its maximal level during N starvation. Although cells grown in NO ₃ ^? medium exhibited high NR activity, only 0.33% of the total NR was found in intact chloroplasts. We suggest that the ability, to induce NR in darkness is dependent on the level of N starvation, and that NR in D. salina is located in the cytosol. Light seems to play an indirect regulatory role on NO ₃ ^? uptake and NR induction due to the expression of NR and NO ₃ ^? -transporter mRNAs.     

Small-conductance chloride channels in human peripheral T lymphocytes

During whole-cell patch-clamp recording from normal (nontransformed) human T lymphocytes a chloride current spontaneously activated in >98% of cells (n > 200) in the absence of applied osmotic or pressure gradients. However, some volume sensitivity was observed, as negative pressure pulses reduced the current. With iso-osmotic bath and pipette solutions the peak amplitude built up (time constant ≈23 sec at room temperature), a variable-duration plateau phase followed, then the current ran down spontaneously (time constant ≈280 sec). The anion permeability sequence, calculated from reversal potentials was I^?, Br^? > NO ₃ ^? , Cl^? > CH₃SO ₃ ^? , HCO ₃ ^? > CH₃COO^? > F^? > aspartate, gluconate, SO ₄ ^2? and there was no measurable monovalent cation permeability. The Cl^? current was independent of time during long voltage steps and there was no evidence of voltage-dependent gating; however, the current showed intrinsic outward rectification in symmetrical Cl^? solutions. The conductance of the channels underlying the whole-cell current was calculated from fluctuation analysis, using power-spectral density and variance-vs.-mean analysis. Both methods yielded a single channel conductance of about 0.6 pS at ?70 mV (close to the normal resting potential of T lymphocytes). The power spectral density function was best fit by the sum of two Lorentzian functions, with corner frequencies of 30 and 295 Hz, corresponding to mean open times of 0.54 and 5.13 msec. The pharmacological profile included rapid block by external application of flufenamic acid (50 μm), 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB, 100 μm, [6,7-dichloro-2-cyclopentyl-2,3-dihydro-2-methyl-1-oxo-1H-inden-5-y1) oxy] acetic acid (IAA-94, 250 μm) or 100 μm 1,9-dideoxyforskolin. The stilbene derivatives DIDS (4,4′-diisothiocyano-2,2′ di-sulphonic acid stilbene, 500 μm) and SITS (4-acetamido-4′-isothiocyano-2, 2′-disulphonic acid stilbene, 500 μm) prevented buildup of Cl^? current after a 30-min preincubation at 500 μm. When tested in a mitogenic assay, DIDS, flufenamic acid, NPPB and IAA-94 all inhibited T-cell proliferation, suggesting a physiological function in addition to the observed volume sensitivity.     

Growth kinetics and nitrogen-nutrition of the marine diatom Phaeodactylum tricornutum in continuous dialysis culture

The growth kinetics and nitrogen (N)-nutrition of the marine pennate diatom Phaeodactylum tricornutum Bohlin were determined in continuous dialysis culture at different cell densities. Inflow nutrient medium was supplied as natural unenriched estuarine seawater to a dialysis culture system with a high ratio of membrane surface area/culture volume (Am/Vc). Under the experimental conditions, the supply of inorganic macronutrients (NO ₃ ^? + NO ₄ ^? and PO ₄ ^?3 ) by diffusion (Nd) was markedly greater than that provided by the dilution (FfCN) of the culture (Nd ? FfCN), thereby establishing an inverse relationship between the cell density and the dilution rate (D). This continuous dialysis system allows for the maintenance of prolonged growth (> two weeks) at various cell densities (1.4 to 27.2 × 10⁹ cells 1^?1) within a range of dilution rates between 0.30 to 1.08 d^?1. In high cell density cultures, where the extracellular medium was characterized as nutrient deficient, a lower growth rate (μ_e) was exhibited than in cultures with lower cell densities. The growth rate (μ_e) remained equivalent to the dilution rate (D) throughout the culture cycle, indicating that equilibrated growth was achieved. High cell density cultures yielded higher productivity (P), relative to that of cultures grown at lower cell densities, in terms of cell-N and ?C produced per unit time. However, cell quotas of both N and C declined with increasing cell concentrations. Denser cultures were characterized by an enhanced N-conversion efficiency (Y_N) and a higher cellular N/C atomic ratio. The nutritional response of this diatom in dense cultures reveals an efficient use of N-nutrients, presumably as a result of cellular nutrient adaptation to oligotrophic conditions.     

Effects of exogenous l-arginine on in vitro rooting, chlorophyll, carbohydrate, and proline concentrations in the sweet cherry rootstock M × M 14 (Prunus avium L. × Prunus mahaleb L.)

The effects of indole-3-butyric acid (IBA) alone and in combination with l-arginine on the morphogenic and biochemical responses in shoot tip explants of the cherry rootstock M × M 14 (Prunus avium × Prunus mahaleb) were examined. The maximum root number per rooted explant (16), root fresh (FW) and dry (DW) weights, as well as the rooting percentage (100 %) were recorded when 2 mg l^?1 IBA (alone) were applied. Including the lowest IBA concentration (0.5 mg l^?1) with the lowest and highest l-arginine concentrations (0.5 and 2 mg l^?1, respectively) resulted in the greatest root length. The maximum leaf chlorophyll concentration and shoot length of the initial explant were recorded when 0.5 mg l^?1 IBA plus 2 mg l^?1 l-arginine were applied. In addition, l-arginine in combination with IBA (1 and 2 mg l^?1) was found to suppress shoot FW and DW. On the other hand, l-arginine enhanced the promoting effect of IBA on both root length and leaf chlorophyll concentration. The carbohydrate and proline concentrations in leaves were not significantly altered with the application of IBA alone or in combination with l-arginine. On the other hand, the carbohydrate and proline concentrations in roots were decreased with the application of 1 and 2 mg l^?1 IBA with l-arginine, resulting in the suppression of the promoting effects of IBA. It is clear from the findings that l-arginine has a direct effect on the in vitro rooting of M × M 14 explants, is involved in the function of the photosythetic apparatus, influences leaf chlorophyll content, participates in carbohydrate biosynthesis and metabolism, and is involved in proline accumulation both in leaves and roots.     

Improved method for the identification of the fluoride-resistant plasmacholinesterase genotypes

This investigation was prompted by the findings that (1) dibucaine-resistant homozygotes and heterozygotes for plasmacholinesterase also exhibit resistance to fluoride inhibition, (2) the differentiation of dibucaine-resistant from the fluoride-resistant genotypes is ambiguous with the method of Harris and Whittaker, (3) the plasmacholinesterase inhibition by Na fluoride (FN) is markedly influenced by the temperature. Therefore, we modified their method by increasing (1) the temperature of the reaction from 25C to 37C and (2) the concentration of Na fluoride from 5.0×10^?5 m to 2.5×10^?4 m. With this method, genetically normal individuals have a mean FN±sd=77.0±3.22 while atypical dibucaine-resistant homozygotes have a mean FN±sd=43.0±10.0 and atypical dibucaine-resistant heterozygotes 67.0±5.37. Since a linear correlation was observed between DN and FN by our new method, a fluoride number 2 sd lower than the predicted FN from the DN can distinctly identify the fluoride-resistant plasmacholinesterase genotype E ₁ ^f .     

Microbial N turnover processes in three forest soil layers following clear cutting of an N saturated mature spruce stand

Microbial N turnover processes were investigated in three different forest soil layers [organic (O) layer, 0–10 cm depth (M₁), 10–40 cm depth (M₂)] after the clear cutting of a nitrogen (N) saturated spruce stand at the Höglwald Forest (Bavaria, Germany). The aim of the study was to provide detailed insight into soil-layer specific microbial production and the consumption of inorganic N within the main rooting zone. Furthermore, we intended to clarify the relevance of each soil layer investigated in respect of the observed high spatial variation of seepage water nitrate (NO ₃ ^? ) concentration at a depth of 40 cm. The buried bag and the ¹⁵N pool dilution techniques were applied to determine the net and gross N turnover rates. In addition, soil pH, C:N ratio, pool sizes of soil ammonium (NH ₄ ⁺ ) and NO ₃ ^? , as well as quantities of microbial biomass carbon (C_mic) and nitrogen (N_mic) were determined. The 40 cm thick upper mineral soil was found to be the main place of NO ₃ ^? production with a NO ₃ ^? supply or net nitrification three times higher than in the considerably thinner O layer. Nevertheless, O layer nitrification processes determined via in situ field experiments showed significant correlation with seepage water NO ₃ ^? . An improved correlation noted several months after the cut may result from a transport-induced time shift of NO ₃ ^? with downstream hydrological pathways. In contrast, the soil laboratory incubation experiments found no indication that mineral soil is relevant for the spatial heterogeneity of seepage water NO ₃ ^? . The results from our study imply that in situ experiments may be better suited to studies investigating N turnover in relation to NO ₃ ^? loss via seepage water in similar ecosystems in order to gain representative data.