ATP-independent luminal oscillations and release of Ca2+ and H+ from mast cell secretory granules: implications for signal transduction

InsP(3) is an important link in the intracellular information network. Previous observations show that activation of InsP(3)-receptor channels on the granular membrane can turn secretory granules into Ca(2+) oscillators that deliver periodic trains of Ca(2+) release to the cytosol (T. Nguyen, W. C. Chin, and P. Verdugo, 1998, Nature, 395:908-912; I. Quesada, W. C. Chin, J. Steed, P. Campos-Bedolla, and P. Verdugo, 2001, BIOPHYS: J. 80:2133-2139). Here we show that InsP(3) can also turn mast cell granules into proton oscillators. InsP(3)-induced intralumenal [H(+)] oscillations are ATP-independent, result from H(+)/K(+) exchange in the heparin matrix, and produce perigranular pH oscillations with the same frequency. These perigranular pH oscillations are in-phase with intralumenal [H(+)] but out-of-phase with the corresponding perigranular [Ca(2+)] oscillations. The low pH of the secretory compartment has critical implications in a broad range of intracellular processes. However, the association of proton release with InsP(3)-induced Ca(2+) signals, their similar periodic nature, and the sensitivity of important exocytic proteins to the joint action of Ca(2+) and pH strongly suggests that granules might encode a combined Ca(2+)/H(+) intracellular signal. A H(+)/Ca(2+) signal could significantly increase the specificity of the information sent by the granule by transmitting two frequency encoded messages targeted exclusively to proteins like calmodulin, annexins, or syncollin that are crucial for exocytosis and require specific combinations of [Ca(2+)] "and" pH for their action.     

The Na+ cycle of extreme alkalophiles: A secondary Na+/H+ antiporter and Na+/solute symporters

Extremely alkalophilic bacteria that grow optimally at pH 10.5 and above are generally aerobic bacilli that grow at mesophilic temperatures and moderate salt levels. The adaptations to alkalophily in these organisms may be distinguished from responses to combined challenges of high pH together with other stresses such as salinity or anaerobiosis. These alkalophiles all possess a simple and physiologically crucial Na⁺ cycle that accomplishes the key task of pH homeostasis. An electrogenic, secondary Na⁺/H⁺ antiporter is energized by the electrochemical proton gradient formed by the proton-pumping respiratory chain. The antiporter facilitates maintenance of a pH_in that is two or more pH units lower than pH_out at optimal pH values for growth. It also largely converts the initial electrochemical proton gradient formed by respiration into an electrochemical sodium gradient that energizes motility as well as a plethora of Na⁺/solute symporters. These symporters catalyze solute accumulation and, importantly, reentry of Na⁺. The extreme nonmarine alkalophiles exhibit no primary sodium pumping dependent upon either respiration or ATP. ATP synthesis is not part of their Na⁺ cycle. Rather, the specific details of oxidative phosphorylation in these organisms are an interesting analogue of the same process in mitochondria, and may utilize some common features to optimize energy transduction.     

Sequences of initiator and elongator methionine tRNAs in bean mitochondria

Summary Two bean mitochondria methionine transfer RNAs, purified by RPC-5 chromatography and two-dimensional gel electrophoresis, have been sequenced usingin vitro post-labeling techniques.One of these tRNAs^Met has been identified by formylation using anE. coli enzyme as the mitochondrial tRNA_F ^Met. It displays strong structural homologies with prokaryotic and chloroplast tRNA_F ^Met sequences (70.1–83.1%) and with putative initiator tRNA_m ^Met genes described for wheat, maize andOenothera mitochondrial genomes (88.3–89.6%).The other tRNA^Met, which is the mitochondrial elongator tRNA_F ^Met, shows a high degree of sequence homology (93.3–96%& with chloroplast tRNA_m ^Met, but a weak homology (40.7%) with a sequenced maize mitochondrial putative elongator tRNA_m ^Met gene.Bean mitochondrial tRNA_F ^Met and tRNA_m ^Met were hybridized to Southern blots of the mitochondrial genomes of wheat and maize, whose maps have been recently published (15, 22), in order to locate the position of their genes.     

Effects of macro elements and nitrogen source on adventitious root growth and ginsenoside production in ginseng (Panax ginseng C. A. Meyer)

We investigated the effects on ginseng adventitious root growth and ginsenoside production when macro-element concentrations and nitrogen source were manipulated in the culture media. Biomass growth was greatest in the medium supplemented with 0.5-strength NH₄PO₃, whereas ginsenoside accumulation was highest (9.90 mg g^-1 DW) in the absence of NH₄PO₃. At levels of 1.0-strength KNO₃, root growth was maximum, but a 2.0 strength of KNO₃ led to the greatest ginsenoside content (9.85 mg g^-l). High concentrations of MgSO₄ were most favorable for both root growth and ginsenoside accumulation (up to 8.89 mg g^-1 DW). Root growth and ginsenoside content also increased in proportion to the concentration of CaCI₂ in the medium, with the greatest accumulation of ginsenoside (8.91 mg g^-1 DW) occurring at a 2.0 strength. The NH₄/NO₃ ^-- ratio also influenced adventitious root growth and ginsenoside production; both parameters were greater when the NO₃ ^- concentration was higher than that of NH₄ ⁺. Maximum root growth was achieved at an NH₄ ⁺/NO₃ ^- ratio of 7.19/18.50, while ginsenoside production was greatest (83.37 mg L^-1) when NO₃ ^- was used as the sole N source.     

Mechanism of the gas phase reactions of the C5H5Ni and C5H5Co ions with substituted pyridines. A combined experimental and theoretical study

Different products have been observed in the reactions of C₅H₅Co⁺ and C₅H₅Ni⁺ ions with halogen-substituted pyridines (XPy) that have been studied by ion trap mass spectrometry (ITMS) techniques. In particular, an addition product C₅H₅M(XPy)⁺ and a product ion C₅H₄M(Py)⁺ corresponding to a loss of a HX molecule (X = F, Cl, Br) have been detected. The relative yield of these products is determined by the nature of the metal and by the nature and position of the halogen on the pyridine ring. A computational study at the DFT level on model-systems formed by 2-fluoro and 2-bromopyridine reacting either with the C₅H₅Ni⁺ or the C₅H₅Co⁺ ion has been carried out. This study shows the existence of a general mechanistic pattern. The rate-determining step of this mechanism is the migration of the halogen from the pyridine ring to the metal. A final hydrogen abstraction step carried out by the halogen leads to the expulsion of a HX molecule. The existence of avoided crossings between surfaces of different multiplicities (ground and first excited state) allows the system to follow lower energy reaction pathways. The barrier determined for the reactions involving 2-bromopyridine is significantly lower than that found for 2-fluoropyridine. This is mainly due to the poor migrating/leaving character and low polarizability of fluorine compared to that of bromine.     

Involvement of mitogen-activated protein kinases and reactive oxygen species in the inotropic action of ouabain on cardiac myocytes. A potential role for mitochondrial KATP channels

Binding of ouabain to Na⁺/K⁺-ATPase activated multiple signal transduction pathways including stimulation of Src, Ras, p42/44 MAPKs and production of reactive oxygen species (ROS) in rat cardiac myocytes. Inhibition of either Src or Ras ablated ouabain-induced increase in both [Ca²⁺]_i and contractility. While PD98059 abolished the effects of ouabain on [Ca²⁺]_i, it only caused a partial inhibition of ouabain-induced increases in contractility. On the other hand, pre-incubation of myocytes with N-acetyl cysteine (NAC) reduced the effects of ouabain on contractility, but not [Ca²⁺]_i. Furthermore, 5-hydroxydecanoate (5-HD) blocked ouabain-induced ROS production and partially inhibited ouabain-induced increases in contractility in cardiac myocytes. Pre-incubation of myocytes with both 5-HD and PD98059 completely blocked ouabain's effect on contractility. Finally, we found that opening of mitochondrial K_ATP channel by diazoxide increased intracellular ROS and significantly raised contractility in cardiac myocytes. These new findings indicate that ouabain regulates cardiac contractility via both [Ca²⁺]_i and ROS. While activation of MAPKs leads to increases in [Ca²⁺]_i, opening of mitochondrial K_ATP channel relays the ouabain signal to increased ROS production in cardiac myocytes.     

Overproduction and purification of Escherichia coli tRNALeu

Chemically synthesized genes encodingEscherichia coli tRNA ₁ ^Leu and tRNA ₂ ^Leu were ligated into the plasmid pTrc99B. then transformed intoEscherichia coli MT102, respectively. The positive transformants, named MT-Leu1 and MT-Leu2, were confirmed by DNA sequencing, and the conditions of cultivation for the two transformants were optimized. As a result, leucinc accepting activity of their total tRNA reached 810 and 560 pmol/A₂₆₀, respectively: the content of tRNA ₁ ^Leu was 50% of total tRNA from MT-Leu1, while that of tRNA ₂ ^Leu was 30% of total tRNA from MT-Leu2. Both tRNA^Leus from their rotal tRNs were fractionated to 1 600 pmol/A₂₆₀ after DEAE-Sepharose and BD-cellulose column chromatography. The accurate kinetic constants of aminoacylation of the two isoacceptors of tRNA^Leu catalyzed by leucyl-tRNA synthetase were determined. Project supported by the National Natural Science Foundation of China (Grant No. 39570164).     

Mechanisms of signal transduction in photo-stimulated secretion in Phaeocystis globosa

Phaeocystis globosa, a leading agent in marine carbon cycling, releases its photosynthesized biopolymers via regulated exocytosis. Release is elicited by blue light and relayed by a characteristic cytosolic Ca(2+) signal. However, the source of Ca(2+) in these cells has not been established. The present studies indicate that Phaeocystis' secretory granules work as an intracellular Ca(2+) oscillator. Optical tomography reveals that photo-stimulation induces InsP(3)-triggered periodic lumenal [Ca(2+)] oscillations in the granule and corresponding out-of-phase cytosolic oscillations of [Ca(2+)] that trigger exocytosis. This Ca(2+) dynamics results from an interplay between the intragranular polyanionic matrix, and two Ca(2+)-sensitive ion channels located on the granule membrane: an InsP(3)-receptor-Ca(2+) channel, and an apamin-sensitive K(+) channel.     

Canopy throughfall of Picea abies (L.) Karst. as depending on trace gas concentrations

At six sites in central Germany consequences of SO₂, NO_X and O₃ deposition and of acid precipitation on canopy throughfall of sulphate, nitrate, ammonium, organic acids and of metal cations from Norway spruce crowns were investigated in the field. Measured canopy throughfall rates (mmol ion kg^-1 needle dw a^-1 are separated in (i) background ion throughfall rates in clean air and (ii) trace gas-(or acid interception)-dependent throughfall rates at ambient trace gas concentrations. Based on synchronously measured pollution, precipitation and canopy throughfall data, statistical response functions are given, which allow the separate estimation of annual rates of sulphur and nitrogen deposition into spruce canopies if only annual means of SO₂ or NO₂ concentrations in air are known. The specific SO₂ deposition rate of (0.841±0.214) mmol S kg^-1 needle dw a^-1 (nPa SO₂ Pa^-1)^-1 is 2.3 times higher than the specific stomatal SO₂ uptake. The NO₂-dependent nitrogen deposition of (2.464±0.707) mmol N kg^-1 needle dw a^-1 (nPa NO₂ Pa^-1)^-1 is 2.2 times higher than the specific stomatal NO_X (NO₂+NO) uptake. These ratios (2.32.2) are explained by the percentage of annual hours with open needle stomata. The shape of observed epicuticular SO₂ and NO_X deposition curves and of stomatal SO₂ and NO_X uptake curves are congruent. As for stomatal NO_X uptake, there is an apparent compensation point at (5 to 8) nPa NO₂ Pa^-1. There is significant SO₂-dependent canopy throughfall of Ca>K>Al>Mg>Fe in this order of relative importance. NO_X deposition in spruce canopies reduces K⁺ throughfall and it weakly promotes throughfall of Mn²⁺ and Zn²⁺. There was no significant codeposition of sulphate and ammonium and no ion exchange of intercepted H₃O⁺ with nutrient cations at the measured ambient pH values of the precipitation water. In the presence of O₃, throughfall of Mn²⁺ is reduced and throughfall of K⁺, Ca²⁺ and Al³⁺ is enhanced. In the cooperative presence of SO₂, NO₂ and O₃ pollution in the field there is a 1.3-fold increase of the annual K⁺ demand and a 1.5-fold Mg²⁺ demand of spruce canopies relative to the situation in clean air. This trace gas-dependent additional cation demand of spruce canopies corresponds to a needle loss percentage of (23 to 33)% if the additional K⁺ and Mg²⁺ throughfall could not be recycled in spruce ecosystems. Observed canopy thinning ranges from (13 to 26)% at the investigated six spruce stands.Abbreviations A_spec Specific needle surface area per kg needle dry matter (m²kg^-1 needle dw) - A_tot Total needle surface of spruce stands (ha ha^-1) - [gas]_a Ambient trace gas concentration (gas=SO₂; NO₂ or O₃) in air (nPa Pa^-1=ppb) - GP Number of days per annual growth period d a^-1) - IC_H30 ⁺ Acid interception rate (Eq H₃O⁺ kg^-1 needle dw a^-1) - k_o Trace gas-independent ion throughfall rate constant (mmol kg^-1 needle dw a^-1) - k_gas SO₂-,NO₂-or O₃-dependent ion throughfall rate per unit of trace gas pollution (mmol kg^-1 needle dw a^-1 (nPa Pa^-1)^-1) - k_H30 Specific H₃O⁺/Me⁺ exchange ratio (mol mol^-1) - L_o Background throughfall rate at [gas]_a=0 (mmol kg^-1 needle dw a^-1) - L_ion Canopy throughfall rate of ions (mmol kg^-1 needle dw a^-1) - L'_ion Trace gas dependent ion throughfall (mEq kg^-1 needle dw a^-1 (nPa Pa^-1)^-1) - LAI Leaf area index of the canopy (m² projected needle surface m^-2 ground) - Me⁺ Equivalents of metal cations (Eq) - N Stock of needles of spuce stands in the field (kg needle dw ha^-1) - P_% Percentage of needle loss relative to a healthy reference (%) - r Pearson correlation coefficient (no dimension) - R COO^--Sum of all organic anion equivalents Cat⁺ - An^- (Eq kg^-1 needle dw a^-1) - An^- Sum of all measured inorganic anion equivalents (Eq kg^-1 needle dw a^-1) - Cat⁺ Sum of all measured inorganic cation equivalents (Eq kg^-1 needle dw a^-1)     

Permeation properties of inward-rectifier potassium channels and their molecular determinants

The structural domains contributing to ion permeation and selectivity in K channels were examined in inward-rectifier K(+) channels ROMK2 (Kir1.1b), IRK1 (Kir2.1), and their chimeras using heterologous expression in Xenopus oocytes. Patch-clamp recordings of single channels were obtained in the cell-attached mode with different permeant cations in the pipette. For inward K(+) conduction, replacing the extracellular loop of ROMK2 with that of IRK1 increased single-channel conductance by 25 pS (from 39 to 63 pS), whereas replacing the COOH terminus of ROMK2 with that of IRK1 decreased conductance by 16 pS (from 39 to 22 pS). These effects were additive and independent of the origin of the NH(2) terminus or transmembrane domains, suggesting that the two domains form two resistors in series. The larger conductance of the extracellular loop of IRK1 was attributable to a single amino acid difference (Thr versus Val) at the 3P position, three residues in front of the GYG motif. Permeability sequences for the conducted ions were similar for the two channels: Tl(+) > K(+) > Rb(+) > NH(4)(+). The ion selectivity sequence for ROMK2 based on conductance ratios was NH(4)(+) (1.6) > K(+) (1) > Tl(+) (0.5) > Rb(+) (0.4). For IRK1, the sequence was K(+) (1) > Tl(+) (0.8) > NH(4)(+) (0.6) > Rb(+) (0.1). The difference in the NH(4)(+)/ K(+) conductance (1.6) and permeability (0.09) ratios can be explained if NH(4)(+) binds with lower affinity than K(+) to sites within the pore. The relatively low conductances of NH(4)(+) and Rb(+) through IRK1 were again attributable to the 3P position within the P region. Site-directed mutagenesis showed that the IRK1 selectivity pattern required either Thr or Ser at this position. In contrast, the COOH-terminal domain conferred the relatively high Tl(+) conductance in IRK1. We propose that the P-region and the COOH terminus contribute independently to the conductance and selectivity properties of the pore.     

应用15N示踪研究欧美杨对PM2.5无机成分NH4+和NO3-的吸收与分配

通过气溶胶发生系统模拟PM2.5颗粒的发生,运用15N示踪技术研究了欧美杨107(Populus euramericana Neva.)对PM2.5中水溶性无机成分NH+4和NO-3的吸收与分配规律。结果表明,欧美杨能够有效吸收PM2.5中的NH+4和NO-3。轻度和重度污染下,欧美杨叶片对NH+4和NO-3的吸收速率均于处理后第1天达到峰值,之后,轻度污染下对NH+4和NO-3的吸收速率迅速降低以后趋于稳定,而重度污染下对NH+4和NO-3的吸收速率缓慢下降至趋于稳定。轻度污染下的欧美杨叶片的15N含量在处理后第1天达到峰值,15N(NH+4)的含量为0.11 mg/g,干重,15N(NO-3)的为0.14 mg/g,干重,之后15N含量迅速下降至趋于稳定。重度污染下的叶片15N含量在处理第1天迅速增长,之后缓慢增长至处理后第7天达到最高值,15N(NH+4)的含量为0.11 mg/g,干重,15N(NO-3)的为0.13 mg/g,干重。处理7 d后,欧美杨不同组织器官吸收或通过再分配获取的15N含量存在差异。轻度污染下,细根对NH+4和NO-3的吸收量最高,树皮、叶柄、叶片次之,髓最低。而重度污染下,叶片对NH+4和NO-3的吸收量最高,细根、叶柄、树皮次之,髓最低。欧美杨各组织器官中NH+4和NO-3的含量均表现为重度污染大于轻度污染,且两种污染程度下的欧美杨各组织器官对NO-3的吸收均大于对NH+4的吸收。重度污染下,欧美杨茎木质部对15N(NH+4和NO-3)的吸收征调能力(Ndff,Nitrogen derived from fertilizer)最大,其次为髓,叶片最小;欧美杨各组织器官中的15N分配率表现为叶片细根叶柄树皮粗根茎木质部髓。研究结果对进一步揭示植物吸收PM2.5的机制及有效利用植物降低颗粒物污染、净化环境提供了重要的科学理论依据。     

Regulation of Na/Mg antiport in rat erythrocytes

In rat erythrocytes, the regulation of Na⁺/Mg²⁺ antiport by protein kinases (PKs), protein phosphatases (PPs), intracellular Mg²⁺, ATP and Cl⁻ was investigated. In untreated erythrocytes, Na⁺/Mg²⁺ antiport was slightly inhibited by the PK inhibitor staurosporine, slightly stimulated by the PP inhibitor calyculin A and strongly stimulated by vanadate. PMA stimulated Na⁺/Mg²⁺ antiport. This effect was completely inhibited by staurosporine and partially inhibited by the PKC inhibitors Ro-31-8425 and BIM I. Participation of other PKs such as PKA, the MAPK cascade, PTK, CK I, CK II, CAM II-K, PI 3-K, and MLCK was excluded by use of inhibitors. Na⁺/Mg²⁺ antiport in rat erythrocytes can thus be stimulated by PKCα.In non-Mg²⁺-loaded erythrocytes, ATP depletion reduced Mg²⁺ efflux and PMA stimulation in NaCl medium. A drastic activation of Na⁺/Mg²⁺ antiport was induced by Mg²⁺ loading which was not further stimulated by PMA. Staurosporine, Ro-31-8425, BIM I and calyculin A did not inhibit Na⁺/Mg²⁺ antiport of Mg²⁺-loaded cells. Obviously, at high [Mg²⁺]_i Na⁺/Mg²⁺ antiport is maximally stimulated. PKC_α or PPs are not involved in stimulation by intracellular Mg²⁺. ATP depletion of Mg²⁺-loaded erythrocytes reduced Mg²⁺ efflux and the affinity of Mg²⁺ binding sites of the Na⁺/Mg²⁺ antiporter to Mg²⁺. In non-Mg²⁺-loaded erythrocytes Na⁺/Mg²⁺ antiport essentially depends on Cl⁻. Mg²⁺-loaded erythrocytes were less sensitive to the activation of Na⁺/Mg²⁺ antiport by [Cl⁻]_i.     

Scavenging of free radicals in gas-phase mainstream cigarette smoke by immobilized catalase at filter level

Catalase is well known as capable of inducing the decomposition of H₂O₂. In this study, a kind of immobilized catalase (entrapped in cross-linked chitosan beads) was dispersed in conventional acetate filter as an antioxidant additive. Quantitative estimation of the free radicals in mainstream cigarette smoke (MCS) was performed to address the effect of this modified filter. It was found that the levels of PBN adduct and NO^?/NO₂^? associated with the gas-phase mainstream cigarette smoke (GPCS) were efficiently decreased by ～40% through catalase filtering. Besides, the modified filter was found to lower the MCS-induced adverse biological effects including lipid peroxidation and mutagenicity. This was proved to be substantially attributed to the catalase-dependent breakdown of NO^?, which was stimulated by some of peroxides (most probably being H₂O₂), the dismutation products of tar particulate matters (TPM). These results highlighted a promising approach to reduce the smoking-associated health risks to passive smokers. Moreover, the mechanisms of catalase filtering may be helpful for the development of appropriate immobilized enzyme systems to be applied for reducing health risks associated with gaseous pollutants.     

Airway smooth muscle relaxation induced by 5-HT(2A) receptors: role of Na(+)/K(+)-ATPase pump and Ca(2+)-activated K(+) channels

AIMS: Although 5-hydroxytryptamine (5-HT) contracts airway smooth muscle in many mammalian species, in guinea pig and human airways 5-HT causes a contraction followed by relaxation. This study explored potential mechanisms involved in the relaxation induced by 5-HT. MAIN METHODS: Using organ baths, patch clamp, and intracellular Ca(2+) measurement techniques, the effect of 5-HT on guinea pig airway smooth muscle was studied. KEY FINDINGS: A wide range of 5-HT concentrations caused a biphasic response of tracheal rings. Response to 32 muM 5-HT was notably reduced by either tropisetron or methiothepin, and almost abolished by their combination. Incubation with 10 nM ketanserin significantly prevented the relaxing phase. Likewise, incubation with 100 nM charybdotoxin or 320 nM iberiotoxin and at less extent with 10 muM ouabain caused a significant reduction of the relaxing phase induced by 5-HT. Propranolol, L-NAME and 5-HT(1A), 5-HT(1B)/5-HT(1D) and 5-HT(2B) receptors antagonist did not modify this relaxation. Tracheas from sensitized animals displayed reduced relaxation as compared with controls. In tracheas precontracted with histamine, a concentration response curve to 5-HT (32, 100 and 320 muM) induced relaxation and this effect was abolished by charybdotoxin, iberiotoxin or ketanserin. In single myocytes, 5-HT in the presence of 3 mM 4-AP notably increased the K(+) currents (I(K(Ca))), and they were completely abolished by charybdotoxin, iberiotoxin or ketanserin. SIGNIFICANCE: During the relaxation induced by 5-HT two major mechanisms seem to be involved: stimulation of the Na(+)/K(+)-ATPase pump, and increasing activity of the high-conductance Ca(2+)-activated K(+) channels, probably via 5-HT(2A) receptors.     

The dynamics of mitochondrial Ca fluxes

We have investigated the kinetics of mitochondrial Ca²⁺ influx and efflux and their dependence on cytosolic [Ca²⁺] and [Na⁺] using low-Ca²⁺-affinity aequorin. The rate of Ca²⁺ release from mitochondria increased linearly with mitochondrial [Ca²⁺] ([Ca²⁺]_M). Na⁺-dependent Ca²⁺ release was predominant al low [Ca²⁺]_M but saturated at [Ca²⁺]_M around 400 μM, while Na⁺-independent Ca²⁺ release was very slow at [Ca²⁺]_M below 200 μM, and then increased at higher [Ca²⁺]_M, perhaps through the opening of a new pathway. Half-maximal activation of Na⁺-dependent Ca²⁺ release occurred at 5-10 mM [Na⁺], within the physiological range of cytosolic [Na⁺]. Ca²⁺ entry rates were comparable in size to Ca²⁺ exit rates at cytosolic [Ca²⁺] ([Ca²⁺]_c) below 7 μM, but the rate of uptake was dramatically accelerated at higher [Ca²⁺]_c. As a consequence, the presence of [Na⁺] considerably reduced the rate of [Ca²⁺]_M increase at [Ca²⁺]_c below 7 μM, but its effect was hardly appreciable at 10 μM [Ca²⁺]_c. Exit rates were more dependent on the temperature than uptake rates, thus making the [Ca²⁺]_M transients to be much more prolonged at lower temperature. Our kinetic data suggest that mitochondria have little high affinity Ca²⁺ buffering, and comparison of our results with data on total mitochondrial Ca²⁺ fluxes indicate that the mitochondrial Ca²⁺ bound/Ca²⁺ free ratio is around 10- to 100-fold for most of the observed [Ca²⁺]_M range and suggest that massive phosphate precipitation can only occur when [Ca²⁺]_M reaches the millimolar range.     

Sources of N uptake by wheat (Triticum aestivum L.) and N transformations in soil treated with a nitrification inhibitor (nitrapyrin)

Rates of N uptake by spring wheat as ammonium and as nitrate, and rates of nitrification, gross N immobilization and gross N mineralization were measured in a pot experiment during 84 days of growth in a clay soil. Soil treatments included an unfertilized control and addition of ¹⁵NH₄NO₃ or NH₄ ¹⁵NO₃ in the absence and presence of N-serve 24E. Incorporation of ammonium into the soil organic N pool was considerably higher in the presence compared to the absence of nitrapyrin, but the processes contributing to this effect could not be positively identified. Both dry matter and grain yield as well as N uptake by wheat were enhanced in the presence of the inhibitor in N fertilized soil, despite the increased immobilization of N. On the other hand, inhibitor application had a detrimental effect on yield and N uptake by wheat in unfertilized soil. Both ammonium and nitrate forms of inorganic N were absorbed by wheat, but nitrate uptake was dominant in the absence of the inhibitor. The uptake of N as ammonium was higher and the uptake of N as nitrate was less, both in absolute and proportional terms, in the presence compared to the absence of inhibitor. In addition, the proportion of N taken up as ammonium was higher than the proportion of N as ammonium in the available N pool up to day 56 in the inhibitor treatment, which indicated a preference for ammonium uptake by wheat. Evidence was obtained which suggested that several factors may have contributed to the positive response of wheat to inhibitor application in N fertilized soil, including reduced N losses, higher gross N mineralization and a physiological response due to the proportional increase in uptake of inorganic N as ammonium.     

天山林区不同类型群落土壤氮素对冻融过程的动态响应

季节性冻融过程对北方温带森林土壤氮素的转化与流失具有重要影响,但不同类型群落对冻融过程响应的差异尚不明确。通过在林地、草地、灌丛上设置系列监测样地,采用原位培养的方法,利用林冠遮挡形成的自然雪被厚度差异,监测分析了冻融期天山林区不同群落表层土壤(0—15 cm)的氮素动态及净氮矿化速率间的差异。结果表明:(1)不同类型群落土壤的铵态氮(NH+4-N)含量、微生物量氮(MBN)含量基本与土壤(5 cm)温度呈正相关,深冻期林地土壤铵态氮含量低于其他群落类型而硝态氮含量高于其他群落类型;(2)硝态氮(NO-3-N)为天山林区季节性冻融期间土壤矿质氮的主体,占比达78.4%。灌丛土壤硝态氮流失风险较大,融化末期较融化初期灌丛土壤硝态氮含量下降了64.6%;(3)冻融时期对整体氮素矿化速率影响显著,群落类型对氨化速率影响显著;(4)天山林区土壤氮素在冻结期主要以氮固持为主。通过揭示不同类型群落土壤氮素对冻融格局的响应,能够助益于对北方林区冬季土壤氮素循环的认识。