Effects of spironolactone and RU486 on gene expression and cell proliferation after freshwater transfer in the euryhaline killifish

We have explored the possible mechanisms by which mineralocorticoid (MR) and glucocorticoid (GR) receptors regulate the response to freshwater transfer in the gills of the euryhaline killifish Fundulus heteroclitus. Killifish were implanted with RU486 (GR antagonist) or spironolactone (MR antagonist) at doses of 0.1–1.0 mg g⁻¹, and subsequently transferred from 10‰ brackish water to freshwater. Compared to brackish water sham fish, mRNA expression of CFTR and NKCC1 decreased in the gills of sham fish transferred to freshwater, whereas Na⁺,K⁺–ATPase α_1a mRNA expression and α protein abundance, as well as cell proliferation (detected using BrdU) increased. Spironolactone inhibited the normal increase in cell proliferation and Na⁺,K⁺-ATPase expression after freshwater transfer. RU486 increased plasma cortisol levels and may have slightly inhibited Na⁺,K⁺–ATPase activity, but did not change α _1a expression. RU486 had no effect on cell proliferation in the non-lamellar region of the gills, but increased proliferation in the lamellar region. Neither antagonist inhibited the suppression of CFTR or NKCC1 expression after freshwater transfer. Glucocorticoid receptor expression was reduced in all sham and antagonist treatments compared to untreated controls, but no other consistent differences were observed. The effects of spironolactone suggest that MR is important for regulating ion transport in killifish gills after freshwater transfer.     

Fluxes of elements in rain passing through forest canopies in south-eastern Australia

The elemental content of rainfall (bulk deposition), throughfall and stemflow was measured inPinus radiata D. Don andEucalyptus forests in Gippsland, Victoria. Accessions in rainfall (mg m^–2 year^–1) averaged: organic-C 551, NO₃ ^–-N 96, NH₄ ⁺-N 62, total-N 303, K⁺ 382, Na⁺ 2250, Ca²⁺ 1170, and Mg²⁺ 678. The mean pH of rainfall was 5.9. Concentrations of all elements were greater in throughfall than in rainfall, and generally greater in stemflow than in throughfall. However, pH of pine throughfall was higher than that of rainfall, and pH of eucalypt throughfall was lower than that of rainfall. There was a net efflux of inorganic-N from pine crowns to rainfall, whilst in eucalypts there was generally net sorption of inorganic-N from rainfall. In both species organic-N was leached from the crowns and the net efflux of total-N from eucalypt crowns (50 mg m^–2 year^–1) averaged one-quarter of that in pines. Increases in the organic-C content of throughfall relative to rainfall in eucalypts were two to four times those in pines. Increases in the content of other elements in throughfall were comparable in pines and eucalypts and within the ranges K⁺ 615–1360, Na⁺ 480–-1840, Ca²⁺ 123–780 and Mg²⁺ 253–993 mg m^–2 year^–1. However, enrichment of Ca²⁺ may have been due to dust trapped in the canopies. Stemflow contributed significantly to the total amounts of elements reaching the forest floor in water.     

间伐强度对秦岭锐齿栎林冠层和枯落物层水化学效应的影响

将森林抚育间伐与森林水化学效应结合起来进行研究,探讨小强度间伐对森林水质的影响。基于固定样地的研究方法,在秦岭火地塘林区选择天然锐齿栎林,设置抚育间伐强度分别为5%、10%、15%和20%的样地和对照样地,定期采集大气降雨、林内雨和枯透水样品,测定其水化学物质浓度,采用对比分析的方法,研究间伐强度对锐齿栎林内雨和枯透水化学效应的影响。结果表明:间伐样地林内雨和枯透水的pH值均低于对照样地,呈弱酸性,在5%的间伐强度下,森林冠层和枯落物层对大气降雨pH值的调升作用较显著,随着间伐强度的增加,调升幅度逐渐减小;大气降雨对森林冠层和枯落物层中的SO_4~(2-)、NO_3~-和PO_4~(3-)均具有淋溶作用,尤其是对照样地林内雨和枯透水中SO_4~(2-)的浓度增幅最显著,NO_3~-次之,PO_4~(3-)最不显著。间伐样地,雨水对林冠层和枯落物层SO_4~(2-)、NO_3~-和PO_4~(3-)的淋溶作用均低于对照样地,20%的间伐强度最有利于净化雨水中的SO_4~(2-),其在林内雨和枯透水中的含量较对照样地降幅最大,间伐强度为5%时,林内雨中NO_3~-、NH_4~+和PO_4~(3-)的含量最低,三者较对照样地的含量分别降低了56.3%、46%和9.2%而枯透水中三者的降幅分别为64.6%、45%和60.8%;在10%的间伐强度下,大气降雨对林冠层和枯落物层中K~+、Ca~(2+)、Mg~(2+)的淋溶作用最强,3种离子中以Ca~(2+)和Mg~(2+)的含量增幅最为显著。林内雨中Ca~(2+)和Mg~(2+)的含量分别较对照样地增加了89.9%和120%,枯透水中二者较对照样地分别增加了72.4%和40%,K~+的增幅相对不明显;大气降雨中的Pb~(2+)、Zn~(2+)和Cd~(2+)经过森林冠层和枯落物层的阻减,其在林内雨和枯透水中的含量随着间伐强度的增加呈先增大后减小的趋势,当间伐强度达到20%时,三者含量明显降低。总体上,20%的间伐强度最有利于森林冠层及枯落物层对重金属Pb~(2+)、Zn~(2+)和Cd~(2+)的截留净化。     

Characterization of the Mn2+-stimulated (di)adenosine polyphosphate hydrolase encoded by the Deinococcus radiodurans DR2356 nudix gene

The DR2356 nudix hydrolase gene from Deinococcus radiodurans has been cloned and the product expressed as an 18 kDa histidine-tagged protein. The enzyme hydrolysed adenosine and diadenosine polyphosphates, always generating ATP as one of the initial products. ATP and other (deoxy)nucleoside triphosphates were also substrates, yielding (d)NDP and Pi as products. The DR2356 protein was most active at pH 8.6–9.0 and showed a strong preference for Mn²⁺ as activating cation. Mg²⁺ ions at 15 mM supported only 5% of the activity achieved with 2 mM Mn²⁺. K _m and k _cat values for diadenosine tetra-, penta- and hexaphosphates were 2.0, 2.4 and 1.1 μM and 11.4, 28.6 and 12.0 s⁻¹, respectively, while for GTP they were 20.3 μM and 1.8 s⁻¹, respectively. The K _m for adenosine 5′-pentaphosphate was <1 μM. Expression analysis showed the DR2356 gene to be induced eight- to ninefold in stationary phase and in cells subjected to slow dehydration plus rehydration. Superoxide (but not peroxide) treatment and rapid dehydration caused a two-to threefold induction. The Mn-requirement and induction in stationary phase suggest that DR2356 may have a specific role in maintenance mode metabolism in stationary phase as Mn²⁺ accumulates.     

Purification and characterization of two cold-adapted extracellular tannin acyl hydrolases from an Antarctic strain <Emphasis Type="Italic">Verticillium</Emphasis> sp. P9

Two extracellular tannin acyl hydrolases (TAH I and TAH II) produced by an Antarctic filamentous fungus Verticillium sp. P9 were purified to homogeneity (7.9- and 10.5-fold with a yield of 1.6 and 0.9%, respectively) and characterized. TAH I and TAH II are multimeric (each consisting of approximately 40 and 46 kDa sub-units) glycoproteins containing 11 and 26% carbohydrates, respectively, and their molecular mass is approximately 155 kDa. TAH I and TAH II are optimally active at pH of 5.5 and 25 and 20°C, respectively. Both the enzymes were activated by Mg²⁺and Br⁻ ions and 0.5–2.0 M urea and inhibited by other metal ions (Zn²⁺, Cu²⁺, K⁺, Cd²⁺, Ag⁺, Fe³⁺, Mn²⁺, Co²⁺, Hg²⁺, Pb²⁺ and Sn²⁺), anions, Tween 20, Tween 60, Tween 80, Triton X-100, sodium dodecyl sulphate, β-mercaptoethanol, α-glutathione and 4-chloromercuribenzoate. Both tannases more efficiently hydrolyzed tannic acid than methyl gallate. E _a of these reactions and temperature dependence (at 0–30°C) of k _cat, k _cat/K _m, ΔG*, ΔH* and ΔS* for both the enzymes and substrates were determined. The k _cat and k _cat/K _m values (for both the substrates) were considerably higher for the combined preparation of TAH I and TAH II.     

Effect of Sesbania,Azolla and rice straw incorporation on the kinetics of NH4, K,Fe, Mn,Zn and P in some flooded rice soils

In a greenhouse study, with and without rice plants, of five flooded Philippine rice soils whose organic C (OC) content varied from 0.5 to 3.6%, incorporation ofSesbania rostrata, Azolla microphylla and rice straw affected the kinetics of soil solution NH ₄ ⁺ −N, K⁺, Fe²⁺, Mn²⁺, Zn²⁺, and P. Sesbania and Azolla increased NH ₄ ⁺ −N concentration above the control treatment, whereas rice straw depressed it. In all soils Azolla released less NH ₄ ⁺ −N than Sesbania. The apparent net N release depended on the soil and ranged from 44–81% for Sesbania and 27–52% for Azolla. These effects persisted throughout the growth of IR36. Soil solution and exchangeable NH ₄ ⁺ −N increased initially but levelled off between 30 to 80 days and between 20 to 40 days after flooding (DF), respectively. With rice, soil solution NH ₄ ⁺ −N concentration, reached a peak at 15–40 DF and declined to very low levels (<4mg L⁻¹). In the 3 soils of low OC content nitrogen derived from green manure ranged from 34–53% and the apparent revovery of added green manure N varied from 29–67%. Almost all N released from both Azolla and Sesbania were recovered in the rice plant in all soils except Concepcion with only 77%. The concentration of K⁺, Fe²⁺, Mn²⁺ and P in the soil solution were higher with rice straw than Sesbania and Azolla in all soils except Hanggan which showed no change in Fe²⁺ and Mn²⁺ but increased K⁺ and P. In general, rice straw, Sesbania and Azolla decreased Zn²⁺ concentration in all soils.     

A novel highly acidic β-mannanase from the acidophilic fungus Bispora sp. MEY-1: gene cloning and overexpression in Pichia pastoris

Using degenerate polymerase chain reaction (PCR) and thermal asymmetric interlaced PCR, a 1,347-bp full-length complementary DNA fragment encompassing the gene man5A, which encodes a 429-amino acid β-mannanase with a calculated mass of 46.8 kDa, was cloned from acidophilic Bispora sp. MEY-1. The deduced amino acid sequence (catalytic domain) displayed highest identity (54.1%) with the Emericella nidulans endo-β-1,4-d-mannanase, a member of the glycoside hydrolase family 5. Recombinant MAN5A was overexpressed in Pichia pastoris, and its activity in the culture medium reached 500 U ml⁻¹. The enzyme was acidophilic, with highest activity at pH 1.0–1.5, lower than any known mannanases, and optimal temperature for activity was 65°C. MAN5A had good pH adaptability, excellent thermal and pH stability, and high resistance to both pepsin and trypsin. The specific activity, K _m, and V _max for locust bean gum substrate was 3,373 U mg⁻¹, 1.56 mg ml⁻¹, and 6,587.6 μmol min⁻¹ mg⁻¹, respectively. The enzymatic activity was not significantly affected by ions such as Ca²⁺, Cr³⁺, Co²⁺, Zn²⁺, Na⁺, K⁺, and Mg²⁺ and enhanced by Ni²⁺, Fe³⁺, Mn²⁺ and Ag⁺. These favorable properties make MAN5A a potential candidate for use in various industrial applications.     

Water chemistry and nutrient budgets in an undisturbed evergreen rainforest of southern Chile

In a pristine evergreen rainforest of Nothofagus betuloides, located at the Cordillera de los Andes in southern Chile (41 °S), concentrations and fluxes of nutrients in bulk precipitation, cloud water, throughfall water, stemflow water, soil infiltration and percolation water and runoff water were measured. The main objectives of this study were to investigate canopy-soil-atmosphere interactions and to calculate input-output budgets. From May 1999 till April 2000, the experimental watershed received 8121 mm water (86% incident precipitation, 14% cloud water), of which the canopy intercepted 16%. Runoff water volume amounted 9527 mm. Bulk deposition of inorganic (DIN) and organic (DON) nitrogen amounted 3.6 kg ha^–1 year^–1 and 8.2 kg ha^–1 year^–1 respectively. Occult deposition (clouds + fog) contributes for 40% to the atmospheric nitrogen input (bulk + occult deposition) of the forest. An important part of the atmospheric ammonium deposition is retained within the canopy or converted to nitrate or organic nitrogen by epiphytic bacteria or lichens. Also the export of inorganic (0.9 kg ha^–1 year^–1) and organic (5.2 kg ha^–1 year^–1) nitrogen via runoff is lower than the input to the forest floor via throughfall and stemflow water (3.2 kg DIN ha–1 year^–1 and 5.6 kg DON ha^–1 year^–1). The low concentrations of NO ₃ ^– and NH ₄ ⁺ under the rooting depth suggest an effective biological immobilization by vegetation and soil microflora. Dry deposition and foliar leaching of base cations (K⁺, Ca²⁺, Mg²⁺) was estimated using a canopy budget model. Bulk deposition accounted for about 50% of the total atmospheric input. Calculated dry and occult deposition are both of equal value (about 25%). Foliar leaching of K⁺, Ca²⁺, and Mg²⁺ accounted for 45%, 38% and 6% of throughfall deposition respectively. On an annual basis, the experimental watershed was a net source for Na⁺, Ca²⁺ and Mg²⁺.     

Purification and characterization of polygalacturonase produced by thermophilic Thermoascus aurantiacus CBMAI-756 in submerged fermentation

An extracellular polygalacturonase was isolated from 5-day culture filtrates of Thermoascus aurantiacus CBMAI-756 and purified by gel filtration and ion-exchange chromatography. The enzyme was maximally active at pH 5.5 and 60–65°C. The apparent K _m with citrus pectin was 1.46 mg/ml and the V _max was 2433.3 μmol/min/mg. The apparent molecular weight of the enzyme was 30 kDa. The enzyme was 100% stable at 50°C for 1 h and showed a half-life of 10 min at 60°C. Polygalacturonase was stable at pH 5.0–5.5 and maintained 33% of initial activity at pH 9.0. Metal ions, such as Zn⁺², Mn⁺², and Hg⁺², inhibited 50, 75 and 100% of enzyme activity. The purified polygalacturonase was shown to be an endo/exo-enzyme, releasing mono, di and tri-galacturonic acids within 10 min of hydrolysis.     

Fluorescent labeling of (Na + K)-ATPase by 5-iodoacetamidofluorescein

5-Iodoacetamidofluorescein (5-IAF) covalently labels dog kidney (Na⁺ + K⁺)-ATPase with approximately 2 moles incorporated per mole of enzyme. ATPase and K⁺-phosphatase activities are fully retained after reaction, and the kinetic parameters for Na⁺, K⁺, Mg²⁺, ATP and p-nitrophenyl phosphate are likewise not significantly affected. The fluorescence of the bound 5-IAF is increased by ATP, Na⁺, and Mg²⁺, and decreased by K⁺. These fluorescence changes likely reflect ligand-induced stabilization of the E₁ or E₂ states of the enzyme.     

Expression,purification and characterization of pectate lyase A from <Emphasis Type="Italic">Aspergillus nidulans</Emphasis> in <Emphasis Type="Italic">Escherichia coli</Emphasis>

Pectate lyase A (PelA) of Aspergillus nidulans was successfully expressed in Escherichia coli and effectively purified using a Ni²⁺-nitrilotriacetate-agarose column. Enzyme activity of the recombinant PelA could reach 360 U ml⁻¹ medium. The expressed PelA exhibited its optimum level of activity over the range of pH 7.5–10 at 50°C. Mn²⁺, Ca²⁺, Fe²⁺, Mg²⁺ and Fe³⁺ ions stimulated the pectate lyase activity, but Cu²⁺ and Zn²⁺ inhibited it. The recombinant PelA had a V _max of 77 μmol min⁻¹ mg⁻¹ and an apparent K _m of 0.50 mg ml⁻¹ for polygalacturonic acid. Low-esterified pectin was the optimum substrate for the PelA, whereas higher-esterified pectin was hardly cleaved by it. PelA efficiently macerated mung bean hypocotyls and potato tuber tissues into single cells.     

Characterization of Active Lentinula edodes Glucoamylase Expressed and Secreted by Saccharomyces cerevisiae

The gene encoding Lentinula edodes glucoamylase (GLA) was cloned into Saccharomyces cerevisiae, expressed constitutively and secreted in an active form. The enzyme was purified to homogeneity by (NH₄)₂SO₄ fractionation, anion exchange and affinity chromatography. The protein had a correct N-terminal sequence of WAQSSVIDAYVAS, indicating that the signal peptide was efficiently cleaved. The recombinant enzyme was glycosylated with a 2.4% carbohydrate content. It had a pH optimum of 4.6 and a pH 3.4–6.4 stability range. The temperature optimum was 50°C with stability ≤50°C. The enzyme showed considerable loss of activity when incubated with glucose (44%), glucosamine (68%), galactose (22%), and xylose (64%). The addition of Mn⁺⁺ activated the enzyme by 45%, while Li⁺, Zn⁺⁺, Mg⁺⁺, Cu⁺, Ca⁺⁺, and EDTA had no effect. The enzyme hydrolyzed amylopectin at rates 1.5 and 8.0 times that of soluble starch and amylose, respectively. Soluble starch was hydrolyzed 16 and 29 times faster than wheat and corn starch granules, respectively, with the hydrolysis of starch granules using 10× the amount of GLA. Apparent K_m and V_max for soluble starch were estimated to be 3.0 mg/ml and 0.13 mg/ml/min (40°C, pH 5.3), with an apparent k_cat of 2.9×10⁵ min⁻¹.     

De novo synthesis,constitutive expression of <Emphasis Type="Italic">Aspergillus sulphureus</Emphasis> β-xylanase gene in <Emphasis Type="Italic">Pichia pastoris</Emphasis> and partial enzymic characterization

The endo-β-1, 4-xylanase gene xynA from Aspergillus sulphureus, encoded a lack-of-signal peptide protein of 184 amino acids, was de novo synthesized by splicing overlap extension polymerase chain reaction according to Pichia pastoris protein’s codon bias. The synthetic DNA, composed of 572 nucleotides, was ligated into the downstream sequence of an α-mating factor in a constitutive expression vector pGAPzαA and electrotransformed into the P. pastoris X-33 strain. The transformed yeast screened by Zeocin was able to constitutively secrete the xylanase in yeast–peptone–dextrose liquid medium. The heterogenous DNA was stabilized in the strain by 20-times passage culture. The recombinant enzyme was expressed with a yield of 120 units/mL under the flask culture at 28°C for 3 days. The enzyme showed optimal activity at 50°C and pH 2.4–3.4. Residual activity of the raw recombinant xylanase was not less than 70% when fermentation broth was directly heated at 80°C for 30 min. However, the dialyzed xylanase supernatant completely lost the catalytic activity after being heated at 60°C for 30 min. The recombinant xylanase showed no obvious activity alteration by being pretreated with Na₂HPO₄-citric acid buffer of pH 2.4 for 2 h. The xylanase also showed resistance to certain metal ions (Na⁺, Mg²⁺, Ca²⁺, K⁺, Ba²⁺, Zn²⁺, Fe²⁺, and Mn²⁺) and EDTA. These biochemical characteristics suggest that the recombinant xylanase has a prospective application in feed industry as an additive.     

珍稀濒危植物长白松(Pinus sylvestris var. sylvestriformis)天然种群生存压力

为了揭示珍稀濒危植物长白松（Pinus sylvestris var. sylvestriformis）天然种群生存压力状况,在全面调查长白山国家级自然保护区长白松分布的基础上,基于邻体干扰模型,引入树高、冠幅、方位等因子,提出3种生存压力指数：个体生存压力指数、种群生存压力指数和群落生存压力指数,分析天然长白松所处6种群落类型中的生存压力。结果表明：长白松承受群落生存压力（PI）从大到小依次为：白桦-臭冷杉群落（PI=21.532）、红松-长白松群落（PI=14.185）、白桦群落（PI=13.262）、臭冷杉-长白松群落（PI=8.752）、长白落叶松-鱼鳞云杉群落（PI=7.780）和蒙古栎群落（PI=5.440）。多重比较单向方差分析表明,6种群落类型中长白松生存压力总体上差异明显,白桦-臭冷杉群落中长白松生存压力最大,显著高于其他5种群落;竞争树种主要为长白落叶松、红松、长白松、山杨和白桦,这5个树种生存压力大小占群落生存压力的87%;红松-长白松群落和白桦群落中长白松生存压力无明显差异,但显著高于臭冷杉-长白松群落、长白落叶松-鱼鳞云杉群落和蒙古栎群落;臭冷杉-长白松群落、长白落叶松-鱼鳞云杉群落和蒙古栎群落中长白松生存压力相对较小,彼此无明显差异。长白松生存压力与其所处植物群落演替阶段及其龄级结构有关。目前,保护区采取严格保护和管理方式不完全有利于长白松种群的稳定发展。根据长白松种群所处的植物群落生境特点、种群生存压力状况并结合种群年龄结构特征,针对不同群落类型提出相应抚育措施建议以期为长白松天然种群的保护提供参考。     

Na<Superscript>+</Superscript>,K<Superscript>+</Superscript>-ATPase Activity in the Posterior Gills of the Blue Crab, <Emphasis Type="Italic">Callinectes ornatus</Emphasis> (Decapoda,Brachyura): Modulation of ATP Hydrolysis by the Biogenic Amines Spermidine and Spermine

We investigated the effect of the exogenous polyamines spermine, spermidine and putrescine on modulation by ATP, K⁺, Na⁺, NH₄ ⁺ and Mg²⁺ and on inhibition by ouabain of posterior gill microsomal Na⁺,K⁺-ATPase activity in the blue crab, Callinectes ornatus, acclimated to a dilute medium (21‰ salinity). This is the first kinetic demonstration of competition between spermine and spermidine for the cation sites of a crustacean Na⁺,K⁺-ATPase. Polyamine inhibition is enhanced at low cation concentrations: spermidine almost completely inhibited total ATPase activity, while spermine inhibition attained 58%; putrescine had a negligible effect on Na⁺,K⁺-ATPase activity. Spermine and spermidine affected both V and K for ATP hydrolysis but did not affect ouabain-insensitive ATPase activity. ATP hydrolysis in the absence of spermine and spermidine obeyed Michaelis–Menten behavior, in contrast to the cooperative kinetics seen for both polyamines. Modulation of V and K by K⁺, Na⁺, NH₄ ⁺ and Mg²⁺ varied considerably in the presence of spermine and spermidine. These findings suggest that polyamine inhibition of Na⁺,K⁺-ATPase activity may be of physiological relevance to crustaceans that occupy habitats of variable salinity.     

Throughfall chemistry in a loblolly pine plantationunder elevated atmospheric CO2 concentrations

Accelerated tree growth under elevatedatmospheric CO₂ concentrations may influencenutrient cycling in forests by (i) increasingthe total leaf area, (ii) increasing the supplyof soluble carbohydrate in leaf tissue, and (iii) increasing nutrient-use efficiency. Here wereport the results of intensive sampling andlaboratory analyses of NH ₄ ⁺ , NO ₃ ^– , PO ₄ ^3– , H⁺, K⁺, Na⁺,Ca²⁺, Mg²⁺, Cl^–, SO ₄ ^2– , and dissolved organic carbon (DOC) in throughfallprecipitation during the first 2.5+ years of the DukeUniversity Free-Air CO₂ Enrichment (FACE)experiment. After two growing seasons, a largeincrease (i.e., 48%) in throughfall deposition of DOCand significant trends in throughfall volume and inthe deposition of NH ₄ ⁺ , NO ₃ ^– , H⁺, and K⁺ can be attributed to the elevatedCO₂ treatment. The substantial increase indeposition of DOC is most likely associated withincreased availability of soluble C in plant foliage,whereas accelerated canopy growth may account forsignificant trends toward decreasing throughfallvolume, decreasing deposition of NH ₄ ⁺ ,NO ₃ ^– , and H⁺, and increasing deposition of K⁺ under elevated CO₂. Despiteconsiderable year-to-year variability, there wereseasonal trends in net deposition of NO ₃ ^– ,H⁺, cations, and DOC associated with plant growthand leaf senescence. The altered chemical fluxes inthroughfall suggest that soil solution chemistry mayalso be substantially altered with continued increasesin atmospheric CO₂ concentrations in the future.     

Leaching of nitrate and ammonium in heathland and forest ecosystems in Northwest Germany under the influence of enhanced nitrogen deposition

To study the impact of high atmospheric nitrogen deposition on the leaching of NO₃^– and NH₄⁺ beneath forest and heathland vegetation, investigations were carried out in adjacent forest and heathland ecosystems in Northwest Germany. The study area is subjected to high deposition of nitrogen ranging from 15.9 kg ha^–1 yr^–1 in bulk precipitation to 65.3 kg ha^–1 yr^–1 beneath a stand of Pinus sylvestris L. with NH₄–N accounting for 70–80% of the nitrogen deposited. Considerable leaching of nitrogen compounds from the upper horizons of the soil, mostly as nitrate, occurred at most of the forest sites and below a mixed stand of Calluna vulgaris (L.) Hull. and Erica tetralix, but was low in a Betula pubescens Ehrh. swamp forest as well as beneath Erica tetralix L. wet heath and heath dominated by Molinia caerulea(L.) Moench. Ground water concentrations of both NO₃–N and NH₄–N did not exceed 1 mg L^–1 at most of the sites investigated.     

Participation of vacuoles in regulation of levels of K+, Mg2+ and orthophosphate ions in cytoplasm of the yeast Saccharomyces carlsbergensis

Intracellular distributions of K⁺, Mg²⁺ and orthophosphate under various conditions of cultivation or incubation of the yeast Saccharomyces carlsbergensis were studied by differential extraction of ion pools. The decisive role of vacuolar compartmentation of ions in regulation of K⁺, Mg²⁺ and orthophosphate levels in the yeast cytoplasm was shown. The content of intracellular K⁺ and Mg²⁺ in yeast increased or decreased primarily depending on the increase or decrease in the vacuolar ion pool. The levels of K⁺ and Mg²⁺ in the cytoplasm were practically unchanged. Vacuoles were involved in regulation of Mn²⁺ concentration in the cytoplasm of the yeast S. carlsbergensis accumulating this ion in the presence of glucose. Alongside the vacuolar compartmentation, the chemical compartmentation, i. e. formation of bound Mg²⁺, Mn²⁺ and K⁺ was, evidently, also involved in the control of ion levels in the cytoplasm. The orthophosphate level in the yeast cytoplasm was regulated by its accumulation in vacuoles and biosynthesis of inorganic polyphosphates in these organelles. The biosynthesis of low-molecular weight polyphosphates occurred parallel to the accumulation of Mg²⁺ or Mn²⁺ in vacuoles, thus confirming the availability of the other mechanism for the transport of these ions through the tonoplast differing from the transport mechanism through the plasmalemma.     

Natural 15N abundance of soil N pools and N2O reflect the nitrogen dynamics of forest soils

Natural ¹⁵N abundance measurements of ecosystem nitrogen (N) pools and ¹⁵N pool dilution assays of gross N transformation rates were applied to investigate the potential of δ¹⁵N signatures of soil N pools to reflect the dynamics in the forest soil N cycle. Intact soil cores were collected from pure spruce (Picea abies (L.) Karst.) and mixed spruce-beech (Fagus sylvatica L.) stands on stagnic gleysol in Austria. Soil δ¹⁵N values of both forest sites increased with depth to 50 cm, but then decreased below this zone. δ¹⁵N values of microbial biomass (mixed stand: 4.7 ± 0.8‰, spruce stand: 5.9 ± 0.9‰) and of dissolved organic N (DON; mixed stand: 5.3 ± 1.7‰, spruce stand: 2.6 ± 3.3‰) were not significantly different; these pools were most enriched in ¹⁵N of all soil N pools. Denitrification represented the main N₂O-producing process in the mixed forest stand as we detected a significant ¹⁵N enrichment of its substrate NO₃⁻ (3.6 ± 4.5‰) compared to NH₄⁺ (−4.6 ± 2.6‰) and its product N₂O (−11.8 ± 3.2‰). In a ¹⁵N-labelling experiment in the spruce stand, nitrification contributed more to N₂O production than denitrification. Moreover, in natural abundance measurements the NH₄⁺ pool was slightly ¹⁵N-enriched (−0.4 ± 2.0 ‰) compared to NO₃⁻ (−3.0 ± 0.6 ‰) and N₂O (−2.1 ± 1.1 ‰) in the spruce stand, indicating nitrification and denitrification operated in parallel to produce N₂O. The more positive δ¹⁵N values of N₂O in the spruce stand than in the mixed stand point to extensive microbial N₂O reduction in the spruce stand. Combining natural ¹⁵N abundance and ¹⁵N tracer experiments provided a more complete picture of soil N dynamics than possible with either measurement done separately.     

Osmotic adjustment and ion balance traits of an alkali resistant halophyte Kochia sieversiana during adaptation to salt and alkali conditions

Kochia sieversiana (Pall.) C. A. M., a naturally alkali-resistant halophyte, was chosen as the test organism for our research. The seedlings of K. sieversiana were treated with varying (0–400 mM) salt stress (1:1 molar ratio of NaCl to Na₂SO₄) and alkali stress (1:1 molar ratio of NaHCO₃ to Na₂CO₃). The concentrations of various solutes in fresh shoots, including Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, SO₄²⁻, NO₃⁻, H₂PO₃⁻, betaine, proline, soluble sugar (SS), and organic acid (OA), were determined. The water content (WC) of the shoots was calculated and the OA components were analyzed. Finally, the osmotic adjustment and ion balance traits in the shoots of K. sieversiana were explored. The results showed that the WC of K. sieversiana remained higher than 6 [g g⁻¹ Dry weight (DW)] even under the highest salt or alkali stress. At salinity levels >240 mM, proline concentrations increased dramatically, with rising salinity. We proposed that this was not a simple response to osmotic stress. The concentrations of Na⁺ and K⁺ all increased with increasing salinity, which implies that there was no competitive inhibition for absorption of either in K. sieversiana. Based on our results, the osmotic adjustment feature of salt stress was similar to that of alkali stress in the shoots of K. sieversiana. The shared essential features were that the shoots maintained a state of high WC, OA, Na⁺, K⁺ and other inorganic ions, accumulated largely in the vacuoles, and betaine, accumulated in cytoplasm. On the other hand, the ionic balance mechanisms under both stresses were different. Under salt stress, K. sieversiana accumulated OA and inorganic ions to maintain the intracellular ionic equilibrium, with close to equal contributions of OA and inorganic ions to anion. However, under alkali stress, OA was the dominant factor in maintaining ionic equilibrium. The contribution of OA to anion was as high as 84.2%, and the contribution of inorganic anions to anion was only 15.8%. We found that the physiological responses of K. sieversiana to salt and alkali stresses were unique, and that mechanisms existed in it that were different from other naturally alkali-resistant gramineous plants, such as Aneurolepidium chinense, Puccinellia tenuiflora. Responsible Editor: John McPherson Cheeseman.