Thermal stratification and the stability of meromixis in the Pretoria Salt Pan,South Africa

The Pretoria Salt Pan, South Africa, a small (0.076 km²), shallow (Z_max = 2.85 m), hypersaline, maar lake, lies within a clearly-defined crater and is fed by a perennial, slightly saline (3 g l^-1) artesian spring. The lake has two distinct solar-heated peaks in its temperature profile, each of these peaks located in a highly turbid (>80 JTU) layer below a steep chemocline. The upper thermal peak, located at a depth of 10 cm, was transient, with a distinct diel pattern of diurnal heating and nocturnal cooling. The lower thermal peak, located below a steep chemocline and centred at approximately 60 cm, was stable and showed a seasonal pattern of winter heating (maximum: 38.5°C) and summer cooling (minimum: 27.4°C). The unusual bathymetry of the lake, combined with the sheltering effect of the crater rim and steep salinity gradient between the surface (30–80 g l^-1) and bottom water (280–310 g l^-1) prevented windmixing of surface waters beyond a depth of approximately 50 cm. During a 28 month study all water deeper than 55 cm remained anaerobic, and the lake appeared to be meromictic.     

Vertical profiles of primary productivity,biomass and physico-chemical properties in meromictic Big Soda Lake,Nevada, U.S.A.

The contribution of bacteria to total primary production was estimated in Big Soda Lake and related to vertical profiles of biomass and various physical and chemical properties. The purple sulfur bacteriaThiocapsa sp. was responsible for 25% of the total primary production. Bacteriochlorophyll (BChl) distribution and DCMU sensitivity experiments confirmed this bacterial activity. High concentrations of photosynthetically inactive phytoplankton were detected in anaerobic-low redox water and were attributed to an early season algal bloom that had settled into a zone of maximal viscosity. Nutrient enrichment bioassay experiments indicated that iron was the most important nutrient controlling early season algal growth.     

Ca2+位于H2O2上游参与H2S诱导的拟南芥气孔关闭过程

以拟南芥为材料,利用药理学实验,结合分光光度法和激光共聚焦显微技术,研究了Ca2+在硫化氢(H2S)诱导拟南芥气孔关闭过程中的作用及其与过氧化氢(H2O2)的关系。结果表明： H2S诱导气孔关闭, Ca2+螯合剂EGTA和质膜Ca2+通道阻断剂硝苯地平(Nif)能不同程度抑制H2S诱导的气孔关闭,而内质网钙泵阻断剂毒胡萝卜素(Thaps)对H2S的作用无显著影响。由此推测, Ca2+参与调节H2S诱导的拟南芥气孔关闭过程,且胞质中Ca2+来源于胞外Ca2+的内流。另外, H2S诱导拟南芥叶片NADPH氧化酶基因AtRBOHD和AtRBOHF以及细胞壁过氧化物酶基因AtPRX34表达增强,促进叶片和保卫细胞中H2O2积累, EGTA对此起抑制作用,而外源CaCl2处理上调AtRBOHD、AtRBOHF和AtPRX34的表达。表明Ca2+可能位于H2O2上游参与H2S诱导的拟南芥气孔关闭过程。     

Growth kinetics of the photosynthetic bacterium Chlorobium thiosulfatophilum in a fed-batch reactor

Hydrogen sulfide dissolved in water can be converted to elementary sulfur or sulfate by the photosynthetic bacterium Chlorobium thiosulfatophilum. Substrate inhibition occurred at sulfide concentrations above 5.7 mM. Light inhibition was found at average light intensities of 40,000 lux in a sulfide concentration of 5 mM, where no substrate inhibition occurred. Light intensity, the most important growth parameter, was attenuated through both scattering by sulfur particles and absorption by the cells. Average cell and sulfur particle sizes were 1.1 and 9.4 mum, respectively. Cells contributed 10 times as much to the turbidity as sulfur particles of the same weight concentration. The light attenuation factor was mathematically modeled, considering both the absorption and scattering effects based on the Beer-Lambert law and the Rayleigh theory, which were introduced to the cell growth model. Optimal operational conditions relating feed rate vs. light intensity were obtained to suppress the accumulation of sulfate and sulfide and save light energy for 2- and 4-L fed-batch reactors. Light intensity should be greater for the same performance (H(2)S removal rate/unit cell concentration) in larger reactors due to the scaleup effect on light transmission. Knowledge of appropriate growth kinetics in photosynthetic fed-batch reactors was essential to increase feed rate and light intensity and therefore cell growth. A mathematical model was developed that describes the cell growth by considering the light attenuation factor due to scattering and absorption and the crowding effect of the cells. This model was in good agreement with the experimental results. (c) 1992 John Wiley & Sons, Inc.     

A family of pneumatically-operated thin layer samplers for replicate sampling of heterogeneous water columns

A series of inexpensive, pneumatic thin layer water samplers is described. They can be operated from small boats, and permit sampling at 2.5 cm intervals with little or no disturbance of stratified systems such as oxyclines or redoxclines of meromictic lakes, or microstratification of flagellates in sheltered epilimnia. Some models permit replicate sampling at closely-spaced intervals in a two-dimensional array. Their performance abilities are illustrated with examples of microstratification.     

Intervention de l'oxygène atmosphériqoe sur l'absorption d'eau chez Helianthus annuus

The role of atmospheric oxygen on root water absorption in Helianthus annuus . The effect of atmospheric anoxia on root water absorption was studied. The experiments were carried out on intact young sunflowers in controlled temperature, light and gas environment; roots were kept in aerated nutrient solution at constant temperature. The evolution of root water absorption and transpiration rate was measured continuously. Before the experiment, the plant was preconditioned at a high transpiration rate by illumination or by CO₂ free air in darkness. Then the atmospheric oxygen was suppressed for 1 h, after which the normal conditions were restored.
In anoxia and darkness, the root water absorption cannot balance transpiration, so that an important water stress develops in the plant; the light compensates this effect through the photosynthetic oxygen. The supply of oxygen, in darkness or in light, immediately removes inhibition of stomatal closure and of root water absorption. Two mechanisms control water absorption by roots: the fast one occurs in the leaves and the slower one cannot develop without the root system.     

Chemical analysis of Lake Shira water (1997–2000)

The paper presents the results of chemical analysis of Shira during summer (July-August). The chemical composition of waters in the water body was found to be fairly homogeneous horizontally. However, the concentrations of most ions increased with depth. The near-bottom layers were characterised by higher total mineral content and ash content, higher concentration of sulphates, sulphites, sulphide, phosphorus, ammonium nitrogen, as compared to the layers above. Maximum concentration of oxygen was recorded in 6–8 m stratum, where the photosynthetic processes were most active. The anaerobic layer which lay below the 12 m depth contained high concentrations of sulphide and sulphite. The composition of the lake water could be characterised as sulphate-chloride-bicarbonate sodium-magnesium. The changes in the water quality due to any anthropogenic emissions were not marked.     

大豆叶绿素分子光能吸收特性

明确叶绿素分子有效光能吸收截面对深入了解植物光合过程具有重要意义。为定量且全面探讨光合色素分子有效光能吸收截面对光强的响应,以大豆(Glycine max)为例,设置全日照和遮荫两种光强处理,首先测量CO₂浓度分别为300、400、500 μmol/mol和600 μmol/mol时叶片电子传递速率对光强的响应曲线(J/I曲线);测量大豆叶片的叶绿素含量;然后结合光合机理模型计算本征光能吸收截面(σ_ik)、有效光能吸收截面(σ''_ik)和捕光色素分子处于激发态的最小平均寿命(τ_min)等光合参数。结果表明,光合机理模型可很好地拟合两种光强条件下不同CO₂浓度下大豆叶片的J/I曲线,其决定系数均大于0.99;不同CO₂浓度下,遮荫和全日照下最大电子传递速率(J_max)范围分别为126.03-164.34 μmol m^-2 s^-1和273.33-326.92 μmol m^-2 s^-1,τ_min值范围分别为16.15—22.93 ms和3.65-4.64 ms。与全日照相比,遮荫条件下大豆叶片捕光色素分子的光能吸收能力明显较低,而处于最低激发态的叶绿素分子数则明显较大。相同光照处理下,不同CO₂浓度对大豆叶片的σ_ik和τ_min值无显著影响,而σ''_ik值随着CO₂浓度增加而整体呈减小趋势。以400 μmol/mol CO₂浓度时的相关光合参数为例,结合电子传递速率计算公式,首次从叶绿素分子光能吸收特性角度定量解释了全日照条件下大豆叶片具较高J_max的原因。这为定量研究叶绿素分子有效光能吸收截面提供了新的研究手段。     

光照强度对小麦苗期草酸氧化酶活性的影响

以小麦品种‘烟优361’(Triticum aestivum L.cv.Yanyou 361)萌发4 d幼苗为试验材料,分析了草酸氧化酶(OxO)在幼苗中的定位和表达,以及光照强度处理对小麦幼苗OxO活性的影响。实验结果显示,萌发后小麦幼苗的OxO分布在子叶与根的连接处和成熟的根中,其活性随光照强度的增加而下降;200μmol.m-2.s-1的强光显著抑制了OxO活性,该处理培养4 d幼苗的OxO活性仅为40μmol.m-2.s-1光照培养条件下的18.7%;强光还缩短OxO在苗期的表达时间,抑制了OxO的mRNA表达量。同时,光照强度还能影响小麦幼苗中H2O2的含量,200μmol.m-2.s-1处理幼苗的H2O2的含量显著下降,其培养4 d的幼苗H2O2含量仅为40μmol.m-2.s-1光照强度培养条件下的18.0%。研究发现,光照强度可通过调节OxO的活性和表达量来控制H2O2的产量,从而影响幼苗的生长发育。     

硫化氢对大鼠血小板精氨酸转运的影响

目的:观察新型气体信号分子硫化氢(H2S)对血小板L-精氨酸(L-Arg)转运的影响以探讨硫化氢对血小板功能的影响。方法:采用饱和H2S溶液作为H2S供体,制备大鼠富血小板血浆,使用含有不同浓度硫化氢的孵育液对大鼠血小板进行预孵育,检测同位素标记的L-Arg在血小板转运的情况,以判断硫化氢对血小板精氨酸转运的影响。结果:不同浓度的H2S(6.25、12.5、25、50、100μmol/L)存在时均血小板对L-Arg转运速率均低于对照组;H2S可以快速降低血小板L-Arg转运速率;转运动力学显示H2S显著降低血小板L-Arg转运Vmax(P0.05),但对Km值无明显影响。结论:硫化氢可能通过快速改变血小板L-精氨酸转运系统功能影响血小板功能。     

硫化氢与细胞的增殖和凋亡

硫化氢是内源性气体分子家族中的一员,是一种气体递质（gasotransmitter）。近年来,内源性硫化氢的产生及生理意义已经被认识,其代谢异常与许多疾病有关。本文综述了最近发现的硫化氢对细胞增殖和凋亡的调节作用,并重点概述硫化氢细胞效应的分子机制,包括丝裂原活化蛋白激酶、细胞周期相关激酶、细胞死亡相关基因以及离子通道等的改变。对硫化氢调节细胞生长或死亡的深入了解将为新药设计及许多疾病的治疗提供新的思路。     

十字花科蔬菜细菌性黑斑病研究概述

文中介绍了十字花科蔬菜细菌性黑斑病的研究进展,主要包括病症、病害分布、病原菌特征、冠毒素及检测技术等,并介绍了十字花科蔬菜细菌性黑斑病的防治对策,从而为十字花科蔬菜的生产提供更关心翔实的理论依据。     

Characterization of Thiobacillus thioparus isolated from an activated sludge bioreactor used for hydrogen sulfide treatment

AIMS: To compare Thiobacillus thioparus population dynamics in a control and a test activated sludge (AS) bioreactor, used for hydrogen sulfide (H(2)S) degradation. METHODS AND RESULTS: Denaturing gradient gel electrophoresis (DGGE) was used to confirm the presence of T. thioparus, and real-time PCR was used to quantify the level of this bacterium in the AS samples. The DGGE analysis showed a band for T. thioparus in all samples, with the band being more prominent in the test sample with H(2)S diffusion. It also showed that although a change occurred in the diversity of the microbial population in the test sludge after 6 weeks of H(2)S diffusion, the microbial community structure of the test and control was still similar. Thiobacillus thioparus-specific PCR primers confirmed that 50% of the isolates from both the test and control bioreactors were T. thioparus. The thiobacilli population became more efficient at degrading the diffused H(2)S. This increase in efficiency was confirmed by a significant increase in the number of isolates from the test sludge compared with those from the control sludge, when they were grown in a thiosulfate-rich liquid medium. CONCLUSIONS: It was concluded that the use of AS process for H(2)S removal encourages the population of T. thioparus to increase even at times when the total biomass concentration shows a decrease. SIGNIFICANCE AND IMPACT OF THE STUDY: The research results give an insight into the dynamics of the microbial population in an AS pilot plant used in a dual role, to treat the wastewater and H(2)S.     

Vertical distribution and rotifer concentrations in the chemocline of meromictic lakes

The vertical distribution of planktonic rotifers has been analysed in relation to season in several meromictic lakes; a coastal lagoon with sea-water intrusion and three dissolution lakes from two karstic systems. Two species, Filinia hofmanni and a form of Anuraeopsis fissa have been found to be more or less restricted to the chemocline or adjacent strata any time they occurred. Many species common in the upper water layers developed large populations near or in the chemocline and more strikingly in summer. Some species had two vertical maxima (one in the surface or the thermocline and another near the chemocline), while others successively shifted their maxima between the upper layers and the chemocline. It is hypothetized that these rotifers are either very versatile or are differentiated as ecotypes, one of them adapted to the chemocline environment. This distribution in a peculiar fluctuating, anoxic, H₂S-rich environment poses questions about the biology of those rotifers which there develop extraordinary populations.     

S‐sulfhydration of MEK1 leads to PARP‐1 activation and DNA damage repair

The repair of DNA damage is fundamental to normal cell development and replication. Hydrogen sulfide (H₂S) is a novel gasotransmitter that has been reported to protect cellular aging. Here, we show that H₂S attenuates DNA damage in human endothelial cells and fibroblasts by S‐sulfhydrating MEK1 at cysteine 341, which leads to PARP‐1 activation. H₂S‐induced MEK1 S‐sulfhydration facilitates the translocation of phosphorylated ERK1/2 into nucleus, where it activates PARP‐1 through direct interaction. Mutation of MEK1 cysteine 341 inhibits ERK phosphorylation and PARP‐1 activation. In the presence of H₂S, activated PARP‐1 recruits XRCC1 and DNA ligase III to DNA breaks to mediate DNA damage repair, and cells are protected from senescence.     

硫化氢抗衰老作用的分子机制

衰老的特征包括蛋白质稳态失衡、氧化损伤积累、干细胞衰竭、细胞间通信改变、慢性炎症和微生态失调等,且与心血管疾病、糖尿病和阿尔茨海默病等常见的增龄性疾病相关。硫化氢(hydrogen sulfide,H₂S)是一种内源性的气体信号分子,在细菌、动物和植物中均存在其相关代谢。众所周知,生理浓度下的H₂S通过对人体蛋白质的硫巯基化修饰调控细胞信号转导,维持内稳态。近年的研究发现,生物体衰老常伴随内源性H₂S产生的减少和蛋白质硫巯基化水平的普遍下降,补充外源性H₂S可抑制其衰老。例如,阿尔兹海默病、老年性重症肌无力、骨质疏松症等衰老相关疾病中,补充H₂S可改善其症状。上述现象提示生理浓度范围的H₂S具有抗衰老作用。本文从抑制氧化应激、抗炎、保护线粒体功能、维持蛋白质稳态和上调自噬等方面总结了H₂S抗衰老的分子机制,并讨论了目前对H₂S抗衰老机制研究存在的问题和未来研究方向,为抗衰老和治疗衰老相关疾病提供新思路。