5种速生柳无性系对Pb~(2+)胁迫的生理抗性比较

以5种一年生速生柳(竹柳、苏柳172、苏柳795、旱快柳、旱柳)幼苗为材料,通过盆栽铅胁迫实验,测定其生长过程中的生理生化指标,分析其对铅胁迫的生理响应及耐受性。结果表明:(1)随着Pb2+浓度的增加,5种速生柳叶片保护酶SOD、POD和CAT活性均呈先升高后降低的趋势,其中竹柳的3种保护酶活性均为最高。(2)随着Pb2+浓度的增加,各无性系叶片中渗透性调节物质可溶性蛋白、脯氨酸和可溶性糖含量均呈先上升后下降的趋势,竹柳和苏柳172在高Pb2+浓度(1500mg·kg-1)胁迫下表现出对Pb2+的强耐受性。(3)随着Pb2+浓度的增加,各速生柳无性系叶片丙二醛含量均呈逐渐增高的趋势,但增幅有所不同,竹柳增幅最小,旱柳增幅最大。(4)随着Pb2+浓度的增加,5种速生柳叶片中叶绿素含量均呈先上升后下降的趋势,但各无性系的下降幅度存在差异,其中竹柳的下降幅度最小,旱柳下降幅度最大。(5)随着Pb2+浓度的增加,5种速生柳根系活力都呈先上升后下降的趋势,其中竹柳的根系活力最强,苏柳795的最弱。(6)各速生柳根系对铅均有一定的吸附能力,竹柳对铅积累量最大。(7)对各生理指标的Fuzzy数学隶属函数综合评价结果表明,5种速生柳对Pb2+耐受性强弱表现为:竹柳旱快柳旱柳苏柳795苏柳172。     

Cu2+胁迫对2种速生柳幼苗生长及生理特性的影响

以营养溶液中培养的‘苏柳172’(Salix jiangsuensis CL J-172)和垂柳(Salix babylonica Linn)幼苗为材料,分析它们在不同浓度Cu2+溶液(0、20、40、80、100、200、300μmol.L-1)下的生长以及部分生理指标的变化,以明确2种速生柳树用于植物修复的潜力。结果显示:2种柳树幼苗的生物量、叶片色素含量、根系活力以及根系形态的各指标都随Cu2+浓度的增加而显著降低。它们叶片SOD和POD活性以及脯氨酸含量随Cu2+浓度的增加呈先上升后下降的趋势,‘苏柳172’和垂柳中SOD活性在Cu2+浓度为20μmol.L-1时最大,其POD活性分别在Cu2+浓度为100和40μmol.L-1时达到最大,而其脯氨酸含量在Cu2+浓度为200μmol.L-1时达到最大。可见,2种柳树生长均受到Cu2+胁迫的抑制,它们能够在一定程度上通过增加保护酶活性和脯氨酸含量来提高对Cu2+的耐受性,且‘苏柳172’对Cu2+的忍耐力强于垂柳。     

外源水杨酸对镉胁迫甜瓜幼苗生长与光合气体交换和叶绿素荧光特性的影响

以甜瓜品种‘哈密绿’为试验材料,采用基质栽培方式,研究了10~200μmol·L-1外源水杨酸(SA)对镉胁迫(100mg·L-1 Cd2+)下甜瓜幼苗生长、叶绿素含量、光合气体交换参数和叶绿素荧光参数的影响,以探讨外源SA调控Cd2+胁迫伤害的可行性。结果显示:Cd2+胁迫能显著影响甜瓜幼苗的生长和相关光合指标。适宜浓度外源SA能不同程度缓解甜瓜幼苗所受Cd2+胁迫伤害,并以100μmol·L-1 SA处理效果最好,其显著促进了幼苗生长,提高了叶片叶绿素含量、净光合速率(Pn)、蒸腾速率(Tr)和气孔导度(Gs),以及PSⅡ最大光化学效率(Fv/Fm)、PSⅡ天线转化效率(Fv′/Fm′)、实际光化学效率(ФPSⅡ)、光化学荧光猝灭系数(qP)和光化学反应能量(P);显著降低了初始荧光(F0)、非光化学荧光猝灭系数(NPQ)、天线热耗散能量(D)和非光化学反应耗散能量(E)。研究表明,外源SA缓解甜瓜幼苗Cd2+胁迫伤害具有剂量效应,以100μmol·L-1 SA的效果最好,有利于甜瓜幼苗在Cd2+胁迫下光合作用的维持,提高光合电子传递效率和对光能的捕获与转换,降低Cd2+胁迫对植物的损伤,从而促进生长。     

不同能源柳无性系对NaCl胁迫的生理响应

为了探索不同能源柳无性系的耐盐潜力,在盆栽条件下,对1年生能源柳无性系2、4、C、E扦插苗设置NaCl盐分梯度,使其土壤含盐量保持在0、0.2%、0.4%、0.6%、0.8%,并以乡土旱柳为对照,胁迫45d后,对5个无性系的气体交换参数、保护酶活性和有机渗透调节物质进行测定。研究发现:(1)在低浓度盐胁迫下(土壤含盐量0 0.4%),导致各能源柳光合速率降低的是气孔因素;在高浓度盐胁迫下(土壤含盐量大于0.4%),导致各能源柳无性系光合速率下降的主要是非气孔因素。(2)随着土壤盐浓度的增加,各能源柳无性系的过氧化氢酶(CAT)活性逐渐减小,过氧化物酶(POD)活性先增加后减小,而超氧化物歧化酶(SOD)活性呈现增加的趋势,并且4个能源柳无性系在盐胁迫条件下保护酶活性强于旱柳。(3)在土壤含盐量小于0.6%时,4个能源柳无性系的可溶性蛋白含量始终大于旱柳;在整个胁迫过程中,能源柳C的脯氨酸含量始终大于旱柳。(4)与旱柳相比,4个能源柳无性系在土壤含盐量0 0.4%的土壤中都能良好生长,其中能源柳C的耐盐潜力更大,可在土壤含盐量为0.6%的土壤中正常生长。这说明,4个能源柳无性系均可在天津轻、中度盐渍化地区栽培。     

汞胁迫对白骨壤(Avicennia marina)幼苗生理生态的影响

为了解红树植物的重金属抗性机制,对白骨壤(Avicennia marina)幼苗进行不同浓度Hg2+(1、5、10、50、100 mg·L-1)的胁迫实验,测定并分析了Hg2+胁迫对白骨壤幼苗叶片的光合作用和抗氧化酶活性的影响.结果表明:叶片净光合速率随着胁迫时间的延长而降低,高浓度(≥150 mg·L-1)Hg2+胁迫下叶片的净光合速率低于中低浓度胁迫,且高浓度胁迫的叶片净光合速率在48 h后快速下降;叶片净光合速率与胞间二氧化碳浓度呈极显著负相关,叶绿素含量随Hg2+浓度的增加而降低.气孔导度在不同浓度胁迫下反应不同,低浓度Hg2+对白骨壤幼苗光合的影响可能是气孔因素,中高浓度Hg2+对白骨壤幼苗光合作用的抑制主要是非气孔因素.低浓度Hg2+胁迫,白骨壤幼苗叶片SOD、POD活性升高,表现了一定的抗逆性,而高浓度表现为抑制作用,基本在100 mg·L-1 Hg2+胁迫下活性达到最低值.说明Hg2+可以抑制白骨壤叶片的光合活性,高浓度Hg2+胁迫削弱了白骨壤的活性氧清除能力,植物极易受到伤害.     

速生柳树苗对土壤铅的耐性、积累与分配特性研究

耐性植物为环境污染植物修复提供了一条良好的途径。通过盆栽试验研究了垂柳(Salix babylonica Linn.)和苏柳172(Salix jiangsuensis J172)扦插苗对人工添加土壤铅污染的耐性及其对铅的积累和分配。结果发现:柳树生物量与土壤有效铅含量呈显著负相关关系,中低浓度的铅污染对两种柳树的根系生物量影响不大,Pb2+浓度为1600 mg·kg-1时显著降低垂柳根系生物量,苏柳172在Pb2+浓度为1 200和1 600 mg·kg-1时根系生物量极显著降低,说明垂柳对高浓度的Pb2+耐性要好于苏柳172;垂柳和苏柳172根系长度、根表面积、根体积和根直径随着土壤铅浓度的增加持续下降,在Pb2+浓度为1600 mg·kg-1时,垂柳根系长度、根表面积、根体积和根直径分别比对照下降了50.40%、45.15%、44.44%、9.10%,苏柳172分别下降了45.00%、45.88%、47.02%、37.14%。柳树吸收的铅绝大部分积累在根部,迁移到茎部和叶部的数量较少,铅在2种柳树体内不同部位的积累量均为根茎叶。当Pb2+浓度为800 mg·kg-1时,垂柳和苏柳172的耐性指数为91.15%和84.26%,其对土壤中铅的吸收量达140.20和149.49 mg,表明两种柳树对中等土壤铅污染的修复具有较大潜力。     

盐胁迫对甜樱桃砧木生理特性及光合荧光参数的影响

以1年生甜樱桃砧木‘吉塞拉6号’和‘考特’幼苗为材料,采用盆栽试验,研究不同浓度NaCl(0、50、100、150 mmol·L^(-1))处理对其主要渗透调节物质、抗氧化酶活性、光合特性以及叶绿素荧光参数的影响,探究甜樱桃砧木对盐胁迫响应的生理机制。结果表明:(1)NaCl处理促进了甜樱桃砧木叶片中可溶性糖、可溶性蛋白和脯氨酸等渗透调节物质的积累。(2)随着NaCl处理浓度的升高,甜樱桃砧木叶片中SOD活性呈现升高趋势,而POD活性表现出先升高后降低趋势。(3)随着NaCl处理浓度的升高,甜樱桃砧木叶片的净光合速率(P_(n))、气孔导度(G_(s))逐渐降低,而胞间CO_(2)浓度(C i)逐渐升高,非气孔限制为甜樱桃砧木叶片P_(n)下降的主要因素。(4)NaCl处理抑制了甜樱桃砧木叶片的最大光化学效率(F_(v)/F_(m))、光化学淬灭系数(q P)和电子传递效率(ETR),增加了非光化学淬灭系数(NPQ)。研究发现,盐胁迫破坏了甜樱桃砧木的光合机构,抑制了电子传递速率和光化学量子效率,降低了对光能的利用率,导致光合速率降低;甜樱桃砧木在盐胁迫条件下主要通过增加渗透调节物质含量和提高抗氧化酶活性来缓解渗透胁迫并降低氧化损伤,从而提高对盐胁迫的适应能力;‘吉塞拉6号’在盐胁迫条件下表现出更强的适应能力,其耐盐性更强;甜樱桃砧木在高于100 mmol·L^(-1)NaCl处理时表现出明显受害症状。     

紫花苜蓿叶输导组织解剖结构和光合特性对外源氮的响应

以紫花苜蓿品种‘甘农3号’和‘陇东苜蓿’为研究材料,采用室外(防雨网室)盆栽营养液砂培法,研究了2种氮素形态(NO3--N,NH4+-N)的5个氮素水平(0、105、210、315、420mg·L-1)处理对叶片输导组织解剖结构及光合特性的影响。结果显示:(1)与无氮处理相比,供氮处理下‘甘农3号’和‘陇东苜蓿’输导组织的解剖结构和光合特性发生明显变化,叶片输导组织维管束、木质部和韧皮部面积显著增大,导管数显著增多,净光合速率、气孔导度、叶面积和叶绿素含量均显著增加,且在210mg·L-1供氮水平下达到最大值。(2)2种氮素形态相比,‘甘农3号’和‘陇东苜蓿’叶片输导组织维管束面积、木质部面积、韧皮部面积、导管数、净光合速率、气孔导度、叶面积、叶绿素含量均表现为NH4+-N处理好于NO3--N处理。(3)2品种相比,叶片输导组织维管束面积、木质部面积、韧皮部面积、导管数、净光合速率、气孔导度、叶面积、叶绿素含量表现为‘甘农3号’大于‘陇东苜蓿’。研究表明,氮素能通过改善紫花苜蓿叶片输导组织的解剖结构和光合特性,促进紫花苜蓿光合作用;各处理中以NH4+-N、210mg·L-1表现最佳,维管束面积最大,木质部、韧皮部面积大且发育好,导管数最多,而且‘甘农3号’表现更优。     

五节芒不同种群对Cd污染胁迫的光合生理响应

通过盆栽模拟试验,以分别来自粤北大宝山矿区和惠州博罗非矿区的两个五节芒种群为试验材料,比较研究了两个种群在Cd胁迫下的气体交换参数、叶绿素荧光特性、光合色素含量和叶绿体超微结构变化的差异。结果表明:(1)Cd胁迫下五节芒两种群叶片净光合速率(Pn)、蒸腾速率(E)、气孔导度(Gs)、胞间二氧化碳浓度(Ci)、叶绿素含量(Chl)都有不同幅度的下降;叶绿体超微结构遭到破坏。矿区种群随Cd胁迫程度的加深,净光合速率下降较慢,叶绿体的外形及基粒结构受到的影响较小。(2)轻度Cd胁迫下气孔限制是五节芒非矿区种群Pn降低的主要因素,中度和重度Cd胁迫下非气孔限制是Pn降低的主要因素。(3)Cd胁迫下五节芒两种群PSⅡ反应中心最大光化学效率(Fv/Fm)、PSⅡ潜在活性(Fv/Fo)、PSⅡ有效光化学效率Fv′/Fm′均有所下降。总体上矿区种群降幅较小,PSⅡ利用光能的能力及PSⅡ的潜在活性均较强。PSⅡ光化学猝灭系数(qP)、非光化学猝灭系数(NPQ)的变化表现为Cd胁迫下两种群qP值降低、NPQ值升高,总体上抗性强的矿区种群qP降低的幅度低且NPQ升高幅度大。随着Cd胁迫浓度增加,矿区种群实际光化学反应效率(ΦPSⅡ)和电子传递速率(ETR)变化幅度不大,而非矿区种群显著下降,表明矿区种群PSⅡ反应中心电子传递活性受到的影响小,光合机构的损伤程度低。研究表明,五节芒矿区种群对重金属Cd有较强的耐受能力,适合作为金属矿区植被恢复建设的禾本科先锋物种。     

外源水杨酸对镉胁迫下甜瓜幼苗生长、光合作用和活性氧代谢的缓解效应

以甜瓜耐镉品种‘哈密绿’和镉敏感品种‘秀绿’为试验材料,在人工气候箱内采用基质栽培法,研究了外源水杨酸(SA)处理对镉(Cd)胁迫下甜瓜幼苗生长、光合作用和活性氧代谢的缓解效应。结果显示:与对照(CK)比较,Cd处理显著抑制了甜瓜幼苗的生长和光合作用,降低了叶绿素含量,抗氧化酶活性、脯氨酸(Pro)含量、丙二醛(MDA)含量和超氧阴离子(O2ˉ·)产生速率增加;在Cd胁迫下,SA处理可以有效促进甜瓜幼苗的生长,增加了叶绿素含量、净光合速率(Pn)、气孔导度(Gs)、蒸腾速率(Tr)、气孔限制值(Ls)和水分利用效率(WUE),降低了胞间CO2浓度(Ci);提高了超氧化物歧化酶(SOD)、过氧化酶酶(POD)、过氧化氢酶(CAT)和抗坏血酸过氧化物酶(APX),增强植株抗氧化能力,使Pro和可溶性蛋白含量升高,MDA含量和O2ˉ·产生速率下降,能有效抑制镉胁迫引起的膜脂过氧化伤害;镉敏感品种‘秀绿’变化幅度大于耐镉品种‘哈密绿’。研究结果说明,SA有利于甜瓜幼苗在Cd胁迫下活性氧代谢的提高和对光能的捕获与转换,促进了甜瓜幼苗的生长,降低Cd胁迫对甜瓜幼苗的抑制作用,且对镉敏感品种‘秀绿’效果大于耐镉品种‘哈密绿’。     

Changes in the selected hematological parameters and gill Na/K ATPase activity of juvenile crucian carp Carassius auratus during elevated ammonia exposure and the post-exposure recovery

The increase in concentration of ammonia in lake water during the degradation of algal blooms may last for several weeks and thus cause chronic toxicity to aquatic organisms. The purpose of this study was to assess the chronic toxicity of ammonia on the selected hematological parameters and gill Na⁺/K⁺ ATPase activity of juvenile crucian carp Carassius auratus during elevated ammonia exposure and the post-exposure recovery. Juvenile crucian carp were exposed in different ammonia solutions for 45 days and then immediately transferred to pristine freshwater to initiate a 15-day recovery period. Results showed sub-lethal ammonia significantly deters growth and a 15-day recovery period was not sufficient for the fish to compensate for the loss of growth. The fish exhibited a continuous decrease in red blood cell (RBC), the total hemoglobin (Hb), and gill Na⁺/K⁺ ATPase activity as the concentration of NH₃-N increased. After the 15-day recovery period, RBC, Hb, and gill Na⁺/K⁺ ATPase activity had recovered to similar levels as the controls.     

Effects of Power Frequency Electromagnetic Fields on Growth of Germinating Vicia faba L., the Broad Bean

Experimental investigations were carried out to evaluate the effect of continuous and delayed exposure of power frequency electromagnetic fields at 5, 50 and 100 μT on germinating Vicia faba seedlings as a model system. These studies included physical parameters (length and girth of primary roots, number as well as length of lateral roots and imbibition), major biochemical constituents (total sugar, protein, and fat) and activities of important housekeeping enzymes (amylases, proteases, and lipase) at 2, 4, and 8 days of growth. Also, mitotic index and rate of DNA synthesis were studied at day 8 of growth. There was no significant change in physical parameters and major biochemical constituents between control and experimental groups. Also, the comparison between the control and experimental group of seeds showed that α-amylase activity significantly decreased at 5, 50 and 100 μT on day 2 and 4 of growth. β-amylase and protease (37^○C & 50^○C) showed a significant decrease in activity on day 2 and 4 of growth at 100 μT, whereas activity of lipase significantly decreased only on day 2 of growth at 100 μT. At day 8 of growth, all enzyme activities reverted back to the same as control. Also, there was a significant increase in mitotic index as well as ³H-thymidine uptake at 100 μT delayed exposure on day 8. The present study suggests that exposure to power frequency electromagnetic fields up to 100 μT on germinating seedlings does not cause any permanent damage since the initial alteration under the magnetic fields in some important housekeeping enzymes involved in the onset of seed germination were returened to control values on day 8 of growth. Also, the growth of the germinated seedlings was found to be enhanced by the application of power frequency magnetic fields (100 μT) as evidenced by mitotic index and ³H-thymidine uptake.     

Acyl chain conformational ordering in liquid-crystalline bilayers: comparative FT-IR and 2H-NMR studies of phospholipids differing in headgroup structure and chain length

FT-IR spectroscopy has been used to evaluate the acyl chain conformational ordering of DMPC, DMPE, DMPA (pH 6 and 12), DMPG (pH 1 and 7), and DPPC, DPPE, DPPA (pH 6). The frequencies of the symmetric and antisymmetric methylene stretching vibrations were determined as a function of temperature. In the liquid-crystalline phase the frequencies show a qualitative dependence on the amount of chain disorder. Quantitative data for trans-gauche isomerization were obtained from the integral intensities of the conformation sensitive methylene wagging absorptions at ca. 1368 cm^–1 (gtg and gtg sequences), 1356 cm ^–1 (double gauche) and 1342 cm^–1 (end gauche). The integral band intensities were converted to the number of gauche conformers per acyl chain using the calibration factors published by Senak et al. (1991). At 69°C the highest number of gauche conformers excluding contributions from single gauche conformers and jogs (gtttg) are found for PCs (DMPC: 2.6; DPPC: 2.4), followed by DMPG^– (2.0), phosphatidylethanolamines (DMPE: 1.4; DPPE: 2.0), protonated DMPG (1.5), and phosphatidic acids (DPPA^–: 1.7; DMPA^–: 1.4, DMPA^2–: 1.7). From ²H-NMR measurements of perdeuterated samples of DMPC, DMPA, DPPC, and DPPA the quadrupolar splittings _Qi and the order parameter S _CDi of the CD₂-segments close to the chain ends could be determined whereas splittings in the plateau region of the chains could not be resolved. The quadrupolar splittings are affected by trans-gauche isomerization, long axis rotation, and restricted wobbling motions of the acyl chains. In the simplest assumption, the order parameter S_CD can be expressed as a product of a segmental order parameter S and a lhain order parameter S . For comparison of the different lipids we used average order parameters S_CD, obtained by averaging over all values, and S determined from the total number of gauche conformers per chain by FT-IR-spectroscopy, to calculate an empirical average chain order parameter S. The combination of ²H-NMR and FT-IR results allows the estimation of the relative extent of chain wobbling for the different lipid molecules. S is lowest for PCs (S 0.475) while PEs (S 0.51) and PAs (S0.52) show less chain wobbling.Abbreviations FT-IR Fourier transform infrared - ²H-NMR deuterium nuclear magnetic resonance - DMPC(–d₅₄) (perdeuterated) dimyristoyl-phosphatidylcholine - DMPE(–d₅₄) (perdeuterated) dimyristoyl-phosphatidylethanolamine - DMPA(–d₅₄) (perdeuterated) dimyristoyl-phosphatidic acid - DMPG dimyristoyl-phosphatidylglycerol - DPPC(–d₆₂) (perdeuterated) dipalmitoyl-phosphatidylcholine - DPPE(–d₆₂) (perdeuterated) dipalmitoyl-phosphatidylethanolamine - DPPA(–d₆₂) (perdeuterated) dipalmitoyl-phosphatidic acid - gtg gauche ^±-trans-gauche^± - gtg gauche^±-trans-gauche^± - dg double gauche - eg end gauche Correspondence to: A. Blume     

Internal mobility of the ologonucleotide duplexes d(TCGCG)2 and d(CGCGCG)2 in aqueous solution from molecular dynamics simulations

Summary In this paper we present longitudinal relaxation times, order parameters and effective correlation times for the base and sugar carbons in both strands of the oligonucleotide duplexes d(TCGCG)₂ and d(CGCGCG)₂, as calculated from 400 ps molecular dynamics trajectories in aqueous solution. The model-free approach (Lipari and Szabo, 1982) was used to determine the amplitudes and time scales of the internal motion. Comparisons were made with NMR relaxation measurements (Borer et al., 1994). The order parameters could acceptably be reproduced, and the effective correlation times were found to be lower than the experimental estimates. Reasonable T₁ relaxation times were obtained in comparison with experiment for the nonterminal nucleosides. The T₁ relaxation times were found to depend mainly on the order parameters and overall rotational correlation time.Abbreviations MD molecular dynamics - CSA chemical shift anisotropy To whom correspondence should be addressed.     

Stabilization of glucoso-6-phosphate dehydrogenase by its substrate and cofactor in an ultrasonic field

The inactivation kinetics of glucoso-6-phosphate dehydrogenase (GPDH) and its complexes with glucoso-6-phosphate and NADP⁺ was characterized in aqueous solutions at 36–47°C under treatment with low frequency (27 kHz, 60 W/cm²) and high frequency ultrasound (880 kHz, 1 W/cm²). To this end, we measured three effective first-order inactivation rate constants: thermal k _in ^* , total (thermal and ultrasonic) k _in, and ultrasonic k _in(US). The values of the constants were found to be higher for the free enzyme than for its complexes GPDH-GP and GPDH-NADP⁺ at all temperatures, which confirms the enzyme stabilization by its substrate and cofactor under both thermal and ultrasonic inactivation. Effective values of the activation energies (E _a) were determined and the preexponential factors of the rate constants and thermodynamic activation parameters of inactivation processes (ΔH*, ΔS*, and ΔG*) were calculated from the temperature dependences of the inactivation rate constants of GPDH and its complexes. The sonication of aqueous solutions of free GPDH and its complexes was accompanied by a reduction of E _a and ΔH* values in comparison with the corresponding values for thermal inactivation. The E _a, ΔH*, and ΔS* inactivation values for GPDH are lower than the corresponding values for its complexes. A linear dependence between the growth of the ΔH* and ΔS* values was observed for all the inactivation processes for free GPDH and its complexes.     

Prediction of methyl-side Chain Dynamics in Proteins

A simple analytical model is presented for the prediction of methyl-side chain dynamics in comparison with S(2) order parameters obtained by NMR relaxation spectroscopy. The model, which is an extension of the local contact model for backbone order parameter prediction, uses a static 3D protein structure as input. It expresses the methyl-group S(2) order parameters as a function of local contacts of the methyl carbon with respect to the neighboring atoms in combination with the number of consecutive mobile dihedral angles between the methyl group and the protein backbone. For six out of seven proteins the prediction results are good when compared with experimentally determined methyl-group S(2) values with an average correlation coefficient r = 0.65+/-0.14. For the unusually rigid cytochrome c(2) no significant correlation between prediction and experiment is found. The presented model provides independent support for the reliability of current side-chain relaxation methods along with their interpretation by the model-free formalism.     

A kinetic study on pyridine exchange reactions at a bis(μ-acetato)(μ-oxo)diruthenium(III) center: effects of monodentate and bidentate N-heterocyclic ligands cis to the oxo bridge

A series of (μ-oxo)bis(μ-acetato)diruthenium(III) complexes containing two pyridine (py) ligands and varied N-heterocyclic ligands in the positions trans and cis to μ-O, respectively, have been prepared to study py/py-d₅ exchange reactions using ¹H NMR spectroscopy. The diruthenium(III) complexes under investigation are [Ru₂(μ-O)(μ-CH₃COO)₂(py)₆](PF₆)₂ (1), [Ru₂(μ-O)(μ-CH₃COO)₂(bpy)₂(py)₂](PF₆)₂ (2), [Ru₂(μ-O)(μ-CH₃COO)₂(acpy)₄(py)₂](FF₆)₂ (3), and [Ru₂(μ-O)(μ-CH₃COO)₂(dmbpy)₂(py)₂](PF₆)₂ (4), where bpy=2,2′-bipyridine, acpy=4-acetylpyridine, and dmbpy=4,4′-dimethyl-2,2′-bipyridine. Pseudo-first order rate constants for the ligand-exchange reactions are 10⁻⁶−10⁻⁵ s⁻¹ for 1-4 in CD₃CN at 298 K. It is found that the rate of the py/py-d₅ exchange reactions is controlled by the electronic nature of the cis-oriented ancillary ligands, while the exchange mechanisms are tuned principally by the ligand steric factors. The activation parameters (ΔH^‡ and ΔS^‡) indicate that exchange reactions proceed through the dissociative (D) or the interchange dissociative (I_d) mechanism for 1 and 3. Negative ΔS^‡ values observed for 2 and 4 suggest a significant contribution of incoming ligands to the exchange pathway. The kinetic and thermodynamic parameters for the diruthenium series and the corresponding data for Ru-based oxo bridged trinuclear complexes established previously are compared and discussed.     

The sodium cycle: A novel type of bacterial energetics

The progress of bioenergetic studies on the role of Na⁺ in bacteria is reviewed. Experiments performed over the past decade on several bacterial species of quite different taxonomic positions show that Na⁺ can, under certain conditions, substitute for H⁺ as the coupling ion. Various primary Na⁺ pumps ( generators) are described, i.e., Na⁺-motive decarboxylases, NADH-quinone reductase, terminal oxidase, and ATPase. The formed is shown to be consumed by Na⁺ driven ATP-synthase, Na⁺ flagellar motor, numerous Na⁺, solute symporters, and the methanogenesis-linked reverse electron transfer system. InVibrio alginolyticus, it was found that , generated by NADH-quinone reductase, can be utilized to support all three types of membrane-linked work, i.e., chemical (ATP synthesis), osmotic (Na⁺, solute symports), and mechanical (rotation of the flagellum). InPropionigenum modestum, circulation of Na⁺ proved to be the only mechanism of energy coupling. In other species studied, the Na⁺ cycle seems to coexist with the H⁺ cycle. For instance, inV. alginolyticus the initial and terminal steps of the respiratory chain are Na⁺ - and H⁺-motive, respectively, whereas ATP hydrolysis is competent in the uphill transfer of Na⁺ as well as of H⁺. In the alkalo- and halotolerantBacillus FTU, there are H⁺ - and Na⁺-motive terminal oxidases. Sometimes, the Na⁺-translocating enzyme strongly differs from its H⁺-translocating homolog. So, the Na⁺-motive and H⁺-motive NADH-quinone reductases are composed of different subunits and prosthetic groups. The H⁺-motive and Na⁺-motive terminal oxidases differ in that the former is ofaa ₃-type and sensitive to micromolar cyanide whereas the latter is of another type and sensitive to millimolar cyanide. At the same time, both Na⁺ and H⁺ can be translocated by one and the sameP. modestum ATPase which is of the F₀F₁-type and sensitive to DCCD. The sodium cycle, i.e., a system composed of primary generator(s) and consumer(s), is already described in many species of marine aerobic and anaerobic eubacteria and archaebacteria belonging to the following genera:Vibrio, Bacillus, Alcaligenes, Alteromonas, Salmonella, Klebsiella, Propionigenum, Clostridium, Veilonella, Acidaminococcus, Streptococcus, Peptococcus, Exiguobacterium, Fusobacterium, Methanobacterium, Methanococcus, Methanosarcin, etc. Thus, the sodium world seems to occupy a rather extensive area in the biosphere.     

Role of the furosemide-sensitive Na+/K+ transport system in determining the steady-state Na+ and K+ content and volume of human erythrocytesin vitro andin vivo

Summary To study the physiological role of the bidirectionally operating, furosemide-sensitive Na⁺/K⁺ transport system of human erythrocytes, the effect of furosemide on red cell cation and hemoglobin content was determined in cells incubated for 24 hr with ouabain in 145mm NaCl media containing 0 to 10mm K⁺ or Rb⁺. In pure Na⁺ media, furosemide accelerated cell Na⁺ gain and retarded cellular K⁺ loss. External K⁺ (5mm) had an effect similar to furosemide and markedly reduced the action of the drug on cellular cation content. External Rb⁺ accelerated the Na⁺ gain like K⁺, but did not affect the K⁺ retention induced by furosemide. The data are interpreted to indicate that the furosemide-sensitive Na⁺/K⁺ transport system of human erythrocytes mediates an equimolar extrusion of Na⁺ and K⁺ in Na⁺ media (Na⁺/K⁺ cotransport), a 1:1 K⁺/K⁺ (K⁺/Rb⁺) and Na⁺/Na⁺ exchange progressively appearing upon increasing external K⁺ (Rb⁺) concentrations to 5mm. The effect of furosemide (or external K⁺/Rb⁺) on cation contents was associated with a prevention of the cell shrinkage seen in pure Na⁺ media, or with a cell swelling, indicating that the furosemide-sensitive Na⁺/K⁺ transport system is involved in the control of cell volume of human erythrocytes. The action of furosemide on cellular volume and cation content tended to disappear at 5mm external K⁺ or Rb⁺. Thein vivo red cell K⁺ content was negatively correlated to the rate of furosemide-sensitive K⁺ (Rb⁺) uptake, and a positive correlation was seen between mean cellular hemoglobin content and furosemide-sensitive transport activity. The transport system possibly functions as a K⁺ and waterextruding mechanism under physiological conditiosin vivo. The red cell Na⁺ content showed no correlation to the activity of the furosemide-sensitive transport system.