脱水胁迫对连翘和冬青卫矛叶片细胞质外体和微环境的影响

用压力室、电导法和原子吸收分光光度分析法综合分析测定了连翘[Forsythiasuspensa (Thunb.) Vahl]和冬青卫矛(Euonymus japonicus Thunb.)在不同程度脱水胁迫时细胞外部微环境的变化.结果表明:(1)在脱水胁迫条件下,叶片细胞随着脱水胁迫强度的加大,细胞内离子外渗的累计量不断加大,但细胞内离子外渗的速度在不同的区间内并无明显的改变,即细胞膜的透性在所测范围内没有明显变化.(2)脱水胁迫同时造成了叶片质外体和共质体溶液中钠、钾离子浓度的增加,但质外体比共质体溶液中钠、钾离子浓度的增加幅度更高,导致细胞内、外离子浓度梯度的改变和离子平衡膜电位的改变,这些改变有可能引起细胞的次生生理变化,并有可能与植物的伤害反应和抗性有关.     

盐胁迫下珠眉海棠与山定子叶片Na+区域化的研究

以盐敏感型山定子实生苗和耐盐型珠眉海棠组培苗为材料,采用灌注离心技术研究了叶片质外体和共质体中Na^＋和Ca^2＋浓度的变化。结果表明：随盐胁迫强度的加强,叶片水势下降;叶片Na^＋含量、质外体和共质体中Na^＋浓度升高,珠眉海棠明显低于山定子;叶片Ca^2＋含量、共质体Ca^2＋浓度随盐胁迫的增加而升高,但珠眉海棠高于山定子,50mmol／L NaCl胁迫对质外体Ca^2＋没有明显影响,100mmol／LNaCl胁迫下增加,珠眉海棠低于山定子;叶片共质体与质外体中Na^＋浓度的比值,珠眉海棠明显高于山定子,说明在盐胁迫下珠眉海棠具有较强的离子区域化能力,离子区域化是珠眉海棠的主要耐盐机制。     

植物组织电阻及其应用

植物组织可分为质外体和共质体,其中,质外体由细胞壁、细胞间隙和导管组成,共质体由胞间连丝把相邻的原生质贯穿在一起而成。对于一鲜嫩植物组织来说,可将组织中质外体部分和共质体部分分别看作一连续整体,在两者之间有近似绝缘层的高电阻膜存在。此细胞膜的比电阻一般可达10~3—10~4Ω·cm,和5nm厚的油层相近。因此,可以近似地将共质体和质外体看作是电学上相并联的两条支路。其中,共质体电阻由膜电阻、胞内电阻和胞问电阻相互串联而成。由于胞内离子强度较     

胞间连丝：共质体运输的动态通道

胞间连丝作为一种细胞质结构将相邻的细胞连系起来而形成植物的共质体。胞间连丝通过调控许多离子和分子的共质体运输而广泛地参与植物的生命活动。胞间连丝的主要构成部分是细胞质膜、连丝小管、以及位于二之间的环层细胞质。这三都很容易在电子显微镜下观察到。细胞骨架的成分（肌动蛋白和肌球蛋白）起到稳定胞间连丝的作用。同时,钙结合蛋白可能具有调节间连丝功能的作用。在胞间连丝里,环层细胞质为大多数溶质提供共质体运输的通道,而有些 共质体运输则可能是通过连丝小管的内腔、连丝小管的壳层、甚或是细胞质膜来实现的。共质体可以细分为数个区块,它们各自允许不同大小的分子（从低于1000到高于10000道尔顿）通过。从发生上看,胞间连丝可以是初生的,也可以是次生的。前是伴随着新细胞壁的形成则产生的,而后则是在已有的细胞壁上产生的。胞间连丝的动态性质还表现在它们的频率是处于变化之中,这是由于组织或植物整体的发育和生理状态决定的。虽然共质体运输的基本形式是扩散,但胞间连丝对于某些离子和分子却是选择性的。在病毒感染细胞时,病毒的移动蛋白作用于胞间连丝的受体蛋白,结果,胞间连丝被显地扩张（其机理尚不清楚）。于是,病毒的移动蛋白连同与之结合在一起的病毒基因组进入毗邻的健康细胞。一些植物源性的蛋白质也能够通过胞间连丝来运输;推测其方式类似于病毒的移动蛋白。有些植物蛋白质本身就是信号分子,它们调节分化和其他活动。与此相反,还有一些植物蛋白质的共质体运输并不是通过特异的方式来实现的。     

菜豆茎韧皮部卸出的细胞途径以及激素的促进作用(英文)

通过缩小叶面积和去茎尖改变源库比率,以调节韧皮部卸出的途径,证明了韧皮部卸出的共质体与质外体途径的季节变化,和由对氯高汞苯磺酸所诱发的从质外体向共质体途径的转变,是与光合产物的输入有关。缩小叶面积而降低源库比率,能增加夏季生长植株茎韧皮部的质外体卸出,但对冬季生长植株无影响。去尖而增加源库比率,则促进共质体卸出。赤霉酸和激动素能促进共质体的横向转运,但对质外体转运无作用。当质外体为主要运输途径时,赤霉酸和激动素开启共质体途径。赤霉酸和激动素刺激光合产物,通过共质体从筛管一伴胞复合体向韧皮部薄壁纽胞输送,并可能在韧皮部薄壁细胞被动扩散到自由空间。由此可进一步说明蔗糖在激素处理部位自由空间的增加。     

长春花(Catharanthus roseus)培养物中长春朵灵和泻花碱的薄层色谱分离

对长春花(Catharanthus roseus)纵生芽中长春朵灵和泻花碱进行薄层色谱分离。讨论了吸附剂、溶剂系统对长春朵灵和泻花碱比移值(R_t)的影响。给出了不同系统下长春朵灵和泻花碱的R_t的值。     

光周期对光敏胞质不育小麦花药发育过程中Ca^2＋分布的影响

运用焦锑酸钾沉淀法,研究了不同光照条件下光敏胞质不育小麦（Ｔｒｉｔｉｃｕｍ ａｅｓｔｉｖｕｍ Ｌ．）花药发育过程中Ｃａ＾２＋的分布。短日照条件下,小孢子形成和花粉发育过程中胞内Ｃａ＾２＋在数量、分布上有变化;小孢子表面逐渐积累Ｃａ＾２＋,至成熟花粉表面覆盖一层Ｃａ＾２＋,胞质Ｃａ＾２＋较少;药隔和药壁组织通过抽外体或共质体途径运输Ｃａ＾２＋供给花粉的发育;长日照条件下,花粉败育发生在不同时期,早期     

重金属镉(Cd)在植物体内的转运途径及其调控机制

重金属镉(Cd)的毒害效应与其由土壤向植物地上部分运输有关,揭示Cd~(2+)转运途径及其调控机制可为提高植物抗镉性以及镉污染的植物修复提供依据。对Cd~(2+)在植物体内的转运途径,特别是限制Cd~(2+)移动的细胞结构和分子调控机制研究进展进行了回顾。Cd~(2+)通过共质体和质外体途径穿过根部皮层进入木质部的过程中,大部分在皮层细胞间沉积,少部分抵达中柱后转移到地上部分。为了免受Cd~(2+)的危害,植物体产生了多种限制Cd~(2+)吸收和转移的生理生化机制:1)环绕在内皮层径向壁和横向壁上的凯氏带阻止Cd~(2+)以质外体途径进入木质部;2)螯合剂与进入根的Cd~(2+)螯合形成稳定化合物并区隔在液泡中;3)通过H+/Cd~(2+)离子通道等将Cd~(2+)逆向转运出根部。植物共质体和质外体途径转运重金属镉的能力以及两条途径的串扰尚待进一步明晰和阐明。     

根系抗坏血酸在小麦幼苗铝耐性中的作用

以3个铝耐性不同的小麦品种为材料,研究了Al胁迫下小麦幼苗根系质外体和共质体抗坏血酸含量以及抗坏血酸氧化酶和过氧化物酶活性的变化。结果显示,Al耐性品种‘Atlas 66’质外体中抗坏血酸总含量随着处理 Al浓度的增加显著升高,而在Al敏感品种‘Scout 66’和‘扬麦9号’中显著降低。同时,‘Atlas 66’质外体中还原型抗坏血酸含量在高浓度Al处理下显著升高,2个敏感品种则在低浓度Al处理下还原型抗坏血酸含量略有升高。耐性品种‘Atlas 66’根系共质体还原型抗坏血酸和抗坏血酸总量在5～40μmol·L-1AlCl3处理下无显著变化,而在 2个敏感品种中则随处理Al浓度的增加显著下降。80μmol·L-1AlCl3处理下‘Atlas 66’根系质外体和共质体抗坏血酸氧化酶以及抗坏血酸过氧化物酶活性与对照相比均无显著变化,而在‘Scout 66’和‘扬麦9号’中则均显著降低。因此Al胁迫下‘Atlas 66’根系质外体抗坏血酸含量的升高和共质体抗坏血酸含量的维持以及Al毒害下抗坏血酸利用率较高可能是其Al耐性的一个重要机制。     

植物体内的短距运输

植物体内水和溶质的运输,可分为短距离运输和长距离运输两种类型。短距离运输是指从细胞到细胞的运输,它包括共质体运输和非原质体(质外体)运输。长距离运输是指通过维管系统进行的运输。在这里,我们只讨论短距离运输。短距离运输,包括共质体运输和非原质体运输。植物细胞内的原生质体,由胞间连丝联系起来,形成一个整体,即共质体。所以,我们把从细胞到细胞通过胞间连丝的运输称为共质     

The colon of Leucophaea maderae: fine structure and physiological features

The colon of L. maderae consists of a single columnar epithelium covered with a cuticle and of a musculo-connective sheath. The apical plasma membranes form a system of leaflets with numerous mitochondria inserted in association with microfilaments. Lateral plasma membranes are linked together by junctional complexes consisting of a zonula adherens and a long convoluted septate junction of the pleated type. In the basal region of the cell, numerous membrane infolds and scattered scalariform junctions with associated mitochondria are present. These cell specializations are typical of arthropod transporting organs, being distinctive features of ion and fluid transporting epithelia. The isolated colon exhibited a transepithelial electrical potential difference (PD) of about 100 mV, lumen side positive with respect to the haemolymph side. The PD was almost abolished by metabolic inhibitors, it was reduced by acetazolamide and SITS, and it was unaffected by ouabain. These effects suggest that HCO3- and Cl- are involved in the genesis of the PD, whereas Na+ is not directly responsible of the PD. Measurements of Na+ and Cl- fluxes across the colon wall confirm that Na+ moves following the PD across the tissue, while Cl- movement occurs against an electrochemical potential difference. The electrical profile of the epithelial cells is of the well type and it suggests that the primary or secondary active step for Cl- transport across the epithelium should be located at the mucosal border of the cell.     

Electrical bistability in a neuron model with monostable dendritic and axosomatic membranes

In a two-compartment mathematical model, we studied the reason for and conditions of manifestation of electrical bistability in a neuron composed of monostable parts. One compartment of the model simulated the dendrites; their membrane was monostable at high depolarization and characterized by an N-shaped steady current-voltage (I–V) characteristic endowed by inward synaptic current through voltage-dependent channels sensitive to N-methyl-D-aspartate (NMDA). Another compartment simulated the axosomatic region with a positively sloped linearizedI–V characteristic of the membrane monostable at the resting membrane potential. For the whole cell, bistability was obvious at a subcritical intensity of NMDA activation; the reason was the current directed from the more depolarized dendritic region into the somatic region, and the necessary condition was that the above somatopetal core current must exceed the net inward transmembrane current (the latter was the sum of the inward synaptic and outward passive extrasynaptic currents) of the dendritic compartment. This relation essentially depended on the size of the dendrites. Neirofiziologiya/Neurophysiology, Vol. 32, No. 2, pp. 98–101, March–April, 2000.     

Molecular determinants of electrical rectification of single channel conductance in gap junctions formed by connexins 26 and 32.

The fully open state of heterotypic gap junction channels formed by pairing cells expressing connexin 32 (Cx32) with those expressing connexin 26 (Cx26) rectifies in a way that cannot be predicted from the current-voltage (I-V) relation of either homotypic channel. Using a molecular genetic analysis, we demonstrate that charged amino acids positioned in the amino terminus (M1 and D2) and first extracellular loop (E42) are major determinants of the current-voltage relation of the fully open state of homotypic and heterotypic channels formed by Cx26 and Cx32. The observed I-V relations of wild-type and mutant channels were closely approximated by those obtained with the electrodiffusive model of Chen and Eisenberg (Chen, D., and R. Eisenberg. 1993. Biophys. J. 64:1405-1421), which solves the Poisson-Nernst-Plank equations in one dimension using charge distribution models inferred from the molecular analyses. The rectification of the Cx32/Cx26 heterotypic channel results from the asymmetry in the number and position of charged residues. The model required the incorporation of a partial charge located near the channel surface to approximate the linear I-V relation observed for the Cx32*Cx26E1 homotypic channel. The best candidate amino acid providing this partial charge is the conserved tryptophan residue (W3). Incorporation of the partial charge of residue W3 and the negative charge of the Cx32E41 residue into the charge profile used in the Poisson-Nernst-Plank model of homotypic Cx32 and heterotypic Cx26/Cx32 channels resulted in I-V relations that closely resembled the observed I-V relations of these channels. We further demonstrate that some channel substates rectify. We suggest that the conformational changes associated with transjunctional voltage (V(j))-dependent gating to these substates involves a narrowing of the cytoplasmic entry of the channel that increases the electrostatic effect of charges in the amino terminus. The rectification that is observed in the Cx32/Cx26 heterotypic channel is similar although less steep than that reported for some rectifying electrical synapses. We propose that a similar electrostatic mechanism, which results in rectification through the open and substates of heterotypic channels, is sufficient to explain the properties of steeply rectifying electrical synapses.     

Electrodynamics of interactions in electrolyte media. Possible consequences in biological functions

Attention is drawn to the fact that electric charge interactions in aqueous electrolyte solutions, such as physiological media, depend not only on the distance between the interacting charges but also on the frequency at which they move. This fact has important consequences for some biological processes, particularly the kinetic ones. Consideration of charge screening, including the dynamic effects, shows that electrical interactions in quasi-physiological systems are effective even above Debye’s length, provided that charges move at frequencies higher than ～250 MHz. For each electrolyte solution, it is possible to define a threshold frequency, the Maxwell frequency, as the point of crossover between a conducting and a dielectric regime in the solution.     

Problems of structural and functional identification of biological tissues

Theoretical methods for identification of topological and functional parameters of biological tissues (e.g., myocardium) are considered. Unknown topological parameters include the network dimension and connectivity, while unknown functional parameters include the resistivity of the cellular membrane and cytoplasm. The cell size (length and diameter), the input resistance of the tissue, and the fundamental electric potential field formed by a “point” current source (intracellular microelectrode) are treated as experimentally known parameters.     

In vivo DNA gene electro-transfer: a systematic analysis of different electrical parameters

BACKGROUND: Intramuscular plasmid injection followed by electroporation is an efficient method for gene therapy or vaccination. Several protocols have been described that give good transduction levels with several reporter genes. METHODS: In this work we have explored the efficiency of gene delivery upon variation of the different electrical parameters such as pulse length frequency and voltage monitoring both on short- and long-term protein production. RESULTS: Having defined the best performing parameters, we have designed a short electric treatment that gives good levels of plasmid-encoded protein in different species such as mice, rabbits and monkeys.     

Observations on bioluminescence in some deep-water anthozoans

The luminous responses to electrical stimulation of isolated polyps of 4 deep-water anthozoans are described. All show facilitatory responses and summation at stimulus frequencies > 2 s^–1. The responses of the gorgonian Acanella arbuscula comprise a slow summation of weak individual flashes. It is suggested that there is no fundamental difference between deep and shallow species, nor between the responses of scyphozoans, such as Pelagia and Atolla, and anthozoans, such as those described here. Both facilitated and decremental responses can be obtained from each of the 2 groups and the complexity of in vivo responses may be as much a reflection of selective pressures on the neural pathways as on the bioluminescent systems themselves.     

Probing neural circuitry and function with electrical microstimulation

Since the discovery of the nervous system's electrical excitability more than 200 years ago, neuroscientists have used electrical stimulation to manipulate brain activity in order to study its function. Microstimulation has been a valuable technique for probing neural circuitry and identifying networks of neurons that underlie perception, movement and cognition. In this review, we focus on the use of stimulation in behaving primates, an experimental system that permits causal inferences to be made about the effect of stimulation-induced activity on the resulting behaviour or neural signals elsewhere in the brain.     

Magnetic field influence on electrical properties of human blood measured by impedance spectroscopy

The impedance spectroscopy technique (IST) was used for studying the effect of a 0.5 T magnetic field on the electrical properties of whole human blood. A Solartron SI 1260 spectrometer was used to measure the impedance spectra of magnetic field exposed blood samples compared to non-exposed samples. An equivalent electrical circuit model, consisting in a resistance Rs in series with a parallel circuit formed by a constant phase element (CPE) and another resistance Rp, is proposed to fit the data in both cases. The experiment used 3 ml human blood samples from 160 healthy donors. A Wilcoxon matched pairs statistical test was applied to the data. The data analysis seems to show a statistically significant increase of the values of resistance Rp (Z = 5.06, P < 0.001) and capacitance CT (Z = 3.32, P < 0.001) of the blood exposed to magnetic field, by approximately 10.4% and 1.9%, respectively.     

Role of interneuronal systems in the formation of main patterns of field electrical activity in the hippocampus

Studies on the cellular and subcellular levels promote elucidation of the fundamental principles of formation of effective neuronal systems from cell units. To estimate the interrelations between electrical activity of neuronal networks and processes realized on the cellular level, we need to adequately understand the general patterns of behavior of populations of interneurons, which are components of these networks, under different physiological conditions. In this review, we describe and discuss the relations between the electrical activity of single hippocampal neurons and different components of the field electrical activity, as well as modern concepts on the mode of involvement of the system of hippocampal interneurons in the formation of physiologically important patterns of efferent activity of the above-mentioned structure (in particular in encoding of information on the neuronal level). Neirofiziologiya/Neurophysiology, Vol. 40, No. 1, pp. 58–68, January–February, 2008.