Effects of water stress on the water relations of Phaseolus vulgaris and the drought resistant Phaseolus acutifolius

The tepary bean ( Phaseolus acutifolius Gray var. latifolius ), a drought resistant species, was compared under water stress conditions with the more drought susceptible P. vulgaris L. cvs Pinto and White Half Runner (WHR). In order to better understand the basis for the superior drought resistance of tepary, this study was designed to determine the relationships among leaf water potential, osmotic potential, turgor potential, and relative water content (RWC).
Plants were prestressed by withholding irrigation water. These stress pretreatments changed the relation between leaf water potential and relative water content of both species so that prestressed plants had lower water potentials than controls at the same leaf RWC. Tepary had lower water potentials at given RWC levels than Pinto or WHR; this can account for part of the superior resistance of tepary. In all genotypes, prestressed plants maintained osmotic potentials approximately 0.2 MPa lower than controls. Tepary reached osmotic potentials that were significantly lower (0.15 to 0.25 MPa) than Pinto or WHR. Both control and prestressed tepary plants had 0.05 to 0.25 MPa more turgor than Pinto or WHR at RWC values between 65 and 80%. Both prestressed and control tepary plants had greater elasticity (a lower elastic modulus) than Pinto or WHR. This greater turgor of tepary at low RWC values could be caused by several factors including greater tissue elasticity, active accumulation of solutes, or greater solute concentration.
Tepary had significantly lower osmotic potentials than the P. vulgaris cultivars, but there was little difference in osmotic potential between Pinto and WHR. Knowledge of differences in osmotic and turgor potentials among and within species could be useful in breeding for drought resistance in Phaseolus.     

Light-triggered action potentials in the liverwort Conocephalum conicum

The response to light of a liverwort, Conocephalum conicum L., measured as a change in the resting potential, consists of two stages. The first stage is a slight depolarization dependent on light intensity. This plays the role of a generator potential (GP) which induces the second stage - an action potential of the all-or-none character. Action potentials induced by light and by electrical stimuli have the same properties, i.e. identical time course, propagation velocity, and refractory periods. A summation occurs of sub threshold light stimuli and of light and electrical stimuli. The presence of 5⋅10-⁻⁶ M DCMU cancelled the light response and blocked - by inhibition of the electron transport chain - the mechanism leading to GP generation. However, this effect did not produce any change in the response to electrical stimuli.     

Membrane potential and surface potential in mitochondria: Uptake and binding of lipophilic cations

Summary The uptake and binding of the lipophilic cations ethidium⁺, tetraphenylphosphonium⁺ (TPP⁺), triphenylmethylphosphonium⁺ (TPMP⁺), and tetraphenylarsonium⁺ (TPA⁺) in rat liver mitochondria and submitochondrial particles were investigated. The effects of membrane potential, surface potentials and cation concentration on the uptake and binding were elucidated. The accumulation of these cations by mitochondria is described by an uptake and binding to the matrix face of the inner membrane in addition to the binding to the cytosolic face of the inner membrane. The apparent partition coefficients between the external medium and the cytosolic surface of the inner membrane (K' _o) and the internal matrix volume and matrix face of the inner membrane (K' _i) were determined and were utilized to estimate the membrane potential from the cation accumulation factorR _c according to the relation =RT/ZF ln [(R _cV_o–K'_o)/(V_i+K'_i)] whereV _o andV _i are the volume of the external medium and the mitochondrial matrix, respectively, andR _c is the ratio of the cation content of the mitochondria and the medium. The values of estimated from this equation are in remarkably good agreement with those estimated from the distribution of⁸⁶Rb in the presence of valinomycin. The results are discussed in relation to studies in which the membrane potential in mitochondria and bacterial cells was estimated from the distribution of lipophilic cations.     

Some physiological and growth responses of kiwi fruit (Actinidia chinensis) to flooding

The effects of long-term flooding on the growth of six-month-old Actinidia chinensis Planch cv. Abbot plants and some effects on stomatal behaviour and leaf water relations were examined under controlled conditions for 28 days. Flooding caused stomatal closure and decreases in transpiration rate, xylem water potential, osmotic potential and turgor potential. Flooding also caused inhibition of the dry weight increase of leaves plus stems and of roots, chlorosis and necrosis of leaves, production of hypertrophied lenticels and the appearance of a small number of adventitious roots on the submerged portions of the stems. Rapid and partial stomatal closure by flooding may not only be due to the passive mechanical response which follows leaf dehydration, since flooded plants showed an increase in xylem water potential and osmotic potential during the first days of the experiment. The marked intolerance of Actinidia chinensis to flooding has been a serious barrier to its culture in poorly drained soils, hence careful irrigation management is required.     

微电极矩阵研究小鼠胚胎心脏电生理活动

本实验采用一种新方法——微电极矩阵技术从整体水平研究小鼠胚胎离体整体心脏电生理活动。我们用微电极矩阵记录与60个电极相接触的心肌细胞的电活动(细胞外记录),称为场电位(field potentials,FPs),并与全细胞膜片钳记录的动作电位(action potentials,APs)(细胞内记录)进行比较,发现心房、心室处场电位形态类似于负向的细胞动作电位,场电位时程亦与动作电位时程类似。为研究兴奋的传导,我们比较了不同电极处场电位发生时间,发现在房室结构还未形成的胚胎发育第9．5天(E9．5)已经观察到明显的房室传导延迟(A-V delay)[(50．21±9．7)ms],而心室不同部位兴奋几乎是同步的。在发育晚期(E16．5),房室传导延迟为(82．21±10．50)ms。进一步研究基本的神经体液因素对心脏兴奋的调控,表明: 在E9．5,异丙肾上腺素(isoproterenol,Iso)使胚胎兴奋频率加快(34．04±7．31)％,房室传导延迟缩短(20．00±6．44)％,同时场电位时程增宽;相反,卡巴唑(carbachol,CCh)则使兴奋频率降低(42．32±5．36)％,房室传导缩短(26．00±4．81)％, 场电位时程减小。而在E16．5,Iso的作用显著增强,兴奋频率加快(101．54±10．23)％,房室传导延迟缩短(56．62±6．43)％, 而CCh则几乎使所有晚期心脏兴奋完全消失。所以,心脏的传导系统在胚胎发育早期4个腔室还未形成时已经建立,神经体液因子对心脏基本电生理活动的调控是在发育过程中逐渐成熟的。     

Induced fluctuations of electric potentials in the apoplast of leaves

Extracellular recordings of electrical potential in leaves of different species by means of band-pass amplifiers showed the occurrence of fast, small changes (spikes) with an amplitude below 1 mV. Local illumination of leaves induced temporal patterns of spikes outside the illuminated region. The light-induced patterns recorded by a given electrode in a particular experimental setup were similar for successive illuminations. The patterns recorded at different sites on the same leaf were different. Locally repetitive patterns of spikes at the electrode outside the illuminated region indicate the occurrence of some signals transmitted from this region to the cells in the neighborhood of the electrode.     

Leaf age and salinity influence water relations of pepper leaves

Plant growth is reduced under saline conditions even when turgor in mature leaves is maintained by osmotic adjustment. The objective of this study was to determine if young leaves from salt-affected plants were also osmotically adjusted. Pepper plants (Capsicum annuum L. cv. California Wonder) were grown in several levels of solution osmotic potential and various components of the plants' water relations were measured to determine if young, rapidly growing leaves could accumulate solutes rapidly enough to maintain turgor for normal cell enlargement. Psychrometric measurements indicated that osmotic adjustment is similar for both young and mature leaves although osmotic potential is slightly lower for young leaves. Total water potential is also lower for young leaves, particularly at dawn for the saline treatments. The result is reduced turgor under saline conditions at dawn for young but not mature leaves. This reduced turgor at dawn, and presumably low night value, is possibly a cause of reduced growth under saline conditions. No differences in leaf turgor occur at midday. Porometer measurements indicated that young leaves at a given salinity level have a higher stomatal conductance than mature leaves, regardless of the time of day. The result of stomatal closure is a linear reduction of transpiration.     

柠条抗旱的生理生态与土壤水分关系的研究

采用LI－1600气孔计和压力室测试了风沙土上生长的柠条的SPAC系统的水分关系和P－V水分特征曲线,结果表明：当沙土含水率（W）的水分特征曲线的回归方程为：ψs=-40．32196×0．427905W,沙土平均含水率大于45％,柠条固沙林生长正常,叶水势高。沙土含水率小于4．5％时,柠条生长速度显著下降,柠条清晨叶水势（ψm）与沙土含水率（W）的回归方程为：ψm=－0．35926·e6．31144／W,风沙土上生长的柠条的“经济水阈”大约在4．5％左右,“生命水阈”大约在3．5％左右。     

α2 isoform of Na+,K+-ATPase via Na+,Ca2+ exchanger modulates myelin basic protein synthesis in oligodendrocyte lineage cells in vitro

Oligodendrocytes in the CNS myelinate neuronal axons, facilitating rapid propagation of action potentials. Myelin basic protein (MBP) is an essential component of myelin and its absence results in severe hypomyelination. In oligodendrocyte lineage cell (OLC) monocultures MBP synthesis starts at DIV4. Ouabain (10 nM), a Na⁺,K⁺-ATPase (NKA) blocker, stimulates MBP synthesis. As OLCs express the α2 isoform of NKA (α2-NKA) that has a high affinity for ouabain, we hypothesized that α2-NKA mediates this effect. Knockdown of α2-NKA with small interfering (si)RNA (α2-siRNA) significantly potentiated MBP synthesis at DIV4 and 5. This effect was completely blocked by KB-R7943 (1 μM), a Na⁺,Ca²⁺ exchanger (NCX) antagonist. α2-NKA ablation increased the frequency of NCX-mediated spontaneous Ca²⁺ transients ([Ca²⁺]t) at DIV4, whereas in control OLC cultures comparable frequency of [Ca²⁺]t was observed at DIV5. At DIV6 almost no [Ca²⁺]t were observed either in control or in α2-siRNA-treated cultures. Immunocytochemical analyses showed that α2-NKA co-localizes with MBP in proximal processes of immature OLCs but is only weakly present in MBP-enriched membrane sheets. Knockdown of α2-NKA in cortical slice cultures did not change MBP levels but reduced co-localization of neurofilament- and MBP-positive compartments. We conclude that α2-NKA activity in OLCs affects NCX-mediated [Ca²⁺]t and the onset of MBP synthesis. We suggest therefore that neuronal activity, presumably in form of local extracellular [K⁺] changes, might locally influence NCX-mediated [Ca²⁺]t in OLC processes thus triggering local MBP synthesis in the vicinity of an active axon.     

2‐photon excitation fluorescence microscopy enables deeper high‐resolution imaging of voltage and Ca2+ in intact mice,rat, and rabbit hearts

We describe a novel two‐photon (2P) laser scanning microscopy (2PLSM) protocol that provides ratiometric transmural measurements of membrane voltage (V_m) via Di‐4‐ANEPPS in intact mouse, rat and rabbit hearts with subcellular resolution. The same cells were then imaged with Fura‐2/AM for intracellular Ca²⁺ recordings. Action potentials (APs) were accurately characterized by 2PLSM vs. microelectrodes, albeit fast events (<1 ms) were sub‐optimally acquired by 2PLSM due to limited sampling frequencies (2.6 kHz). The slower Ca²⁺ transient (CaT) time course (>1ms) could be accurately described by 2PLSM. In conclusion, V_m ‐ and Ca²⁺‐sensitive dyes can be 2P excited within the cardiac muscle wall to provide AP and Ca²⁺ signals to ～400 µm. (© 2013 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Studies on Water Movement Into and Out of Grapevine Fruits During the Ripening

The experiment was carried out during the ripening of grape (Vitis vinifera L. and V. vinifera × V. labrusca) fruits using the technique of dye tracing and measurement of water potential. Under the natural conditions of sufficient soil water supply and those of a high evapotranspiration potentiality on clear days, the water in fruits was transfered, during the morning and afternoon, out of the clusters and into the xylem of shoots; but the fruits capture water in the late afternoon and evening from the xylem of shoots. The diurnal variations of the water exchange between fruits and the xylem of shoots have been described and these variations seemed to be relevant not only to the differences of water potential between leaves and fruits but also to the hydraulic status of fruits. Under the mild water stress, the variations of the diurnal "fruits-shoots" water exchange were similar to those under the conditions of ample water supply, but the rate of "fruits-shoots" water exchange in the lightly stressed vine was decreased as compared with the fully watered vines. After a certain period of severe water stress, the fruits possessed a great capacity of conserving their water and an equilibrium in water potential was set up between leaves and fruits so that the fruits did not lose any more water. Under a sudden severe water stress, the fruits lost water at a higher outflux rate than when the water supply was sufficient. However, this water loss ceased rapidly. The water flowing out from the fruits was privileged to pass in the lateral shoots located above and on the same side of the fruits, and then the water might enter the primary shoot leaves situated above and on the same side of the fruits. Water captured by the fruits of the well watered vines in the evening came from the roots while under severe stress water might be obtained from the roots and also from the leaves as well. The fruit cell water potential, solute potential and pressure potential were different from those of leaves, mainly in the more important differences of water potential necessitated for the volume changes of fruit cell after incipient plasmolysis in com parison with leaves. Finally the relationships between water exchange and water potential dif ferences between "fruits-shoots", associated with the fruits hydraulic status, have been discussed. The possible relationships between water "sink-source" of fruits and the fruit development have been analysed.     

Water relations of Capsicum genotypes under water stress

Pepper species and cultivars, Capsicum annuum cv. Bell Boy, C. annuum cv. Kulai and C. frutescens cv. Padi, differing in drought tolerance were investigated for their water relations, stomatal responses and abscisic acid (ABA) content during water stress. C. frutescens cv. Padi exhibited a greater osmotic adjustment than C. annuum cultivars. Stomatal conductance of cv. Bell Boy was more sensitive to water stress than that of cvs. Kulai and Padi. In all pepper genotypes, stomatal closure was triggered in the absence of a large decrease in leaf water status. ABA content in xylem sap and leaf was higher in C. annum cultivars compared to C. frutescens cv. Padi. This revised version was published online in July 2006 with corrections to the Cover Date.     

催产素对豚鼠听觉机能作用的电生理研究

本实验利用听觉电生理学方法,研究了催产素(Oxytocin)对豚鼠内耳听觉机能的作用。给豚鼠肌内注射催产素后,由短声引起的耳蜗微音器电位和听神经复合动作电位幅值增加,听神经复合动作电位和听皮层诱发电位的阈值降低。说明催产素具有提高豚鼠内耳听觉机能的作用。     

低镁和缺镁对离体豚鼠右心室肌单细胞动作电位的效应

取豚鼠右心室肌,在改良 Krebs 溶液灌注下,用微电极记录动作电位(AP)12只豚鼠72次心肌单细胞 AP 有关参数的平均值为:静息电位(RP)-76±9mV;动作电位振幅(APA)107±7mV;动作电位时程(APD)_(_30mv)为254±123ms;APD_(100)为312±133ms。当灌注液中镁离子浓度减低到0.6mol/L 时,72次 AP 的 APD_(_30mv)和APD_(100)分別为对照值的80.7%和83%;在无镁溶液中,改变更为显著,分别为对照值的70.9%和76.7%;RP 和 APA 则变化均不大。实验提示:低镁可使 APD 缩短,从而可能影响体表心电图 T 波的第3位相;此外,APD 的缩短意味着不应期相对缩短,这或许是低镁症时出现室性早搏的因素。     

L-glutamate as an excitatory transmitter at the neuromuscular junction of a beetle larva

The effects of L-glutamate and acetylcholine on the ventral muscle fibres of the larval mealworm Tenebrio molitor were studied by means of microelectrodes. Bath application of L-glutamate at concentrations higher than 1 × 10 ⁴M suppressed excitatory postsynaptic potentials (EPSPs) and evoked both a depolarisation and a reduction in the input resistance of the muscle fibre. In contrast, acetylcholine chloride (up to 1 mM) had no effect at all. Circumscribed spots could be detected on the fibre surface where iontophoretic applications of L-glutamate caused transient depolarizations (glutamate potentials). Focal extracellular recordings revealed that the glutamate sensitive spots were identical with synaptic sites. The reversal potentials of the EPSP and the L-glutamate potential were identical. These results are compatible with the hypothesis that L-glutamate is an excitatory transmitter at the neuromuscular junction.     

中国潜在植被NPP的空间分布模拟

在对1980年以来气候要素进行空间化的基础上,利用分类回归树模型CART计算中国的潜在归一化植被指数(NDVI),采用改进的光能利用率模型(CASA)和潜在NDVI数据对中国的潜在植被净初级生产力(NPP)进行模拟。结果表明:中国潜在NDVI和潜在NPP均呈现出南高北低、东高西低的格局,低值多分布在沙漠、戈壁等干旱地带,高值多出现在低、中山平原区;400 mm等降水量线是潜在NDVI和潜在NPP高值与低值的分界线;全国潜在NDVI和潜在NPP的平均值分别为0.396和319.31 g C·m-2;夏季潜在NPP的平均值最大,其次是春季,冬季最小;依据潜在NPP与2015年现实NPP的差异,可将中国植被恢复区划分为西部高潜力区、北部低潜力区和南部非潜力区3部分;潜在NDVI和潜在NPP的空间模拟可以将人类活动对自然生态系统的直接影响与气候变化的影响分离,量化了外界压力下真实的生态状况和潜在生态状况的差异,为制定差别化的生态恢复对策提供了科学依据。     

Water relations in grapevine micro-cuttings grownin vitro

Dry mater, water content, water, osmotic and pressure potentials, content of saccharides and potassium were measured duringin vitro cultivation ofVitis rootstocks. Three cases were compared: a) the micro-cuttings with normal growth; b) micro-cuttings which stop their growth after 15 d of culture, and c) micro-cuttings reactivated by 6 d of continuous darkness. Major differences were observed in water content and osmotic potential. The stopping of growth was not a specific property of buds, but was probably due to restriction of translocation of saccharides and water in the shoot.     

Voltage dependence of cellular current and conductances in frog skin

Summary Knowledge of the voltage dependencies of apical and basolateral conductances is important in determining the factors that regulate transcellular transport. To gain this knowledge it is necessary to distinguish between cellular and paracellular currents and conductances. This is generally done by sequentially measuring transepithelial current/voltage (I _t /V _t ) and conductance/voltage (g _t /V _t ) relationships before and after the abolition of cellular sodium transport with amiloride. Often, however, there are variable time-dependent and voltage-dependent responses to voltage perturbation both in the absence and presence of amiloride, pointing to effects on the paracellular pathway. We have here investigated these phenomena systematically and found that the difficulties were significantly lessened by the use of an intermittent technique, measuringI _t andg _t before and after brief (<10 sec) exposure to amiloride at each setting ofV _t .I/V relationships were characterized by these means in frog skins (Rana pipiens, Northern variety, andRana temporaria). Cellular current,I _c , decreased with hyperpolarization (larger serosa positive clamps) ofV _t . DerivedI _c /V _t relationships betweenV _t =0 and 175 mV (serosa positive) were slightly concave upwards. Because values of cell conductance,g _c , remained finite, it was possible to demonstrate reversal ofI _c . Values of the reversal potentialV' averaged 156±14 (sd,n=18) mV. Simultaneous microelectrode measurements permitted also the calculation of apical and basolateral conductances,g _a andg _b . The apical conductance decreased monotonically with increasing positivity ofV _t (andV _a ). In contrast, in the range in which the basolateral conductance could be evaluated adequately (V _t <125 mV),g _b increased with more positive values ofV _t (andV _b ). That is, there was an inverse relation betweeng _b and cellular current at the quasi-steady state, 10–30 sec after the transepithelial voltage step.     

An atomic environment potential for use in protein structure prediction

We describe the derivation and testing of a knowledge-based atomic environment potential for the modeling of protein structural energetics. An analysis of the probabilities of atomic interactions in a dataset of high-resolution protein structures shows that the probabilities of non-bonded inter-atomic contacts are not statistically independent events, and that the multi-body contact frequencies are poorly predicted from pairwise contact potentials. A pseudo-energy function is defined that measures the preferences for protein atoms to be in a given microenvironment defined by the number of contacting atoms in the environment and its atomic composition. This functional form is tested for its ability to recognize native protein structures amongst an ensemble of decoy structures and a detailed relative performance comparison is made with a number of common functions used in protein structure prediction.