Determination of the hydraulic conductivity of Lamprothamnium by use of the pressure clamp

By use of the pressure-clamp technique, the hydraulic conductivity of the brackish-water alga Lamprothamnium was found to be 5·10^-6 cm s^-1 bar^-1. The dimensions of the internodes are so small that it is possible, for the first time, to measure a complete volume relaxation upon clamping the turgor pressure to a preset value by a feedback control of the pressure probe. As theoretically predicted, the values of the hydraulic conductivity obtained from the initial slope of the volume relaxation induced by the pressure clamp are in agreement (within experimental error) with those obtained from the half-time of the relaxation process. The cell volume also obtained from the analysis of the volume relaxation is the osmotically effective cell volume and is therefore slightly smaller than the value obtained by taking the dimensions of the cell including the cell wall.Abbreviations and symbols Lp hydraulic conductivity - P turgor pressure - S_v initial slope of volume relaxion - T_1/2 half-time of volume relaxation Dedicated to Professor Dr. H. Ziegler on the occasion of his 60th birthday     

Effect of cell turgor on hydraulic conductivity and elastic modulus of Elodea leaf cells

Water relation parameters of leaf cells of the aquatic plant Elodea densa have been measured using the pressure probe. For cells in both the upper and lower epidermis it was found that the elastic modulus () and the hydraulic conductivity (Lp) were dependent on cell turgor (P). Lp was (7.8±5.5)·10^-7 cm s^-1 bar^-1 (mean±SD; n=22 cells) for P>4 bar in cells of the upper epidermis and was increasing by a factor of up to three for P0 bar. No polarity of water movement or concentration dependence of Lp was observed. For cells of the lower epidermis the Lp-values were similar and the hydraulic conductivity also showed a similar dependence on turgor. No wall ingrowth or wall labyrinths (as in transfer cells) could be found in the cells of the lower epidermis. The elastic modulus () of cells of the upper epidermis could be measured over the whole pressure range (P=0–7 bar) by changing the osmotic pressure of the medium. increased linearly with increasing turgor and ranged between 10 and 150 bar. For cells of the lower epidermis the dependence of on P was similar, although the pressure dependence could not be measured on single cells. The Lp-values are compared with literature data obtained for Elodea by a nuclear magnetic resonance (NMR)-technique. The dependence of Lp on P is discussed in terms of pressure dependent structural changes of the cell membranes and interactions between solute and water transport.Abbreviations P cell turgor pressure - Lp hydraulic conductivity - volumetric elastic modulus - T _1/2 half-time of water exchange of individual cell     

The interaction of water with the phospholipid head group and its relationship to the lipid electrical conductivity

We have studied the interaction of water with the lipid head group by gravimetrically measuring the lipid water adsorption and the lateral dc electrical conductivity increase resulting from this hydration. We have done this for dimyristoyl phosphatidylcholine (DMPC) having protonated or deuterated hydrocarbon chains. These studies were also done for two cationic lipids having rather different polar head groups. All three lipids behave as strong water adsorbers and all three display a steep, logarithmic increase in the conductivity as the first 1-3 waters per lipid are adsorbed. This increase is usually 5-6 orders of magnitude. After the initial 1-3 waters are adsorbed, the conductivity increases much more gradually, upon additional water adsorption. This electrical behavior is also found for weak water adsorbers and appears to be independent of the head group composition. The conductivity behavior suggests two types of water interacting with the head group. Our studies also indicate that a choline-like component is responsible for the strong water binding nature of the lipids, although, both phosphate and choline make significant contributions to the total amount of adsorbed water. The conductivity behavior, however, does not depend on the presence of both these head group components.     

An analysis of the hydraulic conductivity of the extracisternal space of the cochlear outer hair cell

 The cylindrically shaped cochlear outer hair cell (OHC) plays an important role in the transduction of acoustic energy into electrical energy in the cochlea. The extracisternal space (ECiS) of the lateral wall of the OHC is the fluid-filled space between the plasma membrane (PM) and the intracellular subsurface cisterna (SSC). In the ECiS, an array of cylindrical micropillars extends from the SSC to the PM. We obtain equations for the pressure, osmotic concentration and fluid velocity in the ECiS from the Brinkman-Stokes equations for steady incompressible flow in a plane channel that encloses an array of cylinders and whose upper wall, i.e. the plasma membrane, has a hydraulic conductivity of P _PM . From these equations we obtain an estimate for the hydraulic conductivity of the ECiS, P _ECiS . We show that the ECiS geometry accounts for P _ECiS being several orders of magnitude larger than P _PM and that P _ECiS increases with the width of the ECiS and decreases with the length of the ECiS. Received: 6 January 1998 / Revised version: 12 October 1998     

Cryopreservation of umbilical cord blood: 1. Osmotically inactive volume,hydraulic conductivity and permeability of CD34(+) cells to dimethyl sulphoxide

Umbilical cord blood (UCB) is an accepted treatment for the reconstitution of bone marrow function following myeloablative treatment predominantly in children and juveniles. Current cryopreservation protocols use methods established for bone marrow and peripheral blood progenitors cells that have largely been developed empirically. Such protocols can result in losses of up to 50% of the nucleated cell population: losses unacceptable for cord blood. The design of optimal cryopreservation regimes requires the development of addition and elution protocols for the chosen cryoprotectant; protocols that minimise damaging osmotic transients. The biophysical parameters necessary to model the addition and elution of dimethyl sulphoxide to and from cord blood CD34(+) cells have been established. An electronic particle counting method was used to establish the volumetric response of CD34(+) cells to changes in osmolality of the suspending medium. The non-osmotic volume of the cell was 0.27 of the cells isotonic volume. The permeation kinetics of CD34(+) cells to water and dimethyl sulphoxide were investigated at two temperatures, +1.5 and +20 degrees C. Values for the hydraulic conductivity were 3.2 x 10(-8) and 2.8 x 10(-7)cm/atm/s, respectively. Values for the permeability of dimethyl sulphoxide at these temperatures were 4.2 x 10(-7) and 7.4 x 10(-6)cm/s, respectively. Clonogenic assays indicated that the ability of CD34(+) cells to grow and differentiate was significantly impaired outside the limits 0.6-4x isotonic. Based on the Boyle van't Hoff plot, the tolerable limits for cell volume excursion were therefore 45-140% of isotonic volume. The addition and elution of cryoprotectant was modelled using a two-parameter model. Current protocols for the addition of cryoprotectant based on exposure at +4 degrees C would require additional time for complete equilibration of the cryoprotectant. During the elution phase current protocols are likely to cause CD34(+) cells to exceed tolerable limits. The addition of a short holding period during elution reduces the likelihood of this occurring.     

Root morphology, hydraulic conductivity and plant water relations of high-yielding rice grown under aerobic conditions

Background and Aims

Increasing physical water scarcity is a major constraint for irrigated rice (Oryza sativa) production. ‘Aerobic rice culture’ aims to maximize yield per unit water input by growing plants in aerobic soil without flooding or puddling. The objective was to determine (a) the effect of water management on root morphology and hydraulic conductance, and (b) their roles in plant–water relationships and stomatal conductance in aerobic culture.

Methods

Root system development, stomatal conductance (g_s) and leaf water potential (Ψ_leaf) were monitored in a high-yielding rice cultivar (‘Takanari’) under flooded and aerobic conditions at two soil moisture levels [nearly saturated (> –10 kPa) and mildly dry (> –30 kPa)] over 2 years. In an ancillary pot experiment, whole-plant hydraulic conductivity (soil-leaf hydraulic conductance; K_pa) was measured under flooded and aerobic conditions.

Key Results

Adventitious root emergence and lateral root proliferation were restricted even under nearly saturated conditions, resulting in a 72–85 % reduction in total root length under aerobic culture conditions. Because of their reduced rooting size, plants grown under aerobic conditions tended to have lower K_pa than plants grown under flooded conditions. Ψ_leaf was always significantly lower in aerobic culture than in flooded culture, while g_s was unchanged when the soil moisture was at around field capacity. g_s was inevitably reduced when the soil water potential at 20-cm depth reached –20 kPa.

Conclusions

Unstable performance of rice in water-saving cultivations is often associated with reduction in Ψ_leaf. Ψ_leaf may reduce even if K_pa is not significantly changed, but the lower Ψ_leaf would certainly occur in case K_pa reduces as a result of lower water-uptake capacity under aerobic conditions. Rice performance in aerobic culture might be improved through genetic manipulation that promotes lateral root branching and rhizogenesis as well as deep rooting.     

Control of light-induced bean leaf expansion: Role of osmotic potential,wall yield stress,and hydraulic conductivity

The role of three-turgor-related cellular parameters, the osmotic potential ( _s), the wall yield stress (Y) and the apparent hydraulic conductivity (L'p), in the initiation of ligh-induced expansion of bean (Phaseolus vulgaris L.) leaves has been determined. Although light causes an increase in the total solute content of leaf cells, the water uptake accompanying growth results in a slight increase in _s. Y is about 4 bar; and is unaffected by light. L'p, as calculated from growth rates and isopiestic measurements of leaf water potential, is only slightly greater in rapidly-growing leaves. The turgor pressure of growing cells is lower than that of the controls by about 35%. We conclude that light does not induce cell enlargement in the leaf by altering any of the above parameters, but does so primarily by increasing wall extensibility.Abbreviations and symbols RL red light - WL white light - L'p apparent hydraulic conductivity - OC osmotic concentration - Y wall yield stress - _s osmotic potential     

Effect of boundary conditions,impact loading and hydraulic stiffening on femoral fracture strength

Patient specific quantitative CT (QCT) imaging data together with the finite element (FE) method may provide an accurate prediction of a patient's femoral strength and fracture risk. Although numerous FE models investigating femoral fracture strength have been published, there is little consent on the effect of boundary conditions, dynamic loading and hydraulic strengthening due to intra-medullary pressure on the predicted fracture strength. We developed a QCT-derived FE model of a proximal femur that included node-specific modulus assigned based on the local bone density. The effect of three commonly used boundary conditions published in literature were investigated by comparing the resulting strain field due to an applied fracture load. The models were also augmented with viscoelastic material properties and subject to a realistic impact load profile to determine the effect of dynamic loads on the strain field. Finally, the effect of hydraulic strengthening was investigated by including node specific permeability and performing a coupled pore diffusion and stress analysis of the FE model. Results showed that all boundary conditions yield the same strain field patterns, but peak strains were 22% lower and fracture load was 18% higher when loaded at the greater trochanter than when loaded at the femoral head. Comparison of the dynamic models showed that material viscoelasticity was important, but inertial effects (vibration and shock) were not. Finally, pore pressure changes did not cause significant hydraulic strengthening of bone under fall impact loading.     

Sulphate deprivation depresses the transport of nitrogen to the xylem and the hydraulic conductivity of barley (Hordeum vulgare L.) roots

During the first 4 d after the removal of SO ₄ ^2- from cultures of young barley plants, the net uptake of ¹⁵N-nitrate and the transport of labelled N to the shoot both decline. This occurred during a period in which there was no measurable change in plant growth rate and where the incorporation of [³H]leucine into membrane and soluble proteins was unaffected. Reduced N translocation was associated with six- to eightfold increases in the level of asparagine and two- to fourfold increases in glutamine in root tissue; during the first 4 d of SO ₄ ^2- deprivation there were no corresponding increases in amides in leaf tissue. The provision of 1 mol · m^–3 methionine halted, and to some extent reversed the decline in NO ₃ ^- uptake and N translocation which occurred during continued SO ₄ ^2- deprivation. This treatment had relatively little effect in lowering amide levels in roots. Experiments with excised root systems indicated that SO ₄ ^2- deprivation progressively lowered the hydraulic conductivity, Lp, of roots; after 4 d the Lp of SO ₄ ^2- -deprived excised roots was only 20% of that of +S controls. In the expanding leaves of intact plants, SO ₄ ^2- deprivation for 5 d was found to lower stomatal conductance, transpiration and photosynthesis, in the order given, to 33%, 37% and 18% of control values. The accumulation of amides in roots is probably explained by a failure to export either the products of root nitrate assimilation or phloem-delivered amino-N. This may be correlated with the lowered hydraulic conductivity. Enhanced glutamine and-or asparagine levels probably repressed net uptake of NO ₃ ^- and ¹³NO ₃ ^- influx reported earlier (Clarkson et al. 1989, J. Exp. Bot. 40, 953–963). Attention is drawn to the similar hydraulic signals occurring in the early stages of several different types of mineral-nutrient stresses.Abbreviations Asn asparagine - Gln glutamine - Lp hydraulic conductivity J.L.K. is extremely grateful to the British Council for supporting his working visit to Long Ashton. We thank John Radin for helpful discussion and encouragement.     

Inter-species variation of photosynthetic and xylem hydraulic traits in the deciduous and evergreen Euphorbiaceae tree species from a seasonally tropical forest in south-western China

The objective of the present study was to examine the functional coordination among hydraulic traits, xylem characteristics and gas exchange rates across three deciduous Euphorbiaceae tree species (Hevea brasiliensis, Macaranga denticulata and Bischofia javanica) and three evergreen Euphorbiaceae tree species (Drypetes indica, Aleurites moluccana and Codiaeum variegatum) from a seasonally tropical forest in south-western China. The deciduous tree species were more vulnerable to water stress-induced embolism than the evergreen tree species. However, the deciduous tree species generally had higher maximal rates of sapwood and leaf-specific hydraulic conductivity (K _S and K _L), respectively. Compared with the evergreen tree species, the deciduous tree species, however, possessed a lower density of sapwood and a wider diameter of xylem vessels. Regardless of leaf phenology, the hydraulic vulnerability and conductivity were significantly correlated with sapwood density and mean vessel diameter. Furthermore, the hydraulic vulnerability was positively correlated with water transport efficiency. In addition, the deciduous tree species exhibited higher maximal photosynthetic rates (A _max) and stomatal conductance (g _max), but lower water use efficiency (WUE). Interestingly, the A _max, g _max and WUE were strongly correlated with K _S and K _L across the deciduous and evergreen tree species. These results suggest that xylem structure, rather than leaf phenology, accounts for the difference in hydraulic traits between the deciduous tree species and the evergreen tree species. Meanwhile, our results show that there is a significant trade-off between hydraulic efficiency and safety, and a strong functional correlation between the hydraulic capacity and gas exchange rates across the deciduous and evergreen tree species.     

Ion-mediated increase in the hydraulic conductivity of Laurel stems: role of pits and consequences for the impact of cavitation on water transport

Changes in hydraulic conductivity (K(h)) were measured in stems of Laurus nobilis L. during perfusion with KCl, NaCl or sucrose solutions. Ionic solutes induced marked increase of K(h) with respect to deionized water but sucrose had no effect. The kinetics of KCl-induced K(h) increase was measured together with changes in [K(+)] of the perfused solution. K(h) increases were paralleled by increases in the [K(+)](out)/[K(+)](in) ratio. Samples of different lengths or with increasing percentage loss of conductivity (PLC) due to xylem cavitation were tested, with the aim of increasing radial flow through intervessel pits. KCl solutions enhanced the K(h) of 12-cm-long samples with a concentration-dependent effect up to 100 mm KCl. DeltaK(h) increased from 3 to 30% in 1.5- and 12-cm-long samples, respectively and remained constant for longer samples. Increasing PLC induced an exponential increase in DeltaK(h). PLC measured with KCl solutions was significantly less than that measured with deionized water, suggesting that measurements of PLC can be affected by the composition of the perfused solution. Experiments support the hypothesis that the 'ionic effect' is mediated by physico-chemical changes of pectins of the pit membranes and raise the possibility that plants might alter the ionic composition of the xylem sap to alleviate the hydraulic impact of cavitation.     

逆境下植物组织伤害程度测定方法--电导法的改进

针对实验教学中存在的问题,改用紫鸭趾草作为电导法的实验材料,并改进了一些实验技术,使实验结果重复性好,实验时间缩短,更适合于学生完成该实验。     

Estimating hydraulic conductivity of a sandy soil under different plant covers using minidisk infiltrometer and a dye tracer experiment

The objective of this study was to estimate the hydraulic conductivity of sandy soil under different plant cover at the locality Mláky II at Sekule (southwest Slovakia). Two sites were demarcated at the locality, with mainly moss species at glade site, and pine forest at forest site. The estimation of unsaturated hydraulic conductivity was conducted by (a) minidisk infiltrometer and (b) the analysis of a dye tracer total resident concentration. The latter approach assumed the applicability of the stochastic—convective flow theory in the sandy soil. In the dye tracer experiment, two plots (1 × 1 m each) were established in both sites, and 100 mm of dye tracer (Brilliant Blue FCF) solution was applied on the soil surface. Similar results were obtained in both plots, with more than 70 % area of horizons stained in the depth of 30–50 cm. In some cases, the predicted and measured hydraulic conductivity were found within an order of magnitude, thus revealing similar impact of different plant cover on hydraulic properties of sandy soil studied. In contrast to sandy soils used for agriculture, the influence of the plant/surface humus and topsoil interface extended in the form of a highly heterogeneous matrix flow to the depth of 50–60 cm, where it was dampened by horizontal layering.     

Abscisic acid and hydraulic conductivity of maize roots: a study using cell- and root-pressure probes

Using root- and cell-pressure probes, the effects of the stress hormone abscisic acid (ABA) on the water-transport properties of maize roots (Zea mays L.) were examined in order to work out dose and time responses for root hydraulic conductivity. Abscisic acid applied at concentrations of 100–1,000 nM increased the hydraulic conductivity of excised maize roots both at the organ (root Lp_r: factor of 3–4) and the root cell level (cell Lp: factor of 7–27). Effects on the root cortical cells were more pronounced than at the organ level. From the results it was concluded that ABA acts at the plasmalemma, presumably by an interaction with water channels. Abscisic acid therefore facilitated the cell-to-cell component of transport of water across the root cylinder. Effects on cell Lp were transient and highly specific for the undissociated (+)-cis-trans-ABA. The stress hormone ABA facilitates water uptake into roots as soils start drying, especially under non-transpiring conditions, when the apoplastic path of water transport is largely excluded. Received: 26 February 2000 / Accepted: 17 August 2000     

Root hydraulic conductivity of Larrea tridentata and Helianthus annuus under elevated CO2

While investigations into shoot responses to elevated atmospheric CO₂ are extensive, few studies have focused on how an elevated atmospheric CO₂ environment might impact root functions such as water uptake and transport. Knowledge of functional root responses may be particularly important in ecosystems where water is limiting if predictions about global climate change are true. In this study we investigated the effect of elevated CO₂ on the root hydraulic conductivity (L_p) of a C₃ perennial, Larrea tridentata, and a C₃ annual, Helianthus annuus. The plants were grown in a glasshouse under ambient (360 μmol mol^–1) and elevated (700 μmol mol^–1) CO₂. The L_p through intact root systems was measured using a hydrostatic pressure-induced flow system. Leaf gas exchange was also determined for both species and leaf water potential (ψ_leaf) was determined in L. tridentata. The L_p of L. tridentata roots was unchanged by an elevated CO₂ growth environment. Stomatal conductance (g_s) and transpiration (E) decreased and photosynthetic rate (A_net) and Ψ_leaf increased in L. tridentata. There were no changes in biomass, leaf area, stem diameter or root : shoot (R : S) ratio for L. tridentata. In H. annuus, elevated CO₂ induced a nearly two-fold decrease in root L_p. There was no effect of growth under elevated CO₂ on A_net, g_s, E, above- and below-ground dry mass, R : S ratio, leaf area, root length or stem diameter in this species. The results demonstrate that rising atmospheric CO₂ can impact water uptake and transport in roots in a species-specific manner. Possible mechanisms for the observed decrease in root L_p in H. annuus under elevated CO₂ are currently under investigation and may relate to either axial or radial components of root L_p.     

Growth and root hydraulic conductivity of several citrus rootstocks under salt and polyethylene glycol stresses

The water relations responses to salt of several important citrus rootstocks such as Swingle citrumelo, sour orange, and Milam lemon have not been studied in detail before. Studies were set up to compare growth and root hydraulic properties of these rootstocks to other citrus rootstocks by exposing them to NaCl and polyethylene glycol (PEG) stresses. Seedlings of 7 citrus rootstocks were irrigated for 5 months with nutrient solutions containing NaCl or PEG that had been adjusted to osmotic potentials of -0.10, -0.20 or -0.35 MPa. The 7 rootstocks studied were sour orange (Citrus aurantium), Cleopatra mandarin (Citrus reticulata Blanco), Swingle citrumelo (C. paradisi x P. trifoliata), Carrizo citrange (C. sinensis x P. trifoliata), rough lemon (Citrus jambhiri Lush), Milam lemon (C. jambhiri hybrid), and trifoliate orange (Poncirus trifoliata [L.] Raf.). In both shoot and root growth, Cleopatra mandarin and sour orange were the least sensitive to salt, Milam and trifoliate orange were the most sensitive, and rough lemon, Swingle, and Carrizo were intermediate in sensitivity. Even though the roots were exposed to solutions of equal osmotic potentials, plant growth and root conductivity were reduced more by the PEG treatments than the corresponding NaCl treatments. At -0.10 and -0.20 MPa, shoot and root dry weights were reduced 16 to 55% by NaCl and 24 to 68% by PEG. Shoot root ratio was lowered at the higher concentrations, particularly by PEG. There was a major decrease in root conductivity caused by NaCl at -0.10 MPa (19 to 30% in sour orange and Cleopatra mandarin and 78 to 85% in trifoliate orange and Milam). Conductivity decreased more at -0.20 and -0.35 MPa, but not proportionally as much as at -0.10 MPa. Root weight per unit length increased at the higher salt levels, particularly in trifoliate orange. Water flow rate through root systems followed the same trend as root conductivity; salt affected sour orange and Cleopatra mandarin the least and trifoliate orange and Milam the most. However, reductions in fibrous root length by salt treatment differed. Root lengths of Swingle and Carrizo were least affected by salt while sour orange. Milam, and rough lemon were the most affected. Hence, even though sour orange and Cleopatra mandarin were more tolerant than the other rootstocks in terms of water flow rate or root conductivity, these 2 rootstocks showed a proportionally greater decrease in root length than Carrizo, Swingle, or trifoliate orange.     

Growth of the medicinal leech, Himudo medicinalis, under natural and laboratory conditions

SUMMARY 1. The growth of the medicinal leech, Hirudo medicinalis L., was studied in the wild by a mark and recapture technique, and in the laboratory. Growth in the wild, even after 2 years, was generally small and variable.
2. After being offered regular feeds of various preparations of bovine blood through a pig-ileum membrane and being allowed to feed to satiation, hatchling leeches in the laboratory showed a saltatory pattern of weight gain with increases greatly in excess of those seen in the wild. Twelve of twenty-five leeches starved from hatching survived for about 250 days. The ability to survive for long periods without feeding may well be important for the overwintering survival of late hatchlings.     

The relevance of xylem network structure for plant hydraulic efficiency and safety

The xylem is one of the two long distance transport tissues in plants, providing a low resistance pathway for water movement from roots to leaves. Its properties determine how much water can be transported and transpired and, at the same time, the plant's vulnerability to transport dysfunctions (the formation and propagation of emboli) associated to important stress factors, such as droughts and frost. Both maximum transport efficiency and safety against embolism have classically been attributed to the properties of individual conduits or of the pit membrane connecting them. But this approach overlooks the fact that the conduits of the xylem constitute a network. The topology of this network is likely to affect its overall transport properties, as well as the propagation of embolism through the xylem, since, according to the air-seeding hypothesis, drought-induced embolism propagates as a contact process (i.e., between neighbouring conduits). Here we present a model of the xylem that takes into account its system-level properties, including the connectivity of the xylem network. With the tools of graph theory and assuming steady state and Darcy's flow we calculated the hydraulic conductivity of idealized wood segments at different water potentials. A Monte Carlo approach was adopted, varying the anatomical and topological properties of the segments within biologically reasonable ranges, based on data available from the literature. Our results showed that maximum hydraulic conductivity and vulnerability to embolism increase with the connectivity of the xylem network. This can be explained by the fact that connectivity determines the fraction of all the potential paths or conduits actually available for water transport and spread of embolism. It is concluded that the xylem can no longer be interpreted as the mere sum of its conduits, because the spatial arrangement of those conduits in the xylem network influences the main functional properties of this tissue. This brings new arguments into the long-standing discussion on the efficiency vs. safety trade-off in the plants' xylem.