Water Flow Through Vessel Perforation Plates--The Effects of Plate Angle and Thickness for Liriodendron tulipifera

The effects of scalariform perforation plate thickness and anglewithin vessel elements of Liriodendron tulipifera were studiedwith a computational fluid dynamical model. The pressure gradientand hence resistance to flow through the plate increased asthe perforation plate increased in thickness. Increasing theangle of the plate relative to the axis of the vessel (samenumber of pores) also increased the pressure gradient alongthe modelled cell. For the model matching the actual vesselelement, the plate contributed 8% to the flow resistance ofthe vessel element. This contribution increased only to 11%for doubled plate thickness, and to 14% for a plate at an angleof 60° to the vessel axis. The perforation plate alteredthe velocity profile across the vessel element, but to a differentextent depending on the angle of the plate. A plate at an acuteangle to the vessel axis has little effect on the paraboloidprofile as found upstream from the plate, while obtuse angleplates change the flow profile such that fluid through poresnear the wall is accelerated to a greater velocity than foundin the centre of the cell. Key words: Conductance, perforation plate, vessel, water flow     

A Continuum Mechanical Approach to the Flow Equations for Membrane Transport: I. Water Flow

A concept is presented for modeling flows through membranes using continuum mechanics. Viscous interactions (due to velocity gradients) are explicitly incorporated and position-dependent local water-membrane interactions are taken into account before obtaining slab averages. This is in distinction to other treatments where strictly one-dimensional force balance equations are written using slab average friction coefficients which are really composite functions of local interactions. It is shown that the viscous and other frictional interactions do not simply form linear combinations in the solutions to the equations of motion. Flow profiles for pressure-driven flows ranging from Poiseuille's flow to “diffusion” flow are obtained depending on the strength and extent of the water-membrane interaction. The model is also applied to self-diffusion flows and the measurement of “equivalent pore size.” It is shown that for a fixed pore size the ratio of filtration flow to self-diffusion flow for equal driving forces is able to vary over a wide range depending on the water-membrane interaction.     

Water Flow in Vessels with Simple or Compound Perforation Plates

Hydraulic conductance of vessels was studied in young stem internodesand petioles of five species of dicotyledons that have simpleor compound perforation plates. Measured conductances of Clematisdioscoreifolia, Hardenbergia violacea, and Olea europaea, whichhave simple perforation plates, ranged from 92 to 106% of predictedvalues based on Hagen-Poiseuille flow through ideal capillaries.Petioles of Liquidambar styraciflua and Liriodendron tulipifera,which have compound perforation plates, had measured hydraulicconductances in spring-collected material that matched predictedconductances, but values averaged 60% of predicted in materialfrom late summer, suggesting blockage of vessels with time.An analog model of a vessel with and without compound perforationplates was developed from tygon tubing and steel pins to determinethe effect of obstruction by bars, which produced little flowreduction. Likewise, calculations based on the observed geometryof a scalariform perforation plate suggested that the platetypically reduced flow by only 1%. These data suggest that flowrates in vessels with simple as well as compound perforationplates are essentially equal to flows in ideal capillaries ofthe appropriate diameters. Clematis dioscoreifolia, Hagen-Poiseuille, Hardenbergia violacea, hydraulic conductance, Liquidambar styraciflua, Liriodendron tulipifera, Olea europaea, xylem     

Plant Influence on Water Flow Through Artificial Membranes

This paper describes a simple, reproducible method of monitoringwater uptake by plants operating in an ad libitum system. Thesystem consists of a thin microporous membrane interfaced witha water reservoir on one side and potted plant on the other.The plant establishes control over the membrane through itsroots, which modify the permeability of the microporous waterbarrier in accordance with autonomic cycles in growth activity.It was shown that the pattern of water flow is modified in themanner expected by changes in environment that affect wholeplant physiology. Impatiens, Ficus indica, Coleus blumei, water flow, artificial membranes, periodicity, surfactant, root exudate     

Pressure-Induced Water and Solute Flow Through Plant Roots

Water and salt flows through detopped sunflower, tomato andred kidney bean roots under applied pressure were studied usinga pressure chamber. Values of J_v for these root systems weremeasured applying variable pressure on the root medium, andL_p calculated. The K, Na and Cl fluxes under applied pressure were comparedwith those in intact plants at the same water flow rates. Tento 100 times higher Na and Cl fluxes were observed through detoppedroots under pressure as compared to those in the unpressurized,intact plants. It is suggested that the roots under pressureare not completely analogous to intact plant roots, and thatpressure-induced flow may not be a reliable method of determiningcharacteristics of ion flow in roots in relation to water flow. Key words: Volume flow, Hydraulic conductivity, K selectivity     

An Efficient Multi-Scale Modelling Approach for ssDNA Motion in Fluid Flow

The paper presents a multi-scale modelling approach for simulating macromolecules in fluid flows. Macromolecule transport at low number densities is frequently encountered in biomedical devices, such as separators, detection and analysis systems. Accurate modelling of this process is challenging due to the wide range of physical scales involved. The continuum approach is not valid for low solute concentrations, but the large timescales of the fluid flow make purely molecular simulations prohibitively expensive. A promising multi-scale modelling strategy is provided by the meta-modelling approach considered in this paper. Meta-models are based on the coupled solution of fluid flow equations and equations of motion for a simplified mechanical model of macromolecules. The approach enables simulation of individual macromolecules at macroscopic time scales. Meta-models often rely on particle-corrector algorithms, which impose length constraints on the mechanical model. Lack of robustness of the particle-corrector algorithm employed can lead to slow convergence and numerical instability. A new FAst Linear COrrector （FALCO） algorithm is introduced in this paper, which significantly improves computational efficiency in comparison with the widely used SHAKE algorithm. Validation of the new particle corrector against a simple analytic solution is performed and improved convergence is demonstrated for ssDNA motion in a lid-driven micro-cavity.     

Water Flow Through Cotton Roots in Relation to Xylem Anatomy

The effect of root anatomy on water flow was studied in 7-d-oldcotton (Gossypium hirsutum L.) seedlings grown in solution culture.The total water flux of the intact root system was measuredusing a pressure chamber. Then successive terminal root sectionswere removed at 2,6,10 and 12 cm behind the root tip and theflux was remeasured after each successive cut was made. Xylemdevelopment at different distances behind the root apex wasstudied with a microscope using sections cut free-hand and stainedwith toluidine blue. Water flux increased with the removal ofsuccessive terminal root sections and this coincided with thedegree of basipetal primary xylem development. The large increasein water flux at 10 to 12 cm was associated with secondary xylemdevelopment and increased xylem vessel number. A comparison of water flow and xylem anatomy between roots withtetrarch (Stoneville 506 and Deltapine 41) and pentarch (T25strain) vascular bundle arrangements showed no significant differencesin the measured values of water flux for the primary root. Waterflux, estimated using Poiseuille's equation and measured xylemdimensions, was greater for the tetrarch roots, primarily becauseof the larger diameter of individual vessel elements. The increasednumber of vessel elements in the pentarch primary root of T25did not result in any apparent decrease in axial resistanceto water flow. Key words: Gossypium hirsutum L., roots, vascular bundle, xylem water flux, xylem     

Collagen Network of Articular Cartilage Modulates Fluid Flow and Mechanical Stresses in Chondrocyte

The extracellular matrix of articular cartilage modulates the mechanical signals sensed by the chondrocytes. In the present study, a finite element model (FEM) of the chondrocyte and its microenvironment was reconstructed using the information from fourier transform infrared imaging spectroscopy. This environment consisted of pericellular, territorial (mainly proteoglycans), and inter-territorial (mainly collagen) matrices. The chondrocyte, pericellular, and territorial matrix were assumedto be mechanically isotropic and poroelastic, whereas the inter-territorial matrix, due to its high collagen content, was assumed to be transversely isotropic and poroelastic. Under instantaneous strain-controlled compression, the FEM indicated that the fluid pressure within the chondrocyte increased nonlinearly as a function of the in-plane Young’s modulus of the collagen network. Under instantaneous force-controlled compression, the chondrocyte experienced the highest fluid pressure when the in-plane Young’s modulus of the collagen network was ~4 MPa. Based on the present results, the mechanical characteristics of the collagen network of articular cartilage can modify fluid flow and stresses in chondrocytes. Therefore, the integrity of the collagen network may be an important determinant in cell stimulation and in the control of the matrix maintenance.     

木通科4属植物导管穿孔板的比较研究

运用扫描电子显微镜法(SEM)对木通科(Lardizabalaceae)4属植物茎的次生木质部导管分子进行观察,结果表明:(1)端壁均具有单穿孔板;(2)串果藤属的导管分子具有丰富的穿孔板类型,包括网状、梯状、单穿孔及过渡类型,穿孔具有网状、丝状、片状的纹孔膜残余;大血藤属和八月瓜属的导管分子具有相似的特征,端壁具有梯状、单穿孔及梯—单混合穿孔板;野木瓜属只具有单穿孔板;(3)侧壁上具有穿孔板,多为梯状或梯—网混合类型(除了野木瓜属);(4)野木瓜属的导管侧壁具有独特的螺旋状加厚。各属导管的不同特征为木通科的系统演化提供比较可靠的依据。     

Mechanical Vessel Injury in Zebrafish Embryos

Zebrafish (Danio rerio) embryos have proven to be a powerful model for studying a variety of developmental and disease processes. External development and optical transparency make these embryos especially amenable to microscopy, and numerous transgenic lines that label specific cell types with fluorescent proteins are available, making the zebrafish embryo an ideal system for visualizing the interaction of vascular, hematopoietic, and other cell types during injury and repair in vivo. Forward and reverse genetics in zebrafish are well developed, and pharmacological manipulation is possible. We describe a mechanical vascular injury model using micromanipulation techniques that exploits several of these features to study responses to vascular injury including hemostasis and blood vessel repair. Using a combination of video and timelapse microscopy, we demonstrate that this method of vascular injury results in measurable and reproducible responses during hemostasis and wound repair. This method provides a system for studying vascular injury and repair in detail in a whole animal model.     

猫儿屎导管分子穿孔板新类型的发现

运用扫描电镜(SEM)对木通科(Lardizabalaceae)猫儿屎属(Decaisnea Hook.f. & Thoms.)植物猫儿屎[Decaisnea insignis (Griff.) Hook.f.et Thoms.]茎的次生木质部导管分子进行观察,以期为该属的系统演化提供依据.结果表明,猫儿屎的导管分子具有多个穿孔板,端壁穿孔板除了梯状以外,还有梯-网、梯-网-单、梯-单混合穿孔板等类型;侧壁穿孔板包括梯状、网状、梯-网混合状穿孔板;穿孔板上纹孔膜的残余有丝状、网状和片状.同时对导管分子的长度、宽度及端壁倾斜度等特征进行统计,并讨论了木通科各类群的穿孔板特征.     

台湾青枣导管分子及其穿孔板研究

运用细胞图象分析系统及显微照相的方法对台湾青枣Z iziphus mauritiana次生木质部导管分子进行了观察研究。在台湾青枣的次生木质部导管分子中存在着许多不同的样式,并且导管分子穿孔板存在着3种类型:两端均为一个单穿孔板;一端为一个单穿孔板,另一端为梯状穿孔板;具纤毛的单穿孔板。分别对其进行了描述,并从导管分子个体发育与系统发育的角度进行了讨论,认为3种类型的穿孔板为导管分子穿孔板的系统演化提供了新的证据。     

细枝木麻黄导管分子及穿孔板解剖学研究

运用细胞图象分析系统和显微照相的方法对细枝木麻黄(CasuarinacunninghamianaMiq.)次生木质部导管分子进行了观察研究。细枝木麻黄次生木质部导管分子有3种类型,即两端具尾导管、一端具尾导管和无尾导管。导管分子穿孔板有4种类型:两端均为梯状穿孔板、一端为单穿孔板,另一端为梯状穿孔板、两端均为单穿孔板、一梯状穿孔板与一单穿孔板位于同一端壁两侧相互对应以及一些过渡类型穿孔板。根据观察结果,分析了各类型穿孔板之间的演化关系。     

Blood Vessel Adaptation with Fluctuations in Capillary Flow Distribution

Throughout the life of animals and human beings, blood vessel systems are continuously adapting their structures – the diameter of vessel lumina, the thickness of vessel walls, and the number of micro-vessels – to meet the changing metabolic demand of the tissue. The competition between an ever decreasing tendency of luminal diameters and an increasing stimulus from the wall shear stress plays a key role in the adaptation of luminal diameters. However, it has been shown in previous studies that the adaptation dynamics based only on these two effects is unstable. In this work, we propose a minimal adaptation model of vessel luminal diameters, in which we take into account the effects of metabolic flow regulation in addition to wall shear stresses and the decreasing tendency of luminal diameters. In particular, we study the role, in the adaptation process, of fluctuations in capillary flow distribution which is an important means of metabolic flow regulation. The fluctuation in the flow of a capillary group is idealized as a switch between two states, i.e., an open-state and a close-state. Using this model, we show that the adaptation of blood vessel system driven by wall shear stress can be efficiently stabilized when the open time ratio responds sensitively to capillary flows. As micro-vessel rarefaction is observed in our simulations with a uniformly decreased open time ratio of capillary flows, our results point to a possible origin of micro-vessel rarefaction, which is believed to induce hypertension.     

Water Movement Through Plant Roots

Mathematical analysis of the hydraulics of water movement throughplant roots, in terms of radial and axial resistances, has ledto equations which provide new insights into the effects ofthe component resistan ces on water uptake by and movement throughindividual roots and root systems. The ratio of axial to radialresistance determines the optimum length of a root and its totalresistance to water movement. The equations permit direct calculationsof the plant water potentials necessary, at the base of theplant, to sustain given flow rates through root systems withgiven characteristics. Lateral spacing and the resistance ofindividual laterals are the dominant factors determining totalflux per unit area into a root. When soil water potential increases with depth (surface layersdrier) root resistance tends to decrease with increasing flowrate; the reverse occurs when the surface is wetter than thelower layers. Calculated patterns of water movement into andthrough roots, in relation to soil water potential and flowrate through the root, indicate efflux from root to soil undercertain conditions. This is considered to reflect reality, althoughthe fluxes are probably transient or intermittent. The equations presented should be combined with equations describingwater movement through soil to define the behaviour of the wholeroot-soil system adequately.     

The Role of Intervessel Pits and Vessel Plugs in Determining Flow Pathways Through and Between Vessels in Sycamore (Acer pseudoplatanus L.)

It has previously been suggested from physical evidence thatvessels in twigs of sycamore (Acer pseudoplatanus L.) are connectedby small pores in intervessel pit membranes. From results obtainedusing a combination of physical techniques and electron microscopyit is clear that this is an oversimplification: almost all intervesselpit membranes are absent in sycamore twig and stem wood, yetphysical tests still suggest that vessels are connected by poressmaller than pit apertures. Where these pores are is less certain.They may be in plugs observed to fill vessel lumens. They maypossibly be in a small number of intact intervessel pit membranesin the terminal elements of vessels, but such membranes couldnot be found under the microscope. In either case, the resultsof physical tests suggest that vessels connected by membranelessintervessel pits must effectively end together at a particularpoint in the tree. Key words: Flow, vessels, sycamore     

维管植物导管及其穿孔板的研究进展

介绍了导管及其穿孔板的研究进展,包括导管的特征(穿孔板的类型、多穿孔板与侧壁穿孔板、纹孔膜残留),导管的起源与穿孔板的演化,蕨类植物、裸子植物与被子植物导管的比较,并就导管进化与穿孔板演化．导管的二型性现象、侧壁穿孔板、多穿孔板与穿孔中纹孔膜．生态对导管进化的影响等方面以及对今后的研究作了展望。