Hydraulic conductance and tracheid anatomy in six species of extant seed plants

1988 ◽  
Vol 66 (6) ◽  
pp. 1073-1079 ◽  
Author(s):  
Paul J. Schulte ◽  
Arthur C. Gibson
Keyword(s):  
Capillary Flow ◽  
Large Diameter ◽  
Membrane Resistance ◽  
Hydraulic Conductance ◽  
Linear Increase ◽  
Biophysical Model ◽  
Lumen Diameter ◽  
Seed Plants ◽  
Pit Membrane ◽  
Conductance Increase

Hydraulic conductance of tracheids was studied in either petioles or young stems of six species of seed plants having various types of intertracheid pitting. Measured conductances were compared with estimates based on Hagen–Poiseuille flow through ideal capillaries and with predictions from a biophysical model incorporating observed anatomical characteristics of tracheids and intertracheid pits. Conductance of the xylem, expressed as a percentage of the ideal capillary flow prediction, varied from an average of 88% for a species containing only very narrow tracheids to less than 35% for species with large-diameter tracheids. The biophysical model allowed fairly close predictions of conductance for all species except one, where an estimate of the pit membrane resistance could not be experimentally obtained. For individual tracheids, conductance was largely a function of lumen diameter, pit membrane resistivity, and the exposed area of the pit membranes, as determined by pit shape, size, and frequency. For wide tracheids, scalariform-pitted elements showed a linear increase in conductance with an increase in lumen diameter; however, for tracheids with large circular pits, the conductance increase afforded by a wider lumen declines as lumen diameter increases. These model simulations demonstrate the increasing significance of intertracheid pitting in obstructing flow as lumen diameter increases.

Basic determinants of epicardial transudation

1997 ◽  
Vol 273 (3) ◽  
pp. H1408-H1414 ◽  
Author(s):  
R. H. Stewart ◽  
D. A. Rohn ◽  
S. J. Allen ◽  
G. A. Laine
Keyword(s):  
Reflection Coefficient ◽  
Coronary Sinus ◽  
Myocardial Edema ◽  
Hydraulic Conductance ◽  
Linear Increase ◽  
Left Ventricular ◽  
Edema Formation ◽  
Anesthetized Dogs ◽  
The Difference ◽  
Osmotic Reflection Coefficient

Myocardial edema formation, which has been shown to compromise cardiac function, and increased epicardial transudation (pericardial effusion) have been shown to occur after elevation of myocardial venous and lymphatic outflow pressures. The purposes of this study were to estimate the hydraulic conductance and osmotic reflection coefficient for the epicardium and to determine the effect of coronary sinus hypertension and cardiac lymphatic obstruction on epicardial fluid flux (JV,e/Ae). A Plexiglas hemispheric capsule was attached to the left ventricular epicardial surface of anesthetized dogs. JV,e/Ae was determined over 30-min periods for three intracapsular pressures (-5, -15, and -25 mmHg) and two intracapsular solutions exerting colloid osmotic pressures of 7.0 and 2.0 mmHg. Hydraulic conductance was estimated to be 3.7 +/- 0.5 microliters.h-1.cm-2.mmHg-1. An osmotic reflection coefficient of 0.9 was calculated from the difference in JV,e/Ae of 16.5 +/- 8.4 microliters.h-1.cm-2 between the two solutions. Graded coronary sinus hypertension induced a linear increase in JV,e/Ae, which was significantly greater in dogs without cardiac lymphatic occlusion than in those with occlusion.

scholarly journals Testing for ion-mediated enhancement of the hydraulic conductance of the leaf xylem in diverse angiosperms

2017 ◽  
Vol 4 ◽  
pp. e004 ◽  
Author(s):  
Christine Scoffoni ◽  
Grace John ◽  
Herve Cochard ◽  
Lawren Sack
Keyword(s):  
Water Solution ◽  
Pure Water ◽  
Xylem Sap ◽  
Hydraulic Conductance ◽  
Membrane Pores ◽  
Whole Plant ◽  
Pit Membrane ◽  
Major Bottleneck ◽  
The Difference ◽  
Xylem Conduits

Replacing ultra-pure water solution with ion solution closer to the composition of natural xylem sap increases stem hydraulic conductance by up to 58%, likely due to changes in electroviscosity in the pit membrane pores. This effect has been proposed to contribute to the control of plant hydraulic and stomatal conductance and potentially to influence on carbon balance during dehydration. However, this effect has never been directly tested for leaf xylem, which constitutes a major bottleneck in the whole plant. We tested for an ion-mediated increase in the hydraulic conductance of the leaf xylem (Kx) for seven species diverse in phylogeny and drought tolerance. Across species, no significant changes in Kx were observed between 0 and 15 mM KCl. We further tested for an effect of ion solution during measurements of Kx vulnerability to dehydration in Quercus agrifolia and found no significant impact. These results for leaf xylem contrast with the often strong ion effect reported for stems, and we suggest several hypotheses to account for the difference, relating to the structure of xylem conduits across vein orders, and the ultrastructure of leaf xylem pores. A negligible ion response in leaves would weaken xylem sap ion-mediated control of plant hydraulic conductance, facilitating modeling of whole plant hydraulic behavior and its influence on productivity.

Characterization and comparison of the wood anatomical traits of plantation grown Quercus acutissima and Quercus variabilis

IAWA Journal ◽  
2021 ◽  
pp. 1-14
Author(s):  
Jie Wang ◽  
Shan Li ◽  
Juan Guo ◽  
Haiqing Ren ◽  
Yurong Wang ◽  
...  
Keyword(s):  
Wall Thickness ◽  
Ring Width ◽  
Value Added ◽  
Lumen Diameter ◽  
Membrane Thickness ◽  
Quercus Acutissima ◽  
Fibre Wall ◽  
Growth Ring Width ◽  
Cambial Age ◽  
Pit Membrane

Abstract Oaks are important tree species, providing essential biomaterial for the wood industry. We characterize and compare wood anatomical traits of plantation grown Quercus acutissima Carruth. and Q. variabilis Blume to provide more detailed information to understand xylem radial growth, structure, and function, as well as differences between sapwood and heartwood, to provide data relevant for tree breeding and value-added wood utilization of oak plantations in China. In this study, radial strips were collected at breast height from the main trunk of the two species. Latewood percentage and growth ring width were investigated by X-ray densitometry and a Tree Ring Analysis System, respectively. Vessel and fibre lumen diameter, vessel and fibre wall thickness, vessel density, fibre wall thickness/diameter ratio, tissue proportions, and pit membrane thickness in between vasicentric tracheids were observed with light microscopy and electron microscopy and quantified. There were significant differences in a few wood anatomical traits between the two species: vessel wall thickness and vessel lumen diameter were higher in Q. acutissima than in Q. variabilis, while higher axial parenchyma proportion in sapwood was found in Q. variabilis than in Q. acutissima. More abundant tyloses were found in heartwood than in sapwood of both species. Our work showed the intraspecific and interspecific variation of the two species. Most differences between sapwood and heartwood must be attributed to differences in cambial age during their formation.

Confirmation of conductance increase by adrenalin in the guinea-pig taenia coli (α-action)

1977 ◽  
Vol 198 (1133) ◽  
pp. 473-477 ◽  
Keyword(s):  
Guinea Pig ◽  
Time Constant ◽  
Membrane Resistance ◽  
Taenia Coli ◽  
Frequency Range ◽  
Tissue Impedance ◽  
Membrane Capacity ◽  
Sucrose Gap ◽  
Conductance Increase ◽  
Sinusoidal Currents

In the guinea-pig taenia coli, adrenalin hyperpolarized the membrane and decreased the amplitude of electrotonic potentials when recorded with micro electrodes from the centre pool (500 μm in width) of the double sucrose-gap apparatus. The reduction of the time constant of electrotonic potentials was proportional to that of the amplitude, indicating that the membrane capacity remained constant. The tissue impedance, measured by sinusoidal currents with a frequency range of 0.1–50 Hz, also indicated that the decrease of membrane resistance by adrenalin was accompanied by little change in the membrane capacity.

The hydraulic architecture of roses (Rosa hybrida)

1991 ◽  
Vol 69 (4) ◽  
pp. 702-710 ◽  
Author(s):  
Alan B. Darlington ◽  
Michael A. Dixon
Keyword(s):  
Large Diameter ◽  
Distal Segment ◽  
Hydraulic Conductance ◽  
Rosa Hybrida ◽  
Abscission Zone ◽  
Conducting System ◽  
Hydraulic Architecture ◽  
A Site ◽  
The Rose ◽  
Structural Aspects

The presence of an abscission zone in the stem of greenhouse roses (Rosa hybrida) between the vegetative and reproductive components was verified. This led to a description of the hydraulic architecture of the rose stem. The structural aspects of the xylem conducting system in stem, abscission zone and peduncle were examined to define their relative roles in the delivery of water via the stem to the transpiring plant surfaces and the extent to which their functional capacity may be influenced by environmental variables such as humidity. The stem exhibited a highly developed xylem with many large-diameter tracheary elements. Contrary to this the distal segment of the peduncle was poorly vascularized. The remainder of the peduncle, which included the abscission zone, was a transition between these two extremes. The abscission zone was a site of reduced hydraulic conductance that was not due to a reduction in the number or size of xylem conduits but to changes in the alignment of the elements. The variable conductances across the abscission zone and peduncle regions may play an important role in floral development and the response of the plant to water stress. Rose plants grown at constantly high humidity (77% RH) did not exhibit significantly different internal anatomical features of the xylem conducting system relative to roses grown in ambient, uncontrolled humidity (30 to 60% RH). Key words: abscission zone, hydraulic conductance, humidity.

scholarly journals Endothelial struts, a mechanism to generate large lumenized blood vessels de novo

2019 ◽  
Author(s):  
Bart Weijts ◽  
Iftach Shaked ◽  
Wenqing Li ◽  
Mark Ginsberg ◽  
David Kleinfeld ◽  
...  
Keyword(s):  
Endothelial Cells ◽  
Blood Vessels ◽  
Alternative Model ◽  
Vessel Wall ◽  
De Novo ◽  
Large Diameter ◽  
Lumen Diameter ◽  
The Future

Lumenization of de novo formed blood vessels occurs either through cell hollowing (intracellular lumen)1–3 or cord hollowing (extracellular lumen)4–6 and restricts thereby the initial lumen diameter to one or two endothelial cells (ECs) respectively. However, vasculogenesis can result in large diameter blood vessels, raising the question how these vessels are formed. Here, we describe an alternative model of vasculogenesis that results in the formation of large diameter vessels. In this model, ECs coalesce into a branched network of EC struts within the future lumen of the vessel. These struts maintain the patency of the vessel and serve as a scaffold for the ECs forming the vessel wall, which initially consists out of a few patches of ECs. Together, we show that endothelial struts facilitate the formation of large blood vessels without being bound by the prerequisite of a cord-like structure, nor are they restricted in size.

scholarly journals Capillary Transit Time Heterogeneity and Flow-Metabolism Coupling after Traumatic Brain Injury

2014 ◽  
Vol 34 (10) ◽  
pp. 1585-1598 ◽  
Author(s):  
Leif Østergaard ◽  
Thorbjørn S Engedal ◽  
Rasmus Aamand ◽  
Ronni Mikkelsen ◽  
Nina K Iversen ◽  
...  
Keyword(s):  
Traumatic Brain Injury ◽  
Brain Injury ◽  
Transit Time ◽  
Capillary Flow ◽  
Biophysical Model ◽  
Therapeutic Consequences ◽  
Capillary Flows ◽  
Flow Disturbances ◽  
Show Evidence ◽  
Diffuse Brain Swelling

Most patients who die after traumatic brain injury (TBI) show evidence of ischemic brain damage. Nevertheless, it has proven difficult to demonstrate cerebral ischemia in TBI patients. After TBI, both global and localized changes in cerebral blood flow (CBF) are observed, depending on the extent of diffuse brain swelling and the size and location of contusions and hematoma. These changes vary considerably over time, with most TBI patients showing reduced CBF during the first 12hours after injury, then hyperperfusion, and in some patients vasospasms before CBF eventually normalizes. This apparent neurovascular uncoupling has been ascribed to mitochondrial dysfunction, hindered oxygen diffusion into tissue, or microthrombosis. Capillary compression by astrocytic endfeet swelling is observed in biopsies acquired from TBI patients. In animal models, elevated intracranial pressure compresses capillaries, causing redistribution of capillary flows into patterns argued to cause functional shunting of oxygenated blood through the capillary bed. We used a biophysical model of oxygen transport in tissue to examine how capillary flow disturbances may contribute to the profound changes in CBF after TBI. The analysis suggests that elevated capillary transit time heterogeneity can cause critical reductions in oxygen availability in the absence of ‘classic’ ischemia. We discuss diagnostic and therapeutic consequences of these predictions.

Hydraulic Conductance and Xylem Structure in Tracheid-Bearing Plants

IAWA Journal ◽  
1985 ◽  
Vol 6 (4) ◽  
pp. 293-302 ◽  
Author(s):  
Arthur C. Gibson ◽  
Howard W. Calkin ◽  
Park S. Nobel
Keyword(s):  
Water Flow ◽  
Unit Length ◽  
Hydraulic Conductance ◽  
Distal Portion ◽  
Pteris Vittata ◽  
Root Tips ◽  
Xylem Structure ◽  
Pit Membrane ◽  
Potential Gradients ◽  
Uniform Diameter

To understand water flow in tracheary elements, hydraulic conductances per unit length were measured and then compared with theoretical values calculated from xylem anatomical measurements using the Hagen -Poiseuille relation for nine species of pteridophytes, including Psilotum and eight species of ferns. In ferns the water potential gradients were essentially constant from the root tips to the distal portion of the leaf rachises, although somewhat larger gradients were found from the petiolule onward. Although tracheid number and diameter apparently controlled water flow in xylem, estimates of hydraulic conductance per unit length predicted from tracheid numbers and diameters were generally twice those actually measured from plants under steady-state conditions. A model was developed to account for this discrepancy for Pteris vittata, indicating that pit membrane resistances may contribute 70% of the total resistance to water flow in this fern. This may account for the generally observed deviation of tracheid performance from that predicted for ideal capillaries of uniform diameter.

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