Measuring plant hydraulic conductance and xylem vulnerability under close to natural conditions

2020 ◽  
Author(s):  
Louis Krieger ◽  
Stanislaus Schymanski
Keyword(s):  
Water Transport ◽  
Common Factor ◽  
Hydraulic Conductance ◽  
Pressure Gradients ◽  
Natural Conditions ◽  
Flow Meters ◽  
Xylem Vulnerability ◽  
Large Pressure ◽  
Low Pressures

<p>Usually hydraulic conductance and vulnerability are measured under extreme conditions never experienced by living plants (e. g. centrifugation, bench dehydration, and large pressure gradients). A common factor that is known to inhibit the water transport in plants is cavitation, which is believed to occur either by air entry through the pit valves on the walls of the xylem, or by ex-solution of dissolved gases, or vaporization of water at very low pressures. Various physical characteristics of the xylem influence the efficiency of transport and the vulnerability to cavitation.</p><p>Here we explore possibilities to measure hydraulic conductance and induce cavitation under close to natural conditions. We designed a very simple “artificial plant” consisting of a root and a transpiring membrane, equipped with pressure and flow meters, where a twig can be inserted in the flow path to measure its hydraulic conductance. Attempts to induce cavitation resulted in surprising results, provoking new questions on the role of xylem structural traits and their relevance for water transport in plants.</p>

Measuring plant hydraulic conductivity: Should we push or should we pull?

2021 ◽  
Author(s):  
Louis Krieger ◽  
Stan Schymanski ◽  
Steven Jansen
Keyword(s):  
Hydraulic Conductivity ◽  
Flow Direction ◽  
Common Factor ◽  
Hydraulic Conductance ◽  
Flow Path ◽  
Positive Pressure ◽  
Pressure Gradients ◽  
Natural Conditions ◽  
Large Pressure ◽  
Plant Hydraulic Conductivity

<p>Usually hydraulic conductance and vulnerability are measured under extreme conditions never experienced by living plants (e. g. centrifugation, bench dehydration, and large pressure gradients). A common factor that is known to inhibit the water transport in plants is embolism, which is believed to occur either by air entry through the pit valves on the walls of the xylem, or by ex-solution of dissolved gases, or vaporization of water at very low pressures.</p><p>Here we explore possibilities to measure hydraulic conductance and induce embolism under close to natural conditions. The setup consists of a syringe pump to control water flow, where a twig is inserted in the flow path to measure its hydraulic conductivity using pressure and flow meters. This setup has enabled us to imitate natural conditions where transpiration rate induces a pressure difference between the sink (leaf) and source (root) along the flow path. It has also allowed us to induce flow in both directions through the twig without having to rotate or change out the sample. Using our setup, we found that the conductivity of the same twig was 50% lower when pulling compared to pushing. This can be explained by the emptying and filling of cut end vessels and the pressure gradient along the twig, which is induced by the flow rate and flow direction. Our findings are discussed in the context that currently employed methods for measuring wood hydraulic conductance employ either centrifugation, where water is pulled on both ends, or pushing of water by applying positive pressure on one end.</p>

Hemodynamic analysis of Hyrtl anastomosis in human placenta

2007 ◽  
Vol 292 (2) ◽  
pp. R977-R982 ◽  
Author(s):  
Zoya Gordon ◽  
Osnat Eytan ◽  
Ariel J. Jaffa ◽  
David Elad
Keyword(s):  
Blood Flow ◽  
Arterial Blood Flow ◽  
Pressure Gradients ◽  
Fetal Blood ◽  
Placental Perfusion ◽  
Arterial Blood ◽  
Large Pressure ◽  
Umbilical Arteries ◽  
Hemodynamic Characteristic

The Hyrtl anastomosis is a common connection between the umbilical arteries near the cord insertion in most human placentas. It has been speculated that it equalizes the blood pressure between the territories supplied by the umbilical arteries. However, its functional role in the regulation and distribution of fetal blood flow to the placenta has not yet been explored. A computational model has been developed for quantitative analysis of hemodynamic characteristic of the Hyrtl anastomosis in cases of discordant blood flow in the umbilical arteries. Simulations were performed for cases of either increased placental resistance at the downstream end or reduced arterial blood flow due to some pathologies upstream of one of the arteries. The results indicate that when placental territories of one artery impose increased resistance to fetal blood flow, the Hyrtl anastomosis redistributes the blood flow into the second artery to reduce the large pressure gradients that are developed in the affected artery. When one of the arteries conducts a smaller blood flow into the placenta and a relatively smaller pressure gradient is developed, the Hyrtl anastomosis rebuilds the pressure gradients in the affected artery and redistributes blood flow from the unaffected artery to the affected one to improve placental perfusion. In conclusion, the Hyrtl anastomosis plays the role of either a safety valve or a pressure stabilizer between the umbilical arteries at the placental insertion.

scholarly journals SAFETY AND EFFICIENCY OF XYLEM WATER TRANSPORT IN TWO CASHEW (Anacardium occidentale L.) STRAINS AT THE SEEDLING STAGE

2020 ◽  
Vol 18 (4) ◽  
pp. 156
Author(s):  
JOKO PITONO ◽  
TSUDA MAKOTO
Keyword(s):  
High Pressure ◽  
Water Transport ◽  
Applied Pressure ◽  
Vessel Diameter ◽  
Hydraulic Conductance ◽  
Seedling Stage ◽  
Wet Season ◽  
Flow Meter ◽  
Pressure Flow ◽  
Xylem Vulnerability

<p>ABSTRACT<br />As cashew trees are grown by transplanting seedlings, the seedling<br />often suffers from drought damaged due to prolonged dry season. Previous<br />study found that the ability to maintain water transport in xylem related to<br />drought resistant character. To determine whether there was trade-off<br />between the ability to maintain water transport in xylem and an efficiency<br />of water transport, differences in xylem vulnerability to dysfunction,<br />hydraulic conductance, and the relationship to xylem vessel diameter were<br />examined in two cashew strains. The xylem vulnerability to dysfunction<br />was evaluated by the applied pressure which induced 50% loss of stem<br />hydraulic conductivity (P 50 ). The hydraulic conductance on root, stem, and<br />leaf were determined with High Pressure Flow Meter (HPFM). Variations<br />in the P 50 values were found between A3-1 and Pangkep, whereas the<br />values were 1.75 and 0.50 MPa, respectively. However, since there was no<br />difference in the hydraulic conductance and the vessel diameter, the trade-<br />off between the ability to maintain water transport in xylem and an<br />efficiency of water transport did not occur in cashew. It was suggested that<br />good combination of efficiency and safety of water transport enables A3-1<br />to strongly uptake soil water either in dry or wet season resulting in good<br />adaptation to drought prone environment, and the P 50 value would be<br />suitable parameter for evaluating drought tolerance of cashew at the<br />seedling stage.<br />Key words: cashew strain, vessel, xylem dysfunction, hydraulic<br />conductance, drought</p><p>ABSTRAK<br />Pengembangan jambu mete secara transplanting sering diikuti<br />cekaman kekeringan pada bibit akibat musim kering yang berkepanjangan.<br />Studi awal memperlihatkan bahwa kemampuan xylem mempertahankan<br />fungsi transportasi air merupakan karakter pertahanan penting terhadap<br />cekaman kekeringan. Untuk mengetahui apakah terjadi kompensasi antara<br />kemampuan pertahanan fungsi xylem dan tingkat efisiensi transportasi<br />airnya dilakukan pengujian pada aspek kepekaan fungsi xylem, hantaran<br />hidraulik, dan ukuran vesselnya. Kepekaan fungsi xylem ditentukan dari<br />nilai tekanan udara yang menyebabkan kehilangan 50% hydraulic<br />conductance (P 50 ). Nilai hydraulic conductance pada akar, batang, dan<br />daun ditentukan dengan menggunakan metode High Pressure Flow Meter<br />(HPFM). Hasil pengujian menunjukkan terdapat perbedaan nilai P 50<br />diantara dua strain jambu mete yang diuji, yakni secara berturut-turut 1,75<br />dan 0,50 MPa pada strain A3-1 dan Pangkep. Karena tidak disertai<br />perbedaan pada hydraulic conductance dan ukuran vesselnya, maka<br />disimpulkan tidak ditemukan nilai adanya mekanisme kompensasi antara<br />kemampuan pertahanan fungsi xylem dan tingkat efisiensi pengangkutan<br />air. Hal ini memungkinkan A3-1 tetap dapat menyerap air tanah secara<br />cukup, baik pada musim kering maupun musim basah, dan mampu<br />beradaptasi dengan baik di daerah rawan kekeringan. Dan nilai P 50 dapat<br />dijadikan sebagai parameter representatif untuk evaluasi toleransi bibit<br />jambu mete terhadap cekaman kekeringan.<br />Kata kunci:  strain jambu mete, vessel, fungsi xylem, hydraulic<br />conductance, cekaman kekeringan</p>

Pressure Gradients Affecting the Labyrinth during Hypobaric Pressure

1997 ◽  
Vol 106 (6) ◽  
pp. 495-502 ◽  
Author(s):  
Konrád S. Konrádsson ◽  
Björn I. R. Carlborg ◽  
Joseph C. Farmer
Keyword(s):  
Cerebrospinal Fluid ◽  
Eustachian Tube ◽  
Ambient Pressure ◽  
Pressure Gradients ◽  
Cochlear Aqueduct ◽  
Fluid Compartment ◽  
Large Pressure ◽  
Fluid Compartments ◽  
Pressure Changes ◽  
Considerable Pressure

Hypobaric effects on the perilymph pressure were investigated in 18 cats. The perilymph, tympanic cavity, cerebrospinal fluid, and systemic and ambient pressure changes were continuously recorded relative to the atmospheric pressure. The pressure equilibration of the eustachian tube and the cochlear aqueduct was studied, as well as the effects of blocking these channels. During ascent, the physiologic opening of the eustachian tube reduced the pressure gradients across the tympanic membrane. The patent cochlear aqueduct equilibrated perilymph pressure to cerebrospinal fluid compartment levels with a considerable pressure gradient across the oval and round windows. With the aqueduct blocked, the pressure decrease within the labyrinth and tympanic cavities was limited, resulting in large pressure gradients toward the chamber and the cerebrospinal fluid compartments, respectively. We conclude that closed cavities with limited pressure release capacities are the cause of the pressure gradients. The strain exerted by these pressure gradients is potentially harmful to the ear.

scholarly journals Ethylene enhances root water transport and aquaporin expression in trembling aspen (Populus tremuloides) exposed to root hypoxia

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Xiangfeng Tan ◽  
Mengmeng Liu ◽  
Ning Du ◽  
Janusz J. Zwiazek
Keyword(s):  
Gas Exchange ◽  
Water Transport ◽  
Populus Tremuloides ◽  
Leaf Gas Exchange ◽  
Hydraulic Conductance ◽  
Root Hydraulic Conductance ◽  
Trembling Aspen ◽  
Expression Levels ◽  
Root Hypoxia ◽  
Exogenous Ethylene

Abstract Background Root hypoxia has detrimental effects on physiological processes and growth in most plants. The effects of hypoxia can be partly alleviated by ethylene. However, the tolerance mechanisms contributing to the ethylene-mediated hypoxia tolerance in plants remain poorly understood. Results In this study, we examined the effects of root hypoxia and exogenous ethylene treatments on leaf gas exchange, root hydraulic conductance, and the expression levels of several aquaporins of the plasma membrane intrinsic protein group (PIP) in trembling aspen (Populus tremuloides) seedlings. Ethylene enhanced net photosynthetic rates, transpiration rates, and root hydraulic conductance in hypoxic plants. Of the two subgroups of PIPs (PIP1 and PIP2), the protein abundance of PIP2s and the transcript abundance of PIP2;4 and PIP2;5 were higher in ethylene-treated trembling aspen roots compared with non-treated roots under hypoxia. The increases in the expression levels of these aquaporins could potentially facilitate root water transport. The enhanced root water transport by ethylene was likely responsible for the increase in leaf gas exchange of the hypoxic plants. Conclusions Exogenous ethylene enhanced root water transport and the expression levels of PIP2;4 and PIP2;5 in hypoxic roots of trembling aspen. The results suggest that ethylene facilitates the aquaporin-mediated water transport in plants exposed to root hypoxia.

Water transport across mammalian cell membranes

1996 ◽  
Vol 270 (1) ◽  
pp. C12-C30 ◽  
Author(s):  
A. S. Verkman ◽  
A. N. van Hoek ◽  
T. Ma ◽  
A. Frigeri ◽  
W. R. Skach ◽  
...  
Keyword(s):  
Water Transport ◽  
Cell Membranes ◽  
Water Channel ◽  
Water Channels ◽  
Channel Structure ◽  
Level Information ◽  
Selective Channel ◽  
Transcriptional Units ◽  
Measurement Strategies

This review summarizes recent progress in water-transporting mechanisms across cell membranes. Modern biophysical concepts of water transport and new measurement strategies are evaluated. A family of water-transporting proteins (water channels, aquaporins) has been identified, consisting of small hydrophobic proteins expressed widely in epithelial and nonepithelial tissues. The functional properties, genetics, and cellular distributions of these proteins are summarized. The majority of molecular-level information about water-transporting mechanisms comes from studies on CHIP28, a 28-kDa glycoprotein that forms tetramers in membranes; each monomer contains six putative helical domains surrounding a central aqueous pathway and functions independently as a water-selective channel. Only mutations in the vasopressin-sensitive water channel have been shown to cause human disease (non-X-linked congenital nephrogenic diabetes insipidus); the physiological significance of other water channels remains unproven. One mercurial-insensitive water channel has been identified, which has the unique feature of multiple overlapping transcriptional units. Systems for expression of water channel proteins are described, including Xenopus oocytes, mammalian and insect cells, and bacteria. Further work should be directed at elucidation of the role of water channels in normal physiology and disease, molecular analysis of regulatory mechanisms, and water channel structure determination at atomic resolution.

Effects of distributed pressure gradients on the pressure–strain correlations in a supersonic nozzle and diffuser

2014 ◽  
Vol 742 ◽  
pp. 466-494 ◽  
Author(s):  
Somnath Ghosh ◽  
Rainer Friedrich
Keyword(s):  
Supersonic Nozzle ◽  
Turbulent Pipe Flow ◽  
Pressure Gradients ◽  
Reynolds Stresses ◽  
Streamline Curvature ◽  
Flow Parameters ◽  
Diffuser Flow ◽  
Remarkable Agreement ◽  
Distributed Pressure

AbstractDirect numerical simulation (DNS), based on high-order numerical schemes, is used to study the effects of distributed pressure gradients on the redistribution of fluctuating kinetic energy in supersonic nozzle and diffuser flow with incoming fully developed turbulent pipe flow. Axisymmetric geometries and flow parameters have been selected such that shock waves are avoided and streamline curvature remains unimportant. Although mean extra rates of strain are quite small, strong changes in Reynolds stresses and their production/redistribution mechanisms are observed, in agreement with findings of Bradshaw (J. Fluid Mech., vol. 63, 1974, pp. 449–464). The central role of pressure–strain correlations in changing the Reynolds stress anisotropy is highlighted. A Green’s function-based analysis of pressure–strain correlations is presented, showing remarkable agreement with DNS data.

Is central hyperacusis a symptom of 5-hydroxytryptamine (5-HT) dysfunction?

1995 ◽  
Vol 109 (10) ◽  
pp. 915-921 ◽  
Author(s):  
Josephine Marriage ◽  
N. M. Barnes
Keyword(s):  
Common Factor ◽  
Subjective Symptom ◽  
Research Literature ◽  
Auditory Sensitivity ◽  
Sensory Modulation ◽  
Hearing Sensitivity ◽  
Symptom Profile ◽  
Neurological Conditions

AbstractThe subjective symptom of hyperacusis is described. The terms ‘hyperacusis’ and ‘phonophobia’ are considered to be synonymous as there is no recognized distinction between these two descriptions. Peripheral auditory pathologies with associated hearing sensitivity are reviewed and the likely mechanisms underlying the hyperacusis are listed. The neurological conditions, which have been reported to occur with hyperacusis, are reviewed. A separate aetiology of central hyperacusis is therefore proposed, with a symptom profile distinct from the peripheral hyperacusisA common factor to neurological conditions with hyperacusis, is disturbance of 5-HT (5-hydroxytryptamine) or serotonin function. The research literature on the role of 5-HT in sensory modulation (specifically auditory startle) in animals is presented. It is proposed that 5-HT dysfunction is a probable cause of increased auditory sensitivity manifested as central hyperacusis or phonophobia

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