A thermodynamic analysis of the feasibility of water secretion into xylem vessels against a water potential gradient

2015 ◽  
Vol 42 (9) ◽  
pp. 828 ◽  
Author(s):  
Lars H. Wegner
Keyword(s):  
Free Energy ◽  
Water Potential ◽  
Thermodynamic Analysis ◽  
Cell Membranes ◽  
Chemical Potential ◽  
Potential Gradient ◽  
Energy Status ◽  
Hordeum Vulgare L ◽  
Water Potential Gradient ◽  
Water Secretion

A series of recent publications has launched a debate on trans-membrane water secretion into root xylem vessels against a water potential gradient, energised by a cotransport with salts (e.g. KCl) that follow their chemical potential gradient. Cation–chloride–cotransporter -type transporters that function in this way in mammalian epithelia were detected in root stelar cells bordering on xylem vessels. Using literature data on barley (Hordeum vulgare L.) seedlings, one study confirmed that K+ and Cl– gradients across stelar cell membranes favour salt efflux. Moreover, the energetic costs of putative water secretion into the xylem (required for maintaining ionic gradients) would amount to just 0.12% of the energy captured by photosynthetic C assimilation if transpirational water flow relied exclusively on this mechanism. Here, a detailed thermodynamic analysis of water secretion into xylem vessels is undertaken, including an approach that exploits its analogy to a desalinisation process. Water backflow due to the passive hydraulic conductivity of stelar cell membranes is also considered. By comparing free energy consumption by putative water secretion with (i) the free energy pool provided by root respiration and (ii) stelar ATPase activity, the feasibility of this mechanism is confirmed but is shown to depend critically on the plant’s energy status.

scholarly journals Molecular mechanisms mediating root hydrotropism: what we have observed since the rediscovery of hydrotropism

2019 ◽  
Vol 133 (1) ◽  
pp. 3-14
Author(s):  
Yutaka Miyazawa ◽  
Hideyuki Takahashi
Keyword(s):  
Arabidopsis Thaliana ◽  
Water Potential ◽  
Water Availability ◽  
Molecular Mechanisms ◽  
Current Knowledge ◽  
Potential Gradient ◽  
Regulatory Mechanisms ◽  
Directional Growth ◽  
Plant Adaptation ◽  
Water Potential Gradient

AbstractRoots display directional growth toward moisture in response to a water potential gradient. Root hydrotropism is thought to facilitate plant adaptation to continuously changing water availability. Hydrotropism has not been as extensively studied as gravitropism. However, comparisons of hydrotropic and gravitropic responses identified mechanisms that are unique to hydrotropism. Regulatory mechanisms underlying the hydrotropic response appear to differ among different species. We recently performed molecular and genetic analyses of root hydrotropism in Arabidopsis thaliana. In this review, we summarize the current knowledge of specific mechanisms mediating root hydrotropism in several plant species.

The decline in xylem flow to mango fruit at the end of its development is related to the appearance of embolism in the fruit pedicel

2015 ◽  
Vol 42 (7) ◽  
pp. 668 ◽  
Author(s):  
Thibault Nordey ◽  
Mathieu Léchaudel ◽  
Michel Génard
Keyword(s):  
Hydraulic Conductivity ◽  
Water Potential ◽  
Fruit Development ◽  
Hydraulic Properties ◽  
Potential Gradient ◽  
Mango Fruit ◽  
Xylem Flow ◽  
Water Potential Gradient ◽  
The Impact ◽  
Late Growth

The decline in xylem flow during the late growth stage in most fruits may be due either to a decrease in the water potential gradient between the stem bearing the fruit and the fruit tissues or to a decrease in the hydraulic conductivity of xylem vessels, or both. In this study, we analysed changes in xylem flows to the mango Mangifera indica L. fruit during its development to identify the sources of variation by measuring changes in the water potential gradient and in the hydraulic properties of the fruit pedicel. The variations in xylem and transpiration flows were estimated at several stages of mango fruit development from the daily changes in the fresh mass of detached and girdled fruits on branches. The water potential gradient was estimated by monitoring the diurnal water potential in the stem and fruit. The hydraulic properties of the fruit pedicel were estimated using a flow meter. The results indicated that xylem flow increased in the early stages of fruit development and decreased in the late stage. Variations in xylem flow were related to the decrease in the hydraulic conductivity of xylem vessels but not to a decrease in the water potential gradient. The hydraulic conductivity of the fruit pedicel decreased during late growth due to embolism caused by a decrease in the fruit water potential. Further studies should establish the impact of the decrease in the hydraulic conductivity of the fruit pedicel on mango growth.

Simultaneous measurements of tomato fruit and stem water potentials using in situ stem hygrometers

1989 ◽  
Vol 67 (8) ◽  
pp. 2352-2355 ◽  
Author(s):  
D. R. Lee ◽  
M. A. Dixon ◽  
R. W. Johnson
Keyword(s):  
Water Potential ◽  
Tomato Fruit ◽  
Potential Gradient ◽  
Diurnal Changes ◽  
Stem Water Potential ◽  
Simultaneous Measurements ◽  
Water Potentials ◽  
Stem Water ◽  
Water Potential Gradient

Simultaneous measurements were made of the water potentials of the stem and fruit of intact tomato plants (Lycopersicon esculentum Mill. var. Heinz 2653) using in situ temperature-corrected stem psychrometers. Water potential of the fruit remained consistently lower than the water potential of the stem except when the plant had been subjected to prolonged water stress. Stem water potential recovered quickly with rewatering, increasing by approximately 0.5 MPa in 1 h, but the water potential of the fruit remained consistently near −1.0 MPa. The results indicate a significant resistance to water flow between the stem and the fruit and a substantial hydraulic capacitance represented by the volume of the fruit. Diurnal changes in dimensions of tomato fruit were also measured. Fruit diameter expanded at night and contracted during the day even when the water potential gradient favoured flow towards the fruit. This indicates that bidirectional flow (to and from the fruit) is not responsible for the observed diurnal changes in the fruit dimensions.

scholarly journals 275 Water Relations of Fruit Cracking in Single-truss Tomato Plants

HortScience ◽  
1999 ◽  
Vol 34 (3) ◽  
pp. 489E-489
Author(s):  
Takashi Ikeda ◽  
Kunio Okano ◽  
Yuka Sakamoto ◽  
Shin-ichi Watanabe
Keyword(s):  
Water Potential ◽  
Water Relations ◽  
Water Status ◽  
Potential Gradient ◽  
Culture Solution ◽  
Tomato Plants ◽  
Fruit Flesh ◽  
Fruit Cracking ◽  
Fruit Skin ◽  
Water Potential Gradient

This study was undertaken to investigate the water relations of tomato (Lycopersicon esculentum Mill.) fruit cracking for single-truss tomato plants. The tomato plants were cultured on a closed hydroponic system in greenhouse. Water status of culture solution and plant tissues was measured with psychrometers. Water potential of the culture solution for the stressed plant was changed from -0.06 MPa (control plants) to -0.36 MPa at 24 days after anthesis. Hardness of the fruit skin was not different significantly between the stressed plants and the control plants. Fruit cracking occurred frequently in the control plants, but not in the stressed plants. Water potential gradient between the tissue of fruit flesh and water source for the control plants was bigger than that of the stressed plants. Turgors were increased at the tissues of fruit flesh and fruit skin at the control plants between predawn and morning but not at the stressed plants. These results indicated that the water potential gradient and the increased turgor in these tissues might be a trigger for the occurrence of fruit cracking on single-truss tomato plants.

scholarly journals Intermittent CaCl2 Sprays during Rain to Prevent Sweet Cherry Cracking

HortScience ◽  
1995 ◽  
Vol 30 (4) ◽  
pp. 793F-793 ◽  
Author(s):  
R. Thomas Fernandez ◽  
James A. Flore
Keyword(s):  
Water Potential ◽  
Sweet Cherry ◽  
Prunus Avium ◽  
Irrigation System ◽  
Potential Gradient ◽  
Daily Rainfall ◽  
Controlled Irrigation ◽  
Computer Controlled ◽  
Water Potential Gradient ◽  
Rain Events

Fruit of sweet cherry (Prunus avium L.) crack during or after rain due, in part, to absorption of water through the fruit surface driven by the water potential gradient. In 1972, J. Vittrup-Christensen suggested that overhead misting of calcium salts during precipitation may be an effective way to prevent cherry cracking by reducing the water potential gradient. We tested this hypothesis by designing a computer-controlled irrigation system to intermittently spray a 10% CaCl2 solution on trees during rain events. Spray emitters were placed in the middle and at the top of the canopy. The program turned the system on for 90 s at each 0.3 mm of rain and monitored daily rainfall and accumulated mist times. Two `Emperor Francis' and two `Ulster' were treated with equal number of controls. Intact and cracked cherries were counted on four branches per tree at three times when cherries were susceptible to cracking. Overall, cracking was reduced from 33% to 11% by the CaCl2 spray at the end of the experiment. Treated `Ulster' had 9% cracked fruit, while control had 43% cracked fruit. Differences for `Emperor Francis' were not significant. Phytotoxicity was estimated at about 15 % of leaf area. This system will be reevaluated in 1995 with the added objective of quantifying and reducing phytotoxicity.

Transport of Tritiated Water and 14C-Labelled Assimilate Into Grains of Wheat. I. Entry of Tho Through and in Association With the Stalk of the Grain

1985 ◽  
Vol 12 (6) ◽  
pp. 573 ◽  
Author(s):  
CF Jenner
Keyword(s):  
Water Potential ◽  
Dry Matter ◽  
Tritiated Water ◽  
Potential Gradient ◽  
Grain Filling ◽  
Vapour Phase ◽  
Reasonable Estimate ◽  
Intact Plants ◽  
Water Potential Gradient ◽  
Negligible Contribution

Dry matter is transported through the stalk of the wheat grain, and during grain filling is accumulated within it with no change in the quantity of water in the grain, and with little or no net transfer of water through the stalk. Accumulation of dry matter is also independent of the magnitude and the direction of a water potential gradient imposed between the plant and the atmosphere surrounding the grain. A procedure is described, based on sealing the grain (minus its bracts) within an impermeable capsule, for measuring the total net influx of radioactive water into the grain (FT). Tritiated water, THO, is used as a tracer for water. FT is assumed to comprise transport in the liquid phase and transport in the vapour phase, by mass flow and by diffusion. Apoplastic flow makes a negligible contribution in the system described because the water potential gradient is minimized. FT was obtained by adding to the quantity of THO accumulating in the encapsulated assemblies an estimate of the amount of THO lost from the assemblies by leakage. Two types of ears were compared: ears on intact plants assimilating 14CO2 and growing in small pots watered with THO, and detached ears cultured on [14C]sucrose in a solution of THO. Both types gave similar results but the detached ear system probably furnished the most reasonable estimate, a rate of 10.1 �l of THO per assembly per day.

Routine measurement of the soil water potential gradient near saturation using a pair of tube tensiometers

Soil Research ◽  
2001 ◽  
Vol 39 (5) ◽  
pp. 1147 ◽  
Author(s):  
P. A. Hutchinson ◽  
W. J. Bond
Keyword(s):  
Hydraulic Conductivity ◽  
Water Potential ◽  
Soil Water ◽  
Soil Water Potential ◽  
Potential Gradient ◽  
Darcy's Law ◽  
Deep Drainage ◽  
Soil Hydraulic Conductivity ◽  
Soil Hydraulic ◽  
Water Potential Gradient

We describe a new tensiometer for routine measurements of the soil water potential near saturation. The device is called the tube tensiometer because it is a long, open-topped, vertical tube (>1 m long) that is filled with porous material. The tube tensiometer has advantages over other known tensiometers as it does not require maintenance when the sensing tip dries beyond its air entry pressure and it is capable of being completely buried beyond the cultivation zone so that it does not foul tillage and harvesting equipment. The disadvantage of the tube tensiometer is that it only operates in the range of soil water potentials from –L to 0 cm of water, where L is the length of the tube tensiometer. The output from the tube tensiometer was compared with mercury tensiometers in a 120-day controlled field drainage and evaporation experiment. The regression between instruments was high (r2 = 0.99) and the accuracy of the tube tensiometer was <0.5 cm of water. The soil water potential gradient near saturation can be measured by installing a pair of vertically separated tube tensiometers. If the soil hydraulic conductivity is known then the soil water flux near saturation can be estimated using Darcy's Law. When the installation depth is below the active rooting zone of a crop then deep drainage can be estimated. This application of the tube tensiometer was demonstrated by measuring the vertical soil water potential gradient at a depth of 1 m beneath a wheat field near Harden, NSW, in response to winter rainfall. The major limitation to the use of Darcy's Law for the routine monitoring of deep drainage remains the estimation of the soil hydraulic conductivity. Ongoing work is focussing on the use of tube tensiometers to provide simultaneous measurements of both hydraulic gradient and hydraulic conductivity.

scholarly journals Measurement of a growth-induced water potential gradient in tall fescue leaves

1999 ◽  
Vol 142 (3) ◽  
pp. 435-439 ◽  
Author(s):  
PIERRE MARTRE ◽  
MARIE-BEATRICE BOGEAT-TRIBOULOT ◽  
JEAN-LOUIS DURAND
Keyword(s):  
Water Potential ◽  
Tall Fescue ◽  
Potential Gradient ◽  
Water Potential Gradient
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