Negative transport &amp; resistance to water flow through plants

Jensen, R. D.; Taylor, Sterling A.; Wiebe, Herman H.

doi:10.1104/pp.36.5.633

Cited by 58 publications

(24 citation statements)

References 23 publications

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“…We conclude that a similar reduction in the number or radius, or both, of vascular strands occurs between the stem and petiole of tobacco and that this was responsible for the low conductance (conductance is the reciprocal of resistance) reported at all times of day in the petiole. The small stem resistance reported previously for sunflower and tomato (1,2,8) and assumed to be small by other workers (9,11) did not hold true under the high evaporative conditions of the field. Although the resistances within the plant do not control transpiration directly (9), they may indirectly affect transpiration by decreasing the water potential in the leaves until this, in turn, increases the stomatal resistance.…”

Section: Resultsmentioning

confidence: 82%

“…The major resistance to water movement through the plant is, for the liquid phase, generally considered to be located in the root, and for the vapor phase, in the stomata (11). The resistance to water flow in the xylem, particularly in the stem, is considered small (1,8,11). However, observations of gradients in leaf water potential, limited to controlled environments, have indicated that the resistances within the leaf and in the stem may be significant in tobacco (6,9).…”

mentioning

confidence: 99%

“…The major resistance to water movement through the plant is, for the liquid phase, generally considered to be located in the root, and for the vapor phase, in the stomata (11). The resistance to water flow in the xylem, particularly in the stem, is considered small (1,8,11 The t/stem was determined by measuring the xylem sap pressure of the basal portion of a leaf that had been enclosed the previous afternoon in a polyethelene bag covered with aluminum foil (Fig. 1); this prevented evaporation from the enclosed leaf and, since the vascular bundles are assumed to be interconnected at the node as in tomato (5), enabled it to come to equilibrium with the potential in the stem.…”

mentioning

confidence: 99%

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Water Potential Gradients in Field Tobacco

1970

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A pressure chamber was used to establish the vertical gradients of leaf water potential (*I,eaf) and stem water potential (Istem) in field-grown tobacco (Nicotiana tabacum L. var. Havanna seed 211) at three different times of day. Leaves enclosed in polyethylene bags and aluminum foil the previous afternoon and left to equilibrate overnight were used to determine "'tem. The greatest difference between *'I,af and Isttem occurred in the upper part of the plant at 1100 hours Eastern Standard Time and was 5.5 bars.The largest vertical gradient in "8tem occurred at 1300 hours. The soil water potential (Is9il), extrapolated from the potential of leaves on a completely enclosed plant, was higher than -1 bar. The vertical gradient in 's,5tem and the difference between *uIAaf and "'stem showed the existence of a resistance to water movement within the stem (r,tem) and a further resistance between the stem and leaf (rpetiole).The rpetiole and root resistance (rroot) were estimated to be 931 and 102 bars seconds per cubic centimeter, respectively. The r,tem was low (94 bars seconds per cubic centimeter) at 1100 houirs but increased to 689 bars seconds per cubic centimeter at 1300 hours.Water movement through the soil-plant-atmosphere continuum occurs in both the liquid and vapor phases and is believed to be a physical process, driven largely by a potential gradient between the soil and the atmosphere. As a simplification, under isothermal conditions liquid phase transport through any portion of the continuum will be proportional to the water potential difference across each portion and inversely proportional to the resistance which develops across it, while vapor transport is a function of differences in vapor pressure, not of water potential (2, 7). The major resistance to water movement through the plant is, for the liquid phase, generally considered to be located in the root, and for the vapor phase, in the stomata (11). The resistance to water flow in the xylem, particularly in the stem, is considered small (1,8,11 The t/stem was determined by measuring the xylem sap pressure of the basal portion of a leaf that had been enclosed the previous afternoon in a polyethelene bag covered with aluminum foil (Fig. 1); this prevented evaporation from the enclosed leaf and, since the vascular bundles are assumed to be interconnected at the node as in tomato (5), enabled it to come to equilibrium with the potential in the stem.The vertical gradients in l{Leaf and PSterm were established from four to five observations at different heights on the plant. The measurements of water potentials were made in pairs, i.e., on an enclosed leaf from the western side of the plant and then on an adjacent exposed leaf on the eastern side of the plant (plant B , Fig. 1); this enabled the difference in water potential between the leaf and the stem to be evaluated in addition to vertical gradients of Leaf and lit/Stem. Measurements were made at three times of day on 13 September 1968. Alternating with these measurements on plant B (Fig. 1...

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Section: Resultsmentioning

confidence: 82%

mentioning

confidence: 99%

“…The major resistance to water movement through the plant is, for the liquid phase, generally considered to be located in the root, and for the vapor phase, in the stomata (11). The resistance to water flow in the xylem, particularly in the stem, is considered small (1,8,11 The t/stem was determined by measuring the xylem sap pressure of the basal portion of a leaf that had been enclosed the previous afternoon in a polyethelene bag covered with aluminum foil (Fig. 1); this prevented evaporation from the enclosed leaf and, since the vascular bundles are assumed to be interconnected at the node as in tomato (5), enabled it to come to equilibrium with the potential in the stem.…”

mentioning

confidence: 99%

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Water Potential Gradients in Field Tobacco

1970

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“…In several plant species, it has been found that the hydraulic resistance in roots is higher than the resistances in water pathways in stems, petioles and leaves (2,3,11,13,16,17,19,20 (10). From several analog models of the plant hydraulic system, it has been suggested that water storage in the stem is important for water balance in the plant hydraulic system (5,17,18,20,23).…”

Section: Materials and Methods Hfc Methodsmentioning

confidence: 99%

Quantitative Analysis of Transpiration Stream Dynamics in an Intact Cucumber Stem by a Heat Flux Control Method

Kitano¹,

Eguchi²

1989

Plant Physiol.

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Water flux of transpiration stream in an intact stem of the 10 leaf stage cucumber plant (Cucumis sativus L. cv. Chojitsu-Ochiai) was measured by a novel system of heat flux control method with a resolution of 1 x 10-3 grams per second and a time constant of 1 minute; two heat flux control sensors were attached to the seventh intemode and the stem base. The transpiration stream responded clearly to leaf transpiration and root water absorption when the plant was exposed to light, and the water flux at the stem base corresponded to the transpiration rate per plant in steady state. Root water absorption lagged about 10 minutes behind leaf transpiration. Dynamics of water fluxes were affected by the lag of water absorption in roots, and temporary water loss caused by rapid increase in leaf transpiration was buffered by about 5% of the water content in the stem.The transpiration stream in the stem is located between transpiration in leaves and water absorption in roots, and can be considered as an essential component of the water balance in the plant. Heat pulse (4,8,9,25), stem heat balance (6, 21) and magnetohydrodynamic (22) methods, hitherto, have been employed for the studies of the transpiration stream, and the aspects of the stream have been observed in relation to the leaf transpiration. For adequate analysis of water balance in the plant, it is further necessary to measure directly the water flux (mass of flowing water per unit time) in the intact stem in course of time: the on-line measurement of the water flux in the stem could contribute to the examination of dynamic characteristics ofthe transpiration stream relating to the leaf transpiration and the root water absorption. We have developed a novel system (12), HFC,' for on-line measurement of the water flux in the intact stem in real time without the need for any calibrations. The present paper deals with the application of the HFC system to the analyses oftranspiration stream dynamics by using two HFC sensors attached to the upper stem and the stem base of an intact cucumber plant, aiming at better understanding of water balance in a plant. MATERIALS AND METHODS HFC MethodThe HFC method is based on the heat balance with control of the heat fluxes from a heater attached to the intact stem 'Abbreviation: HFC, heat flux control.surface. Figure 1 shows

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“…These measurements were obtained by A, placing the plants in a special water-filled system which sealed the roots and leaves in separate adjoining chambers, B, applying a mechanical pressure (suction) difference to the system, and C, measuring the amount of water that flowed from one chamber through the plant to the other chamber by means of the movement of a mercury droplet in calibrated horizontal capillary tubes placed in both sides of the system. The apparatus was the same as that reported in the preceding paper (7).…”

Section: Methodsmentioning

confidence: 99%