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E L Fiscus

Publications and source records attributed to E L Fiscus.

15 recordsLinked to original sources
PubMed1986

Diurnal changes in volume and solute transport coefficients of phaseolus roots.

Volume (J(v)) and solute (J(s)) fluxes through Phaseolus root systems were observed over a 24-hour period. The volume flux was varied in a pressure chamber by altering the hydrostatic pressure in 10 steps, from 0 to 0.41 megapascals. All root systems showed strong diurnal peaks in volume flux. The five transport coefficients (sigma, omega, J(s) (*), L(p), and pi(*)) were estimated from a nonlinear least squares algorithm. Analysis of the data revealed that all the coefficients exhibited a diurnal rhythm. When the total differential of the volume flux was considered it was possible to show that the diurnal changes in volume flux were due to a complex interaction between the diurnally shifting coefficients with the role of each highly dependent on the level of volume flux. At low volume fluxes, omega, J(s) (*), and pi(*) accounted for nearly all the diurnal change in volume flux. At high volume fluxes, however, the major influence shifted to L(p) and pi(*), while omega and J(s) (*) became relatively unimportant. Thus, pi(*) was the only coefficient of interest across the entire range of J(v) and appeared to be the single most important one in determining the diurnal rhythm of J(v) under conditions of a constant applied pressure.

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PubMed1986

Detection of Xylem Cavitation in Corn under Field Conditions.

We report the detection of cavitation events in corn (Zea mays) plants growing under field conditions in Greeley, CO. To our knowledge this study reports the first successful attempt to monitor continuously for long periods the cavitation events of a crop plant using acoustic detection techniques. Cavitation events occur in corn plants using acoustic detection techniques. Cavitation events occur in corn plants irrigated daily when the xylem pressure potentials fall below about -1.0 megapascals. In unirrigated corn we estimate that approximately half of all vessels cavitate on any one day when xylem pressure potentials fall below about -1.8 megapascals. We postulate that root pressure developed every night in irrigated and unirrigated corn is adequate to rejoin cavitated water columns.

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PubMed1983

An interpretation of some whole plant water transport phenomena.

A treatment of water flow into and through plants to the evaporating surface of the leaves is presented. The model is driven by evaporation from the cell wall matrix of the leaves. The adsorptive and pressure components of the cell wall matric potential are analyzed and the continuity between the pressure component and the liquid tension in the xylem established. Continuity of these potential components allows linking of a root transport function, driven by the tension in the xylem, to the leaf water potential. The root component of the overall model allows for the solvent-solute interactions characteristic of a membrane-bound system and discussion of the interactions of environmental variables such as root temperature and soil water potentials. A partition function is developed from data in the literature which describes how water absorbed by the plant might be divided between transpiration and leaf growth over a range of leaf water potentials.Relationships between the overall system conductance and the conductance coefficients of the various plant parts (roots, xylem, leaf matrix) are established and the influence of each of these discussed.The whole plant flow model coupled to the partition function is used to simulate several possible relationships between leaf water potential and transpiration rate. The effects of changing some of the partition function coefficients, as well as the root medium water potential on these simulations is illustrated.In addition to the general usefulness of the model and its ability to describe a wide range of situations, we conclude that the relationships used, dealing with bulk fluid flow, diffusion, and solute transport, are adequate to describe the system and that analogically based theoretical systems, such as the Ohm's law analogy, probably ought to be abandoned for this purpose.

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PubMed1982

Abscisic Acid transport coefficients of phaseolus root systems.

Diffusive and convective transport coefficients of Phaseolus vulgaris L. cv. Ouray root systems for abscisic acid for (ABA) were measured. The convective coefficient (reflection coefficient or osmotic efficiency factor) sigma was determined to be 0.96 for ABA while the diffusive coefficient, omega, was found to be 1.44 x 10(-11) mole per square centimeter per second per bar. Steady-state concentrations of ABA in the root system exudates were not achieved until at least three hours after the applications suggesting either a slow saturation of binding sites or equilibration with tissues surrounding the xylem.

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PubMed1981

Effects of Abscisic Acid on the Hydraulic Conductance of and the Total Ion Transport through Phaseolus Root Systems.

The response of solute and volume fluxes of Phaseolus root systems to applied AbA was observed under conditions of applied pressure which were used to enhance the volume flow. The growth regulator elicited three separate responses: a transient release of solutes to the xylem which was responsible for an initial increase in volume flux; a long term increase in the total ion flux; and a long term decrease in the hydraulic conductance of the root systems. The exact response was highly dependent on the magnitude of the pre-AbA volume flux density, the relative contributions of osmotic and pressure-induced flow, and the applied dosage.Calculations suggested that the volume flux in naturally exuding root systems is relatively insensitive to changes in the conductance.

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PubMed1979

Effect of temperature on water and ion transport in soybean and broccoli systems.

Steady-state flow rates and exudate osmotic potentials were measured from complete root systems from warm- (28/23 C) or cold-(17/11 C) grown soybean or broccoli (Brassica oleracea) plants at various pressures or different temperatures.In warm-grown soybean roots systems, a break occurred at 14.7 C in the Arrhenius plot of total flow at constant pressure. When plants were grown at lower temperatures, the break point shifted to 8 C. Broccoli, a chilling-resistant species, showed no break for the temperature range used, but cooler growth temperatures decreased the activation energy for water flow through the root system from 18 kilocalories per mole to 9 kilocalories per mole. In both broccoli and soybean, cold-grown plants had lower exudate potentials and greater flow rates at low hydrostatic pressures than the warm-grown plants.These observations indicate that the rate-limiting site for passive water transport is a membrane which may be modified as the plant acclimates to varying growth temperatures. An additional part of the acclimation process is an increase in activity of root ion pumps.

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PubMed1979

Effect of abscisic Acid on root hydraulic conductivity.

Reports of the effects of abscisic acid (ABA) on ion and water fluxes have been contradictory. Some of the confusion seems due to the interaction of ion and water transport across membranes. In these experiments root systems were subjected to hydrostatic pressures up to 5.0 bars to enable measurement of root conductance that was independent of measurement of osmotic potentials or ion fluxes.ABA between 5 x 10(-5) molar and 2 x 10(-4) molar resulted in a decrease in the conductance of the soybean root systems as compared with the controls. ABA treatment also eliminated the discontinuity in the Arrhenius plot of total flow versus reciprocal temperature at constant pressure. The results suggest that ABA acts at the membrane that is rate-limiting to water flow directly, or by altering metabolism that in turn affects the membrane.

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PubMed1979

Relationships between Root System Water Transport Properties and Plant Size in Phaseolus.

Root system hydraulic conductivity (L(P)) was measured on Phaseolus plants of different ages and sizes. Data analysis showed that L(P) changed in a complex manner depending on plant size. As the plants increased in size, L(P) increased initially then gradually decreased followed by a final modest increase. Values for L(P) ranged between 0.8 x 10(-6) and 6.1 x 10(-6) centimeter per second per bar. Relationships between the root flow per unit leaf area at a pressure differential of 3 bars (QPL(3)), as well as the total root system conductance (L(R)), and plant size were also examined. Values for QPL(3) varied with plant size, somewhat like L(P). L(R) values continuously increased with plant size at rates which depended on the growth rate of the root surface area as well as L(P). Comparison of our data with the root conductivity constant (k(r)) of Taylor and Klepper (1975 Soil Sci, 120: 57-67) showed good agreement. The observations on Phaseolus were also confirmed for Glycine. Values for L(P) and k(r) of both species were within the same range.

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PubMed1977

Determination of hydraulic and osmotic properties of soybean root systems.

An analytical technique which allows the experimental determination of soybean (Glycine max L.) root properties is presented. Two major problems hamper the interpretation of experimental data. These are: (a) the influence of a possible boundary layer which raises the effective value of pi degrees above that of the bulk solution; and (b) the difficulty of obtaining an adequate measure of the internal osmotic pressure except at high values of volume flow rate due primarily to possible exchanges of solutes between the xylem and adjacent tissues. Consideration of these two problems leads to an interpretation of previous models which is reconcilable with the criticisms of Newman (Plant Physiology 1975 57: 738-739).In these experiments, estimates of hydraulic conductivity and reflection coefficient are based on high flow rate data where the osmotic effects are minimized. Because of the difficulties attached to the evaluation of pi(i), at low and moderate flow rates, any technique for evaluating root parameters which depends on knowledge of when the osmotic pressure difference (in bars) is zero will be subject to large errors, at least until both problems metioned above have been adequately resolved.An additional problem which must be dealt with in terminal root segments is the effect of a standing osmotic gradient. It is thought that this is not a serious problem in a complex root system.Transpiration rates are calculated on the basis of leaf and root surface areas and experimentally determined root volume flow. It is shown that root flow rates necessary to sustain high transpiration rates in the shoots are easily accommodated by the model at moderate levels of applied pressure difference.

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PubMed1975

General model for osmotic and pressure-induced flow in plant roots.

This paper presents a general model to describe coupled solute and water flow through plant roots when they are subjected to osmotic or hydrostatic pressure gradients, or both simultaneously. The model is based on well-established membrane transport equations derived from irreversible thermodynamic considerations. A variety of experimentally observed phenomena such as changes in root resistance with flow rate, apparent negative resistance effects, xylem sap dilution, and apparent non-osmotic water transport can be adequately explained with this model. The model also predicts that an exuding excised root system will be very insensitive to changes in the hydraulic conductivity coefficient. Previous work with a flat membrane of unit surface area and uniform properties is confirmed for a cylindrical coordinate system of nonuniform characteristics.

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PubMed1975

The effects of water stress on the development of the photosynthetic apparatus in greening leaves.

The effects of low and high relative humidity and of polyethylene glycol-induced root water stress on chlorophyll accumulation, on formation of the lamellar chlorophyll-protein complexes, and on the development of photosynthetic activity during chloroplast differentiation were examined. Low relative humidity or polyethylene glycol-induced root water stress (stress conditions) resulted in a 3 to 4 hour lag in chlorophyll accumulation, retarded the rate of chlorophyll b accumulation, and reduced the rate of formation of the light-harvesting chlorophyll a/b protein. All of these effects could be overcome by high relative humidity (nonstress) conditions. Concomitant measurement of leaf water potential showed that under stress conditions greening leaves were subjected to initial water deficits of -8 bars which decreased to -5 bars after 3 to 4 hours of illumination corresponding to the end of the lag phase. Leaves greening under nonstress conditions did not experience leaf water deficits greater than about -5 bars. It seems that the attainment of a minimum leaf water potential of -5 bars may be critical in the control of early chloroplast development. These results demonstrate that the lag phase is not indicative of a programmed event in chloroplast development, but rather is attributable to environmental conditions prevailing during leaf development and greening.

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PubMed1975

The Interaction between Osmotic- and Pressure-induced Water Flow in Plant Roots.

This paper presents a general model for coupled solute and water flow through plant roots based on the thermodynamics of irreversible processes. The model explains in a straight-forward manner such experimentally observed phenomena as changes in root resistance, increased solute flux, and apparent negative resistance, which have been reported for root systems under the influence of a hydrostatic pressure gradient. These apparent anomalies are explained on the basis of the interaction between the osmotic and hydrostatic driving forces and the well known "sweeping away" or dilution effect. We show that with a constant hydraulic conductivity the only features necessary to explain these phenomena are some type of membrane or membranelike structure and a mechanism for actively accumulating solutes.

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PubMed1974

A digital diffusion porometer circuit.

An automatic digital diffusion porometer circuit is described. The circuit is highly stable with respect to temperature and supply voltage. The device is capable of high timing accuracy over very short measurement intervals, so that measurements may be made rapidly without the danger of stomatal changes occurring during the measurement period.

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PubMed1970

Radial movement of oxygen in plant roots.

The radial movement of oxygen in excised corn and jack bean roots was measured with a platinum wire electrode embedded in the root tissue. Measurements were made with the roots exposed to air and with the roots immersed in nutrient solution in the presence and absence of millimolar sodium azide. Effective rates of oxygen diffusion in the root tissue were also measured from 5 to 30 C and compared to the respiration rates of similar root segments over the same temperature range. Under conditions which allow the roots to exude freely, the interior of the root operates under an oxygen deficit. Inhibition of respiratory oxygen uptake by low temperature or azide treatment increased the flux of oxygen to the root interior.

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