Effect of Temperature on Water and Ion Transport in Soybean and Broccoli Systems

Abstract

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 chileing-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.Since the time of Hales (1727) it has been known that cold soil reduces the absorption of water by plants. Differences among species in reaction to water absorption at low temperatures were reviewed by Kramer (1 1). Kuiper (13) was among the first to note that at a "critical" temperature, which varied with the temperature at which roots were grown, a sharp drop occurred in water absorption. Some investigators attributed anomalies such as this to discontinuities in properties of surface water at 15, 30, 45, and 60 C (7, 15, 18).A more likely hypothesis attributes sharp breaks in Arrhenius plots of biological phenomena to phase transitions in membrane lipids in which the hydrophobic core changes from a liquid to a solid or crystalline state at some specific temperature. Such changes alter membrane permeability and enzyme activity (8,10,19). Arrhenius plots were used by Clarkson (2) to study exudation rates and ion concentration of the xylem exudate from excised barley and rye roots preconditioned at various temperatures. With rye roots grown at 20 C he found a break in the Arrhenius plot of exudation rate versus temperature at 10 C, but for roots preconditioned at 8 C for 3 days the break occurred at 5 C.

Penetration of Soybean Root Systems by Abscisic Acid Isomers

“…As seen in Figure 1, the trans-trans isomer has a shorter retention time than the cis-trans isomer indicating the greater hydrophilicity of the trans-trans isomer. This is consistent with the hypothesis that a lipid membrane is the rate limiting barrier for solvent and solute movement through root systems (12,14). If, as has been suggested (14), ABA effects cell membranes, this observation suggests that the reason the cis-trans Plant Physiol.…”

“…Ransom) plants were grown hydroponically in 3-L plastic pots containing half-strength Hoagland solution for 20 to 40 days in controlled environment chambers at the Duke University Phytotron as described previously (14). All plants were kept under a long day photoperiod of 14- Twenty 1d aliquots were analyzed directly with an Altex Model 310 high performance liquid chromatograph with a UV (254 nm) detector for the presence of ABA.…”

Mercuric Chloride Effects on Root Water Transport in Aspen Seedlings

“…E a depends on the nature of the rate-limiting barrier for water movement and on the energetics of the waterpore interactions (Verkman et al, 1996). Moreover, Arrhenius plots of water movement in soybean (Markhart et al, 1979a) and in renal proximal tubule cell membranes (Meyer and Verkman, 1987) were found to be nonlinear. In our experiment, when the temperature was decreased from 25°C to 4°C and then increased back to 25°C, control roots did not yield a linear Arrhenius plot (Fig.…”

“…The steady-state flow rate (Q v ) was measured using the hydrostatic pressure method (Markhart et al, 1979a;Rü dinger et al, 1994) with some modifications. A glass cylinder was inserted into a pressure chamber (PMS Instruments, Corvallis, OR) and filled with one-half-strength Hoagland solution, which was continuously stirred with a magnetic stirrer.…”

“…In the present study, we employed a pressure-flux approach (Markhart et al, 1979a;Rü dinger et al, 1994) to examine the effects of HgCl 2 on the properties of water transport and its E a in the intact root systems of aspen (Populus tremuloides Michx.) seedlings grown in solution culture.…”