Amelioration of Chilling-Induced Water Stress by Abscisic Acid-Induced Changes in Root Hydraulic Conductance

Abstract

ABSTRACrPretreatment of soybean (Glycine max L. var Ransom) root systems with abscisic acid (ABA) ameliorates the deleterious effect of low temperatures on root hydraulic conductance. ABA treatment of root systems subsequently chilled to 10°C with shoots at 25°C resulted in higher leaf water potentials and lower stomatal resistances. If the root systems are left at 25C, ABA causes stomatal closure. Membrane alterations are suggested as a mechanism for the ABA action in plant response to chilling stress.Abscisic acid has been implicated in plant response to environmental stress. ABA accumulates in plants during water stress (8,21) and closes stomata when applied to the transpiration stream (15,16,19). ABA also plays a role in plant response to low temperature stress (2,17,18 that treatment of root systems with ABA reduces the decrease in the hydraulic conductance of root systems at low temperatures. MATERIALS AND METHODSSoybean plants (Glycine max L. var Ransom) were grown in environmental growth chambers under a 12-h photoperiod at 25C. The photosynthetic photon flux density at plant height was 600 gE m-2 s-'. Seeds were sown in plastic pots (7.5 x 30 cm) containing a 1:1 mixture of sand and Turface. The bottom of the pot was cut off and replaced with a single hole stopper. Plants were watered daily with alternate applications of halfstrength Hoagland solution and distilled H20. Plants were 21 to 25 d old with one fully expanded trifoliolate leaf at the time of the experiment.A stock solution containing 0.1 M ABA (Sigma ± cis-trans) in 95% ethanol was prepared and stored in the dark at 4°C. Treatment solutions were prepared with distilled H20 the day before the experiment and kept in the dark at 22°C. One and one-half hours prior to the beginning of the photoperiod, the holes in the pots were sealed and 100 ml of 50 AM ABA or 100 ml of distilled H20 (with equivalent amounts of ethanol) were added. After 1 h of treatment, the drainage holes were uncovered and the pots allowed to drain for 5 min. The holes of eight treated and eight nontreated plants were resealed and the pots randomly placed into a water bath cooled to 10°C. Thermocouples placed in the center of selected pots indicated that the roots reached 10°C in 15 min and that there was less than 0.5C variation in temperature among individual pots. One-half hour after cooling, the lights were turned on. The remaining ABA-treated and nontreated plants were left with both roots and shoots at 25°C.Stomatal resistances of the upper and lower leaf surface were measured every 2 h with a diffusion porometer (Delta Instruments). Because of a limitation in the number of plants which would fit into the water bath, plant wiltedness, a nondestructive technique, was used to measure plant water status. Plant wiltedness was measured every 2 h by placing a protractor behind the stem of the plant. The angle of the apical internode relative to the rest of the stem was recorded. Zero degress meant a completely turgid plant, whereas 1800 meant a completely wilted plant. Four ho...

Responses of Transpiration and Hydraulic Conductance to Root Temperature in Nitrogen- and Phosphorus-Deficient Cotton Seedlings

“…The L of intact plants was estimated as the ratio of transpiration rate to absolute value of *w. Transpiration is expressed here as volume flux per unit root length, as the root provides the major resistance to water flow, especially in chilled seedlings (1,5,6). In fully-nourished plants, L was high at root temperatures 220°C, but it decreased sharply in a narrow temperature range centered on about 15C (Fig.…”

Abscisic Acid-Induced Chilling Tolerance in Maize Suspension-Cultured Cells

“…Although induction of chilling tolerance with ABA in maize plants has not been demonstrated (29), ABA has been reported to increase chilling tolerance of eggplant, soybean, and cucumber seedlings (5,15,21), cotton cotyledonary discs (19,20), and maize callus culture (4). The inability of ABA to induce chilling tolerance in maize plants could result from lack of uptake or biodegradation of applied exogenous ABA.…”

Effect of Temperature Conditioning on Chilling Injury of Cucumber Cotyledons

“…Among these changes are increases in the degree of unsaturation of fatty acids in the phospholipids of membranes in a number of plants (26). The (17) reported that ABA-induced changes in root hydraulic conductance alleviated the chilling-induced water stress in soybean. Rikin and Richmond (20) found that ABA applications to whole cucumber seedlings 15 h before the cotyledons were detached and exposed to chilling temperatures, resulted in less ion leakage than from the nonsprayed, chilled control plants.…”