Abscisic Acid Raises the Permeability of Plant Cells to Water

Abstract

A number of recent observations have indicated a role for abscisic acid in maintaining water balance. Treatment with ABA reduces the transpiration rate (3,5), probably by bringing about stomatal closure (2, 4). Furthermore, water stress leads to a significant increase in ABA concentration in leaves (5, 7). On the other hand, ABA increases the rate of root exudation (6).The present communication reports a marked effect of ABA on the permeability of plant tissues to water. The effect is observable both on Lp, the coefficient of hydraulic conductivity, and on Pd, the coefficient of diffusional permeability to water.The effect on hydraulic conductivity was detected in experiments in which osmotic water flux between cells and medium was followed with time. The equations for net osmotic flux into or out of cells can be written as follows:J, (out) = Lp(-oiri + oe're + P) (2) where JL = volume flow of water; -rx and 1re are the osmotic values for the cell and for the external solution respectively; ai and U-e are the average reflection coefficients for the internal and external solutes; and P is the turgor pressure. Changes in water flux would thus follow from alterations in Lp, in 7ri, in P, or in a. We have earlier (1) defined conditions under which a change in Lp may be distinguished from changes in the other parameters. Figure 1 shows the effect of ABA observed under these defined conditions. Discs excised from the xylem of root storage tissue of Daucus carota L. were washed in running tap water for about 16 hr. In the case of the efflux experiments, they were then immersed for 3 hr in 20 mg/liter ABA or in distilled water, after which they were transferred to 0.45 M mannitol. This concentration is hypotonic to the tissue. Net water efflux was determined by weighing the tissue at intervals. In the case of the influx experiments, the discs were first equilibrated for 3 hr in 0.45 M mannitol with or without 20 mg/liter ABA. They were then transferred to distilled water, and net influx was determined at intervals again by weighing. All experiments reported here were carried out at 27 C. Figure 1 shows that ABA increased the flux of water both into and out of the tissue. This fact rules out the possibility that the change in flux was due to a change in -ri or in P, since it is clear from the reversal of signs in equations 1 and 2 that if a factor affected flux via an alteration in either -xi or P, the effect on influx would have to be the opposite of that on efflux. Moreover, the fact that efflux was measured into hypotonic solution excludes the possibility that ABA treatment was changing a-(1 Pd, the coefficient of diffusional permeability to water, is also raised by ABA treatment. This was detected by measuring the flux of tritiated water between the tissue and the medium. In the experiment sunmmarized in Figure 2, cylinders of carrot tissue were first equilibrated with tritiated water (specific activity 50 ,uc/ml) for 3 hr, with or without added ABA. Each cylinder was then sequentially transferred through a series of...

Hormonal Modification of Plant Response to Water Stress

“…and wilting has obvious economic potential, as already mentioned by Jones and Mansfield (1970). Although many compounds that reduce transpiration are already known, the finding that ABA increases root exudation (Tal and Imber 1971), chloride accumulation (Mizrahi and Richmond, unpublished data), and the permeability of plant tissues to water (Glinka and Reinhold 1971) suggests a more complex mode of action than merely that of an antitranspirant. In addition, commercial utilization of ABA to improve water balance of water-stressed plants seems advantageous in that ABA is an endogenous material with a high turnover (Milborrow 1969;Milborrow and Nodle 1970), thereby diminishing problems of residual toxicity and deleterious metabolic side effects.…”

“…Cytokinins increase transpiration by effecting stomatal opening (Livne and Vaadia 1965;Meidner 1967;Luke and Freeman 1968), and abscisic acid (ABA) effects closure of stomata and consequent reduction of transpiration (Little and Eidt 1968;Mittelheuser and Van Steveninck 1969;Jones and Mansfield 1970;Mizrahi, Blumenfeld, and Richmond 1970), as well as enhancement of root exudation (Tal and Imber 1971). It was also reported recently that ABA increases the permeability of plant tissues to water (Glinka and Reinhold 1971). In addition, work on a wilty tomato mutant has shown that the impairment of the closure of its stomata may be corrected by treatment with ABA (Imber and Tal 1970).…”

Penetration of Soybean Root Systems by Abscisic Acid Isomers

“…Exogenously applied as well as endogenously produced ABA hardened plants to exposure to low temperatures (18,19). ABA is known to cause stomatal closure (16,20) and has been reported to alter root permeability to water (5,(7)(8)(9)13). In experiments where ABA is added to the irrigation water (18), it is often unclear whether the hormone acts on the root or is transported to the shoot and directly effects the stomata.…”

Control of Seed Germination by Abscisic Acid

“…Water uptake during the imbibition period (up to about 8 h after sowing) is not influenced by ABA. It thus seems unlikely that ABA acts in germination by impairing the water permeability of membranes (8). It rather appears appropriate to discuss the action of ABA in terms of the water potential equation (Iw = IP + I, + I').…”