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Effects of abscisic acid on sequestration and exchange of Na + by barley roots

R. Behl and K. Raschke
Planta
Vol. 167, No. 4 (1986), pp. 563-568
Published by: Springer
Stable URL: http://www.jstor.org/stable/23377967
Page Count: 6
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Effects of abscisic acid on sequestration and exchange of Na
          +
          by barley roots
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Abstract

Excised Na+-starved barley roots were suspended in solutions of Na+ in combination with NO3-, Cl-, and SO42-, and effects of the added phytohormone, abscisic acid (ABA), to the medium were determined. Abscisic acid increased the rate of Na+ (22Na+) accumulation and the amount of Na+ deposited in the vacuoles. These stimulating effects of ABA were modified by anions following the sequence NO3- > Cl- > SO42-. Testing whether the magnitude of the pH gradient across the plasmalemma of the cells of the root cortex affects rates of Na+ accumulation and their dependence upon ABA, we observed that, in the pH range from 4 to 8, the ABA-induced stimulation was strongest at pH 5.8, and least at pH 4. Changes in pH during the experiment caused changes in the rates of Na+ accumulation in agreement with experiments performed at constant pH values. Simultaneously with ABA-enhanced accumulation, loss of Na+ occurred. Loss of Na+ was strongest at pH 4 and was affected by anions, being greatest with SO42- and following the sequence SO42- > Cl- > NO3-. On the basis of the finding that initial acceleration of uptake as well as loss of Na+ depended on the pH of the medium we suggest that, in barley roots, ABA stimulates an exchange of Na+ for H+ at the plasmalemma of the cortical cells. The results indicate that ABA-stimulated expulsion of Na+, in combination with ABA-stimulated sequestration in the vacuoles, constitutes one of the mechanisms which enable barley plants to tolerate higher than normal levels of Na+.

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