Influence of exogenously supplied potassium and sodium salts on the abscisic acid‐induced proline accumulation in barley leaf segments

A stimulation of the abscisic acid (ABA)‐induced increase in proline was observed in leaf segments of barley (Hordeum vulgare L. cv. Georgie) if K+ or Na+ were supplied in the external medium as salts of monovalent anions such as NO3, Br, Cr and I, but not when sulphate or phosphate were used. To a lesser extent, the effect was evident also with RbCl, but it did not occur when chlorides of Li+. Cs+, NH4+, Mg:+ and Ca2+ were used. Both KC1 and NaCl in the concentration range 2–100 mM influence the ABA‐dependent proline accumulation to the same extent; the increase induced was about 100% at 10 mM, and reached a maximum between 60 and 100 mM. The effect is not due to the osmotic activity of the salts and does not seem to depend on changes in K+ and Na+ levels within the leaf tissue, but it is somehow linked to their external concentration. The existence of a specific interaction between ABA and K+ or Na+, possibly at the cell membrane level, is proposed.