The regulation of K(+) influx in excised barley roots : Relationships between K(+) influx and electrochemical potential differences.

The electrochemical potential differences [Formula: see text] for potassium, between excised barley (Hordeum vulgare L.) roots and external media containing 0.05 mM KCl+0.5 mM CaSO4, were determined over a 4-h period during which initially low-K(+) roots accumulated K(+) by pretreatment in 50 mM KCl plus 0.5 mM CaCl2. This pretreatment resulted in increased internal [K(+)], decreased K(+) influx (as measured from 0.05 mM KCl+0.5 mM CaSO4) and decreased values of [Formula: see text]. These observations indicate that the decline of K(+) influx associated with increased internal K(+) concentration cannot be accounted for by passive adjustment to the electrochemical gradient for this ion.