Potassium Transport in Corn Roots : IV. Characterization of the Linear Component

A detailed examination was conducted on the linear, or first-order kinetic component for K(+)((86)Rb(+)) influx into root segments of both low- and high-salt grown corn seedlings (Zea mays [A632 x Oh 43]). In tissue from both low- and high-salt grown roots, replacement of Cl(-) in the uptake solution by either SO(4) (2-), H(2)PO(4) (-), or NO(3) (-) caused a significant (50-60%) and specific inhibition of the linear component of K(+) influx. The anion transport inhibitor, 4,4'-diisothiocyano-2,2'-disulfonic acid, was found to abolish saturable Cl(-) influx in corn roots while causing a significant (50-60%) and specific inhibition of the linear K(+) uptake system; this inhibition was identical to that observed when Cl(-) was replaced by other anions in the K(+) uptake solution. Additionally, the quaternary ammonium cation, tetraethylammonium, which has been shown to block K(+) channels in nerve axons, also caused a dramatic (70%) and specific inhibition of the linear component of K(+) influx, but this was obtained only in high-salt roots. The reasons for this difference are discussed with respect to the differing abilities of low- and high-salt roots to absorb tetraethylammonium.Our present results indicate that the linear component of K(+) influx may occur by a passive process involving transmembrane K(+) channels. Fluxes through these K(+) channels may be partly coupled to a saturating Cl(-) influx mechanism.