Potassium Transport in Corn Roots

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Abstract
A detailed examination was conducted on the linear, or first-order kinetic component for K+(86Rb+) influx into root segments of both low- and high-salt grown corn seedlings (Zea mays [A632 .times. Oh 43]). In tissue for both low- and high-salt grown roots, replacement of Cl- in the uptake solution by either SO42-, H2PO4-, or NO3- 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 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 standing Cl- influx mechanism.