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Potassium Transport in Corn Roots ¹

IV. Characterization of the Linear Component

Department of Botany, University of California, Davis, California 95616

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 x Oh 43]). In tissue from both low- and high-salt grown roots, replacement of Cl^– in the uptake solution by either SO₄^2–, 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 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.

¹ Supported by National Science Foundation Grant PCM 8117721 to W. J. L. and by a University of California, Davis Graduate Fellowship and a Jastro-Shields Research Award to L. V. K.

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