Lateral transport of ions into the xylem of corn roots: I. Kinetics and energetics.

A technique is described for study of the kinetics of lateral transport of ions across single roots of corn, Zea mays, in short term experiments under steady state conditions. The kinetics of chloride transfer to the vessels reflected the kinetics of absorption of chloride by the root cells. Efflux from the root vacuoles contributed to only a small extent to transport of chloride into the exudate. Lateral transport of chloride was inhibited by bromide at chloride concentrations in the ranges of both mechanisms 1 and 2 in a manner implicating competition. The uncoupler carbonylcyanide m-chlorophenylhydrazone used at 1 mum caused transfer of chloride to cease almost immediately at both low and high concentrations of chloride. Oligomycin depressed transport of chloride to the vessels within 10 to 15 minutes after application at 2 micrograms per milliliter. Inhibition by oligomycin was 75% at 0.5 mm chloride and 55% at 5 mm.It is concluded that lateral transport of chloride across corn roots is mediated by the dual mechanisms of ion absorption which reside in the plasmalemma. Transfer of chloride is inhibited by bromide and depends upon ATP as energy source. Chloride moves from the plasmalemma, the site of carriermediated absorption, to the xylem vessels by way of the symplasm. There is no evidence in these experiments that lateral transport of chloride in corn roots is governed by diffusion at any concentrations of chloride used in these experiments.