Regulation of Potassium Absorption in Barley Roots

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Abstract
Plasmalemma influx isotherms for K+ were measured in the system I concentration range (0.01-0.32 mM), for barley (Hordeum vulgare L.) roots of varying internal K+ concentration, and Km values for influx calculated. In plants grown for several days in CaSO4 or in CaSO4 plus KCl solutions, and in plants grown in CaSO4 for several days and then rapidly loaded with KCl during a pretreatment period, Km values were positively correlated with internal K+ concentrations. Influx of K+ is shown to be sigmoidally related to internal K+ concentration and Hill plots of influx data give linear transformations with n = 4. This information is taken as support for an allosteric model for the regulation of K+ influx in which the "carrier" is envisaged as possessing a single external binding site for K+ as well as 4 internal sites for allosteric control of influx.
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