Regulation of K+Influx in Barley: Evidence for a Direct Control of Influx by K+Concentration of Root Cells

Siddiqi, M. Y. and Glass, A. D. M. 1987. Regulation of K+ influx in barley: Evidence for a direct control of influx by K+ concentration of root cells.—J. exp. Bot. 38: 935–947. The kinetics of K+ (86Rb+) influx into intact roots of barley (Hordeum vulgare L. cv. Fergus) seedlings having different combinations of root and shoot [K+], different growth rates and different root:shoot weight ratios were studied. K+ influx was strongly correlated with root [K+]; shoot [K+], growth rates, and root: shoot ratios appeared to have little effect on K+ influx. A detailed study showed that both Vmax and Km for K+ influx were affected by root [K+] but not by shoot [K+]. We have suggested that factors such as growth rates and root: shoot ratio may affect K+ influx indirectly primarily via their influence on root factors such as root [K+]. We have reiterated that other types of kinetic control, e.g. increased or decreased synthesis of ‘carrier systems’, may operate in addition to direct (allosteric?) control of K+ influx by root [K+]. The negative feedback signal from root [K+] appeared to be the prime effector in the regulation of K+ influx.