The regulation of potassium influx into intact roots of barley by internal potassium levels

Abstract

Isotherms were obtained for the influx of K+ into roots of intact barley (Hordeum vulgare (L.) cv. Conquest) plants which had previously been grown in either 0.5 mM CaSO4 solution or 0.5 mM CaSO4 plus 5 mM KGl solution. Km and Vmax values obtained from these influx data were 0.03 ± 0.003 mM and 10.8 μmol g−1 h−1 respectively for the low-K+ plants and 0.1 ± 0.01 mM and 1.74 ± 0.08 μmol g−1 h−1 for the high-K+ plants.When the K+ content of low-K+ plants was increased, by pretreating the roots of intact plants in 10 mM KCl plus 0.5 mM CaSO4 solution, K+ influx values, as determined from 0.1 mM KCl plus 0.5 mM CaCl2 solutions, declined continuously during the 12 h of pretreatment. Hill plots of this data revealed a consistent biphasic response to internal K+. Below 50 μmol K+ g−1 the Hill coefficient was close to unity. Above 50 μmol g−1 the Hill coefficient increased to values close to 3. The time, or root K+ concentration, at which this change in Hill coefficient occurred corresponded to the first indications of net transfer of K+ to the shoot.