Compartmental analysis of Rb+ efflux from roots of intact high-salt barley plants

The validity of compartmental analysis of Rb⁺ efflux from roots of intact high-salt barley plants ( Hordeum vulgare L. cv. Salve) was examined. ⁸⁶Rb⁺ was used as a tracer. Rb⁺ (1 m M ) was included together with 3 m M K⁺ in the growth medium, and steady-state conditions were assumed to prevail during the experiment. Three phases of efflux were revealed with half-times of 23 min, 109 min and 12 h, respectively; and the time span of the experiment had to be at least 20 h to make determination of the slow phase possible. We cannot state what compartments in the root the 3 different slopes represent. A comparison of slopes was made between the plots of In efflux vs time and In content vs time. In spite of correction for tracer transport from the roots to the shoot, the slopes for the slow phase did not agree unless up to 85% of the root content of Rb⁺ is assumed not to participate in efflux.