Kinetics of rubidium absorption & translocation by barley

Abstract

Short time steady-state accumulation studies of radioactive Rb by roots and shoots of 7-day-old barley plants indicate the relationship between active and passive processes in ion accumulation by shoots. If the carrier mechanism is used to describe the active process, the observed data are consistent with 2 competing active processes for an active intermediate, 1 leading to root accumulation and the other to accumulation in the shoot. The data are also consistent with 2 parallel active processes, 1 leading to root accumulation and the other to shoot accumulation. Shoot accumulation showed 2 concentration functions, 1 that predominated at high Rb concentration and another that predominated at lower Rb concentrations. These corresponded with the 2 concentration functions for Rb uptake by roots. Azide, methylene blue, DNP, K, and H ion were all shown to inhibit active Rb accumulation, but not always in the same way. The action of these inhibitors and the apparent dissociation constant, Km, of the Rb carrier combination were similar for roots and shoots.