Figure 2.

NH₄⁺ effect on Rb⁺ uptake depends on the time of exposure as well as on the presence of K⁺ in the growth medium. Time course of Rb⁺(⁸⁶Rb) uptake in plants exposed to the presence (black symbols) or the absence (white symbols) of 100 μm K⁺ at different NH₄⁺ concentrations: squares, 0 mm; triangles, 0.15 mm; and inverted triangles, 5 mm NH₄⁺. Measurements were made at 100 μm Rb⁺ 0, 6, and 66 h after the beginning of the treatments. The composition of the loading solution was the same as used for each growth condition, except for the exclusion of K⁺. Results are from an experiment consisting of three independent replicates. The presence of the same letter for a given time of exposure to different treatments indicates the absence of significant differences at P = 0.05.