Figure 4.

OsHKT2;2 but not OsHKT2;1 mediates Rb⁺ (K⁺) accumulation and influx in BY2 cells. A, OsHKT2;2-expressing tobacco BY2 cells exhibit increased Rb⁺ accumulation. Rb⁺ contents are shown for transgenic BY2 cell lines exposed to a buffer containing 0.1 mm Rb⁺ and 0.01 mm Na⁺ for 0, 30, or 60 min, as determined by ICP-OES (n = 6; ±sd; * P < 0.001 compared with vector controls). B, OsHKT2;2 mediates Rb⁺ (K⁺) influx, whereas OsHKT2;1 does not, compared with vector controls. Rb⁺ influx kinetics are shown for time-dependent short-term ⁸⁶Rb⁺ influx assays using transgenic BY2 cell lines in influx buffer solution containing 0.1 mm Rb⁺ and 0.01 mm Na⁺ (n = 3; ±sd). C, OsHKT2;2 mediates enhanced Rb⁺ (K⁺) influx as a function of the external Rb⁺ concentration, whereas OsHKT2;1 does not, compared with vector controls. Concentration-dependent short-term ⁸⁶Rb⁺ influx rates of transgenic BY2 cell lines were analyzed at 0 to 0.2 mm external Rb⁺ with 0.01 mm Na⁺ (n = 3; ±sd; time = 15 min). D, OsHKT2;2 mediates Na⁺-stimulated K⁺ (Rb⁺) influx. Concentration-dependent short-term ⁸⁶Rb⁺ influx rates of transgenic BY2 cell lines were analyzed at 0 to 0.2 mm external Rb⁺ with or without 0.01 mm Na⁺ (n = 3; ±sd; time = 15 min). Samples in C and D were measured in parallel.