Figure 7.

Efflux of ²²Na⁺ from excised roots expressed as decrease in tissue ²²Na⁺ after transfer to nonradioactive solution (black circles). Data were fitted with a double exponential equation (lines) to estimate plasma membrane and tonoplast efflux rates. Half-times for exchange of the cytoplasm (k1) and tonoplast (k2) in min⁻¹ were 0.060 and 0.0012 (line 149) and 0.0726 and 0.0007 (Tamaroi), respectively. Initial contents of the cytoplasm (Q_c) and vacuole (Q_v) in nmol g FW⁻¹ were 5,676 and 4,224 (line 149) and 1,494 and 4,956 (Tamaroi), respectively. Data are presented as root Na⁺ (calculated using the specific activity of the loading solution) and are equivalent to ²²Na⁺ remaining in the tissue. A, Salt tolerant line 149. B, Salt sensitive Tamaroi. Data represent mean ± sem (n = 5).