Fig. 1.

Time course of rubidium depletion from tanks of Vriesea splenriet. Tanks were filled with a mixture of 2·5 × 10⁷ d.p.m. ⁸⁶Rb⁺ and 75 nmol unlabelled RbCl in 1·5 mL Mes-buffer, 1 mm, pH 6·1, containing 1 mm CaCl₂. Tissue recovery was calculated from the label reanalysed in plant tissue. Data are means ± s.d.; n = 4. The regression equation is indicated.