Figure 3.

Superior K⁺ retention in the mature root zone is attributed to an intrinsically higher rate of H⁺-ATPase extrusion activity. A, Changes in the plasma membrane (PM) potential in epidermal root cells in two different zones upon exposure to 100 mm NaCl (indicated by the arrow). Values shown are means ± se (n = 6–8). B, Net K⁺ fluxes measured from the epidermal root cells in the apical and mature zones in response to 100 mm NaCl treatment (indicated by the arrow). Values shown are means ± se (n = 7–10). C, H⁺ pumping measured by ACMA quenching. PMs containing the H⁺-ATPase were incubated with ATP, and H⁺ pumping was activated by the addition of Mg²⁺ (indicated by the arrow). This experiment is representative of three independent PM purifications.