Table 1. Apparent K_m for K⁺ and Na⁺ transport in vacuoles isolated from the wild type and nhx knockout mutants.

The apparent K_m values were calculated by the intersection of the fitted line with the abscissa of the double reciprocal plots for the K⁺-dependent PBFI fluorescence changes (Fig. 6, insets) and the Na⁺-dependent SBFI fluorescence changes (Fig. 7, insets). Values are means ± sd (n = 6).

Plant	K+	Na+
Wild type	20.3 ± 2.4	17.6 ± 3.4
(NHX1) nhx2/3/4	25 ± 5.3	17.1 ± 5.5
(NHX2) nhx1/3/4	26 ± 3.4	18.2 ± 1.9
(NHX3) nhx1/2/4	0	15.3 ± 6.4
(NHX4) nhx1/2/3	8.5 ± 3.5	15.8 ± 1.9
(None) nhx1/2/3/4	0	9.9 ± 0.2