Figure 6.

Root High-Affinity Mn Uptake Is Defective in the nramp1-1 Mutant.

(A) Time dependence of Mn accumulation in the wild type, nramp1-1, and nramp1-1–complemented line #4. Plants were grown in Mn-replete hydroponic culture for 2 weeks and then transferred to Mn-free medium for 1 week prior to the assay. At the time point 0, plants were supplemented with 18 μM MnSO₄. Roots were harvested at the time points indicated in the figure and washed with CaNO₃/bathophenanthroline disulphonate prior to Mn measurement by atomic absorption spectrometry.

(B) Concentration-dependent Mn uptake at 10 min by wild-type and nramp1-1 roots.

(C) NRAMP1-dependent uptake. The rate of NRAMP1-dependent uptake was calculated by subtracting the amount of Mn taken up by nramp1-1 roots from that taken up by wild-type roots. The data were fitted to a Michaelis-Menten function by nonlinear least squares analysis. The apparent K_m and V_max were calculated by expressing the data in the form of a double reciprocal Lineweaver-Burk plot (inset). Values shown are means ± sd (n = 3) of one representative experiment (n = 2). DW, dry weight.