Figure 6.

Time course of Mn efflux from 13-d-old barley roots (genotype Vanessa) preloaded with ⁵⁴Mn. The remaining ⁵⁴Mn in the root tissue was calculated and plotted against time. The regression lines were drawn through the linear part of the curve and extrapolated to a given value at time zero. The extrapolation to time zero in A represents the size of the vacuolar Mn pool. Subtraction of the linear component from the data points in A produced the curve in B, which linear part represents the cytoplasmic Mn pool. A similar procedure was used to obtain the value in C representing the cell-wall-bound Mn pool. The mean values of five independent regression estimates similar to the one outlined above are listed in Table I. R² values for A and B were always >0.99 and for C >0.93.