Fig. 3. Net NO^-₃ uptake rates (expressed as % of the control) by roots of Pima cotton seedlings grown in 0.01, 0.02, 0.10, or 1.0 mM NO^-₃ for 3 d, then exposed to uptake solutions. Net NO^-₃ uptake was measured in the presence of 0.1 mM NO^-₃ ± 10 mM NH⁺₄. Tissue NO^-₃ concentrations for roots grown in 0.01, 0.02, 0.10, and 1.0 mM NO^-₃ were 4.7, 13.8, 35.5, and 67.8 µmol g^-1 FW, respectively. Vertical lines through data points reflect ± SE of means of three replicates. Net NO^-₃ uptake rates at 100% varied from 4 to 5 µmol g^-1 FW h^-1.