Fig. 4. Nitrate uptake activities and kinetic analyses using wild-type CHL1-, T28A-, T101A-, or T101D-injected oocytes. Nitrate uptake in oocytes injected with cRNAs encoding wild-type CHL1 or mutants T28A (A and B), T101A (C and D), or T101D (E and F). (A, C and E) High-affinity nitrate uptake activity determined by incubating oocytes with 150 µM NO₃^– for 1.5 h; (B, D and F) nitrate uptake activities determined by incubating oocytes with 10 mM NO₃^– for 1.5 h. The numbers above the striped bars indicate the activity expressed as a percentage of wild-type CHL1 activity after subtraction of background activity (water-injected oocytes), while the numbers in parentheses show the actual low-affinity nitrate uptake activity calculated by subtracting the contribution of the high-affinity component from the 10 mM nitrate uptake activity.