Fig. 5. Cumulative net NO^-₃ uptake and efflux from roots of Pima (A) and Acala (B) cotton grown in 0.1 mM NO^-₃ for 3 d, then exposed to the uptake or efflux solutions. Net NO^-₃ uptake and efflux were measured in the presence or absence of 10 mM NH⁺₄. Root tissue NO^-₃ concentrations for Pima and Acala were, respectively, 44.8 ± 2.3 and 48.9 ± 2.7 µmol g^-1 FW.