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Inhibition of Net Nitrate Uptake by Ammonium in Pima and Acala Cotton Roots

Dep. of Agronomy and Range Science, Univ. of California, One Shields Avenue, Davis, CA 95616-8515

View larger version (35K): [in a new window]   Fig. 1. Cumulative net NO-3 uptake by roots of Pima (left panel) and Acala (right panel) cotton grown in 0.01 (A, D), 0.10 (B, E) or 1.00 (C, F) mM NO-3 for 3 d, and then exposed to uptake solutions. Cumulative Net NO-3 uptake was measured by following the depletion of NO-3 from uptake solutions initially containing 0.1 mM NO-3 ± 1 or 10 mM NH+4. See Table 1 for root NO-3 concentrations.

View larger version (20K): [in a new window]   Fig. 2. Net NO-3 uptake by roots of Pima cotton grown in 0.10 mM NO-2 for 2 d, then exposed to uptake solutions containing 0.1 mM NO-3 ± 10 mM NH+4. Uptake rates were determined after 0, 15, and 60 min treatment with NH+4. Root NO-3 concentration was 1.8 ± 0.3 µmol g-1 FW. Vertical lines above the bars represent the respective +SE of the means of four replicates.

View larger version (35K): [in a new window]   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.

View larger version (27K): [in a new window]   Fig. 4. Cumulative net NO-3 uptake by roots of Pima cotton grown in 0.1 mM NO-3 for 4 d and pretreated with 0.02 mM NO-3 for 6 h. Control seedlings were left in 0.1 mM NO-3 (A), while pretreated seedlings (B) were placed in 0.02 mM NO-3 for 6 h. Net NO-3 uptake was measured in the presence of 0.1 mM NO-3 ± 10 mM NH+4. Initial root NO-3 concentrations were 52.6±1.5 (control) and 47.2 ± 1.5 (pretreated) µmol g-1 FW. Results are from a representative experiment.

View larger version (25K): [in a new window]   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.