Comparison of nitrate uptake kinetic parameters across maize inbred lines

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Abstract
Eighty‐five maize lines were evaluated in a primary screen for differences in uptake rate at 1 mM KNO3; 15 were statistically separable into either “high”; or “low”; populations. Kinetic parameters were determined by iterative, least‐squares regression using a model combining both a saturable and a linear component. Using the inbred B73 as an arbitrary standard, it was determined that the saturable component had a Km of 224 μM and a Vmax of 0.107 μmolNO3/mg root dry weight/hr. The ,linear component had a first order rate constant of 6.1 × 10‐2 μmol NO3/mg root dry weight‐hr/mM. These values compared favorably with other published determinations of nitrate uptake kinetic parameters for saturable systems. No other constants have been reported for a linear component of nitrate uptake in higher plants. Only Vmax was shown to vary across the 15 genotypes for which kinetic parameters were determined. There was a non‐significant correlation between calculated Vmax and uptake rate at 1 mM in the primary screen suggesting that this parameter is not always a good predictor of nitrate uptake. This conclusion is discussed from the point of view that the transport proteins(s) involved in nitrate uptake need to be identified so that quantitative methods can be developed to obviate the problems associated with accurate assessment of genotypic differences for nitrate uptake in maize.