title: Nitrate Uptake into Barley (Hordeum vulgare) Plants : A New Approach Using ClO(3) as an Analog for NO(3).
abstract: Evidence is presented that chlorate is an extremely good analog for nitrate during nitrate uptake by intact barley (Hordeum vulgare cv. Fergus) roots. The depletion of ClO(3) (-) or NO(3) (-) from uptake media over 2 to 6 hours by seedlings was found to be dependent on combined NO(3) (-) plus ClO(3) (-) concentrations, and total anion uptake was equivalent at different NO(3) (-)/ClO(3) (-) ratios. After loading barley seedlings with (36)ClO(3) (-) for 6 hours, kinetic parameters were derived from the analysis of efflux of [(36)Cl] chlorate into unlabeled solution. On the basis of this analysis, the half times for exchange for the cytoplasmic and vacuolar phases were 17 minutes and 20 hours, respectively.Data pooled from a number of different experiments were used to calculate kinetic constants (K(m) and V(max)) for (36)ClO(3) (-) influx into barley roots at different external ClO(3) (-)/NO(3) (-) ratios, using short (10 minutes) influx times. There appeared to be no discrimination by the root cells between ClO(3) (-) and NO(3) (-). Lineweaver-Burk analysis of the interaction between nitrate and chlorate were characteristic of competitive inhibition at low nitrate concentrations (0-0.5 mm). At higher concentrations, in the range of >1 mm, similar interactions between these ions were evident.
authors: Botany Department, University of British Columbia, Vancouver, British Columbia V6T 2B1 Canada.
authors: C E
authors: CE
authors: Deane-Drummond
authors: A D
authors: AD
authors: Glass