Inhibition of Nitrate Uptake by Ammonium in Barley. Analysis of Component Fluxes

摘要: NO3- uptake by plant roots is rapidly inhibited exposure to NH4+. The rapidity of the effect has led presumption that inhibition results from direct effects NH4+ at plasma membrane. mechanism this inhibition, however, been in contention. In present study we used radiotracer 13N determine relative short-term exposures on 13NO3- influx, efflux, and partitioning absorbed barley (Hordeum vulgare) roots. Plants were grown without or NO2- (uninduced for uptake), with 0.1, 1.0, 10 mM NO3-, 0. 1 (to generate induced uptake). Exposure strongly reduced influx; was most pronounced plants when absorption measured low external NO3-. At higher [NO3-] uninduced inhibitory much diminished, indicating influx mediated via inducible high-affinity transport system rather than constitutive low-affinity system. also caused increased efflux; largest plants. absolute terms, reduction made dominant contribution observed net Differences response between those indicate may not be an appropriate analog under all conditions.