Constancy of nitrogen turnover kinetics in the plant cell: Insights into the integration of subcellular N fluxes

Abstract

Compartmental analysis with 13N was used to determine cytosolic nitrate (NO3-) pools, and their turnover rates, in roots of intact barley (Hordeum vulgate L. cv Klondike) seedlings. Influx, efflux, flux to the vacuole and assimilation, and flux to the xylem, varied as much as 300-fold over a wide range of external NO3- conditions. By contrast, the kinetic constant kc describing cytosolic NO3- turnover varied by less than 4% from a mean value of 0.0407 min-1. Accordingly, cytosolic NO3- pools varied linearly with influx. A literature survey showed that kc constancy is observed with both NO3- and ammonium (NH4+) fluxes in many plant species, including H. vulgare, Arabidopsis thaliana, Picea gl..