Nitrate uptake by Vicia faba L. Plants: A physiological approach1

Abstract

This study was conducted to obtain information on the properties of the nitrate (NO3 ‐) uptake system in Vicia faba. The results showed that in plants grown in the absence of NO3 ‐, they cannot absorb it upon initial exposure to this anion. When this plant makes contact with environmental NO3 ‐, NO3 ‐uptake by the roots is progressively induced. However, in NO3 ‐‐grown plants, the uptake system is yet induced so they had the ability to take up NO3 ‐ at high rates from the beginning. The Michaelis’ constant (K,M) and maximum uptake rate (Vmax) were estimated from measurements of NO3 ‐ depletion in the uptake medium. The apparent KM value for net NO3 ‐ uptake in induced V. faba plants was 60 μM and the corresponding Vmax 0.44 umol NO3 ‐ (g FW)‐1 h‐1. This last value was low compared with that of other species, while KM is in the range for other higher plants. From the results of our experiments at low and high NO3 ‐ concentrations, we discuss the possibility of the existence of two NO3 ‐ uptake systems, one of a high affinity (functioning at low NO3 ‐concentrations) and another of low affinity (operative at high NO3 ‐ level in the medium).