Potassium uptake by Faba bean roots: Effects of root type, plant age and salinity

Potassium uptake by tap and lateral root of different aged faba bean plants (Vicia faba L.) was investigated by rubidium (⁸⁶Rb) tagging. The time course of K uptake was near linear (R² = 0.97 − 0.99) for the period between 5 min to 60 min of incubation. Potassium uptake was close to linearity in 0.01 mM to 0.1 mM range of external K. At higher concentrations i.e., from 0.01 mM to 10 mM uptake rates tended to decline. Uptake of K by tap roots was higher than that by an equivalent mass of lateral roots. The addition of NaCl (0.01−10 mM) to the uptake medium, reduced the K uptake by the laterals, but only at the higher KCl concentrations. The interactions between K and Na in tap roots seem to differ from those in the laterals. Potassium uptake by the apical 2 cm segment was higher than that of the older segments