Uptake of neutral and acidic amino acids by Lemna gibba correlated with the H+‐electrochemical gradient at the plasmalemma

Uptake rates of L‐alanine, L‐serine and L‐aspartate and trans‐membrane electrical potentials (Δψ) were determined for a pH range in the external medium between 3.5 and 9.0. The proton electrochemical gradients () were calculated from Δψ, pH of the medium, and an assumed cytoplasmic pH of 7.5. At external amino‐acid concentrations of 0.1 mol m−3, where carrier‐mediated uptake dominates total uptake, a linear correlation between uptake rates and is obtained, which extrapolates to zero uptake at zero . This corroborates the contention that neutral and acidic amino acids are taken up by Lemna gibba L. by H+‐cotransport.