Sodium-coupled solute transport in charophyte algae: A general mechanism for transport energization in plant cells?

Ion-gradient-coupled transport systems in plants are normally electrophoretic and carry inward current. Rapid inward electrical currents elicited by K(+), by urea and by lysine in the freshwater acidophilic alga Nitella translucens Agh. are all very strongly dependent on the presence of Na(+) or (except in the case of K(+)) Li(+). These results indicate that Na(+)-coupled solute transport in plants, which had previously been demonstrated only in an alkalophilic species (Chara australis), did not evolve recently as an alternative to H(+)-coupled transport in high-pH environments, and might therefore be more widely distributed than has hitherto been recognised.