MODULATION OF THE PLASMA-MEMBRANE ELECTRON-TRANSFER SYSTEM IN ROOT-CELLS OF LIMNOBIUM-STOLONIFERUM BY EXTERNAL PH

The influence of ferricyanide on transmembrane electron transfer, proton secretion, membrane potential, and cytoplasmic pH of Limnobium stoloniferum (G.F. Mey) Griseb. root cells was investigated at different external pH. HCF III reduction by the roots was accompanied by membrane depolarization, an increase in proton secretion and by alkalinization of the cytoplasm. Change of membrane potential and cytoplasmic pH as well as transmembrane e- transfer was more pronounced at acid external pH. The rate of proton flux was linearly dependent on the rate of electron transfer. The slope of the relationship was around 1, independent of external pH. The data are in agreement with the hypothesis that electron transfer at the plasma membrane is directly coupled to proton secretion. It is suggested that both e- and redox-coupled H+ transport are activated by acid external pH.