Abstract
In this work we demonstrate the effect of different ascorbate redox states on the plasma membrane potential and on proton secretion of onion root cells. Ascorbate and dehydroascorbate induced plasmalemma hyperpolarization and stimulated acidification of the incubation medium. Both effects were transient and a repolarization of the membrane to the resting potential was reached within 10–15 min. The free radical of ascorbate had a permanent stimulatory effect on both parameters: a concentration dependent hyperpolarization of about 25 mV, partially inhibited by vanadate, could be observed immediately after addition. Medium acidification was increased by a factor of 20 and sustained for hours in the presence of the free radical. Additionally, ascorbate may increase the potassium permeability of the membrane, thus hyperpolarizing at low external potassium concentrations. Possible interactions of the free radical with the energization of the plasma membrane via an NAD(P)H-ascorbate free radical reductase (EC 1.6.5.4) will be discussed.
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