Redox agents regulate ion channel activity in vacuoles from higher plant cells

The ability of redox agents to modulate certain characteristics of voltage- and calcium-activated channels has been recently investigated in a variety of animal cells. We report here the first evidence that redox agents regul ate the activation of ion channels in the tonoplast of higher plants. Using the patch-clamp technique, we have demonstrated that, in tonoplasts from t he leaves of the marine seagrass Posidonia oceanica and the root of the sug ar beet, a variety of sulphydryl reducing agents, added at the cytoplasmic side of the vacuole, reversibly favoured the activation of the voltage-depe ndent slow vacuolar (SV) channel. Antioxidants, like dithiothreitol (DTT) a nd the reduced form of glutathione, gave a reversible increase of the volta ge-activated current and faster kinetics of channel activation. Other reduc ing agents, such as ascorbic acid, also increased the SV currents, although to a lesser extent in comparison with DTT and glutathione, while the oxidi sing agent chloramine-Tr irreversibly abolished the activity of the channel . Single channel experiments demonstrated that DTT reversibly increased the open probability of the channel, leaving the conductance unaltered. The re gulation of channel activation by glutathione may correlate ion transport w ith other crucial mechanisms that in plants control turgor regulation, resp onse to oxidative stresses, detoxification and resistance to heavy metals. (C) 1999 Federation of European Biochemical Societies.