Tributylbenzylammonium (TBBA(+))-dependent fusicoccin (FC)-induced H(+) extrusion in maize roots: relationship between the stimulating effects of TBBA(+) on H (+) extrusion and on Cl (-) efflux.

The mechanism of the stimulating effect of lipophilic cations on H(+) extrusion in maize root segments (Zea mays L.) has been investigated. The measurement of the uptake of [(3)H]tributylbenzylammonium ([(3)H]TBBA(+)), the most active lipophilic cation on H(+) extrusion, indicated that although a relevant fraction of TBBA(+) taken up by the tissue is adsorbed to cell surfaces, a fraction of the cation enters the cells. However no correlation was observed between the rate of TBBA(+) uptake and that of H(+) extrusion. On the other hand, the lipophilic cations active on H(+) extrusion (TBBA(+) and dibenzyldimethylammonium (DDA(+))), in the presence of fusicoccin (FC), induced under the same conditions an efflux of Cl(-), while tetramethylammonium (TMA(+)), inactive on H(+) extrusion, did not. The stimulation of Cl(-) efflux by TBBA(+) was independent of the anion present in the medium and was inhibited by Na-orthovanadate, an inhibitor of plasma membrane ATPase and of TBBA(+)-induced H(+) extrusion. These results suggest that the stimulation of H(+) extrusion by TBBA(+) depends on its effect on Cl(-) efflux rather than on its penetration into the cells.