Ionic nature of burn-induced variation potential in wheat leaves.

Variation potential (VP) in higher plants cells is a transitory depolarization of the plasma membrane occurring in response to external damage. The effects of VP on different physiological processes are actively studied, but little is known about their ionic nature, which limits the interpretation of VP-induced functional changes. It is thought that VP generation is based on transient inactivation of plasma membrane proton pumps and is not connected to passive ionic fluxes. To study burn-induced VP in wheat seedlings, we measured membrane electric potential and cell input resistance. Cell input resistance decreased during VP generation, indicating that ionic channels were activated. In addition, VP amplitude decreased when the extracellular calcium concentration was lowered. When anion channels were blocked by ethacrynic acid addition, the VP had poor depolarization speed and amplitude. A decrease in the chlorine gradient by extracellular chlorine concentration shift leads to lowering of the VP amplitude and depolarization speed. This result indicates the role of chlorine efflux in depolarization phase formation. The VP repolarization is connected to potassium ion efflux, that is confirmed by repolarization suppression under addition of the potassium channel blocker tetraethylammonium (TEA) and an increase in the extracellular potassium concentration. We also showed that the addition of a proton pump inhibitor leads to membrane potential depolarization and inhibition of VP generation. These results suggest that the VP may be formed not only by transient suppression of proton pumps but also by passive ionic fluxes through the membrane.