Dissimilar Responses of Membrane Potential (E M ), Permeability Properties and Respiration to Cadmium and Nickel in Maize Root Cells

The short-term treatment with Cd 2+ and Ni 2+ triggered transient depolarization of transplasma membrane potential (E M ) in the outer cortical root cells of two maize cultivars (cv. Premia and cv. Blitz), however, both metals changed the E M in a quantitatively different way. The magnitude and duration of E M depolarization were concentration dependent and were greater in the metal susceptible cv. Blitz. The highest E M depolarization was recorded with simultaneous application of Cd 2+ + Ni 2+ in both maize cultivars. The E M depolarization induced by Cd 2+ or Cd 2+ + Ni 2+ but not Ni 2+ alone was accompanied with a tremendous increase of membrane conductivity, but it was not accompanied with the effect of heavy metals (HM) on respiration. Simultaneous application of fusiccocin (FC) with Cd 2+ or Cd 2+ + Ni 2+ during the E M depolarization, inability of FC to stop the depolarization by FC-enhanced proton extrusion and rapid restoration of E M , suggested a transient inhibition of the plasma membrane H + -ATPase by these toxic metals. Our data support the opinion that differences in the effects of the studied ions were not the result of their direct action on PM, but rather of their different influence on intracellular processes within root cells.