Early Effects of Penconazole on H+ and K+ Transport,Electrolyte Leakage and Transmembrane Electrical Potential in Egeria densa Leaves

The early effects of penconazole (PCZ) at relatively high concentration (10^?4 to 5 × 10^?4 M) on changes in pH and in titratable acidity of the medium, transmembrane electrical potential difference (Em), electrolyte leakage and cell morphology were investigated in Egeria densa leaves. At the lowest (10^?4 M) concentration and in the presence of a very low (10 μM) K⁺ concentration, triazole induced an early, moderate hyperpolarization of Em, associated with a decrease of net K⁺ uptake, suggesting some increase in the passive permeability to K⁺. This Em hyperpolarization was no longer detectable at high (2 mM) K⁺_out concentration. At high PCZ concentrations (3 × 10^?4 M and 5 × 10^?4 M) the early hyperpolarization detectable in the presence of a low K⁺_out concentration became transient, and was followed by a marked depolarization. PCZ, at these concentrations, suppressed acidification of the medium, stimulated electrolyte leakage and, in the mesophyll cells, induced some shrinking of the cytoplasm and its disconnection from the cell walls. These results are interpreted as due to an early effect of this triazole leading to the disorganization of the plasma membrane.