Effect of triazole fungicides on the membrane permeability and on FC-induced H +-extrusion in higher plants

Abstract

The early effects (0–6 h) of two triazole fungicides (penconazole and propiconazole) on some parameters connected with membrane permeability of higher plants were investigated. In barley leaf segments the triazoles at dosages from 0.1 to 0.5 mM caused leakage of both electrolytes (K +, Cl − mainly) and solutes absorbing at 260–280 nm and alkalinized the incubation medium. At the lower (0.1 mM) concentration the effect of penconazole on the leakage of electrolytes and other solutes was almost undetectable, while the alkalinization increase of the medium was only slightly smaller than at the higher concentration. In conditions of marked activation of the proton pump by fusicoccin, both triazoles, tested at the 0.5 mM concentration, induced an early, strong inhibition of fusicoccin-induced, H + extrusion. In red beetroot disks, 0.25 mM penconazole caused leakage of beta cyanin and other solutes already after 3 h treatments, suggesting a modification of transport processes also at the tonoplast. These data indicate that both compounds display some early effects on transport activity at the plasma membrane, independently of their known activity on phytosterol and gibberellin biosyntheses. The difference between the effects induced by the higher (0.25 – 0.5 mM) and by the lower (0.1 mM) concentrations and the inhibition of the effect of fusicoccin suggest two different modes of action: at 0.1 mM concentrations the triazoles would inhibit some specific mechanism involved in proton transport (possibly the H + pump), while at the higher concentration they would engender a disorganization of the plasma membrane leading to the passive, non-specific release of intracellular solutes.