Effect of some triazole fungicides on intracellular pH and on cell membrane permeability in leaves of Elodea densa (Planch.) Casp
Romani, G. | BEFFAGNA, N.
Recent data obtained in this laboratory have shown that a number of triazole fungicides induce in leaves of barley and Elodea densa an early release of solutes and an inhibition of H⁺ extrusion. This paper deals with the early effects of two triazoles, penconazole and flusilazol, on intracellular pH and plasmamembrane permeability in Elodea densa leaves. Different effects were found at low (0.1–0.15 mM) or at high (0.3–0.5 mM) triazole concentrations. At the low concentrations the triazoles induced a marked intracellular acidification (corresponding to an acidification of both the cytosol and the vacuole) as evaluated by the weak acid and weak base distribution method. For higher triazole concentrations (0.3–0.5 mM) the intracellular pH became very close to that of the external medium (pH 5.5), and cytosolic and vacuolar pH measurements became unreliable. Triazoles at concentrations higher than 0.1–0.15 mM induced an early and very marked increase in net efflux of K⁺ and Cl⁻. At these ‘toxic’ concentrations the sorbitol‐permeable space (apparent free space) was increased from about 20% to more than 90%. These results suggest that triazoles at low ‘sub‐toxic’ concentrations inhibit some mechanism involved in the regulation of intracellular pH (possibly the plasmalemma proton pump), whilst at higher concentrations they induce a non‐specific increase in passive permeability of the plasmamembrane.
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