Effect of some triazole fungicides on intracellular pH and on cell membrane permeability in leaves of Elodea densa (Planch.) Casp.*

Abstract

SUMMARYRecent 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 (O-3-O-5 mivi) 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 (O-3-O-5 mM) the intracellular pH became very close to that of the external medium (pH 55), and cytosolic and vacuolar pH measurements became unreliable. Triazoles at concentrations higher than 01-015 mM induced an early and very marked increase in net efflux of K"^ and Cl". At these 'toxic' concentrations the sorbitolpermeable 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.

Abscisic acid effects on intracellular pH and ion fluxes in barley leaf segments

“…This parameter, according to the biochemical pH-stat theory of Davies (1973), should reflect the changes in the rate of synthesis or decarboxylation of malate, due to cytosolic alkalinization or acidification, respectively. The results of experiments carried out in the presence of KCl or FC plus KCl, indicated that while FC markedly increased COj fixation, as already shown in other materials (Johnson and Rayle, 1976;Romani et al 1983), ABA induced a clear inhibition of CO2 fixation rate in both cases (Fig. 4).…”

“…Thus, neither a decrease in H* apparent net influx oor an increase in cell sap pH should be found in these conditions, unless an overstimulation of the proton pump, possibly by acid load, had been induced (for similar effects in other materials see Romani et al 1985, Reid et ai. 1989, Beffagna and Romani 1991.…”

“…At different times of treatment leaves were collected, then rapidly washed in 0.5 mM CaSOj to remove radiolabel from the free space. The radioactivity incorporated was measured by a liquid scintillation analyser (Tri-Carb-1500 model, Packard Instrument Co., Downwrs Grove, IL, USA), after digestion and bleaching of the samples carried out according to the procedure of Recalcati et al (1982), partially modified as described by Romani and Beffagna (1991).…”

H+ Fluxes at Plasmalemma Level: In Vivo Evidence for a Significant Contribution of the Ca2+‐ATPase and for the Involvement of its Activity in the Abscisic Acid‐Induced Changes in Egeria Densa Leaves

“…The radioactivity incorporated was always measured by liquid scintillation counting, after digestion and bleaching of the tissue, as described in a previous paper (Romani and Beffagna, 1991 [35] ), and determined by a Packard TriCarb counter after addition of 10 ml scintillation liquid (Hionic Fluor, Packard).…”

“…The present work deals with the results of some experiments aimed at characterizing in vivo both features of the Ca 2+ fluxes and the significance of the Ca 2+ pump-mediated H + /Ca 2+ exchanges at plasmalemma level in Egeria densa leaves. This material is particularly suitable for in vivo transport studies and accurate pH cyt measurements, and has been extensively characterized in the past in our laboratory (Marrè et al, 1987 [26] ; Beffagna and Romani, 1988 [3] , 1989 [4] , 1991 [5] ; Marrè et al, 1989 [27] ; Romani and Beffagna, 1991 [35] ; Beffagna et al, 1995 [6] ; Meraviglia et al, 1996 [28] ). Some results, aimed at a better understanding of the sequence of events occurring in adult tissues under ABA treatment, are also presented, suggesting the possible involvement of Ca 2+ -ATPase activity in inducing the -∆H + decrease and early cytoplasmic acidification, previously detected in the presence of ABA, either in leaves of barley and Elodea densa or in Arabidopsis thaliana seedlings (Beffagna, 1992 [2] , Beffagna et al, 1995 [6] , 1997 [7] ).…”