The respiratory burst and electrolyte leakage induced by sulfhydryl blockers in egeria densa leaves are associated with H2O2 production and are dependent on Ca2+ influx.

In leaves of Egeria densa Planchon, N-ethylmaleimide (NEM) and other sulfhydryl-binding reagents induce a temporary increase in nonmitochondrial respiration (DeltaQO2) that is inhibited by diphenylene iodonium and quinacrine, two known inhibitors of the plasma membrane NADPH oxidase, and are associated with a relevant increase in electrolyte leakage (M. Bellando, S. Sacco, F.

A Mutant of Arabidopsis thaliana with a Reduced Response to Fusicoccin. I.

Because fusicoccin (FC) has the the capacity to promote solute uptake, a selective procedure for isolating mutants of Arabidopsis thaliana with a reduced response to the toxin has been developed. The procedure is based on the incubation of A. thaliana seedlings in a solution containing the cation Paraquat (Pq) at a concentration that per se does not produce bleaching of the leaves upon illumination but does in the presence of FC because of the increased uptake of the toxic cation.

Ethanol-Induced Activation of ATP-Dependent Proton Extrusion in Elodea densa Leaves.

In Elodea densa leaves, ethanol up to 0.17 m stimulates H(+) extrusion activity. This effect is strictly dependent on the presence of K(+) in the medium and is suppressed by the presence of the plasmalemma H(+)-ATPase inhibitor vanadate.

Plasmalemma redox activity and h extrusion: I. Activation of the h-pump by ferricyanide-induced potential depolarization and cytoplasm acidification.

Ferricyanide reduction by Elodea densa leaves, in the dark, is associated with: (a) acidification of the medium; (b) decrease (about 0.2-0.3 units) of intracellular pH (measured in cell sap, cytoplasm, and vacuole); (c) depolarization of the transmembrane potential; (d) net efflux of K(+) to the medium.

Stimulation of Weak Acid Uptake and Increase in Cell Sap pH as Evidence for Fusicoccin- and K-Induced Cytosol Alkalinization.

In maize root segments fusicoccin induced a consistent increase in cell sap pH (taken as representative of vacuolar pH). This effect was markedly enhanced by the presence of K(+) in the medium, whereas in the absence of fusicoccin K(+) did not significantly influence cell sap pH. Treatment with a weak acid at 2 mm concentration inhibited the uptake of a different ((14)C-labeled) weak acid fed at a lower concentration, thus suggesting that acidification of the cytoplasm inhibits weak acid uptake.

H extrusion and potassium uptake associated with potential hyperpolarization in maize and wheat root segments treated with permeant weak acids.

The rapid uptake of weak acids permeant in the uncharged form is accompanied in maize and wheat root segments by a hyperpolarization of the transmembrane electrical potential and an increase in K(+) uptake, suggesting a stimulation of the plasmalemma H(+) pump. The evaluation of weak acid-induced H(+) extrusion must take into account the alkalinization of the medium due to the rapid uptake of the uncharged form of the acid, partially masking the proton pump-mediated extrusion of H(+). The data corrected for this interference show that the lipophilic butyric acid and trimethyl acetic acid induce in maize and in wheat root segments a significant increase in ;real' H(+) extrusion, roughly matching the increase in net K(+) uptake.

Transmembrane electrical potentials in growing maize roots : Anti-auxin effects.

The anti-auxin 4-chlorophenoxyisobutyric acid (PCIB) applied at a concentration of 10(-2) mol m(-3) to maize root segments was found to induce a transmembrane electrical potential of up to-130 mV (Δpd of 30 mV). The kinetics of this response were comparable to the time scale for PCIB-stimulated H(+)-extrusion. Both effects are eliminated by the addition of p-fluoromethoxycarbonyl cyanide phenylhydrazone (FCCP).