Abstract
Little is known about the effect of lead on the activity of the vacuolar K+ channels. Here, the patch-clamp technique was used to compare the impact of lead (PbCl2) on the slow-activating (SV) and fast-activating (FV) vacuolar channels. It was revealed that, under symmetrical 100-mM K+, the macroscopic currents of the SV channels exhibited a typical slow activation and a strong outward rectification of the steady-state currents, while the macroscopic currents of the FV channels displayed instantaneous currents, which, at the positive potentials, were about three-fold greater compared to the one at the negative potentials. When PbCl2 was added to the bath solution at a final concentration of 100 µM, it decreased the macroscopic outward currents of both channels but did not change the inward currents. The single-channel recordings demonstrated that cytosolic lead causes this macroscopic effect by a decrease of the single-channel conductance and decreases the channel open probability. We propose that cytosolic lead reduces the current flowing through the SV and FV channels, which causes a decrease of the K+ fluxes from the cytosol to the vacuole. This finding may, at least in part, explain the mechanism by which cytosolic Pb2+ reduces the growth of plant cells.
Highlights
The patch-clamp recordings, which were performed in the whole-vacuole configuration, showed a typical SV-type channel activity in the vacuoles that had been isolated from Beta vulgaris L. taproots
A one-minute exposure of the vacuoles to 100-μM PbCl2 caused a decrease in the SV outward current in the red beet vacuoles
From the experiments described here, we propose that cytosolic lead decreases the current flowing through the SV and FV channels
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. It is well-established that the plant vacuole is a dynamic cellular compartment that can occupy more than 90% of the cell volume and is essential to plant growth and physiological characteristics [1,2,3,4]. Potassium (K+ ) constitutes a chief osmoticum, which plays a key role, among others, in regulating turgor and cell expansion [5]. Vacuolar turgor and vacuolar signalling depend on the concerted actions of the tonoplast transporters and channels
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