Ion transport and metal sensitivity of vacuolar channels from the roots of the aquatic plant Eichhornia crassipes

Abstract

Using the patch-clamp technique, we investigated the transport properties of vacuolar ion channels from the roots of water hyacinth, Eichhornia crassipes (Mart. Solms, Pontederiacae). Eichhornia crassipes vacuoles displayed large voltage-dependent rectifying slow-vacuolar (SV) currents, which activated in a few seconds at positive potentials and deactivated at negative voltages in a few hundreds of millseconds. Similarly to SV channel previously identified in the tonoplast of terrestrial plants, SV currents in E. crassipes were activated by micromolar concentrations of Ca 2+ and current slightly increased (25%) on addition (10 m M ) of the reducing agent dithiothreitol (DTT). Eichhornia crassipes SV channels were equally permeable to K + and Na + . The permeability sequence derived from current values is: K + ≈ ≈ ≈ ≈ Na + > Rb + > NH 4 + ≈ ≈ ≈ ≈ Cs + >> TEA + . Excised membrane patches displayed single channel transitions typical of SV-type single channel openings with a conductance of (83·0 ± ± ± ± 5·6) pS; a smaller channel with a conductance of (31·0 ± ± ± ± 2·7) pS was also identified. Metals such as Ni 2+ and Zn 2+ decreased the vacuolar current in a reversible manner. However, although Zn 2+ inhibition is comparable to that induced by the same metal in vacuoles from the main root of sugar beet ( Beta vulgaris L.), the inhibition of the SV currents by Ni 2+ is not as substantial in E. crassipes as in sugar beet. To our knowledge, this is the first electrophysiological characterization of ionic transport in E. crassipes , a pervasive troublesome aquatic weed, which has exceptional absorption properties of several water contaminants such as heavy metals, pesticides and phenols.

Assessment of the Hyperaccumulating Lead Capacity of Salvinia minima Using Bioadsorption and Intracellular Accumulation Factors

“…membrane transporters) and/or facilitated diffusion (ion channels). Most of the reports dealing with lead transport are related to terrestrial plants (Sunkar et al 2000;Wang et al 2007) and little is known about floating aquatic plants (Paganetto et al 2001). Olguín et al (2005) have suggested that in S. minima, Pb 2+ is accumulated intracellularly through the use of calcium channels.…”

K+ currents through SV‐type vacuolar channels are sensitive to elevated luminal sodium levels

“…, 1994; Dobrovinskaya et al. , 1999; Paganetto et al. , 2001; Schulz‐Lessdorf and Hedrich, 1995; Weiser et al.…”

Mechanism of luminal Ca2+ and Mg2+ action on the vacuolar slowly activating channels

“…In addition, different factors, such divalent cations (Pottosin et al 2001), polyamines (Dobrovinskaya et al 1999a(Dobrovinskaya et al , 1999b, and heavy metals (Paganetto et al 2001;Carpaneto 2003), control the ion flux through the open channel. Most studies have concentrated on the regulation of the SV channel by cytosolic factors.…”