Membrane depolarization induces K⁺ efflux from subapical maize root segments

Abstract

Summary• The role of potassium efflux from maize ( Zea mays ) root segments in maintaining transmembrane electric potential difference (E m ) was studied in vivo , together with the involvement of outward rectifying K + channels (ORCs).• Measurements were made of the efflux of potassium (K + ) from roots when its uptake was competitively inhibited by rubidium (Rb + ), of the E m of the root cells by microelectrodes and of the unidirectional fluxes of monovalent cations.• The influx of Rb + , caesium (Cs + ) or ammonium (NH 4 + ) into the segments induced an efflux of K + . Lithium (Li + ) and sodium (Na + ) were not taken up and did not induce K + efflux. The permeating cations induced membrane depolarizations, which were closely related to the values of K + efflux. Two K + -channel blockers, tetraethylammoniumchloride and quinidine, inhibited K + efflux. The inhibition was accompanied by a higher membrane depolarization induced by Rb + , whose influx was not affected.• The results suggest that a depolarizing event caused by cation uptake increased K + efflux from the cells, probably through the activation of ORCs involved in restoration and stabilization of E m .

Sodium as nutrient and toxicant

“…Thus, a suppression of [K + ] cyt is one of the clear consequences of sodium's actions (perhaps not necessitating the invoking of the miraculous powers of a "cytosolic K + /Na + ratio"), as is a depolarization of the plasma-membrane potential, both instantaneously, upon first exposure to Na + (Shabala et al 2003(Shabala et al , 2006Mian et al 2011;cf. Bowling andAnsari 1971, 1972;Cheeseman 1982;Nocito et al 2002), and in the longer term (Malagoli et al 2008) (Fig. 1a).…”

K+ transport in plants: Physiology and molecular biology

“…Pharmacological agents that have been extensively tested on channel-mediated transport systems in animals (Hille, 1992), including TEA + , Cs + , Ba 2+ , calcium (Ca 2+ ), lanthanum (La 3+ ), and quinidine, have powerful effects on plant systems, demonstrating strong similarities between the two kingdoms (Leonard et al, 1975; Ketchum and Poole, 1990;Blatt, 1992;Wegner et al, 1994; Roberts and Tester, 1995;White and Lemtiri-Chlieh, 1995;Nocito et al, 2002; also see below).…”

Salinity-induced ion flux patterns from the excised roots of Arabidopsis sos mutants

“…Salinity may reduce K + uptake as a result of competition between Na + and K + for plasma membrane uptake sites (Tyerman and Skerrett 1999;Maathuis and Amtmann 1999;Tester and Davenport 2003). Furthermore, salt stress causes an excessive leakage of K + from the cell (Shabala 2000;Shabala et al 2003;Chen et al 2005), primarily due to plasma membrane depolarisation (Nocito et al 2002;Shabala et al 2003). It is not clear which of the numerous K + transport systems at the plasma membrane might be affected by the SOS signalling pathway, and what are their modes of regulation.…”