PT  - JOURNAL ARTICLE
AU  - Shabala, Sergey
AU  - Demidchik, Vadim
AU  - Shabala, Lana
AU  - Cuin, Tracey A.
AU  - Smith, Susan J.
AU  - Miller, Anthony J.
AU  - Davies, Julia M.
AU  - Newman, Ian A.
TI  - Extracellular Ca<sup>2+</sup> Ameliorates NaCl-Induced K<sup>+</sup> Loss from Arabidopsis Root and Leaf Cells by Controlling Plasma Membrane K<sup>+</sup>-Permeable Channels
AID  - 10.1104/pp.106.082388
DP  - 2006 Aug 01
TA  - Plant Physiology
PG  - 1653--1665
VI  - 141
IP  - 4
4099  - http://www.plantphysiol.org/content/141/4/1653.short
4100  - http://www.plantphysiol.org/content/141/4/1653.full
SO  - Plant Physiol.2006 Aug 01; 141
AB  - Calcium can ameliorate Na+ toxicity in plants by decreasing Na+ influx through nonselective cation channels. Here, we show that elevated external [Ca2+] also inhibits Na+-induced K+ efflux through outwardly directed, K+-permeable channels. Noninvasive ion flux measuring and patch-clamp techniques were used to characterize K+ fluxes from Arabidopsis (Arabidopsis thaliana) root mature epidermis and leaf mesophyll under various Ca2+ to Na+ ratios. NaCl-induced K+ efflux was not related to the osmotic component of the salt stress, was inhibited by the K+ channel blocker TEA+, was not mediated by inwardly directed K+ channels (tested in the akt1 mutant), and resulted in a significant decrease in cytosolic K+ content. NaCl-induced K+ efflux was partially inhibited by 1 mm Ca2+ and fully prevented by 10 mm Ca2+. This ameliorative effect was at least partially attributed to a less dramatic NaCl-induced membrane depolarization under high Ca2+ conditions. Patch-clamp experiments (whole-cell mode) have demonstrated that two populations of Ca2+-sensitive K+ efflux channels exist in protoplasts isolated from the mature epidermis of Arabidopsis root and leaf mesophyll cells. The instantaneously activating K+ efflux channels showed weak voltage dependence and insensitivity to external and internal Na+. Another population of K+ efflux channels was slowly activating, steeply rectifying, and highly sensitive to Na+. K+ efflux channels in roots and leaves showed different Ca2+ and Na+ sensitivities, suggesting that these organs may employ different strategies to withstand salinity. Our results suggest an additional mechanism of Ca2+ action on salt toxicity in plants: the amelioration of K+ loss from the cell by regulating (both directly and indirectly) K+ efflux channels.