Journal
NEW PHYTOLOGIST
Volume 186, Issue 2, Pages 373-384Publisher
WILEY
DOI: 10.1111/j.1469-8137.2009.03169.x
Keywords
barley (Hordeum vulgare); efflux; ion channels; membrane integrity; potassium transport; salt stress
Categories
Funding
- University of Toronto
- Natural Sciences and Engineering Research Council of Canada (NSERC)
- Canada Research Chair (CRC) program
- Canadian Foundation for Innovation (CFI)
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Stimulation of potassium (K+) efflux by sodium (Na+) has been the subject of much recent attention, and its mechanism has been attributed to the activities of specific classes of ion channels. The short-lived radiotracer K-42(+) was used to test this attribution, via unidirectional K+-flux analysis at the root plasma membrane of intact barley (Hordeum vulgare), in response to NaCl, KCl, NH4Cl and mannitol, and to channel inhibitors. Unidirectional K+ efflux was strongly stimulated by NaCl, and K+ influx strongly suppressed. Both effects were ameliorated by elevated calcium (Ca2+). As well, K+ efflux was strongly stimulated by KCl, NH4Cl and mannitol, and NaCl also stimulated (NH4+)-N-13 efflux. The Na+-stimulated K+ efflux was insensitive to cesium (Cs+) and pH 4.2, weakly sensitive to the K+-channel blocker tetraethylammonium (TEA(+)) and quinine, and moderately sensitive to zinc (Zn2+) and lanthanum (La3+). We conclude that the stimulated efflux is: specific neither to Na+ as effector nor K+ as target; composed of fluxes from both cytosol and vacuole; mediated neither by outwardly-rectifying K+ channels nor nonselective cation channels; attributable, alternatively, to membrane disintegration brought about by ionic and osmotic components; of limited long-term significance, unlike the suppression of K+ influx by Na+, which is a greater threat to K+ homeostasis under salt stress.
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