Ca2+ effects on K+ fluxes in Arabidopsis seedlings exposed to Al3+

Potassium transport was investigated in the root elongation zone of Arabidopsis seedlings during the first minutes of Al3+ exposure, using the non-invasive MIFE microelectrode technique. To prevent pH changes during Al3+ application, and to separate aluminium from acidic stress, plants were pre-treated with 5 mm homoPIPES before addition of AICl(3). (pH 4.2). The 30-min treatment with 50 or 500 mu m AICl(3) led to a significant increase in K+ efflux in solutions containing 100 ttm CaCl2. This efflux was suppressed by high concentrations of Ca2+ (10 mm) in the bathing solution. Our results suggest that elevated external Ca2+ activities can sustain K+ influx in the root elongation zone during Al3+ exposure either by maintaining [Ca2+](cyt) or by affecting Al3+ uptake across the plasma membrane.