Ethylene activates a plasma membrane Ca2+-permeable channel in tobacco suspension cells

Here, the effects of the ethylene-releasing compound, ethephon, and the ethylene precursor, 1-aminocyclopropane-1-carboxylic acid (ACC), on ionic currents across plasma membranes and on the cytosolic Ca2+ activity ([Ca2+](c)) of tobacco (Nicotiana tabacum) suspension cells were characterized using a patch-clamp technique and confocal laser scanning microscopy. Exposure of tobacco protoplasts to ethephon and ACC led to activation of a plasma membrane cation channel that was permeable to Ba2+, Mg2+ and Ca2+, and inhibited by La3+, Gd3+ and Al3+. The ethephon- and ACC-induced Ca2+-permeable channel was abolished by the antagonist of ethylene perception (1-metycyclopropene) and by the inhibitor of ACC synthase (aminovinylglycin), indicating that activation of the Ca2+-permeable channels results from ethylene. Ethephon elicited an increase in the [Ca2+](c) of tobacco suspension cells, as visualized by the Ca2+-sensitive probe Fluo-3 and confocal microscopy. The ethephon-induced elevation of [Ca2+](c) was markedly inhibited by Gd3+ and BAPTA, suggesting that an influx of Ca2+ underlies the elevation of [Ca2+](c). These results indicate that an elevation of [Ca2+](c), resulting from activation of the plasma membrane Ca2+-permeable channels by ethylene, is an essential component in ethylene signaling in plants.