Ethylene activates a plasma membrane Ca(2+)-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 Ca(2+) activity ([Ca(2+)](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 Ba(2+), Mg(2+) and Ca(2+), and inhibited by La(3+), Gd(3+) and Al(3+). The ethephon- and ACC-induced Ca(2+)-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 Ca(2+)-permeable channels results from ethylene. Ethephon elicited an increase in the [Ca(2+)](c) of tobacco suspension cells, as visualized by the Ca(2+)-sensitive probe Fluo-3 and confocal microscopy. The ethephon-induced elevation of [Ca(2+)](c) was markedly inhibited by Gd(3+) and BAPTA, suggesting that an influx of Ca(2+) underlies the elevation of [Ca(2+)](c). These results indicate that an elevation of [Ca(2+)](c), resulting from activation of the plasma membrane Ca(2+)-permeable channels by ethylene, is an essential component in ethylene signaling in plants.