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• 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. [ABSTRACT FROM AUTHOR]

• Aluminum (Al) is toxic to plants when solubilized into Al3+ in acidic soils, and becomes a major factor limiting plant growth. However, the primary cause for Al toxicity remains unknown. • Nitric oxide (NO) is an important signaling molecule modulating numerous physiological processes in plants. Here, we investigated the role of NO in Al toxicity to Hibiscus moscheutos. • Exposure of H. moscheutos to Al3+ led to a rapid inhibition of root elongation, and the inhibitory effect was alleviated by NO donor sodium nitroprusside (SNP). NO scavenger and inhibitors of NO synthase (NOS) and nitrate reductase had a similar inhibitory effect on root elongation. The inhibition of root elongation by these treatments was ameliorated by SNP. • Aluminum inhibited activity of NOS and reduced endogenous NO concentrations. The alleviation of inhibition of root elongation induced by Al, NO scavenger and NOS inhibitor was correlated with endogenous NO concentrations in root apical cells, suggesting that reduction of endogenous NO concentrations resulting from inhibition of NOS activity could underpin Al-induced arrest of root elongation in H. moscheutos. [ABSTRACT FROM AUTHOR]