Effects of mechanical signaling on plant cell cytosolic calcium.

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Abstract
Mechanical signals are important influences on the development and morphology of higher plants. Using tobacco transformed with the Ca(2+)-sensitive luminescent protein aequorin, we recently reported the effects of mechanical signals of touch and wind on the luminescence and thus intracellular calcium of young seedlings. When mesophyll protoplasts are isolated from these transgenic tobacco plants and mechanically stimulated by swirling them in solution, cytoplasmic Ca2+ increases immediately and transiently up to 10 microM, and these transients are unaffected by an excess of EGTA in the medium. The size of the transient effect is related to the strength of swirling. Epidermal strips isolated from transgenic tobacco leaves and containing only viable guard cells and trichomes also respond to the strength of swirling in solution and can increase their cytoplasmic Ca2+ transiently up to 10 microM. Finally, the moss Physcomitrella patens containing recombinant aequorin exhibits transient increases in cytoplasmic Ca2+ up to 5 microM when swirled in solution. This effect is strongly inhibited by ruthenium red. Our data indicate that the effect of mechanical stimulation can be found in a number of different cell types and in a lower plant as well as tobacco and suggest that mechanoperception and the resulting increase in cytoplasmic Ca2+ may be widespread.