Higher plants sense and respond to osmotic and mechanical stresses such as turgor, touch, flexure and gravity. Mechanosensitive (MS) channels, directly activated by tension in the cell membrane and cytoskeleton, are supposed to be involved in the cell volume regulation under hypotonic conditions and the sensing of these mechanical stresses based on electrophysiological and pharmacological studies. However, limited progress has been achieved in the molecular identification of plant MS channels. Here, we show that MCA1 (mid1-complementing activity 1; a putative mechanosensitive Ca ( 2+) -permeable channel in Arabidopsis thaliana) increased MS channel activity in the plasma membrane of Xenopus laevis oocytes. The functional and kinetic properties of MCA1 were examined by using a Xenopus laevis oocytes expression system, which showed that MCA1-dependent MS cation currents were activated by hypo-osmotic shock or by membrane stretch produced by pipette suction. Single-channel analyses suggest that MCA1 encodes a possible MS channel with a conductance of 34 pS.
