Journal of Experimental Botany Regulation of channel activity underlying cell volume

Polarized zygotes of the marine alga Fucus have been used to investigate the spatial control of Ca2 + signals in a plant cell during apical growth and cell volume regulation in response to external osmotic fluctu-ations. UV laser microsurgery has been refined to enable plasma membrane patch clamp recordings from localized regions of the polarizing or polarized zygote. A plasma membrane cation channel that is mechano-sensitive and significantly permeable to Ca2 + was characterized in cell-attached and excised patch con-figurations. Parallel measurements of intracellular Ca2 + using ratio photometric and imaging techniques were used to monitor temporal and spatial changes in cytoplasmic Ca2 + (Ca~~) in response to activation of these ion channels by osmotic swelling of the rhizoid. In polarized rhizoid cells spatial regulation of voltage-and rnechanosensltive-ca " + channels in the plasma membrane underlie changes in Ca2 + that are crucial in signal-response transduction. Direct mechanical stimulation of channels in the plasma membrane of isolated sub-protoplasts from the apex of rhizoid cells can elicit changes in Ca2 + in the underlying cytosol