REGULATION OF CHANNEL ACTIVITY UNDERLYING CELL-VOLUME AND POLARITY SIGNALS IN FUCUS

Polarized zygotes of the marine alga Fucus have been used to investiga te the spatial control of Ca2+ signals in a plant cell during apical g rowth and cell volume regulation in response to external osmotic fluct uations. UV laser microsurgery has been refined to enable plasma membr ane patch clamp recordings from localized regions of the polarizing or polarized zygote. A plasma membrane cation channel that is mechanosen sitive and significantly permeable to Ca2+ was characterized in cell-a ttached and excised patch configurations. Parallel measurements of int racellular Ca2+ using ratio photometric and imaging techniques were us ed to monitor temporal and spatial changes in cytoplasmic Ca2+ (Ca-cyt (2+)) in response to activation of these ion channels by osmotic swell ing of the rhizoid. In polarized rhizoid cells spatial regulation of v oltage- and mechanosensitive-Ca2+ channels in the plasma membrane unde rlie changes in Ca2+ that are crucial in signal-response transduction. Direct mechanical stimulation of channels in the plasma membrane of i solated sub-protoplasts from the apex of rhizoid cells can elicit chan ges in Ca2+ in the underlying cytosol.