Measurement of cytosolic-free Ca²+ in plant tissue.

Several techniques have been used to measure the concentration of cytosolic-free Ca(2+) ([Ca(2+)](cyt)) in plants. These include Ca(2+)-sensitive microelectrodes, luminescent photoproteins, cameleons, and fluorescent Ca2(+) indicators. Ca(2+)-sensitive microelectrodes can be used only in cells that are able to withstand impalement with two electrodes or a double-barrelled electrode. In addition, microelectrodes suffer from slow response times and difficulties with calibration. These problems are particularly acute in plant cells in which the high turgor often results in partial displacement of the sensor, and the subsequent loss of sensitivity, following impalement. Consequently, the use of Ca(2+)-sensitive electrodes has been limited to only a few studies in plants and algae.