Ca-selective microelectrodes and their application to plant cells and tissues.

The use of Ca(2+)-selective microelectrodes is difficult because of some basic problems: (a) electrodes with submicron tips may display non-Nernstian slopes; (b) liquid membrane microelectrodes respond only slowly (within seconds) to changes in ion activity; (c) turgid plant cells with tough walls damage the sensitive tip. This article describes concisely recent advances in fabricating Ca(2+)-selective single and double-barreled microelectrodes and their intracellular applications to different plant cell materials. Beveling the electrodes, mixing the sensor components with polyvinylchloride, insulation of the hydrated glass, and stabilization of the tips with inert materials are considered the basic concepts to circumvent most difficulties. It is concluded that the Ca(2+)-electrode can be a useful tool in plant physiology, but in spite of recent progress this technique remains experimentally demanding.