Calcium and plant action potentials

Under normal conditions the action potential in Characeae is dependent on the presence of both Cl− and Ca2+. Cl− seems to play a straightforward part as a transient depolarizing flow. The role of Ca2+, however, is emerging as an increasingly complex one: there are Ca2+ concentration changes in the cytoplasm, as well as transient Ca2+ currents across the plasmalemma and possibly the tonoplast. In most Characeae Ca2+ is necessary for the Cl− channel to function, and it is also involved in the cessation of the cytoplasmic streaming observed at the time of excitation. The function of Ca2+ at the time of the action potential is being revealed by experimental techniques of increasing sophistication. The development of these methods and possible associated artefacts are considered.