Tonoplast Action Potential of Characeae

Abstract

The plasmalemma action potential was found to be indispensable to the production of the tonoplast action potential. In a solution lacking Ca2+ and containing other divalent cations such as Ba2+, Mg2+ or Mn2+, the plasmalemma excited in Nitella but did not in Chara. In Nitella, however, both the tonoplast action potential and EC-coupling were abolished due to depletion of Ca2+ from the external medium. Ca2+ ions injected into the cytoplasmic layer caused a transient change in both plasmalemma and tonoplast potentials. These results suggest that a transient rise in Ca2+ concentration during excitation of the plasmalemma may trigger the tonoplast action potential.