Abstract

<jats:p> By insertion of microelectrodes into the vacuoles of two adjacent internodal cells of Chara corallina, the changes of the potential differences across the plasma membranes and node were noted when a current of 0.40 μA was passed through the cells bathed in artificial pond water. When the solution bathing one cell was changed to artificial pond water + 10<jats:sup>2</jats:sup> mol m<jats:sup>−3</jats:sup> mannitol, a significant increase was detected both in the membrane potential difference response and in the nodal potential difference response. This indicates that the lowering of turgor on one cell by 0.24 MPa increased the electrical resistance of the membrane of that cell and also the resistance of the plasmodesmata connecting the two internodal cells via the node. This is evidence in support of valving in plasmodesmata when a pressure difference is induced across their ends. </jats:p>