Effects of microtubule agents on the spatial and electrical properties of the plasma membrane inChara corallina.

The freshwater algaChara corallina Klein ex Willd., em. R.D.W. (=C. australis R.Br.) develops alternating outward (acid) and inward (alkaline) current areas on its surface when illuminated. Exposure of cells to vinblastine, colchicine, or oryzalin caused a reduction in and a shifting of this extracellular current pattern. Removal of these agents from the bathing media resulted in regeneration of the initial current profile. Because these agents all affect tubulin, microtubules may be responsible for orchestrating the transmembrane currents responsible for the acid and alkaline banding phenomenon. Analysis of the membrane potential showed a fast depolarization after vinblastine exposure; however, analysis of the current-voltage curve did not show a change in membrane conductance. A 30-min colchicine treatment decreased the conductance of the plasma membrane with either an hyperor a depolarization in the membrane potential. In contrast, although a 9-h exposure to oryzalin caused a major reduction in the extra-cellular current pattern, only minor changes were observed in the membrane potential and conductance. However, in the presence of oryzalin, the time constants in the light response of the membrane potential increased over this 9-h period. Collectively, these results implicate an involvement of microtubules in spatial control of plasma-membrane transport events inC. corallina.