Galvanic Stimulation of Volvox globator I. Electroosmotic Patterns Associated with the Ion Exchange Properties.

Application of direct electric potentials across immobilized Volvox globator colonies produced patterns in the ambient solution that were observable by dark field microscopy by the use of polystyrene spheres in the medium. Two large elliptical swirls occurred immediately adjacent to the colony nearest the anode. A clear area developed outwards from the cathodal side of the colony. Since similar patterns were obtained with live, dead, and deflagellated colonies, it was assumed that the phenomena were purely physical. The electric potential induced an electroosmosis in the glass stimulation chamber. Live or dead colonies, immobilized by being secured with a glass coverslip, experienced an anodal movement of water and associated polystyrene spheres. The electroosmosis gave rise to solution patterns which were shown not to be the result of hydrostatic pressure (turbulence) or thermal convection currents. When anion-exchange beads were substituted for colonies in the stimulation chamber, application of the electric potential produced a smooth laminar flow around the positively charged beads. Cation-exchange beads, on the other hand, produced 2 large anodal swirl patterns. Clearly, the colony surface behaved like a weakly charged cation exchanger. Other investigators have determined that the cell walls of pond water plants and algae are negatively charged and have ion-exchange abilities. The negatively charged Volvox cell wall caused an electroosmosis in the colony, in the cathodal direction. Previous explanations for the galvanotaxis of Volvox are not adequate because they do not take into account the negatively charged cell wall.