Growth and the Current Pattern Around Internodal Cells ofNitella flexilisL.

The ionic currents that traverse the internodal cells of the green alga Nitella flexilis L. have been measured with an extracellular vibrating probe. In adult interriodes illuminated with white light a pattern of self-generated currents exists along the cell, featuring alternating zones of inward and outward current. At inward current zones current densities of up to 25 μA cm⁻² were measured, at outward current zones the maximal density recorded was 7.5 μA cm⁻². The zones with inward current had an average length of 1.0 mm, and those with outward current averaged 1.5 mm. When the light was turned off the overall current density decreased drastically and the pattern changed. Currents first appear in growing internodal cells that are about 1.0 mm long. With increasing length a current pattern develops, with the zones of inward and outward current at first shifting laterally along the surface. Only in adult cells do the zones become stationary and form a typical current pattern. In addition to the current pattern different chloroplast volumes can be observed along the internode. In outward current zones the volumes of chloroplasts are 3.2 times those of inward current zones. The natural current pattern observed in Nitella internodes causes loops of electric current that extend outward from the cell surface into the bathing medium. We speculate that these current loops might provide a mechanism of electrophoretic ion transport through the medium. Such a mechanism could increase the supply of $HCO3-$ for the internodal cells in their natural stagnant water habitat.