Effect of Light on Sodium Influx, Membrane Potential, and Protoplasmic Streaming in Nitella

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Abstract
In Nitella clavata cells kept under constant conditions, Na influxes and protoplasmic streaming rates eventually assumed constant values. One to 5 weeks were required. Na influx was strongly correlated with light intensity, although the membrane potential and vacuolar sap concentration of Na (and thus the electrochemical gradient) were not influenced by light. Since Na movement into the cell is down an electrochemical gradient, the results may be attributable to a light-induced increase in Na permeability of the plasmalemma. Another possible explanation is that active transport occurs in the same direction as that favored by the electrochemical gradient. Na influx was also influenced by the other constituents of the external solution. Protoplasmic streaming was dependent on light intensity only below 700 ergs/cm2sec; above this the maximum rate was 107 [mu]/sec at 27[degree]. So long as a cell had adequate light for survival (120 ergs/cm2sec), the streaming rate was at least 67 [mu]/sec.