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

The -,vay in which the various activities of a cell relate to the level of available energy can conveniently be studied in photosynthetic cells of size large enough to permit measurements on individual cells. Internodal cells of the Characeae approach ideality for such a purpose in that they are, to a good approximation, right circular cylinders of macroscopic dimensions. Moreover, a certain internal symmetry prevails in that the chloroplasts are uniformly distributed in a single layer in the outer, nonstreaming layer of cytoplasm. The purpose of this study was to investigate the manner in which light intensity and the composition of the external medium interact to influence a number of cellular activities and properties including sodium influx, membrane potential, the Na, K, and Cl concentrations in the vacuole, and protoplasmic streaming. For this, mature internodal cells of Nitella clavata were placed under a number of environmental concitions in each of which light intensity, solution Comllposition, and temperature were kept constant. The Na influxes and rates of protoplasmic streaming reported here are the constant rates eventually established under a given set of conditions. These constant rates are indicative of a stabilization of certain metabolic processes, but the establishment of steadystate concentrations of the cellular constituents cannot be claimed.