Relationship of Cell Transmembrane Electropotential to Potassium and Sodium Accumulation Ratios in Oat and Pea Seedlings

Abstract

Many higher plants contain more potassium than sodium in their cells even though the surrounding medium usually contains more sodium than potassium (2). This situation is found also in the bacterium Escherichia coli (10), in a variety of animal cells (6, 11), and in the cells of several lower plants (1, 8, 9). In the squid axon (6), the low internal sodium and the high internal potassium concentrations appear to be maintained by a sodium pump which transports sodium out of the cell against an electrochemical potential gradient. There is also an inwardly directed potassium pump, but because of the relatively high permeability of the cell membrane to potassium, the distribution of potassium is close to that predicted by passive movement under the action of the concentration gradient and electrical forces only. Investigations have shown that the low internal concentrations of sodium and the high internal concentrations of potassium in other animal cells and in the cells of certain bacteria and lower plants appear also to be the result of an active efflux mechanism for sodium and either an active influx mechanism for passive distribution of potassium. In view of these apparently general phenomena, I was interested in seeing whether some higher plant cells maintained low internal sodium and high internal potassium concentrations in the same way as these other cells. Electrochemical theory provides the best criteria for active transport. If an ion is in passive flux equilibrium on the 2 sides of a membrane, then the concentration and electrical potentials must be related by the equation: