Ionic Relations of Cells of Chara Australis VI. Fluxes of Potassium

Abstract

Measure-ments have been made of the kinetics of the movement of potassium into and out of single internodal cells of Chara australis, with the aid of solutions labelled with 42K. Analysis of the results suggests that an appropriate model describing the kinetics is that of three compartments connected in series[long dash]the cell wall, cytoplasm, and vacuole. In these cells, in media containing 0.1 m[image] potassium, fluxes across the tonoplast exceeded those across the plasmalemma by a factor of about 20. Fluxes across the plasmalemma ranged from about 0.4 p-equiv.cm-2.sec-l (1 p-equiv.=10-12 equiv.) when potassium was 0.1 m[image] in the external medium to 2-5 p-equiv.cm-2.sec-l when potassium concentration was rasied to 1.0 m[image]. Calcium in the external medium had the effect of reducing the rate of vacuolar labelling; biocarbonate ions and dark conditions had no significant effect on the fluxes. The present data are discussed in relation to the electric resistance of the plasmalemma in comparable cells. The conductance calculated from the estimates of passive fluxes of potassium and sodium is less than the conductance from electrical measurements by a factor of about 10. Therefore it is concluded that ions do not migrate independently of one another but may move in file in long narrow pores in both the plasmalemma and tonoplast.