Fluxes and compartmentation of potassium and chloride in the green alga Mougeotia

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Abstract
Some ionic relations of the filamentous green alga Mougeotia sp. have been analyzed under different light conditions. Data from influx and efflux measurements using 86Rb+ and 36Cl- fit the model of three cellular compartments (cell wall, cytoplasm, vacuole) in series. This result is remarkable, since in a Mougeotia cell at least two thirds of the cytoplasmic compartment are occupied by the cell-filling, flat and nearly rectangular chloroplast which is axially oriented. The chloroplast is concluded to be part of the cytoplasmic flux compartment. Photosynthetically saturating irradiances of continuous white light enhance the active and passive fluxes of K+ and Cl- at the plasmalemma by a factor of 3. Photosystem II is responsible for the light-dependent increase of the uptake of Cl- (36Cl-) whereas the uptake of K+ (86Rb+) depends additionally on energy from photosystem I. Ion flux measurements performed after irradiations with red and far-red, respectively, show that the fluxes of K+ and Cl- across the plasmalemma are not affected by the state of phytochrome.