Ion compartmentation in Porphyra umbilicalis determined by electron-probe X-ray microanalysis

The ion composition of cell compartments in the intertidal red alga Porphyra umbilicalis adapted for two weeks in 3.5 x artificial seawater was determined by X-ray microanalysis of unfixed, frozen, bulk specimens. A procedure is described for the calculation of ion concentrations in the main cell compartment, cytoplasm, vacuoles and plastid. The results indicate high K(+) and low Na(+) concentrations in cytoplasm and plastid. Sodium ions are preferentially localized in vacuoles. Both, vacuoles and plastid contain high Cl(-) concentrations.