Ion compartmentation in the red alga Caloglossa leprieurii in response to salinity changes: freeze-substitution and X-ray microanalysis

Abstract

The elemental content of cell compartments in the euryhaline red macroalga Caloglossa leprieurii (Montague) J. Agardh subjected to different salinities, was determined by X-ray microanalysis of freeze-substituted thin sections. Duty are given for three compartments; cell wall, vacuole and cytoplasm. The most abundant elements detected were potassium, sodium and chlorine, with a Sulphur peak in the cell wall indicating the presence of sulphated polysaccharides. With salinity upshock the cytoplasm is maintained low in K, Na and Cl, whereas in the vacuoles they increased. High levels of K and Na located in the cell wall reflect cation binding to negatively charged polysaccharides. Hyposaline shock resulted in decreased K, Na and Cl levels in all compartments, though K was retained in the cytoplasm. Results are discussed with regard to the role of ion compartmentation in the salt tolerance of this alga, and the cation exchange properties of the cell wall are emphasized.

Keywords: Caloglossa; X-ray microanalysis; freeze-substitution; ion compartmentation; salt tolerance.