Regulation of Turgor Pressure in Marine Algae: Ions and Low-molecular-weight Organic Compounds

Abstract

Seventeen species of thalloid or giant-celled marine algae representing the three major classes, Chlorophyceae, Rhodophyceae and Phaeophyceae maintain turgor pressure constant over the range of 470-1860 mosmol/kg external osmotic concentration. This is achieved by changing internal concentrations of Na+, K+ and Cl-. Three different groups can be distinguished: (1) species with high Na+ ; (2) those with high K+; and (3) algae with both cations in about equal amounts. In general, a Cl- pump seems to be involved in turgor regulation. There is no correlation between ion composition and taxonomic class. The concentration of low-molecular-weight organic compounds also changes during regulation. As a rule, these compounds are the main photosynthetic products and are probably located in the cytoplasm.