Ion distribution and transport in the red marine algae, gracilaria foliifera.

Abstract

1. Distribution and transport of alkali and halide ions were studied in Gracilaria foliifera, a red marine alga. Ion concentrations, fluxes and rate coefficients were measured with radioisotopes and standard chemical techniques. The intracellular (vacuole) potential was measured with microcapillary electrodes and a high-impedance voltmeter.2. Intracellular ion concentrations were estimated after correcting for 89% tissue water and 19% extracellular space. Intracellular concentrations of the major ions were (meq./kg. cell water): Na+, 66; K+, 680; Cl-, 462. All of the intracellular ions except I- appeared to be completely exchangeable and were probably in solution in the large cell vacuole.3. Nernst equilibrium potentials, calculated for each ion under conditions of approximate flux equilibrium, were (mv.) : Na+, 50; K+, -105; Rb+, -127; Cs+, -85; Cl-, -4; Br-, -14; and I-, +128. Comparison of these values with the measured vacuole potential of -81 mv. suggested active extrusion of Na+ and active uptake of K+, Rb+, Cl- and Br-. Cesium was in approximate electrochemical equilibrium, and the status of I- was uncertain due to some intracellular binding.4. Cation fluxes were stimulated by light and, to a lesser extent, by exogenous substrate (glutamate). Previous exposure to light had a temporary stimulating effect on cation fluxes, provided oxygen was present. Anaerobiosis (nitrogen) depressed both influx and efflux of cations. Rate coefficients for the cation were in the order Na+ > K+ > Rb+,Cs+.5. Anion fluxes were variably affected by light. Chloride uptake was promoted by light, Br- uptake was slightly stimulated, and I- uptake was depressed. Anion efflux, however, was consistently stimulated by light. Anaerobiosis inhibited the uptake of all anions. Rate coefficients for anion fluxes were similar to each other but were generally lower than the rate coefficients for cation fluxes.6. With the exception of I-, neither light nor anaerobiosis had much effect on the steady-state distribution of ions in Gracilaria. The intracellular I- concentration was much higher in the dark than in the light. This was also found in several other seaweeds, and appeared to be due to an increased amount of bound I- in non-photosynthesizing tissues.