Subcellular Distribution of Free Amino Acids in Relation to Protein Synthesis in Cells of Chara corallina

Abstract

AbstractThe influence of protein‐synthesis inhibitors on the subcellular distribution of free amino acids was studied in internodal cells of Chara corallina. Use of an intracellular perfusion technique allowed separate measurements of amino acids in the vacuole, in the flowing sol endoplasm and in the gel layer. The sol endoplasm predominantly represents the cytosol, while the gel layer is occupied, for the most part, by chloroplasts.When cells were treated with 0.5 mM chloramphenicol (CRP) in the dark, both the total concentration of amino acids and the subcellular distribution were almost the same as in cells without treatment. In the light, however, the subcellular distribution changed dramatically, although the total concentration of amino acids was unchanged. The vacuolar concentration of amino acids was 3 times greater in CRP‐treated cells than in the control. The concentrations of amino acids in the sol endoplasm and in the gel layer were only half of those in the control. Amino acid permeability of the chloroplast envelope, measured using the perfused internodal cells, slightly increased after the CRP treatment in the light.Time‐dependent changes in concentrations of amino acids in the CRP‐treated cells were also measured in the light. The total concentration of amino acids in the cytoplasm gradually decreased, while that in the vacuole increased commensurately. The concentration and/or subcellular distribution of alanine, glutamine, glutamate and glycine changed dramatically. The concentration of alanine increased considerably both in the vacuole and in the cytoplasm. The cytoplasmic concentration of glutamine increased transiently within 1 −2 h after treatment with CRP. The cytoplasmic concentrations of glutamate and glycine decreased. Although the concentrations of some amino acids changed so markedly both in the vacuole and cytoplasm, only small differences in the activities of glutamic‐pyruvic transaminase, glutamic‐oxaloacetic transaminase and glutamine synthetase were detected between the control and the CRP‐treated cells.