PROTEIN-BIOSYNTHESIS IN SALT-SHOCKED CELLS OF STICHOCOCCUS-BACILLARIS(CHLOROPHYCEAE)

We have developed an in vivo C-14-amino acid labelling procedure for m onitoring protein synthesis in salt-shocked cells of Stichococcus baci llaris Naeg. This alga possesses an efficient transport system for the uptake of leucine, methionine, and phenylalanine and rapidly incorpor ates these amino acids into proteins. Of the three amino acids tested, C-14-phenylalanine is ideally suited for labelling proteins in S. bac illaris, as it establishes an early equilibrium between uptake and inc orporation of the amino acid into proteins. The uptake of phenylalanin e shows little inhibition following transfer of cells to higher salini ties and is also not affected in short-term experiments by the presenc e of the protein inhibitors cycloheximide and chloramphenicol. While S tichococcus bacillaris grows slowly at salinities equal to, or higher than, 150% artificial seawater (ASW), it shows surprising rates of rec overy of major physiological functions following considerable salt sho cks. Cells transferred from 33 to 150% ASW show complete recovery of p hotosynthetic activity and protein synthesis within 10-15 min, and cel ls transferred from 33 to 300% ASW recover 50% of their capacity to sy nthesize proteins within 1 h. Cytoplasmic and organellar protein synth esis appear to be equally sensitive to the effects of salt shocks acco rding to studies with protein synthesis inhibitors.