PROTEIN-SYNTHESIS IN HALOPHYTES - THE INFLUENCE OF POTASSIUM, SODIUM AND MAGNESIUM INVITRO

The amino acid (S-35-methionine) incorporating activity of an in vitro wheat germ translation system was found to be maximal in 80 to 125 mol m-3 K with 2 to 4 mol m-3 Mg both as the acetate. Substitution of Na for K, or chloride for acetate at concentrations above 80 mol m-3 inhibited incorporation. When the K acetate concentration was raised to 200 mol m-3, no incorporation of radioactive methionine occurred. Translation by polysomes extracted from leaf tissue of S. maritima, supplemented with post-ribosomal supernatant from wheat germ, showed activity which was optimal in the presence of 225 mol m-3 K acetate and 8 mol m-3 Mg acetate. However, the translation system was not directly comparable with the wheat germ system, as studies with an initiation inhibitor, aurintricarboxylic acid, suggested that the S. maritima system was essentially elongation-dependent, while initiation occurred in the wheat germ system. Elongation-dependent polysomal preparations were extracted from leaves of the glycophytes Pisum sativum, Triticum aestivum, Oryza sativa and Hordeum vulgare, and from the halophytes Atriplex isatidea and Inula crithmoides. Translation by polysomes from the salt-tolerant plants was optimal at higher K and Mg concentrations, than by polysomes from the glycophytes. Furthermore, NaCl was better able partially to substitute for the role of K in polysomal preparations from halophytes than glycophytes.