Protein synthesis in tomato-fruit locule tissue. Incorporation of amino acids into protein by aseptic cell-free systems

Abstract

Osmotically disrupted protoplasts and isolated plastids from tomato-fruit locule tissue were found capable of incorporating 14C-labelled amino acids under aseptic conditions into an exhaustively washed trichloroacetic acid-insoluble protein fraction. The disrupted protoplast system incorporated 20-45[mu][mu]moles of amino acid/mg. of protein in 10 min. The isolated plastid system incorporated 10-20[mu][mu]moles of amino acid/ml. of protein; 40-150[mu][mu]g. of carbon/mg. of protein was incorporated in 10 min. from 14C-labelled amino acid mixture. Incorporation is stimulated by added ATP in the dark, but no added ATP is required when the system is illuminated. The cell-free plastid system is to some extent self-sufficient and does not normally require an added supernatant fraction or unlabelled amino acids. Amino acid incorporation by plastids in inhibited by chloramphenicol. puromycin, actinomycin D, ribonuclease and deoxyribonuclease. It is suggested that the mechanism of protein synthesis in the cell-free plastids, and in the tissue generally, is basically the same as established for bacteria. Ribosomes and high-speed supernatant from this tissue were to some extent interchangeable with Escherichia coli ribosomes and supernatant in cell-free incubations. Incorporation of amino acids by isolated plastids was stimulated by indol-3-ylacetic acid and kinetin, and, whereas incorporation normally proceeds for only 10-20 min., the time-course was extended in the presence of these growth substances. It is suggested that hormones may be involved in the regulation of protein synthesis in plants.