Ion Uptake and Protein Synthesis in Enzymatically Isolated Plant Cells

Abstract

THE D-threo isomer of chloramphenicol is an antibiotic and a specific inhibitor of protein synthesis in bacteria¹. It also inhibits protein synthesis (net synthesis or turnover) in higher plants^2–6, including cell-free systems^7,8. Suppression of the induced increase in oxygen uptake in potato disks by D-chloramphenicol⁹ has been considered as indirect evidence of an inhibition of protein (possibly cytochrome oxidase) synthesis. Enzyme development during germination was also inhibited by D-chloramphenicol^10,11. Recently, this chemical has also been used in several systems to relate ion uptake to protein synthesis in higher plants^{2,3,6,12–16}. Others oppose this interpretation^17–20. Meanwhile, the extrapolation of information on chloramphenicol from bacteria to higher plant systems has been criticized^4,18. Ellis¹⁸, for example, observed that D-chloramphenicol did not affect incorporation of amino-acids into protein (trichloroacetic acid (TCA)-insoluble fraction) and yet it reduced ion uptake in higher plants. In contrast, the L-threo-isomer of chloramphenicol, which is neither an antibiotic nor an inhibitor of protein synthesis in bacterial systems, does inhibit ion uptake¹⁸ and root growth²¹ in higher plants. Thus, further elucidation was necessary as to the action of chloramphenicol as an inhibitor of ion uptake via an effect on protein synthesis.