Amino acid uptake and protein synthesis in cultured cells and protoplasts of Zea mays L.

Abstract

Summary The uptake and incorporation into proteins of leucine and of methionine by protoplasts from Zea mays was studied as a function of development of protoplasts to cells. The maximum uptake and incorporation of amino acids occurred 12–24 hours after isolation of the protoplasts. At 24 hours of culture both uptake and protein synthesis could be completely inhibited by cycloheximide, whereas in freshly isolated protoplasts only protein synthesis was affected. This suggested the existence of a regulatory mechanism linking uptake with incorporation which, however, was not functioning at very early hours of culture. Internal pools of leucine determined in isolated protoplasts, 24-hour protoplasts and cells showed a decreasing order which paralleled the uptake and incorporation of leucine. A possible pool effect is therefore not excluded. In the presence of methionine the incorporation (but not the uptake) of leucine into proteins was increased as shown by the increase in ratio of the amino acids. This effect was most prominent at 24 hours of culture and was temperature dependent. The development of freshly isolated protoplasts to cells over a period of 5 days was also monitored by light microscopy and the biochemical findings were correlated with the changes in morphology.