Light-induced Changes of Pyrimidine Uptake in Euglena gracilis

Abstract

Summary The uptake of pyrimidines such as uracil and thymine is inhibited in wild-type cells of Euglena gracilis strains Z and bacillaris as well as in the apoplastic mutant W 3 BUL under conditions of lightinduced chloroplast synthesis, but it is increased in N/C–depleted cells. Light as well as medium caused changes of uptake of pyrimidines are not related to any alterations in the mechanism of uptake nor the course of chloroplast–specific events. The light–induced decrease and the medium–caused enhancement of pyrimidine uptake clearly correspond to paramylum degradation releasing glucose: (1) Uptake of pyrimidines and paramylum breakdown have the same time–dependence. (2) Obviously, both of them require the blue–light receptor system. (3) Both of them are located in the cytoplasma and are influenced by cyloheximide. (4) Both of them are dependent upon culture conditions, such as the N/C ratio, the availability of glucose, and ammonium ions. We can speculate that paramylum breakdown resulting in glucose formation might ultimatively redistribute protons inside and outside the cell membrane, thus influencing the uptake of pyrimidines.