Cycloheximide delays chlorophyll loss but not the inhibition of plastid protein synthesis during heat-bleaching in Euglena gracilis

Abstract

Growth at the bleaching temperature of 33 °C induces chlorophyll loss and inhibits chloroplast protein synthesis in photoheterotrophic cultures of Euglena gracilis Z. We now show that brief incubations in the presence of cycloheximide during the early hours of the treatment at the elevated temperature delay the onset of chlorophyll loss. Incubations in the presence of cycloheximide, however, do not bring temporary protection to plastids against the inhibitory effect of temperature on plastid protein synthesis. We conclude that protein synthesis on cytoplasmic ribosomes appears to be required to bring about the loss of chlorophyll at 33 °C. Furthermore, the inability of Euglena gracilis to develop and maintain functional chloroplasts at the elevated temperature can be explained by changes in the ability of plastids to synthesize proteins that are independent from the effect of temperature on chlorophyll accumulation.