ABSTRACTMutations at thechsllocus inArabidopsis thaliana(L.) confer a chilling‐sensitive phenotype in which plants become chlorotic and die after more than 3 d of exposure to temperatures in the range of 18 to 10°C. Within 8h after transfer of mutant plants from growth at 23 to 13°C, accumulation of the newly synthesized chloroplast‐localized polypeptides stearoyl‐ACP desaturase, glutamine synthetase and OEC 23 was severely impaired. By contrast, there was no apparent deleterious effect on the accumulation of two extrachloroplastic proteins examined: the elongation factor lα, and the phloem‐specific, extrachloroplastic isoform of glutamine synthetase. In one instance examined in detail, chilling did not decrease the accumulation of mRNA for stearoyl‐ACP desaturase, indicating that the effect was post‐transcriptional. Chloroplasts isolated from chilled wild‐type andchslplants were equally able to process and protect from protease digestionin vitrosynthesized pre‐plastocyanin. The results suggest that thechslmutant may be defective in some aspect of chloroplast protein accumulation