A chilling‐sensitive mutant of <i>Arabidopsis</i> is deficient in chloroplast protein accumulation at low temperature^*

ABSTRACT Mutations at the chsl locus in Arabidopsis 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 and chsl plants were equally able to process and protect from protease digestion in vitro synthesized pre‐plastocyanin. The results suggest that the chsl mutant may be defective in some aspect of chloroplast protein accumulation at low temperature.