Fig. 1. Incubation at 15°C reversibly inhibits transport of pLHCPII from the Golgi apparatus to the chloroplast. Cell-free extracts were prepared from dark-grown Euglena exposed to light at 26°C for 24 hours, incubated at 15°C or 26°C for 2 hours and pulse-labeled at 15°C or 26°C for 10 minutes with [³⁵S]sulfate. Cells pulse-labeled at 15°C were chased for 20 or 30 minutes at 15°C or 26°C with unlabeled sulfate. Organelles were separated by isopycnic sucrose gradient centrifugation, and each gradient fraction was immunoprecipitated with antibody against Euglena LHCPII. Immunoprecipitates were analyzed on SDS gels, and gels were scanned with a PhosphorImager. To allow direct comparisons between gradients loaded with differing amounts of ³⁵S-labeled protein, the amount of pLHCPII and LHCPII in each fraction is plotted as a percentage of the total immunoprecipitate (pLHCPII and LHCPII) recovered from the gradient. pLHCPII accumulated in the Golgi apparatus in cells maintained at 15°C and was transferred to the chloroplast and converted to mature LHCPII between 20-30 minutes after transfer to 26°C.