Transport of proteins from cytoplasm into plastids in chloramphenicol-treated bean leaf discs : Autoradiographic evidence.

Leaf discs from etiolated bean plants were found to incorporate [(3)H]lysine into 80 S ribosomesynthesized proteins in the presence of chloramphenicol (100 mg l(-1)) when exposed to light. After a 7 min pulse of [(3)H]lysine, the discs were transferred to the same medium but with nonradioactive lysine, and postincubation was carried out for 24 h. The number of silver grains over the plastids, after the first period of a lag phase, indicates a large increase between 12 and 24 h of postincubation. Simultaneously, the labeling of the cytoplasm becomes reduced during that period. The results show that during inhibition of the protein formation within plastids, the synthesis of plastid-destined proteins in cytoplasm, as well as their transport into plastids, can still proceed.