Fig. 1. Nuclear-encoded plastid proteins transit through the Golgi. Gonyaulax cell sections were treated with antibodies raised against two nuclear-encoded plastid proteins, Rubisco and peridinin-chlorophyll a-protein (PCP). In one series of experiments, cells were harvested and fixed at LDT 0 (by convention, the start of the light phase), a time when both proteins are actively synthesized in vivo. As a control for the specificity of the Golgi labeling, cells were also harvested and fixed at times when Rubisco or PCP were not actively synthesized in vivo (LDT 6 and 19, respectively). Sections were stained with either anti-Rubisco (A-C) or anti-PCP (D-F) as a primary antibody and a 20 nm gold-conjugated goat anti-rabbit as a secondary antibody. The Golgi is indicated by arrows in all pictures, and all scale bars represent 1 µm. Note that Rubisco and PCP have different sub-organellar locations (stroma and thylakoid lumen, respectively) within the plastids (P). The thylakoid membranes appear white, as osmium tetroxide was not used during fixation to preserve the antigenicity of the proteins.