Lectin-gold cytochemistry of the Golgi apparatus in rabbit luteal cells,with special emphasis on the formation of a lysosomal-type membrane

Summary In rabbit luteal cells embedded in glycolmethacrylate and stained with PTA at low pH highly glycosylated membrane patches can be observed after vesiculation of the trans-Golgi network. As these membranes could be prelysosomal, their sialic acid content was investigated by postembedding labeling with Limax flavus agglutinin (LFA)/fetuin-Au. Additional labeling of the Golgi apparatus was performed with Wheat germ agglutinin (WGA)/ovomucoid Au, Ricinus communis agglutinin_I (RCA_I)/Au and Helix pomatia agglutinin (HPA)/Au. The sections were then counterstained with PTA at low pH, which allows a clear distinction between the elements of the trans-Golgi network (G₂-G₁) and the saccules of the stack (g).With WGA, LFA and RCA_I the trans-Golgi network was observed to be clearly more reactive than the stack. After vesiculation most intense labeling was found over the highly glycosylated vacuolar membranes derived from the G₂-element. The limiting membrane of lysosomes, the MvB's and the plasma membrane also reacted strongly. Colloidal gold particles were also found over the membranes of the vacuoles derived from G₁. The Golgi stack showed a lower reactivity and label for all three lectins could be found over three to four saccules of the stack (g₃-g₄). The matrix of the lysosomes was slightly labeled. Labeling with HPA was absent from the trans saccules and was consistently found in the cis and cis-most (g₄-g₅) saccules of the stack. Some cytoplasmic vesicles near the cell border were also labeled. With our procedure the Golgi apparatus can easily be detected and it is apparent that in rabbit luteal cells the highest lectin reactivity is found in the trans-Golgi network. A striking similarity is observed between the highly glycosylated membrane structures derived from G₂ and the border of the lysosomes.