Freeze fracture immunocytochemistry of light-harvesting pigment complexes in a cryptophyte

Immunocytochemical techniques using colloidal gold as the marker have been used to examine the location of the two light harvesting pigment-protein complexes in cryptophyte chloroplasts. A comparison of post-embedding thin section labelling and freeze fracture labelling has been carried out on Rhodomonas salina using polyclonal antibodies to a chlorophyll a/c₂ light-harvesting complex, phycoerythrin and the β-subunit of phycoerythrin. The effect of different fixation procedures on the intensity of labelling and ac curacy of antigen location have been examined and the effectiveness of uranyl acetate and tannic acid in improving both the preservation of thylakoid structure and labelling density of phycoerythrin has been demonstrated. Freeze fracture labelling gives better spatial res olution of the different antigens than post-embedding labelling, as well as better definition of thylakoid membranes. It confirms the location of phycoerythrin in the thylakoid lumen and the location of the chlorophyll a/c₂ LHC in both appressed and unappressed thylakoid membranes.