Occurrence and distribution of filipin-sterol complexes in chloroplast envelope membranes of algae and higher plants as visualized by freeze-fracture

The occurrence and planar distribution of 3-β-hydroxysterols in chloroplast envelope membranes of different algae and higher plants has been studied with the freeze-fracture technique using the polyene antibiotic filipin as cytochemical marker. The inner chloroplast envelope membrane in all organisms studied is devoid of filipin-sterol complexes. The outer chloroplast envelope membranes of isolated higher plant chloroplasts (spinach, pea) and of chloroplasts of the moss Polytrichum piliferum are lacking filipin-sterol complexes, thus indicating a very low concentration of 3-β-hydroxysterols in chloroplast envelope membranes of higher plants. In contrast filipin-sterol complexes are abundant in the outer chloroplast envelope membrane of the flagellates Chlamydomonas reinhardii, Cryptomonas erosa, and Euglena gracilis. The chloroplast-ER surrounding the plastid of Cryptomonas erosa also exhibits filipin-sterol complexes. Functional and phylogenetic aspects of these observations are discussed. © 1981 Springer-Verlag.