ULTRASTRUCTURAL-LOCALIZATION OF RUBISCO IN ALGAL CELLS

We investigated the ultrastructural localization of rubisco in whole cells of Dunaliella salina and the mutant Chlamydomonas reinhardtii CW-15 using reactions of binding with specific antibodies and with protein A labelled with colloidal gold. It is clarified that rubisco is localized solely in the pyrenoid and in the vicinity of its starch sheath. Depending upon cultivation conditions, three types of distribution of the label (colloidal gold) in the pyrenoid are isolated: on its surface; on internal lamellae of the pyrenoid; and throughout its entire volume. The authors discuss the functional role of the pyrenoid as a pool of rubisco that can be: a) in the deposited form; b) in the active form; or c) in the active and deposited forms simultaneously.