Immunoelectron Microscopic Evidence for the Occurrence of Ribulose-1 , 5-Bisphosphate Carboxylase/Oxygenase in "Propyrenoids" of Euglena gracilis

When dark-grown wax-rich cells of Euglena gracllts</it> strain Z are transferred to an inorganic medium and the cell suspension is aerated in the dark, the wax is oxidatively metabolized, providing carbon materials and energy for some dark processes of plastld development. Under these conditions, pyrenoid-like structures (“propyrenoids”) are formed at the sites adjacent to the prolamellar bodies localized in the peripheral region of the proplastid. These Euglena</it> cells were fixed In 1% glutaraldehyde and embedded in Epon. Serial sections were Labeled with antiserum to ribulose-1,5-blsphosphate carboxylase/oxygenase (RuBisCO) followed by protein A-gold. Computer-aided construction of three-dimensional models of proplastids revealed that approximately 80% of total RuBisCO was localized over the propyrenoid region in the proplastids. No deposition was seen when preimmune serum was substituted for immune serum.