Immunocytochemical studies on the behavior photosynthetic enzymes during the cell cycle of synchronized cells of Euglena gracilis Z

Abstract

Euglena cells were grown synchronously under photoautotrophic culture conditions on a 14 h light-10 h dark alternations. Changes in morphology of the pyrenoid and those in distribution of RuBisCO in chloroplasts were followed by immunoelectron microscopy during the growth and division phases of Euglena cells. The immunoreactive protein were densely localized in the pyrenoid, and thinly distributed in the stroma during the growth phase. During the division phase, the pyrenoid could not be detected and the gold particles were dispersed throughout the stroma. From a comparison of photosynthetic CO2 -fixation with the total carboxylase activity of RuBisCO extracted from Euglena cells in the growth phase, it is suggested that the carboxylase in the pyrenoid functions in CO2 -fixation in photosynthesis. Cells of Euglena contain a LHC II. The precursors to LHC II are large polyproteins containing multiple copies of LHC II, and photocontrol of their formation is largely translational. Under conditions favoring LHC II accumulation in the thylakoids, a reaction with anti-LHC II antibody can be observed in the Golgi by immunogold electron microscopy. The timing of the immunoreaction in the Golgi in synchronous cells and in cells undergoing normal light-induced chloroplast development suggests that the nascent LHC II passes through the Golgi on the way to the thylakoids.