Behavior of mitochondria, chloroplast and pyrenoid in synchronized cells of Chlamydomonas and Euglena

Abstract

Summary: Giant mitochondria are temporarily formed, probably by fusion of smaller mitochondria, in Chlamydomonas reinhardi cells at an intermediate stage in the growth phase of the cell cycle. The formation of giant mitochondria is accompanied by a marked decrease in the oxygen-uptake activity of the cells and the division of giant mitochondria into smaller forms by a re-increase in the activity. Changes in the morphology of mitochondria of Euglena gracilis Z cells were also followed with an electron microscope during the cell cycle in a synchronous culture under photoautotrophic conditions. Giant mitochondria were temporarily formed, most probably by fusion of smaller forms, in the cells at an intermediate stage in the growth phase of the cell cycle. Furthermore, we found for the first time such phenomena in chloroplasts of Euglena gracilis Z, called?ggiant chloroplast?h, and we clarified their arrangement in the cell cycle. 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 synchronized cells of Euglena.The immuno-reactive 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.