Interactions between the Nucleus and Cytoplasmic Organelles during the Cell Cycle of Euglena gracilis in Synchronized Cultures III. Association between the Nucleus and Chloroplasts at an Early Stage in the Cell Cycle under Photoorganotrophic Conditions (Part II)

Three-dimensional models of chloroplasts before and during theirassociation with the nucleus in Euglena gracilis Z were constructedbased on serial sections of cells taken during an early phaseof the cell cycle in synchronized cultures under photoorganotrophiccondition. Before association, the cell contained two to threechloroplasts which were composed of elongated tubular bodiesextending in different directions toward the cell periphery.These tubular arms of chloroplasts were drawn toward the nucleus,and folded, with concurrent coalescence, into a single giantbody surrounding the nucleus. A DAPI-fluorescence photomicrographof a giant chloroplast revealed that the chloroplast-nucleoidswere in the form of a continuous strand lying throughout thechloroplast body, and that some protuberances from the nucleoidstrand were in especially close proximity to the nuclear periphery. A new mode of the chloroplast-nucleus connection was observed.The nucleus had conspicuous protrusions, whose distal ends wereconnected with the chloroplast. The outer membrane of the nuclearenvelope was continuous with the outer chloroplast membrane,and at some sites, an open space was formed between the innernuclear membrane and the inner chloroplast membrane. ¹ This work was reported at the 48th Annual Meeting of the BotanicalSociety of Japan, held in Kyoto, in October, 1983. For PartI see Ehara et al. (1984).