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

At an early stage in the cell cycle of Euglena gracilis Z, synchronizedunder 10-h light : 14-h dark alternations in an organic medium,the conjoined chloroplasts that formed made up a single giantbody that came close to the nucleus, covering most of the nuclearperiphery. Three different types of association between thesetwo organelles were observed. In one the outer membrane of thenuclear envelope was in contact, in some narrow regions, withthe chloroplast membrane, the site of contact being filled withdense material. A chromosome in the unfolded, fibrillar structurewas very close to the site of contact, the extreme end of thefibril touching the inner membrane of the nuclear envelope.When cells from the culture used above were stained with DAPIand examined under a fluorescence microscope, chloroplast nucleoidsin the giant body appeared to form, at least in part, a threadwith branchings, and some tips of the branchings came closeto the site of contact with the nucleus. In the second type of association, which was rare, part of thenuclear envelope protruded into the chloroplast, and the siteof contact was filled with dense material. A chromosome wasnear the site of this protrusion. In the third type of chloroplast-nucleusassociation the ER was continuous with the outer membrane ofthe nuclear envelope at one end and in contact with the chloroplastmembrane, at the other end. ¹This work was reported at the 48th Annual Meeting of the BotanicalSociety of Japan in Kyoto, October, 1983. (Received March 14, 1984; Accepted June 27, 1984)