Three-dimensional Structures of Giant Mitochondria, Dictyosomes and “Concentric Lamellar Bodies” Formed during the Cell Cycle of <italic>Euglena gracilis</italic> (Z) in Synchronous Culture

Abstract

Based on about 50 serial sections of synchronously grown Euglena gracilis (Z) cells, three-dimensional structures of mitochondria, dictyosomes and “concentric lamellar bodies” were studied. (1) Giant mitochondria of markedly irregular shapes with multiple branchings were formed during the growth phase of the cell cycle. The matrix of giant mitochondria was very large in volume and no cristae were found to extend into the middle of the matrix. It was suggested that a giant mitochondrion is formed by fusion of smaller mitochondria, its newly formed matrix being further enlarged, and that It may be continually changing its configuration. Tubules of 240–260Å in diameter were frequently observed in the matrix of giant mitochondria. (2) Dictyosomes lying in juxtaposition with each other were observed. (3) Spindleshaped bodies composed of 6 to more than 10 concentric lamellae were observed in cells during the growth phase. The concentric lamellae were layered regularly at an interval of about 200 Å. The outermost lamella was often seen in association with a mitochondrion.