MITOCHONDRIAL STRUCTURE IN PARAMECIUM AS REVEALED BY ELECTRON MICROSCOPY

¹ Division of Biological and Medical Research, Argonne National Laboratory, Lemont, Illinois

1. An electron microscopical study of the mitochondria in Paramecium aurelia and P. bursaria has been made from thin sections of cells imbedded in methacrylate plastic. Some of these sections were studied directly (plastic-in), and others were soaked in toluene before examination (plastic-out).

2. Plastic removal reveals structural detail not visible when the plastic remains in the section. At the same time, the relationship between the newly observed structures and those seen in the other sections is accounted for.

3. The undifferentiated mitochondrion in Paramecium is interpreted to consist of a compact mass of twisted tubules, the walls of which are made up of at least two kinds of substances (based on density differences in the photographs). The lumen of the mitochondrial tubule is about 15 mµ in diameter and is seen at times to be continuous with the cytoplasm. A distinct feature of this mitochondrion is the lack of a demonstrable membrane distinct from the material of the walls of the tubules in contrast to some interpretations of mitochondrial structure in many other organisms.

4. The basic tubular structure of the mitochondrion in Paramecium is recognizable in the cytoplasmic inclusions (mitochondria, primary grana) of several phylogenetically distant organisms.