Division of mitochondrial nuclei in protozoa, a green alga and a higher plant.

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Abstract
The division of mitochondrial [mt] nuclei in Amoeba proteus, Paramecium caudatum, Nitella flexilis and Allium cepa was investigated using 4''-6-diamidino-2-phenylindole (DAPI) epifluorescent microscopy. The mitochondria each contained 1 mt-nucleus in A. proteus and P. caudatum and 1 or 2 mt-nuclei in N. flexilis and A. cepa. The ratio of fluorescent intensity (grain density of negative film) among one DNA molecule of a T4 phage particle and mt-nuclei of spherical mitochondria in Physarum polycepahlum, A. proteus, P. caudatum, N. flexilis and A. cepa was about 1:16:22:5:0.4:0.4. That is, the mitochondrial DNA content in N. flexilis and A. cepa was much smaller than those in A. proteus and P. caudatum. The mitochondria and their nuclei in A. proteus and P. caudatum as well as P. polycephalum divided simultaneously by constriction, while segregation of mt-nuclei occurred before the mitochondrial division in N. flexilis and A. cepa. The fluorescent intensity of mt-nuclei in dumbbell-shaped mitochondria of P. caudatum and A. cepa was about twice that in spherical mitochondria. Mitochondrial DNA probably duplicated and divided equally into daughter mitochondria.