Abstract
Distribution of mitochondrial DNA (mtDNA) molecules during mitochondrial division to daughter mitochondria in the plasmodium of Physarum polycephalum has been determined by light and electron microscope autoradiographical studies. The plasmodium was incubated in a [3H]-thymidine solution during the mtDNA synthetic period (mS) to preferentially label one strand each of the mtDNA molecules. Distribution of the labeled strand on successive first and second rounds of replication and division ina nonradioactive medium was determined by quantitative light microscope autoradiographic technique. Results showed that silver grains were always distributed equally over the dividing dumbbell-shaped mitochondrion. Inaddition, the distribution frequency of the grain counts over the mitochondria followed a Poisson distribution, and the mean value decreased on mitochondrial division. We conclude that mtDNA molecules are distributed at random, but that an equal amount is divided between two daughter mitochondria. Electron microscope autoradiograms of dumbbell shaped and daughter mitochondria showed that the equal distribution of mtDNA molecules could be ascribed to an equal distribution of the mitochondrial nucleus.
