Studies on mitochondrial structure and function in Physarum polycephalum. V. Behavior of mitochondrial nucleoids throughout mitochondrial division cycle

Abstract

The fine structure of mitochondria and mitochondrial nucleoids in exponentially growing Physarum polycephalum was studied at various periods throughout the mitochondrial division cycle by light and electron microspcopy. The mitochondrial nucleoid elongates longitudinally while the mitochondrion increases in size. When the nucleoid reaches a length of approximately 1.5 μm the mitochondrial membrane invaginates at the center of the mitochondrion and separates the mitochondrial contents. However, the nucleoid does not divide even when the mitochondrial sections are connected by a very narrow bridge. Just before division of the mitochondrion, the nucleoid divides by constriction of the limiting membrane of the dividing mitochondrion. After division, one end of the nucleoid appears to be associated with the inner mitochondrial memebrane. The nucleoid then again becomes situated in the center of the mitochondrion before repeating these same processes.