Fine-structural changes in the midgut of old Drosophila melanogaster.

Variations of the mitochondrial structure with increasing age are of particular interest because the production of ATP is necessary for most cellular activities. Therefore, a senescent decrease of mitochondrial activity could jeopardize cell survival and function. We combined a statistical with a morphological approach to investigate these changes in mitochondrial size and structure of Drosophila melanogaster. The midgut epithelium is of special interest because previous research shows striking aging changes. Investigations of the mitochondria of flies of three age groups (10, 39, and 65 days) reveal an increase in size as well as in its standard deviation. This is linked to the fact that mitochondrial enlargement occurs especially in the luminal region. Ultrastructural studies show that with increasing age the mitochondria become more osmiophilic, their cristae disarranged, cristae-free areas can also be found, and there is an accumulation of homogeneous, granular and lamellar dense bodies. In addition, an accumulation of virus-like particles, fiber-shaped structures, reticular structures, and dense bodies without a surrounding membrane was found.