Intracellular distribution of mitochondria after geotropic stimulation of the oat coleoptile.

The number of mitochondria is greater in the bottom than in the top of cells in geotropically stimulated oat (Avena sativa) coleoptiles. In the avascular tip and outer epidermis of subapical regions this difference occurs only in the lower tissues. These inequalities are found both in the KMnO(4) (-) and in the glutaraldehyde-fixed tissues; however, they are significant only in the former. Also, the number of mitochondria scored is consistently lower when the tissues were fixed in KMnO(4). These results suggest that mitochondria undergo a small degree of sedimentation after geostimulation, a redistribution reduced by the slower fixation with glutaraldehyde. Differences in mitochondrial number begin later than those in the amyloplast and the Golgi apparatus after geotropic stimulation. The cells in the avascular-tip region (a region having an important role in geotropism) have two to three times more mitochondria than the subapical cells.