Unique positioning of mitochondria in developing microspores and pollen grains inPharbitis nil: mitochondria cover the nuclear surface at specific developmental stages

Summary Changes in the number and distribution of mitochondria in microspores and pollen grains during male gametogenesis inPharbitis nil were examined with Technovit sections stained with 3,3-dihexyloxacarbocyanine iodide. The number of mitochondria per microspore or pollen grain ofP. nil increased constantly and dramatically during male gametogenesis. During this process, mitochondria exhibited characteristic localizations: subpopulations of mitochondria covered the surface of the microspore and vegetative nuclei before and again just after postmeiotic mitosis I (9 and 5 days before flowering, respectively). The mitochondria also surrounded the generative nucleus 2 days after postmeiotic mitosis I (5 days before flowering), although the density of mitochondria on the nuclear surface was lower. Electron microscopy showed that the mitochondria were about 30 nm from the nuclear envelope and that each mitochondrion was located near a nuclear pore. The characteristic localization of mitochondria inP. nil pollen may serve as a model to analyze the mechanisms that control mitochondrial positioning within a cell and interactions between mitochondria and nuclei.Abbreviations DAPI 4,6-diamidino-2-phenylindole - DiOC₆ 3,3-dihexyloxacarbocyanine iodide - PM I postmeiotic mitosis I