Occurrence of Mitochondria in the Nuclei of Tobacco Sperm Cells.

Tobacco sperm cells contain intact mitochondria within their nuclei with a frequency of 0.35 [plusmn] 0.13 per cell. These inclusions appear to originate from mitochondria found among chromatids in the highly elongated metaphase plate of the dividing generative cell. These organelles are apparently captured during the reconstitution of the nuclear envelope. Only sperm cells were observed to contain these nuclear mitochondria; generative cells, vegetative pollen cells, transmitting tissue cells, unfertilized egg cells, and central cells lacked them. Nuclear mitochondria were also seen in the nuclei of the egg and central cell after fusion with sperm nuclei, suggesting that nuclear mitochondria are transmitted into the zygote and primary endosperm cells during double fertilization. Organellar inclusions in the sperm nucleus provide a potential mechanism for transmitting organellar DNA into the next generation and could potentially facilitate the transfer of genetic material between the nucleus and other organelles.