plant mitochondria
Wang D-Y, Zhang Q, Liu Y, Lin Z-F, Zhang S-X, Sun M-X & Sodmergen 2010 The levels of male gametic mitochondrial DNA are highly regulated in angiosperms with regard to mitochondrial inheritance. Plant Cell 22:2402-2416.
- each egg cell from Arabidopsis thaliana, Antirrhinum majus, and Nicotiana tabacum possesses 59.0, 42.7, and 73.0 copies of mtDNA on average, respectively
- sperm or generative cells from Arabidopsis, A. majus, and N. tabacum possess minor amounts of mtDNA, at 0.083, 0.47, and 1 copy on average, respectively
- markedly high levels of mtDNA are found in the male gametic cells of Cucumis melo and Pelargonium zonale (1296.3 and 256.7 copies, respectively)
- a spermatozoon in the mouse maintains only ~50 copies of mtDNA
- this equates to a 20-fold reduction compared with somatic cells, which are known to possess 103 to 104 copies of mtDNA per cell
- a significant amplification of female mtDNA during oogenesis results in 5.0 × 105 copies of mtDNA in mouse oocytes
- the ratio of male to female mtDNA in the zygote is ~1:104
- the inheritance of the male mtDNA (via the small amounts of paternal leakage that inevitably happens during maternal inheritance) occurs at a frequency of 1.0 × 10−4
- the ubiquitin-mediated degeneration of sperm mitochondria in the zygote is suggested to act as a trigger for removing any male contributions after fertilization
- egg cells of P. zonale were found to contain a considerably higher quantity of mtDNA
- 1852.7 ± 483.9 copies per cell
- P. zonale is a rare species among angiosperms in that it employs biparental mitochondrial inheritance
- we could not be sure that this high quantity might relate to this biparental inheritance
- for Cucumis melo, the only angiosperm species known to employ paternal mitochondrial inheritance (Havey et al., 1998), insurmountable technical difficulties unfortunately prevented us from isolating intact egg cells
- the level of pollen mtDNA is downregulated during pollen development
- since all of the mitochondrial genes are necessary for proper mitochondrial function, it is a widely held view that each mitochondrion must possess at least one full copy of mtDNA
- this may not always be the case, at least in plants
- it is not the small size of the sperm cells that blocks paternal transmission
- the male gametic cells act as the key regulators of biparental and paternal mitochondrial inheritance