The vast majority of angiosperms and at least some gymnosperms display a maternal mode of plastid inheritance and thus do not regularly transmit plastids and plastid genes through pollen. Cytological investigations have revealed that there is not a unique mechanism how maternal inheritance of plastids is brought about. Instead, different species can utilize very different mechanisms of eliminating paternal plastids and/or paternal plastid genomes. The correlation of the cytological mechanisms leading to maternal inheritance with plant phylogeny is rather poor, and therefore, the mechanism operating in a given species is hardly predictable. Similarly to the mode of plastid inheritance, the cytological mechanism of maternal inheritance must be determined on a species-by-species basis.
According to the mechanism of paternal plastid elimination, at least four different subtypes of maternal inheritance can be distinguished (Hagemann and Schroder 1989; Hagemann 2002). This classification is largely based on electron microscopic investigations of plastid fate during male gametophyte development.
The subtypes are named after the first species discovered to realize the respective cytological mechanism.
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