- A-Z
- Endocytobiosis and ...
- Volume 24 (2013)
- Indications for nuc...
- Autor(in)
- Seitenbereich
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016-022
- Schlagwort(e)
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plastids, maternal biparental paternal plastid inheritance, nuclear control, active digestion, asymmetric plastid distribution
- Zusammenfsg.
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There are three modes of plastid inheritance in higher and lower plants: uniparental maternal, biparental and uniparental paternal plastid inheritance. These different modes of transmission have in detail been described in numerous reviews and books. In this paper a second aspect of plastid research will be discussed: To what extent and by which molecular and cytological means are nuclear genes able to influence or even determine the modes of transmission of plastids to the next generation? In cases of biparental plastid inheritance the female and the male gametes transmit plastids to the next generation; in some species (e.g. Pelargonium zonale) both types of gametes transmit plastids nearly to the same extent, but in other species there is a bias either of the female or of the male plastid contribution. In the majority of plant genera a uniparental maternal plastid inheritance is observed; that means: the male plastids and their plastid DNA are excluded from transmission to the following generation. Are there different mechanisms? So far two principal mechanisms have been found for the exclusion of paternal plastids from the zygote and thus from the next generation: (1) One way is the exclusion of paternal plastid DNA and paternal plastids by biochemical/molecular biological means using specific nucleases which destroy the paternal plastid DNA. An impressive example is the active digestion of the male plastid DNA in Chlamydomonas reinhardtii; its characteristics will be decribed. (2) The other way is the cytological exclusion of pater-nal plastids by their asymmetric distribution during pollen development or during the fertilization process. Examples are (a) the asymmetric, directed distribution of plastids exclusively into the vegetative cell and not into the generative cell (e.g. in Tulbaghia and Gasteria) and (b) the polarized plastid distribution during the sperm cell formation (in Plumbago). There is no doubt that nuclear genes have an influence on the mechanisms which determine whether plastids are transmited biparentally or uniparentally. Some experimental approaches which indicate a control of plastid transmission by nuclear genes are discussed: In Pelargonium a nuclear gene (Pr) has been identified whose alleles determine – with distinctly varying effects − the frequency with which maternal and paternal plastids are transmitted to the next generation. In experiments with Medicago, different cultivars have been characterized which determine by means of nuclear genes remarkable differences in the frequency with which maternal and/or paternal plastids are transmitted to the next generation. This type of investigations can be a good start for a new research field that opens studies about the cooperation of nuclear and extranuclear genes in determining the processes of plastid inheritance.