Curt Genet (1986)11:1-5 Curr~t 6eflet~c$ © Springer-Verlag 1986 Original articles Plastid inheritance in Epilobium Udo K. Schmitz and Klaus-V. Kowallik BotanischesInstitut der Universit/it,Universit/itsstmsse1, D-4000 Diisseldorf,Federal Republic of Germany Summary. Interspecific hybrids of various Epilobium species have been produced in order to analyse plastid inheritance using restriction fragment polymorphisms of plastid DNA as markers. This analysis reveals that in- terspecific hybrids exhibit only the fragment pattern of the maternal plastome. Southern hybridization experi- ments using cloned species-specific plastid DNA frag- ments as markers confirm the maternal type of plastid inheritance in Epilobium, while providing at least a ten- fold increase of sensitivity to detect restriction polymor- phisms. Within the limit of detection even young seed- lings contain no plastid DNA from the paternal parent. However, investigations of plastomes of large popula- tions have provided evidence that a very low frequency of paternal plastid transmission can occur. Thus, the me- chanism which ensures the elimination of paternal plas- tids is not 100% efficient. This suggestion is also sup- ported by intraspecific reciprocal crosses between plants carrying mutant white and normal green plastids. While the offspring usually exhibit the maternal plastid type, a few cases indicate an apparent paternal plastid transmis- sion. Key words: Epilobium - Plastid DNA - Southern hy- bridizati0n - Plastid inheritance Introduction Plastid inheritance in most flowering plants is known to be maternal. On the one hand, this situation is favoured by quantitative differences of the cytoplasm between Offprint requests to: K.-V.Kowallik Abbreviations: kbp, kilobase pairs; ptDNA, plastid DNA the egg cell and the sperm cell. On the other hand, in some cases where degradation of proplastids at various stages of microgametogenesis have been demonstrated, maternal plastid inheritance is mediated by the structu- ral disintegration of male plastids prior to zygote forma- tion. In those cases where transmission of paternal plas- rids takes place, their subsequent propagation may be controlled by nuclear genes of the female parent result- ing in different division rates of the plastids (cf. Tilney- Bassett 1978; Sears 1980). Biparental plastid transmission leading to mixed em- bryo cells occurs in about 20% of angiosperms thus far studied. In such cases plastome/genome interactions have been followed through later stages of ontogenic de- velopment of the offspring, as for example in Pelargo- nium (Tilney-Bassett and Abdel-Wahab 1982) and Oeno- thera (Stubbe 1959; Stubbe et al. 1978). In Epilobium, which is considered the closest relative to Oenothera (Haussknecht 1884), plastid inheritance has been report- ed to be purely maternal (Michaelis 1935, 1958). How- ever, certain ambiguities with respect to plastid inheri- tance may occur if mutated white plastids are used'in crossing experiments, since the detection of these plastids is difficult if they have a lower propagation rate or if sorting out occurs at early developmental stages of the hybrid plant. The genotypic characterization of the genus Epilo- bium by Seavey and Raven (1977a and b, 1978), and the ease with which interspecific hybrids can be produced (Renner and Kupper 1921; Geith 1923; Michaelis 1932; Kyt6vuori 1976), combined with modern techniques of molecular analysis, provide a favourable basis for the re- investigation of plastid inheritance within this genus. Since we have recently identified ten species-specific plastomes in Epilobium, it is now possible to study plas- rid inheritance in a wide range of species by using ptDNA restriction fragment polymorphisms as markers.