Physico-Chemical and Restriction Endonuclease Analysis of Mitochondrial DNA from Higher Plants

Abstract

The presence of DNA fibrils in plant mitochondria has been reported at the beginning of the 60s; the isolation of mt DNA molecules from higher plants has been achieved some years later and most of the physico-chemical characteristics are now well established (Wells and Birnstiel 1969, Kolodner and Tewari 1972, Vedel and Quétier 1974). The mt-DNA represent nearly 1% of the total cell DNA and must be isolated from DNase-treated intact organelles. The mitochondria of all higher plants so far studied have been shown to contain DNA quite distinguishable from both nuclear and chloroplastic DNAs. The G+C content of this mt-DNA, as determined by CsCl buoyant density, is remarkably constant at 1.706 g.ml^-1 whatever the plant genus and the level of evolution. This constancy is rather puzzling when compared to the buoyant densities of animal mt DNAs which range from 1.686 g.ml^-1 to 1.711 g.ml^-1. The study of both thermal denaturation profiles and analytical CsCl banding patterns achieved at different molecular weights do not reveal any heterogeneity (Vedel and Quétier 1974) while interactions with synthetic homopolyribonucleotides suggest that d-A and d-C rich clusters are present. The only divergent parameters to be reported till 1974 were the length of DNA molecules examined under electron microscope and the Cot value which respectively ranged from 10 to 30 µm and from 74.10⁶ d to 140.10⁶ d. The dispersion within each of these parameters and the discrepancy between them remained unclear till recently, although they indicated that the mt DNA from higher plants is about 6 times larger than the animal mt DNA.