Mei-Hua Li, Lian-Fu Yang and Yi-Xin Cai
Institute of Genetics, Department of Bioengineering, Fudan University, Shanghai, China
Plasmid-like circular DNA molecules in mitochondria, differing in size, have been isolated from some normal and male-sterile cytoplasms in different plants, e.g., maize (Kemble and Bedbrook 1980; Weissinger et al. 1982), sorghum (Pring et al. 1982), sugarbeet (Powling 1981), and Brassica (Palmer et al. 1983). They may or may not have something to do with the cytoplasmic male- sterility. In order to determine whether or not such DNA molecules are found in rice, mitochondrial DNA molecules were investigated.
Electron microscopy showed that the different-sized plasmid-like circular DNA molescules with a low molecular weight were present in rice mitochondria, as shown in Fig. 1. Their molecular weight varied between 106 and 107 dalton. They were much smaller than the major mitochondria-DNA molecules and were invisible on the agarose gel due to their low concentration and diversity in size.
Fig. 1. The electron micrographs of plasmid-like small circular
DNA molecules found in rice mitochondrial DNA molecule populations.
a. x 40,000; b. x 50,000; c. 16,000; d. x 75,000; e. x 90,000; f. x 36,000.
Kemble, R.J. and J.R. Bedbrook, 1980. Low molecular weight circular and linear DNA in mitochondria from normal and male-sterile Zea mays cytoplasm. Nature 284: 565-566.
Palmer, J.D., C.R. Shields, D.B. Cohen and T.J. Orton, 1983. An unusual mitochondrial DNA plasmid in the genus Brassica. Nature 301: 725-728.
Powling, A., 1981. Species of small DNA molecules found in mitochondria from sugarbeet with normal and male-sterile cytoplasms. Mol. Gen. Genet. 183: 82- 84.
Pring, D.R., M.F. Conde, K.F. Schertz and C.S. Levings, 1982. Plasmid-like DNAs associated with mitochondria of cytoplasmic male-sterile Sorghum. Mol. Gen. Genet. 186: 180-184.
Weissinger, A.K., D.H. Timothy, C.S. Levings, W.W.L. Hu and M.M. Goodman, 1982. Unique plasmid-like mitochondrial DNAs from indigenous maize races of Latin America. Proc. Nat. Acad. Sci. USA 79: 1-5.