Abstract
Mitochondrial (mt) DNAs were prepared from ten strains of rice with cytoplasmic male sterility (cms) and fractionated by agarose gel electrophoresls to investigate plasmid-like DNA in different male-sterile cytoplasms. All of the cytoplasms had plasmid-like DNAs of low molecular weight besides their high-molecular-weight mtDNAs. Cms-R cytoplasm had two plasmid-like DNAS of 1.09 and 0.96kb, cms-UR106 cytoplasm had three plasmid-like DNAs of 1.60, 1.09, and 0.96kb, and the others had four plasmid-like DNAs of 1.60, 1.25, 1.09, ancl 0.96kb. Cytoplasmic properties of Oryza rufipogon and Oryza nivara used as source of male-sterlle cytoplasms are suggested to be closer to Indica rice than Japonica rice. The 1.09-kb DNA molecule from cms-Bo cytoplasm was suggested to be intimately associated wlth protein(s) in linear form and the other three DNA molecules seemed to be circular forms by the experiment of extraction with or without proteinase K. Southern hybridization analyses showed high sequence homology between the plasmid-like DNAS with the same size from different cytoplasms, and low sequence homology between the plasmicl-like DNAs with clifferent size. Some of the plasmid-like DNAs from cms-Bo cytoplasm showed no sequence homology between those in cms-T, cms-C, cms-S, and N cytoplasms of maize.
