Abstract
We attempted to analyse the mechanism of cytoplasmic male sterility (cms) in two strains of rice, that is, cms-Bo Taichung 65 with cytoplasm of cultivar Chinsurah Boro II and cms-R Reimei with cytoplasm of a strain of Oryza rufipogon. Mitochondrial DNAs (mtDNAs) were purified from cms and fertile (normal) rice varieties and the electrophoretic pattern of their restriction fragments was compared. MtDNA purified from cultivar Chinsurah Boro II cytoplasm contained two plasmid-like low molecular weight DNAS and the pattern of the restriction fragments of mtDNA from Chinsurah Boro II cytoplasm was clearly different from that of the normal cytoplasm. Plasmid-like DNAs have not been detected yet in the mtDNA from a strain of Oryza rufipogon cytoplasm but the pattern of the restriction fragments of mtDNA was also obviously different from that of the normal cytoplasm. Moreover the pattern of the restriction fragments of mtDNAS from a strain of Oryza rufipogon and Chinsurah Boro II cytoplasms was clearly different. In contrast, the pattern of the restriction fragments of chloroplast DNAS from normal and cms cytoplasms of Taichung 65 or Reimei was identical. We speculate that the difference in the mitochondrial genome between cms and normal 'cytoplasms of Taichung 65 or Reimei is, at least partly, responsible for the occurrence of cms.
