Stability of mitochondrial DNA in tissue-cultured cells of rice

Restriction analysis of mitochondrial (mt) DNA from 3-month-old callus cultures of the cytoplasmic male sterile rice, V41A, which contains S2 or "wild abortive" cytoplasm, and its fertile maintainer, V41B, showed the same BamHI restriction profiles as mtDNA from the corresponding leaf material. Similarly, mtDNA of rice (var. Taipei 309) from leaves, a 2-month-old cell suspension (T3MS2/A), a totipotent suspension (T3MS) and a 19-month-old suspension, which had lost its protoplast regeneration ability (LB3), showed indistinguishable BamHI restriction profiles. However, clear differences in mtDNA restriction profiles were observed between LB3 and a 30-month-old suspension culture of Taipei 309 (LB1), which appeared to reflect substantial changes in the relative abundance of specific DNA sequences. Hybridisation of a maizecoxII gene probe to blots of restricted mtDNA confirmed that, while the relative abundance of certain mtDNA sequences was preserved during long-term tissue culture of rice, major changes in abundance were observed with other sequences.