Mitochondrial DNA variation in long-term tissue cultured rice lines.

The effects of long-term tissue culture on mitochondrial DNAs were examined using rice (Oryza sativa) cell suspension cultures. Mitochondrial DNAs were isolated from P. I. 353705 (an indica subspecies of rice similar to 'Asam 5'), its anther-culture-derived line BL2 (an 8-year-old cell suspension culture), and five other cell lines (A1, A7, A11, A13, and A23), also derived from BL2 and independently selected for resistance to the lysine analog, S-(2-amino)-ethyl-L-cysteine. Mitochondrial DNAs of the rice lines were digested with ten restriction endonucleases (BamHI, BglII, EcoRI, EcoRV, HindIII, PstI, PvuII, SalI, SmaI, and XhoI), electrophoresed, and transferred to nylon membranes. Southern blots were hybridized with one rice and five maize probes containing mitochondrial genes. The restriction patterns of ten Southern blots and hybridization patterns of 60 endonuclease/probe combinations were analyzed. DNAs from all sources produced unique restriction patterns when digested with HindIII or BglII; with the other endonucleases an array of similarities and differences was observed. Lines BL2 and A11 showed unique patterns with all restriction endonucleases tested. No hybridization pattern differences were observed among the lines when probes containing apt9 and atpA were used. However, extensive hybridization pattern differences were observed with coxI, coxII, rrn18-rrn5, and atp6 probes. Both restriction and hybridization patterns revealed variation due to tissue culture effect. Coxll was most efficient in revealing the uniqueness of BL2. Among the analog selected lines A11 was most divergent, and probes rrn18-rrn5 and atp6 were most efficient in revealing its distinctiveness. Unique mitochondrial genomic organizations were found to be associated with long-term tissue culture.