Protoclones of Sorghum Bicolor with Unusually High Mitochondrial DNA Variation
We are analyzing genomic variations at the molecular level in tissue-cultured cells of corn and sorghum with the ultimate aim of characterizing the parts of the genome that are stable or unstable in the tissue culture environment. The main focus of our effort is on tissue-cultured cells rather than regenerated plants since regenerated plants are lacking in most of the random variation due to the inherent developmental selection pressure in the plant regeneration process. We have obtained cell suspension cultures from 3 cultivars of sorghum. Protoplasts from these cultures are readily obtained and give rise to callus that can be returned to cell suspensions (Chourey and Sharpe, manuscript in preparation) which are designated here as protoclones. The analysis of 6 such independently derived, randomly selected protoclones from the cultivar NK 300 is reported in this study. Mitochondrial DNA (mtDNA) is prepared, restriction digested, and electrophoresed according to a newly developed rapid method for mtDNA isolation (Wilson and Chourey, manuscript submitted). In addition to comparing the UV fluorescing bands from stained agarose gels, we have also compared those segments which share homology with 4 EcoRl fragments analyzable by membrane hybridization techniques. The following observations are noteworthy.