Effects of tissue culture on a highly repetitive DNA sequence (E180 satellite) in Medicago sativa

Genomic DNA extracted from leaves of sixteen alfalfa genotypes, six-week-old callus cultures derived from them and from a suspension culture was used in Southern blots and slot blots probed with alfalfa E180 satellite DNA. The restriction patterns revealed by the E180 probe did not differ among alfalfa genotypes and no differences between the leaf and callus restriction patterns were seen. However, the number of copies of the E180 satellite was lower in the callus samples than in the corresponding leaf samples and significant differences in copy number among callus samples were detected. Genomic stress induced by tissue culture may have caused the reduction in copy number. This phenomenon may be important in the generation of somaclonal variation in alfalfa.