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-ol d callus cultures derived from them and from a suspension culture was used in Southern blots and slot blots probed with alfalfa E180 satellite DNA. Th e restriction patterns revealed by the E180 probe did not differ among alfa lfa genotypes and no differences between the leaf and callus restriction pa tterns were seen. However, the number of copies of the E180 satellite was l ower in the callus samples than in the corresponding leaf samples and signi ficant differences in copy number among callus samples were detected. Genom ic stress induced by tissue culture may have caused the reduction in copy n umber. This phenomenon may be important in the generation of somaclonal var iation in alfalfa.