Molecular cytogenetic analysis of repeated sequences in a long term wheat suspension culture

A rapidly growingTriticum aestivum L. (wheat) derived long term suspension culture (named TaKB1), that is probably not regenerable, was analysed for karyotype rearrangements, stability and changes in repetitive DNA. The cell line has an average chromosome number of 21 and the DNA amount of unreplicated cells of TaKB1 measured by flow cytometry is about 30% lower than an unreplicated (1C) bread wheat genome.In situ hybridization of a repetitive DNA sequence (pSc119.2), which occurs as tandemly repeated blocks (heterochromatin) in wheat, shows that chromosomes from the TakB1 line have fewer and weaker subtelomeric locations of the sequence than wheat, suggesting deletions of distal chromosome segments and a reduction in the sites and copy number of the sequence. Thein situ hybridization pattern and chromosome morphology allowed 27 chromosome types to be identified in the cell line. No two analysed cells contained the same chromosome complement, although some chromosome types were present in every cell. Using Southern hybridization the structure and copy number of a retroelement (Wis-2) and its flanking sequence was shown to be the same in the TaKB1 cell line and wheat. Anin situ analysis of rDNA in the TaKB1 cell line (using the probe pTa71) showed a reduction in number of sites and rRNA genes in each cell from that in wheat. Interphase cells of the cell line showed dispersed signal throughout the nucleolus with no evidence for clusters of condensed and inactive rRNA genes.