Selection and osmotic treatment exacerbate cytological aberrations in transformed barley (Hordeum vulgare)

A much higher percentage (78 %) of karyotypically abnormal cells were observed in transgenic barley callus cultures, compared with the 15% cytological abnormality in cells from nontransgenic callus cultures. Out of 22 independently transformed callus lines generated by microprojectile bombardment of immature embryos, only 7 lines had a relatively high percentage (35-76%) of diploid chromosomes (2n=2x=14); 5 (71 %) of these lines were regenerable. Of the remaining 15 lines a high percentage (92-100%) of cells in these lines had cytological abnormalities, primarily ploidy changes [tetraploidy (2n=4x=28), octaploidy (2n=8x=56) and aneuploidy] and structural variations; 8 (53 %) of these lines were regenerable. There was a high correlation between the cytological status of callus tissues and their regenerated plants. We studied which factor(s) in the transformation process were responsible for the increased cytological aberrations. Only 18-21 % of 6- and 12-week-old callus cells had observable cytological changes in the absence of transformation. In contrast, imposing osmotic or selection treatment triggered extensive cytological aberrations, 41 % and 40-46 % in 6-week-old callus cultures and 60 % and 48-51 % in 12-week-old callus cultures, respectively. Bombardment itself did not appear to affect the frequency of cytological aberration in cells of callus cultures.