Comparative analysis of sister-chromatid exchanges in plant and human chromosomes

Species specificity concerning the two main SCE characteristics, namely frequency and localization, of "spontaneous" SCEs in plant cells (root tips of Crepis capillaris) and in human lymphocytes was investigated under comparable conditions. The FPG technique was used for detection of SCEs after bifilar incorporation of BrdU into DNA (TB-BB). Data of parallel experiments showed that the frequency of SCEs in plant cells was considerably higher than that observed in human lymphocytes--13.2 and 7.3 SCEs per cell respectively. The difference was even more pronounced when the SCE frequency was estimated on the basis of DNA content/cell (pg). Analysis of SCE distribution was limited to SCEs localized in the centromere, since contradictory results most frequently concerned this chromosome region. The data of the present experiments showed that the frequency of SCEs localized in the centromere regions of plant chromosomes was considerably lower than that observed in human chromosomes. Compared with the relative sizes of the centromere regions in the two genomes, however, these frequencies proved to be quite similar. In both systems the centromeres were involved in SCE, as could be expected for random distribution, along the length of the chromosomes.