Evidences for the control of chromosome number variation by a programmed-cell-death-like pathway in citrus callus

Chromosome number variations were found in citrus callus induced from diploid genotypes. Further cytological examination of single-protoplast-derived cell lines showed that these chromosome number variations arose spontaneously from mitotic irregularities, but that the ploidy level remained relatively stable over one year in culture. The frequent occurrence of tetraploid cells and the stable maintenance of ploidy level seemed paradoxical. To explain this, the mitotic indexes of diploid and tetraploid sub-populations were calculated, respectively. The results showed that the division of tetraploid cells was inhibited. The results of a TUNEL (TdT-mediated dUTP Nick-End Labeling) assay, DNA staining and comet-electrophoresis further suggested that tetraploid cells were eliminated by a programmed-cell-death-like pathway. An erratum to this article is availbale at .