DNA-content in isolated nuclei of postembryonic stages of progeny from normal and irradiated males of Tetranychus urticae Koch (Acari, Tetranychidae)

Karyotype variation in aminoethylcysteine resistant cell and callus cultures and regenerated plants of a dihaploid potato (Solanum tuberosum)

Karyotypic studies on cell suspensions and calli of an S-(2-aminoethyl)cysteine resistant cell line of the interdihaploid potato H(2)578 (2n=24) revealed a high degree of variation in the number of chromosomes (33-217) and dicentric chromosomes (0-8). The suspensions also exhibited megachromosomes and fused chromosomes. Differential staining showed that in suspensions dicentrics survived mitotic cycles mainly by parallel separation of the chromatids during anaphase and hardly by the breakage-fusion-bridge cycle. Two phenotypes of plantlets regenerated, each with 34 or 35 chromosomes with gross structural mutations and with the triploid amount of DNA. Chromosomal variation was related to the degree of tissue organization.

Variability of DNA content and karyotype in cell cultures of an interdihaploid Solanum tuberosum

Karyological and DNA cytophotometric observations were carried out to follow nuclear events in cell cultures of an interdihaploid potato, genotype H(2)578, 2n=2x=24. The percentage of polyploid cells increased in leaf calluses, but decreased and then remained at a constant level when these cells were cultured in suspension. These suspension cultures did not survive, maybe because they did not become tetraploid. Another suspension culture proliferated with hypotetraploid cells only. Unlike the DNA contents of their interphase nuclei, the karyotypes varied considerably because of numerical and structural chromosome mutations.

Ploidy levels in leaf callus and regenerated plants of Solanum tuberosum determined by cytophotometric measurements of protoplasts

In potato (Solanum tuberosum) instabilities in nuclear DNA content in callus cells of a monohaploid and a dihaploid and in tuberprogenies of a regenerated, doubled dihaploid plant were assessed by cytophotometry in isolated, purified protoplasts. Leaf protoplasts of a tetraploid variety have nuclei with 3.6±0.08 pg of DNA. In callus protoplasts a dihaploid showed 3 and a monohaploid 6 ploidy levels. Progeny of a plant, doubled and regenerated from dihaploid callus, showed mixo-euploidy, indicating an instability similar to the dihaploid callus; in addition, there are mixo-aneuploid cells.These findings confirm and extend earlier observations based on chromosome counts in other genotypes of potato. The experimental approach can be applied to a variety of other purposes.