Behaviour of chromosomes in potato leaf tissue cultured in vitro as studied by BrdC-Giemsa labelling

Sister chromatid exchanges in cultured immature embryos of wheat species and regenerants

Immature embryos of Triticum aestivum (ten cultivars and lines), T. durum, T. dicoccum and T. monococcum were cultured in vitro on MS medium supplemented with 1 or 2 mg/l of 2,4-D and 20 or 30 g/l of sucrose for 3 days and processed to score sister chromatid exchanges (SCEs) per chromosome. Media components affect DNA replication from the start of the culture. The SCE frequencies were dependent on the genotype and were not correlated with the degree of ploidy. They increased after doubling of the concentration of 2,4-D and/or sucrose, except in one cultivar of T. aestivum. The mean numbers were lower than observed in root meristems of T. aestivum (two cultivars) and T. dicoccum. Immature embryos of regenerants of T. aestivum (one cultivar) and T. durum demonstrated variable SCE frequencies, which may have been caused by mutations in the parental cell cultures. In the T. aestivum embryos the lowest frequencies were found in regenerants obtained from explants with the highest frequencies.

Inheritance of a bacterial hygromycin phosphotransferase gene in the progeny of primary transgenic pea plants

An analysis of the progeny of primary transgenic pea plants in terms of transmission of the transferred DNA, fertility and morphology is presented. A transformation system developed for pea that allows the regeneration of fertile transgenic pea plants from calli selected for antibiotic resistance was used. Expiants from axenic shoot cultures were co-cultivated with a nononcogenic Agrobacterium tumefaciens strain carrying a gene encoding hygromycin phosphotransferase as selectable marker, and transformed callus could be selected on callus-inducing media containing 15 mg/l hygromycin. After several passages on regeneration medium, shoot organogenesis could be reproducibly induced on the hygromycin resistant calli, and the regenerated shoots could subsequently be rooted and transferred to the greenhouse, where they proceeded to flower and set seed. The transmission of the introduced gene into the progeny of the regenerated transgenic plants was studied over two generations, and stable transmission was shown to take place. The transgenic nature of the calli and regenerated plants and their progeny was confirmed by DNA and RNA analysis. The DNA and ploidy levels of the progeny plants and primary regenerants were studied by chromosome analysis, and the offspring of the primary transformants were evaluated morphologically.

Nucleolar organizer function in developing potato calli

The number of transcriptionally active nucleolar organizer regions (NORs) of one monohaploid, one dihaploid and two tetraploids of Solanum tuberosum and one diploid S. phureja was established by the silver staining of metaphases in root meristems and in in vitro-cultured leaf explants. The maximum number of active NORs per cell was one per haploid set of chromosomes. One or more NORs could be inactive in cells of the tetraploid meristems and in non-polyploidized and polyploidized cells of the dihaploid and tetraploid explants. Inactivation was determined by genotype and tissue and could remain constant during in vitro culture.

Flow cytometric and karyological analysis of polysomaty and polyploidization during callus formation from leaf segments of various potato genotypes

Flow cytometry and karyological analysis were used to study polysomaty and polyploidization during the first 15 days of callus formation in leaf segments from shoot cultures and greenhouse-grown plants of various lines and genotypes of Solanum tuberosum and S. phureja. The greenhouse-grown plants showed a higher degree of polysomaty (77% and 49% of polyploidized nuclei) than the shoot cultures (< 3%). During the in vitro culture period, polyploidization occurred through endoreduplication. Segments of the five shoot cultures showed up to 87%, 53%, 59%, 45% and 56% polyploidization, respectively; the DNA content of corresponding interphase nuclei amounted to 8C, 16C, 16C, 16C and 8C, and the chromosome numbers to 96. Segments from the two greenhouse-grown genotypes showed up to 87% and 84% polyploidization; the DNA content amounted to 32C and 16C, and the chromosome numbers to 192 and 96. The number of reduplication cycles was species-dependent; the degree of polyploidization was dependent on the initial ploidy level of the genotypes. Cell proliferation did not take place at a constant rate. The maximum frequencies of metaphases (52-171 per segment) occurred after 1 week of culture and were correlated with the ploidy level of the genotypes. Cells were triggered to mitosis rather than to endoreduplication. Cell cycles with normal monochromosomes could be shorter than 1 day, and those with diplochromosomes lasted at least 1 day. Polysomaty, degree of polyploidization and abnormal nuclear processes are discussed in relation to the origin of genetic instability early in culture.

Intergeneric asymmetric hybrids between Nicotiana plumbaginifolia and Atropa belladonna obtained by "gamma-fusion"

Asymmetric nuclear hybrids have been obtained by fusion of cells from a nitrate-reductase deficient mutant of Nicotiana plumbaginifolia (cnx20) and gamma irradiated protoplasts of Atropa belladonna (irradiation doses tested were 10, 30, 50 and 100 krad). The hybrid formation frequency following selection for genotypic complementation in the NR function was in the range of 0.7%-3.7%. Cytogenetic studies demonstrated that all hybrid plants tested possessed multiple (generally tetra- or hexaploid) sets of N. plumbaginifolia (n = 10) chromosomes along with 6-29 Atropa chromosomes (n = 36), some of which were greatly deleted. Besides the cnxA gene (the selection marker), additional material of the irradiated partner was expressed in some of the lines, as shown by analyses of multiple molecular forms of enzymes. Surprisingly, rDNA genes of both parental species were present and amplified in the majority of the hybrids. Whenever studied, the chloroplast DNA in the hybrids was derived from the Nicotiana parent. Regenerants from some lines flowered and were partially fertile. It is concluded that irradiation of cells of the donor parent before fusion can be used to produce highly asymmetric nuclear hybrid plants, although within the dose range tested, the treatment determined the direction of the elimination but not the degree of elimination of the irradiated genome.

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.

Ploidy variability in greenhouse cultured and in vitro propagated potato (Solanum tuberosum) monohaploids (2n=x=12) as determined by flow cytometry

The DNA distributions of 23 different monohaploid potato clones were investigated by flow-cytometric measurements. All monohaploid clones differed in DNA distribution but none of them contained only monoploid cells in the leaves. All were highly stable on the monohaploid level for 2-3 years. Investigation of the influence of different factors on the DNA distribution in leaf cells showed that the material derived from in vitro shoot tip propagation contained a lower proportion of polyploidized cells than greenhouse grown plants. With protoplast isolation the enzyme treatment of in vitro cultured plant material induced a striking shift of DNA distribution towards the lower C-value whereas the mechanical purification steps caused a selective loss of monoploid nuclei. Seasonal influence on the DNA patterns could be detected.

Chromosome variation in dividing protoplasts and cell suspensions of wheat

The cytology of bread wheat (Triticum aestivum) suspension lines, recycled lines (selected for high division frequency) and their dividing protoplasts, have been examined. Extensive numerical and structural chromosome variation was present in all the lines. The most frequently observed chromosome numbers were around 2n=32, indicating that considerable chromosome loss from the normal wheat complement (2n=6x=42) had occurred during selection of the lines. Chromosome aberrations also indicated loss of chromosome arms and chromosome segments. The implications of this variation for studies on transformation and for the potential regeneration of whole plants from protoplasts of bread wheat are discussed.