DNA/Histone Ratio in Different Regions of Polytene Chromosomes in the Embryo Suspensor Cells of Phaseolus Coccineus

SUMMARYThe DNA/histone ratio was calculated through Feulgen/fast green absorption in different regions of polytene chromosomes in Phaseolus coccineus embryo suspensor cells. A great variability of ratios, related with the structural characteristics of DNA in the different regions, has been found. This seems to indicate that complexes of histone with DNA may depend on changes in DNA metabolic activity. In one and the same cell, and even in one and the same chromosome, different chromosome segments have different DNA/histone ratios.These findings are discussed in relation to some characteristics of polytene chromosomes in Phaseolus suspensor cells

molecular and chromosomal characterization of repeated and single copy dna sequences in the genome of dasypyrum villosum

Restriction fragment length polymorphism of ribosomal DNA repeated unit and single-copy DNA fragments and chromosomal distribution of a highly repeated sequence, have been studied to assess molecular markers and the extent of their heterogeneity in Dasypyrum villosum. Substantial variation has been found for the length of the intergenic spacer of ribosomal genes clustered in different alleles at Nor- VI locus of heterozygous individuals, but not within the cluster of rDNA of homozygous individuals. After Southern blots and hybridization to an intergenic spacer probe, each cluster of rDNA was detected as a single band with at least four variants differing for the number of 130 bp subrepeats in the intergenic spacer. One recombinant plasmid contained a 2270 bp DNA insert from the D. villosum genome that upon Sph I restriction endonuclease digestion was cleaved in three 380 bp repeat elements and one 1090 bp fragment. When Southern blots of Sph 1 digested D. villosum DNAs of different genotypes were hybridized to the 32P-labelled 380 bp repeat, a distinct ladder consisting of multiples of a basic repeat unit of about 380 bp in length was revealed on autoradiograms. The in situ hybridization of the 3H-labelled 380 bp repeat element showed that one chromosome pair (7V) was not labelled. In the other pairs, silver grains remained clustered at or near the telomeres. Dot-blot hybridization analysis of DNAs from a range of diploid, tetraploid, and hexaploid Triticeae species indicated that the 380 bp repeated element was a specific feature of the D. villosum genome. Other cloned DNA sequences of D. villosum showed a large restriction length polymorphism and one was located on V chromosomes

CYTOPHOTOMETRY OF NUCLEAR-DNA IN BUDS AND FLOWERS OF NICOTIANA-TABACUM

Feulgen/DNA absorptions were measured by scanning cytophotometry on the nuclei of meristematic cells in buds and flowers of Nicotiana tabacum developing in vivo or regenerating in vitro from thin cell layers excised from different plant parts and characterized by significant changes in the amount and organization of nuclear DNA. The results obtained indicated that, in vivo, nuclear DNA contents were significantly higher in flowers than in buds. Significant differences in the amount of nuclear DNA were also observed when comparing buds developing in vivo and in vitro and, among the latter, those regenerated from explants taken from different plant parts. Flowers developed in vivo and those regenerated in vitro, independent of which explants they were formed from, always have the same DNA content. These findings seem to suggest that rapid quantitative changes in the nuclear DNA having a possible role in developmental regulation can occur in Nicotiana tabacum

CYTOPHOTOMETRY OF NUCLEAR-DNA IN BUDS AND FLOWERS OF NICOTIANA-TABACUM

Feulgen/DNA absorptions were measured by scanning cytophotometry on the nuclei of meristematic cells in buds and flowers of Nicotiana tabacum developing in vivo or regenerating in vitro from thin cell layers excised from different plant parts and characterized by significant changes in the amount and organization of nuclear DNA. The results obtained indicated that, in vivo, nuclear DNA contents were significantly higher in flowers than in buds. Significant differences in the amount of nuclear DNA were also observed when comparing buds developing in vivo and in vitro and, among the latter, those regenerated from explants taken from different plant parts. Flowers developed in vivo and those regenerated in vitro, independent of which explants they were formed from, always have the same DNA content. These findings seem to suggest that rapid quantitative changes in the nuclear DNA having a possible role in developmental regulation can occur in Nicotiana tabacum

RNA-SYNTHESIS IN THE EMBRYO SUSPENSOR OF PHASEOLUS-COCCINEUS AT 2 STAGES OF EMBRYOGENESIS, AND THE EFFECT OF SUPPLIED GIBBERELLIC-ACID

RNA synthesis in giant cells containing polytene chromosomes in the embryo suspensor of Phaseolus coccineus was analyzed by autoradiography after [ 3H]-uridine treatment. Embryos at the heart-shaped stage of development and at a cotyledonary stage were studied. Discontinuous labelling of the polytene chromosomes was always observed. The chromosomes were subdivided into segments (chromosome regions) which behaved as functional units, since discontinuous labelling was never seen within any of the regions. It was found that most chromosome regions were engaged in RNA synthesis to different degrees at the two embryo developmental stages. Regions showing identical labelling patterns tended to lie close together in the chromosome arms and to keep their functional activity coordinated at both stages of embryo development. The chromosome regions bearing 18 S+25 S ribosomal genes were never simultaneously active in RNA synthesis and different regions were preferentially transcribed at each stage of embryo development. However, at both stages, all the chromosome regions bearing 5 S ribosomal genes showed comparable labelling frequencies. The effect on transcription of gibberellic acid (GA 3) treatments was also studied. At both embryo developmental stages, GA 3 enhanced the rate of RNA synthesis in the polytene suspensor cells. The frequency with which certain chromosome regions were transcribed was also increased significantly (P≤0.001) and this stimulatory effect was greater in embryos at the cotyledonary stage than in heart-shaped embryos. At the latter developmental stage, RNA synthesis was repressed by GA 3 in a few chromosome regions. These results are discussed briefly in relation to previous findings using different methods of studying the organization of polytene chromosomes and the functional activity of the embryo suspensor of Phaseolus coccineus