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  • 1
    Electronic Resource
    Electronic Resource
    Location of heitz's zerstäubungsstadium (dispersion phase) in the mitotic cycle ofPhaseolus coccineus and the concept of Angiosperm endomitosis (1981)
    Springer
    Protoplasma 109 (1981), S. 403-414 
    Details
    ISSN: 1615-6102
    Keywords: Angiosperm endomitosis ; Dispersion phase ; Mitotic cycle ; Phaseolus coccineus ; Zerstäubungsstadium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary DNA microdensitometry and autoradiography after treatment with3H-thymidine were used to study the phase of dispersion of chromocenters (Z phase) in parallel with chromocentric nuclei inPhaseolus coccineus. In all materials studied, two types of chromocentric nuclei were present. In radicle apices of dry seeds, two classes of nuclear DNA contents were measured, 2 C (G1) and 4 C (G2). The 2 C DNA class comprised all chromocentric type I nuclei, the 4 C class included Z phases and chromocentric type II nuclei. The 4 C (G2) condition of Z phases implies that Z phases maintain their nuclear structure for some time after the end of DNA replication. Shoot apices also contain 2 C (G1) and 4 C (G2) nuclei but 4 C nuclei (Z phases and chromocentric type II nuclei) are rare. In seedling root apices, Z phases are from 1.02 to 4.08 times as frequent as prophases. This excludes that Z phase is a very early prophase. DNA microdensitometry shows that the chromocentric type I includes 2 C (G1) nuclei and nuclei in the first part of the S phase, Z phases include 4 C (G2) nuclei and nuclei in the last stage of the S phase and chromocentric type II includes mainly 4 C (G2) nuclei and nuclei in the second part of S. After 90 minutes of treatment with3H-thymidine all Z phase nuclei are labeled. This result and the microdensitometric data unequivocally demonstrate that Z phase is located at the end of S. The present results and those of previous authors on Z phase are discussed in relation to Geitler's concept of Angiosperm endomitosis. It is concluded that the term “Angiosperm endomitosis” must be abandoned and substituted by the term “chromosome endoreduplication”.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01287455
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  • 2
    Electronic Resource
    Electronic Resource
    RNA synthesis in the embryo suspensor ofPhaseolus coccineus at two stages of embryogenesis, and the effect of supplied gibberellic acid (1992)
    Springer
    Protoplasma 167 (1992), S. 152-158 
    Details
    ISSN: 1615-6102
    Keywords: Embryo development ; Embryo suspensor ; Gibberellin ; Phaseolus coccineus ; Polytene chromosomes ; RNA synthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary RNA synthesis in giant cells containing polytene chromosomes in the embryo suspensor ofPhaseolus 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 (GA3) treatments was also studied. At both embryo developmental stages, GA3 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 GA3 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 ofPhaseolus coccineus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01403378
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