Summary
DNA synthesis in the embryo suspensor cells ofPhaseolus coccineus has been studied by autoradiography after 30 minutes and 12 hours feedings with3H-thymidine (3H-TdR). It has been observed that two different DNA syntheses occur in cell nuclei of the suspensor, one concerned with the process of chromosome endoreduplication, the other with the process of extra DNA synthesis in several heterochromatic regions of the genome. Characteristics of the extra DNA synthesis in our material are:
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i)
a greater3H-TdR uptake occurs during extra DNA synthesis than during DNA synthesis involved in chromosome endoreduplication;
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ii)
extra DNA synthesis is not concomitant with the process of chromosome endoreduplication;
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iii)
only some of the DNA strands in one and the same polytene chromosome region seem to be involved in the phenomenon of extra DNA synthesis;
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iv)
extra DNA synthesis occurs in both chromosome regions known to carry ribosomal cistrons and in other regions of the genome.
These results are discussed in relation to other literature data on DNA synthesis inP. coccineus embryo suspensor cells.
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Cremonini, R., Cionini, P.G. Extra DNA synthesis in embryo suspensor cells ofPhaseolus coccineus . Protoplasma 91, 303–313 (1977). https://doi.org/10.1007/BF01281953
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DOI: https://doi.org/10.1007/BF01281953