Activation of latent nucleolus organizers induced by experimental polyploidization in cells of hexaploid wheat Triticum aestivum L.
The effect of prolonged colchicine-induced polyploidization on activation of latent nucleolus-organizing regions (NOR) of chromosomes was studied in diploid meristematic cells and polyploid root cells of Triticum aestivum L. It has been shown that control diploid and tetraploid cells have maximal number of nucleoli equal to four, which corresponds to the number of nucleolar chromosomes (NC) with active (visualized by staining with AgNO3) NOR (two pairs of homologous chromosomes 1B and 6B). Treatment of wheat seedlings with colchicine for 30 h results in following changes in polyploid cells: (1) impregnation of NOR with silver is observed on homologues of either chromosomes 1A or 5D in all tetraploid metaphase plates (4n, 2x, 4c), which is indicative of the NOR activation on this chromosome in pre-mitotic polyploid interphase; (2) In tetraploid metaphase, NOR in all four homologues of activated chromosomes or in only two of them may be stained; (3) maximal number of nucleoli in tetraploid nuclei is increased till 12, which confirms activation of transcription of additional rRNA gene clusters in polyploids; (4) activation of the rRNA gene expression is induced by the cell polyploidization rather than by colchicine, since in the colchicine-treated diploid cells both maximal number of nucleoli and the number of metaphase chromosomes with active NOR is not changed as compared with control. The obtained data allow us to suggest that structural "separation" of NC in polyploid nuclei stimulates activation of latent NOR.
Lazareva
E M
EM
Lomonosov Moscow State University, Biological Faculty, Cytology Department, Russia. cytos@proteinBio.msu.su
Khoudoleeva
O A
OA
Chentsov YuS
Polyakov VYu
D003078:Colchicine / Q000494:pharmacology; D006074:Gout Suppressants / Q000494:pharmacology; D049671:History, 18th Century; D009697:Nucleolus Organizer Region / Q000235:genetics / Q000648:ultrastructure*; D011123:Polyploidy; D014908:Triticum / Q000235:genetics / Q000648:ultrastructure*
D006074:Gout Suppressants; D003078:Colchicine