The behavior of nucleolus organizers in structurally changed karyotypes of barley

Transcriptional Activity of Translocated NORs in Barley (Hordeum VulgareL.)

“…2). the proportions of cells with different numbers of macronucleoli (Table 3) support the pattern of fusion of nucleoli described by nicoloff et al (39). in both lines the number of cells with four nucleoli was under 1% compared to the control line (7.5%) which is probably due to the acceleration of the nucleolar fusion process (Table 3).…”

“…this is a preferential silencing of ribosomal genes of one of the noRs -when both noR6h and noR5h are located on only one chromosome (2,23,52). Intraspecific nucleolar dominance was described for barley lines with reconstructed karyotypes (2,23,38,39,41,48,52), and to our knowledge has not been observed in other species. in lines t505 and t506 noR6h is dominant over noR5h regardless of whether it is transposed or is in its original location.…”

“…Due to the transcription of the four rDnA loci, four primary nucleoli are formed at late telophase of mitosis (1,39). the percent of cells containing the maximum number of nucleoli depends on the rate of association after mitosis and is different in the various studied samples (1).…”

“…3). As a rule the number of the secondary constrictions corresponds to the maximum number of primary nucleoli in the telophase (1,18,39,41). According Medina et al (33) "the number of active AgnoRs per metaphase cell corresponds to the maximum number of nucleoli per nucleus, and only the functionally active noRs during interphase are stained by silver at the next mitotic metaphase".…”

“…As a rule, the number of transcriptionally active rDnA-encoding loci in a cell is related to the number of the formed nucleoli. the size of the nucleolus formed in association with a particular noR is proportional to rRnA gene dosage and the level of gene activity (1,2,26,27,39,41). Due to translocation with breakpoints within or close to the noRs, the localization of all or part of their ribosomal genes may be changed in the genome, which results in modification of the expression patterns of the transposed genes as well as of those in the original location.…”