rRNA gene expression and location in triticale assayed by silver staining and in situ hybridisation techniques.

摘要

In durum wheat x rye hybrids and the derived amphiploid triticale, AABBRR, the expression of the 1R rRNA genes is largely suppressed. Alloauto-octoploid triticales, AABBRRRR, allows the evaluation if rye NOR inactivation can be overcome by the increase of rye genome number. In the present work, we used silver staining and in situ hybridization techniques to study the nucleolar activity and to localize the rRNA genes in hexaploid and alloauto-octoploid triticales. The use of rye genomic DNA as probe allowed the identification of the rye chromosomes present in both hexaploid and octoploid triticales (14 and 28, respectively). The simultaneous use of the ribosomal sequence enabled the localization of 18S-25S rDNA on the satellite chromosomes of both triticales. On hexaploid triticale, we detected 6 rDNA sites (4 on wheat chromosome pairs 1B and 6B, and 2 on rye chromosome pair 1R), whereas on alloauto-octoploid triticale 8 rDNA sites (4 on wheat-pairs 1B and 6B and 4 on rye chromosome pairs 1R) were observed. As expected, the maximum number of active Ag-NORs per metaphase cell was coincident with the maximum number of nucleoli per interphase nucleus, confirming that all and only the NORs functionally active during interphase are stained by silver at the next mitotic metaphase. Comparison of the nucleolar activity between hexaploid and octoploid triticales analysed here indicates that the increase in 1R chromosomes from 2 to 4 does not change the suppression of rye nucleolar activity. This supports the suggestion that genomic interactions are under strong genetic control..