EN
Conventional and C-banding chromosome studies and nuclear DN A estimations were performed on six Bromus species (B. arvensis, 2n = 2x = 14; B. hordeaceus, 2n = 4x = 28; B. carinatus, 2n = 8x = 56; B. willdenowii, 2n = 6x = 42; B. erectus, 2n = 8x = 56; and B. inermis, 2n = 8x = 56) belonging to three subgenera: subg. Bromus, subg. Ceratochloa and subg. Festucaria. Three species (B. carinatus, B. erectus and B. inermis) show different chromosome numbers within root-tip meristem. Root-tip cells of these high polyploid species (2n = 8x = 56) showed substantial DNA variability. Densitometric and flow-cytometric analyses clearly showed that many interphase nuclei are beyond the expected 2C-4C limit characteristic of cycling cells. The most distinct DNA instabilities were observed in B. carinatus, where we found especially high numerical chromosome variations and many chromosome numbers higher and lower than 2n = 8x = 56. Such quantitative DNA variability is substantially reduced beyond the meristematic part of the roots and virtually absent within leaf mesophyll cells. Estimated nuclear 2C DNA content was 11.63 pg in B. arvensis, 23.03 pg in B. hordeaceus, 22.94 pg in B. carinatus, 12.99 pg in B. willdenowii, 24.65 pg in B. erectus and 24.54 pg in B. inermis. By DNA amount, the analyzed taxa formed two distinct groups: with 2C DNA value at about 12 pg (B. arvensis and B. willdenowii), and at about 24 pg (B. hordeaceus, B. carinatus, B. erectus and B. inermis). Estimated DNA values were not linked with ploidy level. All species showed a similar, mainly telomeric heterochromatin distribution, but small amounts of intercalary and centromeric heterochromatin were also seen. The majority of analyzed species also had similar heterochromatin amounts within karyotype. The only exception was B. carinatus with 16.20% heterochromatin (calculated as percent of karyotype length). It is suggested that the observed 77% nuclear DNA difference between two closely related representatives of subg. Ceratochloa (B. carinatus and B. willdenowii) is to some extent a result of heterochromatin accumulation in B. carinatus chromosomes.