Karyotype structure and interphase chromatin organization in Rhoeo spathacea [Sw.] Stearn [Commelinaceae]

Karyotype of conventionally stained and C-banded mitotic chromosomes of Rhoeo spathacea was analyzed. Chromosomes of this diploid species (2n = 12) were classified according to their meiotic sequence described by earlier authors. The chromosome complex of Rhoeo is comparatively rich in heterochromatin (~ 18% of karyotype length), and the main differences between C-banded chromosomes concern the amount of pericentromeric heterochromatin and the presence of distally located segments. It is suggested that the karyotype of R. spathacea presented here fulfills the criteria of Bennett’s "natural karyotype." C-banding of somatic interphase nuclei and mitotic prophases revealed a highly polarized arrangement of chromosomes (Rabl orientation). The centromeres have a distinct tendency to form rings within nuclei, and to gather into 1-3 large collective chromocenters. The presumptive role of non-random distribution of chromosomes at interphase is discussed.