Figure 3.

Arrangement and Condensation State of Chromatin Domains in Cycling Nuclei.

(A) and (B) F1 hybrid between Oe. elata ssp hookeri strain johansen Standard and Oe. grandiflora strain grandiflora Tuscaloosa. Premeiotic interphase with chromocenters well developed (A) or completely decondensed (B). The chromocenters in premeiotic interphase are more compact than their counterparts from the root meristem. This difference is most likely due to the fact that root meristems, compared with other tissues, were subjected to longer enzymatic treatment and more harshly squashed (to obtain well-spread and flattened metaphase plates).

(C) to (G) Oe. glazioviana strain r/r-lamarckiana Sweden. C-banding/DAPI with standard ([C], [F], and [G]) or prolonged ([D] and [E]) hot saline incubation performed on root-tip nuclei. Facultative chromocenters are still visible in (C) and (F) (some of them marked with arrowheads); however, in (D) and (E) (left image), they could not be differentiated and only terminal heterochromatin and NOR-heterochromatin were clearly detectable. This was due the difference between constitutive and facultative heterochromatin in response to the degradative action of the prolonged incubation in hot SSC. This difference probably reflects structural differences between the two chromatin fractions. The nucleus in (E) was after C-banding/DAPI with prolonged SSC incubation, subjected to double-target FISH with 45S rDNA (middle, five signals) and 5S rDNA (right, two signals) probes. Arrows in (E) indicate NOR-heterochromatin blocks that reside on chromosomes possessing 5S rDNA sites; arrowheads point to the remaining NOR-heterochromatin blocks. The rest of the heterochromatin blocks represent terminal heterochromatin that shows a clear tendency for fusion.

(F) and (G) Nuclei with a clear Rabl arrangement. Arrowheads indicate arbitrarily indicated centromere-containing chromosomal parts; arrows indicate terminal heterochromatin blocks.

(F) Interphase nucleus from root meristem.

(G) Mitotic prophase.

(H) F1 hybrid between Oe. elata ssp hookeri strain johansen Standard and Oe. grandiflora strain grandiflora Tuscaloosa. Meiotic prophase. Centromere-containing condensed chromosome regions are more clustered than they are in somatic prophase.

Bars = 5 μm.