Ultrastructural analysis of chromatin in meiosis I plus II of rye (Secale cereale L.)

Scanning electron microscopy (SEM) proves to be an appropriate
technique for imaging chromatin organization in meiosis I and II of
rye (Secale cereale) down to a resolution of a few nanometers. It
could be shown for the first time that organization of basic
structural elements (coiled and parallel fibers, chromomeres)
changes dramatically during the progression to metaphase I and II.
Controlled loosening with proteinase K (after fixation with
glutaraldehyde) provides an enhanced insight into chromosome
architecture even of highly condensed stages of meiosis. By
selective staining with platinum blue, DNA content and distribution
can be visualized within compact chromosomes as well as in a
complex arrangement of fibers. Chromatin interconnecting threads,
which are typically observed in prophase I between homologous and
non-homologous chromosomes, stain clearly for DNA. In zygotene
transversion of chromatid strands to their homologous counterparts
becomes evident. In pachytene segments of synapsed and non-synapsed
homologs alternate. At synapsed regions pairing is so intimate that
homologous chromosomes form one filament of structural entity.
Chiasmata are characterized by chromatid strands which traverse
from one homolog to its counterpart. Bivalents are
characteristically fused at their telomeric regions. In metaphase I
and II there is no structural evidence for primary and secondary
constrictions. Copyright (C) 2003 S. Karger AG, Basel.