63. Triemer, R. E. and R. M. Brown, Jr.
1976. Ultrastructural studies of meiosis in Chlamydomonas reinhardi.
British Phycol. J. 12:33-44.
Ultrastructural details of meiosis in Chlamydomonas
reinhardtii are presented. Zygotes undergo a resting stage
prior to meiosis, during which a multi-layered zygote wall is
deposited. Basal bodies reappear at interphase. Heterochromatin
is not visible in the interphase nucleus. Leptotene is characterized
by the appearance of axial cores and the condensation of chromenemata.
By early zygotene, axial elements associated with the condensing
chromatin associate with the nuclear envelope. Tubular elements
appear in the perinuclear space adjacent to the associated chromosomes.
Bivalents begin to associate with the nucleolus. By pachytene,
typical synaptinemal complexes have formed. The synaptinemal
complexes possess two lateral elements associated with the chromosomes
and separated by a central space of about 130 nm. A central element
may form midway between the lateral elements and be joined to
them via transverse elements. Separated synaptinemal complexes
appear in the cytoplasm by diplotene-diakinesis. At this stage
the chromosomes become most condensed and chiasmata occur. The
nucleolus disappears. The later stages of meiosis are described.
By metaphase I the nuclear envelope is fenestrated and a spindle
develops. Daughter nuclei reform at telophase. Basal bodies
are associated with a ribosome-free zone adjacent to the nuclear
membrane. The interzonal spindle degenerates. Cleavage occurs
via a phycoplast. At the initiation of the second division, basal
bodies are present at the incipient cleavage furrow. Basal body
replication appears to occur at pre-prophase. By metaphase II,
the basal bodies migrate to the poles of the fenestrated spindle.
Completion of the second meiotic division results in the formation
of haploid zoospores.