Ultrastructural Studies of Spermatogenesis in the Anthocerotales. Ii. The Blepharoplast and Anterior Mitochondrion in Phaeoceros Laevis: Later Development

Abstract

Chromatin condensation begins as the multilayered structure (MLS) in Phaeoceros reaches its maximally structured differentiation. As nuclear elongation and chromatin condensation proceed, the S2–4 strata disappear, and the nuclear beak extends between the S1 and the nearly spherical anterior mitochondrion. In a mature sperm the mitochondrion is elongate and lies completely anterior to the blunt front end of the nucleus. The 12 S1 tubules extend over the anterior mitochondrion and nucleus, but their number becomes reduced to five at the level where the nucleus' midportion is constricted. The anterior ends of the S1 tubules lie embedded in a rather conical osmiophilic crest. Flagellar insertion is restricted to the extreme anterior tip of the S1 tubules. The locomotory apparatus in Phaeoceros is compared with that of other bryophytes.

Motile Gametes of Land Plants: Diversity, Development, and Evolution

“…Constituent centrioles possess the ninefold symmetry of microtubule triplets that are characteristics of eukaryotic centrioles ( Figure 21D). However, triplet imbrication is in opposite directions in the two connected centrioles (Moser et al, 1977). Bicentrioles of lycophytes are longer than those in bryophytes (Robbins and Carothers, 1978;Renzaglia et al, 1999) ( Figure 21C).…”

“…In general, flagellar length coincides with the length of the cell body. Exceptions include hornwort and lycophyte sperm where the flagella are more than twice as long as the cell proper (Moser et al, 1977;Maden et al, 1996Maden et al, , 1997. Flagella of archegoniate gametes differ from flagella in algal motile cells in that they are surrounded by morphologically undifferentiated plasmalemma.…”

“…Ventral triplets extend slightly in front of the basal body proper and slight variations in the length of the transition zone in the two basal bodies may occur (Carothers et al, 1977). Unlike the transition zone in most archegoniates (except Sphagnum) and charophytes, the transition region in hornworts lacks a stellate pattern.…”

“…In biflagellated cells, the bicentriole initiates separation into its two constituent centrioles (basal bodies) during the final mitosis. In the newly formed spermatid, the two basal bodies undergo planar rotation in opposite directions until they lie parallel and side by side ( Figure 24C) (Moser et al, 1977). The proximal end of each basal body derives from the central point of attachment of the two basal bodies in the bicentriole.…”

The evolution of land plant cilia

“…As sperm cells mature, the lamellar strip extends leading to an increase in length (bryophytes) and/or number (tracheophytes) of spline microtubules. The mature spline thus comprises a band of regularly spaced microtubules that number around 10–25 in most bryophytes, typically 150–200 in monilophytes and thousands in gymnosperms, Basal bodies become associated with the extending lamellar strip (Carothers et al. , 1977), such that the extent of elongation correlates with basal body number (Norstog, 1974; Li et al.…”