Spermatogenesis in Lycopodium: The Mature Spermatozoid

Abstract

The mature spermatozoid of Lycopodium cernuum is a blunt ended, fusiform cell, 8–10 μm long by 4–5 μm wide. A multilayered structure (MLS) and a subtending anterior mitochondrion are located at the anterior of the cell. The MLS is coiled through 1–1.5 gyres in a shallow sinistral helix around the periphery of the cell. The MLS would be triangular in outline if unwound and laid flat, about 1.4 μm wide, 7.5–8 μm long, and 80 nm thick. The MLS comprises four layers, S1–S4. The S1 forms the spline, a supportive sheet of microtubules; the S2, lamellate in younger stages, is an homogeneous, darkly staining layer in the mature sperm; the S3 and S4 retain their lamellate appearance and are delimited by lateral connections. Approximately 200 S1 microtubules extend posteriorly from the MLS at about 45° to the MLS long axis and form a partial sheath around the nucleus. The two basal bodies are located on opposite sides of the cell external to the MLS. Each is tangential to the curve of the MLS and surrounded by a globular matrix. At their attachment, the axonemes are oriented laterally and are antiparallel to each other. Distally, the flagella, each about 38 μm long, trail behind the cell as it swims. The nucleus is roughly ovoid, about 4 μm diam, and centrally or sometimes laterally located. The greater volume of the nucleus is occupied by condensed, amorphic chromatin. Cavities within the chromatin are often seen to contain spheroidal inclusions that have two differently staining regions. The inclusions are also located at the periphery of the chromatin. The posterior of the cell is occupied by several small mitochondria and an amyloplast, about 2 μm diam containing numerous starch grains.

Ultrastructure of Cephaleuros virescens (Chroolepidaceae; Chlorophyta). III. Zoospores

“…The variation in the number of spline microtubules also may be related to the stage of development. In view of the developmental changes which occur during maturation of the sperm of some mosses (see Kreitner, 1977;Robbins and Carothers, 1978), it is possible that the MLS's in free-living zoospores would be different (presumably simpler) from those shown in the present report. Both additional maturity and active function could alter the morphology of the MLS's and their angles of approach to and contact with the basal bodies.…”

Estimates of Nuclear DNA Content in Bryophyte Sperm Cells: Phylogenetic Considerations

“…Of the other lycophytes, only Lycopodium sensu latu (011gaard, 1987) produces biflagellated gametes (Robbins and Carothers, 1978;Maden, Renzaglia, and Whittier, 1993;Maden, 1994). Architecturally, the spermatozoids in this genus are unique among archegoniates, in that they are ovoid to slightly elongated and the flagella are not positioned in a strictly anterior to posterior stagger as they are in mosses, liverworts, and Selaginella.…”

“…Nevertheless, the genome size of L. lucidulum, which has a chromosome number of n = 132, is relatively small (10 pg DNA) when compared with other seedless vascular plants. Similarly, L. cernuum with a high chromosome number of n = 104 or 208 (Wagner, 1992) possesses a relatively small ovoid spermatozoid that is 8-10 JLm in length (Robbins and Carothers, 1978) (cf., 275 JLm length of the ovoid spermatozoid of the cycad Dioon edule) (Bierhorst, 1971). Genome size estimates in those spermatids of Lycopodium that have been detailed at the ultrastructural level would aid in accurately evaluating the influence of ploidy level on sperm organization.…”

The evolution of land plant cilia

“…The bicentriole is composed of two centrioles that are positioned end-to-end and are connected by a fibrous central core (Carothers et al, 1977). In most cases, a pair of bicentrioles forms de novo within the sperm mother cell and one of the pair is distributed to each of the daughter sperm cells after mitosis (Robbins & Carothers, 1978). In hornworts, this process is modified slightly in that the bicentriole pair is formed in the cell generation preceding the sperm mother cell, but the end result in the sperm cells is the same (reviewed in Renzaglia & Garbary, 2001).…”

“…In hornworts, this process is modified slightly in that the bicentriole pair is formed in the cell generation preceding the sperm mother cell, but the end result in the sperm cells is the same (reviewed in Renzaglia & Garbary, 2001). These double centriolar units function in the biciliated sperm cells of both bryophytes and lycophytes, but bicentriole length is greater in lycophytes (Robbins & Carothers, 1978;Maden et al, 1997). In monilophytes, instead of bicentrioles, a pair of spherical blepharoplasts forms de novo in either the sperm mother cell or the preceding cell generation.…”