Ultrastructure of the spermatozoid ofLycopodiella lateralis(Lycopodiaceae)

Abstract

The spermatozoid of Lycopodiella lateralis (R. Br.) B. Øllgaard is ovoid and biflagellated and contains little cytoplasm. A large, rounded, condensed nucleus occupies the central region of the cell. At the rear of the cell is a cluster of starch-containing plastids associated with numerous elongated mitochondria and small pockets of remnant cytoplasm. The multilayered structure coils laterally around the cell anterior for just over one revolution. An anterior mitochondrion underlies the multilayered structure over its entire length and several smaller mitochondria line the inner anterior coil. Some 150 spline microtubules extend from the multilayered structure and coil posteriorly at approximately a 45° angle to the longitudinal axis of the cell. Microtubules progressively increase in length from the margins of the multilayered structure to the center and thus only a central core of approximately 30 microtubules encircles the organelles at the base of the cell. The two basal bodies are parallel and staggered in their position over the multilayered structure and are separated by about 80° around the circumference of the cell anterior. The flagella emerge in parallel and coil for nearly two revolutions. Comparisons among Lycopodiella, Palhinhaea, and Lycopodium provide the basis for evolutionary inferences associated with modifications in spermatozoid structure such as changes in cell size, whole cell coiling, and distance between basal bodies. Phylogenetic analysis of male gametogenesis suggests that Lycopodiella is part of a monophyletic lycopsid assemblage near the base of the vascular plants. Within this clade, Lycopodiella is most closely related to Palhinhaea, with Lycopodium, Phylloglossum, and Selaginella forming a sister clade. Key words: Lycopodiella, Lycopodium, spermatozoid, land plant phylogeny, locomotory apparatus, ultrastructure.