The Blepharoplast of the Midstage Spermatid of Andreaeobryum macrosporum (Bryophyta: Andreaeopsida)

Abstract

The blepharoplast of the midstage spermatid of Andreaeobryum macrosporum has a four-layered multilayered structure (MLS) and two superposed, slightly staggered, and overlapping basal bodies. The spline is composed of 30 parallel microtubules at its maximum width. Subtending the spline anteriorly, the lamellar strip (LS) is 1.83 pm long and 0.92 pm wide and has an elongated, wedge-shape with a pointed right anterior tip. Viewing the blepharoplast dorsally from anterior to posterior, the anterior basal body (ABB), approximately 0.95 pm in length, is situated over the right side of the MLS and is inserted at a level 0.42 pCm behind the spline's anterior apex. The posterior basal body (PBB), 2.75 pcm long, is positioned over the left side of the MLS and inserted 0.75 pm behind the spline's anterior apex. The ABB is essentially parallel with the spline microtubules over its entire length, while the anterior portion of the PBB curves outward gradually and becomes parallel with the spline in its posterior region. The combination of features that distinguish the midstage spermatid of Andreaeobryum from other mosses are its wide spline, wedge-shaped lamellar strip, comparatively short basal bodies, small length of stagger between basal bodies, and the PBB that curves gradually outward from its anterior tip. The data available for Andreaea suggest that its midstage spermatid resembles that of Andreaeobryum, although reconstructions and additional micrographic data are needed for both Andreaea and Takakia before generalizations for the class Andreaeopsida can be made. Andreaeobryum belongs to an unusual line of bryophyte evolution that also includes Andreaea and Takakia (Murray 1988; Renzaglia et al. 1991). While Andreaea is an old and well-established genus, Andreaeobryum is relatively new, having been described in 1976 by Steere and Murray (1976) and further defined by Murray (1988). Andreaea and Andreaeobryum have been grouped together in either the class Andreaeopsida (Crum & Anderson 1981; Murray 1988) or subclass Andreaeidae (Schofield 1985; Vitt 1984). According to Murray (1988), Andreaea and Andreaeobryum belong to separate orders, Andreaeales and Andreaeobryales, within the primitive class Andreaeopsida. The two genera are united by sporeling features and mode SAuthor for correspondence. e-mail: AnnRushing@ baylor.edu FIGUREs 1-6. Blepharoplast anatomy of Andreaeobryum macrosporum. -1-3. Tangential sections. -1. The spline anterior with its acutely curved left margin and closed aperture. Above, the extended triplet is part of the posterior basal body (cf. Fig. 18). -2. Slightly oblique section showing the left-marginal curvature of the subtending lamellar strip and the spline aperture (between arrows). -3. The spline aperture extends posteriorly beyond the lamellar strip where it closes by convergence of the microtubules on its right side with those on the left. -4. Near-median longitudinal section through the anterior basal body and the distal transition zone with its stellate pattern. The anterior mitochondrion is just becoming positioned beneath the lamellar strip. -5. Oblique-tangential section showing the full longitudinal extent of the anterior stellate pattern. -6. Oblique-tangential section section through the posterior basal body and the subtending spline and nucleus. Key to labeling: ABB, anterior basal body; AF, anterior flagellum; AM, anterior mitochondrion; ASP, anterior stellate pattern; EH, extended hub of basal body; ET, extended triplet; LS, lamellar strip; N, nucleus; PBB, posterior basal body; PSP, posterior stellate pattern; S, spline; S1-S4, specific strata of the multilayered structure; SA, spline aperture; bracket ([), lamellar strip. All micrographs are printed at a magnification of X67,500 except Fig. 6 where the magnification is X47,500. Except as otherwise noted for Figure 18, each scale bar represents