Ultrastructure of Cephaleuros Virescens (Chroolepidaceae; Chlorophyta). Iv. Absolute Configuration Analysis of the Cruciate Flagellar Apparatus and Multilayered Structures in the Pre‐ and Post‐release Gametes

Abstract

Transmission electron microscopy of pre‐release and post‐release biflagellate gametes of Cephaleuros virescens has produced comparative data on these cells and on the detailed absolute arrangement of the flagellar apparatus. In all major respects including the presence of two multilayered structures (MLS's) the closely compacted, non‐motile but mature pre‐release gametes are similar to the mature, free swimming post‐release gametes. The elongated shape of the free‐swimming gametes differs from the more compact form of the pre‐release gametes, but does not reflect a major difference in the arrangement of internal components. The flagella are bilaterally keeled and each keel contains a cylindrical element. Each flagellar base is encircled by a densely staining collar of modified plasmalemma at the point of entry into the apical papilla. The equal anterior flagella enter the papilla from opposite sides; their basal bodies are parallel and overlapping. Each terminates in a densely staining terminal cap. No capping plate is present. Each basal body is associated both with a three‐layered MLS, the anterior layer of which becomes a lateral microtubular spline of 2 to 8 microtubules, and with an additional medial compound root of two layers of microtubules (2 over 4 or 5). Both the compound microtubule root and the spline may acquire additional microtubules as they extend distally in close proximity to mitochondria and the plasmalemma. No striated roots, or rhizoplasts, have been observed. Two densely staining plaques are associated with the plasma membrane at specific anterior sites and may be comparable to the presumptive mating structures seen in other green algal motile cells. The reversed bilateral symmetry of the cells produces two possible arrangements of the flagellar apparatus, namely, a 11/5 (or left‐handed) arrangement or a 1/7 (or right‐handed) arrangement. Only 11/5 cells have been found. Despite the presence of distinct multilayered structures, some aspects of the gametes of Cephaleuros quite closely resemble the cruciate motile cells of algae now regarded by some authors as typical of Ulvophyceae, sensu Stewart and Mattox.

Aspects ultrastructuraux de la fécondation chez l'Acrosiphonia spinescens(Kütz.) Kjellm. (Acrosiphoniales, Chlorophyta)

“…L'arrangement des racines flagellaires des zoïdes des algues vertes se fait selon deux types fondamentaux : type crucié avec 2-X-2-X microtubules, caractéristique de la majorité des algues vertes proprement dites, et type unilatéral avec faisceau microtubulaire associé à une structure multistrate (M LS = multilayered structure), observé chez les Charale~ (Moestrup, 1978). Cette seconde disposition, dont il existe divt~rses variante,; importantes (Chapman et Henk, 1983 ;Sluiman, 1983), se retrouvent dans lt>s spermatozoïdes des Bryophytes, Ptéridophytes et des Préphanérogames (Carothers et Duckett, 1980 ;Robert, 1982) suggérant l'origine algale des végétaux vasculaires (Chadefaud, 1979). L'organisation de l'appareil flagellaire du planozygote de rA.…”

Phylogenetic affinities of the Trentepohliales inferred from small-subunit rDNA

“…Based on biochemical, biophysical and physiological features, Raven (1987) classified the Trentepohliales among a third class, the Pleurastrophyceae. Moreover, it was noted that the Trentepohliales even share a rare ultrastructural feature (presumptive mating structures in the gametes) with members of a fourth class, the Chlorophyceae (Chapman & Henk, 1983, 1985. Therefore, the Trentepohliales exhibit some features associated with four of the five major classes of green algae in the system proposed by Mattox & Stewart (1984); however, the major discussions have been focused on ulvophycean versus charophycean affinities of this enigmatic order.…”

De Novo Transcriptome Analysis of an Aerial Microalga Trentepohlia jolithus: Pathway Description and Gene Discovery for Carbon Fixation and Carotenoid Biosynthesis

“…Diversity, life history and ecology were examined in detail by Rindi et al [14] . Others have investigated physiology, photosynthesis and ultrastructure [6] , [7] , [15] – [18] . The classification and phylogeny of the Trentepohliales at the genus level have been determined, using morphological characteristics and molecular data [1] , [3] , respectively.…”