Karen S. Renzaglia

The phylogeny of land plants: A cladistic analysis based on male gametogenesis

A cladistic analysis was carried out to resolve phylogenetic pattern among bryophytes and other land plants. The analysis used 22 taxa of land plants and 90 characters relating to male gametogenesis.Coleochaete orChara/Nitella were the outgroups in various analyses using HENNIG86, PAUP, and MacClade, and the land plant phylogeny was unchanged regardless of outgroup utilized. The most parsimonious cladograms from HENNIG86 (7 trees) have treelengths of 243 (C.I. = 0.58, R.I. = 0.82). Bryophytes are monophyletic as are hornworts, liverworts, and mosses, with hornworts identified as the sister group of a liverwort/moss assemblage. In vascular plants, lycophytes are polyphyletic andSelaginella is close to the bryophytes.Lycopodium is the sister group of the remaining vascular plants (minusSelaginella). Longer treelengths (over 250) are required to produce tree topologies in which either lycophytes are monophyletic or to reconstruct the paraphyletic bryophyte phylogeny of recent authors. This analysis challenges existing concepts of bryophyte phylogeny based on more classical data and interpretations, and provides new insight into land plant evolution.

The Gametophyte-Sporophyte Junction in Land Plants

Publisher Summary The chapter presents a comparative analysis of the placenta in land plants. The gametophyte–sporophyte junction is termed as the placental region. Systematic survey of bryophytes, pteridophytes, and placental analogues in seed plants are also explained. The gametophyte–sporophyte junctions in bryophyte groups are distinguished by the presence or absence of cell wall labyrinths in the placental cells, cell wall structure, shape, and arrangement of wall ingrowths and plastid morphology. Two stages of sporophyte development, the pre–meiotic stage and post–meiotic stage are discussed. Studies carried out by using the representatives of bryophyte groups namely mosses, liverworts, and anthocerotes are explained. The chapter also explains characteristic features of placenta like the distribution of transfer cells, distribution of wall ingrowth and time of ingrowth for different organisms belonging to mosses and liverworts. Cytoplasmic features of placental cells like shape, membrane system, plastoglobuli, and starch for sporophyte and gametophyte in mosses and liverworts are described. The anthocerotes are distinguished based on cytological, anatomical, and developmental characteristics. The taxonomic significance of placenta in bryophytes and the implications on phylogeny are also discussed. Differences in the placental regions, cell wall ingrowths, and intercellular spaces between bryophytes and pteridophytes are explained. These differences are related to the transient nature of sporophytic dependence on the gametophyte in pteridophytes. Transfer cell morphology has been described at every site of solute exchange via the apoplast of angiosperms.

Subcellular structures of relevance to the origin of land plants (embryophytes) from green algae

Abstract During the past 2 decades, a substantial body of structural, biochemical, and molecular evidence has been amassed in support of the hypothesis that charophycean green algae are the closest extant protist relatives of the land plants (embryophytes). Charophycean algae include the filamentous and unicellular Zygnematales, represented by the familiar Spirogyra and desmids; the relatively large and complex Charales, such as Chara; the less conspicuous, but well‐studied Coleochaete; and several other less well‐known taxa. Ultrastructural studies of these green algae have revealed a variety of subcellular structures which are shared with land plants, and which are absent from most other algae. This article describes the phylogenetic importance of the cytoskeleton (including mitotic and meiotic division apparatus), peroxisomes, cell wall features, and organelles found in specialized cells such as spermatozoids, by comparison with correlative subcellular structures in embryophytes.

A centrin homologue is a component of the multilayered structure in bryophytes and pteridophytes

SummaryThe multilayered structure (MLS), a component of the locomotory complex of plant sperm, has been utilized extensively by taxonomists in establishing phylogenetic relationships between the lower plants and algae. Unfortunately, there has been almost no biochemical characterization of the MLS and, in those studies that did attempt a characterization, conflicting results were obtained. We utilized antisera to the calcium-binding protein centrin to probe thin sections of the mid-stage spermatids of the anthocerotePhaeoceros laevis, the hepaticSphaerocarpos texanus, and the pteridophyteCeratopteris richardii embedded in L. R. White resin. The lamellar strip (LS; layers S2–S4) of the MLS in each of these species is labelled strongly with anti-centrin, but the S1 layer, composed of microtubules, is not. InCeratopteris, centrin is also detected in the amorphous electron opaque material that connects the basal bodies of the flagella. Both the MLS and the amorphous zones are putative microtubule organizing centers. Extracts from axenic cultures ofCeratopteris subjected for electrophoresis and Western blotting revealed a reactive band at 19.3 kDa, a protein similar in molecular mass to algal centrin. These data indicate that the MLS is composed at least partially of the protein centrin or a protein antigenically-related to centrin. This report is the first electron microscopic immunocytochemical demonstration that a centrin homologue is found in land plants and that it occurs at putative microtubule organizing centers.

The pyrenoid is the site of ribulose 1,5-bisphosphate carboxylase/oxygenase accumulation in the hornwort (Bryophyta: Anthocerotae) chloroplast

SummaryChloroplasts of many species of hornworts (Anthocerotae) have a structure that resembles the pyrenoid of green algae but whether these two structures are homologous has not been determined. We utilized immunogold labelling on thin sections to determine the distribution of ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO), the major protein of algal pyrenoids, in sixteen hornwort species with and without pyrenoids. Several species (Phaeoceros laevis, Anthoceros punctatus, A. formosae, A. laminiferus, Folioceros fuciformis, Folioceros sp.,Dendroceros tubercularis, D. japonicus, D. validus, Notothylas orbicularis, N. temperata, andSpaerosporoceros adscendens) have uniplastidic (or primarily uniplastidic) cells with large prominent multiple pyrenoids. In all of these species, the labelling is found exclusively in the pyrenoid and, with the exception of theFolioceros, Dendroceros, andNotothylas species, the labelling is randomly distributed throughout the pyrenoid. In the exceptional species, the pyrenoids have prominent pyrenoglobuli or other inclusions that are unlabelled. InMegaceros flagellaris andM. longispirus, the cells are multiplastidic (with the exception of the apical cell and some epidermal cells) and the chloroplasts lack pyrenoids.Anthoceros fusiformis andPhaeoceros coriaceus have primarily uniplastidic cells but the chloroplasts lack pyrenoids; only an area of stroma in the center of the plastid devoid of starch, reminiscent of a pyrenoid, is found. In all of the species lacking pyrenoids, RuBisCo is found throughout the stroma, including the stromal spaces made by the so-called channel thylakoids. No preferential accumulation of RuBisCo is found in the pyrenoid-like region inA. fusiformis andP. coriaceus. These data indicate that 1) the hornwort pyrenoid is homologous to algal pyrenoids in the presence of RuBisCo; 2) that at least some of the RuBisCo in the pyrenoid must represent an active form of the enzyme; and 3) that, in the absence of pyrenoids, the RuBisCo is distributed throughout the stroma, as in higher plants.

Ultrastructural studies of spermatogenesis inAnthocerotophyta V. Nuclear metamorphosis and the posterior mitochondrion ofNotothylas orbicularis andPhaeoceros laevis

SummaryUltrastructural observations reveal that the spermatozoids of the hornwortsNotothylas andPhaeoceros contain two mitochondria and not one as described previously. Mitochondrial ontogeny and nuclear metamorphosis during spermiogenesis in these plants differ from all other archegoniates. The discovery that the posterior region of the coiled nucleus (when viewed from the anterior aspect) lies to the left of the anterior, in striking contrast to the dextral coiling of the nucleus of spermatozoids of other embryophytes, underlines the isolated nature of the hornworts among land plants. As the blepharoplast develops, the numerous ovoid mitochondria initially present in the nascent spermatid fuse to form a single elongated organelle which is positioned subjacent to the MLS and extends down between the nucleus and plastid. At the onset of nuclear metamorphosis, the solitary mitochondrion has separated into a larger anterior mitochondrion (AM) associated with the MLS and a much smaller posterior mitochondrion (PM) adjacent to the plastid. The PM retains its association with the plastid and both organelles migrate around the periphery of the cell as the spline MTs elongate. By contrast, in moss spermatids, where mitochondria undergo similar fusion and division, the AM is approximately the same size as the PM and the latter is never associated with the spline. As in other archegoniates, except mosses, spline elongation precedes nuclear metamorphosis in hornworts. Irregular strands of condensed chromatin compact basipetally to produce an elongated cylindrical nucleus which is narrower in its mid-region. During this process excess nucleoplasm moves rearward. It eventually overarches the inner surface of the plastid and entirely covers the PM.