Cell wall polymers in the placenta reflect developmental and functional differences across generations.

The placenta of hornworts is unique among bryophytes in the restriction of transfer cells that are characterized by elaborate wall labyrinths to the gametophyte generation. During development, cells around the periphery of the sporophyte foot elongate, forming smooth-walled haustorial cells that interdigitate with gametophyte cells. Using immunogold labeling with 22 antibodies to diverse cell wall polymers, we examined compositional differences in the developmentally and morphologically distinct cell walls of gametophyte transfer cells and sporophyte haustorial cells in the placenta of .

The origin of the sporophyte shoot in land plants: a bryological perspective.

Background: Land plants (embryophytes) are monophyletic and encompass four major clades: liverworts, mosses, hornworts and polysporangiophytes. The liverworts are resolved as the earliest divergent lineage and the mosses as sister to a crown clade formed by the hornworts and polysporangiophytes (lycophytes, monilophytes and seed plants). Alternative topologies resolving the hornworts as sister to mosses plus polysporangiophytes are less well supported.

Major transitions in the evolution of early land plants: a bryological perspective.

Background Molecular phylogeny has resolved the liverworts as the earliest-divergent clade of land plants and mosses as the sister group to hornworts plus tracheophytes, with alternative topologies resolving the hornworts as sister to mosses plus tracheophytes less well supported. The tracheophytes plus fossil plants putatively lacking lignified vascular tissue form the polysporangiophyte clade. Scope This paper reviews phylogenetic, developmental, anatomical, genetic and paleontological data with the aim of reconstructing the succession of events that shaped major land plant lineages.

The dawn of symbiosis between plants and fungi.

The colonization of land by plants relied on fundamental biological innovations, among which was symbiosis with fungi to enhance nutrient uptake. Here we present evidence that several species representing the earliest groups of land plants are symbiotic with fungi of the Mucoromycotina. This finding brings up the possibility that terrestrialization was facilitated by these fungi rather than, as conventionally proposed, by members of the Glomeromycota.

A cytochemical and immunocytochemical analysis of the wall labyrinth apparatus in leaf transfer cells in Elodea canadensis.

Background And Aims: Transfer cells are plant cells specialized in apoplast/symplast transport and characterized by a distinctive wall labyrinth apparatus. The molecular architecture and biochemistry of the labyrinth apparatus are poorly known. The leaf lamina in the aquatic angiosperm Elodea canadensis consists of only two cell layers, with the abaxial cells developing as transfer cells.

Frogs, sentinels of DNA damage induced by pollution in Naples and the neighbouring Provinces.

Many DNA mutation-based diseases recognised in Campania have recently been related to toxic substances in illegal dumping areas. We performed a comet assay on edible frog erythrocytes to evaluate DNA damage. Differences in genotoxic parameters were observed among populations.

Novel localization of callose in the spores of Physcomitrella patens and phylogenomics of the callose synthase gene family.

Background And Aims: Callose involvement in spore development is a plesiomorphic feature of land plants. Correlated light, fluorescence and immuno-electron microscopy was conducted on the developing spores of Physcomitrella patens to probe for callose. Using a bioinformatic approach, the callose synthase (PpCalS) genes were annotated and PpCalS and AtCalS gene families compared, testing the hypothesis that an exine development orthologue is present in P.

Cellular differentiation in moss protonemata: a morphological and experimental study.

Background And Aims: Previous studies of protonemal morphogenesis in mosses have focused on the cytoskeletal basis of tip growth and the production of asexual propagules. This study provides the first comprehensive description of the differentiation of caulonemata and rhizoids, which share the same cytology, and the roles of the cytoskeleton in organelle shaping and spatial arrangement.

Methods: Light and electron microscope observations were carried out on in vitro cultured and wild protonemata from over 200 moss species.

A novel ascomycetous endophytic association in the rhizoids of the leafy liverwort family, Schistochilaceae (Jungermanniidae, Hepaticopsida).

Liverworts form diverse associations with endophytic fungi similar to mycorrhizas in vascular plants. Whereas the widespread occurrence of glomeromycotes in the basal liverwort lineages is well documented, knowledge of the distribution of ascomycetes and basidiomycetes in derived thalloid and leafy clades is more fragmented. Our discovery that the ramified and septate rhizoids of the Schistochilaceae, the sister group to all other ascomycete-containing liverworts, are packed with fungal hyphae prompted this study on the effects of the fungi on rhizoid morphology, host specificity, the cytology of the association, and a molecular analysis of the endophytes.

Glomeromycotean associations in liverworts: a molecular, cellular, and taxonomic analysis.

Liverworts form endophytic associations with fungi that mirror mycorrhizal associations in tracheophytes. Here we report a worldwide survey of liverwort associations with glomeromycotean fungi (GAs), together with a comparative molecular and cellular analysis in representative species. Liverwort GAs are circumscribed by a basal assemblage embracing the Haplomitriopsida, the Marchantiopsida (except a few mostly derived clades), and part of the Metzgeriidae.

Desiccation tolerance in the moss Polytrichum formosum: physiological and fine-structural changes during desiccation and recovery.

Background And Aims: This study explores basic physiological features and time relations of recovery of photosynthetic activity and CO2 uptake following rehydration of a desiccation-tolerant moss in relation to the full temporal sequence of cytological changes associated with recovery to the normal hydrated state. It seeks reconciliation of the apparently conflicting published physiological and cytological evidence on recovery from desiccation in bryophytes.

Methods: Observations were made of water-stress responses and recovery using infrared gas analysis and modulated chlorophyll fluorescence, and of structural and ultrastructural changes by light and transmission electron microscopy.

Desiccation tolerance in the moss Polytrichum formosum: physiological and fine-structural changes during desiccation and recovery.

Background And Aims: This study explores basic physiological features and time relations of recovery of photosynthetic activity and CO(2) uptake following rehydration of a desiccation-tolerant moss in relation to the full temporal sequence of cytological changes associated with recovery to the normal hydrated state. It seeks reconciliation of the apparently conflicting published physiological and cytological evidence on recovery from desiccation in bryophytes.

Methods: Observations were made of water-stress responses and recovery using infrared gas analysis and modulated chlorophyll fluorescence, and of structural and ultrastructural changes by light and transmission electron microscopy.

A highly differentiated glomeromycotean association with the mucilage-secreting, primitive antipodean liverwort Treubia (Treubiaceae): clues to the origins of mycorrhizas.

Thallus anatomy in three species of the primitive liverwort genus Treubia (Metzgeriidae, Treubiales) was studied by light and electron microscopy. The thallus exudes copious mucilage, a feature shared elsewhere in liverworts only with the mycotrophic subterranean axes of the allied genus Haplomitrium. The central strand in the thallus midrib has a unique histological organization and harbors an intra- and intercellular infection by a glomeromycotean fungus that is far more highly differentiated than most of the glomeromycotean associations described to date.

Effects of de- and rehydration on food-conducting cells in the moss Polytrichum formosum: a cytological study.

Background And Aims: Moss food-conducting cells (leptoids and specialized parenchyma cells) have a highly distinctive cytology characterized by a polarized cytoplasmic organization and longitudinal alignment of plastids, mitochondria, endoplasmic reticulum and vesicles along endoplasmic microtubules. Previous studies on the desiccation biology of mosses have focused almost exclusively on photosynthetic tissues; the effects of desiccation on food-conducting cells are unknown. Reported here is a cytological study of the effects of de- and rehydration on food-conducting cells in the desiccation-tolerant moss Polytrichum formosum aimed at exploring whether the remarkable subcellular organization of these cells is related to the ability of mosses to survive desiccation.

Distribution of cell-wall xylans in bryophytes and tracheophytes: new insights into basal interrelationships of land plants.

Xylans are known to be major cellulose-linking polysaccharides in secondary cell walls in higher plants. We used two monoclonal antibodies (LM10 and LM11) for a comparative immunocytochemical analysis of tissue and cell distribution of xylans in a number of taxa representative of all major tracheophyte and bryophyte lineages. The results show that xylans containing the epitopes recognized by LM10 and LM11 are ubiquitous components of secondary cell walls in vascular and mechanical tissues in all present-living tracheophytes.

Subterranean gametophytic axes in the primitive liverwort Haplomitrium harbour a unique type of endophytic association with aseptate fungi.

•  Haplomitrium, a primitive liverwort taxon with only remote affinities to other liverwort groups, develops root-like subterranean axes harbouring fungal endophytes. Here we report on the fungal association in H. gibbsiae and H.

The structure and development of haustorial placentas in leptosporangiate ferns provide a clear-cut distinction between euphyllophytes and lycophytes.

This light and electron microscope study revealed that leptosporangiate ferns have highly distinctive gametophyte-sporophyte junctions characterized by sporophytic haustoria, the absence of intraplacental spaces and degenerating cells, and the early appearance of wall ingrowths in both generations. Other notable cytological features are highly pleomorphic plastids and mitochondrial aggregates in the gametophytic placental cells. Close similarities with the gametophyte-sporophyte junctions in Tmesipteris and major differences from those of homosporous lycophytes are in line with the placement of psilophytes and ferns in the same clade and distance both from lycophytes.

Diversity in the distribution of polysaccharide and glycoprotein epitopes in the cell walls of bryophytes: new evidence for the multiple evolution of water-conducting cells.

•   Although histologically much simpler than higher plants, bryophytes display a considerable degree of tissue differentiation, notably in those groups that possess an internal system of specialized water-conducting cells (WCCs). Here, using a battery of monoclonal antibodies, we examined the distribution of cell wall polysaccharide and glycoprotein carbohydrate epitopes in the gametophyte of four hepatics and eight mosses, with special reference to water-conducting cells. •   CCRC-M7, an antibody against an arabinogalactan epitope, gave a highly consistent and generally specific labelling of WCCs; more variable results were obtained with other antibodies.

The leafy stems of Sphagnum (Bryophyta) contain highly differentiated polarized cells with axial arrays of endoplasmic microtubules.

Contrary to the long-held belief that, internal to the cortical sterome, the central region of Sphagnum stems comprises unspecialized parenchyma, the present light- and electron-microscope study has revealed that these cells in fact have a highly specialized cytoplasmic organization. Their key features are: (a) the absence of large central vacuoles; (b) a spindle-shaped nucleus positioned internally; (c) a prominent axial system of endoplasmic microtubules associated with the nucleus, mitochondria, pleomorphic vacuoles, and membrane-bounded tubules and vesicles; (d) a distinct cytoplasmic polarization, with the cellular region near the capitulum being richer in organelles than the basal region; and (e) a high frequency of plasmodesmata in the cross walls with an enlarged median region containing no discernible desmotubule. Such a distinctive combination of cytological features has been hitherto only described for putative food-conducting cells in bryoid mosses.

Development of the leafy shoot in Sphagnum (Bryophyta) involves the activity of both apical and subapical meristems.

This light- and electron-microscope study of four species of Sphagnum reveals that stem elongation involves meristematic activities unique to the group and hitherto unrecognized. The internal tissue of the mature stem arises by the concerted activity of an apical (primary) and a subapical (secondary) meristem. The primary meristem comprises the immediate derivatives of the single apical cell.

Development of water-conducting cells in the antipodal liverwort Symphyogyna brasiliensis (Metzgeriales).

The thallus of the metzgerialean liverwort Symphyogyna brasiliensis Nets contains a strand of dead thick-walled tells with helicoidally-arranged pits that arc presumably involved in water transport. During the first phase of differentiation these cells undergo a 13-16-fold elongation while remaining thin-walled and almost unchanged in diameter. During subsequent maturation the walls become strongly thickened by deposition of highly electron-opaque material on extraplasmodesmal areas and of transparent material forming collars around plasmodesmata.