Phaeoceros Laevis Research Articles

Predicting the spatial distribution of Turkish hornworts (Anthocerotophyta) under changing climatic conditions

Climate change is a phenomenon that can affect all living organisms. To see its effect, many methods and techniques have been improved recently. Species distribution modelling (SDM) is the most popular technique for this. Here, the distribution of hornworts (Anthoceros caucasicus, Anthoceros punctatus, Phaeoceros laevis and Phymatoceros bulbiculosus), which are a group of non-vascular land plants native to Türkiye, was studied under changing climate using SDM. Three global climate models (GCMs) (CMCC-ESM2, HadGEM3-GC31-LL and MIROC6), two scenarios (SSP1-2.6 and 5-8.5) and four time periods (2021–2040, 2041–2060, 2061–2080 and 2081–2100) were considered. A total of 89 occurrence records of the hornwort species A. caucasicus, A. punctatus and P. laevis were considered for SDM. The potential distribution of P. bulbiculosus could not be modelled due to a lack of sufficient coordinates. Although the patterns between current and future distributions did not change significantly, there were notable differences in the distribution of modelled species in the SSP 5–8.5 scenario. In particular, the MIROC6 model showed an anomalous pattern for A. punctatus in the SSP 5–8.5 scenario. The SDMs indicate that the model will be a valuable resource for the conservation of these species at local and regional levels throughout Türkiye.

Phymatoceros Stotler et al. (Anthocerotophyta) newly recorded from India with a new species, P. binsarensis

ABSTRACT Introduction Phymatoceros Stotler et al., one of the 14 extant genera of hornworts, is known from only two species worldwide. During our studies of Indian hornworts, a distinctly variable population was found at Binsar, Uttarakhand, and sharing the same habitat as Phaeoceros himalayensis (Kashyap) Prosk. ex Bapna & G.G.Vyas and Phaeoceros laevis (L.) Prosk. Methods A critical study of the specimens housed at CSIR–NBRI, Lucknow (LWG) was conducted. An SEM study of spores was also carried out to examine their ultramorphological characters. Key results The plants were found to be remarkably characterised by a narrow thallus with prolific stalked tubers arising from the mid-ventral surface; female plants with short involucres; single rounded to irregular chloroplast per cell, without a pyrenoid; and spore distal face with a large, central, single, pitted central hump, and the proximal face with a distinct single dimple on each tetrahedral area between triradiate rays. A detailed morphotaxonomic account is presented, along with detailed SEM observations of spores of the Indian plants. Conclusion Our critical comparative study has revealed that the plants of the newly recorded population belong to the genus Phymatoceros and are distinct from hitherto known species. They are described here as a new species, Phymatoceros binsarensis A.K.Asthana, D.Shukla & Reesa Gupta, and are the first record of Phymatoceros in India. As such, they represent a remarkable and interesting disjunct occurrence of the genus in Asia, separate from its distribution in four other continents (Africa, Europe, and North and South America).

Cuticle structure and chemical composition of waxes in Phaeoceros laevis (L.) Prosk (Notothyladaceae, Anthocerotophyta).

The development of a hydrophobic cuticle covering the epidermis was a crucial evolutionary novelty ensuring the establishment of land plants. However, there is little information about its structure and chemical composition, as well as its functional implications in avascular lineages such as Anthocerotophyta. The main goal of the present study was to compare the gametophyte and sporophyte cuticles of Phaeoceros laevis. Semithin sections were analyzed through light microscopy (LM), cuticle structure was evaluated by transmission electron microscopy (TEM) and epicuticular wax morphology was analyzed by scanning electron microscopy (SEM). Total waxes were analyzed by CG/MS, and the components were identified based on the mass spectra. A thin lipophilic layer was detected on the sporophyte surface, structured as a stratified cuticular layer, similar to the well-known structure described for vascular plants. On the other hand, the gametophyte cuticle was observed only with TEM as a thin osmiophilic layer. SEM analyses showed a film-type wax on the surface of both life phases. The wax layer was eight-fold thicker on the sporophyte (0.8 µg cm-2) than on gametophyte (0.1 µg cm-2). Possible mechanical and/or drought protection are discussed. Fatty acids, primary alcohols, and steroids were identified in both life phases, while the kauren-16-ene diterpene (3%) was detected only on the sporophyte. Although no alkanes were detected in P. laevis, our findings unveil great similarity of the sporophyte cuticle of this hornwort species with the general data described for vascular plants, reinforcing the conservative condition of this character and supporting the previous idea that the biosynthetic machinery involved in the synthesis of wax compounds is conserved since the ancestor of land plants.

Three new records of Anthocerotophyta for Western Africa (Sierra Leone) based on spore ornamentation of a specimen collected by A. Harrington, with an emphasis on Anthoceros sect. Fusiformes Grolle

ABSTRACT Introduction. During an investigation into the world-wide distribution of Anthoceros caucasicus Steph., we examined a voucher collected from Sierra Leone by A. J. Harrington in 1966 and subsequently studied by E. W. Jones. Methods. Based on spore observations using light and scanning electron microscopy we found that three Anthocerotophyta taxa were present in this mixed collection. Key results. We report Anthoceros aff. bharadwajii Udar & A.K.Asthana new to Africa, Phaeoceros laevis (L.) Prosk. new to Sierra Leone and tropical Africa, and Anthoceros punctatus L. new to Sierra Leone and western mainland Africa. Conclusions. Anthoceros caucasicus should be removed from the Sierra Leone bryoflora list, and possibly from tropical Africa.

Complete mitochondrial genome sequence of Anthoceros angustus: conservative evolution of the mitogenomes in hornworts

The architecture and composition of the mitochondrial genome of bryophytes is currently considered much more stable and invariant than that of vascular plants. For example, liverworts and mosses appear to have nearly static mitochondrial genomes, whereas neither of two vascular plant mitogenomes sequenced to date share the same gene order. By contrast, the two available mitogenomes of hornworts, Nothoceros aenigmaticus and Phaeoceros laevis, show high consistency in gene content but differ in their gene order. To explore the patterns of hornwort mitogenome structure at a broader phylogenetic breadth and provide insights into plant mitogenome evolution, we assembled the complete mitochondrial genome from a third hornwort species, Anthoceros angustus Steph. Its mitogenome comprises 242,410 base pairs, and encodes 21 protein coding genes, three rRNA genes and 20 tRNA genes, with 38 introns disrupting 16 protein-coding genes, including three newly described introns, making it the most intron-rich plant mitochondrial genome determined to date. A total of ten putatively pseudogenized protein coding genes were found in Anthoceros; eight of them are shared with Nothoceros and Phaeoceros. The genic composition of the Anthoceros mitogenome differs from that of the other two hornworts by only one or two gene insertions or losses. The gene order in the Anthoceros mtDNA differs from that in Phaeoceros and Nothoceros by only one and three events of inversion or translocations, respectively. Overall, hornworts appear to have kept a stable mt genome structure, which could have characterized early land plant mt genome evolution.

Identificación del tipo morfológico de micorriza arbuscular en Phaeoceros laevis (Anthocerotophyta).

Las micorrizas arbusculares han sido registradas para distintos representantes del Phylum Anthocerotophyta, entre ellos Phaeoceros laevis (L.) Prosk. En este trabajo se da a conocer el tipo morfológico de colonización por parte de hongos micorrícicos arbusculares en P. laevis, el cual corresponde a un intermedio entre los tipos Arum y Paris. Además, esta asociación se menciona por primera vez para los bosques templados del hemisferio sur. Se presentan descripciones breves e imágenes de las estructuras características de las micorrizas arbusculares presentes en P. laevis.

Survey of bryophytes in Serra da Canastra National Park, Minas Gerais, Brazil

Serra da Canastra National Park is located in southwestern Minas Gerais State and contains several phytophysiognomies of the Brazilian Cerrado. To date, no study on bryophytes has been conducted in this area and the present study is the first to be carried out in this major biological reserve of Cerrado located on the Brazilian Plateau. This study found 289 species of bryophytes, including mosses, liverworts, and one species of hornwort, representing fourty-one Brazilian endemic species and 56 new records for Minas Gerais State. Most species are widely distributed in Brazil, with only 16% having restricted distributions. Regarding worldwide distribution, 31% are Neotropical. Lejeuneaceae had the highest species richness among liverwort families with 53 species, whereas Sphagnaceae had the highest richness among moss families with 26 species. Phaeoceros laevis was the only hornwort species found in the park. This study contributes to the understanding of bryophyte species richness and distribution, and provides the worldwide and Brazilian distribution of the bryophyte flora of Serra da Canastra National Park, an important center for biodiversity conservation.

Stomatal density and aperture in non-vascular land plants are non-responsive to above-ambient atmospheric CO2 concentrations.

Following the consensus view for unitary origin and conserved function of stomata across over 400 million years of land plant evolution, stomatal abundance has been widely used to reconstruct palaeo-atmospheric environments. However, the responsiveness of stomata in mosses and hornworts, the most basal stomate lineages of extant land plants, has received relatively little attention. This study aimed to redress this imbalance and provide the first direct evidence of bryophyte stomatal responsiveness to atmospheric CO2. A selection of hornwort (Anthoceros punctatus, Phaeoceros laevis) and moss (Polytrichum juniperinum, Mnium hornum, Funaria hygrometrica) sporophytes with contrasting stomatal morphologies were grown under different atmospheric CO2 concentrations ([CO2]) representing both modern (440 p.p.m. CO2) and ancient (1500 p.p.m. CO2) atmospheres. Upon sporophyte maturation, stomata from each bryophyte species were imaged, measured and quantified. Densities and dimensions were unaffected by changes in [CO2], other than a slight increase in stomatal density in Funaria and abnormalities in Polytrichum stomata under elevated [CO2]. The changes to stomata in Funaria and Polytrichum are attributed to differential growth of the sporophytes rather than stomata-specific responses. The absence of responses to changes in [CO2] in bryophytes is in line with findings previously reported in other early lineages of vascular plants. These findings strengthen the hypothesis of an incremental acquisition of stomatal regulatory processes through land plant evolution and urge considerable caution in using stomatal densities as proxies for paleo-atmospheric CO2 concentrations.

Simple sequence repeats in bryophyte mitochondrial genomes

Simple sequence repeats (SSRs) are thought to be common in plant mitochondrial (mt) genomes, but have yet to be fully described for bryophytes. We screened the mt genomes of two liverworts (Marchantia polymorpha and Pleurozia purpurea), two mosses (Physcomitrella patens and Anomodon rugelii) and two hornworts (Phaeoceros laevis and Nothoceros aenigmaticus), and detected 475 SSRs. Some SSRs are found conserved during the evolution, among which except one exists in both liverworts and mosses, all others are shared only by the two liverworts, mosses or hornworts. SSRs are known as DNA tracts having high mutation rates; however, according to our observations, they still can evolve slowly. The conservativeness of these SSRs suggests that they are under strong selection and could play critical roles in maintaining the gene functions.

New and interesting bryophyte records for the flora of Serbia

During a revision of the bryophyte collections in the Herbarium of the Balkan Peninsula, Natural History Museum of Belgrade (BEO) and the Herbarium of the University of Belgrade (BEOU), as well as historical literature data, four bryophytes were identified as new to the flora of Serbia, namely, the mosses Fontinalis hypnoides, Leucobryum juniperoideum, Dicranum spurium and the hornwort Phaeoceros laevis. Fontinalis hypnoides is relatively recently recorded in SW Serbia, while Leucobryum juniperoideum and Dicranum spurium are known from historical collections. The hornwort Phaeoceros laevis was cited for SE Serbia in 1907, but up to now not found again.

Invited perspective: bryophytes as models for understanding the evolution of sexual systems

One of the first life history characters that students of bryology learn is the bryophyte life cycle. Roughly half of the bryophytes have separate sexes (dioicous) and half are hermaphroditic (monoicous). This variation is important for taxonomic purposes but also has major consequences for nearly every aspect of bryophyte biology. For example, dioicous species generally reproduce less frequently than monoicous species (Longton & Schuster 1983) but harbor more genetic variation than monoicous species (Eppley et al. 2006). More broadly, however, the maintenance of both sexual systems at nearly equal frequencies in the bryophytes is quite unusual among the eukaryotes. This situation makes bryophytes an important model system for studying the evolutionary consequences of changes in sexual system. Bryophytes have a long history as model systems in cytology and genetics. Sex chromosomes in plants were first discovered in the liverwort Sphaerocarpus donnellii (Allen 1917), and the term ‘‘heterochromatin’’ was coined for the dark staining heteromorphic pair of chromosomes in many bryophytes (Heitz 1932). Bryophytes have long served as model genetic systems because the dominant part of the life cycle (i.e., the gametophyte) is haploid, and the phenotype of the plant directly reflects its genotype without the masking of dominance (Allen 1919; Ashton & Cove 1977; Engel 1968; von Wettstein 1924). More recently, efficient gene targeting via homologous recombination was discovered in Physcomitrella patens (Kammerer & Cove 1996; Schaefer & Zryd 1997; Strepp et al. 1998) and Ceratodon purpureus (Brucker et al. 2005; Mittmann et al. 2009; Trouiller et al. 2007). With this tool researchers can construct powerful tests for associations between genes and traits. In addition, the genome of P. patens has now been completely sequenced (Rensing et al. 2008), and sequencing projects for C. purpureus (http://www.jgi.doe.gov/ sequencing/why/ceratodon.html), Phaeoceros laevis (http://ldl.genomics.org.cn/page/searchplant. jsp?speciesname5phaeoceros), and Marchantia polymorpha (http://www.jgi.doe.gov/sequencing/ why/99191.html) are now underway. Together the natural variation in sexual system and the potential for laboratory study make bryophytes ideal for studying the causes and consequences of changes in sexual system. The purpose of this perspective is to highlight areas where interdisciplinary research can provide new insights into the evolution of bryophyte sexual systems. We have structured the perspective around three major evolutionary transitions: 1) the evolution of dioicy; 2) the evolution of sex chromosomes; and 3) the evolution of monoicy. We first provide a brief outline of the evolutionary theory underlying each of these phenomena. Since much of this theory was developed for angiosperms, we suggest how it can be applied to bryophytes. Second, we indicate how 3 Corresponding author’s e-mail: stuartmcdaniel@ufl.edu DOI: 10.1639/0007-2745-115.1.1

The mitochondrial genomes of the early land plants Treubia lacunosa and Anomodon rugelii: dynamic and conservative evolution.

Early land plant mitochondrial genomes captured important changes of mitochondrial genome evolution when plants colonized land. The chondromes of seed plants show several derived characteristics, e.g., large genome size variation, rapid intra-genomic rearrangement, abundant introns, and highly variable levels of RNA editing. On the other hand, the chondromes of charophytic algae are still largely ancestral in these aspects, resembling those of early eukaryotes. When the transition happened has been a long-standing question in studies of mitochondrial genome evolution. Here we report complete mitochondrial genome sequences from an early-diverging liverwort, Treubia lacunosa, and a late-evolving moss, Anomodon rugelii. The two genomes, 151,983 and 104,239 base pairs in size respectively, contain standard sets of protein coding genes for respiration and protein synthesis, as well as nearly full sets of rRNA and tRNA genes found in the chondromes of the liverworts Marchantia polymorpha and Pleurozia purpurea and the moss Physcomitrella patens. The gene orders of these two chondromes are identical to those of the other liverworts and moss. Their intron contents, with all cis-spliced group I or group II introns, are also similar to those in the previously sequenced liverwort and moss chondromes. These five chondromes plus the two from the hornworts Phaeoceros laevis and Megaceros aenigmaticus for the first time allowed comprehensive comparative analyses of structure and organization of mitochondrial genomes both within and across the three major lineages of bryophytes. These analyses led to the conclusion that the mitochondrial genome experienced dynamic evolution in genome size, gene content, intron acquisition, gene order, and RNA editing during the origins of land plants and their major clades. However, evolution of this organellar genome has remained rather conservative since the origin and initial radiation of early land plants, except within vascular plants.

Distribution patterns in British and Irish liverworts and hornworts

The 300 species of British and Irish liverworts and hornworts are classified into 10 groups, based on their recorded presence in 10×10 km grid squares (hectads). A two-stage classification (CLUSTASPEC) initially amalgamated single species into clusters and then systematically removed the smallest clusters, redistributing their species until only 10 clusters remained; in the second stage, species were reassigned to the cluster to which they showed the greatest similarity until they all remained stationary. The groups were named after the species with distributions which were most similar to that of the cluster as a whole (Pellia epiphylla, Phaeoceros laevis sens. lat., Cladopodiella fluitans, Lophocolea heterophylla, Scapania undulata, Anastrepta orcadensis, Harpalejeunea molleri, Moerckia blyttii, Scapania degenii, Marsupella condensata). Most groups are nested within at least one other group but the south-eastern L. heterophylla cluster is distinctive. Four groups, Phaeoceros laevis, Cladopodiella fluitans, Scapania degenii and (especially) Marsupella condensata contain a high percentage (30–73) of species which are classed by IUCN criteria as Critically Endangered, Endangered or Vulnerable.

The complete mitochondrial genome sequence of the hornwort Phaeoceros laevis: retention of many ancient pseudogenes and conservative evolution of mitochondrial genomes in hornworts

Plants have large and complex mitochondrial genomes in comparison to other eukaryotes. In bryophytes, the mitochondrial genomes exhibit a mixed mode of conservative and dynamic evolution. Here, we sequenced the complete mitochondrial genome from hornwort Phaeoceros laevis, to investigate the level of conservation in mitochondrial genome evolution within hornworts. The circular molecule consists of 209,482 base pairs and represents the largest known mitochondrial genome of bryophytes. It contains 30 protein genes, 3 rRNA genes, and 21 tRNA genes, with 34 cis-spliced group II introns disrupting 16 protein genes. There are 11 pseudogenes in this genome, and nine of them are shared with the other fully sequenced hornwort chondriome from Megaceros aenigmaticus, a distant relative of P. laevis. These pseudogenes were likely formed during an early stage of hornwort evolution. The two hornwort chondriomes differ by four inversions and translocations, seven genes, and four introns in the genome structure and organization. At the sequence level, they are very similar, with the identity values ranging mostly from 80 to 95% in intergenic spacers, introns, and exons. These data indicate that mitochondrial genome evolution in hornworts is less conservative than in liverworts, but has not reached the dynamic level as seen in seed plants.

Evolutionary Patterns in the Auxin Metabolism of Green Plants

The metabolism, transport, and action of the hormone auxin (indole‐3‐acetic acid; IAA) is thought to regulate the morphological processes responsible for generating the characteristic body plans of green plants. One objective of this study was to determine the general class of the IAA biosynthetic pathway operating in the vegetative apices of the liverwort Pallavicinia lyellii, the moss Polytrichum ohioense, and the pteridophyte Selaginella kraussiana. A new methodology, which is based on the relative ability of unlabeled tryptophan to affect the conversion of 14C‐anthranilate into labeled IAA, established that the predominant IAA biosynthetic pathway(s) in all these plants are tryptophan‐independent pathways. A second objective was to characterize auxin metabolism in the charophycean green alga Nitella sp. and the hornwort Phaeoceros laevis. Gas chromatography–mass spectrometry was used to measure the levels of free IAA and IAA conjugates, and thin‐layer chromatography was used to determine the nature of IAA conjugates and the rates of IAA conjugate biosynthesis. Growing tips of Nitella thalli have low steady state levels of free IAA and IAA conjugates. Moreover, this alga exhibits very slow rates of IAA conjugate formation, which indicates that its free IAA level is primarily regulated via the balance between the biosynthesis of new IAA molecules and the degradation of existing molecules, as has already been shown for liverworts. By contrast, apical regions of Phaeoceros thalli have much higher free IAA and IAA‐amide conjugate levels under steady state conditions. This hornwort has intermediate to rapid rates of conjugate formation, and, thus, it appears to regulate free IAA levels via the equilibrium between conjugate synthesis versus conjugate hydrolysis, as has repeatedly been observed for mosses and vascular plants. The data presented in this study lead to a more comprehensive perspective on the evolutionary patterns of auxin metabolism in green plants.

The role of carbonic anhydrase in photosynthesis and the activity of the carbon‐concentrating‐mechanism in bryophytes of the class Anthocerotae

The role of carbonic anhydrase in the carbon‐concentrating‐mechanism of bryophytes of the class Anthocerotae was investigated by comparing the gas‐exchange characteristics of material which had been incubated in the membrane‐permeable Carbonic Anhydrase inhibitor ethoxyzolamide, with those of untreated material and material which had been incubated in buffer solution. In Phaeoceros laevis (Anthocerotae), incubation in ethoxyzolamide caused a depression in the rate of gross assimilation and a decrease in CO2 affinity beyond that which could be attributed to increased diffusion limitation. A range of liverworts and mosses, in which a carbon‐concentrating‐mechanism is absent, were also investigated. These showed no depression of rates of gross assimilation after incubation in ethoxyzolamide relative to those of untreated material. The CO2 compensation point and CO2 uptake characteristics of Phaeoceros laevis were significantly affected by incubation in ethoxyzolamide. Values of CO2 compensation point for Phaeoceros laevis rose from 2.5 Pa, after incubation in buffer, to 20 Pa after incubation in ethoxyzolamide. The CO2 compensation point for the liverworts Pellia epiphylla and Marchantia polymorpha was not significantly affected by incubation in ethoxyzolamide. Measurements of the release of CO2 at the end of a short (15 min) period of illumination revealed that, after suppression of carbonic anhydrase activity, the rapid release of a CO2 pool occurred in Phaeoceros laevis but not in the liverworts. There were also significant differences between values for fractionation measured in units per mil (‰), measured instantaneously, for Phaeoceros laevis incubated in ethoxyzolamide, compared with fractionation values for this species after incubation in buffer. Incubation in ethoxyzolamide caused fractionation values to rise from 12.4–22.7‰, indicating that the carbon‐concentrating‐mechanism of this species had been inactivated. Incubation in ethoxyzolamide had no effect on fractionation values for the liverworts. The convexity of the light saturation curves of liverworts and Phaeoceros laevis was also investigated, but there were no differences between groups before or after the two treatments. The data indicate an important role for carbonic anhydrase in the functioning of the carbon‐concentrating‐mechanism in the Anthocerotae.

Pyrolysis mass spectrometry analysis of free-living and symbiotic cyanobacteria.

The potential of pyrolysis mass spectrometry to distinguish closely related cyanobacterial strains was assessed by using the technique to compare symbiotic cyanobacteria isolated from the hornwort Phaeoceros laevis and free-living cyanobacterial strains at the same field site. The same strains had previously been compared using polymerase chain reaction-based DNA fingerprinting techniques (West & Adams 1997, Appl. Environ. Microbiol. 63: 4479-4484). Many of the strains were grouped identically by the two techniques, although there were some differences, possibly resulting from the ability of these cyanobacteria to develop a range of specialised cell types having different chemical compositions to the vegetative cells. Although growth conditions were chosen to suppress cellular differentiation, this may not always have been completely successful. With careful control of growth conditions pyrolysis mass spectrometry has considerable potential as an additional tool for the phenetic comparison of cyanobacterial strains. It has the advantage that analysis is directly derived from whole cells, and hence is simpler and cheaper than DNA-based methods, although it does require the growth of axenic strains. The technique may be particularly useful in the study of some of the more cryptic unicellular and non-heterocystous filamentous cyanobacterial groups, in which the lack of cellular differentiation should minimise any variability in the chemical composition of cells.

Hornworts in Switzerland—endangered?

Maps of the distribution of Anthoceros punctatus L. var. cavernosus auct. and Phaeoceros laevis (L.) Prosk. ssp. carolinianus (Michx.) Prosk. in Switzerland are presented. They are based on herbarium specimens and field studies and distinguish between records before and since 1960. According to bibliographical data from the beginning of this century, both taxa were widespread throughout Central Europe, A. punctatus being more common than P. laevis. This view is not supported by herbarium collections. Detailed field research from 1981 to 1989 in the vicinity of Berne showed that the occurrence of hornworts depends largely on the type and treatment of cultivation. P. laevis seems to be more sensitive to changes in habitat conditions caused by modern agricultural practice (mechanical stress, increase in fertilizer input and use of pesticides) than A. punctatus. In conclusion, P. laevis is classified as endangered in Switzerland.

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

Chloroplasts 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.

Ultrastructure, development and cytochemistry of storage cells in the‘tubers’of Phaeoceros laevis Prosk. (Anthocerotophyta)

summaryThe gametophyte of Phaeoceros laevis Prosk. forms small parenchymatous tubers as perennating organs. The development of tuber cells is characterized by marked cytoplasmic proliferation. The chloroplasts are packed with starch and abundant lipid bodies (spherosomes) are produced in the cytoplasm in association with rough endoplasmic reticulum. The vacuoles become pleomorphic and accumulate electron‐dense deposits. These were negative to PATAg staining for carbohydrates and were digested by pronase; therefore they are assumed to be protein. No ultrastructural evidence was found for the participation of either ER or dictyosomes in the biogenesis of the protein‐storing vacuoles. The mature tubers have a distinct layer of epidermal cells with thick external walls, and frequently harbor intercellular cyanobacteria.