Absence Of Pyrenoids Research Articles

The Rubisco small subunits in the green algal genus Chloromonas provide insights into evolutionary loss of the eukaryotic carbon-concentrating organelle, the pyrenoid

BackgroundPyrenoids are protein microcompartments composed mainly of Rubisco that are localized in the chloroplasts of many photosynthetic organisms. Pyrenoids contribute to the CO2-concentrating mechanism. This organelle has been lost many times during algal/plant evolution, including with the origin of land plants. The molecular basis of the evolutionary loss of pyrenoids is a major topic in evolutionary biology. Recently, it was hypothesized that pyrenoid formation is controlled by the hydrophobicity of the two helices on the surface of the Rubisco small subunit (RBCS), but the relationship between hydrophobicity and pyrenoid loss during the evolution of closely related algal/plant lineages has not been examined. Here, we focused on, the Reticulata group of the unicellular green algal genus Chloromonas, within which pyrenoids are present in some species, although they are absent in the closely related species.ResultsBased on de novo transcriptome analysis and Sanger sequencing of cloned reverse transcription-polymerase chain reaction products, rbcS sequences were determined from 11 strains of two pyrenoid-lacking and three pyrenoid-containing species of the Reticulata group. We found that the hydrophobicity of the RBCS helices was roughly correlated with the presence or absence of pyrenoids within the Reticulata group and that a decrease in the hydrophobicity of the RBCS helices may have primarily caused pyrenoid loss during the evolution of this group.ConclusionsAlthough we suggest that the observed correlation may only exist for the Reticulata group, this is still an interesting study that provides novel insight into a potential mechanism determining initial evolutionary steps of gain and loss of the pyrenoid.

Ultrastructure and LSU rDNA-based Phylogeny of Peridinium lomnickii and Description of Chimonodinium gen. nov. (Dinophyceae)

Several populations of Peridinium lomnickii were examined by SEM and serial section TEM. Comparison with typical Peridinium, Peridiniopsis, Palatinus and Scrippsiella species revealed significant structural differences, congruent with phylogenetic hypotheses derived from partial LSU rDNA sequences. Chimonodinium gen. nov. is described as a new genus of peridinioids, characterized by the Kofoidian plate formula Po, cp, x, 4', 3a, 7'', 6c, 5s, 5''', 2'''', the absence of pyrenoids, the presence of a microtubular basket with four or five overlapping rows of microtubules associated with a small peduncle, a pusular system with well-defined pusular tubes connected to the flagellar canals, and the production of non-calcareous cysts. Serial section examination of Scrippsiella trochoidea, here taken to represent typical Scrippsiella characters, revealed no peduncle and no associated microtubular strands. The molecular phylogeny placed C. lomnickii comb. nov. as a sister group to a clade composed of Thoracosphaera and the pfiesteriaceans. Whereas the lack of information on fine structure of the swimming stage of Thoracosphaera leaves its affinities unexplained, C. lomnickii shares with the pfiesteriaceans the presence of a microtubular basket and the unusual connection between two plates on the left side of the sulcus, involving extra-cytoplasmic fibres.

Parallela Flint: its phylogenetic position in the Chlorophyceae and the polyphyly of Radiofilum Schmidle

Novis P.M., Lorenz M., Broady P.A. and Flint E.A. 2010. Parallela Flint: its phylogenetic position in the Chlorophyceae and the polyphyly of Radiofilum Schmidle. Phycologia 49: 373–383. DOI: 10.2216/09-65.1Analysis of chloroplast protein sequences from the genes atpB, rbcL and psaB demonstrates that the ribbon-forming freshwater alga Parallela novae-zelandiae is a member of the Chlorophyceae. We reject earlier classifications of Parallela as a member of the Tetrasporales or Gloeotilales and also confirm the splitting of the latter order. Molecular analysis shows that it is closely related to Radiofilum transversale but not R. conjunctivum, the latter associating with green algae having counterclockwise-displaced flagellar apparatuses. Since R. conjunctivum is the type species of the genus, we refer R. transversale to Parallela transversale. The two species of Parallela share a ribbon-forming mucilaginous habit and an absence of pyrenoids and layered mucilage. Parallela novae-zelandiae differs from P. transversale in lacking bipartite cell walls and has consistently multiseriate filaments, which are only sporadically present in P. transversale and are entirely absent in R. conjunctivum and other described species of Radiofilum. Radiofilum conjunctivum also contains pyrenoids. The bipartite wall condition has apparently evolved more than once during the evolution of the Chlorophyta.

Systematics of the marine microfilamentous green algaeUronema curvatum andUrospora microscopica (Chlorophyta)

The microfilamentous green alga Uronema curvatum is widely distributed along the western and eastern coasts of the north Atlantic Ocean where it typically grows on crustose red algae and on haptera of kelps in subtidal habitats. The placement of this marine species in a genus of freshwater Chlorophyceae had been questioned. Molecular phylogenetic analysis of nuclear-encoded small and large subunit rDNA sequences reveal that U. curvatum is closely related to the ulvophycean order Cladophorales, with which it shares a number of morphological features, including a siphonocladous level of organization and zoidangial development. The divergent phylogenetic position of U. curvatum, sister to the rest of the Cladophorales, along with a combination of distinctive morphological features, such as the absence of pyrenoids, the diminutive size of the unbranched filaments and the discoid holdfast, warrants the recognition of a separate genus, Okellya, within a new family of Cladophorales, Okellyaceae. The epiphytic Urospora microscopica from Norway, which has been allied with U. curvatum, is revealed as a member of the cladophoralean genus Chaetomorpha and is herein transferred to that genus as C. norvegica nom. nov.

CHUKCHIA PEDICELLATA GEN. ET SP. NOV. AND C. ENDOPHYTICA NOV. COMB., ARCTIC ENDEMIC BROWN ALGAE (PHAEOPHYCEAE)(1).

Study of the north Alaskan brown algal epiphyte Chukchia pedicellata sp. nov. suggests an apparently close relationship to Phaeostroma. Phaeostroma endophyticum S. Lund from east Greenland, Bylot Island, Nunavut, Canada, shows generic identity with Chukchia and specific differences from C.pedicellata. Comparison of C.pedicellata and P.pustulosum Kuck. (the type species of Phaeostroma) shows morphological, cytological, reproductive, and distributional differences. We recognize novelty of C.pedicellata and necessity to broaden the species description of P.endophyticum, which becomes Chukchia endophytica. C.endophytica is distinguished by its dimorphic vegetative habit, its large plurilocular sporangia, and the putative ability of the sporangia to digest host tissue to accommodate development within the host. Absence of pyrenoids and novel plurilocular sporangia in both species suggests that they are not members of the Ectocarpales, sensu lato.

CO2‐CONCENTRATING MECHANISMS OF THE POTENTIALLY TOXIC DINOFLAGELLATE PROTOCERATIUM RETICULATUM (DINOPHYCEAE, GONYAULACALES)1

The low CO2 concentration in seawater poses severe restrictions on photosynthesis, especially on those species with form II RUBISCO. We found that the potentially toxic dinoflagellate Protoceratium reticulatum Clap. et J. Lachm. possesses a form II RUBISCO. To cast some light on the mechanisms this organism undergoes to cope with low CO2 availability, we compared cells grown at atmospheric (370 ppm) and high (5000 ppm) CO2 concentrations, with respect to a number of physiological parameters related to dissolved inorganic carbon (DIC) acquisition and assimilation. The photosynthetic affinity for DIC was about one order of magnitude lower in cells cultivated at high [CO2]. End‐point pH‐drift experiments suggest that P. reticulatum was not able to efficiently use HCO3− under our growth conditions. Only internal carbonic anhydrase (CA) activity was detected, and its activity decreased by about 60% in cells cultured at high [CO2]. Antibodies raised against a variety of algal CAs were used for Western blot analysis: P. reticulatum extracts only cross‐reacted with anti‐ß‐CA sera, and the amount of immunoreactive protein decreased in cells grown at high [CO2]. No pyrenoids were observed under all growth conditions. Our data indicate that P. reticulatum has an inducible carbon‐concentrating mechanism (CCM) that operates in the absence of pyrenoids and with little intracellular CO2 accumulation. Calculations on the impact of the CA activity to photosynthetic growth [CO2] suggest that it is an essential component of the CCM of P. reticulatum and is necessary to sustain the photosynthetic rates observed at ambient CO2.

Light and Electron Microscopic Observations on Erythrolobus coxiae gen.et sp.nov. (Porphyridiophyceae, Rhodophyta) from Texas U.S.A.

Species of the unicellular red algae Dixoniella, Flintiella, Glaucosphaera, Porphyridium, Rhodosorus and Rhodella have been formally described and their fine structure investigated by transmission electron microscopy (TEM; Broadwater and Scott 1994) while the unicellular genus Rhodospora (Geitler 1927, Johansen et al. 2005) is described only at the light microscopic level. Several other new species and genera of unicellular red algae have also been isolated and briefly examined by molecular analysis and light and electron microscopy (Hara et al. 2000, Yokoyama et al. 2004) and formal description of several of these is currently underway (Yokoyama and Hara, personal communication). Recently our understanding of phylogenetic interrelationships of red algal unicells has progressed significantly using molecular techniques in combination with several TEM features (Hara et al. 2000, Saunders and Hommersand 2004, Yoon et al. 2006). Ultrastructural features considered most valuable in unicellular red algal systematics include Golgi apparatus associations with other organelles, presence or absence of pyrenoids and pyrenoid attributes, the morphology and precise details of chloroplasts and certain details of nuclei and mitosis (Broadwater and Scott 1994). In the mid-1970s a unicellular red alga believed to be a new genus was isolated from coastal Texas USA. Initial work describing growth characteristics and behavior in culture, phycobilin pigments and light and electron microscopy was completed but the results were not published (see Baca 1978). Recently, we conducted microscopic studies on this strain in order to formally describe this new coccoid red alga as Erythrolobus coxiae nov.gen et nov. sp. Algae Volume 21(4): 407-416, 2006

Morphology and molecular phylogeny of Phaeostrophion irregulare (Phaeophyceae) with a proposal for Phaeostrophiaceae fam. nov., and a review of Ishigeaceae

H. Kawai, H. Sasaki, S. Maeba & E.C. Henry. 2005. Morphology and molecular phylogeny of Phaeostrophion irregulare (Phaeophyceae) with a proposal for Phaeostrophiaceae fam. nov., and a review of Ishigeaceae. Phycologia 44: 169–182.Phaeostrophion irregulare, which is distributed along the Pacific coast of northwestern America, has been placed in the family Punctariaceae, order Dictyosiphonales (or Ectocarpales sensu lato), because of anatomical resemblances. On the basis of a previous culture study, the species was assumed to have a direct type of life history, with erect thalli forming unilocular or plurilocular zooidangia. However, the occurrence of a perennial prostrate system (holdfast), the presence of marginal meristematic cells on the holdfast and the lack of pyrenoids in chloroplasts suggest that this taxonomic assignment is questionable. Transmission electron microscopy observation confirmed the absence of pyrenoids in the chloroplasts. Molecular phylogenetic studies using rbcL (chloroplast) and partial 18S and 26S ribosomal RNA (nuclear) gene sequences revealed that Phaeostrophion is not included in the clade of Ectocarpales s.l., but forms a clade with Sphacelariales which diverged relatively early in the evolution of Phaeophyceae and shares an apical or marginal meristematic manner of growth with them. Members of Ishigeaceae were also shown to have a distant phylogenetic relationship with Chordariales (or Ectocarpales s.l.) and diverged early in the phaeophycean lineage. We propose a new family Phaeostrophiaceae to accommodate Phaeostrophion, although we suspend taxonomic treatment at the ordinal level.

Differences in pyrenoid morphology are correlated with differences in the rbcL genes of members of the Chloromonas lineage (volvocales, chlorophyceae).

Chloromonas is distinguished from Chlamydomonas primarily by the absence of pyrenoids, which are structures that are present in the chloroplasts of most algae and are composed primarily of the CO2-fixing enzyme Rubisco. In this study we compared sequences of the rbcL (Rubisco large subunit-encoding) genes of pyrenoid-less Chloromonas species with those of closely related pyrenoid-containing Chlamydomonas species in the "Chloromonas lineage" and with those of 45 other green algae. We found that the proteins encoded by the rbcL genes had a much higher level of amino acid substitution in members of the Chloromonas lineage than they did in other algae. This kind of elevated substitution rate was not observed, however, in the deduced proteins encoded by two other chloroplast genes that we analyzed: atpB and psaB. The rates of synonymous and nonsynonymous nucleotide substitutions in the rbcL genes indicate that the rapid evolution of these genes in members of the Chloromonas lineage is not due to relaxed selection (as it presumably is in parasitic land plants). A phylogenetic tree based on rbcL nucleotide sequences nested two Chlamydomonas species as a "pyrenoid-regained" clade within a monophyletic Chloromonas "pyrenoid-lost" clade. Character-state optimization with this tree suggested that the loss and the regain of pyrenoids were accompanied by eight synapomorphic amino acid replacements in the Rubisco large subunit, four of which are positioned in the region involved in its dimerization. However, both the atpB and the psaB sequence data gave robust support for a rather different set of phylogenetic relationships in which neither the "pyrenoid-lost" nor the "pyrenoid-regained" clade was resolved. The appearance of such clades in the rbcL-based tree may be an artifact of convergent evolutionary changes that have occurred in a region of the large subunit that determines whether Rubisco molecules will aggregate to form a visible pyrenoid.

Revision of the classification system of Radiococcaceae FOTT ex KOMÁREK (except the subfamily Dictyochlorelloideae) ( Chlorophyta)

Radiococcaceae (Chlorophyta) is a large and widespread family in terrestrial and freshwater habitats. The taxonomy of this family is difficult because no coherent system of generic criteria exists, fact which led to many species transfers from one genus to another with as a consequence many synonyms. Based on traditional criteria and a study of Radiococcaceae isolated from soils we propose to rearrange the generic system according to only several, easily observable features which are: 1) capacity to form spherical shaped vegetative cells, 2) presence or absence of pyrenoid, 3) number of autospores (only/mainly two or only/mainly four-eight), 4) behaviour of the sporangial cell wall during autospore release (rupture or gelatinisation). As additional secondary criteria are used 5) the capacity to form tubular branched colonies (for separation of the genus Palmodictyon), 6) number of chloroplasts (for definition of the genera Planktosphaeria and Phacomyxa), 7) capacity to form plate-like sarcinoid colonies (for the separation of the genera Dispora and Crucigloea). According to these principles 25 genera (including 10 new genera) comprising about 80 described species are recognised. The system is artifical, but allows to more easily recognise genera and species and also an easier allocation of new taxa.

Molecular Phylogeny and Taxonomic Revision of Chlamydomonas (Chlorophyta). I. Emendation of Chlamydomonas Ehrenberg and Chloromonas Gobi, and Description of Oogamochlamys gen. nov. and Lobochlamys gen. nov.

The genus Chlamydomonas (including Chloromonas) is one of the largest green algal genera comprising more than 600 species. To initiate a comprehensive analysis of the phylogeny and systematics of the genus, we determined nuclear-encoded SSU rRNA sequences from 32 strains of Chlamydomonas, Chloromonas and Chlorogonium with emphasis on oogamous taxa and related strains, and incorporated these into global molecular phylogenetic analyses of 132 strains of Chlorophyceae. In addition, we studied the morphology and reproduction of oogamous and related strains by light microscopy. We recognize and designate 18 monophyletic lineages (clades) within the Chlorophyceae, 11 of which are confined to the CW (basal bodies displaced clockwise) subgroup. The majority of clades recognized within the Chlorophyceae do not correspond to any of the traditional classification systems, which are still largely based on the organization level. Strains assigned to Chlamydomonas and Chloromonas were found in seven different clades confirming the polyphyly of the two genera as presently conceived. To initiate the taxonomic revision of Chlamydomonas, C. reinhardtii is proposed as the conserved type of the genus. In consequence, species in clades other than the clade containing C. reinhardtii must be transferred to other genera, a process initiated in this contribution. The oogamous strains studied represent a monophyletic lineage, which is described as Oogamochlamys gen. nov. comprising three species (O. gigantea, O. zimbabwiensis and O. ettlii spec. nov.). The sister clade to Oogamochlamys consists of isogamous strains characterized by chloroplasts with incisions and is described as Lobochlamys gen. nov. with two species (L. culleus and L. segnis). Another clade is characterized by asteroid or perforated, parietal chloroplasts and contains the type species of Chloromonas (C. reticulata). Thus, the polyphyletic Chloromonas (traditionally defined as "Chlamydomonas without pyrenoids") can be legitimized as a monophyletic genus by restriction to this clade and is here emended on the basis of chloroplast characters (the clade contains strains with or without pyrenoids thus rejecting the character "absence of pyrenoids").

The diversity and coevolution of Rubisco, plastids, pyrenoids, and chloroplast-based CO2-concentrating mechanisms in algae

Algae have adopted two primary strategies to maximize the performance of Rubisco in photosynthetic CO2fixation. This has included either the development of a CO2-concentrating mechanism (CCM), based at the level of the chloroplast, or the evolution of the kinetic properties of Rubisco. This review examines the potential diversity of both Rubisco and chloroplast-based CCMs across algal divisions, including both green and nongreen algae, and seeks to highlight recent advances in our understanding of the area and future areas for research. Overall, the available data show that Rubisco enzymes from algae have evolved a higher affinity for CO2when the algae have adopted a strategy for CO2fixation that does not utilise a CCM. This appears to be true of both Green and Red Form I Rubisco enzymes found in green and nongreen algae, respectively. However, the Red Form I Rubisco enzymes present in nongreen algae appear to have reduced oxygenase potential at air level of O2. This has resulted in a photosynthetic physiology with a reduced potential to be inhibited by O2and a reduced need to deal with photorespiration. In the limited number of microalgae that have been examined, there is a strong correlation between the existence of a high-affinity CCM physiology and the presence of pyrenoids in all algae, highlighting the potential importance of these chloroplast Rubisco-containing bodies. However, in macroalgae, there is greater diversity in the apparent relationships between pyrenoids and chloroplast features and the CCM physiology that the species shows. There are many examples of microalgae and macroalgae with variations in the presence and absence of pyrenoids as well as single and multiple chloroplasts per cell. This occurs in both green and nongreen algae and should provide ample material for extending studies in this area. Future research into the function of the pyrenoid and other chloroplast features, such as thylakoids, in the operation of a chloroplast-based CCM needs to be addressed in a diverse range of algal species. This should be approached together with assessment of the coevolution of Rubisco, particularly the evolution of Red Form I Rubisco enzymes, which appear to achieve superior kinetic characteristics when compared with the Rubisco of C3higher plants, which are derived from green algal ancestors.Key words: Rubisco, CO2-concentrating mechanism, carbonic anhydrase, aquatic photosynthesis, algae, pyrenoids, inorganic carbon.

Presence of the CO2-concentrating mechanism in some species of the pyrenoid-less free-living algal genus Chloromonas (Volvocales, Chlorophyta).

Physiological and morphological characteristics related to the CO2-concentrating mechanism (CCM) were examined in several species of the free-living, unicellular volvocalean genus Chloromonas (Chlorophyta), which differs morphologically from the genus Chlamydomonas only by lacking pyrenoids. The absence of pyrenoids in the chloroplasts of Chloromonas (Cr.) rosae UTEX 1337, Cr. serbinowii UTEX 492, Cr. clatharata UTEX 1970, Cr. rosae SAG 26.90, and Cr. palmelloides SAG 32.86 was confirmed by light and electron microscopy. In addition, immunogold electron microscopy demonstrated that ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) molecules were distributed almost evently throughout the chloroplasts in all five Chloromonas strains. However, Chloromonas exhibited two types of physiological characteristics related to the CCM depending on the species or strains examined. Chloromonas rosae UTEX 1337 and Cr. serbinowii had high photosynthetic affinities for CO2 in cells grown in culture medium bubbled with air (low-CO2 cells), compared with those grown in medium bubbled with 5% CO2 (high-CO2 cells), indicating the presence of the low-CO2-inducible CCM. In addition, these two Chloromonas strains exhibited low-CO2-inducible carbonic anhydrase (CA; EC 4.2.1.1) activity and seemed to have small intracellular inorganic carbon pools. Therefore, it appears that Cr. rosae UTEX 1337 and Cr. serbinowii possess the CCM as in pyrenoid-containing microalgae such as Chlamydomonas reinhardtii. By contrast, Cr. clatharata, Cr. rosae SAG 26.90 and Cr. palmelloides showed low photosynthetic affinities for CO2 when grown under both CO2 conditions. Moreover, these three strains exhibited an apparent absence of intracellular inorganic carbon pools and lacked low-CO2-inducible CA activity. Thus, Cr. clatharata, Cr. rosae SAG 26.90 and Cr. palmelloides, like other pyrenoid-less algae (lichen photobionts) reported previously, seem to lack the CCM. The present study is the first demonstration of the CCM in pyrenoid-less algae, indicating that pyrenoids or accumulation of Rubisco in the chloroplasts are not always essential for the CCM in algae. Focusing on this type of CCM in pyrenoid-less algae, the physiological and evolutionary significance of pyrenoid absence is discussed.

PHYLOGENYOF CHLOROMONAS (CHLOROPHYCEAE): A STUDY OF 185 RIBOSOMAL RNA GENE SEQUENCES1

ABSTRACTThe unicellular, biflagellate genus Chloromonas differs from its ally, Chlamydomonas, primarily by the absence of pyrenoids in the vegetative stage of the former. As with most green flagellate genera, little is known about phylogenetic affinities within and among Chloromonas species. Phylogenetic analyses of nuclear‐encoded small‐subunit ribosomal RNA gene sequences demonstrate that a sampling of five Chloromonas taxa, obtained from major culture collections, do not form a monophyletic group. However, only three of these isolates, Chloromonas clathrata, Chloromonas serbinowi, and Chloromonas rosae, are diagnosable morphologically as Chloromonas species by the absence of a pyrenoid in the vegetative stage. The three diagnosable Chloromonas taxa form an alliance with two pyrenoid‐bearing chlamydomonads, Chlamydomonas augustae and Chlamydomonas macrostellata. With the exception of Chloromonas serbinowi, which represents the basal lineage within the clade, each of the diagnosable Chloromonas taxa and their pyrenoidbearing Chlamydomonas allies were isolated originally from mountain soils, snow, or cold peat. These observations suggest that habitat, independent of pyrenoid status, may be most closely linked to the natural history of this clade of chlamydomonad flagellates.

On a new species ofPavlova (Prymnesiophyceae) from China

Pavlova viridis sp. nov. is described on the basis of light and electron microscope observations. The material was collected from the coast of haiyang county of Shandong, China. It is characterized by 1) yellowish green to green chloroplast, 2) rudimentary short flagellum 0.3 μm long and hook-shaped, 3) long flagellum with small spherical knob-scales, 4) absence of pyrenoid and stigma, and 5) marine habitat. This new species andP. salina seem to be most closely related to each other but their colour, the insertion of their three appendages, the shape of their knob scales, and their cell periplasts are quite different from one another.

Viridiella fridericiana (Chlorococcales, Chlorophyta), a new genus and species isolated from extremely acid environments

Abstract The genus Viridiella gen. nov. with a single species Viridiella fridericiana sp. nov. (Chlorococcales, Chlorophyta) is proposed. Cells are ellipsoidal to globose, and have a smooth cell wall and a single parietal chloroplast without pyrenoids. Reproduction occurs by the formation of 4–8 autospores. Viridiella can be distinguished from the closely related genus Chiorella by its cell wall ultrastructure and the absence of pyrenoids. The cellulosic cell wall is composed of a single layer with an irregular outer polysaccharide covering. Interthylakoidal starch grains are present. Viridiella fridericiana is extremely tolerant of low pH, being capable of growth at pH 0.8–7.2.

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 and taxonomic position of Chlorosarcina stigmaticaDeason (Chlorophyceae, Chlorophyta)

Using cryofixation methods we studied the ultrastructure of thallus cells and zoospores of a chlorosarcinoid alga present in the Innsbruck culture collection (strain nr. T 105). We confirm an earlier observation by Gärtner et al. (1988) that pyrenoids are absent, and that it represents Chlorosarcina stigmatica Deason 1959. This species was recently transferred to another genus because descendents of the original culture were found to possess pyrenoids. Our observations on T 105 demonstrate however that the original concept of C. stigmatica as a species of Chlorosarcina (a genus characterized by the absence of pyrenoids) is still valid. We found the zoospore flagellar apparatus to be characteristic of the class Chlorophyceae sensu Mattox and Stewart . Other species, i.e. C. brevispinosa and C. longispinosa are known to have an ulvophycean flagellar apparatus. It is proposed to transfer these to a separate new genus, Pleurastrosarcina , in the class Ulvophyceae.

Polynuclearity of vegetative cells in coccal green algae from the family neochloridaceae

Summary The division of nuclei in cells of 13 strains of unicellular, zoospore and aplanospore producing green algae during their life cycles was studied. This process is different in the coenocytic (polyenergic) species from the genera Chlorotetraedron, Spongiochloris and Neochloris p.p. (including the type species), and in the mononuclear Neochloris (excl. typo), in which it is similar to the unicellular Chlorella or coenobial Scenedesmus (Chlorellales sensu stricto). The genus Dictyococcus has the similar nuclear division as was recognized in coenocytic types, but several other characters are different (absence of pyrenoids). The simple unicellular coenocytic green algae have to be classified into the special family Neochloridaceae, which is the simplest group of polynuclear line of green algae with “naked” zooids from the order Protosiphonales. The mononuclear species from the genus Neochloris were classified into a special genus Ettlia (zoosporine Chlorellales).

SPHACELARIA LACUSTRIS SP. NOV., A FRESHWATER BROWN ALGA FROM LAKE MICHIGAN1

ABSTRACTThe growth, reproduction and ultrastructure of a new freshwater phaeophyte, Sphacelaria lacustris sp. nov., are described. The plant occurs as a minute calcified thallus at 5–15 m depth along the western shoreline of Lake Michigan. Both freshly collected and laboratory grown plants show apical growth of erect and basal filaments, intermittent longitudinal divisions in filament segments, vegetative reproduction by propagules, numerous parietal chloroplasts and an absence of pyrenoids, characteristics of Sphacelaria. This material is separated from the only other freshwater species in the genus (S. fluviatilis Jao) at least by differences in longitudinal septation, in branching, in its propagules and in general aspect. Between this plant and marine brown algae there are essential similarities of ultrastructure of cell wall and pores, chloroplasts, mitochondria, nucleus and the production/excretion of physodes.