Taxonomy of Pyramimonas obovata and other observations on the subgenus Vestigifera of Pyramimonas (Prasinophyceae, Chlorophyta)

A vestigiferan species commonly referred to as Pyramimonas obovata N. Carter has been redescribed as P. melkonianii sp, nov. Characters of this species and a further six (P. disomata Butcher ex McFadden, Hill et Wetherbee, P. mantoniae Moestrup et Hill, P. mitra Moestrup et Hill. P. moestrupii McFadden, P. aff. nephroidea McFadden, P. orientalis Butcher ex McFadden, Hill et Wetherbee) isolated from South African waters are used to define further the subgenus Vestigifera McFadden. This includes a unique chloroplast shape and basal hyaline region with stellate or cruciform vacuoles, a transitional plate-like structure in the flagellum, and a different microtubular root system. The proximal set of basal body connectives were found to be remarkably symmetrical and like those of the subgenus Trichocystis McFadden, and a duct fibre was found associated with the Id root in all currently investigated species. The validity of the larger body (box and crown) scales as taxonomic markers at a fine level is also questioned.     

AN ADDITIONAL PUNCTATE SPECIES OF PYRAMIMONAS, P. FORMOSA, SP. NOV., AND ITS IMPACT ON THE SUBGENERA PUNCTATAE AND PYRAMIMONAS (PRASINOPHYCEAE, CHLOROPHYTA)

A new punctate species of Pyramimonas Schmarda from South Africa is described. This species is somewhat anomalous and, like P. chlorina Sym et Pienaar (subgenus Pyramimonas McFadden), has characters that bridge the divide between the subgenera Pyramimonas and Punctatae McFadden. Features of these two species, together with the lack of exclusive character sets for either subgenus derived from other species of these subgenera, lead to the conclusion that Punctatae now should be subsumed formally into the subgenus Pyramimonas.     

LIGHT AND ELECTRON MICROSCOPY OF A PUNCTATE SPECIES OF PYRAMIMONAS,P. MUCIFERA SP. NOV. (PRASINOPHYCEAE)1

Pyramimonas mucifera sp. nov., a punctate species of the genus, is unusual both behaviorally and at the fine structural level. It forms two distinct populations in culture, one benthic and one planktonic. Planktonic forms are more conventional for the genus, but benthic forms are found in loosely packed mucilage, have flagellar rather than ciliary beating of the flagella, and display a higher degree of metaboly. Ultrastructurally this species is unusual in that it has a unique scale complement and the cells contain numerous muciferous vesicles, leaving only small pockets of cytoplasm containing the usual organelles. This species has a 3–1 type flagellar apparatus but has an additional fibrillar band, a 4–3-2–3 microtubular root system and a flexible synistosome. The discovery of a mucilage-producing species of Pyramimonas draws attention to possible links with other prasinophytes (Halosphaera) and green algae of questionable affiliation (Oltmannsiellopsis and Hafniomonas). It also provides a model of the primitive pyramimonad.     

PHYLOGENY OF THE GENUS PYRAMIMONAS (PRASINOPHYCEAE,CHLOROPHYTA) INFERRED FROM THE rbcL GENE1

A 1089-basepair fragment (approx. 75%) of the large subunit of the chloroplast-encoded gene, ribulose-1,5-bis-phosphate carboxylase/oxygenase (rbcL), was sequenced from 16 species of the genus Pyramimonas Schmarda. Electron microscopic and biochemical studies of Pyramimonas, one of the most morphologically diverse genera within the potential sister groups to the chlorophyll a- and b-containing plants, suggest that this genus consists of at least four separate subgenera. Using the homologous sequence of rbcL from Cymbomonas tetramitiformis Schiller (Halosphaeraceae) as an outgroup and applying the maximum likelihood method, we show that the inferred topology is congruent with traditional delimitations of the taxa based on observations of periplast, internal ultrastructure, and biochemical features. A bootstrap analysis also supports division at the subgeneric level; however, the low bootstrap support associated with the deep nodes precludes resolution of these branches. A maximum likelihood relative rate test revealed that the rbcL gene in these single-celled green flagellates has a heterogeneous rate of substitution. The rbcL gene in species of the subgenus Pyramimonas has evolved at an accelerated rate relative to that of congenerics.     

Reconstruction of the flagellar apparatus and microtubular cytoskeleton inPyramimonas gelidicola (Prasinophyceae,Chlorophyta)

Summary The absolute configuration of the flagellar apparatus inPyramimonas gelidicola McFadden et al. has been determined and shows identity withP. obovata, indicating that they are closely related. Comparison with the flagellar apparatus of quadriflagellate zoospores from the more advancedChlorophyceae suggest thatPyramimonas may be a primitive ancestral form. The microtubular cytoskeleton has been examined in detail and is shown to be unusual in that it does not attach to the flagellar apparatus. Cytoskeletal microtubules are nucleated individually, and this is interpreted as an adaptation to the methods of mitosis and scale deployment. In view of the primitive nature of these processes, it is proposed that this type of cytoskeletal organization may represent a less advanced condition than that of the flagellar root MTOCs (microtubule organizing centers) observed in theChlorophyceae.     

Transferring the freshwater dinoflagellate Peridinium wisconsinense (Dinophyceae) to the family Thoracosphaeraceae,with the description of Fusiperidinium gen. nov.

Distinctive spindle‐shaped thecae first described by Samuel Eddy in 1930 and assigned to the genus Peridinium Ehrenberg are commonly reported from freshwater environments in eastern North America. We demonstrate that thecae incubated from cysts of Peridinium wisconsinense Eddy have six cingular plates and a protuberant apical pore complex characteristic of the family Thoracosphaeraceae Schiller 1930 emend. Tangen in Tangen et al . 1982. Small subunit ribosomal DNA (SSU rDNA) and internal transcribed spacer (ITS) sequences confirm the close genetic similarity with Chimonodinium lomnickii (Wo?oszyńska) Craveiro, Calado, Daugbjerg, Gert Hansen & Moestrup and with species recently reassigned to the genus Apocalathium Craveiro, Daugbjerg, Moestrup & Calado that was inferred from previously published LSU rDNA analysis of cysts of P. wisconsinense . Despite sharing identical tabulation with the thoracosphaeracean genera Chimonodinium Craveiro, Calado, Daugbjerg, Gert Hansen & Moestrup and Apocalathium , substantial morphological differences in the morphology of both the thecate and cyst stages of P. wisconsinense led us to reassign this species to the genus Fusiperidinium gen. nov. The phylogenetic position of Fusiperidinium wisconsinense comb. nov., inferred from concatenated data of SSU and LSU sequences, suggests that it evolved from the brackish Scrippsiella lineage, independently of the transition that produced the family Peridiniaceae. Cysts described as Geiselodinium tyonekensis Engelhardt from nonmarine strata from Alaska are apparently identical to the resistant cysts produced by F. wisconsinense . The palynologically‐constrained late Middle Miocene age for the Tyonek Formation provides a minimum age of 11.6 Ma for the evolution of this lineage, coinciding with a rapid glacioeustatic decline in sea level. Our findings also call into question the inclusion of the family Thoracosphaeraceae within the order Peridiniales Haeckel.     

THE ULTRASTRUCTURE OF PYRAMIMONAS PSEUDOPARKEAE SP. NOV. (PRASINOPHYCEAE) FROM SOUTH AFRICA1

The ultrastructure of Pyramimonas pseudoparkeae sp. nov., a member of the class Prasinophyceae occurring in tidal pools along the east, south and west coast of South Africa, is described. The cell surface is covered by three distinctive body scales whilst the flagellar surfaces possess four types of scales. The structure of these scales is described. P. pseudoparkeae resembles Pyramimonas parkeae Norris and Pearson but differs in the structure of the type 2 body scale. The symmetry and ultrastructure of the cell are described with special attention given to the flagellar apparatus. Preliminary information on the life cycle of this species is presented. This new species is compared with other closely related members of the genus Pyramimonas.     

Pyramimonas tychotreta, sp. nov. (prasinophyceae), a new marine species from antarctica: light and electron microscopy of the motile stage and notes on growth rates

An undescribed marine prasinophyte, Pyramimonas tychotreta, sp. nov., was isolated from a water sample collected near the ice edge in the Weddell Sea (Antarctica) and is characterized by means of light and electron microscopy. This is the second described Antarctic species in the genus and it possesses a cell ultrastructure typical for members of the subgenus Vestigifera McFadden. The quadriflagellated cells measure 8–12 μm in length and 6–7 μm in width and are equipped with seven types of organic scales that cover the flagella and cell body. The scale floor of the box scales is ornamented by quadrants of parallel striations running perpendicular to one another. The scale floor is further characterized by a number of randomly positioned perforations. The wall of the box scales may be solid or possess up to five perforations. The base of the crown scales is square with rounded corners. It is formed of two crossed ribs, the extremities of which are interconnected by a peripheral rib. Four upright arms, attached to the peripheral rib in positions slightly offset from its junction with the cross ribs, join up with the distal extremity of a central upright strut. Each arm possesses two spines. The limuloid scales are cross‐striped by 10–12 ribs. Some details of the flagellar apparatus are briefly reported. Pyramimonas tychotreta is compared with other species of the genus. Experiments were conducted to study the response of growth rate to variations in temperature and salinity in the clonal culture. The best growth rate (0.45 divisions·24 h ^{? 1}) was found at 4.6° C; growth ceased at temperatures in excess of 12° C. Growth in salinities ranging from 15 to 35 psu was similar, but was arrested at 10 psu. These studies suggest that P. tychotreta as a cold stenotherm and euryhaline taxon. New observations are presented on the geographic distribution of previously described species of Pyramimonas Schmarda from the Northern Foxe Basin, Canada.     

Description of Pyramimonas diskoicola sp. nov. and the importance of the flagellate Pyramimonas (Prasinophyceae) in Greenland sea ice during the winter–spring transition

Pyramimonas Schmarda is a genus of unicellular green flagellates, recorded in marine water and sea ice samples. Pyramimonas is within the prey size range of the most important protozoan grazers in Disko Bay, West Greenland, where this study took place. Despite the potential ecological importance, little is known about the occurrence of the genus. The aim of this study was to explore the biomass of Pyramimonas in developing stages of sea ice and in the water column. Pyramimonas colonized the early stages of sea ice, and the highest percent of Pyramimonas biomass was found in grease ice. The biomass of Pyramimonas was more than a magnitude higher within sea ice compared to the surface water. The results illustrate that Pyramimonas from the ice is an important contributor to the plankton community prior to the spring bloom. An undescribed species, Pyramimonas diskoicola sp. nov., was found. Based on morphology and ultrastructure, combined with molecular phylogeny inferred from the small-subunit SSU rDNA and the large-subunit chloroplast-encoded rbcL, the species was placed in subgenus Vestigifera. The cells possessed four flagella, measured 8.3 ± 2.6 μm in length and 5.1 ± 0.8 μm in width, and were characterized by an uplifted quadrant in the center of the box scales, not seen at any other Pyramimonas species. The phylogenetic analyses indicated P. diskoicola to be closely related to other polar sea ice species of Pyramimonas.     

Neue Arten der Gattung Pyramimonas Schmarda

Zusammenfassung Es wird auf eine grosse Formenfülle der Gattung Pyramimonas hingewiesen. Mehrere neue Arten and eine neue Varietät, die in Nordmähren (Tschechoslowakei) gefunden werden, werden erwähnt und abgebildet. Folgende Arten werden beschrieben: Pyramimonas recta, P. fasciata, P. radiata, P. conradii, P. cribrum, P. polychloris, P. rapa, P. pluristigma, P. fabelliformis und die Varietdt P. reticulata var. conica.

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Summary The great number of Pyramimonas-species is discussed. Some new species, found in Nordmähren (Czechoslovakia) are described and pictured. The new species described are: Pyramimonas recta, P. fasciata, P. radiata, P. conradii, P. cribrum, P. polychloris, P. rapa, P. pluristigma, P. fabelliformis and the variety P. reticulata var. conica.

     

Cover

ON THE COVER: [Benthic unicells plus abandoned cell walls following zoospore release of the new marine, sand‐dwelling genus Chrysoparadoxa australica gen. et sp. nov. (Chrysoparadoxophyceae) photographed with differential interference contrast optics. Two chloroplasts are U‐shaped at the ends of the cells and then split into 2 lobes. Ultrastructure shows the chloroplasts to be surrounded by only 2 membranes, a novel feature within the heterokonts. Photo credit: R Wetherbee. Vol. 55, No. 2, pp. 257–278 ]     

Light and electron microscopical studies onHafniomonas gen. nov. (Chlorophyceae,Volvocales), a genus resemblingPyramimonas (Prasinophyceae)

Based on light and electron microscopical studies ofPyramimonas reticulata the genusPyramimonas is shown to contain a number of unrelated flagellates.P. reticulata andP. montana are transferred to the new genusHafniomonas, cells of which differ fromPyramimonas in shape, in the absence of scales and hairs on the body and flagellar surfaces, in details of the chloroplast, the position of the nucleus, the Golgi apparatus, the internal structure of the flagellar apparatus, and in cell division. The prasinophytePyramimonas contains a characteristic association of a large microbody and a rhizoplast, situated on the nuclear surface. A similar association is being found in an increasing number of prasinophycean flagellates, but is absent inHafniomonas, which is considered related to chlorophycean rather than prasinophycean flagellates. The phylogenetic position ofHafniomonas is discussed, based in particular on details of the unique flagellar apparatus.     

Serial reconstruction of the mitochondrial reticulum in the antarctic flagellate,Pyramimonas gelidicola (Prasinophyceae,Chlorophyta)

Summary A serial reconstruction ofPyramimonas gelidicola McFadden, Moestrup andWetherbee has revealed a large reticulated mitochondrion branching throughout the cell. The possibility of single mitochondria in other members of thePrasinophyceae and the uniformity of the morphology of this organelle within the class is discussed.     

Prasinochloris sessilis gen. et sp. nov., a coccoid member of the prasinophyceae,with some remarks upon cyst formation in Pyramimonas

Prasinochloris sessilis gen. et sp. nov. is described from collected material. It has a sessile coccoid stage and a motile stage resembling Pyramimonas. A table records the non-motile stages reported for species of Pyramimonas, and various genera with Pyramimonas-like stages are discussed.     

RATE OF O2 PRODUCTION DERIVED FROM PULSE‐AMPLITUDE‐MODULATED FLUORESCENCE: TESTING THREE BIOOPTICAL APPROACHES AGAINST MEASURED O2‐PRODUCTION RATE1

Light absorption by phytoplankton is both species specific and affected by photoacclimational status. To estimate oxygenic photosynthesis from pulse‐amplitude‐modulated (PAM) fluorescence, the amount of quanta absorbed by PSII needs to be quantified. We present here three different biooptical approaches to estimate the fraction of light absorbed by PSII: (1) the factor 0.5, which implies that absorbed light is equally distributed among PSI and PSII; (2) the fraction of chl a in PSII, determined as the ratio between the scaled red‐peak fluorescence excitation and the red absorption peak; and (3) the measure of light absorbed by PSII, determined from the scaling of the fluorescence excitation spectra to the absorption spectra by the “no‐overshoot” procedure. Three marine phytoplankton species were used as test organisms: Prorocentrum minimum (Pavill.) J. Schiller (Dinophyceae), Prymnesium parvum cf. patelliferum (J. C. Green, D. J. Hibberd et Pienaar) A. Larsen (Haptophyceae), and Phaeodactylum tricornutum Bohlin (Bacillariophyceae). Photosynthesis versus irradiance (P vs. E) parameters calculated using the three approaches were compared with P versus E parameters obtained from simultaneously measured rates of oxygen production. Generally, approach 1 underestimated, while approach 2 overestimated the gross O₂‐production rate calculated from PAM fluorescence. Approach 3, in principle the best approach to estimate quanta absorbed by PSII, was also superior according to observations. Hence, we recommend approach 3 for estimation of gross O₂‐production rates based on PAM fluorescence measurements.     

CELL CYCLE DEPENDENT VIRUS PRODUCTION IN MARINE PHYTOPLANKTON1

In this study we investigated virus production in two marine phytoplankton species and how it relates to the host's cell cycle. Phaeocystis pouchetii (Hariot) Lagerheim and Pyramimonas orientalis McFadden, Hill & Wetherby, growing synchronously in batch cultures, were infected with their respective viruses (PpV and PoV) at four different stages in the cell cycle and the production of free virus was then measured for 30 h. The virus production in P. orientalis infected with PoV depended on the time of infection, whereas no such relation was found for P. pouchetii infected with PpV. The P. orientalis cultures infected at the end of the dark period and at the beginning of the light period produced three times more virus than those infected in the middle of the light period and eight times more virus than those infected at the beginning of the dark period. The latent periods for PpV and PoV were 12–14 h and 18–20 h, respectively, and in both cases were independent of the host cell cycle. The differences in virus production may be attributed to light or cell cycle dependent regulation of host infection, metabolism, or burst size. Regardless of the mechanism, these differences may be related to differences in the ecological strategies of the hosts and their ability to form blooms.     

PHENOTYPIC VARIATION AND GENOTYPIC DIVERSITY IN A PLANKTONIC POPULATION OF THE TOXIGENIC MARINE DINOFLAGELLATE ALEXANDRIUM TAMARENSE (DINOPHYCEAE)1

Multiple clonal isolates from a geographic population of Alexandrium tamarense (M. Lebour) Balech from the North Sea exhibited high genotypic and phenotypic variation. Genetic heterogeneity was such that no clonal lineage was repeatedly sampled according to genotypic markers specified by amplified fragment length polymorphism (AFLP) and microsatellites. Subsampling of genotypic data from both markers showed that ordination of individuals by pair‐wise genetic dissimilarity indices was more reliable by AFLP (482 biallelic loci) than by microsatellites (18 loci). However, resulting patterns of pair‐wise genetic similarities from both markers were significantly correlated (Mantel test P < 0.005). The composition of neurotoxins associated with paralytic shellfish poisoning (PSP) was also highly diverse among these isolates and allowed clustering of toxin phenotypes based on prevalence of individual toxins. Correlation analysis of pair‐wise relatedness of individual clones according to PSP‐toxin profiles and both genotypic characters failed to yield close associations. The expression of allelochemical properties against the cryptophyte Rhodomonas salina (Wis?ouch) D. R. A. Hill et Wetherbee and the predatory dinoflagellate Oxyrrhis marina Dujard. manifested population‐wide variation of responses in the target species, from no visible effect to complete lysis of target cells. Whereas the high genotypic variation indicates high potential for adaptability of the population, we interpret the wide phenotypic variation as evidence for lack of strong selective pressure on respective phenotypic traits at the time the population was sampled. Population markers as applied here may elucidate the ecological significance of respective traits when followed under variable environmental conditions, thereby revealing how variation is maintained within populations.     

The Disruption of Dictyosome Structure, Polarity and Secretory Activity in the Scale-producing Green Alga, Pyramimonas inconstans

Domozych, D. S. and Korbusieski, T. J. 1985. The disruptionof dictyosome structure, polarity and secretory activity inthe scale-producing green alga Pyramimonas inconstans.—J.exp.Bot.36: 1304–1312. Dictyosome morphology and scale morphogenesis in the green alga,Pyramimonas inconstans, are well-defined ultrastructurally.By applying the sodium-specific ionophore, monensin, to actively-growingcell cultures, both dictyosome micro-architecture and the scale-basedsecretory pathway can be significantly altered. Applicationof 0.1 mol m³ and 0.01 mol m ^–3monensin for short periods(1 -3 h) results in cisternal curling and the disorientationof dictyosome polarity. Prolonged exposure to the ionophore(4-24 h) results in the complete disruption of dictyosome morphologyand scale morphogenesis with the emergence of irregular vesiclesfrom the maturing face. Removal of monensin by repeated washingreturns dictyosome structure and secretory activity to normal.These results indicate that Golgi apparatus integrity and secretoryactivity in Pyramimonas may be controlled by a localized, cytoplasmicproton gradient Key words: Monensin, Pyramimonas, dictyosome     

ABSOLUTE CONFIGURATION ANALYSIS OF THE FLAGELLAR APPARATUS OF PTEROSPERMA CRISTATUM (PRASINOPHYCEAE) AND CONSIDERATION OF ITS PHYLOGENETIC POSITION1

Pterosperma cristatum Schiller, a member of the Pra-sinophyceae, was examined with light and electron microscopy with special attention on the absolute configuration of flagellar apparatus components and associated structures. This alga is characterized by asymmetrically arranged basal bodies, connecting fibers and microtubular roots. The microtubular root system is homologous with the cruciate root system, the so-called X-2-X-2 root system typical of non-charophycean green algae. Two ducts are associated with microtubular roots. A similar flagellar apparatus and duct system was found in two other prasinophyte genera, Pyramimonas and Halosphaera. The close phylogenetic affinity of these three genera is discussed.