Chlorophycean Algae Research Articles

The Alga Uronema belkae Has Two Structural Types of [FeFe]-Hydrogenases with Different Biochemical Properties.

Several species of microalgae can convert light energy into molecular hydrogen (H2) by employing enzymes of early phylogenetic origin, [FeFe]-hydrogenases, coupled to the photosynthetic electron transport chain. Bacterial [FeFe]-hydrogenases consist of a conserved domain that harbors the active site cofactor, the H-domain, and an additional domain that binds electron-conducting FeS clusters, the F-domain. In contrast, most algal hydrogenases characterized so far have a structurally reduced, so-termed M1-type architecture, which consists only of the H-domain that interacts directly with photosynthetic ferredoxin PetF as an electron donor. To date, only a few algal species are known to contain bacterial-type [FeFe]-hydrogenases, and no M1-type enzymes have been identified in these species. Here, we show that the chlorophycean alga Uronema belkae possesses both bacterial-type and algal-type [FeFe]-hydrogenases. Both hydrogenase genes are transcribed, and the cells produce H2 under hypoxic conditions. The biochemical analyses show that the two enzymes show features typical for each of the two [FeFe]-hydrogenase types. Most notable in the physiological context is that the bacterial-type hydrogenase does not interact with PetF proteins, suggesting that the two enzymes are integrated differently into the alga's metabolism.

Growth and metabolism of a freshwater chlorophycean alga Chlorella vulgaris: Toxic effects and ecological implications of two textile dyes

Growth and metabolism of a freshwater chlorophycean alga Chlorella vulgaris: Toxic effects and ecological implications of two textile dyes

Revisiting the supposed oldest bilaterian trace fossils from Uruguay: Late Paleozoic, not Ediacaran

Grazing trails found in the rhythmite beds attributed to the Ediacaran Tacuarí Formation (northern Uruguay) had been identified as the oldest evidence of bilaterians in the world. However, a diverse and abundant invertebrate, mostly arthropod, trace fossil assemblage is found associated with Upper Paleozoic palynomorphs in these same beds at the original localities from where the oldest bilaterian burrows were reported. These ichnoassemblages include Arborichnus repetita, Crescentichnus tesiltus, Cruziana problematica, Diplichnites aff. gouldi, Diplopodichnus biformis, Gluckstadtella cooperi, Helminthoidichnites tenuis, Kingella aff. natalensis, Maculichna varia, Rusophycus isp., Treptichnus pollardi, and Umfolozia sinuosa. The palynological assemblages yielded 89 species composed of 33 spores, 49 pollen grains, four chlorophycean algae, a fungal spore, an acritarch, and an indeterminate species. These occurrences point to a Phanerozoic record. The dominant botanical groups recorded are Lycophyta, Cordaitean, Coniferalean, Glossopteridalean, Corystospermaceae/ Peltaspermaceae, Pteridophyta, algal (Botryococcus, Tetraporina, Brazilea, Quadrisporites), and other groups (Deusilites tenuistriatus, Portalites gondwanensis). The high ichnodiversity, the prevalence of unquestionable arthropod biogenic structures, along with the abundance of ichnotaxa suggests a Carboniferous–Permian age. Therefore, the ichnoassemblages indicate that these strata are not Ediacaran in age and belong to the San Gregorio Formation, which represents the Upper Paleozoic Gondwanan glacial deposits in Uruguay. The ichnofauna is equivalent to others that are well known in deposits of the Late Paleozoic Ice Age from Brazil, Argentina, and South Africa. Furthermore, the new palynologic data from the trace-fossil bearing strata show that they can be correlated to the latest Carboniferous–early Cisuralian Cristatisporites inconstans-Vittatina saccata (IS) Zone of Paraná Basin in Uruguay.

English

In limnological studies Phytoplanktons are the primary considerations.Algae which are freely percolated with mean of water current are considered as phytoplanktons.All algae are not considered as phytoplanktons like Chara, Nitella these are the macroscopic Alga which grows profoundly in any fresh water bodies carrying suaitable ecophysiological environment to them. Algae are the photosynthetic producers which accounts approx. one third of total photosynthetic activity on this planet. Our study deals with a freshwater lake ecosystem. In limnology of a lake we found dominance of algal genera belongs to Chlorophyceae, Bacillariophyceae, Cyanophyceae Class. However, Euglenophyceae class may present but its population depend upon trophic status of Lake. Present paper deals with periodical analysis of few unicellular phytoplanktons and one filamentous genera Prasiola which is a new citation to Bikaner Phycology. Gajner lake was selected for our study which located around 33 kms away from Bikaner toward west side. Study was carried out for one year January 2017 to December 2017.We collected samples from 3 sites of Gajner lake twice in a month. Now Gajner Lake is the part of wildlife sanctuary. A historical tourist site Gajner palace also located along with lake. So, it is less polluted. Due to trophic level of lake Chlorophycean alga profoundly present in the lake. Although a portion of Lake is under village panchayat which is openly accessed by the local people of Gajner village. The open access site of lake has totally different phytoplanktonic density.

The plastid proteome of the nonphotosynthetic chlorophycean alga Polytomella parva

The unicellular, free-living, nonphotosynthetic chlorophycean alga Polytomella parva, closely related to Chlamydomonas reinhardtii and Volvox carteri, contains colorless, starch-storing plastids. The P. parva plastids lack all light-dependent processes but maintain crucial metabolic pathways. The colorless alga also lacks a plastid genome, meaning no transcription or translation should occur inside the organelle. Here, using an algal fraction enriched in plastids as well as publicly available transcriptome data, we provide a morphological and proteomic characterization of the P. parva plastid, ultimately identifying several plastid proteins, both by mass spectrometry and bioinformatic analyses. Data are available via ProteomeXchange with identifier PXD022051. Altogether these results led us to propose a plastid proteome for P. parva, i.e., a set of proteins that participate in carbohydrate metabolism; in the synthesis and degradation of starch, amino acids and lipids; in the biosynthesis of terpenoids and tetrapyrroles; in solute transport and protein translocation; and in redox homeostasis. This is the first detailed plastid proteome from a unicellular, free-living colorless alga.

A multiproxy-based reconstruction of the mid- to late Holocene paleoenvironment in the Laptev Sea off the Lena River Delta (Siberian Arctic)

Land-shelf interactions and related environmental changes were reconstructed for the past 6 cal. kyrs interpreting multiproxy records from the two AMS14C-dated sediment cores from the sites located to the north and northeast of the Lena River delta. Proxies used include terrestrial and aquatic palynomorphs, benthic/planktic foraminifers and ostracods paired with benthic δ18O and δ13C records of Haynesina orbiculare. The study focused on unravelling the relation between river runoff and the regional climate changes on the one hand, and its imprint on the shelf sea environment on timescales beyond the instrumental records on the other.The palynomorph records show that the Lena River outflow largely determined the composition of species associations and the magnitude of terrestrial matter influx from land. Pollen assemblages of the inner Laptev Sea shelf reflect complex pollen contribution of the Arctic tundra and remote taiga zones drained by the Lena River and indicate a vegetation response to warmer-than-present climatic conditions between 6.0 and 4.5 cal. ka and a subsequent gradual cooling. Fluvial influence in the records is manifested by (1) increases in sedimentation rates; (2) high influxes of pollen/spores and freshwater chlorophycean algae, wood and plant remains; (3) negative δ13C excursions due to the introduction of dissolved inorganic carbon (DIC) from river water. Episodes of enhanced freshwater influence in the surface water layers (fluvial events) correlate with positive benthic δ18O excursions and increasing representation of river-distal species among benthics. Altogether, this points to an estuarine-like reversed (north to south) bottom current activity along the submarine paleovalleys on the shelf. The most pronounced fluvial events are recognized at 5.3–5.9, 1.5 and <0.5 cal. ka. The oldest fluvial event coincides with the final stage of mid-Holocene climate warming. A fluvial event at 1.5 cal. ka is specifically strong at the northeastern site thus marking a direction change of the Lena River outflow at this time and the progressive protrusion of the delta. During the past 500 years distinct negative δ13C values at the northeastern site reflect enhanced riverine influence. It is therefore concluded that the unprecedented change in the δ13C trend corroborates the other evidence for a principal diversion of the major Lena River outflows into its present-day, easterly direction.

Subunit Asa3 ensures the attachment of the peripheral stalk to the membrane sector of the dimeric ATP synthase of Polytomella sp.

The mitochondrial ATP synthase of Polytomella exhibits a peripheral stalk and a dimerization domain built by the Asa subunits, unique to chlorophycean algae. The topology of these subunits has been extensively studied. Here we explored the interactions of subunit Asa3 using Far Western blotting and subcomplex reconstitution, and found it associates with Asa1 and Asa8. We also identified the novel interactions Asa1-Asa2 and Asa1-Asa7. In silico analyses of Asa3 revealed that it adopts a HEAT repeat-like structure that points to its location within the enzyme based on the available 3D-map of the algal ATP synthase. We suggest that subunit Asa3 is instrumental in securing the attachment of the peripheral stalk to the membrane sector, thus stabilizing the dimeric mitochondrial ATP synthase.

Discovery of Marine Benthic Chlorophycean Algae in Early Danian Deccan Intertrappean at Jhilmili, Central India: New Insights into Existence of Marine Seaway Close to Cretaceouspaleogene Boundary

Discovery of Marine Benthic Chlorophycean Algae in Early Danian Deccan Intertrappean at Jhilmili, Central India: New Insights into Existence of Marine Seaway Close to Cretaceouspaleogene Boundary

The Role of the Primary Cell Wall in Plant Morphogenesis.

Morphogenesis remains a riddle, wrapped in a mystery, inside an enigma. It remains a formidable problem viewed from many different perspectives of morphology, genetics, and computational modelling. We propose a biochemical reductionist approach that shows how both internal and external physical forces contribute to plant morphogenesis via mechanical stress–strain transduction from the primary cell wall tethered to the plasma membrane by a specific arabinogalactan protein (AGP). The resulting stress vector, with direction defined by Hechtian adhesion sites, has a magnitude of a few piconewtons amplified by a hypothetical Hechtian growth oscillator. This paradigm shift involves stress-activated plasma membrane Ca2+ channels and auxin-activated H+-ATPase. The proton pump dissociates periplasmic AGP-glycomodules that bind Ca2+. Thus, as the immediate source of cytosolic Ca2+, an AGP-Ca2+ capacitor directs the vectorial exocytosis of cell wall precursors and auxin efflux (PIN) proteins. In toto, these components comprise the Hechtian oscillator and also the gravisensor. Thus, interdependent auxin and Ca2+ morphogen gradients account for the predominance of AGPs. The size and location of a cell surface AGP-Ca2+ capacitor is essential to differentiation and explains AGP correlation with all stages of morphogenetic patterning from embryogenesis to root and shoot. Finally, the evolutionary origins of the Hechtian oscillator in the unicellular Chlorophycean algae reflect the ubiquitous role of chemiosmotic proton pumps that preceded DNA at the dawn of life.

Dinoflagellate cyst assemblages across the Oxfordian/Kimmeridgian boundary (Upper Jurassic) at Flodigarry, Staffin Bay, Isle of Skye, Scotland – a proposed GSSP for the base of the Kimmeridgian

Examination of seven ammonite-calibrated palynological samples across the Oxfordian/Kimmeridgian boundary in the Flodigarry sections at Staffin Bay, Isle of Skye, northern Scotland, has revealed dinoflagellate cyst assemblages in general terms in line with previous contributions. The sparse occurrence of Emmetrocysta sarjeantii, Perisseiasphaeridium pannosum and Senoniasphaera jurassica slightly above the proposed Oxfordian/Kimmeridgian boundary may be used as a palynological approximation of the base of the Kimmeridgian. The high abundance of tests resembling modern zygnemataceous chlorophycean alga Spirogyra in two samples above the Oxfordian/Kimmeridgian boundary horizon is probably associated with increased eutrophication and possible association with ‟green tides”. This bloom is proposed as a palynofloral proxy event for the boundary in the Flodigarry section. According to previous studies, various eutrophication events may have a correlation potential in Subboreal Europe.

Exposure to the herbicide 2,4-D produces different toxic effects in two different phytoplankters: A green microalga (Ankistrodesmus falcatus) and a toxigenic cyanobacterium (Microcystis aeruginosa)

The extensive use of 2,4-dichlorophenoxiacetic acid (2,4-D) in agriculture is an important source of pollution to water and soil. Toxicity of commonly used herbicides to non-target, planktonic photosynthetic organisms has not been described completely yet. Therefore, we determined the effect of subinhibitory 2,4-D concentrations on the Chlorophycean alga Ankistrodesmus falcatus and on a toxigenic strain of the cyanobacterium Microcystis aeruginosa. Population growth, photosynthetic pigments, macromolecular biomarkers (carbohydrates, lipids, and protein), and antioxidant enzymes (catalase [CAT], glutathione peroxidase [GPx], and superoxide dismutase [SOD]) were quantified, and the integrated biomarker response (IBR) was calculated. Scanning electron microscope (SEM) and transmission electron microscope (TEM) observations were also performed. The 96-h median inhibitory concentration (IC50) for 2,4-D was 1353.80 and 71.20mgL−1 for the alga and the cyanobacterium, respectively. Under 2,4-D stress, both organisms increased pigments and macromolecules concentration, modified the activity of all the evaluated enzymes, and exhibited ultrastructural alterations. M. aeruginosa also increased microcystins production, and A. falcatus showed external morphological alterations. The green alga was tolerant to high concentrations of the herbicide, whereas the cyanobacterium exhibited sensitivity comparable to other phytoplankters. Both organisms were tolerant to comparatively high concentrations of the herbicide; however, negative effects on the assessed biomarkers and cell morphology were significant. Moreover, stimulation of the production of cyanotoxins under chemical stress could increase the risk for the biota in aquatic environments, related to herbicides pollution in eutrophic freshwater ecosystems.

Cox2A/Cox2B subunit interaction in Polytomella sp. cytochrome c oxidase: role of the Cox2B subunit extension.

Subunit II of cytochrome c oxidase (Cox2) is usually encoded in the mitochondrial genome, synthesized in the organelle, inserted co-translationally into the inner mitochondrial membrane, and assembled into the respiratory complex. In chlorophycean algae however, the cox2 gene was split into the cox2a and cox2b genes, and in some algal species like Chlamydomonas reinhardtii and Polytomella sp. both fragmented genes migrated to the nucleus. The corresponding Cox2A and Cox2B subunits are imported into mitochondria forming a heterodimeric Cox2 subunit. When comparing the sequences of chlorophycean Cox2A and Cox2B proteins with orthodox Cox2 subunits, a C-terminal extension in Cox2A and an N-terminal extension in Cox2B were identified. It was proposed that these extensions favor the Cox2A/Cox2B interaction. In vitro studies carried out in this work suggest that the removal of the Cox2B extension only partially affects binding of Cox2B to Cox2A. We conclude that this extension is dispensable, but when present it weakly reinforces the Cox2A/Cox2B interaction.

Estimating lipids for bioprospecting: A case study with Deepor beel algae

Microalgae have been considered as ideal candidates for biodiesel production and other bio-products. They have received extensive research for bioprospecting during the past few decades. Chlorophycean algae are one of the few microalgae employed for many biotechnological applications. Therefore, the present work was aimed to analyze the growth and lipid contents of four Chlorophycean algae isolated from Deepor beel Ramsar site, Assam (India) to assess their potentiality for industrial means. Of the four species, Carteria cerasiformis showed the highest lipid content (24.4 ± 1.45 %).

Tonian (Neoproterozoic) eukaryotic and prokaryotic organic-walled microfossils from the upper Visingsö Group, Sweden

ABSTRACTThe diversification of protists and multicellular microorganisms is recorded in numerous worldwide Tonian age successions, including the Visingsö Group in Sweden. The Visingsö Group contains a taxonomically rich assemblage of cyanobacteria, stromatolites, algal phytoplankton and vase-shaped microfossils. A new record of organic-walled microfossils from the Visingsö 1 drillcore reveals the high taxonomic diversity. Several species are reported for the first time from the Visingsö Group, and one new species Leiosphaeridia gorda n. sp. is described. They are in gross phycoma-like cysts of the prasinophycean algae Pterospermopsimorpha, Pterospermella, Simia, Macroptycha and Dictyotidium. Morphologically similar to zygotic cysts of chlorophycean algae are Leiosphaeridia gorda n. sp., Cerebrosphaera, Culcitulisphaera and Lanulatisphaera. Schizofusa may represent the earliest yellow-green algae of the Eustigmatiphyte among Stramenopiles. The recorded biodiversity documents the global trend in the evolution of eukaryotic protists during the Tonian Period and the increased radiation of numerous, presumably photoautotrophic biotas, representing various algal lineages.

Phylogenetic interpretation of light and electron microscopic features of selected members of the phylogroup Moewusinia (Chlorophyceae), with new generic taxonomy

:In molecular phylogenetic trees of zoospore-producing unicellular chlorophycean algae, well-resolved lineages often do not correspond to current taxonomic categories, and therefore characterising diagnostic morphological traits of lineages can be challenging. We employed a phylogenetic framework to examine the evolution of light microscopic (LM) and transmission electron microscopic (TEM) features in the phylogroup Moewusinia and a related genus and then assessed the features that could be used to diagnose lineages. Most LM characters were homoplasies, but particular character states uniquely supported lineages. Autospores arranged in isobilateral tetrads made up a suitable generic feature; whereas, tetrahedral tetrads or indefinite groups of autospores were not. Some chloroplast phenotypes lacked phylogenetic signal, especially the sponge-like form previously used to define genera. Pyrenoid types characterised clades at different depths. TEM features of zoospores (i.e. papillar shape, cell wall layers, nuclear position and components of the basal apparatus) were generally consistent with clades. The sawhorse-shaped distal connecting fibre with beam-like extensions was characteristic of some phylogroups. Ultrastructural components of sexual reproduction may serve as a marker at deeper phylogenetic depths. Within Moewusinia, the saline habitat was restricted to one clade. In total, nine phylogenetic clades were defined at generic rank using phenotypic traits. Three new genera were proposed: Eubrownia gen. nov., with the new combinations E. aggregata, E. dissociata, E. illinoisensis and E. isobilateralis; Parachlorococcum turfosum gen. & sp. nov.; and Alvikia gen. nov., with the new combination Al. littoralis. Chlorococcum (Cc.) was emended, with the new combinations Cc. aerium, Cc. macropyrenoidosum and Cc. vacuolatum. Tetracystis with the type species T. aeria was abandoned. Spongiococcum was emended with the new combination S. aplanosporum.

Near-neighbor interactions of the membrane-embedded subunits of the mitochondrial ATP synthase of a chlorophycean alga

Mitochondrial F1FO-ATP synthase of the chlorophycean algae Polytomella sp. can be isolated as a highly stable dimeric complex of 1600kDa. It is composed of eight highly conserved orthodox subunits (α, β, γ, δ, ε, OSCP, a, and c) and nine subunits (Asa1-9) that are exclusive of chlorophycean algae. The Asa subunits replace those that build up the peripheral stalk and the dimerization domains of the ATP synthase in other organisms. Little is known about the disposition of subunits Asa6, Asa8 and Asa9, that are predicted to have transmembrane stretches and that along with subunit a and a ring of c-subunits, seem to constitute the membrane-embedded Fo domain of the algal ATP synthase. Here, we over-expressed and purified the three Asa hydrophobic subunits and explored their interactions in vitro using a combination of immunochemical techniques, affinity chromatography, and an in vivo yeast-two hybrid assays. The results obtained suggest the following interactions Asa6–Asa6, Asa6–Asa8, Asa6–Asa9, Asa8–Asa8 and Asa8–Asa9. Cross-linking experiments carried out with the intact enzyme corroborated some of these interactions. Based on these results, we propose a model of the disposition of these hydrophobic subunits in the membrane-embedded sector of the algal ATP synthase. We also propose based on sequence analysis and hydrophobicity plots, that the algal subunit a is atypical in as much it lacks the first transmembrane stretch, exhibiting only four hydrophobic, tilted alpha helices.

Evolutionarily recent, insertional fission of mitochondrial cox2 into complementary genes in bilaterian Metazoa

BackgroundMitochondrial genomes (mtDNA) of multicellular animals (Metazoa) with bilateral symmetry (Bilateria) are compact and usually carry 13 protein-coding genes for subunits of three respiratory complexes and ATP synthase. However, occasionally reported exceptions to this typical mtDNA organization prompted speculation that, as in protists and plants, some bilaterian mitogenomes may continue to lose their canonical genes, or may even acquire new genes. To shed more light on this phenomenon, a PCR-based screen was conducted to assess fast-evolving mtDNAs of apocritan Hymenoptera (Arthropoda, Insecta) for genomic rearrangements that might be associated with the modification of mitochondrial gene content.ResultsSequencing of segmental inversions, identified in the screen, revealed that the cytochrome oxidase subunit II gene (cox2) of Campsomeris (Dielis) (Scoliidae) was split into two genes coding for COXIIA and COXIIB. The COXII-derived complementary polypeptides apparently form a heterodimer, have reduced hydrophobicity compared with the majority of mitogenome-encoded COX subunits, and one of them, COXIIB, features increased content of Cys residues. Analogous cox2 fragmentation is known only in two clades of protists (chlorophycean algae and alveolates), where it has been associated with piecewise relocation of this gene into the nucleus. In Campsomeris mtDNA, cox2a and cox2b loci are separated by a 3-kb large cluster of several antiparallel overlapping ORFs, one of which, qnu, seems to encode a nuclease that may have played a role in cox2 fission.ConclusionsAlthough discontinuous mitochondrial protein genes encoding fragmented, complementary polypeptides are known in protists and some plants, split cox2 of Campsomeris is the first case of such a gene arrangement found in animals. The reported data also indicate that bilaterian animal mitogenomes may be carrying lineage-specific genes more often than previously thought, and suggest a homing endonuclease-based mechanism for insertional mitochondrial gene fission.

Syndesmorion stellatum (Fijałkowska) Foster et Afonin chlorophycean algae and associated microphytoplankton from lacustrine successions of the La Veteada Formation (late Permian), Paganzo Basin, Argentina. Paleoenvironmental interpretations and stratigraphic implications

A diverse microphytoplankton assemblage recovered from terrestrial deposits of the La Veteada Formation, north of the La Rioja Province, Paganzo Basin, Argentina, is described and illustrated. The ~180m thick sedimentary type section of the unit in the Los Colorados anticline is composed of a basal gray silcrete covered by gypsum beds and a thick succession of purple mudstones inter-layered with varicolored fine sandstone sheets and laminated yellowish dolomites. The aquatic assemblage is mainly characterized by a great variety of Syndesmorion stellatum (Fijałkowska) Foster et Afonin coenobia, recorded for the first time in the late Permian Gondwanic realm. All the previous morphotypes described for this chlorophycean alga are recognized in this assemblage, and new polymorph-coenobia are described and illustrated. The diversity of coenobia morphotypes of this alga is likely to reflect response to stress conditions. The genera Maculatasporites and Mehlisphaeridium are commonly present, and their algal origin is discussed. Maculatasporites gondwanensis, Maculatasporites amplus, Mehlisphaeridium parvum, and Mehlisphaeridium regulare and Mehlisphaeridium sp. are also described and illustrated. Representatives of the zygnematacean algae, Brazilea scissa, Brazilea plurigenus, Brazilea sp. A, Tetraporina tetragona, ?Lecaniella sp., as well as large clusters of sphaeromorphs incertae sedis chlorophyta algae, are described. In addition, planar colonial chlorococcalean Pediastrum-like forms suggesting hydrodictyaceaen algae are recorded for the first time in late Paleozoic strata of Argentina, and the zygnematalean affinity of Reduviasporonites chalastus as green algae is discussed. The highly diverse La Veteada microphytoplanktonic assemblage is composed by algae that grew in hypersaline lacustrine environment together with species commonly associated with either fresh or brackish water conditions; presumably these taxa were washed in after heavy rainfall and/or flooding events. In general terms, the land-derived palynological composition of the La Veteada assemblage at Central Famatina Range reflects parent vegetation adapted to arid or semi-arid climate as reported from late Guadalupian to late Lopingian in the Paganzo Basin. The whole palynological composition suggests a Lopingian age for the La Veteada Formation at its stratotype, based on the stratigraphic range of all the land-derived miospore species recognized, resulting younger than assemblages assigned to the Lueckisporites–Weylandites Biozone (LW: Wordian–Capitanian). Therefore, it is the youngest Permian palynofloral assemblage recorded up to now in Argentina and South America.

Deglacial variability in Okhotsk Sea Intermediate Water ventilation and biogeochemistry: Implications for North Pacific nutrient supply and productivity

The modern North Pacific plays a critical role in marine biogeochemical cycles, as an oceanic sink of CO2 and by bearing some of the most productive and least oxygenated waters of the World Ocean. The capacity to sequester CO2 is limited by efficient nutrient supply to the mixed layer, particularly from deeper water masses in the Pacific's subarctic and marginal seas. The region is in addition only weakly ventilated by North Pacific Intermediate Water (NPIW), which receives its characteristics from Okhotsk Sea Intermediate Water (OSIW). Here, we present reconstructions of intermediate water ventilation and productivity variations in the Okhotsk Sea that cover the last glacial termination between eight and 18 ka, based on a set of high-resolution sediment cores from sites directly downstream of OSIW formation. In a multi-proxy approach, we use total organic carbon (TOC), chlorin, biogenic opal, and CaCO3 concentrations as indicators for biological productivity. C/N ratios and XRF scanning-derived elemental ratios (Si/K and Fe/K), as well as chlorophycean algae counts document changes in Amur freshwater and sediment discharge that condition the OSIW. Stable carbon isotopes of epi- and shallow endobenthic foraminifera, in combination with 14C analyses of benthic and planktic foraminifera imply decreases in OSIW oxygenation during deglacial warm phases from c. 14.7 to 13 ka (Bølling-Allerød) and c. 11.4 to 9 ka (Preboreal). No concomitant decreases in Okhotsk Sea benthic-planktic ventilation ages are observed, in contrast to nearby, but southerly locations on the Japan continental margin. We attribute Okhotsk Sea mid-depth oxygenation decreases in times of enhanced organic matter supply to maxima in remineralization within OSIW, in line with multi-proxy evidence for maxima in primary productivity and supply of organic matter. Sedimentary C/N and Fe/K ratios indicate more effective entrainment of nutrients into OSIW and thus an increased nutrient load of OSIW during deglacial warm periods. Correlation of palynological and sedimentological evidence from our sites with hinterland reference records suggests that millennial-scale changes in OSIW oxygen and nutrient concentrations were largely influenced by fluvial freshwater runoff maxima from the Amur, caused by a deglacial northeastward propagation of the East Asian Summer Monsoon that increased precipitation and temperatures, in conjunction with melting of permafrost in the Amur catchment area. We suggest that OSIW ventilation minima and the high lateral supply of nutrients and organic matter during the Allerød and Preboreal are mechanistically linked to concurrent maxima in nutrient utilization and biological productivity in the subpolar Northwest Pacific. In this scenario, increased export of nutrients from the Okhotsk Sea during deglacial warm phases supported subarctic Pacific shifts from generally Fe-limiting conditions to transient nutrient-replete regimes through enhanced advection of mid-depth nutrient- and Fe-rich OSIW into the upper ocean. This mechanism may have moderated the role of the subarctic Pacific in the deglacial CO2 rise on millennial timescales by combining the upwelling of old carbon-rich waters with a transient delivery of mid-depth-derived bio-available Fe and silicate.

Near-Neighbor Relationships of the Atypical Subunits that Form the Peripheral Stalk of the Mitochondrial ATP Synthase in Chlorophycean Algae

Mitochondrial F1Fo-ATP synthase (complex V) is an oligomeric complex that exhibits a molecular mass around 550 kDa. The F1Fo-ATP synthase of the green chlorophycean alga Chlamydomonas reinhardtii and of its close colorless relative Polytomella sp. is isolated as a highly-stable dimer of 1600 kDa after solubilization of algal mitochondria with lauryl-maltoside. Each monomer of the enzyme is constituted by 17 polypeptides, eight of which are the conserved subunits alpha, beta, gamma, delta, epsilon, a (Atp6), c (Atp9), and OSCP, plus nine atypical polypeptides, named Asa1 to Asa9, that seem to be present only in the chlorophycean lineage. The Asa subunits (named after ATP Synthase Associated subunits) form the very robust peripheral stalk that has been observed in several electron-microscope studies of the algal enzyme. We have addressed the close-neighbor relationships of the ASA subunits and their interactions with the orthodox, conserved subunits. For this purpose, we have generated sub-complexes after partial dissociation of the dimeric ATP synthase with high detergent concentrations or with amphiphilic polymers; detected several subunit-subunit interactions based on cross-linking experiments; reconstituted various sub-complexes of the peripheral arm using recombinant subunits; and silenced the synthesis of certain subunits in vivo. Recently, an electron cryo-microscopy map of the enzyme was obtained. Putting together all the structural data available to date, we suggest a model of the complete topological disposition of the subunits that constitute the atypical, algal mitochondrial ATP synthase. The presence of such a stout peripheral stalk in the ATP synthase of chlorophycean alga, seems to have more than the necessary stiffness to counteract the rotation of the central stalk, but will probably make less twisting motions, and thus will store less transient elastic energy.