Respiratory frequency, dive behaviour and social interactions of leatherback turtles, Dermochelys coriacea during the inter-nesting interval

We collected simultaneous dive Time Depth Recorder (TDR) data and video images from free swimming adult female leatherback turtles, Dermochelys coriacea, during the first 24 h after nesting on the beach, in order to determine relationships between dive parameters, activity, overall respiratory frequency and behaviour.We identified three different underwater locomotory activities (subsurface swimming, V-shaped dives and U-shaped dives) from video and TDR data that varied in their mean depth, duration and a number of other parameters. Overall respiratory frequency (overall f_R) was significantly different between all locomotory activities, with turtles taking 1.7±0.1 breaths min⁻¹ while subsurface swimming, 0.78 breaths min⁻¹ after V-shaped dives and 0.57 breaths min⁻¹ after U-shaped dives. Descent rates and ascent rates were significantly faster in U-shaped dives (descent 0.19±0.010 m s⁻¹, ascent 0.28±0.015 m s⁻¹) than in V-shaped dives (descent 0.10±0.008 m s⁻¹, ascent 0.12±0.012 m s⁻¹). Flipper stroke rates were significantly lower during the bottom component of U-shaped dives (0.18±0.02 strokes s⁻¹) than during the descent (0.29±0.03 strokes s⁻¹) or ascent (0.29±0.03 strokes s⁻¹). From overall f_R and flipper stroke rate data, we inferred that turtles used less energy during U-shaped dives than the other activity types. We recorded interactions between male turtles and the study females that lasted up to 11 min, during which male turtles displayed the characteristic courtship behaviour of sea turtles. It appeared that females attempted to avoid males by aborting ascent and extending dive duration to swim to the sea floor when males were present.     

Growth of captive leatherback turtles, Dermochelys coriacea, with inferences on growth in the wild: Implications for population decline and recovery

Leatherback turtles (Dermochelys coriacea) are endangered, and declining population trends suggest that they are vulnerable to becoming extinct in the Pacific Ocean. Population recovery depends on strong conservation measures (e.g., nest protection, reduction of bycatch, and foraging habitat preservation) and on how fast leatherbacks grow and reach maturity, making the latter of grave concern. The research reported here marks the first time that several leatherback turtles have been maintained in captivity for nearly 2 years, from hatchlings (6.31 ± 0.13 cm straight carapace length (SCL) and 46.0 ± 1 g) to juveniles (largest, 72.0 cm SCL and 42.65 kg). Leatherbacks maintained an average growth rate of 31.9 ± 2.8 cm year^− 1 in SCL throughout the study period. A length-mass relationship of the form, mass (kg) = 0.000214 ? SCL (cm) 2.86, fitted our data and data from four other captive studies, 11 wild juveniles, and five studies of adult leatherbacks. Von Bertalanffy, Gompertz and logistic growth functions predicted age-at-maturity for leatherbacks of 16.1, 8.7 and 6.8 years, respectively. The accuracy of these age-at-maturity estimates is discussed in the light of skeletochronological studies as well as estimates obtained from conservation and genetic studies. Our data, in combination with data from sightings, suggest that leatherbacks spend their early years (0 to 5 years of age) growing in the warmer waters of the tropical and subtropical seas before entering cooler temperate waters. Information obtained from turtles incidentally captured in fisheries, supplemented with growth curve data, indicates that leatherbacks are vulnerable to entanglement or hooking in various pelagic gear types, such as drift gill nets and longline within 3 years from nest emergence. Consequently, leatherbacks are exposed to threats from marine fisheries for > 80% of their early life before carapace length characteristic of reproductive maturity is attained.     

Protracted rainfall decreases temperature within leatherback turtle (Dermochelys coriacea) clutches in Grenada, West Indies: Ecological implications for a species displaying temperature dependent sex determination

Protracted or intense rainfall may affect the reproductive success of reptilian species on a number of levels ranging from the availability of prey, the integrity of the nesting site and the subsequent survivability of offspring. For sea turtles (a species displaying temperature sex determination) nesting throughout the tropics and subtropics, rainfall has previously been shown to influence the development environment of clutches; in its extreme resulting in high levels of egg or hatchling mortality. Yet when compared to other abiotic variables affecting clutch success, rainfall has received relatively little attention. We therefore examined how fluctuations in local rainfall at a tropical nesting site for leatherback turtles (Dermochelys coriacea) affected the nest environment. Temperature data loggers placed within clutches (n = 8) revealed that protracted rainfall had a marked cooling effect on nests, so that seasonally improbable male-producing temperatures (< 29.75 °C) were produced. We use these data to explore how rainfall may ultimately influence the sex ratios of sea turtle hatchlings both within and between nesting seasons, and discuss the importance of robust estimates of rainfall for future demographic models.     

Stable carbon and nitrogen isotope discrimination in soft tissues of the leatherback turtle (Dermochelys coriacea): Insights for trophic studies of marine turtles

The trophic ecology of marine vertebrates has been increasingly studied via stable isotope analysis of body tissues. However, the theoretical basis for using stable isotopes to elucidate consumer–prey relationships remains poorly validated for most taxa despite numerous studies using this technique in natural systems. In this study, we measured stable carbon and stable nitrogen diet-tissue discrimination (Δ_dt) in whole blood, red blood cells, blood plasma solutes, and skin of leatherback sea turtles (Dermochelys coriacea; N = 7) maintained in captivity for up to 424 days and fed an isotopically consistent control diet with a mean C:N ratio of 2.94:1.00 and an energetic content of 20.16 ± 0.39 kJ g^− 1 Dry Mass. We used a random-effect repeated measure model to evaluate isotopic consistency among tissue samples collected on days 276, 348, and 424. Both δ¹³C and δ¹⁵N remained consistent among sampling events in all tissues (all 95% posterior intervals for the slopes of a linear model included zero), indicating that all tissues had fully integrated diet-derived stable isotope compositions. Mean tissue-specific δ¹³C ranged from − 18.30 ± 0.16‰ (plasma solutes) to − 15.54 ± 0.14‰ (skin), whereas mean δ¹⁵N was from 10.06 ± 0.22‰ (whole blood) to 11.46 ± 0.10‰ (plasma solutes). The computed Δ_dt factors for carbon ranged from − 0.58‰ (plasma solutes) to + 2.25‰ (skin), whereas Δ_dt for nitrogen was from + 1.49 (red blood cells) to + 2.85 (plasma solutes). As the only discrimination factors available for leatherback turtles, our data will be useful for future interpretations of field-derived stable isotope data for this species. The inherent variability in Δ_dt values among individuals was low, which supports the value of these data for dietary reconstructions. However, it is important to note that tissue-specific discrimination factors for leatherbacks contrast with the widely accepted values for endothermic species (0–1‰ for C, 3–5‰ for N), and are also different from values established for hard-shelled turtles. This underscores the need for species- and tissue-specific discrimination factors before interpreting trophic studies of wild animals, including marine turtles.     

First records of flower biology and pollination in African Annonaceae: Isolona, Piptostigma, Uvariodendron, Monodora and Uvariopsis

Seven species from five genera of Annonaceae were studied with regard to their flower biology and pollination in the Southwest Province of Cameroon, West Africa. They have protogynous hermaphroditic flowers, with exception of Uvariopsis species, which are monoecious. Fused petals of Isolona campanulata remain apically spreading and open during anthesis but form a deep basal urceolate tube around the reproductive organs. At anthesis the yellow pendent flowers emit a fruit-like scent and attracted small beetles, the likely pollinators. Piptostigma sp. flowers also emit a fruit-like scent but provide a closed pollination chamber formed by the three inner petals. Small staphylinid beetles attracted during the female stage of anthesis are released from the flowers at the end of the male stage 2-3 days later. Both species have diurnal anthesis, attracting and releasing the flower visitors during daytime. In contrast, Uvariodendron connivens and U. calophyllum have nocturnal anthesis with floral thermogenesis, produce spicy, aromatic and fruity scents and attract large Scarabaeidae beetles, the pollinators, along with many curculionid beetles, which were principally predators of the thick petals. The very large flowers of Monodora tenuifolia have yellowish petals which are spotted with dark red markings. Together with the sweetish, slightly disagreeable scent the flowers attract flies, principally dung flies. The two investigated Uvariopsis species are monoecious with pistillate and staminate flowers being functional at the same time. The violet red flowers of U. bakeriana visually seem to mimic the fruiting body of certain stinkhorn fungi (Phallaceae) although without producing their strong unpleasant carcass stench. Flower-visiting dung flies were rare. Conversely, U. congolana has a strong fungus-like scent, its flowers are presented at litter height and dung flies living in the litter were the flower visitors, albeit sporadic. The 4-5 days lasting anthesis of both Uvariopsis species appears to be an evolutionary consequence of their diffuse pollinator spectra. The studied African Annonaceae therefore have either cantharophilous or myiophilous/sapromyiophilous flowers with, in part, respectively, remarkably long anthesis, thermogenesis, and widely open, large flowers - all attributes unknown or rare in the hitherto better studied Neotropical Annonaceae.     

Molecular characterization and expression profiles of IscA1 gene in a long-distance migrant, Agrotis segetum

Cryptochrome (CRYs) proteins have been elucidated as the molecular basis for magnetoreception in Drosophila, and a putative magnetic receptor (named IscA1) protein may aslo be involved in sensing magnetic fields in Drosophila. However, whether IscA1 has a conserved role in diverse animals and functions in orientation during animal migration is unknown. Here we report on the cloning and sequencing of the IscA1 gene from Agrotis segetum, which encodes a predicted protein IscA1 that has 131 amino acids and two conserved iron-sulphur cluster binding domains. Multiple sequence alignment and phylogenetic analysis were used to show that IscA1 had a relatively high homology from species of Noctuoidea. Quantitative polymerase chain reaction showed that IscA1 was ubiquitously expressed in adult organs and, among all developmental stages, expression was higher in adults. When Agrotis segetum was exposed to 14?h light/10?h dark, IscA1 expression also showed daily oscillations, and constant light or dark disturbed these oscillations. IscA1 expression levels in a migratory population were higher than in a reared population and higher in a southward migratory population than in a northward. These findings suggest that the IscA1 gene in A. segetum might be associated with migration and provide a molecular basis for further study on the functions of IscA1 gene in magnetoreception and potential control of the turnip moth.     

Partial venom gland transcriptome of a Drosophila parasitoid wasp, Leptopilina heterotoma, reveals novel and shared bioactive profiles with stinging Hymenoptera

Analysis of natural host-parasite relationships reveals the evolutionary forces that shape the delicate and unique specificity characteristic of such interactions. The accessory long gland-reservoir complex of the wasp Leptopilina heterotoma (Figitidae) produces venom with virus-like particles. Upon delivery, venom components delay host larval development and completely block host immune responses. The host range of this Drosophila endoparasitoid notably includes the highly-studied model organism, Drosophila melanogaster. Categorization of 827 unigenes, using similarity as an indicator of putative homology, reveals that approximately 25% are novel or classified as hypothetical proteins. Most of the remaining unigenes are related to processes involved in signaling, cell cycle, and cell physiology including detoxification, protein biogenesis, and hormone production. Analysis of L. heterotoma's predicted venom gland proteins demonstrates conservation among endo- and ectoparasitoids within the Apocrita (e.g., this wasp and the jewel wasp Nasonia vitripennis) and stinging aculeates (e.g., the honey bee and ants). Enzyme and KEGG pathway profiling predicts that kinases, esterases, and hydrolases may contribute to venom activity in this unique wasp. To our knowledge, this investigation is among the first functional genomic studies for a natural parasitic wasp of Drosophila. Our findings will help explain how L. heterotoma shuts down its hosts' immunity and shed light on the molecular basis of a natural arms race between these insects.     

1914G variant of BCHE gene associated with enzyme activity,obesity and triglyceride levels

Polymorphisms of butyrylcholinesterase (BChE) have been reported to be associated to weight, BMI variance and hypertriglyceridemia in adults and adolescents. The aim of the present study was to investigate the association of −116A (SNP: G/A; rs1126680) and 1914G (SNP: A/G; rs3495) variants of BCHE gene with anthropometric and biochemical variables associated with obesity in population sample of 115 individuals, from Southern Brazil. Participants were grouped in two categories: obese (BMI ≥ 30) and non-obese (BMI < 30). The 1914G allele showed significantly higher frequency in the obese group, and carriers of 1914G allele showed lower mean BChE activity when compared to 1914A carriers (p = 0.006). Higher means of BMI (p = 0.02) and triglyceride (TG; p = 0.01) were found in 1914G carriers (BMI = 27.57kg/m²; TG = 150.8 mg/dL) when compared to 1914A homozygotes (BMI = 25.55 kg/m²; TG = 107.9 mg/dL). Carriers of the −116A allele showed lower mean BChE activity than usual homozygotes, and the −116A variant was found in cis with 1914G (p < 0.0001; D′ = 1). The region of BCHE gene that contains the 1914G mutation site is target of microRNAs (miRs) and the response of BChE to glucocorticoids is especially influenced by these miRs. Therefore, it is possible that the 1914G allele can be interfering in gluconeogenesis, hyperglycemia, lipolysis and body fat distribution. This lower activity may cause an imbalance in lipid metabolism, which may lead to an increased predisposition to obesity and to a lower ability to maintain metabolic homeostasis.     

Cryptic diversity,pathogenicity, and evolutionary species boundaries in Cercospora populations associated with Cercospora leaf spot of Beta vulgaris

The taxonomy and evolutionary species boundaries in a global collection of Cercospora isolates from Beta vulgaris was investigated based on sequences of six loci. Species boundaries were assessed using concatenated multi-locus phylogenies, Generalized Mixed Yule Coalescent (GMYC), Poisson Tree Processes (PTP), and Bayes factor delimitation (BFD) framework. Cercospora beticola was confirmed as the primary cause of Cercospora leaf spot (CLS) on B. vulgaris. Cercospora apii, C. cf. flagellaris, Cercospora sp. G, and C. zebrina were also identified in association with CLS on B. vulgaris. Cercospora apii and C. cf. flagellaris were pathogenic to table beet but Cercospora sp. G and C. zebrina did not cause disease. Genealogical concordance phylogenetic species recognition, GMYC and PTP methods failed to differentiate C. apii and C. beticola as separate species. On the other hand, multi-species coalescent analysis based on BFD supported separation of C. apii and C. beticola into distinct species; and provided evidence of evolutionary independent lineages within C. beticola. Extensive intra- and intergenic recombination, incomplete lineage sorting and dominance of clonal reproduction complicate evolutionary species recognition in the genus Cercospora. The results warrant morphological and phylogenetic studies to disentangle cryptic speciation within C. beticola.     

In vivo events associated with entomopathology of Beauveria bassiana for the corn earworm (Heliothis zea)

When conidia of Beauveria bassiana are injected into the hemocoel of corn earworm larvae, it appears that a positive correlation exists between exocellular proteolytic activity of the fungus and entomopathological manifestations. Once inside the hemolymph, defense mechanisms (including phagocytosis) are incapable of overcoming the fungus and one important event in a terminal mycocidal cascade involves preferential invasion of the gut wall. Such invasion helps explain the observed inhibition of feeding by infected larvae. Although histopathological changes seen in gut tissues suggest that a gut toxin is produced, evidence for such a toxin could not be obtained in preliminary tests. Biochemical changes are seen in hemolymph components; however, these are viewed as being due to general starvation rather than to specific activities of the fungus, at least up to the time that a general mycosis is established. With the host larva under physiological stress (starvation, nutrient depletion, and, possibly, toxin production in gut tissues) and failure of defense mechanisms, the infection spreads quickly and a terminal mycosis results.     

Macrophage migration inhibition by complement activators,migration inhibitory factor,and Lotus fucolectin: Evidence for common involvement of cell-associated esterase activity

Activators of the complement pathway were compared with migration inhibitory factor (MIF) and Lotus fucolectin, which mimics MIF, for their macrophage migration inhibitory (MMI) activity. Endotoxin (LPS), cobra venom factor (CVF), and zymosan, known complement (C3) activators, were found to produce dose-dependent MMI activity, similar to MIF, independent of requirements for nonadherent lymphocytes and serum complement. Comparable activity was observed by all migration inhibitors in the presence of freshly harvested unheated or heat-inactivated guinea pig serum as well as zymosan-adsorbed (C3-depleted) serum. Iscove's serum-free medium also promoted migration inhibition confirming a lack of requirement for serum complement in the reaction. Polymyxin B reversed MMI by LPS, but had no effect on the other inhibitors, indicating that the MMI activity of CVF, zymosan, MIF, and Lotus fucolectin was not primarily due to LPS contamination. Peritoneal macrophages (PM), depleted of nonadherent lymphocytes, responded as well as unpurified PM to the complement activators and MIF. ?-Amino-n-caproic acid (EACA), l-lysine, and tranexamic acid (TA), known inhibitors of the fibrinolytic activity of plasminogen activator (PA), were found to reverse migration inhibition of C3 activators, MIF, and Lotus fucolectin. In contrast bovine pancreatic trypsin inhibitor (BPTI) and soybean trypsin inhibitor (STI) had no effect on MMI activity. These results suggest a common mechanism for mediation of migration inhibition by complement activators and MIF which may involve activation of cell-associated complement to produce esterolytic end products capable of triggering the activation process.     

Fungal communities associated with species of Fraxinus tolerant to ash dieback,and their potential for biological control

Ash dieback, caused by the fungus Hymenoscyphus fraxineus, has threatened ash trees in Europe for more than two decades. However, little is known of how endophytic communities affect the pathogen, and no effective disease management tools are available. While European ash (Fraxinus excelsior) is severely affected by the disease, other more distantly related ash species do not seem to be affected. We hypothesise that fungal endophytic communities of tolerant ash species can protect the species against ash dieback, and that selected endophytes have potential as biocontrol agents. These hypotheses were tested by isolating members of the fungal communities of five tolerant ash species, and identifying them using ITS regions. Candidate endophytes were tested by an in vitro antagonistic assay with H.fraxineus. From a total of 196 isolates we identified 9 fungal orders, 15 families, and 40 species. Fungi in orders Pleosporales, such as Boeremia exigua and Diaporthe spp., and Hypocreales (e.g., Fusarium sp.), were recovered in most communities, suggesting they are common taxa. The in vitro antagonistic assay revealed five species with high antagonistic activity against H. fraxineus. These endophytes were identified based on ITS region as Sclerostagonospora sp., Setomelanomma holmii, Epicoccum nigrum, B. exigua and Fusarium sp. Three of these taxa have been described previously as antagonists of plant pathogenic microbes, and are of interest for future studies of their potential as biological control agents against ash dieback, especially for valuable ash trees in parks and urban areas.     

Optimization of melting analysis with TaqMan probes for detection of KRAS,NRAS, and BRAF mutations

The TaqMan probes that have been long and effectively used in real-time polymerase chain reaction (PCR) may also be used in DNA melting analysis. We studied some factors affecting efficiency of the approach such as (i) number of asymmetric PCR cycles preceding DNA melting analysis, (ii) choice of fluorophores for the multiplex DNA melting analysis, and (iii) choice of sense or antisense TaqMan probes for optimal resolution of wild-type and mutant alleles. We also determined ΔT_m (i.e., the temperature shift of a heteroduplex relative to the corresponding homoduplex) as a means of preliminary identification of mutation type. In experiments with serial dilution of mutant KRAS DNA with wild-type DNA, the limit of detection of mutant alleles was 1.5–3.0%. Using DNA from both tumor and formalin-fixed paraffin-embedded tissues, we demonstrated a high efficiency of TaqMan probes in mono- and multiplex mutation scanning of KRAS, NRAS (codons 12, 13, and 61), and BRAF (codon 600) genes. This cost-effective method, which can be applied to practically any mutation hot spot in the human genome, combines simplicity, ease of execution, and high sensitivity—all of the qualities required for clinical genotyping.     

New species and distribution records for Clavulina (Cantharellales,Basidiomycota) from the Guiana Shield,with a key to the lowland neotropical taxa

Three new and one previously described species of Clavulina (Clavulinaceae, Cantharellales, Basidiomycota) are reported from the central Guiana Shield region from tropical rainforests dominated by ectomycorrhizal trees of the leguminous genus Dicymbe (Fabaceae subfam. Caesalpinioideae). We provide morphological, DNA sequence, habitat, and fruiting occurrence data for each species. The new species conform to a generic concept of Clavulina that includes coralloid, branched basidiomata with amphigenous hymenia, basidia with two or 2−4 incurved sterigmata and postpartal septa present or absent, and smooth, hyaline, guttulate basidiospores. Placements of the new species in Clavulina were corroborated with DNA sequence data from the internal transcribed spacer and large subunit of the nuclear ribosomal repeat, and their infrageneric relationships were examined with phylogenetic analyses based on DNA from the region coding for the second largest subunit of DNA-dependent RNA polymerase II (rpb2). To facilitate future studies of the genus in the neotropics, a key is provided for all Clavulina species described from the lowland neotropics.     

First records of Fistularia petimba and Diodon eydouxii for the Azores, with notes on the occurrence of three additional species

Two new records of fishes from the Azores are reported: Fistularia petimba and Diodon eydouxii . The occurrence of Centracanthus cirrus, Decapterus macarellus and Priacanthus arenatus in Azorean waters is confirmed.     

Assimilation and oxygen uptake associated with two different feeding habits of Munida gregaria (=M. subrugosa) (Crustacea, Decapoda)

Munida gregaria is the most abundant galatheid crab species in the Beagle Channel (55 °S 68 °W) off Tierra del Fuego, Argentina. This species has two different and simultaneous feeding habits: predator and deposit feeder. The objectives of this work were to determine whether either of the two different feeding habits imply differences in assimilation and oxygen consumption. Subsamples of 40 and 20 crabs of each sex were randomly selected, transported to the laboratory, and used in assimilation and oxygen consumption experiments, respectively. Animals were placed in individual chambers at 8 ± 1 °C. The assimilation experiment was conducted using four types of diet: isopods (CRU), algae (ALG), pulverized fish food (PFF), and particulate organic matter (POM). The crabs' routine metabolism and postprandial oxygen consumption - or specific dynamic action SDA - were measured using Clark-type polarographic electrodes. Two kinds of food were offered: CRU and PFF to simulate both feeding habits. Assimilation in M. gregaria for both feeding habits presented values > 90% for dry mass and energetic content. Consumption rate varied between 15 and 50 mg_ingested g_DM^− 1, and was significantly higher for CRU and PFF diets. Females showed significantly higher consumption rates than males for all diets. On average, the routine metabolism of M. gregaria was 15 ± 5 μlO₂ h^− 1 g^− 1. Deposit feeding may confer energetic advantages to female M. gregaria, especially because this diet has a low energetic cost of assimilation. Deposits of high-energy content showed the highest consumption rates among four the experimental diets. In terms of mass and energy, the deposit diet also showed the highest assimilation efficiency. The postprandial oxygen consumption was lower in females and in the deposit feeding experiment. We suggest that females may prefer the deposit feeding habit to maximize their ingested energy, allowing them to devote more energy to reproduction. This is attained by a high consumption rate and by minimizing the energy used in assimilation.     

A helical,polymeric extracellular protein associated with the luminal surface of Haemonchus contortus intestinal cells

The structure of the intestinal cells of the parasitic nematode Haemonchus contortus is described. The cells have numerous microvilli about 0.09 μ in diameter; most being 5.5–7.5 μ in length. The microvillar (plasma) membrane is coated with a layer of amorphous material (glycocalyx) about 60 Å thick which is electron dense in sectioned preparations. Associated with the surface of this material, and filling the spaces between the microvilli, are filaments in the form of helices about 400 Å in diameter and of variable pitch. The helices appear to be flexible but they are aligned approximately with the long axes of the microvilli. There are up to ten helices per microvillus; they extend beyond the tips of the microvilli and are up to 10 μ long. The material has been obtained nearly pure in small amounts. It is primarily protein and it is proposed that it should be called contortin. The monomeric form (of molecular weight about 60,000) has been identified with a Y-shaped structure with arms about 45 Å long and 25 Å wide seen in negatively stained preparations. The helical filament appears to be formed by lateral polymerization of pairs of these units.     

Changes in thylakoid structure associated with the differentiation of heterocysts in the cyanobacterium, Anabaena cylindrica

The thylakoids of vegetative cells of the filamentous cyanobacterium, Anabaena cylindrica, are capable of oxygen-evolving photosynthesis and contain both Photosystems I and II (PSI and PSII). The heterocysts, cells specialized for nitrogen fixation, do not produce oxygen and lack Photosystem II activity, the major accessory pigments, and perhaps the chlorophyll a associated with PSII. Freeze-fracture replicas of vegetative cells and of heterocysts reveal differences in the structure of the thylakoids. A histogram of particle sizes on the expolasmic fracture face (E-face, EF) of vegetative cell thylakoids has two major peaks, at 75 and 100 Å. The corresponding histogram for heterocyst thylakoids lacks the 100 Å size class, but has a very large peak at about 55 Å with a shoulder at 75 Å. Histograms of protoplasmic fracture face (P-face, PF) particle diameters show single broad peaks, the mean diameter being 71 Å for vegetative cells and 64 Å for heterocysts. The thylakoids of both cell types have about 5600 particles/μm² on the P-face. On the E-face, the density drops from 939 particles/μm² on vegetative cell thylakoids to 715 particles/μm² on heterocyst thylakoids. The data suggest that the 100 Å E-face particle of vegetative cell thylakoids is a PSII complex. The 55 Å EF particle of heterocysts may be part of the nitrogenase complex or a remnant of the PSII complex. The role of the 75 Å EF particle is unknown. Other functions localized on cyanobacterial thylakoids, such as respiration and hydrogenase activity, must be considered when interpreting the structure of these complex thylakoids.     

Composition of a methylated,acidic polysaccharide associated with coccoliths of Emiliania huxleyi (Lohmann) Kamptner

The water-soluble, acidic polysaccharide isolated from the coccoliths of the alga Emiliania huxleyi (Lohmann) Kamptner contains residues of the following sugars: l-galactose, d-glucose, d-mannose, l-mannose, l-rhamnose, l-arabinose, d-ribose, d-xylose, 6-O-methyl-d-mannose, 6-O-methyl-l-mannose, 2,3-di-O-methyl-l-rhamnose, 3-O-methyl-d-xylose, and d-galacturonic acid. l-Mannose, 6-O-methyl-d-mannose, 6-O-methyl-l-mannose, and 2,3-di-O-methyl-l-rhamnose are novel constituents of a polysaccharide. In addition, the presence of sulphate groups was found. Galacturonic acid and sulphate in the polysaccharide bind Ca²⁺ ions apparently in a ratio of one mol of Ca²⁺ per mol of acidic residue. This feature is relevant for the proposed matrix function of the polysaccharide in the formation of the calcified cell-wall plates (coccoliths) of the alga.