STUDIES ON DEVELOPING AND RELEASED SPERMATIA IN THE RED ALGA,TIFFANIELLA SNYDERAE (RHODOPHYTA)1

Developing and released spermatia of the red alga, Tiffaniella snyderae (Farl.) Abb. were studied. Spermatia were observed under hydrodynamically defined conditions and found to be released from the exposed spermatangial heads in a spermatium-plus-strand unit that remained connected to the spermatangial head. Interactions of single-spermatial strands resulted in the formation of multi-spermatial strands as long as 600 μm with as many as 47 spermatia along their length; however, most were 100–200 μm with 8–21 spermatia. Strand length and number of spermatia were correlated. Spermatial strands contracted or extended and rotated as the water velocity past the plant was changed, and in still water the strands retracted into a clump on the spermatangial head surface. Each strand type exhibited a characteristic threshold water velocity at which it reached maximum length, and above which it broke and was carried away. Fluorescence microscopy showed that the strands did not contain nucleic acid (DNA) and could thus be differentiated from filamentous blue-green algal and bacterial epiphytes. Histochemical staining indicated that the strands and spermatial vesicles contained an acidic, sulfated polysaccharide. Chelation of Ca²⁺ with EGTA resulted in strand breakdown suggesting that this divalent cation may be involved in strand integrity. Scanning electron microscopy revealed that release from the spermatangia occurred through tears in the cuticle covering the spermatangial head if it was still present, or from exposed spermatangia. Individual spermatia were attached tangentially to a well-defined strand 0.64 μm in diameter in the contracted state to 0.2 μm in the extended state. Transmission electron microscopy of spermatangial heads showed that immature spermatangia were characterized by a centrally positioned nucleus and abundant ER cisternae filled with a moderately electron dense granular material. Later in development the spermatangia acquire two spermatial vesicles containing highly convoluted fibrillar contents. The cell becomes polarized with the nucleus displaced apically and the spermatial vesicles occupying the basal half of the spermatangium. At maturity one of the vesicles is released basally. Liberated spermatia contain a membrane-bound nucleus and mitochondria and are associated with an oblong accumulation of fibrous material similar in size and position to the strand observed with the SEM. These strands are discussed in relation to red algal fertilization and other phases of the red algal life-history.     

ULTRASTRUCTURE AND CYTOCHEMISTRY OF EARLY SPERMATANGIAL DEVELOPMENT IN ANTITHAMNION NIPPONICUM (CERAMIACEAE,RHODOPHYTA)1

Spermatial development and differentiation of wall components were investigated by electron microscopy and cytochemical methods in Antithamnion nipponicum Yamada et Inagaki. The spermatium is composed of two parts, a globular head and two appendages projecting from near the basal portion. The appendages originate form spermatangial vesicles (SVs) and follow a developmental sequence beginning as amorphous material and ending as fully formed fibrous structures compressed with in the SVs. SV formation is due to contributions initially from endoplasmic reticulum and later form dictyosome-derived vesicles. Chemical differentiation of the spermatial wall occurs early in its development. Calcofluor white ST does not label spermatial walls, indicating an absence of cellulose polysaccharides, which are abundant in vegetative cell walls. Labeled lectins show that α-d -methyl manose and / or α-d -glucose as well as N-acetyl-glucosamine, β-d -galactose, and α-l -fucose moieties are present on the spermatial wall but not in the vegetative cell wall. The glyconjugate with α-d -methyl mannose and / or glucose residues, previously reported as a gamete recognition molecule in this species, is distributed along the surface of spermatia as well as in the SV during spermatangial development.     

137 Gamete Recognition and Sexual Isolation in a Red Alga,Aglaothamnion Byssoides (Rhdophyta)

The binding of fluorescein isothiocyanate (FITC) conjugated lectins to gametes of Aglaothamnion byssoides Itono during the fertilization was studied by the use of confocal microscope. The physiological effects of lectins and carbohydrates on gamete binding were also examined. Three lectins, concanavalin A (ConA), Soybean agglutinin (SBA) and wheat germ agglutinin (WGA) bound to the surface of spermatia, but each lectin labeled different region of the spermatium. SBA bound only to the spermatial appendages but ConA bound to the whole spermatial surface except spermatial appendages. WGA labeled narrow region which connects spermatial body and appendages. During fertilization, ConA and WGA specific substances on the spermatial surface moved towards the area contacting with trichogyne and accumulated on the surface of fertilization canal. Spermatial binding to trichogynes was inhibited by pre‐incubation of spermatia with SBA, while trichogyne receptors were blocked by the complementary carbohydrate, N‐acetyl‐D‐galactosamine. WGA and its complementary carbohydrate had little effect on gamete binding. For searching the step of sexual isolation, crossing experiment was performed between Aglaothamnion byssoides and twelve other red algal species. Results showed that the gamete recognition was genus‐specific: the gametes bound freely with their partners of the same genus. When two species from same genus were crossed, sexual isolation occurs gradually during the fertilization process. Therefore, sexual isolation in red algae appears to be determined by multi‐step process and gamete binding is the initial step.     

ATTACHMENT AND FUSION OF GAMETES DURING FERTILIZATION OF PALMARIA SP. (RHODOPHYTA)1

Fertilization of cultured microscopic female gametophytes by spermatia from field-collected male gametophytes of Palmaria sp. was observed by light and transmission electron microscopy. Liberated spermatia had a prophase-arrested nucleus with a pair of polar rings. The protoplast of spermatia was covered with ca. a 3-μm-thick hyaline covering. After spermatium inoculation, the spermatial covering was attached specifically to the coat surrounding the cell wall of the trichogyne. The spermatial covering was eliminated only at the site of gamete attachment, resulting in direct attachment of the spermatial plasma membrane to the trichogyne within 5 min after spermatium inoculation. This direct attachment was followed by completion of spermatial nuclear division and cell wall formation. The polar rings disappeared before prometaphase. The cytoplasm of the binucleate spermatium invaded the trichogyne cell wall and subsequently fused with the trichogyne cytoplasm. The trichogyne could fuse with many spermatia, and many male nuclei (the derivative nuclei of spermatial nuclear division) could enter the trichogyne cytoplasm.     

Fertilization and the cytoskeleton in the red alga Bostrychia moritziana (Rhodomelaceae,Rhodophyta)

Time-lapse videomicroscopy was used to observe the effects of various cytoskeletal inhibitors on three important fertilization events in Bostrychia moritziana: spermatial mitosis, gamete fusion (formation of a fertilization pore) and nuclear migration along the trichogyne. The microtubule inhibitor oryzalin disrupted spermatial mitosis but had no other effect on fertilization. The actin inhibitors, jasplakinolide, cytochalasin B, latrunculin A and B and mycalolide B inhibited gamete fusion while BDM, a myosin-disrupting drug, inhibited all three major fertilization events. FL-Phallacidin was used to stain actin filaments in spermatia and trichogynes while microtubules were labelled with antibodies at appropriate stages of fertilization. Microtubules were only evident during spermatial nuclear division. Actin filaments were present in both trichogynes and spermatia throughout fertilization; they formed a discrete ring around the fertilization pore and ensheathed male nuclei as the latter migrated into and along the trichogyne. These results suggest that the actin/myosin system plays a role in the events of fertilization.     

Morphology of Sinophysis minima sp. nov. and three Sinophysis species (Dinophyceae, Dinophysiales) from the Sea of Japan

Four sand‐dwelling species of the marine dinoflagellate genus Sinophysis, including one new species, have been examined from intertidal and subtidal sand, from the Sea of Japan. The morphological features of these species were observed by light and scanning electron microscopy. Sinophysis minima sp. nov. is flattened laterally and is 17.5–35.0 μm in length and 15.0–27.5 μm in depth, with a length/depth ratio of 1.1–1.4, an epitheca depth of 5.0–7.5 μm, and a sulcus length of about three‐quarters the hypotheca length. Sinophysis ebriola (Herdman) Balech, Sinophysis grandis Hoppenrath and Sinophysis stenosoma Hoppenrath were recorded for the first time in the seas of Russia. Sinophysis stenosoma is the most common species in the Sea of Japan. All species usually occurred together in the region investigated. Additional information on the known species is provided.     

Systematic implications of pollen morphology in Elsholtzia (Elsholtzieae–Lamiaceae)

Pollen morphology of 18 species (32 specimens) representing all three currently recognized sections of the genus Elsholtzia (Elsholtzieae–Lamiaceae) was investigated in detail using light, scanning electron and transmission electron microscopy. Elsholtzia pollen grains are small to medium in size (P=20–50 μm, E=16–45 μm), mostly prolate‐spheroidal to prolate, and rarely oblate‐spheroidal to subprolate in shape (P/E=0.95–1.46), hexacolpate (the amb more or less circular or ellipsoid) with granular aperture membranes. Three distinct types of sexine ornamentation are observed in Elsholtzia: perforate, rugulose‐bireticulate, and bireticulate. The bireticulate pattern is the most common, showing a wide range of morphological variation among species. The exine thickness varies from 1.2 to 2.5 μm. Among the present palynological data, the variability observed in sexine ornamentation of Elsholtzia could be of systematic significance. Current infrageneric classification of the genus Elsholtzia is partially congruent with pollen morphological data.     

Morphology of the proboscis of Hubrechtella Juliae (nemertea,pilidiophora): Implications for pilidiophoran monophyly

The proboscis of Hubrechtella juliae was examined using transmission electron microscopy, scanning electron microscopy, and confocal laser scanning microscopy to reveal more features of basal pilidiophoran nemerteans for morphological and phylogenetic analysis. The proboscis glandular epithelium consists of sensory cells and four types of gland cells (granular, bacillary, mucoid, and pseudocnidae‐containing cells) that are not associated with any glandular systems; rod‐shaped pseudocnidae are 15–25 μm in length; the central cilium of the sensory cells is enclosed by two rings of microvilli. The nervous plexus lies in the basal part of glandular epithelium and includes 26–33 (11–12 in juvenile) irregularly anastomosing nerve trunks. The proboscis musculature includes four layers: endothelial circular, inner diagonal, longitudinal, and outer diagonal; inner and outer diagonal muscles consist of noncrossing fibers; in juvenile specimen, the proboscis longitudinal musculature is divided into 7–8 bands. The endothelium consists of apically situated support cells with rudimentary cilia and subapical myocytes. Unique features of Hubrechtella's proboscis include: acentric filaments of the pseudocnidae; absence of tonofilament‐containing support cells; two rings of microvilli around the central cilium of sensory cells; the occurrence of subendothelial diagonal muscles and the lack of an outer diagonal musculature (both states were known only in Baseodiscus species). The significance of these characters for nemertean taxonomy and phylogeny is discussed. The proboscis musculature in H. juliae and most heteronemerteans is bilaterally arranged, which can be considered a possible synapomorphy of Hubrechtellidae + Heteronemertea (= Pilidiophora). J. Morphol. 274:1397–1414, 2013. © 2013 Wiley Periodicals, Inc.     

A Light and Electron Microscopical Study of Trichoduboscqia epeori Léger (Microspora: Duboscqiidae)1

Trichoduboscqia epeori Léger was found to parasitize nymphs of the mayfly Rhithrogena iridina Kolenati in southwest Germany for a new host record. It was studied by light and electron microscopy. The pansporoblast membrane is evaginated at several points, usually four, to produce long needle-like appendages >20 μm in length with a resilient inner core superficially resembling collagen, which is thought to maintain their orientation. It is suggested that the pansporoblast appendages may play a role in host infection. The structure and ultrastructure of developmental stages are recorded for the first time. Apart from the pansporoblast appendages, the ultrastructure of T. epeori conforms to the general pattern seen in many other pansporoblastic Microspora. Typically 16 spores are produced per pansporoblast but 32-spore pansporoblasts were also found, and the taxonomic significance of this is discussed.     

Micropropagation through excised root culture of Clitoria ternatea and comparison between in vitro–regenerated plants and seedlings

An efficient protocol has been developed for high‐frequency shoot regeneration and plant establishment of Clitoria ternatea – a potential medicinal legume. Adventitious shoots were regenerated from young excised root segments of aseptic seedlings on Murashige and Skoog (MS) medium supplemented with various concentrations of 6‐benzyladenine (BA), kinetin, α‐naphthalene acetic acid (NAA) or 2,4‐dichlorophenoxy acetic acid (2,4‐D) either singly or in various combinations. The highest frequency (100%) of shoot regeneration and maximum number (16.4 ± 0.24) of shoots per explant was obtained on MS medium supplemented with 20 μm BA and 2.0 μm NAA. Organogenic calli were produced on a medium containing 2,4‐D (10 or 20 μm ) and BA (5.0 μm ). The calli were differentiated into multiple shoots on MS medium supplemented with 2.5–10 μm BA and 2.0 μm NAA. The microshoots were rooted on half‐strength MS medium supplemented with 5.0 μm indole‐3‐butyric acid and transplanted successfully in field conditions. After 12 months of transfer to ex vitro conditions, the performance of micropropagated plants were evaluated on the basis of some physiological and biochemical parameters and compared with the in vivo–grown plants of the same age. The sodium dodecyl sulphate polyacrylamide gel electrophoresis protein profile was same between regenerated and naturally growing shoots. Total soluble protein in aerial part as well as in seeds of in vitro–regenerated and in vivo–grown plants was almost the same. The mitotic study showed normal chromosomal movement and numbers (2x = 16).     

Gamete recognition during fertilization in a red alga,Antithamnion nipponicum

Summary Fertilization in the marine red algaAntithamnion nipponicum is a highly specific process involving non-motile male gametes, spermatia, and female receptive structures, carpogonia. FITC-lectin and Calcofluor white ST labelling show that the outer cell walls of spermatia differ from vegetative cells in carbohydrate composition. Specific binding of the lectins to spermatial walls was confirmed by lectin-gold labelling on thin sections. Gametic recognition inAntithamnion nipponicum is based on the interaction of a surface carbohydrate on the spermatia with a surface carbohydrate receptor on the trichogynes. Spermatial binding to trichogynes is inhibited by pre-incubation with concanavalin A and trichogyne receptors are blocked by the complementary carbohydrate -D-methyl mannose. The inhibitory effects of concanavalin A to spermatial binding of trichogynes is reversed by preincubation with -D-methyl mannose. The combination of long spermatial appendages and a carbohydrate-carbohydrate receptor-based gamete recognition mechanism make fertilization in this species an efficient process.     

Palynological characters of Glycyrrhiza,Glycyrrhizopsis, and Meristotropis (Leguminosae), with special reference to their taxonomic significance

Abstract The pollen morphology of 11 species of the genus Glycyrrhiza L. with one from each of the genera Glycyrrhizopsis Boiss. & Bal. and Meristotropis Fisch. & C. A. Mey. was investigated by scanning electron microscopy. In pollen morphology, the main differences between Glycyrrhizopsis and Glycyrrhiza are: Glycyrrhizopsis—pollen grains 36.63 × 40.42 μm in size, oblate spheroidal in shape; and Glycyrrhiza—pollen grains 24.47–33.18 × 23.82–31.83 μm in size, prolate spheroidal in shape. Glycyrrhizopsis and Glycyrrhiza should be recognized as two distinct genera based on palynological and morphological characters. Meristotropis and Glycyrrhiza are similar in many important palynological and morphological characters, suggesting that the two should be merged. In Glycyrrhiza, two types of pollen grains, 3‐lobed‐circular or subtriangular in polar view, are found in different species, in accordance with morphological differences in the two groups, shedding light on the classification and evolution of the genus.     

First record of dill powdery mildew caused by Erysiphe heraclei DC in Egypt

In Egypt, powdery mildew was observed for the first time on dill plants, during annual disease surveys of March–May 2003 and 2005. Typical symptoms of powdery mildew of dill plant (Anethum graveolens L.) were observed in Gharbeia Governorate. Symptoms of powdery mildew became common on leaves, stems inflorescences and fruits as white irregular areas. These symptoms appeared at vegetative and early flowering stages then gradually increased through fruiting and pre-maturity stages. Samples of infected leaflets, stem, inflorescences and fruits were collected for examination by light and scanning electron microscope (SEM). Microscopic examination revealed that conidiophores were short, erect–69 × 6–10 μm in dimension, conidia were observed without conspicuous fibrosin bodies singly, elliposid to ovoid 25–33 × 10–16 μm in dimension, and the length to width ratio of conidia ranged from 1.7 to 2.0 and were produced singly. Cylindrical foot cells (22.0 × 8.0 μm) were followed by one or two shorter cells (12.5 × 7.5 μm). In spring, the sexual stage (cleistothecia) appeared on infected leaves and stems in spherical, gregarious measures 105–117 (111) × 100– 87.5 μm in diameter. Each cleistothecium contained (2–4) round to ovoid asci, 45–55 (50) × 45–25 (35) μm in dimension. The ascus contained (3–4) ellipsoid to ovoid ascospores, 20–17.5 × 15–10 (13.2) μm. Cleistothecia appendages are simple myceloid branched tips measuring 80–200 (140) μm in length and 3–5 (4) μm in diameter. Based on the observations of the morphology of its anamorph and teleomorph stages, the causal agent of dill powdery mildew was identified as Erysiphe heraclei which is reported for the first time in Egypt.     

Ichthyosporidium weissii n. sp. (Microsporidia) infecting the arrow goby (Clevelandia ios)

Gonadal infections by a novel microsporidium were discovered in 34% (13/38) of arrow gobies, Clevelandia ios, sampled over a 3‐yr period from Morro Bay Marina in Morro Bay, California. Gonadal tumors had been reported in arrow gobies from this geographic area. The infected gonads, found primarily in females, typically appeared grossly as large, white‐gray firm and lobulated masses. Histological examination revealed large, multilobate xenomas within the ovaries and no evidence of neoplasia. Typical of the genus Ichthyosporidium, the large xenomas were filled with developmental stages and pleomorphic spores. Wet mount preparations showed two general spore types: microspores with mean length of 6.2 (7.0–4.9, SD = 0.6, N = 20) μm and mean width of 4.3 (5.3–2.9, SD = 0.8) μm; and less numerous macrospores with mean length of 8.5 (10.1–7.1, SD = 1.0, N = 10) μm and mean width of 5.5 (6.2–4.8, SD = 0.5) μm. Transmission electron microscopy demonstrated stages consistent with the genus and 35–50 turns of the polar filament. Small subunit rDNA gene sequence analysis revealed that the parasite from arrow gobies was most closely related to, but distinct from Ichthyosporidium sp. based on sequences available in GenBank. We conclude that this microsporidium represents a new species of Ichthyosporidium, the first species of this genus described from a member of the family Gobiidae and from the Pacific Ocean.     

An environmentally regulated pilus-like appendage involved in Campylobacter pathogenesis

Examination of strains of Campylobacter jejuni, Campylobacter coli, and Campylobacter fetus by electron microscopy revealed that they produced peritrichous pilus-like appendages when the bacteria were grown in the presence of bile salts. Various bile-salt supplements were used and it was found that deoxycholate and chenodeoxycholic acid caused a significant enhancement of pilus production and resulted in a highly aggregative phenotype. Morphologically, the pili were between 4 and 7 nm in width and were greater than 1 μm in length. A gene, termed pspA, which encodes a predicted protein resembling protease IV of Escherichia coli, was identified in C. jejuni strain 81–176. A site-specific insertional mutation within this gene resulted in the loss of pilus synthesis as determined by electron microscopy. Insertions upstream and downstream of the gene had no effect on pilus production. The non-piliated mutant of strain 81–176 showed no reduction in adherence to or invasion of INT 407 cells in vitro. However, this mutant, while still possessing the ability to colonize ferrets, caused significantly reduced disease symptoms in this animal model.     

Comparative morphology of the foot structure of four genera of Loxosomatidae (Entoprocta): Implications for foot functions and taxonomy

Entoprocta is a group of mostly cryptic, benthic invertebrates with a sedentary lifestyle. Here, we investigate the morphology of the entoproct foot, which is an important structure in attachment and locomotion. We describe the foot structure of four solitary entoprocts, Loxosoma monilis, Loxosomella stomatophora, Loxocorone allax, and Loxomitra mizugamaensis, by means of light and transmission electron microscopy. Gland cells containing secretory granules were found in the foot of all the four species. In L. monilis, the gland cells densely paved the underside of the disc‐shaped foot, but no duct or groove was found. In L. stomatophora and L. allax, a foot gland was present at the frontal end of a foot groove. The foot gland was a solid cell mass in the former species but a sac‐like structure in the latter. Two types of groove accessory cells were recognized in both species; groove bulge cells (GBCs) showed large cytoplasmic bulges extending into the groove lumen, while groove microvillus cells have microvillus mats in the lateral wall of the groove. The bulges of GBCs in L. stomatophora are slender and attached to one another with desmosomes, forming appendages that extend down to the substratum, hinting at their contribution to attachment and locomotion. The bulges in L. allax form large swellings that fill the groove lumen and are connected to the surrounding cells with hemidesmosomes. In the liberated buds of L. mizugamaensis, tripartite gland cell masses were found at the basal end of the stalk, but no groove was found. A small invagination, which may be the opening of the gland, was found at the center of the foot tip, where the liberated buds attach themselves to the substratum and then metamorphose into adults. No openings were found at the lateral terminal wings, which support locomotion in Loxomitra species. J. Morphol. 271:1185–1196, 2010. © 2010 Wiley‐Liss, Inc.     

Comparative pollen morphology of Glechoma and Marmoritis (Nepetinae,Lamiaceae)

Abstract The pollen morphology of 13 taxa (34 specimens) of the genera Glechoma L., and Marmoritis Benth. was investigated in detail using light, scanning electron, and transmission electron microscopy. Pollen grains of all studied taxa are small to large in size (P= 32.5–60.4 μm, E= 20.2–50.5 μm), prolate‐spheroidal to prolate in shape and mostly hexacolpate (the amb more or less circular or rarely ellipsoid) with granular membranes. The sexine ornamentation of Glechoma is bireticulate; the muri of the primary reticulum are irregularly circled, and lumen size is short. In contrast, the sexine surfaces of the Marmoritis pollen tend to more elongate or wider at the muri of the primary reticulum than those of the Glechoma. The pollen wall stratification of selected taxa (three from Glechoma and one from Marmoritis) is characterized by unbranched columellae, and continuous or distinctly discontinuous endexine based on transmission electron microscopy observation. The results of Glechoma and Marmoritis reveal rather similar pollen morphological features, however, fine details of sexine ornamentation are characteristic to differentiate the pollen taxa. Although these differences may be useful in establishing the taxonomic boundary between two genera, they are too weak to segregate diagnostic characters.     

Stramenopile Microorganisms Associated with the Massive Coral Favia sp.

ABSTRACT. The surfaces of massive corals of the genus Favia from Eilat, Red Sea, and from Heron Island, Great Barrier Reef, are covered by a layer of eukaryotic microorganisms. These microorganisms are embedded in the coral mucus and tissue. In the Gulf of Eilat, the prevalence of corals covered by patches of eukaryotic microorganisms was positively correlated with a decrease in water temperatures (from 25–28 °C in the summer to 20–23 °C in winter). Comparisons carried out using transmission and scanning electron microscopy showed morphological similarities between the microorganisms from the two geographically distant reefs. The microorganisms found on and in the tissues were approximately 5–15 μm in diameter, surrounded by scales in their cell wall, contained a nucleus, and included unique auto‐florescent coccoid bodies of approximately 1 μm. Such morphological characters suggested that these microorganisms are stramenopile protists and in particular thraustochytrids. Molecular analysis, carried out using specific primers for stramenopile 18S rRNA genes, revealed that 90% (111/123) of the clones in the gene libraries were from the Thraustochytriidae. The dominant genera in this family were Aplanochytrium sp., Thraustochytrium sp., and Labyrinthuloides sp. Ten stramenopile strains were isolated and cultured from the corals. Some strains showed ≥97% similarity to clones derived from libraries of mucus‐associated microorganisms retrieved directly from these corals. Fatty acid characterization of one of the prevalent strains revealed a high percentage of polyunsaturated fatty acids, including omega‐3. The possible association of these stramenopiles in the coral holobiont appeared to be a positive one.     

AgNO3 dependant modulation of glucose mediated respiration kinetics in Escherichia coli at different pH and temperature

The inhibitory role of AgNO₃ on glucose‐mediated respiration in Escherichia coli has been investigated as a function of pH and temperature using Clark‐type electrode, environmental scanning electron microscopy, and computational tools. In the given concentration of bacterial suspension (1 × 10⁸ CFU/ml), E. coli showed an increasing nonlinear trend of tetra‐phasic respiration between 1–133 μM glucose concentration within 20 min. The glucose concentrations above 133 μM did not result any linear increment in respiration but rather showed a partial inhibition at higher glucose concentrations (266–1066 μM). In the presence of glucose, AgNO₃ caused a concentration‐dependent (47–1960 μM) inhibition of the respiration rate within 4 min of its addition. The respiration rate was the highest at pH 7–8 and then was decreased on either side of this pH range. The inhibitory action of AgNO₃ upon bacterial respiration was the highest at 37 °C. The observations of the respiration data were well supported by the altered bacterial morphology as observed in electron microscopic study. Docking study indicated the AgNO₃ binding to different amino acids of all respiratory complex enzymes in E. coli and thereby explaining its interference with the respiratory chain. Copyright © 2016 John Wiley & Sons, Ltd.     

Septate‐tubular textures in 2.0‐Ga pillow lavas from the Pechenga Greenstone Belt: a nano‐spectroscopic approach to investigate their biogenicity

Pillow lava rims and interpillow hyaloclastites from the upper part of the Pechenga Greenstone Belt, Kola Peninsula, N‐Russia contain rare tubular textures 15–20 μm in diameter and up to several hundred μm long in prehnite–pumpellyite to lower greenschist facies meta‐volcanic glass. The textures are septate with regular compartments 5–20 μm across and exhibit branching, stopping and no intersecting features. Synchrotron micro‐energy dispersive X‐ray was used to image elemental distributions; scanning transmission X‐ray microscopy, Fe L‐edge and C K‐edge were used to identify iron and carbon speciation at interfaces between the tubular textures and the host rock. In situ U–Pb radiometric dating by LA‐MC‐ICP‐MS (laser ablation multicollector inductively coupled plasma mass spectrometry) of titanite from pillow lavas yielded a metamorphic age of 1790 ± 89 Ma. Focused ion‐beam milling combined with transmission electron microscopy was used to analyze the textures in three dimensions. Electron diffraction showed that the textures are mineralized by orientated pumpellyite. On the margins of the tubes, an interface between mica or chlorite and the pumpellyite shows evidence of dissolution reactions where the pumpellyite is replaced by mica/chlorite. A thin poorly crystalline Fe‐phase, probably precipitated out of solution, occurs at the interface between pumpellyite and mica/chlorite. This sequence of phases leads to the hypothesis that the tubes were initially hollow, compartmentalized structures in volcanic glass that were mineralized by pumpellyite during low‐grade metamorphism. Later, a Fe‐bearing fluid mineralized the compartments between the pumpellyite and lastly the pumpellyite was partially dissolved and replaced by chlorite during greenschist metamorphism. The most plausible origin for a septate‐tubular texture is a progressive etching of the host matrix by several generations of microbes and subsequently these tubes were filled by authigenic mineral precipitates. This preserves the textures in the rock record over geological time. The micro textures reported here thus represent a pumpellyite‐mineralized trace fossil that records a Paleoproterozoic sub‐seafloor biosphere.