Tissue abscission and wound healing in the operculum of Pomatoceros lamarckii Quatrefages (Polychaeta: Serpulidae)

Following opercular amputation in Pomatoceros lamarckii Quatrefages, wound healing is initiated from a predetermined point on the peduncle. The events of abscission, cell migration and cuticle deposition during wound healing have been studied by light and electron microscopy. Abscission occurs at a predetermined point on the peduncle indicated by specialized epidermal cells, the easy break-point cells (EBP). Following detachment of tissues distal to the EBP cells, the resultant wound is plugged by a knot of coelomocytes which provide a substratum over which epidermal cells migrate to seal and restore the epidermis. During their migration, the epidermal cells undergo differentiation and deposit a new cuticle. Cuticle formation is initiated by the deposition of a finely filamentous matrix. The fine filaments subsequently coalesce to form thicker fibrils which become aggregated into layers of orthogonally-arranged fibril bundles. The mechanisms involved in abscission, cell migration and cuticle deposition during wound healing of the opercular filament are discussed.     

The chemistry of vitamin B12. The coordination of biologically important molecules

The following equilibrium constants (given as logK in units of m⁻¹) were determined for the substitution of co-ordinated H₂O in aquocobalamin by glycine (bound through N) 5.8, cysteine (bound through S) 6.0 or 8.3, depending on the value chosen for the pK of the thiol group, and phenolate 2.9. The spectrum of the phenolate cobalamin shows an additional intense absorption band at 468nm with a molar extinction coefficient of 1.1×10⁴, which is assigned to a charge transfer from the phenolate to the cobalt ion. Equilibrium constants have also been determined for the equilibria between adenylcobamide cyanide and CN⁻, HO⁻ and H⁺, which show that the adenine is more easily displaced by CN⁻ and HO⁻ than is 5,6-dimethylbenziminazole in vitamin B₁₂, but can be protonated by acid while still remaining co-ordinated to the cobalt. It is shown that in the binding of corrinoids to proteins and polypeptides the formation of hydrogen bonds is far more important than co-ordination by the metal.     

Field experiments on interactions between vertebrate predators and larval midges (Diptera: Chironomidae) in the littoral zone of a reservoir

Summary A field experiment was designed to test a frequent assumption in the literature that vertebrate predators (in this case, fish and turtles) are capable of regulating the seasonal abundance and diversity of benthic communities in the littoral zone of lentic environments. Effects of thermal effluents from a nuclear reactor on predator-prey relationships were also examined. Benthic samples were removed after each of three, 3-month test periods from 36 predator exclusion cages (4m²) and 36 control plots located along a thermal gradient in Par Pond, an 1,100 ha freshwater reservoir in the southeastern United States.Results of our field experiments provide little evidence to suggest that either a single keystone species or vertebrate predators as a group were capable of regulating the abundance, diversity or productivity of chironomids in Par Pond. The relationship between predator treatment and community response (changes in density and species richness) was generally unaffected by either plot location or temperature fluctuations. When data from caged and control plots were pooled, however, both location and water temperature individually had significant impacts on the chironomid community. Alternative hypotheses are proposed to explain the lack of regulatory control of the benthic community by individual species or guilds of predators.     

In situ experiments on predatory regulation of a bivalve mollusc (Dreissena polymorpha) in the Mississippi and Ohio Rivers

1. In situ exclosure experiments in the Mississippi and Ohio Rivers determined the importance of fish predation in regulating zebra mussels (Dreissena polymorpha), an increasingly important constituent of the benthic invertebrate assemblages in both rivers. 2. We evaluated the effects of predatory fish on the density, biomass and size distribution of zebra mussels in a floodplain reach of the upper Mississippi River and in a naturally constrained reach of the Ohio River. Fifty, six-sided, predator-exclusion cages and fifty ‘partial’ cages (mesh at the upstream end only) were deployed, with half the cages containing willow snags and half clay tiles suspended 12–16 cm above the bottom. A single snag or tile sample unit was removed from each cage at approximately monthly intervals from July to October 1994. Types and relative abundances of molluscivorous fish were evaluated by electrofishing near the cages in both rivers. Actual and potential recruitment of young zebra mussels on to the substrata were measured using benthic samples in both rivers and estimated (Ohio River only) from counts of planktonic veligers. 3. Zebra mussels were consumed by at least three fish species in the upper Mississippi River (mostly carp, Cyprinus carpio, and redhorse suckers, Moxostoma sp.) and five species in the Ohio River (primarily smallmouth buffalo, Ictiobus bubalus, and channel catfish, Ictalurus punctatus), but potential recruitment seemed adequate to replace consumed mussels, at least in the Ohio River. The number of juvenile benthic mussels showed no apparent link with the density of veligers soon after initiation of reproduction. Recruitment of juveniles on snags and tiles was not affected by cage type (thus eliminating a potentially confounding ‘cage effect’). 4. Fish significantly influenced mussel populations, but the impact was often greatest among low density populations in the upper Mississippi. Density and biomass differed in both rivers for cage type (higher inside cages), substratum (greater on tiles), and date (increased over time). Presumed size-selective predation was present in the Mississippi (greater on larger size classes) but was not evident in the Ohio. We hypothesize that fish in the Mississippi can more easily select larger prey from the low density populations; whereas size-selective predation on tightly packed zebra mussels in the Ohio would be difficult. 5. Although fish can reduce numbers of Dreissena polymorpha in the two rivers, current levels of fish predation seem insufficient to regulate zebra mussel densities because of its great reproductive capacity. The recent invasion of zebra mussels, however, could lead to larger fish populations while promoting greater carbon retention and overall ecosystem secondary production.     

Victims and survivors: Stable isotopes used to identify migrants from the Great Irish Famine to 19th century London

Historical evidence documents mass migration from Ireland to London during the period of the Great Irish Famine of 1845–52. The rural Irish were reliant on a restricted diet based on potatoes but maize, a C₄ plant, was imported from the United States of America in 1846–47 to mitigate against Famine. In London, Irish migrants joined a population with a more varied diet. To investigate and characterize their diet, carbon and nitrogen isotope ratios were obtained from bone collagen of 119 and hair keratin of six individuals from Lukin Street cemetery, Tower Hamlets (1843–54), and bone collagen of 20 individuals from the cemetery at Kilkenny Union Workhouse in Ireland (1847–51). A comparison of the results with other contemporaneous English populations suggests that Londoners may have elevated δ¹⁵N compared with their contemporaries in other cities. In comparison, the Irish group have lower δ¹⁵N. Hair analysis combined with bone collagen allows the reconstruction of perimortem dietary changes. Three children aged 5–15 years from Kilkenny have bone collagen δ¹³C values that indicate consumption of maize (C₄). As maize was only imported into Ireland in quantity from late 1846 and 1847, these results demonstrate relatively rapid bone collagen turnover in children and highlight the importance of age‐related bone turnover rates, and the impact the age of the individual can have on studies of short‐term dietary change or recent migration. Stable light isotope data in this study are consistent with the epigraphic and documentary evidence for the presence of migrants within the London cemetery. Am J Phys Anthropol, 2013. © 2012 Wiley Periodicals, Inc.     

Experimental set up for the irradiation of biological samples and nuclear track detectors with UV C

Aim

In this work we present a methodology to produce an “imprint” of cells cultivated on a polycarbonate detector by exposure of the detector to UV C radiation.

Background

The distribution and concentration of ¹⁰B atoms in tissue samples coming from BNCT (Boron Neutron Capture Therapy) protocols can be determined through the quantification and analysis of the tracks forming its autoradiography image on a nuclear track detector. The location of boron atoms in the cell structure could be known more accurately by the simultaneous observation of the nuclear tracks and the sample image on the detector.

Materials and Methods

A UV C irradiator was constructed. The irradiance was measured along the lamp direction and at different distances. Melanoma cells were cultured on polycarbonate foils, incubated with borophenylalanine, irradiated with thermal neutrons and exposed to UV C radiation. The samples were chemically attacked with a KOH solution.

Results

A uniform irradiation field was established to expose the detector foils to UV C light. Cells could be seeded on the polycarbonate surface. Both imprints from cells and nuclear tracks were obtained after chemical etching.

Conclusions

It is possible to yield cellular imprints in polycarbonate. The nuclear tracks were mostly present inside the cells, indicating a preferential boron uptake.     

Climate Records,Isotopes, and C:N Stoichiometry Reveal Carbon and Nitrogen Flux Dynamics Differ Between Functional Groups of Ectomycorrhizal Fungi

Ecosystems - A major functional division in ectomycorrhizal fungi is between taxa with hydrophobic ectomycorrhizae (strong proteolytic capabilities, deep nitrogen (N) acquisition, and extensive...