Phosphatized soft-bodied squids from the Jurassic Oxford Clay

A diagenetic case study of phosphatized soft-bodied squids from the lower part of the Oxford Clay of Christian Malford, Wiltshire, has dated mineralization in relation to burial history. Complete squids with mantle tissues were examined under the SEM as uncoated specimens at low KV. A simple stage attachment designed for this purpose is described. Soft-parts are preserved in three dimensions and must therefore have been mineralized prior to decay-induced tissue collapse. Such mineralization occurred near to the anoxic/oxic boundary in the 'soupy' upper layer of organic-rich sediment. In acrobic conditions, phosphates were liberated to pore-water solution from decomposing organic matter and became adsorbed to ferric hydroxides within sediment. The reduction of these ferric hydroxides at the anoxic-oxic interface liberated phosphates to solutions which were conccntrated in the decomposing carcasses of the squids. This mineral concentration was favoured by the development of a high pH reducing environment around the carcass and possibly by complexing with protcolipids liberated by decomposition of animal matter. ▭ Soft-part preservation, phosphatization, SEM techniques, cephatopod. Oxford Clay, Wiltshire, England.     

N,N –Disubstituted piperazines and homopiperazines: Synthesis and affinities at α4β2* and α7* neuronal nicotinic acetylcholine receptors

A series of N, N– disubstituted piperazines and homopiperazines were prepared and evaluated for binding to natural α4β2* and α7* neuronal nicotinic acetylcholine receptors (nAChRs) using whole brain membrane. Some compounds exhibited good selectivity for α4β2* nAChRs and did not interact with the α7* nAChRs subtype. The most potent analogs were compounds 8-19 (K_i = 10.4 μM), 8–13 (K_i = 12.0 μM), and 8–24 (K_i = 12.8 μM). Thus, linking together a pyridine π-system and a cyclic amine moiety via a homopiperazine ring affords compounds with low affinity but with good selectivity for α4β2* nAChRs.     

Use of precision cut human liver slices for studying the metabolism and genotoxic potential of xenobiotics by means of the 32P-postlabelling technique: steps towards method validation using testosterone and 2-aminofluorene

In the present study, a new in vitro model combining the short-term incubation of precision-cut human liver slices with DNA-adduct analysis by the ³²P-postlabelling technique is proposed for investigation of the genotoxic potential of xenobiotics. For method validation, the metabolic turnover of testosterone (TES) and the DNA-adduct inducing potential of 2-aminofluorene (2-AF) were used. Precision-cut human liver slices were prepared from a total of 12 human liver samples which were freshly obtained as parts of resectates from liver surgery. The slices were incubated as submersion cultures with TES and 2-AF for up to 6 h in 12-well tissue culture plates at concentrations of 10-50 and 0.06-28 μM, respectively. Slices recovered from the slicing procedure in the 4 °C cold Krebs-Henseleit buffer as indicated by intracellular potassium concentrations which increased for 2 h and then remained stable until the end of the incubation. TES was extensively metabolized by human liver slices with a similar metabolite pattern as observed in vivo. Almost 90% of the metabolites were conjugates. Major phase-I metabolites were androstendione, 6β-OH-androstendione, 6β-OH-TES, and 15β-OHTES. After incubation with 2-AF, substance related DNA-adducts were detected which increased dose-dependently from 12 to 1146 adducts per 10⁹ nucleotides. The adduct pattern consisted of one major adduct spot, A, representing 80-90% of the total adduct level and up to four minor adduct spots, B-E. In summary, the present data demonstrate that precision-cut liver slices are a valuable alternative in vitro system for DNA-adduct determination to screen chemicals for potential genotoxicity in humans.     

THE COMMUNICATIVE SIGNIFICANCE OF TONALITY IN BIRDSONG: RESPONSES TO SONGS PRODUCED IN HELIUM

ABSTRACT

“Pure tones” are a distinctive acoustic feature of many birdsongs. Recent research on songbird vocal physiology suggests that such tonal sounds result from a coordinated interaction between the syrinx and a vocal filter, as demonstrated by the emergence of harmonic overtones when a bird sings in helium. To investigate the communicative significance of vocal tract filtration in the production of birdsong, we used field playback experiments to compare the responses of male swamp sparrows Melospiza georgiana to normal songs and those same songs recorded in helium. We also measured responses to pure tone songs that had been shifted upward in frequency to match the average spectra of those songs with added harmonics. Male sparrows were significantly more responsive to the playback of normal songs than to either helium songs with added harmonics or frequency- shifted pure tone songs. Songs with harmonics retained a high degree of salience, however. We conclude that explanations for the occurrence of tonal sounds in birdsongs must consider perceptual attributes of songs as communicative signals, as well as problems of song production and transmission.     

Floral symmetry and nectar guides: ontogenetic constraints from floral development, colour pattern rules and functional significance

The accord between symmetries of flower shape (external contours) and nectar guides (internal contours) was examined using the bulbous flora of South Africa, and in the general floras of Britain, Alpine Colorado, Canadian Arctic and Israel. It was found that radially symmetrical flowers have radially symmetrical nectar guides whereas bilaterally symmetrical flowers have bilaterally symmetrical nectar guides. It is suggested that the complementarity between the external and the internal contours of the flower increases the probability that, and efficiency with which, a bee moves into the flower's centre and towards the sporophylls and access to floral rewards, regardless of the flower's form and the bee's previous experience. Patterns of coloration of tepals against background and nectar guides against tepals also accord with behavioural and sensory characteristics of pollinators. It is suggested that the complementarity of contours is probably constrained by floral development, but patterns of coloration of tepals against background and nectar guides against tepals is constrained by pollinators' sensory physiology.     

Stereological Studies of the Effects of α-MSH and cAMP on Melanosomes in Melanoma Cells

The effects of α-MSH and cAMP on melanosomes in Cloudman S91 melanoma cells were investigated by modern stereological techniques. Cells were cultured for 4 days in medium containing α-MSH or cAMP harvested at 24 hour intervals; some were frozen for melanin assay and the reminder embedded in Epon for light and electron microscopy. Cellular and melanosomal parameters were estimated by new stereological probes. We found that both stimulators induced increases in nuclear volume, cell volume, and the volume fractions and volumes of premelanosomes (V_Vpm,cell’V_pm) and mature melanosomes (V_Vmm,cell’V_mm) and the number of mature melanosomes (N_mm). Both stimulators also caused declines in the volume of individual mature melanosomes (_Vimm) the melanin content per mature melanosome unit volume and the melanin content per individual mature melanosome. The increases in the volume of individual premelanosomes and the number of premelanosomes were only induced by cAME The effect cAMP on some parameters occurred 24 hours prior to α-MSH and was more marked. The response of premelanosomes to the stimulators was more sensitive than mature melanosomes. These results suggest that both stimulators enchanced melanogenesis by increasing the V_Vpm,cell’V_Vmm,cell’V_pm, V_mm and N_mm. The melanogenic level did not depend on the _Vimm and melanin concentration in melanosomes. The maturation of premelanosomes was involved in melanogenesis induced by both stimulators, but, de novo synthesis and enlargement of premelanosomes were only stimulated by cAME It imply that exogenous cAMP may affect melanosomes, and hence melanogenesis in quantitatively or qualitatively different ways to α-MSH.     

Distribution and regulation of urea in lakes of central North America

1. Urea accounts for ～50% of global nitrogen (N)‐based fertiliser; however, little is known of the factors regulating its distribution and abundance in freshwaters. Improved understanding of urea biogeochemistry is essential because its use as fertiliser is expected to double by 2050 and because pollution with urea can promote outbreaks of toxic cyanobacteria in phosphorus (P)‐rich lakes in regions with intensive agricultural or urban development. 2. Biweekly measurements of urea concentration and diverse limnological variables (water chemistry, hydrology, algae, zooplankton) were taken during two summers (2008, 2009) in a chain of seven productive lakes within a 52 000‐km² catchment in central Canada to quantify environmental and anthropogenic correlates of temporal and spatial patterns of urea occurrence. 3. Mean (±SD) urea concentrations varied between 29 ± 14 and 132 ± 65 μg N L^?1, generally increased from headwater to downstream sites and represented 10–50% of bioavailable N (as sum of , and urea). Principal components analysis demonstrated that urea concentrations were elevated in agriculturally impacted lakes with abundant dissolved organic and inorganic nutrients (N, P, C) and low O₂ concentrations, but were not correlated consistently with plankton abundance or community composition. Urea concentrations were more than twofold greater in lakes receiving N from cities than in agriculturally affected basins, despite low summer concentrations of urea in tertiary‐treated urban effluent (c. 50% of lake values). Multiple regression models evaluated using Akaike Information Criterion showed that mean water‐column O₂ concentration was the single best predictor of in situ urea concentrations (r² = 0.91, P = 0.002), but that urea concentrations were also correlated significantly with changes in longitudinal position and Secchi depth and with concentrations of , non‐urea dissolved organic N (DON) and dissolved inorganic carbon. 4. Additional seasonal surveys of up to 69 closed‐basin lakes within a 100 000‐km² region during 2004 and 2008 revealed that urea was abundant in 100% of measured sites and exhibited concentrations (81 ± 48 μg N L^?1) similar to those observed in lakes with surface drainage (58 ± 38 μg N L^?1). Further, non‐urea DON accounted for 50–99% of the total dissolved N pool in both open‐ and closed‐basin lakes. 5. When combined with an extensive literature review and previous mass‐budget analyses of the study lakes, these findings allowed the development of a first‐generation model of the mechanisms regulating urea content of P‐rich lakes of central North America. In this model, water‐column concentrations of urea are predicted to be regulated mainly by algal decomposition in anoxic environments (sediments, hypolimnion), followed by redistribution into surface waters. Consequently, anthropogenic activities can increase the urea content of lakes by stimulating primary production, sedimentation and deepwater anoxia and by increasing influx of undegraded urea from agricultural and urban sources.     

Phosphorus concentrations in the leaves of defoliated white clover affect abscisic acid formation and transpiration in drying soil

Increased leaf phosphorus (P) concentration improved the water-use efficiency (WUE) and drought tolerance of regularly defoliated white clover plants by decreasing the rate of daily transpiration per unit leaf area in dry soil. Night transpiration was around 17% of the total daily transpiration. The improved control of transpiration in the high-P plants was associated with an increased individual leaf area and WUE that apparently resulted from net photosynthetic assimilation rate being reduced less than the reductions in the transpiration (27% vs 58%). On the other hand, greater transpiration from low-P plants was associated with poor stomatal control of transpirational loss of water, less ABA in the leaves when exposed to dry soil, and thicker and smaller leaf size compared with high-P leaves. The leaf P concentration was positively related with leaf ABA, and negatively with transpiration rates, under dry conditions ( P < 0.001). However, leaf ABA was not closely related to the transpiration rate, suggesting that leaf P concentration has a greater influence than ABA on the transpiration rates.