Inhibition of ethylene evolution in papaya pulp tissue by benzyl isothiocyanate

Papaya (Carica papaya L.) pulp tissue disks in an incubation medium composed of 0.4 m sucrose evolve ethylene at an optimum pH of 5.25 at 30 C. Disks of young preclimacteric fruit evolve the gas linearly with fruit age until fruit age reaches 4 months. Disks from 5-month-old postclimacteric fruit produce approximately 5-fold more ethylene than disks from 4-month-old fruit. Ethylene evolution by unaged papaya disks is inhibited potently by benzyl isothiocyanate. The compound inhibits production of ethylene by approximately 60% at a concentration of 0.046 mm. However, in aged papaya disks benzyl isothiocyanate causes no inhibition of ethylene production indicating that the compound inhibits the induction of the ethylene-producing system rather than the evolution of the gas per se. Even at a 2-fold higher concentration benzyl isothiocyanate has no effect on respiration of unaged papaya disks. It is proposed that benzyl isothiocyanate may act as an endogenous regulator of ethylene evolution in papaya fruit.     

Disparate data streams together yield novel survival estimates of Alaska-breeding Whimbrels

Survival estimates are critical components of avian ecology. In well-intentioned efforts to maximize the utility of one's research, survival estimates often derive from data that were not originally collected for survival assessments, and such post hoc analyses may include unintentional biases. We estimated the survival of Whimbrels captured and marked at two breeding sites in Alaska using divergent data streams that in isolation were subject to methodological biases. Although both capture sites were chosen to study the migration ecology of Alaska-breeding Whimbrels, maximizing the conservation value of the data we collected was obviously desirable. We used multi-year telemetry information to infer survival from one site (Colville River) and mark–resight techniques to estimate survival from a second site (Kanuti River). At Colville River, we could not feasibly include a control group of birds to assess potential survival effects of externally mounted transmitters, and at Kanuti River we were unable to account accurately for potential emigration events because we used resightings alone. We integrated these datasets in a Bayesian hierarchical framework, an approach that permitted insights across sites that moderated methodological biases within sites. Using telemetry enabled us to detect permanent emigration events from breeding sites in two of 10 birds, results that informed estimates for birds without tracking devices. These datasets yielded point estimates of true survival of Whimbrels from Colville River equipped with solar-powered satellite transmitters that were higher (0.83) than true survival estimates of Whimbrels from Kanuti River marked with leg flags alone (0.74) or equipped with surgically implanted satellite transmitters (0.50), but the 95% credible intervals on these estimates overlapped across groups. For species such as Whimbrels that are difficult and costly to study, combining information from disparate data streams allowed us to derive novel demographic estimates, an approach with clear application to other similar studies.     

Rate-Dependent Behavior of the Amorphous Phase of Spider Dragline Silk

The time-dependent stress-strain behavior of spider dragline silk was already observed decades ago, and has been attributed to the disordered sequences in silk proteins, which compose the soft amorphous matrix. However, the actual molecular origin and magnitude of internal friction within the amorphous matrix has remained inaccessible, because experimentally decomposing the mechanical response of the amorphous matrix from the embedded crystalline units is challenging. Here, we used atomistic molecular dynamics simulations to obtain friction forces for the relative sliding of peptide chains of Araneus diadematus spider silk within bundles of these chains as a representative unit of the amorphous matrix in silk fibers. We computed the friction coefficient and coefficient of viscosity of the amorphous phase to be in the order of 10⁻⁶ Ns/m and 10⁴ Ns/m², respectively, by extrapolating our simulation data to the viscous limit. Finally, we used a finite element method for the amorphous phase, solely based on parameters derived from molecular dynamics simulations including the newly determined coefficient of viscosity. With this model the time scales of stress relaxation, creep, and hysteresis were assessed, and found to be in line with the macroscopic time-dependent response of silk fibers. Our results suggest the amorphous phase to be the primary source of viscosity in silk and open up the avenue for finite element method studies of silk fiber mechanics including viscous effects.     

EPR-detectable redox centers of the periplasmic hydrogenase from Desulfovibrio vulgaris

The periplasmic hydrogenase of Desulfovibrio vulgaris (Hildenbourough NCIB 8303) belongs to the category of [Fe] hydrogenase which contains only iron-sulfur clusters as its prosthetic groups. Amino acid analyses were performed on the purified D. vulgaris hydrogenase. The amino acid composition obtained compared very well with the result derived from the nucleotide sequence of the structural gene (Voordouw, G., Brenner, S. (1985) Eur. J. Biochem. 148, 515-520). Detailed EPR reductive titration studies on the D. vulgaris hydrogenase were performed to characterize the metal centers in this hydrogenase. In addition to the three previously observed EPR signals (namely, the "isotropic" 2.02 signal, the rhombic 2.10 signal, and the complex signal of the reduced enzyme), a rhombic signal with resonances at the g-values of 2.06, 1.96, and 1.89 (the rhombic 2.06 signal) was detected when the samples were poised at potentials between 0 and -250 mV (with respect to normal hydrogen electrode). The midpoint redox potentials for each of the four EPR-active species were determined, and the characteristics of each EPR signal are described. Both the rhombic 2.10 and 2.06 signals exhibit spectral properties that are distinct from a ferredoxin-type [4Fe-4S] cluster and are proposed to originate from the same H2-binding center but in two different conformations. The complex signal of the reduced hydrogenase has been shown to represent two spin-spin interacting ferredoxin-type [4Fe-4S]1+ clusters (Grande, H. J., Dunham, W. R., Averill, B., Van Dijk, C., and Sands, R. H. (1983) Eur. J. Biochem. 136, 201-207). The titration data indicated a strong cooperative effect between these two clusters during their reduction. In an effort to accurately estimate the number of iron atoms/molecule of hydrogenase, plasma emission and chemical methods were used to determine the iron contents in the samples; and four different methods, including amino acid analysis, were used for protein determination. The resulting iron stoichiometries were found to be method-dependent and vary over a wide range (+/- 20%). The uncertainties involved in the determination of iron stoichiometry are discussed.     

Bayesian geostatistics in health cartography: the perspective of malaria

Maps of parasite prevalences and other aspects of infectious diseases that vary in space are widely used in parasitology. However, spatial parasitological datasets rarely, if ever, have sufficient coverage to allow exact determination of such maps. Bayesian geostatistics (BG) is a method for finding a large sample of maps that can explain a dataset, in which maps that do a better job of explaining the data are more likely to be represented. This sample represents the knowledge that the analyst has gained from the data about the unknown true map. BG provides a conceptually simple way to convert these samples to predictions of features of the unknown map, for example regional averages. These predictions account for each map in the sample, yielding an appropriate level of predictive precision.     

Malsoor Virus,a Novel Bat Phlebovirus,Is Closely Related to Severe Fever with Thrombocytopenia Syndrome Virus and Heartland Virus

During a survey in the year 2010, a novel phlebovirus was isolated from the Rousettus leschenaultii species of bats in western India. The virus was identified by electron microscopy from infected Vero E6 cells. Phylogenic analysis of the complete genome showed its close relation to severe fever with thrombocytopenia syndrome (SFTS) and Heartland viruses, which makes it imperative to further study its natural ecology and potential as a novel emerging zoonotic virus.     

Kinetics of spermatogenesis in megachiropteran bat, Rousettus leschenaulti (Desmarset): seminiferous epithelial cycle, frequency of stages, spermatogonial renewal and germ cell degeneration.

The paper describes in detail the cytomorphology of different types of germ cells, the 10 typical cellular associations or stages of the cycle of seminiferous epithelium (CSE), frequency of appearance of these stages, pattern of spermatogonial stem cell renewal and per cent degeneration of various germ cells in R. leschenaulti. Of the 14 steps of spermiogenesis (stained with PAS-haematoxylin) the first 10 were associated with the stages I-X, whereas, the remaining were found in association with one of the first six stages. The frequency of appearance of the various stages ranged from 3.84% (stage V) to 19.84% (stage I). These observations indicate that stage V is of shortest duration and stage I is of the longest duration in the bat. Five types of spermatogonia (A1, A2, A3, In and B) were identified based on their shape, size and nuclear morphology. Type A spermatogonia are oval with a large nucleus containing 1 or 2 nucleoli. The chromatin showed progressive condensation from A1 to A3 so that the latter appeared darkest among all the A type spermatogonia. The In type derived from A3 are smaller but appear darker than A3 due to heterochromatin crusts along the inner border of the nucleus. The B type spermatogonia derived from In are round and possess single nucleolus. The B type spermatogonia divided mitotically before entering meiosis or the actual production of the primary spermatocytes. The various spermatogonia divided mitotically at fixed stages of the cycle giving rise to their next generations.(ABSTRACT TRUNCATED AT 250 WORDS)