The G0 Experiment: Apparatus for Parity-Violating Electron Scattering Measurements at Forward and Backward Angles

In the G0 experiment, performed at Jefferson Lab, the parity-violating elastic scattering of electrons from protons and quasi-elastic scattering from deuterons is measured in order to determine the neutral weak currents of the nucleon. Asymmetries as small as 1 part per million in the scattering of a polarized electron beam are determined using a dedicated apparatus. It consists of specialized beam-monitoring and control systems, a cryogenic hydrogen (or deuterium) target, and a superconducting, toroidal magnetic spectrometer equipped with plastic scintillation and aerogel Cerenkov detectors, as well as fast readout electronics for the measurement of individual events. The overall design and performance of this experimental system is discussed.Comment: Submitted to Nuclear Instruments and Method

‘Do dead men tell no tales?’ The geographic origin of a colonial period Anglican cemetery population in Adelaide, South Australia, determined by isotope analyses

Tooth enamel and dentine samples from 13 individuals buried in the unmarked ‘free ground’ colonial section of St Mary’s Anglican Cemetery in Adelaide were analysed for oxygen and strontium isotopic composition to assist with the determination of their geographic origin. As the life history of these individuals is not well-documented in the historical record, isotopic data provide important information about migration and mobility in a colonial South Australian population. This was supplemented with further analysis of diet from previously published stable isotope data. While the results are somewhat ambiguous, they suggest that of the 13 individuals in this study, one was probably born in Adelaide, eight in Britain/Ireland, three could have been born in either location; one was born elsewhere. This interpretation supplements and supports the results from the analysis of skeletal morphology, microbiomes, and historical records.Christine Adams, Timothy D. Owen, F. Donald Pate, David Bruce, Kristine Nielson, Robert Klaebe, Maciej Henneberg and Ian Moffa

Different plant viruses induce changes in feeding behavior of specialist and generalist aphids on common bean that are likely to enhance virus transmission

Bean common mosaic virus (BCMV), bean common mosaic necrosis virus (BCMNV), and cucumber mosaic virus (CMV) cause serious epidemics in common bean (Phaseolus vulgaris), a vital food security crop in many low-to-medium income countries, particularly in Sub-Saharan Africa. Aphids transmit these viruses "non-persistently," i.e., virions attach loosely to the insects' stylets. Viruses may manipulate aphid-host interactions to enhance transmission. We used direct observation and electrical penetration graph measurements to see if the three viruses induced similar or distinct changes in feeding behaviors of two aphid species, Aphis fabae and Myzus persicae. Both aphids vector BCMV, BCMNV, and CMV but A. fabae is a legume specialist (the dominant species in bean fields) while M. persicae is a generalist that feeds on and transmits viruses to diverse plant hosts. Aphids of both species commenced probing epidermal cells (behavior optimal for virus acquisition and inoculation) sooner on virus-infected plants than on mock-inoculated plants. Infection with CMV was especially disruptive of phloem feeding by the bean specialist aphid A. fabae. A. fabae also experienced mechanical stylet difficulty when feeding on virus-infected plants, and this was also exacerbated for M. persicae. Overall, feeding on virus-infected host plants by specialist and generalist aphids was affected in different ways but all three viruses induced similar effects on each aphid type. Specifically, non-specialist (M. persicae) aphids encountered increased stylet difficulties on plants infected with BCMV, BCMNV, or CMV, whereas specialist aphids (A. fabae) showed decreased phloem ingestion on infected plants. Probing and stylet pathway activity (which facilitate virus transmission) were not decreased by any of the viruses for either of the aphid species, except in the case of A. fabae on CMV-infected bean, where these activities were increased. Overall, these virus-induced changes in host-aphid interactions are likely to enhance non-persistent virus transmission, and data from this work will be useful in epidemiological modeling of non-persistent vectoring of viruses by aphids

How should toxic secondary metabolites be distributed between the leaves of a fast-growing plant to minimize the impact of herbivory?

1. This paper considers the possibility that the key determinant of leaf age feeding preferences in foliovores is not the concentration of either nutrients or secondary metabolites, but is the ratio of the two. 2. In some fast-growing plants, nitrogen is most heavily defended by defensive toxins in the young leaves. This empowers the use of a simple model of leaf-age preference, based on the conflict between maximizing nutrient intake and minimizing toxicosis. 3. Young leaves are particularly valuable, not only because they lock up nitrogen, but also because their assimilative value is high. We calculate the loss of value due to herbivory and find that, if the herbivore is moderately intolerant of toxicity and feeds selectively on its predicted optimal leaf age, the costs of damage are greatly reduced. However, efficient toxin distribution protects the plant only if it grows rapidly, so that the well protected young foliage retains a high value. 4. The trends are reconcilable with observed leaf-age preferences of both polyphagous and oligophagous species. There is, as yet, little empirical evidence to substantiate the model, but it may be useful for future studies to focus on the toxin:nutrient ratio as a potentially important determinant of feeding preferences

Asparagine in plants

Interest in plant asparagine has rapidly taken off over the past 5 years following the report that acrylamide, a neurotoxin and potential carcinogen, is present in cooked foods, particularly carbohydrate-rich foods such as wheat and potatoes which are subjected to roasting, baking or frying at high temperatures. Subsequent studies showed that acrylamide could be formed in foods by the thermal degradation of free asparagine in the presence of sugars in the Maillard reaction. In this article, our current knowledge of asparagine in plants and in particular its occurrence in cereal seeds and potatoes is reviewed and discussed in relation to acrylamide formation. There is now clear evidence that soluble asparagine accumulates in most if not all plant organs during periods of low rates of protein synthesis and a plentiful supply of reduced nitrogen. The accumulation of asparagine occurs during normal physiological processes such as seed germination and nitrogen transport. However, in addition, stress-induced asparagine accumulation can be caused by mineral deficiencies, drought, salt, toxic metals and pathogen attack. The properties and gene regulation of the enzymes involved in asparagine synthesis and breakdown in plants are discussed in detail