Biological/Biomedical Accelerator Mass Spectrometry Targets. 2. Physical, Morphological, and Structural Characteristics

The number of biological/biomedical applications that require AMS to achieve their goals is increasing, and so is the need for a better understanding of the physical, morphological, and structural traits of high quality of AMS targets. The metrics of quality included color, hardness/texture, and appearance (photo and SEM), along with FT-IR, Raman, and powder X-ray diffraction spectra that correlate positively with reliable and intense ion currents and accuracy, precision, and sensitivity of fraction modern (Fm). Our previous method produced AMS targets of gray-colored iron−carbon materials (ICM) 20% of the time and of graphite-coated iron (GCI) 80% of the time. The ICM was hard, its FT-IR spectra lacked the sp2 bond, its Raman spectra had no detectable G′ band at 2700 cm−1, and it had more iron carbide (Fe3C) crystal than nanocrystalline graphite or graphitizable carbon (g-C). ICM produced low and variable ion current whereas the opposite was true for the graphitic GCI. Our optimized method produced AMS targets of graphite-coated iron powder (GCIP) 100% of the time. The GCIP shared some of the same properties as GCI in that both were black in color, both produced robust ion current consistently, their FT-IR spectra had the sp2 bond, their Raman spectra had matching D, G, G′, D+G, and D′′ bands, and their XRD spectra showed matching crystal size. GCIP was a powder that was easy to tamp into AMS target holders that also facilitated high throughput. We concluded that AMS targets of GCIP were a mix of graphitizable carbon and Fe3C crystal, because none of their spectra, FT-IR, Raman, or XRD, matched exactly those of the graphite standard. Nevertheless, AMS targets of GCIP consistently produced the strong, reliable, and reproducible ion currents for high-throughput AMS analysis (270 targets per skilled analyst/day) along with accurate and precise Fm values

Jasmonic Acid-Induced Changes in Brassica oleracea Affect Oviposition Preference of Two Specialist Herbivores

Jasmonic acid (JA) is a key hormone involved in plant defense responses. The effect of JA treatment of cabbage plants on their acceptability for oviposition by two species of cabbage white butterflies, Pieris rapae and P. brassicae, was investigated. Both butterfly species laid fewer eggs on leaves of JA-treated plants compared to control plants. We show that this is due to processes in the plant after JA treatment rather than an effect of JA itself. The oviposition preference for control plants is adaptive, as development time from larval hatch until pupation of P. rapae caterpillars was longer on JA-treated plants. Total glucosinolate content in leaf surface extracts was similar for control and treated plants; however, two of the five glucosinolates were present in lower amounts in leaf surface extracts of JA-treated plants. When the butterflies were offered a choice between the purified glucosinolate fraction isolated from leaf surface extracts of JA-treated plants and that from control plants, they did not discriminate. Changes in leaf surface glucosinolate profile, therefore, do not seem to explain the change in oviposition preference of the butterflies after JA treatment, suggesting that as yet unknown infochemicals are involved