The Orphan Crop Crassocephalum crepidioides Accumulates the Pyrrolizidine Alkaloid Jacobine in Response to Nitrogen Starvation

Crassocephalum crepidioides is an African orphan crop that is used as a leafy vegetable and medicinal plant. Although it is of high regional importance in Sub-Saharan Africa, the plant is still mainly collected from the wild and therefore efforts are made to promote its domestication. However, in addition to beneficial properties, there was first evidence that C. crepidioides can accumulate the highly toxic pyrrolizidine alkaloid (PA) jacobine and here it was investigated, how jacobine production is controlled. Using ecotypes from Africa and Asia that were characterized in terms of their PA profiles, it is shown that the tetraploid C. crepidioides forms jacobine, an ability that its diploid close relative Crassocephalum rubens appears to lack. Evidence is provided that nitrogen (N) deficiency strongly increases jacobine in the leaves of C. crepidioides, that this capacity depends more strongly on the shoot than the root system, and that homospermidine synthase (HSS) activity is not rate-limiting for this reaction. A characterization of HSS gene representation and transcription showed that C. crepidioides and C. rubens possess two functional versions, one of which is conserved, that the HSS transcript is mainly present in roots and that its abundance is not controlled by N deficiency. In summary, this work improves our understanding of how environmental cues impact PA biosynthesis in plants and provides a basis for the development of PA-free C. crepidioides cultivars, which will aid its domestication and safe use. © Copyright © 2021 Schramm, Rozhon, Adedeji-Badmus, Liang, Nayem, Winkelmann and Poppenberger

XUV Fluorescence Detection of Laser-Cooled Stored Relativistic Ions

An improved moveable in vacuo XUV fluorescence detection system was employed for the laser cooling of bunched relativistic ( β = 0.47) carbon ions at the Experimental Storage Ring (ESR) of GSI Helmholtzzentrum Darmstadt, Germany. Strongly Doppler boosted XUV fluorescence (∼90 nm) was emitted from the ions in a forward light cone after laser excitation of the 2s–2p transition (∼155 nm) by a new tunable pulsed UV laser system (257 nm). It was shown that the detected fluorescence strongly depends on the position of the detector around the bunched ion beam and on the delay (∼ns) between the ion bunches and the laser pulses. In addition, the fluorescence information could be directly combined with the revolution frequencies of the ions (and their longitudinal momentum spread), which were recorded using the Schottky resonator at the ESR. These fluorescence detection features are required for future laser cooling experiments at highly relativistic energies (up to γ ∼ 13) and high intensities (up to 10 11 particles) of ion beams in the new heavy ion synchrotron SIS100 at FAIR

Pyrrolizidine Alkaloids: Biosynthesis, Biological Activities and Occurrence in Crop Plants

Pyrrolizidine alkaloids (PAs) are heterocyclic secondary metabolites with a typical pyrrolizidine motif predominantly produced by plants as defense chemicals against herbivores. They display a wide structural diversity and occur in a vast number of species with novel structures and occurrences continuously being discovered. These alkaloids exhibit strong hepatotoxic, genotoxic, cytotoxic, tumorigenic, and neurotoxic activities, and thereby pose a serious threat to the health of humans since they are known contaminants of foods including grain, milk, honey, and eggs, as well as plant derived pharmaceuticals and food supplements. Livestock and fodder can be affected due to PA-containing plants on pastures and fields. Despite their importance as toxic contaminants of agricultural products, there is limited knowledge about their biosynthesis. While the intermediates were well defined by feeding experiments, only one enzyme involved in PA biosynthesis has been characterized so far, the homospermidine synthase catalyzing the first committed step in PA biosynthesis. This review gives an overview about structural diversity of PAs, biosynthetic pathways of necine base, and necic acid formation and how PA accumulation is regulated. Furthermore, we discuss their role in plant ecology and their modes of toxicity towards humans and animals. Finally, several examples of PA-producing crop plants are discussed

Results of the Arctic Mid-Ocean Ridge Expedition (AMORE 2001) - Seafloor Spreading at the Top of the World

The Arctic Mid-Ocean Ridge Expedition (AMORE 2001) returned in early October 2001 after an incredibly sucessful ten-week study of the Gakkel Ridge and its surrounding basins in the high Arctic. AMORE 2001 was an international effort involving two icebreakers: PFS Polarstern, from the Alfred Wegener Institute in Bremerhaven, Germany and the new U.S. icebreaker, USCGC Healy. It was Healy's maiden scientific voyage, and she proved to be an excellent icebraker and scientific platform. This historic and highly sucessful expedition far exceeded anyone's expectations and went well beyond the goals set forth by InterRidge (Vol. 10 (1), 2001) in charting and sampling the Gakkel Ridge. Some of the highlights of the expedition are:1. Basalts and peridotites were recovered from over 200 sites within and near the axis of Gakkel Ridge, about three times as many sites as were planned. 2. Hydrothermal plumes were discovered and sampled along this ultraslow spreading ridge. 3. A high-resolution, well-navigated map of the ridge was unexpectedly produced using two hull-mounted multibeam sonar systems, which worked far better in the ice than anticipated. 4. Sucessful seismic measurements showed that crustal thickness varies strongly along the axis of Gakkel Ridge, most likely according to distinct volcanic centers. 5. The crustal thickness in the Nansen Basin does not follow theoretical models, which predict thin crust at slow spreading rates. The crust thickens towards the Gakkel Ridge

Determination of the [¹⁵N]-Nitrate/[¹⁴N]-Nitrate Ratio in Plant Feeding Studies by GC–MS

Feeding experiments with stable isotopes are helpful tools for investigation of metabolic fluxes and biochemical pathways. For assessing nitrogen metabolism, the heavier nitrogen isotope, [15N], has been frequently used. In plants, it is usually applied in form of [15N]-nitrate, which is assimilated mainly in leaves. Thus, methods for quantification of the [15N]-nitrate/[14N]-nitrate ratio in leaves are useful for the planning and evaluation of feeding and pulse–chase experiments. Here we describe a simple and sensitive method for determining the [15N]-nitrate to [14N]-nitrate ratio in leaves. Leaf discs (8 mm diameter, approximately 10 mg fresh weight) were sufficient for analysis, allowing a single leaf to be sampled multiple times. Nitrate was extracted with hot water and derivatized with mesitylene in the presence of sulfuric acid to nitromesitylene. The derivatization product was analyzed by gas chromatography–mass spectrometry with electron ionization. Separation of the derivatized samples required only 6 min. The method shows excellent repeatability with intraday and interday standard deviations of less than 0.9 mol%. Using the method, we show that [15N]-nitrate declines in leaves of hydroponically grown Crassocephalum crepidioides, an African orphan crop, with a biological half-life of 4.5 days after transfer to medium containing [14N]-nitrate as the sole nitrogen source

XUV Fluorescence Detection of Laser-Cooled Stored Relativistic Ions

An improved moveable in vacuo XUV fluorescence detection system was employed for the laser cooling of bunched relativistic (β = 0.47) carbon ions at the Experimental Storage Ring (ESR) of GSI Helmholtzzentrum Darmstadt, Germany. Strongly Doppler boosted XUV fluorescence (∼90 nm) was emitted from the ions in a forward light cone after laser excitation of the 2s–2p transition (∼155 nm) by a new tunable pulsed UV laser system (257 nm). It was shown that the detected fluorescence strongly depends on the position of the detector around the bunched ion beam and on the delay (∼ns) between the ion bunches and the laser pulses. In addition, the fluorescence information could be directly combined with the revolution frequencies of the ions (and their longitudinal momentum spread), which were recorded using the Schottky resonator at the ESR. These fluorescence detection features are required for future laser cooling experiments at highly relativistic energies (up to γ∼ 13) and high intensities (up to 10¹¹ particles) of ion beams in the new heavy ion synchrotron SIS100 at FAIR

Laser cooling of stored relativistic ion beams with large momentum spreads using a laser system with a wide scanning range

New results on laser cooling of stored, bunched, relativistic ion beams are presented. For the first time it has been possible to cool an ion beam with large momentum spread without initial electron cooling or scanning of the bunching frequency by using a single cw laser system