Limitations of Linear Dichroism Spectroscopy for Elucidating Structural Issues of Light-Harvesting Aggregates in Chlorosomes

Linear dichroism (LD) spectroscopy is a widely used technique for studying the mutual orientation of the transition-dipole moments of the electronically excited states of molecular aggregates. Often the method is applied to aggregates where detailed information about the geometrical arrangement of the monomers is lacking. However, for complex molecular assemblies where the monomers are assembled hierarchically in tiers of supramolecular structural elements, the method cannot extract well-founded information about the monomer arrangement. Here we discuss this difficulty on the example of chlorosomes, which are the light-harvesting aggregates of photosynthetic green-(non) sulfur bacteria. Chlorosomes consist of hundreds of thousands of bacteriochlorophyll molecules that self-assemble into secondary structural elements of curved lamellar or cylindrical morphology. We exploit data from polarization-resolved fluorescence-excitation spectroscopy performed on single chlorosomes for reconstructing the corresponding LD spectra. This reveals that LD spectroscopy is not suited for benchmarking structural models in particular for complex hierarchically organized molecular supramolecular assemblies

Photocycle of a cyanobacteriochrome: a charge defect on ring C impairs conjugation in chromophore

A large number of novel phytochromes named cyanobacteriochromes (CBCRs) have been recently identified. CBCRs appear to be attractive for further in-depth studies as paradigms for phytochromes because of their related photochemistry, but simpler domain architecture. Elucidating the mechanisms of spectral tuning for the bilin chromophore down to the molecular/atomic level is a prerequisite to design fine-tuned photoswitches for optogenetics. Several explanations for the blue shift during photoproduct formation associated with the red/green CBCRs represented by Slr1393g3 have been developed. There are, however, only sparse mechanistic data concerning the factors controlling stepwise absorbance changes along the reaction pathways from the dark state to the photoproduct and vice versa in this subfamily. Conventional cryotrapping of photocycle intermediates of phytochromes has proven experimentally intractable for solid-state NMR spectroscopy within the probe. Here, we have developed a simple method to circumvent this hindrance by incorporating proteins into trehalose glasses which allows four photocycle intermediates of Slr1393g3 to be isolated for NMR use. In addition to identifying the chemical shifts and chemical shift anisotropy principal values of selective chromophore carbons in various photocycle states, we generated QM/MM models of the dark state and photoproduct as well as of the primary intermediate of the backward-reaction. We find the motion of all three methine bridges in both reaction directions but in different orders. These molecular events channel light excitation to drive distinguishable transformation processes. Our work also suggests that polaronic self-trapping of a conjugation defect by displacement of the counterion during the photocycle would play a role in tuning the spectral properties of both the dark state and photoproduct

Response to Glyphosate in Alopecurus myosuroides Populations from Lower Saxony

Das Totalherbizid Glyphosat wird weltweit im Pflanzenbau zur Unkrautbekämpfung, Ernteerleichterung, Saatbettbereitung und Abtötung von Zwischenfrüchten eingesetzt. Regelmäßig durchgeführte Gewächshaus-Monitoringversuche zum Auftreten und zur möglichen Verbreitung von Herbizidresistenzen in Niedersachsen zeigten, dass die Wirksamkeit von Glyphosat bei bestimmten Populationen von Alopecurus myosuroides reduziert ist. Dies könnte auf eine mögliche Toleranzverschiebung in Richtung einer reduzierten Sensitivität in manchen Populationen hinweisen. Eine Dosis-Wirkungs-Untersuchung wurde mit sechs Alopecurus myosuroides-Populationen aus verschiedenen Regionen Niedersachsens durchgeführt. Eine Glyphosat-sensitive Referenzpopulation wurde zum Vergleich herangezogen. Die Pflanzen wurden mit einer kommerziell erhältlichen, Glyphosat als Kaliumsalz enthaltenden, Formulierung in aufsteigenden Aufwandmengen (0, 225, 450, 900, 1800, 3600 und 7200 g Glyphosat/ha) behandelt. ED50-Werte wurden aus den Dosis-Wirkungskurven ermittelt und Resistenzfaktoren berechnet. Von sechs geprüften Populationen überlebten drei Wochen nach der Glyphosatbehandlung einzelne Individuen aus vier Populationen bei Aufwandmengen von 1800 und 3600 g Glyphosat/ha ohne jeglichen sichtbaren Schaden und wuchsen weiter. Sechs Wochen nach der Glyphosatbehandlung mit 900 g Glyphosat/ha kam es zu einem Neuaustrieb verschiedener zuvor, als vollständig kontrolliert bewerteter, Individuen aus vier Populationen. Die in dieser Studie gemachten Beobachtungen deuten darauf hin, dass die getesteten Populationen ein Potenzial zur Resistenzentwicklung haben könnten. Weitere Experimente müssen durchgeführt werden, um die zugrundeliegenden Mechanismen zu untersuchen.The broad-scale herbicide glyphosate is used worldwide in crop management system to control weeds, facilitate harvests, prepare seed beds, and desiccate cover crops. Greenhouse monitoring trials on herbicide resistance occurrence and potential spread conducted regularly in Lower Saxony, Germany, revealed a reduced glyphosate efficacy against some populations of Alopecurus myosuroides. This could indicate a potential shift towards a reduced sensitivity in some populations. A dose-response experiment was conducted with six Alopecurus myosuroides populations from various regions of Lower Saxony. A reference population, susceptible to glyphosate, was included for comparison. Plants were treated with a commercially available formulation containing the potassium salt of glyphosate. Treatments were 0, 225, 450, 900, 1800, 3600 and 7200 g glyphosate/ha. ED50 values were determined from the dose-response curves and corresponding resistance factors were calculated. When assessed three weeks after glyphosate treatment, single individuals from four out of six tested populations survived doses of 1800 and 3600 g glyphosate/ha without any visible damage and continued to grow. Six weeks after glyphosate application, a regrowth of several individuals from four populations, previously assessed as completely controlled by 900 g glyphosate/ha, occurred. The observations made in this study indicate that the populations tested may have a potential to evolve glyphosate resistance. Further experiments must be conducted to investigate underlying mechanisms

Control of intercrops in succeeding crops

Der Anbau von Zwischenfrüchten hat in vielfältiger Weise Einfluss auf das gesamte Anbausystem. So etwa in Hinblick auf die Speicherung von Nährstoffen, die Bildung von Humus, die Produktion von Biomasse, die Bekämpfung von Nematoden sowie den Erosionsschutz (Lwk-Niedersachsen.de, 2019). Der Anbau von Zwischenfrüchten kann zu Problemen führen, wenn diese vor dem Abschlegeln zur Samenreife kommen oder in milden Wintern nicht abfrieren. Um Erfahrungen zur Bekämpfung von Zwischenfrüchten in Folgekulturen zu gewinnen, wurde in einem Freilandversuch die Wirksamkeit von 23 Herbiziden gegenüber 19 wichtigen im Anbau befindlichen Zwischenfrüchten getestet. Die Auswahl der eingesetzten Herbizide zur Bekämpfung der Zwischenfrüchte erfolgte bis auf wenige Ausnahmen auf Basis zugelassener Indikationen in den Kulturen Zuckerrübe, Mais, Raps, Kartoffel und Getreide. Außerdem kamen zwei nicht selektive Herbizide zum Einsatz. Die Zuckerrübenherbizide wurden praxisüblich zu 3 Terminen gesplittet ausgebracht, die anderen Herbizide wurden einmalig appliziert. Der Versuch bietet einen vielfältigen Einblick unterschiedlicher Wirkspektren der Herbizide in Bezug auf einzelne Zwischenfrüchte.The cultivation of intercrops has an influence on the entire cultivation system in many ways. For example, with regard to the storage of nutrients, the formation of humus, the production of biomass, the control of nematodes and erosion control (Lwk-Niedersachsen.de, 2019). The cultivation of intercrops can lead to problems if they reach seed ripeness before they are cut down or if they do not freeze in mild winters. In order to gain experience in combating intercrops in subsequent crops, the efficacy of 23 herbicides against 19 important intercrops in cultivation was tested in a field trial. The herbicides used to control the intercrops were selected, with a few exceptions, on the basis of approved indications in the crops sugar beet, maize, rapeseed, potato and cereals. In addition, two non-selective herbicides were used. The sugar beet herbicides were applied at 3 dates splitted, the other herbicides were applied once. The experiment offers a varied insight into the different effect spectra of the herbicides in relation to individual intercrops

Shape-Dependent Catalytic Activity of Gold and Bimetallic Nanoparticles in the Reduction of Methylene Blue by Sodium Borohydride

In this study the catalytic activity of different gold and bimetallic nanoparticle solutions towards the reduction of methylene blue by sodium borohydride as a model reaction is investigated. By utilizing differently shaped gold nanoparticles, i.e., spheres, cubes, prisms and rods as well as bimetallic gold–palladium and gold–platinum core-shell nanorods, we evaluate the effect of the catalyst surface area as available gold surface area, the shape of the nanoparticles and the impact of added secondary metals in case of bimetallic nanorods. We track the reaction by UV/Vis measurements in the range of 190–850 nm every 60 s. It is assumed that the gold nanoparticles do not only act as a unit transferring electrons from sodium borohydride towards methylene blue but can promote the electron transfer upon plasmonic excitation. By testing different particle shapes, we could indeed demonstrate an effect of the particle shape by excluding the impact of surface area and/or surface ligands. All nanoparticle solutions showed a higher methylene blue turnover than their reference, whereby gold nanoprisms exhibited 100% turnover as no further methylene blue absorption peak was detected. The reaction rate constant k was also determined and revealed overall quicker reactions when gold or bimetallic nanoparticles were added as a catalyst, and again these were highest for nanoprisms. Furthermore, when comparing gold and bimetallic nanorods, it could be shown that through the addition of the catalytically active second metal platinum or palladium, the dye turnover was accelerated and degradation rate constants were higher compared to those of pure gold nanorods. The results explore the catalytic activity of nanoparticles, and assist in exploring further catalytic applications

Development of resistance in Alopecurus myosuroides HUDS. (blackgrass) against ALS inhibitors after different pre-treatments

Die Resistenzentwicklung von Alopecurus myosuroides HUDS. (Acker-Fuchsschwanz) gegen ALS-Hemmer kann aufgrund unterschiedlicher Vorbehandlungen möglicherweise beschleunigt werden. In diesem Zusammenhang werden Sequenzbehandlungen von ALS-Hemmern in einer Kultur kritisch gesehen. Um diese Frage zu beantworten wurde ein besonderes Biotestverfahren entwickelt. Hier werden unter standardisierten Bedingungen im Freiland mit züchterischen Methoden A. myosuroides-Pflanzen einer Population mit beginnender ALS-Resistenz nach unterschiedlichen Vorbehandlungen vermehrt und die nachfolgende Generation hinsichtlich ihrer Empfindlichkeit gegenüber einem ALS-Hemmer überprüft.The resistance development of Alopecurus myosuroides HUDS. (blackgrass) against ALS inhibitors may possibly be accelerated due to different pretreatments. In this context, sequential applications of ALS inhibitors in a culture are thought to be critically. To answer this question, a special bioassay has been developed. In a first step, A. myosuroides were sequentially treated with different ALS inhibitors and propagated under standardized conditions in the open field using breeding methods. Seeds of these plants were collected and their susceptibility towards ALS inhibitors was determined

Resistance of herbicides against Alopecurus myosuroides in Lower Saxony

Im Pflanzenschutzamt der LWK Niedersachsen werden Samen von Alopecurus myosuroides im sogenannten „Biotest“ auf metabolische Herbizidresistenz und bei Bedarf auf weitergehende Target-site Resistenz (TSR) untersucht. Auf den norddeutschen Flächen brechen ganze Wirkstoffgruppen bei der Bekämpfung von Acker-Fuchsschwanz in allen Ackerbaukulturen weg, insbesondere auf Flächen, die seit Jahren intensiv in engen Getreidefruchtfolgen bewirtschaftet werden. Auf knapp 50 % der untersuchten Standorte wurde eine mittlere bis starke ALS-Resistenz gegenüber Mesosulfuron (enthalten in Atlantis WG, Atlantis OD, Atlantis flex, Niantic) nachgewiesen. Weitere Herbizide aus der Gruppe der ALS-Hemmer sind betroffen, so zeigen rund die Hälfte der gegenüber Mesosulfuron resistenten niedersächsischen Standorte auch eine deutliche Wirkungseinschränkung gegenüber den Wirkstoffen Foramsulfuron und Thiencarbazone (beide enthalten in MaisTer Power) in Mais. Fast die Hälfte der untersuchten Proben zeigt in Niedersachsen keine ausreichende Wirkung mehr für die Wirkstoffgruppe der DIM, Focus Ultra ist besonders betroffen und in einem geringeren Umfang auch Select 240 EC. Die Wirkstoffgruppen A (ACCase-Hemmer), und C (Photosynthese Hemmer) leiden ebenfalls unter einem erhöhten Resistenzrisiko bei den Gräserarten und das gleichzeitig in den Wintergetreidearten, Winterraps und den Sommerungen wie Kartoffeln, Zuckerrüben, Mais und Sommergetreide. In der Wirkstoffgruppe K zeigt der Wirkstoff Flufenacet bei der Acker-Fuchsschwanzbekämpfung ebenfalls erste Ermüdungserscheinungen. Dagegen werden bislang keine Herbizidresistenzen in den Wirkstoffgruppen E (Flumioxazin, Carfentrazone und Bifenox), F (Diflufenican, Clomazone und den Triketonen) sowie in G (Glyphosat), N (Prosulfocarb, Ethofumesat und den Synthetischen Auxinen (Quinmerac, Aminopyralid, Clopyralid) und den sogenannten Wuchsstoffpräparaten beobachtet. Weitere Herbizidresistenzen lassen sich für Alopecurus myosuroides nur durch Wirkstoffwechsel, Wirkstoffkombination und ackerbaulichen Maßnahmen vermeiden.In the Plant Protection Office of the LWK Lower Saxony, seeds from Alopecurus myosuroides are tested in the so-called "bioassay" for metabolic herbicide resistance and, if necessary, for further target site resistance (TSR). On the North German plains, whole groups of active ingredients in the control of A. myosuroides break away in all agricultural crops, in particular on sites that have been cultivated intensively for years in short cereal-based crop rotation. Nearly 50% of the investigated sites showed medium to high resistance to mesosulfuron (contained in Atlantis WG, Atlantis OD, Atlantis flex, Niantic). Other herbicides from the HRAC group of ALS inhibitors are affected, with around half of the mesosulfuron-resistant samples from Lower Saxony also showing a significant reduction in their sensitivity to the active substance thiencarbazone (included in, for example, MaisTer Power) in maize. Almost half of the samples examined in Lower Saxony no longer have a sufficient sensitivity to the active ingredient group of DIMs; Focus Ultra is particularly affected and, to a lesser extent, Select 240 EC. HRAC groups A (ACCase inhibitors) and C (photosynthetic inhibitors) also suffer from an increased risk of resistance in grass species, and at the same time in winter cereals, winter rape and spring crops such as potatoes, sugar beets, maize and summer cereals. In the HRAC group group K, the active ingredient flufenacet also shows the first signs of efficacy loss in the field of A. myosuroides control. In contrast, so far no herbicide resistance in the HRAC groups E (flumioxazine, carfentrazone and bifenox), F (diflufenican, clomazone and the triketones), G (glyphosate), N (prosulfocarb, ethofumesate and the synthetic auxins (quinmerac, aminopyralid, clopyralid) and the so-called growth hormone preparations has been observed. Further herbicide resistance in A. myosuroides can only be mitigated by a rotation of active ingredients with different Mode of Action, the use of active ingredient combinations and agronomic measures

Population and dynamical state of the eta Chamaeleontis sparse young open cluster

We report new results in our continuing study of the unique compact (1 pc extent), nearby (d = 97 pc), young (t = 9 Myr) stellar cluster dominated by the B9 star eta Chamaeleontis. An optical photometric survey spanning 1.3 x 1.3 pc adds two M5-M5.5 weak-lined T Tauri (WTT) stars to the cluster inventory which is likely to be significantly complete for primaries with masses > 0.15 M_sun. The cluster now consists of 17 primaries and approximately 9 secondaries lying within 100 AU of their primaries. The apparent distribution of 9:7:1 single:binary:triple systems shows 2-4 x higher multiplicity than in the field main sequence stars, and is comparable to that seen in other pre-main sequence (PMS) populations. The initial mass function (IMF) is consistent with that of rich young clusters and field stars. By extending the cluster IMF to lower masses, we predict 10-14 additional low mass stars with 0.08 < M < 0.15 M-sun and 10-15 brown dwarfs with 0.025 < M < 0.08 M_sun remain to be discovered. The eta Cha cluster extends the established stellar density and richness relationship for young open clusters. The radial distribution of stars is consistent with an isothermal sphere, but mass segregation is present with > 50 percent of the stellar mass residing in the inner 6 arcmin (0.17 pc). Considering that the eta Cha cluster is sparse, diffuse and young, the cluster may be an ideal laboratory for distinguishing between mass segregation that is primordial in nature, or arising from dynamical interaction processes.Comment: 10 pages, 7 figures, 2 tables, accepted for MNRA

Herbizidresistenzen bei Apera spica-venti - Sachstand in Niedersachsen

Herbizidresistenzen lassen ganze Wirkstoffgruppen weltweit wegfallen. In Deutschland zeigt sich dieses Phänomen auch auf niedersächsischen Flächen, die seit Jahren intensiv in engen Getreidefruchtfolgen bewirtschaftet werden. Neben den Wirkstoffgruppen der ALS-Hemmer und Photosynthesehemmer sind beginnend auch die ACCase-Hemmer resistenzgefährdet. Diese Entwicklung hat sich bei Apera spica-venti durch einseitigen Herbizideinsatz und enge Getreidefruchtfolgen aufgebaut. In den Jahren 2009 bis 2016 wurden auf 269 Monitoringflächen Samenproben von Apera spica-venti gezogen und in Biotestungen die Wirksamkeit von Herbiziden unterschiedlicher Wirkstoffklassen getestet. Die Resistenz bei Apera spica-venti gegenüber Herbiziden der HARC-Gruppe B ist in Niedersachsen weit verbreitet. Auf den ersten Flächen haben sich bereits multiple Resistenzen gegen die HRAC-Gruppen A und B entwickelt