The stereoisomeric Bacillus subtilis HN09 metabolite 3,4-dihydroxy-3-methyl-2-pentanone induces disease resistance in Arabidopsis via different signalling pathways.

BACKGROUND: Plant immune responses can be induced by plant growth-promoting rhizobacteria (PGPRs), but the exact compounds that induce resistance are poorly understood. Here, we identified the novel natural elicitor 3,4-dihydroxy-3-methyl-2-pentanone from the PGPR Bacillus subtilis HN09, which dominates HN09-induced systemic resistance (ISR). RESULTS: The HN09 strain, as a rhizobacterium that promotes plant growth, can induce systemic resistance of Arabidopsis thaliana plants against Pseudomonas syringae pv. tomato DC3000, and the underlying role of its metabolite 3,4-dihydroxy-3-methyl-2-pentanone in this induced resistance mechanism was explored in this study. The stereoisomers of 3,4-dihydroxy-3-methyl-2-pentanone exhibited differential bioactivity of resistance induction in A. thaliana. B16, a 1:1 mixture of the threo-isomers (3R,4S) and (3S,4R), was significantly superior to B17, a similar mixture of the erythro-isomers (3R,4R) and (3S,4S). Moreover, B16 induced more expeditious and stronger callose deposition than B17 when challenged with the pathogen DC3000. RT-qPCR and RNA-seq results showed that B16 and B17 induced systemic resistance via JA/ET and SA signalling pathways. B16 and B17 activated different but overlapping signalling pathways, and these compounds have the same chemical structure but subtle differences in stereo configuration. CONCLUSIONS: Our results indicate that 3,4-dihydroxy-3-methyl-2-pentanone is an excellent immune elicitor in plants. This compound is of great importance to the systemic resistance induced by HN09. Its threo-isomers (3R,4S) and (3S,4R) are much better than erythro-isomers (3R,4R) and (3S,4S). This process involves SA and JA/ET signalling pathways.

Dirhamnolipid Produced by the Pathogenic Fungus Colletotrichum gloeosporioides BWH-1 and Its Herbicidal Activity.

Fungal phytotoxins used as ecofriendly bioherbicides are becoming efficient alternatives to chemical herbicides for sustainable weed management. Previous study found that cultures of the pathogenic fungus Colletotrichum gloeosporioides BWH-1 showed phytotoxic activity. This study further isolated the major phytotoxin from cultures of the strain BWH-1 using bioactivity-guided isolation, by puncturing its host plant for an activity test and analyzing on the HPLC-DAD-3D mode for a purity check. Then, the active and pure phytotoxin was characterized as a dirhamnolipid (Rha-Rha-C10-C10) using the NMR, ESIMS, IR and UV methods. The herbicidal activity of dirhamnolipid was evaluated by the inhibition rate on the primary root length and the fresh plant weight of nine test plants, and the synergistic effect when combining with commercial herbicides. Dirhamnolipid exhibited broad herbicidal activity against eight weed species with IC50 values ranging from 28.91 to 217.71 mg L-1 and no toxicity on Oryza sativa, and the herbicidal activity could be synergistically improved combining dirhamnolipid with commercial herbicides. Thus, dirhamnolipid that originated from C. gloeosporioides BWH-1 displayed the potential to be used as a bioherbicide alone, or as an adjuvant added into commercial herbicides, leading to a decrease in herbicides concentration and increased control efficiency.

Flavonoids from Pronephrium megacuspe.

A chemical investigation of the whole plant of Pronephrium megacuspe (Bak.) Holtt. led to the isolation of four flavonoids, pronephrones A-D (1-4), which were firstly reported. The chemical structures of four compounds were established using spectroscopic methods. These isolates were further evaluated for cytotoxicity to ovarian cells of Spodoptera litura Fabricius.

Insecticidal Activities of Sophora flavescens Alt. towards Red Imported Fire Ants (Solenopsis invicta Buren).

The red imported fire ant (Solenopsis invicta) is a worldwide invasive and dangerous insect that is controlled mainly by chemical insecticides. Plant-derived insecticidal compounds are generally better than synthetic insecticides for environmental compatibility and the biosafety of non-targets. The toxicity of the ethanol extract of Sophora flavescens roots against S. invicta was evaluated under laboratory conditions. The ethanol extract showed toxicity against minor and medium workers of S. invicta with 7-day LC50 values of 1426.25 and 2292.60 mg/L, respectively. By bioactivity-directed chromatographic separations using the minor worker as the test insect, two active compounds, matrine and sophocarpine, were isolated from the S. flavescens total alkaloids; their chemical structure was identified by 13C NMR data. Matrine showed toxicities against minor and medium workers with 7-day LC50 values of 46.77 and 71.49 mg/L, respectively, and for sophocarpine, 50.08 and 85.87 mg/L, respectively. The two compounds could substantially reduce the foraging response, food consumption, and aggregation of S. invicta workers at a sublethal concentration of 15 mg/L. The present research suggests that S. flavescens roots have potential as a natural control agent for red imported fire ants.

Mechanism of Rotenone Toxicity against Plutella xylostella: New Perspective from a Spatial Metabolomics and Lipidomics Study.

The botanical pesticide rotenone can effectively control target pest Plutella xylostella, yet insights into in situ metabolic regulation of P. xylostella toward rotenone remain limited. Herein, we demonstrated metabolic expression levels and spatial distribution of rotenone-treated P. xylostella using spatial metabolomics and lipidomics. Specifically, rotenone significantly affected purine and amino acid metabolisms, indicating that adenosine monophosphate and inosine were distributed in the whole body of P. xylostella with elevated levels, while guanosine 5'-monophosphate and tryptophan were significantly downregulated. Spatial lipidomics results indicated that rotenone may significantly destroy glycerophospholipids in cell membranes of P. xylostella, inhibit fatty acid biosynthesis, and consume diacylglycerol to enhance fat oxidation. These findings revealed that high toxicity of rotenone toward P. xylostella may be ascribed to negative effects on energy production and amino acid synthesis and damage to cell membranes, providing guidelines for the toxicity mechanism of rotenone on target pests and rational development of botanical pesticide candidates.

Design of new glycosyl-O-fipronil conjugates with improved hydrolysis efficiency assisted by molecular simulations.

BACKGROUND: In a previous study, we showed that two glycosyl-pesticide conjugates with a ß-d-glucoside moiety, N-{3-cyano-1-[2,6-dichloro-4-(trifluoromethyl) phenyl]-4-[(trifluoromethyl)-sulfinyl]-1H-pyrazol-5-yl}-2-aminoethyl-ß-d-glucopyranoside (GOF) and N-{3-cyano-1-[2,6-dichloro-4-(trifluoromethyl)phenyl]-4-[(trifluoromethyl) sulfinyl]-1H-pyrazol-5-yl}-1-(2-triazolethyl-ß-d-glucopyranoside)-1H-1,2,3-triazole-4-methanamine (GOTF), can move in the phloem and be hydrolyzed by ß-glucosidase at different rates. Simulations were carried out to investigate differences in the hydrolysis process in GOF, GOTF and p-nitrophenyl ß-d-glucopyranoside (pNPG). A new series of glycosyl-O-fipronil conjugates was then designed and synthesized based on the simulation results. The phloem mobilities of the new conjugates were examined using a Ricinus model, and their hydrolysis efficiencies based on ß-glucosidase were determined. RESULTS: New glycosyl-O-fipronil conjugates GOE2-6 were designed and synthesized. To reduce steric hindrance, the conjugating site of the glycone moiety was moved to the 4'-sulfonyl group on the pyrrole ring. As a result, the hydrolysis efficiencies of the new conjugates were significantly improved, with GOE4 having the highest hydrolysis efficiency. All five conjugates could be transported in Ricinus phloem sap, consistent with previously studied glycosyl-O-fipronil conjugates. The insecticidal activities of the conjugates were tested against Plutella xylostella. CONCLUSION: A strategy for the development of new phloem-mobile pesticides was proposed: linking a glycosyl group to the existing pesticide structure with a linear alkyl connection approximately four carbons in length. The resultant conjugates feature not only good phloem mobility, but also potential high bioactivity due to the efficient release of active pesticide components under the action of glucosidase. © 2022 Society of Chemical Industry.

Azocalixarene-Based Supramolecular System for the Detection of Paraquat via an Improved Indicator Displacement Assay.

In view of the lethal toxicity of paraquat (PQ) on human health, herein, a simple indicator displacement assay (IDA) based on an azo-modified calixarene host (azoCX[4]) and a fluorophore guest (p-DPD) were elaborately constructed for PQ detection in environmental water samples and plant surfaces. The fluorescent signal of p-DPD in the probe can be quenched by azoCX[4] through a photon-induced electron transfer process and recovered upon the addition of PQ within 10 s. The detection range of the p-DPD@azoCX[4] probe was calculated to be 0.35-8 µM in the Tris-HCl buffer solutions (pH = 7.4). Moreover, this probe exhibited excellent detection selectivity toward PQ over five herbicides (glyphosate, bispyribac, atrazine, ametryn, and bensulfuron methyl), together with anti-interference abilities in the presence of inorganic ions (K+, Na+, Zn2+, Ni2+, Li+, F-, Cl-, Br-, CO32-, HCO3-, and NO3-) and amino acids (Asp, Arg, Glu, Ala, and Cys). Particularly, the probe was successfully used to detect PQ in real water samples with acceptable accuracy and showed potential applications for on-site detection with paper-based test strips and on the leaf surface. We believe that this simplified IDA-based probe provided an effective detecting tool for PQ, and the design strategy would guide the further development of new IDA sensing systems.

Enhanced uptake of drip-applied flonicamid by arbuscular mycorrhizal fungi and improved control of cotton aphid.

BACKGROUND: Drip application of insecticides has been used for controlling crop pests, but the application doses are usually higher than those used for foliar spray. Arbuscular mycorrhizal fungi (AMF) have been reported to improve root absorption of nutrients from soil, which may also enhance the uptake of drip-applied insecticides, reducing application doses. In this study, greenhouse and field experiments were carried out to determine if AMF could colonize cotton roots, if the colonization could enhance the absorption of drip-applied flonicamid, and if the enhanced uptake could reduce flonicamid application dose, while maintaining control efficacy against cotton aphid. RESULTS: The applied AMF effectively colonized cotton roots and significantly promoted root growth. Fresh weights of cotton roots inoculated with multiple AMF were 28% greater than those of uninoculated plants. Multiple AMF colonization significantly increased flonicamid concentrations in leaves, which were 44.5-139.7% higher than for non AMF-colonized roots, corresponding to 3.7-31.8% increases in corrected mortalities of cotton aphid compared with uninoculated plants. AMF colonization reduced the application rate of flonicamid and the residue level of flonicamid in soil. CONCLUSION: Drip application of flonicamid to cotton roots inoculated with AMF represents a new approach to insecticide application. AMF colonization increased flonicamid uptake, improved aphid control efficacy and reduced flonicamid application rates. © 2020 Society of Chemical Industry.

Sulfoxaflor Residues in Pollen and Nectar of Cotton Applied through Drip Irrigation and Their Potential Exposure to Apis mellifera L.

Systemic insecticides have been applied through drip irrigation for controlling crop pests, but few studies have addressed potential negative effects of the application on non-target organisms. In this study, the safety of sulfoxaflor applied at 450 or 700 g a.i. ha-1 through drip irrigation at different times before flowering or during flowering to honey bee (Apis mellifera L.) was studied in 2016-2017 in a cotton production field in Xinjiang, China. Results showed that sulfoxaflor residues in pollen and nectar of cotton treated with sulfoxaflor at 450 g a.i. ha-1 before and during flowering through drip irrigation were either undetectable or no more than 17 µg·kg-1. Application of sulfoxaflor at 700 g a.i. ha-1 before flowering resulted in ≤ 14.2 µg·kg-1 of sulfoxaflor in pollen and < 0.68 µg·kg-1 in nectar. Sulfoxaflor applied at this higher rate during flowering had the highest residue, up to 39.2 µg·kg-1 in pollen and 13.8 µg·kg-1 in nectar. Risk assessments by contact exposure and dietary exposure showed that drip application of sulfoxaflor at the two rates before or during flowering posed little risk to honey bees. Thus, drip application of sulfoxaflor could represent an environmentally benign method for controlling cotton aphid.

Microplastic abundance, distribution and composition in the mid-west Pacific Ocean.

Microplastic pollution is widespread across most ocean basins around the world. Microplastics (MPs) are small plastic particles that have a significant impact on the marine environment. Various research on plastic pollution have been conducted in several regions. However, currently, there is limited data on the distribution and concentration of MPs in the mid-west Pacific Ocean. Therefore, this study we investigated the abundance, distribution, characteristics, and compositions of MPs in this region. Sea surface water samples collected from 18 stations showed a microplastic concentration range of 6028-95,335 pieces/km2 and a mean concentration of 34,039 ± 25,101 pieces/km2. Highest microplastic concentrations were observed in the seamount region of western Pacific. We observed a significant positive correlation between microplastic abundance and latitude across the study region. It was observed that microplastic concentrations decreased with increasing offshore distance at sites located on a 154° W transect. Fibres/filaments were the dominant microparticles observed in this study (57.4%), followed by fragments (18.3%). The dominant particle size range was 1-2.5 mm (35.1%), followed by 0.5-1 mm (28.5%), and the dominant particle colour was white (33.8%), followed by transparent (31.0%) and green (24.6%). The most common polymer identified by µ-Raman was polypropylene (39.1%), followed by polymethyl methacrylate (16.2%), polyethylene (14.1%) and polyethylene terephthalate (14.2%). The possible sources and pathways of microplastics in the study area were proposed based on the morphological and compositional characteristics of particles, their spatial distribution patterns, and shipboard current profiling (ADCP). Our study contributes to the further understanding of MPs in remote ocean areas.

Bruceine D Isolated from Brucea Javanica (L.) Merr. as a Systemic Feeding Deterrent for Three Major Lepidopteran Pests.

Systemicity is a desirable property for insecticides. Many phytochemicals show good systemic properties and thus are natural sources of novel systemic insecticidal ingredients. Bruceine D, a quassinoid, was identified in Brucea javanica (L.) Merr. and displayed outstanding systemic properties and excellent antifeedant activity against the diamondback moth (DBM, Plutella xylostella L.), beet armyworm ( Spodoptera exigua Hübner), and cotton leafworm ( Spodoptera litura Fabricius). Its antifeedant effect on third instar larvae of DBM was approximately 6.2-fold stronger than that of azadirachtin. When bruceine D was applied to roots at a concentration of 100 µg/mL for 24 and 48 h, its concentration in flowering Chinese cabbage ( Brassica campestris L. ssp. chinensis var. utiliz Tsen et Lee) leaves was 38.69 µg/g (fresh weight, FW) and 108.45 µg/g (FW), respectively. These concentrations could achieve 93.80% and 96.83% antifeedant effects, which were significantly greater than those of azadirachtin. Similar to azadirachtin, bruceine D also posed a potent growth inhibition effect on insect larvae. After feeding with 20 µg/g bruceine D, no pupae were observed. The results demonstrated that bruceine D is an effective botanical insect antifeedant with outstanding systemic properties, causing potent pest growth inhibitory activity.

Sulfoxaflor Applied via Drip Irrigation Effectively Controls Cotton Aphid (Aphis gossypii Glover).

Aphis gossypii Glover is a major pest of cotton and can severely affect cotton yield and lint quality. In this study, the efficacy of sulfoxaflor applied via drip irrigation and foliar spray on controlling cotton aphids was evaluated in 2016 and 2017 in Xinjiang, China. The distribution of sulfoxaflor in cotton roots, stems, leaves, and aphids, as well as its effects on two natural enemies of aphids, were also investigated. Results showed that sulfoxaflor applied through drip irrigation mainly concentrated in leaves and provided effective control of cotton aphids for 40 days, compared to 20 days when applied through foliar spray. Furthermore, drip application resulted in much lower sulfoxaflor concentrations in aphids than foliar spray. As a result, ladybird beetle and lacewing populations were higher in drip applied plants than in foliar sprayed plants. Additionally, the cost of drip irrigation was lower than foliar spray as cotton plants are commonly irrigated via drip irrigation in Xinjiang. Our results showed that application of sulfoxaflor through drip irrigation is an effective way of controlling cotton aphids in Xinjiang due to a prolonged control period, safety to two natural enemies, and lower cost of application.

AtLHT1 Transporter Can Facilitate the Uptake and Translocation of a Glycinergic-Chlorantraniliprole Conjugate in Arabidopsis thaliana.

Understanding of the transporters involved in the uptake and translocation of agrochemicals in plants could provide an opportunity to guide pesticide to the site of insect feeding. The product of Arabidopsis thaliana gene AtLHT1 makes a major contribution to the uptake into the roots of free amino acids and some of their derivatives. Here, a chlorantraniliprole-glycine conjugate (CAP-Gly-1) was tested for its affinity to AtLHT1 both in planta and in vitro. Seedlings deficient in AtLHT1 exhibited a reduction with respect to both the uptake and root-to-shoot transfer of CAP-Gly-1; plants in which AtLHT1 was constitutively expressed were more effective than wild type in term of their root uptake of CAP-Gly-1. Protoplast patch clamping showed that the presence in the external medium of CAP-Gly-1 was able to induce AtLHT1 genotype-dependent inward currents. An electrophysiology-based experiment carried out in Xenopus laevis oocytes expressing AtLHT1 showed that AtLHT1 had a high in vitro affinity for CAP-Gly-1. The observations supported the possibility of exploiting AtLHT1 as a critical component of a novel delivery system for amino acid-based pesticide conjugates.

Insect spontaneous ultraweak photon emission as an indicator of insecticidal compounds.

The influence of beta-cypermethrin, a commercial insecticide, and Cicuta virosa L. var. latisecta Celak (Umbelliferae:Cicutal), an insecticidal plant, on the spontaneous ultraweak photon emissions from larvae of Spodoptera litura Fabricius and Zophobas morio Fabricius were studied. The increased percentages of spontaneous photon emission intensities from S. litura treated with 0.1 and 1 µg/ml beta-cypermethrin were both lower than those of the control in the 24 post-treatment hours, remarkable difference could also be observed during the same period from Z. morio treated with beta-cypermethrin at 0.156, 0.313 and 0.625 µg/ml. The increased percentages of spontaneous photon emission intensities from the two mentioned insects treated with 10,100 and 1000 µg/ml petroleum ether fraction of C. virosa L. var. latisecta, which displayed little activity against whole insects, could also be changed noticeably. The present study indicated that change in the intensity of spontaneous ultraweak photon emission from insect could be used as a novel method for screening insecticidal compounds with very low content in plant.

Synthesis and photoactivated insecticidal activity of tetraethynylsilanes.

A series of tetraethynylsilanes (TETS) have been synthesized by reaction of silicon tetrachloride (SiCl(4)) with Ar-C triple bond CLi, which was prepared in situ by treatment of Ar-C triple bond CH with n-BuLi. For these TETS thus prepared, their photoactivated insecticidal activities against the 4th-instar larvae of Aedes albopictus (Skuse) were evaluated to enrich the structure-activity relationship. In particular, compound 8 exhibited excellent photoactivated insecticidal activity, the LC(50) value was 0.1346 mg L(-1) under UV light treatment and the irradiation-generated enhancement in the activity was more than 69.58-fold, thus could be exploitable as ideal analog candidates in the search for new photoactivated insecticide leads.

Photoactivated insecticidal thiophene derivatives from Xanthopappus subacaulis.

Three new photoactivated insecticidal thiophene derivatives, xanthopappins A-C (1-3), were isolated from Xanthopappus subacaulis, along with three known thiophene acetylenes, 5-hydroxymethyl-2-(E)-hept-5-ene-1,3-diynylthiophene (4), 5-(1,2-dihydroxyethyl)-2-(E)-hept-5-ene-1,3-diynylthiophene (5), and 5-(1,2-diacetoxyethyl)-2-(E)-hept-5-ene-1,3-diynylthiophene (6). The structures of 1-3 were elucidated by spectroscopic methods. Compounds 1-6 exhibited significant photoactivated insecticidal activity against the fourth-instar larvae of the Asian tiger mosquito.