In situ separation and visualization of isomeric auxin derivatives in Arabidopsis by ion mobility mass spectrometry imaging.

In situ separation and visualization of synthetic and naturally occurring isomers from heterogeneous plant tissues, especially when they share similar molecular structures, are a challenging task. In this study, we combined the ion mobility separation with desorption electrospray ionization mass spectrometry imaging (DESI-IM-MSI) to achieve a direct separation and visualization of two synthetic auxin derivatives, auxinole and its structural isomer 4pTb-MeIAA, as well as endogenous auxins from Arabidopsis samples. Distinct distribution of these synthetic isomers and endogenous auxins in Arabidopsis primary roots and hypocotyls was achieved in the same imaging analysis from both individually treated and cotreated samples. We also observed putative metabolites of synthetic auxin derivatives, i.e. auxinole amino acid conjugates and hydrolysed 4pTb-MeIAA product - 4pTb-IAA, based on their unique drifting ion intensity patterns. Furthermore, DESI-IM-MSI-revealed abundance of endogenous auxins and synthetic isomers was validated by liquid chromatography-mass spectrometry (LC-MS). Our results demonstrate that DESI-IM-MSI could be used as a robust technique for detecting endogenous and exogenous isomers and provide a spatiotemporal evaluation of hormonomics profiles in plants.

Physiological and transcriptomic analysis of IAA-induced antioxidant defense and cell wall metabolism in postharvest mango fruit.

Mango fruit tend to oxidize and senescence rapidly after harvesting, significantly reducing their commercial value. This study investigated the effect of exogenous auxin indole-3-acetic acid (IAA) on fruit quality, antioxidant system, and cell wall metabolism of mango fruit during storage. The results showed that the 1.0 mM IAA treatment delayed weight loss and maintained the firmness, pH and contents of total soluble solids (TSS) and titratable acidity (TA) of the mango fruit. The 1.0 mM IAA treatment increased the peroxidase (POD) and phenylalanine ammonia-lyase (PAL) activities and the ascorbic acid (AsA) and total phenols (TP) contents but decreased the polyphenol oxidase (PPO) activity in postharvest mango fruit. Moreover, beta-galactosidase (ß-Gal) and polygalacturonase (PG) activities were increased, but the pectinesterase (PME) activity was decreased in the IAA-treated fruit. Transcriptome analysis showed that the differentially expressed genes (DEGs) in the IAA vs. control groups were mainly associated with oxidative stress responses, cell wall metabolism, and transcription factors (TFs). The IAA treatment upregulated the antioxidant-related genes (SOD, CAT1, PODs, GSTs, Prxs, and Trxs) and MYB TFs, and downregulated cell wall metabolism-related genes (PG, PME31 and two PME63) and 11 ethylene-responsive transcription factors (ERFs). These results suggested that exogenous IAA could improve the antioxidant system and maintain the storage quality of mango fruit by regulating gene expression and metabolic pathways. The results provide insights into the mechanisms involved in IAA-mediated delayed ripening and senescence of mango fruit.

One-pot fabrication of magnetic adsorbent based on polymeric ionic liquid/aminated carbon nanotubes composite for efficient capture of synthetic auxins in complex samples prior to chromatographic analysis.

Efficient enrichment is a challenging and indispensable step in the quantification of polar synthetic auxins in complex samples. In the current study, a new magnetic adsorbent based on polymeric ionic liquid/aminated carbon nanotube composite was fabricated with a one-pot precipitation copolymerization strategy and employed as the extraction phase of magnetic solid phase extraction of synthetic auxins. Various characterization techniques were utilized to inspect the morphology, structure, magnetic property, and functional groups of the prepared adsorbent. Under the optimal conditions, the obtained adsorbent displayed satisfactory capture performance towards studied auxins through multiple interactions. Adsorption studies evidenced that the adsorption procedure of the developed method towards analytes was fit for the Freundlich adsorption model and pseudo-second-order kinetics. Combining with high-performance liquid chromatography, sensitive and reliable method for the identification and quantification of trace synthetic auxins in environmental water and fruit juice samples was developed. The obtained limits of detection for water and fruit juice samples located in the ranges of 0.0059-0.013 and 0.018-0.031 µg/L, respectively. Recoveries in actual samples with different fortified contents varied from 82.2% to 117%, with satisfactory reproducibility. The results will evidence that the introduced extraction technique is a useful alternative for the entrapment of trace synthetic auxins from complex samples.

Pea root responses under naproxen stress: changes in the formation of structural barriers in the primary root in context with changes of auxin and abscisic acid levels.

Pharmaceuticals belong to pseudo-persistent pollutants because of constant entry into the environment and hazardous potential for non-target organisms, including plants, in which they can influence biochemical and physiological processes. Detailed analysis of results obtained by microscopic observations using fluorescent dyes (berberine hemisulphate, Fluorol Yellow 088), detection of phytohormone levels (radioimmunoassay, enzyme-linked immune sorbent assay) and thermogravimetric analysis of lignin content proved that the drug naproxen (NPX) can stimulate the formation of root structural barriers. In the primary root of plants treated with 0.5, 1, and 10 mg/L NPX, earlier Casparian strip formation and development of the whole endodermis circle closer to its apex were found after five days of cultivation (by 9-20% as compared to control) and after ten days from 0.1 mg/L NPX (by 8-63%). Suberin lamellae (SL) were deposited in endodermal cells significantly closer to the apex under 10 mg/L NPX by up to 75%. Structural barrier formation under NPX treatment can be influenced indirectly by auxin-supported cell division and differentiation caused by its eight-times higher level under 10 mg/L NPX and directly by stimulated SL deposition induced by abscisic acid (higher from 0.5 mg/L NPX), as proved by the higher proportion of cells with SL in the primary root base (by 8-44%). The earlier modification of endodermis in plant roots can help to limit the drug transfer and maintain the homeostasis of the plant.

Using targeted metabolomics to elucidate the indole auxin network in plants.

The plant hormone auxin plays important roles throughout the entire life span of a plant and facilitates its adaptation to a changing environment. Multiple metabolic pathways intersect to control the levels and flux through indole-3-acetic acid (IAA), the primary auxin in most plant species. Measurement of changes in these pathways represents an important objective to understanding core aspects of auxin signal regulation. Such studies have become approachable through the technologies encompassed by targeted metabolomics. By monitoring incorporation of stable isotopes from labeled precursors into proposed intermediates, it is possible to trace pathway utilization and characterize new biosynthetic routes to auxin. Chemical inhibitors that target specific steps or entire pathways related to auxin synthesis aid these techniques. Here we describe methods for obtaining stable isotope labeled pathway intermediates necessary for pathway analysis and quantification of compounds. We describe how to use isotope dilution with methods employing either gas chromatography or high performance liquid chromatography mass spectrometry techniques for sensitive analysis of IAA. Complete biosynthetic pathway analysis in seedlings using multiple stable isotope-labeled precursors and chemical inhibitors coupled with highly sensitive liquid chromatography-mass spectrometry methods are described that allow rapid measurement of isotopic flux into biochemical pools. These methods should prove to be useful to researchers studying aspects of the auxin metabolic network in vivo in a variety of plant tissues and during various environmental conditions.

Sensitive determination of auxins in environmental water and peach beverage by hyper crosslinked polymer-based solid-phase extraction with high performance liquid chromatography-fluorescence detection.

As plant regulators, auxins can promote plant growth. However, they have toxicity and may cause harm to humans. Due to their low concentrations in food sample matrices, the enrichment and analysis of trace auxins in food samples is a challenging work. In this work, a series of hyper crosslinked polymers (HCPs) were synthesized by Friedel-Crafts acylation to extract four auxins (indole-3-acetic acid, indole-3-propionic acid, indole-3-butyric acid and 1-naphthylacetic acid). Among these HCPs, the QP-TC-HCP, synthesized from p-quaterphenyl (QP) and terephthaloyl chloride (TC), showed the best adsorption performance for the auxins. It was then applied as the adsorbent for the solid-phase extraction of the auxins from environmental water and peach beverage samples, followed by high performance liquid chromatography-fluorescence detection. Under the optimized conditions, the limits of detection were 3.0-12.0 pg mL-1 for environmental water and 18.0-36.0 pg mL-1 for peach beverage sample. The method recoveries of the auxins for the spiked samples were in the range of 85.0-110.0%. The established method provided an alternative approach for the determination of auxins in food samples. In addition, different types of organic compounds were tested for the extraction by the QP-TC-HCP to assess its application potential and adsorption mechanism. It was concluded that the QP-TC-HCP had better extraction performance for the compounds with certain hydrophilicity and more hydrogen bonding sites.

Uncovering the effects of kaolin on balancing berry phytohormones and quality attributes of Vitis vinifera grown in warm-temperate climate regions.

BACKGROUND: The application of kaolin particle film is considered a short-term strategy against several environmental stresses in areas with a Mediterranean-like climate. However, it is known that temperature fluctuations and water availability over the season can jeopardize kaolin efficiency in many Mediterranean crops. Hence, this study aims to evaluate the effects of kaolin foliar application on berry phytohormones, antioxidant defence, and oenological parameters at veraison and harvest stages of Touriga-Franca (TF) and Touriga-Nacional (TN) grapevines in two growing seasons (2017 and 2018). The 2017 growing season was considered the driest (-147.1 dryness index) and the warmest (2705 °C growing degree days) of the study. RESULTS: In 2017, TF kaolin-treated berries showed lower salicylic acid (-26.6% compared with unsprayed vines) and abscisic acid (ABA) (-10.5%) accumulation at veraison, whereas salicylic acid increased up to 28.8% at harvest. In a less hot season, TN and TF kaolin-treated grapevines showed a twofold in ABA content and a threefold increase in the indole-3-acetic acid content at veraison and lower ABA levels (83.8%) compared with unsprayed vines at harvest. Treated berries showed a decreased sugar content, without compromising malic and tartaric acid levels, and reactive oxygen species accumulation throughout berry ripening. CONCLUSION: The results suggest kaolin exerts a delaying effect in triggering ripening-related processes under severe summer stress conditions. Treated berries responded with improved antioxidant defence and phytohormone balance, showing significant interactions between kaolin treatment, variety, and developmental stage in both assessed years. © 2021 Society of Chemical Industry.

Endophytic bacteria Bacillus safensis and Pseudomonas hibiscicola and their ability to increase rice seedling growth

Endophytic bacteria Bacillus safensis RS95 and Pseudomonas hibiscicola RS121 were evaluated for their ability to promote the growth of rice seedlings and produce indole-acetic acid (IAA) and siderophores and to solubilize phosphates. 'Guri' rice seeds were immersed in bacterial endophyte cell suspensions (separated and two-strain mixed), as well as in Escherichia coli DH5α, phosphate-buffered saline (PBS) and water treatments (negative controls). Seeds were sown on agar-water in Petri plates placed vertically at an angle of 65°. The ability of plant growth-promoting endophytic bacteria (PGPEB) to produce IAA and siderophores was determined by Salkowski colorimetric and chrome azurol S (CAS) assays, respectively. Mineral phosphate solubilization activity was calculated by inoculating the endophytes onto medium containing insoluble phosphate. PGPEB showed a positive effect on the growth of rice seedlings, causing a mean growth of shoots and primary-roots of 60 and 67%, respectively. Bacterial strains also showed positive traits for IAA and siderophore production, as well as phosphate-solubilization activity

Phytohormone profiles in non-transformed and AtCKX transgenic centaury (Centaurium erythraea Rafn) shoots and roots in response to salinity stress in vitro.

Plant hormones regulate numerous developmental and physiological processes. Abiotic stresses considerably affect production and distribution of phytohormones as the stress signal triggers. The homeostasis of plant hormones is controlled by their de novo synthesis and catabolism. The aim of this work was to analyse the contents of total and individual groups of endogenous cytokinins (CKs) as well as indole-3-acetic acid (IAA) in AtCKX overexpressing centaury plants grown in vitro on graded NaCl concentrations (0, 50, 100, 150, 200 mM). The levels of endogenous stress hormones including abscisic acid (ABA), salicylic acid (SA) and jasmonic acid (JA) were also detected. The elevated contents of total CKs were found in all analysed centaury shoots. Furthermore, increased amounts of all five CK groups, as well as enhanced total CKs were revealed on graded NaCl concentrations in non-transformed and AtCKX roots. All analysed AtCKX centaury lines exhibited decreased amounts of endogenous IAA in shoots and roots. Consequently, the IAA/bioactive CK forms ratios showed a significant variation in the shoots and roots of all AtCKX lines. In shoots and roots of both non-transformed and AtCKX transgenic centaury plants, salinity was associated with an increase of ABA and JA and a decrease of SA content.

Lupeol Accumulation Correlates with Auxin in the Epidermis of Castor.

Lupeol, a natural lupane-type pentacyclic triterpene, possesses various pharmacological properties, and its production attracts attention. Significant quantities of lupeol are deposited on the castor aerial organ surface and are easily extractable as a predominant wax constituent. Thus, castor might be considered as a potential bioreactor for the production of lupeol. The lupeol biosynthesis pathway is well known, but how it is regulated remains largely unknown. Among large numbers of castor cultivars, we targeted one accession line (337) with high levels of lupeol on its stem surface and low levels thereof on its hypocotyl surface, implicating that lupeol synthesis is differentially regulated in the two organs. To explore the underlying mechanisms, we did comparative transcriptome analysis of the first internode of 337 stem and the upper hypocotyl. Our results show that large amounts of auxin-related genes are differentially expressed in both parts, implying some possible interactions between auxin and lupeol production. We also found that several auxin-responsive cis-elements are present in promoter regions of HMGR and LUS genes encoding two key enzymes involved in lupeol production. Furthermore, auxin treatments apparently induced the expression levels of RcHMGR and RcLUS. Furthermore, we observed that auxin treatment significantly increased lupeol contents, whereas inhibiting auxin transport led to an opposite phenotype. Our study reveals some relationships between hormone activity and lupeol synthesis and might provide a promising way for improving lupeol yields in castor.

A Comprehensive Analysis Using Colorimetry, Liquid Chromatography-Tandem Mass Spectrometry and Bioassays for the Assessment of Indole Related Compounds Produced by Endophytes of Selected Wheat Cultivars.

Liquid chromatography-tandem mass spectrometry (LC-MS/MS), colorimetry, and bioassays were employed for the evaluation of the ability of endophytic bacterial strains to synthesize indole-related compounds (IRCs) and in particular indole-3-acetic acid (IAA). A total of 54 endophytic strains belonging to seven bacterial genera isolated from tissues of common and spelt wheat cultivars were studied. The endophytic bacteria isolated from different tissues of the tested wheat types were capable of IRCs production, including IAA, which constituted from 1.75% to 52.68% of all IRCs, in in vitro conditions via the tryptophan dependent pathway. The selected post-culture medium was also examined using a plant bioassay. Substantial growth of wheat coleoptile segments treated with the bacterial post-culture medium was observed in several cases. Our data suggest that the studied endophytic bacteria produce auxin-type compounds to support plant development. Summarizing, our approach to use three complementary methods for estimation of IRCs in different endophytic strains provides a comprehensive picture of their effect on wheat growth.

A biosensor for the direct visualization of auxin.

One of the most important regulatory small molecules in plants is indole-3-acetic acid, also known as auxin. Its dynamic redistribution has an essential role in almost every aspect of plant life, ranging from cell shape and division to organogenesis and responses to light and gravity1,2. So far, it has not been possible to directly determine the spatial and temporal distribution of auxin at a cellular resolution. Instead it is inferred from the visualization of irreversible processes that involve the endogenous auxin-response machinery3-7; however, such a system cannot detect transient changes. Here we report a genetically encoded biosensor for the quantitative in vivo visualization of auxin distribution. The sensor is based on the Escherichia coli tryptophan repressor8, the binding pocket of which is engineered to be specific to auxin. Coupling of the auxin-binding moiety with selected fluorescent proteins enables the use of a fluorescence resonance energy transfer signal as a readout. Unlike previous systems, this sensor enables direct monitoring of the rapid uptake and clearance of auxin by individual cells and within cell compartments in planta. By responding to the graded spatial distribution along the root axis and its perturbation by transport inhibitors-as well as the rapid and reversible redistribution of endogenous auxin in response to changes in gravity vectors-our sensor enables real-time monitoring of auxin concentrations at a (sub)cellular resolution and their spatial and temporal changes during the lifespan of a plant.

Reinvestigation of THOUSAND-GRAIN WEIGHT 6 grain weight genes in wheat and rice indicates a role in pollen development rather than regulation of auxin content in grains.

KEY MESSAGE: Phylogenetic and expression analyses of grain weight genes TaTGW6 and OsTGW6 and investigation of substrate availability indicate TGW6 does not regulate auxin content of grains but may affect pollen development. The THOUSAND-GRAIN WEIGHT 6 genes (TaTGW6 and OsTGW6) are reported to result in larger grains of wheat and rice by reducing production of indole-3-acetic acid (IAA) in developing grains. However, a critical comparison of data on TaTGW6 and OsTGW6 with other reports on IAA synthesis in cereal grains requires that this hypothesis be reinvestigated. Here, we show that TaTGW6 and OsTGW6 are members of a large gene family that has undergone major, lineage-specific gene expansion. Wheat has nine genes, and rice three genes encoding proteins with more than 80% amino acid identity with TGW6, making it difficult to envisage how a single inactive allele could have a major effect on IAA levels in grains. In our study, we show that neither TaTGW6 nor OsTGW6 is expressed in developing grains. Instead, both genes and their close homologues are exclusively expressed in pre-emergent inflorescences; TaTGW6 is expressed particularly in microspores prior to mitosis. This evidence, combined with our observation that developing wheat grains have undetectable levels of ester IAA in comparison to free IAA and do not express an IAA-glucose synthase suggests that TaTGW6 and OsTGW6 do not regulate grain size via the hydrolysis of IAA-glucose. Instead, their similarity to rice strictosidine synthase-like (OsSTRL2) suggests they play a key role in pollen development.

Volatile 1-octanol of tea (Camellia sinensis L.) fuels cell division and indole-3-acetic acid production in phylloplane isolate Pseudomonas sp. NEEL19.

Tea leaves possess numerous volatile organic compounds (VOC) that contribute to tea's characteristic aroma. Some components of tea VOC were known to exhibit antimicrobial activity; however, their impact on bacteria remains elusive. Here, we showed that the VOC of fresh aqueous tea leaf extract, recovered through hydrodistillation, promoted cell division and tryptophan-dependent indole-3-acetic acid (IAA) production in Pseudomonas sp. NEEL19, a solvent-tolerant isolate of the tea phylloplane. 1-octanol was identified as one of the responsible volatiles stimulating cell division, metabolic change, swimming motility, putative pili/nanowire formation and IAA production, through gas chromatography-mass spectrometry, microscopy and partition petri dish culture analyses. The bacterial metabolic responses including IAA production increased under 1-octanol vapor in a dose-dependent manner, whereas direct-contact in liquid culture failed to elicit such response. Thus, volatile 1-octanol emitting from tea leaves is a potential modulator of cell division, colonization and phytohormone production in NEEL19, possibly influencing the tea aroma.

Sensors for the quantification, localization and analysis of the dynamics of plant hormones.

Plant hormones play important roles in plant growth and development and physiology, and in acclimation to environmental changes. The hormone signaling networks are highly complex and interconnected. It is thus important to not only know where the hormones are produced, how they are transported and how and where they are perceived, but also to monitor their distribution quantitatively, ideally in a non-invasive manner. Here we summarize the diverse set of tools available for quantifying and visualizing hormone distribution and dynamics. We provide an overview over the tools that are currently available, including transcriptional reporters, degradation sensors, and luciferase and fluorescent sensors, and compare the tools and their suitability for different purposes.

Changes in the distribution of endogenous hormones in Phyllostachys edulis 'Pachyloen' during bamboo shooting.

In this study, we investigated the changes in the distribution and regulation of endogenous hormones in Phyllostachys edulis 'Pachyloen' during bamboo shooting. Enzyme-linked immunosorbent assay was used to measure the mass fractions of indole-3-acetic acid (IAA), gibberellic acid (GA), zeatin riboside (ZR), and abscisic acid (ABA) in rhizomes, shoots, and maternal bamboo organs during shoot sprouting, shoot growth, and new-bamboo formation. Measurements were compared among bamboo parts and developmental periods. The overall mass fractions of IAA and ABA were significantly higher than those of ZR and GA, driven by differences among bamboo parts and developmental periods. The abundance of each endogenous hormone varied among bamboo parts and developmental periods. During bamboo shooting, ABA had the highest mass fraction in all bamboo parts sampled, followed by IAA, GA, and ZR. Among bamboo parts, rhizomes had more IAA, ZR, and GA than the other parts, but significantly less ABA. Winter shoots had higher ZR: IAA and GA: IAA ratios than rhizomes and maternal bamboo organs. During shoot growth, ABA was the most abundant hormone in rhizomes and maternal bamboo organs, followed by IAA, ZR, and GA. In contrast, IAA was the most abundant hormone in spring shoots, followed by ABA, ZR, and GA. Maternal bamboo organs had a significantly higher ZR: GA ratio, and significantly lower IAA: ABA, ZR: ABA, and GA: ABA ratios than rhizomes. Spring shoots had significantly higher IAA: ABA, ZR: ABA, and GA: ABA ratios than rhizomes and maternal bamboo organs; significantly higher ZR mass fractions, and ZR: GA and ZR: IAA ratios and significantly lower ABA mass fractions than rhizomes; and significantly higher GA: IAA ratio than maternal bamboo organs. During new-bamboo formation, ABA was the most abundant hormone in rhizomes, winter shoots, and maternal bamboo organs, followed by IAA, ZR, and GA. Maternal bamboo organs had significantly lower IAA mass fractions and significantly higher ABA mass fractions than rhizomes and new bamboo tissue. IAA and ABA abundances exhibited an inverse relationship in rhizomes and maternal bamboo organs. GA: ABA and GA: IAA ratios decreased gradually and other hormone ratios exhibited parabolic trends over the bamboo-shooting period, with the highest ratios observed in new bamboo tissues. Overall, the coordination or antagonism among endogenous hormones plays a key regulatory role in bamboo shoot growth. The formation of thick walls in P. edulis 'Pachyloen', one of its major traits, may be partially attributed to the relatively high IAA and ZR and low GA mass fractions.

Phytohormone production by the arbuscular mycorrhizal fungus Rhizophagus irregularis.

Arbuscular mycorrhizal symbiosis is a mutualistic interaction between most land plants and fungi of the glomeromycotina subphylum. The initiation, development and regulation of this symbiosis involve numerous signalling events between and within the symbiotic partners. Among other signals, phytohormones are known to play important roles at various stages of the interaction. During presymbiotic steps, plant roots exude strigolactones which stimulate fungal spore germination and hyphal branching, and promote the initiation of symbiosis. At later stages, different plant hormone classes can act as positive or negative regulators of the interaction. Although the fungus is known to reciprocally emit regulatory signals, its potential contribution to the phytohormonal pool has received little attention, and has so far only been addressed by indirect assays. In this study, using mass spectrometry, we analyzed phytohormones released into the medium by germinated spores of the arbuscular mycorrhizal fungus Rhizophagus irregularis. We detected the presence of a cytokinin (isopentenyl adenosine) and an auxin (indole-acetic acid). In addition, we identified a gibberellin (gibberellin A4) in spore extracts. We also used gas chromatography to show that R. irregularis produces ethylene from methionine and the α-keto γ-methylthio butyric acid pathway. These results highlight the possibility for AM fungi to use phytohormones to interact with their host plants, or to regulate their own development.

Intestinal microbiota-derived tryptophan metabolites are predictive of Ah receptor activity.

Commensal microbiota-dependent tryptophan catabolism within the gastrointestinal tract is known to exert profound effects upon host physiology, including the maintenance of epithelial barrier and immune function. A number of abundant microbiota-derived tryptophan metabolites exhibit activation potential for the aryl hydrocarbon receptor (AHR). Gene expression facilitated by AHR activation through the presence of dietary or microbiota-generated metabolites can influence gastrointestinal homeostasis and confer protection from intestinal challenges. Utilizing untargeted mass spectrometry-based metabolomics profiling, combined with AHR activity screening assays, we identify four previously unrecognized tryptophan metabolites, present in mouse cecal contents and human stool, with the capacity to activate AHR. Using GC/MS and LC/MS platforms, quantification of these novel AHR activators, along with previously established AHR-activating tryptophan metabolites, was achieved, providing a relative order of abundance. Using physiologically relevant concentrations and quantitative gene expression analyses, the relative efficacy of these tryptophan metabolites with regard to mouse or human AHR activation potential is examined. These data reveal indole, 2-oxindole, indole-3-acetic acid and kynurenic acid as the dominant AHR activators in mouse cecal contents and human stool from participants on a controlled diet. Here we provide the first documentation of the relative abundance and AHR activation potential of a panel of microbiota-derived tryptophan metabolites. Furthermore, these data reveal the human AHR to be more sensitive, at physiologically relevant concentrations, to tryptophan metabolite activation than mouse AHR. Additionally, correlation analyses indicate a relationship linking major tryptophan metabolite abundance with AHR activity, suggesting these cecal/fecal metabolites represent biomarkers of intestinal AHR activity.

Transcription profiles reveal sugar and hormone signaling pathways mediating tree branch architecture in apple (Malus domestica Borkh.) grafted on different rootstocks.

Apple trees grafted on different rootstock types, including vigorous rootstock (VR), dwarfing interstock (DIR), and dwarfing self-rootstock (DSR), are widely planted in production, but the molecular determinants of tree branch architecture growth regulation induced by rootstocks are still not well known. In this study, the branch growth phenotypes of three combinations of 'Fuji' apple trees grafted on different rootstocks (VR: Malus baccata; DIR: Malus baccata/T337; DSR: T337) were investigated. The VR trees presented the biggest branch architecture. The results showed that the sugar content, sugar metabolism-related enzyme activities, and hormone content all presented obvious differences in the tender leaves and buds of apple trees grafted on these rootstocks. Transcriptomic profiles of the tender leaves adjacent to the top buds allowed us to identify genes that were potentially involved in signaling pathways that mediate the regulatory mechanisms underlying growth differences. In total, 3610 differentially expressed genes (DEGs) were identified through pairwise comparisons. The screened data suggested that sugar metabolism-related genes and complex hormone regulatory networks involved the auxin (IAA), cytokinin (CK), abscisic acid (ABA) and gibberellic acid (GA) pathways, as well as several transcription factors, participated in the complicated growth induction process. Overall, this study provides a framework for analysis of the molecular mechanisms underlying differential tree branch growth of apple trees grafted on different rootstocks.

Stainless steel sheets as the substrate of disposable electrochemical sensors for analysis of heavy metals or biomolecules.

In this paper, low-cost stainless steel sheets with excellent electric conductivity were utilized as the robust substrate for fabrication of disposable working electrodes. The stainless steel electrodes were modified with carbon cement and then coupled in paper-based analytical devices for analysis of heavy metals (cadmium and lead) in toys or indole-3-acetic acid (IAA) in plants, respectively. For stripping analysis of cadmium and lead, the dilution ratio of the carbon cement, the pH value of the buffer solution, the pre-deposition potential and time, and the bismuth concentration were optimized with the detection limits reaching 1 µg•L-1. After optimization of the dilution ratio of carbon cement, the similar devices could also be used for analysis of IAA at the concentration of less than 0.5 µM. This strategy could be successfully applied for differentiation of migratable lead in toys or in situ amounts of IAA in root tips of Arabidopsis thaliana in real time, respectively. Our results implied that the electric conductivity of the substrate could possibly be critical for the improvement of the analytical performance of the modified electrodes. This study suggested that stainless steel could become a suitable and cost-effective substrate for fabrication of disposable carbon-based electrodes used in electrochemical detection.