Quantification of endogenous brassinosteroids in plant by on-line two-dimensional microscale solid phase extraction-on column derivatization coupled with high performance liquid chromatography–tandem mass spectrometry

Organ-level distribution tandem mass spectrometry analysis of three structural types of brassinosteroids in rapeseed

Background

Brassinosteroids (BRs) are a class of naturally occurring steroidal phytohormones mediating a wide range of pivotal developmental and physiological functions throughout the plant's life cycle. Therefore, it is of great significance to determine the content and the distribution of BRs in plants.Regretfully, although a large number of quantitative methods for BRs by liquid chromatography-tandem mass spectrometry (LC-MS/MS) have been reported, the in planta distribution of BRs is still unclear because of their lower contents in plant tissues and the lack of effective ionizable groups in their chemical structures.

Methods

We stablished a novel analytical method of BRs based on C18 cartridge solid-phase extraction (SPE) purification, 4-(dimethylamino)-phenylboronic acid (DMAPBA) derivatization, and online valve-switching system coupled with ultra-high performance liquid chromatography-electro spray ionization-triple quadrupole mass spectrometry (UHPLC-ESI-MS/MS). This method has been used to quantify three structural types of BRs (epibrassinolide, epicastasterone, and 6-deoxo-24-epicastaster one) in different organs of Brassica napus L. (rapeseed).

Results

We obtained the contents of three structural types of BRs in various organ tissues of rapeseed. The contents of three BRs in rapeseed flowers were the highest, followed by tender pods. The levels of three BRs all decreased during the maturation of the organs. We outlined the spatial distribution maps of three BRs in rapeseed based on these results, so as to understand the spatial distribution of BRs at the visual level.

Conclusions

Our results provided useful information for the precise in situ localization of BRs in plants and the metabolomic research of BRs in future work. The in planta spatial distribution of BRs at the visual level has been studied for the first time.

Online micro solid phase extraction coupled with ultra-performance liquid chromatography-tandem mass spectrometry for trace analysis of endogenous plant hormones in Ulva linza

OBJECTIVE

Ulva linza (L.) is a species of green algae widely distributed in China. We aimed to establish a sensitive online analytical method for quantification of endogenous phytohormones in fresh minute seaweed samples.

METHOD

The method for quantification of endogenous plant hormones in fresh minute samples was developed based on a homemade online micro solid phase extraction (m-SPE) system coupled with an ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) platform. The online m-SPE instrument injected the eluent of m-SPE directly onto the LC separation column, improving the utilization of samples and saving time. The m-SPE column, of which the effective size was 9.6 × 2 mm i.d., was filled with 19 mg of C18 (10 μm).

RESULTS

Under optimized conditions, the limits of detection were 0.002-0.060 ng ml^-1 for five plant hormones. The actual sample recoveries of phytohormones were 76.4-103.4% and the coefficients of variance were below 14.1%. The temporal distribution of these endogenous plant hormones of U. linza during different growth periods is described.

CONCLUSION

The proposed online m-SPE method was successfully applied to quantification of endogenous acidic and alkaline plant hormones in U. linza. It provides important information for the further study of the physiological and ecological effects of plant hormones in lower algal species.

Derivatization, an Applicable Asset for Conventional HPLC Systems without MS Detection in Food and Miscellaneous Analysis

One of the most valuable practices for analyzing not-so-analytical-friendly analytes in complex, heterogenous matrices is derivatization. Availability of numerous derivatizing reagents (DRs) makes the modification of analyte more exploitable in terms of an analytical perspective. A wide array of derivatization techniques like pre or post-column, in-situ, enzymatic, ultrasound-assisted, microwave-assisted, photochemical derivatization has added much-needed methodological strength in analyzing intricate analytical matrices (food, water, and soil). In recent years, analytical chemistry has achieved greater heights through the development of new sensitive methods with simple conventional instruments like High-Performance Liquid Chromatography (HPLC) devoid of Mass detectors. The prompt availability of these straightforward instruments also makes it a favorable option for routine analysis in food, environmental, bioanalytical chemistry. Analyzing food, environmental or bioanalytical specimen has some of the most problematic aspects, like the low concentration of the analytes accompanied by not too suitable analytical properties. Even though conventional HPLC lacks the required sensitivity but merger with derivatization can lead to a remarkable increase in sensitivity. In recent years there has been a lot of application of diverse derivatizations to increase the sensitivity and selectivity of the analyte for available instruments, resulting in notable findings. Therefore, this review describes the application of derivatization principles in the analysis of analytes in food and additional matrices using conventional HPLC instruments such as HPLC-UV, HPLC-DAD, and HPLC-FD. In this article, we will briefly review the different modes and multiple types of derivatizing reagents with their mechanisms and importance for encouraging the use of established HPLC instruments.

A Fast and Selective Approach for Profiling Vicinal Diols Using Liquid Chromatography-Post Column Derivatization-Double Precursor Ion Scanning Mass Spectrometry

Vicinal diols are important signaling metabolites of various inflammatory diseases, and some of them are potential biomarkers for some diseases. Utilizing the rapid reaction between diol and 6-bromo-3-pyridinylboronic acid (BPBA), a selective and sensitive approach was established to profile these vicinal diols using liquid chromatography-post column derivatization coupled with double precursor ion scan-mass spectrometry (LC-PCD-DPIS-MS). After derivatization, all BPBA-vicinal-diol esters gave a pair of characteristic isotope ions resulting from ⁷⁹Br and ⁸¹Br. The unique isotope pattern generated two characteristic fragment ions of m/z 200 and 202. Compared to a traditional offline derivatization technique, the new LC-PCD-DPIS-MS method retained the capacity of LC separation. In addition, it is more sensitive and selective than a full scan MS method. As an application, an in vitro study of the metabolism of epoxy fatty acids by human soluble epoxide hydrolase was tested. These vicinal-diol metabolites of individual regioisomers from different types of polyunsaturated fatty acids were easily identified. The limit of detection (LOD) reached as low as 25 nM. The newly developed LC-PCD-DPIS-MS method shows significant advantages in improving the selectivity and therefore can be employed as a powerful tool for profiling vicinal-diol compounds from biological matrices.

Boronic Acid-Functionalized Scholl-Coupling Mesoporous Polymers for Online Solid-Phase Extraction of Brassinosteroids from Plant-Derived Foodstuffs

Brassinosteroids (BRs) are natural, nontoxic, non-hazardous, biosafe, and eco-friendly plant hormones, possessing diverse pharmacological activities. However, little is known about the type and content of BRs in frequently consumed plant-derived foodstuffs because of their low abundance and high abundance of interference. In this study, a selective, accurate, and sensitive method based on the online solid-phase extraction using the boronic acid-functionalized Scholl-coupling microporous polymer was developed for the analysis of BRs in plant-derived foodstuffs. Under optimum conditions, an excellent linearity (R² ≥ 0.9970) and lower limits of detection (0.010-0.070 pg mL^-1) were obtained. The high relative recoveries were in the range of 90.33-109.34% with relative standard deviations less than 9.73%. The method was successfully used for the determination of BRs in fifteen plant-derived foodstuffs. The present work offers a valuable tool for exploring BRs from the plant-derived foodstuffs and can provide useful information for developing functional foods.

β-Cyclodextrin-/AuNPs-functionalized covalent organic framework-based magnetic sorbent for solid phase extraction and determination of sulfonamides

β-Cyclodextrin-functionalized magnetic covalent organic framework (Fe₃O₄@COF@Au-β-CD) was developed as sorbent for magnetic solid phase extraction of trace sulfonamides in meat samples prior to HPLC-MS/MS analysis. The sorbent was synthesized by loading gold nanoparticles onto a Fe₃O₄@COF surface and then functionalized by thiolated-β-cyclodextrin immobilization via Au-S bonding formation. The prepared composite material was employed for sulfonamides extraction. The main parameters were optimized to obtain the best extraction efficiency. The experiments of adsorption kinetics were carried out to investigate the adsorption mechanism. Results showed the pseudo-second-order kinetic was better fitted with the adsorption kinetics of sulfonamides. Under optimized conditions, the magnetic solid phase extraction-HPLC method showed good linearity (R² ≥ 0.9936), and the limits of detection were in the range of 0.8-1.6 μg kg^-1. The proposed method was successfully used for quantitation of sulfonamides in real samples. The recoveries ranged from 78.9 to 112.0% with relative standard deviations (RSDs) < 10% (n = 5). The proposed method exhibited great potential for enrichment and determination of sulfonamides in many other food or environment samples. Graphical abstract.

The basic helix-loop-helix transcription factor OsBLR1 regulates leaf angle in rice via brassinosteroid signalling

Leaf angle is a key factor in plant architecture and crop yield. Brassinosteroids (BRs) regulate many developmental processes, especially the leaf angle in monocots. However, the BR signalling pathway is complex and includes many unknown members. Here, we propose that Oryza sativa BRASSINOSTEROID-RESPONSIVE LEAF ANGLE REGULATOR 1 (OsBLR1) encodes a bHLH transcription factor, and positively regulates BR signalling to increase the leaf angle and grain length in rice (Oryza sativa L.). Lines overexpressing OsBLR1 (blr1-D and BLR1-OE-1/2/3) had similar traits, with increased leaf angle and grain length. Conversely, OsBLR1-knockout mutants (blr1-1/2/3) had erect leaves and shorter grains. Lamina joint inclination, coleoptile elongation, and root elongation assay results indicated that these overexpression lines were more sensitive to BR, while the knockout mutants were less sensitive. There was no significant difference in the endogenous BR contents of blr1-1/2 and wild-type plants. These results suggest that OsBLR1 is involved in BR signal transduction. The blr1-D mutant, with increased cell growth in the lamina joint and smaller leaf midrib, showed significant changes in gene expression related to the cell wall and leaf development compared with wild-type plants; furthermore, the cellulose and protopectin contents in blr1-D were reduced, which resulted in the increased leaf angle and bent leaves. As the potential downstream target gene of OsBLR1, the REGULATOR OF LEAF INCLINATION1 (OsRLI1) gene expression was up-regulated in OsBLR1-overexpression lines and down-regulated in OsBLR1-knockout mutants. Moreover, we screened OsRACK1A as an interaction protein of OsBLR1 using a yeast two-hybrid assay and glutathione-S-transferase pull-down.

Recent developments and emerging trends of mass spectrometric methods in plant hormone analysis: a review

Plant hormones are naturally occurring small molecule compounds which are present at trace amounts in plant. They play a pivotal role in the regulation of plant growth. The biological activity of plant hormones depends on their concentrations in the plant, thus, accurate determination of plant hormone is paramount. However, the complex plant matrix, wide polarity range and low concentration of plant hormones are the main hindrances to effective analyses of plant hormone even when state-of-the-art analytical techniques are employed. These factors substantially influence the accuracy of analytical results. So far, significant progress has been realized in the analysis of plant hormones, particularly in sample pretreatment techniques and mass spectrometric methods. This review describes the classic extraction and modern microextraction techniques used to analyze plant hormone. Advancements in solid phase microextraction (SPME) methods have been driven by the ever-increasing requirement for dynamic and in vivo identification of the spatial distribution of plant hormones in real-life plant samples, which would contribute greatly to the burgeoning field of plant hormone investigation. In this review, we describe advances in various aspects of mass spectrometry methods. Many fragmentation patterns are analyzed to provide the theoretical basis for the establishment of a mass spectral database for the analysis of plant hormones. We hope to provide a technical guide for further discovery of new plant hormones. More than 140 research studies on plant hormone published in the past decade are reviewed, with a particular emphasis on the recent advances in mass spectrometry and sample pretreatment techniques in the analysis of plant hormone. The potential progress for further research in plant hormones analysis is also highlighted.

Dispersive Matrix Solid-Phase Extraction Method Coupled with High Performance Liquid Chromatography-Tandem Mass Spectrometry for Ultrasensitive Quantification of Endogenous Brassinosteroids in Minute Plants and Its Application for Geographical Distribution Study

An ultrasensitive analysis method for quantification of endogenous brassinosteroids in fresh minute plants was developed based on dispersive matrix solid-phase extraction coupled with high performance liquid chromatography-tandem mass spectrometry. During the dispersive matrix solid-phase extraction, plant samples were first ground with solid sorbent (dispersant) in one microcentrifuge tube and then centrifuged after adding extraction solvent and cleanup materials (another type of sorbent). Three protocols based on dispersive matrix solid-phase extraction were compared and discussed for plant samples with different matrix complexity. The choice of any protocol was a compromise of increasing purification efficiency and decreasing sample loss. Under optimized conditions, the limits of detection were 1.38-6.75 pg mL^-1 for five brassinosteroids in the oilseed rape samples. The intraday and interday precisions were in the range of 0.8%-9.8% and 4.6%-17.3%, respectively. The proposed method was successfully applied to detection of endogenous brassinosteroids in milligram oilseed rape (2.0 mg) and submilligram Arabidopsis thaliana seedlings (0.5 mg). Finally, the geographical distribution of five endogenous brassinosteroids of Brassica napus L. oilseed rape in different provinces of origin in the Yangtze River basin was described.

A new boronic acid reagent for the simultaneous determination of C27-, C28-, and C29-brassinosteroids in plant tissues by chemical labeling-assisted liquid chromatography-mass spectrometry

Brassinosteroids (BRs) are endogenous plant growth-promoting hormones affecting growth and development during the entire life cycle of plants. Naturally occurring BRs can be classified into C₂₇-, C₂₈-, or C₂₉-BRs based on the nature of the alkyl groups occupying the C-24 position in the side chain of the 5a-cholestane carbon skeleton. However, while C₂₇-BRs exhibit similar bioactivities to C₂₈- and C₂₉-BRs, the biosynthetic pathways of C₂₇-BRs in plants have not yet been clearly characterized. In addition to a lack of biochemical and enzymatic evidence regarding the biosynthetic pathways of C₂₇-BRs, even most of the intermediate compounds on their pathways have not been explored and identified due to the lower endogenous levels of C₂₇-BRs. Therefore, the development of highly sensitive analytical methods is essential for studying the biosynthetic pathways and physiological functions of C₂₇-BRs. Accordingly, this study establishes qualitative and quantitative methods for identifying and detecting C₂₇-, C₂₈-, and C₂₉-BRs using a newly synthesized boronic acid reagent denoted as 2-methyl-4-phenylaminomethylphenylboronic acid (2-methyl-4-PAMBA) in conjunction with liquid chromatography-mass spectrometry (LC-MS). Labeling with 2-methyl-4-PAMBA provides derivatives with excellent stability, and the detection sensitivities of BRs, particularly for C₂₇-BRs, are dramatically improved. The limits of detection (with a signal-to-noise ratio of 3) for six BRs, including 2 C₂₇-BRs (28-norCS and 28-norBL), 3 C₂₈-BRs (CS, BL, and TY), and a single C₂₉-BR (28-homoBL), are found to be 0.10-1.68 pg/mL after labeling with 2-methyl-4-PAMBA. Finally, the proposed analytical method is successfully applied for the detection of endogenous BRs in small mass samples of Oryza sativa seedlings, Rape flowers, Arabidopsis shoots, and Arabidopsis flowers. In addition, a method for profiling potential BRs in plants is also developed using LC-MS in multiple reaction monitoring scan mode assisted by 2-methyl-4-PAMBA and 2-methyl-4-PAMBA-d₅ labeling. The developed method is able to identify 10 potential BRs in a Rape flower extract. The proposed quantitative and qualitative methods established by 2-methyl-4-PAMBA labeling are helpful for facilitating an understanding of the physiological functions and biosynthetic pathways of BRs, particularly for C₂₇-BRs. Graphical abstract.

Pursuing extreme sensitivity for determination of endogenous brassinosteroids through direct fishing from plant matrices and eliminating most interferences with boronate affinity magnetic nanoparticles

Brassinosteroids (BRs) are important plant hormones regulating plant growth and development. High-performance analytical methods for quantifying endogenous BRs are important for studying the molecular mechanisms of BR action. Herein we developed a high-performance sample pretreatment method based on boronate affinity magnetic nanoparticles (BAMNPs). The high specificity of boronate affinity enables direct fishing of BRs from plant matrices. The strong binding energy makes it possible to remove most contaminants in plant matrices with a small loss of target BRs. Besides these advantages, the novel two-step oxidation-hydrolysis elution system raised BR recoveries to 70.5%-98.2%, which was much higher than other boronate affinity applications. The high cleanliness of the final eluents lowered the matrix effects to 85.2%-92.4%. As a result, this method enables simultaneously good recoveries of endogenous BRs and thorough removal of matrix interferences, which greatly improves the sensitivity of BR analysis and reduces the use of plant materials for routine analysis to <10 mg. In addition, the sample handling time can be shortened to <3 h due to the operating convenience of BAMNPs and their easy separation from plant powders. Based on these advantages of BAMNP solid phase extraction, the organ-specific BR distribution analysis in Arabidopsis and rice tissues demonstrates excellent sensitivity, good reproducibility and high throughput of the method. Graphical abstract A high-sensitivity and time-saving UPLC-MS/MS-based quantification method for brassinosteroids (BRs) was developed through directly fishing BRs from plant matrices and eliminating most matrix interferences with as-prepared boronate affinity magnetic nanoparticles (BAMNPs).

A mutant in the CsDET2 gene leads to a systemic brassinosteriod deficiency and super compact phenotype in cucumber (Cucumis sativus L.)

A novel dwarf cucumber mutant, scp-2, displays a typical BR biosynthesis-deficient phenotype, which is due to a mutation in CsDET2 for a steroid 5-alpha-reductase. Brassinosteroids (BRs) are a group of plant hormones that play important roles in the development of plant architecture, and extreme dwarfism is a typical outcome of BR-deficiency. Most cucumber (Cucumis sativus L.) varieties have an indeterminate growth habit, and dwarfism may have its value in manipulation of plant architecture and improve production in certain production systems. In this study, we identified a spontaneous dwarf mutant, super compact-2 (scp-2), that also has dark green, wrinkle leaves. Genetic analyses indicated that scp-2 was different from two previously reported dwarf mutants: compact (cp) and super compact-1 (scp-1). Map-based cloning revealed that the mutant phenotype was due to two single nucleotide polymorphism and a single-base insertion in the CsDET2 gene that resulted in a missense mutation in a conserved amino acid and thus a truncated protein lacking the conserved catalytic domains in the predicted steroid 5α-reductase protein. Measurement of endogenous hormone levels indicated a reduced level of brassinolide (BL, a bioactive BR) in scp-2, and the mutant phenotype could be partially rescued by the application of epibrassinolide (EBR). In addition, scp-2 mutant seedlings exhibited dark-grown de-etiolation, and defects in cell elongation and vascular development. These data support that scp-2 is a BR biosynthesis-deficient mutant, and that the CsDET2 gene plays a key role in BR biosynthesis in cucumber. We also described the systemic BR responses and discussed the specific BR-related phenotypes in cucumber plants.

Protocol for Extraction and Isolation of Brassinosteroids from Plant Tissues

Brassinosteroids (BRs) are a class of steroid plant hormones that participate with other plant hormones in the regulation of numerous developmental processes, including root and shoot growth, vascular differentiation, fertility, and seed germination. A characteristic feature of all plant hormones, including BRs, is that their concentration is extremely low in plant tissues and, therefore, the methods dealing with their determination belong to ultra-trace analysis, for which very sensitive analytical tools are needed. The analysis of natural BRs is essential when their functions and roles in plant growth and development are to be elucidated. Here, we describe a reliable protocol for high-throughput extraction and purification of BRs. The procedure consists of two solid-phase extraction steps and provides selective enrichment and efficient cleanup of these compounds from complex plant extracts. The protocol is designed for sensitive liquid chromatography-tandem mass spectrometry-based method for simultaneous detection of 22 naturally occurring BRs, including their biosynthetic precursors and most of their biologically active metabolites, without need for derivatization.

The determination of 22 natural brassinosteroids in a minute sample of plant tissue by UHPLC-ESI-MS/MS

The triterpenoid plant hormones brassinosteroids (BRs) are believed to influence almost every aspect of plant growth and development. We have developed a sensitive mass spectrometry-based method for the simultaneous profiling of twenty-two naturally occurring brassinosteroids including biosynthetic precursors and the majority of biologically active metabolites. Using ultra-high performance liquid chromatographic (UHPLC) analysis, the run time was reduced up to three times (to 9 min) in comparison to standard HPLC BRs analyses, the retention time stability was improved to 0.1-0.2 % RSD and the injection accuracy was increased to 1.1-4.9 % RSD. The procedures for extraction and for two-step purification based on solid-phase extraction (SPE) were optimised in combination with subsequent UHPLC analysis coupled to electrospray ionisation tandem mass spectrometry (ESI-MS/MS) using Brassica flowers and Arabidopsis plant tissue extracts. In multiple reaction monitoring (MRM) mode, the average detection limit for BRs analysed was close to 7 pg, and the linear range covered up to 3 orders of magnitude. The low detection limits for this broad range of BR metabolites enabled as little as 50 mg of plant tissue to be used for quantitative analyses. The results of determinations exploiting internal standards showed that this approach provides a high level of practicality, reproducibility and recovery. The method we have established will enable researchers to gain a better understanding of the dynamics of the biosynthesis and metabolism of brassinosteroids and their modes of action in plant growth and development.

Improved methodology for assaying brassinosteroids in plant tissues using magnetic hydrophilic material for both extraction and derivatization

BACKGROUND

Brassinosteriods (BRs) are a group of important phytohormones that have major effects on plant growth and development. To fully elucidate the function of BRs, a sensitive BR assay is required. However, most of the previously reported methods are tedious and time-consuming due to multiple pretreatment steps. Therefore, it is of great significance to develop a method to increase the throughput and detection sensitivity of BR analysis.

RESULTS

We established a novel analytical method of BRs based on magnetic solid phase extraction (MSPE) combined with in situ derivatization (ISD). TiO2-coated magnetic hollow mesoporous silica spere(TiO2/MHMSS) was served as a double identity- a microextraction sorbent and "microreactor" for the capture and derivatization of BRs in sequence. BRs were first extracted onto TiO2/MHMSS through hydrophilic interaction. The BR-adsorbed TiO2/MHMSS was then employed as a "microreactor" for the derivatization of BRs with 4-(N,N-dimethyamino)phenylboronic acid (DMAPBA). The MSPE-ISD method was simple and fast, which could be accomplished within 10 min. Furthermore, the derivatives of BRs showed better MS response because they were incorporated with tertiary amino groups. Uniquely, endogenous BRs were detected in only 100 mg fresh weight plant tissue.

CONCLUSION

Our proposed MSPE-ISD method for the determination of endogenous BRs is rapid and sensitive. It can be applied to the analysis of endogenous BRs in 100 mg fresh plant tissue (Brassica napus L. (B. napus L)). The proposed strategy for plant sample preparation may be extended to develop analytical methods for determination of a wide range of analytes with poor MS response in other complex sample matrices.