Identification and quantitation of auxins in plants by liquid chromatography/electrospray ionization ion trap mass spectrometry

Formic Acid as a Dopant for Atmospheric Pressure Chemical Ionization for Negative Polarity of Ion Mobility Spectrometry and Mass Spectrometry

Formic acid (FA) is introduced as a potent dopant for atmospheric pressure chemical ionization (APCI) for ion mobility spectrometry (IMS) and mass spectrometry (MS). The mechanism of chemical ionization with the FA dopant was studied in the negative polarity using a corona discharge (CD)-IMS-MS technique in air. Standard reactant ions of the negative polarity present in air are O2-·(CO2)n·(H2O)m (m = 0, 1 and n = 1, 2) clusters. Introduction of the FA dopant resulted in the production of HCOO-·FA reactant ions. The effect of the FA dopant on the APCI of different classes of compounds was investigated, including plant hormones, pesticides, acidic drugs, and explosives. FA dopant APCI resulted in deprotonation and/or adduct ion formation, [M - H]- and [M + HCOO]-, respectively. Supporting density functional theory (DFT) calculations showed that the ionization mechanism depended on the gas-phase acidity of the compounds. FA dopant APCI led to the improvement of detection sensitivity, suppression of fragmentation, and changes in the ion mobilities of the analyte ions for analytes with suitable molecular structures and gas acidity.

Synergistic Effects of Plant Hormones on Spontaneous Late-ripening Mutant of ‘Jinghong’ Peach Detected by Transcriptome Analysis

Objectives

Peach (Prunus persica L.) is an ancient fruit tree that originated from China. It is the climacteric fruit which belongs to genus Prunus in family Rosaceae. Ethylene, which is produced during ripening, accelerates fruit softening, and therefore peaches cannot be stored for a long time.

Materials and Methods

To study the mechanism of fruit late ripening, transcriptome analysis of the fruit of a late-ripening mutant of ‘Jinghong’ peach was performed to identify genes and pathways involved in fruit late ripening.

Results

A total of 1,805, 1,511, and 2,309 genes were found to be differentially expressed in W2_vs_M1, W3_vs_M2, and W3_vs_M3, respectively. Functional enrichment analysis of the differentially expressed genes showed they were related to carotenoid biosynthesis, starch and sucrose metabolism plant hormone signal transduction, flavonoid biosynthesis, and photosynthesis. The expression trends of ripening-related genes that encode transcription factors and plant hormone signal transduction-related genes that encode enzymes were similar.

Conclusions

It will help to elucidate the transcriptional regulatory network of fruit development in the spontaneous late-ripening mutant of ‘Jinghong’ peach and provide a theoretical basis for understanding the molecular regulatory mechanism of fruit ripening.

Mahyoub J. Exploring the Insect Control and Plant Growth Promotion Potentials of Endophytes Isolated From Calotropis procera Present in Jeddah KSA

Pseudomonas bacteria are entomopathogenic that can naturally infect and kill insects upon ingestion. The insecticidal and plant growth-promoting roles of the bacteria were assessed by applying Pseudomonas IUK001 to insects and plants. The culture extract (CE) of IUK001 at the concentration of 1 mL/cm3 of an artificial diet was used as a treatment for Galleria mellonella larvae. The CE was heat stable at 70°C for 30 minutes and proteinase-K stable, showing 100% and 90% insecticidal activity against G. mellonella larvae. Gas chromatography–mass spectrometry (GC–MS) analysis revealed the insecticidal compounds, for example, trans-cinnamic acid, ornithine, and cyclo (l-Pro-l-Val) in the CE of IUK001. Antibacterial activity was assessed through minimal inhibitory concentration and half-maximal inhibitory concentration values, which ranged from 28 ± 0.8 and 18.9 ± 0.7 to 8 ± 1.8 and 4.6 ± 0.6, respectively. Moreover, plants were inoculated with IUK001, which significantly enhanced ( P < 0.05) the total plant lengths (root + shoot), dry and fresh biomasses and chlorophyll content, and also induced lateral roots. Plant growth hormones, auxins: indole-3-butyric acid and indole-3- propionic acid, were then analyzed through GC–MS in the CE using their respective isotopic internal standards. The findings of the study suggest that IUK001 is a significantly valuable candidate to be exploited as a biocontrol agent as well as a plant growth promoter.

Preparation and application of molecularly imprinted polymer solid-phase microextraction fiber for the selective analysis of auxins in tobacco

As signal molecules, auxins play an important role in mediating plant growth. Due to serious interfering substances in plants, it is difficult to accurately detect auxins with traditional solid-phase extraction methods. To improve the selectivity of sample pretreatment, a novel molecularly imprinted polymer -coated solid-phase microextraction fiber, which could be coupled directly to high-performance liquid chromatography, was prepared with indole acetic acid as template molecule for the selective extraction of auxins. The factors influencing the polymer formation, such as polymerization solvent, cross-linker, and polymerization time, were investigated in detail to enhance the performance of indole acetic acid-molecularly imprinted polymer coating. The morphological and chemical stability of this molecularly imprinted polymer-coated fiber was characterized by scanning electron microscopy, infrared spectrometry, and thermal analysis. The extraction capacity of the molecularly imprinted polymer-coated solid-phase microextraction fiber was evaluated for the selective extraction of indole acetic acid and indole-3-pyruvic acid followed by high-performance liquid chromatography analysis. The linear range for indole acetic acid and indole-3-pyruvic acid was 1-100 µg/L and their detection limit was 0.5 µg/L. The method was applied to the simultaneous determination of two auxins in two kinds of tobacco (Nicotiana tabacum L and Nicotiana rustica L) samples, with recoveries range from 82.1 to 120.6%.

Identification of Auxin Metabolites in Brassicaceae by Ultra-Performance Liquid Chromatography Coupled with High-Resolution Mass Spectrometry

Auxins are signaling molecules involved in multiple stages of plant growth and development. The levels of the most important auxin, indole-3-acetic acid (IAA), are regulated by the formation of amide and ester conjugates with amino acids and sugars. In this work, IAA and IAA amide conjugates with amino acids bearing a free carboxylic group or a methyl ester group, along with some selected IAA metabolites, were studied in positive and negative electrospray ionization (ESI) modes, utilizing high-resolution mass spectrometry (HRMS) as a tool for their structural analysis. HRMS/MS spectra revealed the fragmentation patterns that enable us to identify IAA metabolites in plant extracts from eight vegetables of the Brassicaceae family using a fast and reliable ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry (UPLC-QToF-MS) method. The accurate m/z (mass to charge) ratio and abundance of the molecular and fragment ions of the studied compounds in plant extracts matched those obtained from commercially available or synthesized compounds and confirmed the presence of IAA metabolites.

Gene Expression Profiling of Development and Anthocyanin Accumulation in Kiwifruit (Actinidia chinensis) Based on Transcriptome Sequencing

Red-fleshed kiwifruit (Actinidia chinensis Planch. ‘Hongyang’) is a promising commercial cultivar due to its nutritious value and unique flesh color, derived from vitamin C and anthocyanins. In this study, we obtained transcriptome data of ‘Hongyang’ from seven developmental stages using Illumina sequencing. We mapped 39–54 million reads to the recently sequenced kiwifruit genome and other databases to define gene structure, to analyze alternative splicing, and to quantify gene transcript abundance at different developmental stages. The transcript profiles throughout red kiwifruit development were constructed and analyzed, with a focus on the biosynthesis and metabolism of compounds such as phytohormones, sugars, starch and L-ascorbic acid, which are indispensable for the development and formation of quality fruit. Candidate genes for these pathways were identified through MapMan and phylogenetic analysis. The transcript levels of genes involved in sucrose and starch metabolism were consistent with the change in soluble sugar and starch content throughout kiwifruit development. The metabolism of L-ascorbic acid was very active, primarily through the L-galactose pathway. The genes responsible for the accumulation of anthocyanin in red kiwifruit were identified, and their expression levels were investigated during kiwifruit development. This survey of gene expression during kiwifruit development paves the way for further investigation of the development of this uniquely colored and nutritious fruit and reveals which factors are needed for high quality fruit formation. This transcriptome data and its analysis will be useful for improving kiwifruit genome annotation, for basic fruit molecular biology research, and for kiwifruit breeding and improvement.

Ultra-high performance liquid chromatography coupled to high resolution Orbitrap mass spectrometry for metabolomic profiling of the endogenous phytohormonal status of the tomato plant

Phytohormones are key signalling biomolecules and are of particular interest because of their regulating role in numerous physiological and developmental plant processes. Since the plant response to a given stimulus results amongst others from the complex interaction between phytohormones, there is a mounting interest for multiple phytohormone analysis. Therefore, with the primary aim of profiling the hormonal status of the tomato plant, a generic extraction protocol and an U-HPLC-Orbitrap-MS analysis were developed and validated for both tomato fruit and leaf tissue. To this end, eight phytohormones were considered, i.e. gibberellic acid, indol-3-acetic acid, abscisic acid, jasmonic acid, salicylic acid, zeatin, N6-benzyladenine and epibrassinolide, representing the major hormonal classes. The sample pre-treatment involved liquid extraction with a buffer of methanol, ultrapure water and formic acid (75:20:5, v/v/v), after which the extract was purified by means of an Amicon® Ultra centrifugal unit. Subsequently, analytes were chromatographically separated on a sub-2 μm particles Nucleodur Gravity C18 column and detected by an Exactive™ high-resolution mass spectrometer. Validation of the analytical method demonstrated that linearity (≥0.99), precision (CV≤15%) and mean corrected recovery (between 80% and 110%) performed well for the majority of the eight targeted phytohormones. In addition, the generic nature of the extraction protocol and the full scan approach of the Orbitrap mass spectrometer allowed metabolomic profiling of the hormonal status of the tomato plant.

Post-transcriptional silencing of flavonol synthase mRNA in tobacco leads to fruits with arrested seed set

Flavonoids are synthesized by phenylpropanoid pathway. They are known to participate in large number of physiological and biochemical processes in plants. Parthenocarpy and male sterility has earlier been reported by silencing chalcone synthase (CHS) encoding gene. Silencing of CHS has blocked the synthesis of most of useful flavonoids including flavan-3-ols and flavonols. Also, these studies could not identify whether parthenocarpy/male sterility were due to lack of flavan-3-ols or flavonols or both. Flavonol synthase (FLS) is an important enzyme of flavonoid pathway that catalyzes the formation of flavonols. In this article, we propose a novel strategy towards the generation of seedless or less-seeded fruits by downregulation of flavonol biosynthesis in tobacco (Nicotiana tabacum cv Xanthi) through post-transcriptional gene silencing (PTGS) of FLS encoding mRNA. The FLS silenced lines were observed for 20-80% reduction in FLS encoding gene expression and 25-93% reduction in flavonol (quercetin) content. Interestingly, these FLS silenced tobacco lines also showed reduction in their anthocyanidins content. While the content of flavan-3-ols (catechin, epi-catechin and epi-gallocatechin) was found to be increased in FLS silenced lines. The delayed flowering in FLS silenced lines could be due to decrease in level of indole acetic acid (IAA) at apical region of their shoots. Furthermore, the pollen germination was hampered and pollens were unable to produce functional pollen tube in FLS silenced tobacco lines. Pods of FLS silenced lines contained significantly less number of seeds. The in vitro and in vivo studies where 1 µM quercetin was supplied to germination media, documented the restoration of normal pollen germination and pollen tube growth. This finding identified the role of flavonols particularly quercetin in pollen germination as well as in the regulation of plant fertility. Results also suggest a novel approach towards generation of seedless/less-seeded fruits via PTGS of FLS encoding gene in plants.

Simultaneous analysis of multiple endogenous plant hormones in leaf tissue of oilseed rape by solid-phase extraction coupled with high-performance liquid chromatography-electrospray ionisation tandem mass spectrometry

INTRODUCTION

Plant hormones are important signalling molecules that act at lower concentrations to regulate numerous plant physiological and developmental processes. In order to study the functions of plant hormones, it is necessary to develop a high-throughput and highly selective and sensitive method for determination of plant hormones.

OBJECTIVE

Based on SPE-HPLC-ESI-MS/MS method, a highly selective and sensitive method for determination of six plant hormones in leaf tissue of oilseed rape was developed.

METHODOLOGY

The extraction was performed with C₁₈ solid-phase extraction cartridge and the sample was subsequently analysed by HPLC-ESI-MS/MS. Methanol and H₂O with 0.05% formic acid was selected as the mobile phase for HPLC, using a gradient of increasing methanol content. The plant hormones were quantified in MRM mode and identified in IDA mode by the hybrid triple quadrupole/linear ion trap mass spectrometer with high sensitivity and selectivity.

RESULTS

Under the optimal conditions, good linearities were obtained for six plant hormones with the correlation coefficients above 0.9924. The detection limits of the target compounds were in the range of 0.005-0.2 ng/mL. Reproducibility of the method was obtained with intra-day and inter-day relative standard deviations. The extraction recovery yields of plant hormones under SPE conditions ranged from 67.03 to 119.83%. Compared with previous methods, sample preparation time and amount of sample required for analysis of plant hormones were reduced, and more classes of hormones were quantitatively measured.

Extraction and analysis of auxins in plants using dispersive liquid-liquid microextraction followed by high-performance liquid chromatography with fluorescence detection

Auxin plays an important role in cell differentiation, apical dominance, and tropism in plants. A new method based on dispersive liquid-liquid microextraction (DLLME) combined with high-performance liquid chromatography-fluorescence detection (HPLC-FLD) has been established to detect auxin. A mixture of CHCl(3) (extraction solvent) and acetone (disperser solvent) was injected quickly into a sample solution with desired salt concentration and pH value, and then a cloudy solution consisting of many dispersed fine droplets of CHCl(3) was formed. After centrifugation, the sedimented phase was withdrawn and directly analyzed by HPLC-FLD. Under optimal conditions, four auxins were baseline separated within 3.5 min, with the minimal limit of detection of 0.02 ng mL(-1) and coefficient correlations in the range of 0.9980-0.9995. This simple method was successfully applied to real sample analysis. Experimental results showed that DLLME was a high-performance and powerful preconcentration method to extract and enrich related plant auxin.

Development of a method for comprehensive and quantitative analysis of plant hormones by highly sensitive nanoflow liquid chromatography-electrospray ionization-ion trap mass spectrometry

In recent plant hormone research, there is an increased demand for a highly sensitive and comprehensive analytical approach to elucidate the hormonal signaling networks, functions, and dynamics. We have demonstrated the high sensitivity of a comprehensive and quantitative analytical method developed with nanoflow liquid chromatography-electrospray ionization-ion trap mass spectrometry (LC-ESI-IT-MS/MS) under multiple-reaction monitoring (MRM) in plant hormone profiling. Unlabeled and deuterium-labeled isotopomers of four classes of plant hormones and their derivatives, auxins, cytokinins (CK), abscisic acid (ABA), and gibberellins (GA), were analyzed by this method. The optimized nanoflow-LC-ESI-IT-MS/MS method showed ca. 5-10-fold greater sensitivity than capillary-LC-ESI-IT-MS/MS, and the detection limits (S/N=3) of several plant hormones were in the sub-fmol range. The results showed excellent linearity (R(2) values of 0.9937-1.0000) and reproducibility of elution times (relative standard deviations, RSDs, <1.1%) and peak areas (RSDs, <10.7%) for all target compounds. Further, sample purification using Oasis HLB and Oasis MCX cartridges significantly decreased the ion-suppressing effects of biological matrix as compared to the purification using only Oasis HLB cartridge. The optimized nanoflow-LC-ESI-IT-MS/MS method was successfully used to analyze endogenous plant hormones in Arabidopsis and tobacco samples. The samples used in this analysis were extracted from only 17 tobacco dry seeds (1mg DW), indicating that the efficiency of analysis of endogenous plant hormones strongly depends on the detection sensitivity of the method. Our analytical approach will be useful for in-depth studies on complex plant hormonal metabolism.