Determination of 1-aminocyclopropane-1-carboxylic acid and its structural analogue by liquid chromatography and ion spray tandem mass spectrometry

The dependence of leaf senescence on the balance between 1-aminocyclopropane-1-carboxylate acid synthase 1 (ACS1)-catalysed ACC generation and nitric oxide-associated 1 (NOS1)-dependent NO accumulation in Arabidopsis

Ethylene and nitric oxide (NO) act as endogenous regulators during leaf senescence. Levels of ethylene or its precursor 1-aminocyclopropane-1-carboxylate acid (ACC) depend on the activity of ACC synthases (ACS), and NO production is controlled by NO-associated 1 (NOA1). However, the integration mechanisms of ACS and NOA1 activity still need to be explored during leaf senescence. Here, using experimental techniques, such as physiological and molecular detection, liquid chromatography-tandem mass spectrometry and fluorescence measurement, we investigated the relevant mechanisms. Our observations showed that the loss-of-function acs1-1 mutant ameliorated age- or dark-induced leaf senescence syndrome, such as yellowing and loss of chlorophyll, that acs1-1 reduced ACC accumulation mainly in mature leaves and that acs1-1-promoted NOA1 expression and NO accumulation mainly in juvenile leaves, when compared with the wild type (WT). But the leaf senescence promoted by the NO-deficient noa1 mutant was not involved in ACS1 expression. There was a similar sharp reduction of ACS1 and NOA1 expression with the increase in WT leaf age, and this inflection point appeared in mature leaves and coincided with the onset of leaf senescence. These findings suggest that NOA1-dependent NO accumulation blocked the ACS1-induced onset of leaf senescence, and that ACS1 activity corresponds to the onset of leaf senescence in Arabidopsis.

The Receptor-Like Kinase SIT1 Mediates Salt Sensitivity by Activating MAPK3/6 and Regulating Ethylene Homeostasis in Rice

High salinity causes growth inhibition and shoot bleaching in plants that do not tolerate high salt (glycophytes), including most crops. The molecules affected directly by salt and linking the extracellular stimulus to intracellular responses remain largely unknown. Here, we demonstrate that rice (Oryza sativa) Salt Intolerance 1 (SIT1), a lectin receptor-like kinase expressed mainly in root epidermal cells, mediates salt sensitivity. NaCl rapidly activates SIT1, and in the presence of salt, as SIT1 kinase activity increased, plant survival decreased. Rice MPK3 and MPK6 function as the downstream effectors of SIT1. SIT1 phosphorylates MPK3 and 6, and their activation by salt requires SIT1. SIT1 mediates ethylene production and salt-induced ethylene signaling. SIT1 promotes accumulation of reactive oxygen species (ROS), leading to growth inhibition and plant death under salt stress, which occurred in an MPK3/6- and ethylene signaling-dependent manner in Arabidopsis thaliana. Our findings demonstrate the existence of a SIT1-MPK3/6 cascade that mediates salt sensitivity by affecting ROS and ethylene homeostasis and signaling. These results provide important information for engineering salt-tolerant crops.

Determination of 1-aminocyclopropane-1-carboxylic acid in apple extracts by capillary electrophoresis with laser-induced fluorescence detection

A rapid and sensitive method for the determination of 1-aminocyclopropane-1-carboxylic acid (ACC) in apple tissues has been described. This method is based on the derivatization of ACC with 3-(2-furoyl)quinoline-2-carboxaldehyde (FQ), and separation and quantification of the resulting FQ-ACC derivative by capillary electrophoresis coupled to laser-induced fluorescence detection (CE-LIF). Our results indicated that ACC derivatized with FQ could be well separated from other interfering amino acids using 20 mM borate buffer (pH 9.35) containing 40 mM sodium dodecyl sulfate and 10 mM Brij 35. The linearity of ACC was determined in the range from 0.05 to 5 microM with a correlation of 0.9967. The concentration detection limit for ACC was 10 nM (signal-to-noise = 3). The sensitivity and selectivity of this described method allows the analysis of ACC in crude apple extracts without extra purification and enrichment procedure.

The simultaneous determination of 1-aminocyclopropane-1-carboxylic acid and cyclopropane-1,1-dicarboxylic acid in Lycopersicum esculentum by high-performance liquid chromatography--electrospray tandem mass spectrometry

Varying concentrations of cyclopropane-1,1-dicarboxylic acid (CDA), an inhibitor of 1-aminocyclopropane-1-carboxylic acid oxidase, added to the solid culture medium of tomato nodal shoot segments resulted in a reduction in the level of endogenous ethylene according to the concentration of inhibitor applied. Following treatment with inhibitor, plants were homogenised and the concentrations of CDA and of 1-aminocyclopropane-1-carboxylic acid (ACC) were measured simultaneously in the resulting juice using an HPLC-ESI/MS-MS method. The levels of CDA and ACC measured in the plant tissues were associated with the concentration of inhibitor added to the solid medium. The HPLC-ESI/MS-MS method described produced limits of detection of 0.8 pmol for ACC and of 4 pmol for CDA.

Extraction and quantitative analysis of 1-aminocyclopropane-1-carboxylic acid in plant tissue by gas chromatography coupled to mass spectrometry

We developed a new method for the determination of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) using quantitative GC-negative chemical ionisation MS as a detection and quantification system, in combination with isotope dilution using [2H4]ACC and an off-line solid-phase extraction. By derivatisation with pentafluorobenzyl bromide, ACC could easily be detected with m/z 280 being the most abundant ion. Determination of this component resulted in a detection limit of 10 fmol and a linear fit in the 100 fmol-100 pmol range. The combination of a rapid, high yield purification method with a stable derivatisation procedure and a sensitive detection method allowed the detection of ACC in samples as low as 100 mg fresh mass.

A comparative study of commercial liquid chromatographic detectors for the analysis of underivatized amino acids

This study compares the main commercial detectors that can detect amino acids in their underivatized form. The detectors tested are: the chemiluminescent nitrogen detector (CLND), the evaporative light scattering detector (ELSD), the nuclear magnetic resonance spectrometer, conductivity detector, refractive index, UV, and electrospray quadrupole mass spectrometry (in simple and tandem MS mode). As ELSD, CLND and MS require a volatile mobile phase, an ion-pair reversed-phase liquid chromatographic system was selected, consisting of an octadecyl column and an aqueous mobile phase containing pentadecafluorooctanoic acid as volatile ion-pairing reagent. Underivatized taurine, hypotaurine, aspartic acid, hydroxyproline, asparagine, serine, glycine, glutamine, cysteine, glutamic acid, threonine and alanine were simultaneously analysed with each detector. In order to test the applicability of these detectors to "real world" samples, the amino acid stoichiometry of the tetrapeptide Gly-Gly-Asp-Ala was determined with each detector after acid hydrolysis. The detectors were compared in terms of linearity, limit of detection, advantages and disadvantages as well as special features (capacity to provide structural information, specificity, quantification with single calibration curve, etc.).

Ion-pair reversed-phase liquid chromatography-electrospray mass spectrometry for the analysis of underivatized small peptides

The single run analysis of 23 small peptides (principally glycyl and lysyl dipeptides) is performed by ion-pair reversed-phase liquid chromatography coupled with evaporative light scattering detection or electrospray (tandem) mass spectrometry. Several perfluorinated carboxylic acid homologues are evaluated with an octadecyl silica stationary phase (Supelcosil ABZ+ Plus). Among the perfluorocarboxylic acids tested the nonafluoropentanoic acid and the tridecafluoroheptanoic acid gave the best results. Special attention was paid to the separation of isomer/isobar dipeptides (e.g., Gly-Ile, Gly-Leu, Leu-Gly, as well as Gly-Gln, Gly-Lys, etc.) which is usually necessary in spite of the high specificity of mass spectrometry. Before LC-MS analysis, ion-spray fragmentation as well as optimization of MS parameters of the analysed peptides was investigated. The optimum collision energy of glysyl peptides, Ala-Gln, Asp-Asp and Asp-Asp-Asp (13-18 eV) was different from that of the lysyl peptides, Tyr-Glu and oxidised glutathione (25-32 eV). Limits of detection varied from 0.1 to 1.2 mg l(-1) for simple MS and 0.05 to 25 mg l(-1) for tandem MS.

Simultaneous analysis of underivatized chiral amino acids by liquid chromatography–ionspray tandem mass spectrometry using a teicoplanin chiral stationary phase

Simultaneous chiral separations of underivatized amino acids have been performed using a teicoplanin-based chiral stationary phase and ionspray tandem mass spectrometry for their ionisation and detection. Different amino acid enantiomer pairs were separated simultaneously, including those of positional isomeric amino acids (e.g., L,D-Leu/Ile, or L,D-Val/Iva). Due to the specificity of tandem mass spectrometry, co-eluting enantiomers of different amino acids could also be determined. Fifteen chiral underivatized proteinogenic and non-proteinogenic amino acids were analysed simultaneously under isocratic conditions (acetonitrile-water, 75:25) in less than 25 min. For maximum sensitivity, post-column addition of 500 mM aqueous HCOOH was necessary. Detection limits varied from 2.5 to 50 microg l(-1) depending on the amino acid. The signal vs. concentration relationship was linear for all D- and L-amino acids (0.9995 < or = r2 < or = 1) for three orders of magnitude.