Insight of low-abundance proteins in rice leaves under Cd stress using combinatorial peptide ligand library technology.

Low-abundance proteins (LAPs) play a very important role in interaction, regulation, and metabolism of plant biological processes. A combinatorial peptide ligand library (CPLL) can solve the problem of high-abundance proteins (HAPs) masking LAPs and enlarging the dynamic range of protein concentrations perfectly and be considered as one of the most advanced approaches for plant proteomics research. In this paper, a proper CPLL method to rice leaf proteins was established for the first time and 1056 proteins were identified in rice leaf extracts, and 624 (59.1%) LAPs were newly detected after CPLL. Based on this technology, we detected the response of rice to Cd stress and analyzed the differential LAPs and the biological significance of misexpressed proteins before and after Cd stress by bioinformatics analysis. An important contribution has also been made to a better understanding of the complex mechanisms by which rice adapts to Cd stress. Graphical abstract.

Dissipation of two field-incurred pesticides and three degradation products in rice (Oryza sativa L.) from harvest to dining table.

BACKGROUND: High levels of harmful pesticide residues in rice can cause undesirable side effects and are a source of great concern to consumers. Reduction of pesticide residues to provide rice security has thus became an urgent problem. RESULTS: In this study, the effects of commercial and home processing on removal of chlorpyrifos and carbosulfan residues from rice, and the formation of metabolites during processing, were studied. The results showed that 3,5,6-trichloro-2-pyridinol (0.87 mg kg-1 ) and carbofuran (0.43 mg kg-1 ) were the predominant components detected in paddy rice. All detected residues were primarily deposited on the rice hull and bran. Washing twice followed by high-pressure cooking was able to further decrease residues in polished rice with the processing factor value <0.25. Following application of pesticides at the recommended rate and twice the recommended rate, with a preharvest interval of 28 days, changes in residues from harvest to dining table based on efficient processing techniques were investigated. The final residues dropped to below maximum residue levels after washing twice followed by high-pressure cooking. CONCLUSION: This simple cooking process thus reduces the risk of dietary exposure, and it is recommended that it is adopted by all consumers. © 2019 Society of Chemical Industry.

Analysis of bronopol (2-bromo-2-nitropropan-1, 3-diol) residues in rice (Oryza sativa L.) by SPE using Bond Elut Plexa and liquid chromatography-tandem mass spectrometry.

A novel method has been developed for the direct, sensitive, and rapid detection of bronopol in rice using a simple solid-phase extraction (SPE) procedure followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS), with electrospray ionization (ESI). Bronopol was stable under acidic conditions, and an acidic environment was thus needed before sample loading to ensure the stability of bronopol. Rice extracts containing bronopol were pretreated using a hydrophilic-lipophilic balanced (Bond Elut Plexa) cartridge to reduce the matrix effect. An XDB-C18 column (150 mm × 2.1 mm, 3.5 µm) was used for chromatographic separations, with a mobile phase comprising methanol and aqueous ammonium formate (5 mM). The linearity of the method was satisfactory with regression coefficient (R 2) = 0.9992. The limit of quantification was 3.3 µg kg-1. Three spiked levels (25, 125 and 625 µg kg-1) were used to determine the recovery of bronopol, which was found to be 73.3-96.7%, with relative standard deviations (RSD) in the range 1.2-7.9%. The RSD for intra-day precision (n = 7) was 7.6% and the RSD for inter-day precision (n = 15) was 8.3%. The newly developed analytical method was successfully used to quantify bronopol in rice samples.

Correction to: Analysis of bronopol (2-bromo-2-nitropropan-1,3-diol) residues in rice (Oryza sativa L.) by SPE using Bond Elut Plexa and liquid chromatography-tandem mass spectrometry.

The authors would like to call the reader's attention to the fact that unfortunately during a recent cross-check of the experimental record, they found that the positions of intercept and slope were reversed in Table 1 in the original manuscript. The authors apologize for the mistake.

Separation of selenium species and their sensitive determination in rice samples by ion-pairing reversed-phase liquid chromatography with inductively coupled plasma tandem mass spectrometry.

A highly sensitive method was developed for the simultaneous separation and determination of organic and inorganic selenium species in rice by ion-pairing reversed-phase chromatography combined with inductively coupled plasma tandem mass spectrometry. To achieve a good separation of these species, a comparison between anion-exchange chromatography and ion-pairing reversed-phase chromatography was performed. The results indicated that ion-pairing reversed-phase chromatography was more suitable due to better separation and higher sensitivity for all analytes. In this case, a StableBond C18 column proved to be more robust or to have a better resolution than other C18 columns, when 0.5 mM tetrabutylammonium hydroxide and 10 mM ammonium acetate at pH 5.5 were used as the mobile phase. Moreover, an excellent sensitivity was obtained in terms of interferences by means of tandem mass spectrometry in the hydrogen mode. The detection limits were 0.02-0.12 µg/L, and recoveries of five selenium species were 75-114%, with relative standard deviations ≤ 9.4%. This method was successfully applied to the analysis of rice samples. Compared with previous studies, the proposed method not only gave comparable results when used for measuring selenium-enriched rice, but it can provide greater sensitivity for the detection of low concentrations of selenium species in rice.

An aquaporin gene MdPIP1;2 from Malus domestica confers salt tolerance in transgenic Arabidopsis.

Aquaporins are known as water channel proteins. In this study, an aquaporin gene MdPIP1;2 was cloned from Malus domestica cv. Qinguan encoding a protein of 289 amino acids that formed the typical structure of aquaporin by six transmembrane domains, two asparagine-proline-alanine motifs, aromatic/arginine filter, and Forger's position. MdPIP1;2 was highly expressed in the water-sensitive or water-requiring tissues, and upregulated by salt and PEG stresses. MdPIP1;2 transgenic Arabidopsis exhibited enhanced salt stress tolerance with less Na + accumulation, lower malondialdehyde (MDA) content, lower electrolyte leakage (EL) level, and higher superoxide dismutase (SOD) and peroxidase (POD) activities compared with WT plants. Additionally, transcriptome analysis indicated MdPIP1;2 transgenic Arabidopsis could present healthier growth and development condition probably through regulating morphological structures and accumulating specific secondary metabolites under salt stress. Our results are a useful reference for better understanding the biological function of aquaporin in apple tree, especially in plant response to abiotic stress.

[Two-dimensional liquid chromatography separation and high resolution mass spectrometry analysis for proteome of rice leaves based on different extraction methods].

A two-dimensional liquid chromatography (2D LC) system was developed to separate proteins from rice leaves, which was extracted by phenol method, followed by the analysis with linear trap quadrupole orbitrap mass spectrometry (LTQ/Orbitrap MS). After proteins were extracted with phenol method, the enzymolytic peptides were separated by offline two-dimensional RP-RP system and detected by LTQ/Orbitrap MS, yielding 2712 proteins. Liquid chromatography separation system (1D LC and 2D LC) and protein extraction methods (phenol method, sodium dodecyl sulfate method (SDS method) and trichloroacetic acid/acetone method (TCA/acetone method)) were compared. Proteins identified by 2D LC were 2712, 2415 and 1914 with the above three extraction methods, respectively. The proteins were 2.7-fold, 2.5-fold and 1.9-fold the number of proteins identified by 1D LC respectively. And in terms of 2D LC, the proteins identified by phenol method were 297 and 798 more than SDS method and TCA/acetone method, respectively. Some proteins with extreme properties, such as very acidic or basic protein and high relative molecular mass proteins, were only identified in phenol method. Furthermore, proteins, which were extracted by different extraction methods and separated by 2D LC, were classified according to biological functions. It was found that protein functions by the three extraction methods were complementary. However, phenol method had the most variety of functions. The method provides technological support for rice proteomics and reference for research techniques of other crop proteomics.

Analysis of four sulfonylurea herbicides in cereals using modified Quick, Easy, Cheap, Effective, Rugged, and Safe sample preparation method coupled with liquid chromatography-tandem mass spectrometry.

A modified Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) sample preparation method, coupled with liquid chromatography-electrospray ionization tandem mass spectrometry, has been developed for the simultaneous analysis of four commonly used sulfonylurea herbicides, ethoxysulfuron, halosulfuron-methyl, mesosulfuron-methyl and orthosulfamuron, in rice, maize, wheat and soybean. Adsorption of the analytes onto the primary-secondary amine used in the clean-up step was avoided by using 1% formic acid in acetonitrile as the extraction solvent to maintain the acidic herbicides in a non-ionized state. Trueness studies were carried out at three levels (2.5, 25 and 250 µg/kg for ethoxysulfuron and 5, 50 and 500 µg/kg for the other three analytes). Promising trueness (70.2%-119.8%) was achieved for all herbicides in all matrices after clean-up, with relative standard deviations (RSDr) < 18.6%. Satisfactory matrix effects (-19.7% to 14.8%) were also obtained. Good linearity of the calibration curves was achieved, with determination coefficients (r) ≥ 0.9956, when the concentration of ethoxysulfuron was in the range 0.5-50 µg/L and that of the other three analytes was in the range 1.0-500 µg/L. The RSDwR for within-laboratory reproducibility was 5.7%. The validated method was successfully used to analyze real samples.

[Determination of pyriminobac-methyl and bispyribac-sodium residues in rice by liquid chromatography-tandem mass spectrometry based on QuEChERS].

A method was developed for the determination of pyriminobac-methyl and bispyribac-sodium residues in rice by liquid chromatography-tandem mass spectrometry (LC-MS/MS) coupled with modified QuEChERS. The samples were extracted with acidified acetonitrile, and then purified by octadecylsilane bonded silica (C18) adsorbents. The analytes were separated on a ZORBAX SB C18 column through a gradient elution using 0.1% (v/v) aqueous formic acid aqueous containing 5 mmol/L ammonium acetate and acetonitrile as mobile phases. Positive electrospray ionization (ESI+) was used. Qualitative work was performed using selected dynamic multiple reaction monitoring (dynamic MRM) mode. Quantization was performed using external standard method. The results showed good linearities of pyriminobac-methyl and bispyribac-sodium with correlation coefficients (r2) not less than 0.996. The limits of detection (LODs) of the method were 0.8 µ g/kg for pyriminobac-methyl, and 3 µ g/kg for bispyribac-sodium. The mean spiked recoveries of pyriminobac-methyl and bispyribac-sodium at three spiked levels were 76.6%-85.6% and 73.0%-86.7%, respectively, and the relative standard deviations (RSDs) of pyriminobac-methyl and bispyribac-sodium were 0.9%-3.4% and 1.2%-5.5%, respectively. This method is simple, rapid, sensitive, and suitable for the simultaneous determination of pyriminobac-methyl and bispyribac-sodium in rice.