A low iridium content greatly improves the peroxidase-like activity of noble metal nanozymes for sensitive colorimetric detection.

The enzyme-like activity of noble metal nanomaterials has been widely demonstrated. However, as an important noble metal, iridium (Ir) and its alloy nanomaterials have been less studied, particularly regarding the effect of Ir content on enzyme-like activity. Here, we demonstrated for the first time that a low Ir content can greatly improve the peroxidase-like activity of Pt-based nanozymes. When the weight percentage of Ir was 3.45% in trimetallic PtAuIr hollow nanorods (HNRs) and 2.86% in bimetallic PtIr HNRs, their specific activity increased by approximately 70% compared to their PtAu and Pt counterparts, respectively. However, a slightly higher percentage of Ir significantly diminished the enhancement effect on their specific activity. Density functional theory (DFT) calculations show that the rate-determining step (RDS) energy barrier of the nanozyme with low Ir content is lower than that of the nanozyme with slightly higher Ir content. Furthermore, we studied the kinetic properties of the PtAuIr nanozyme using TMB as the substrate. Its Michaelis-Menten constant (Km) and Vmax were 1.756 mM and 2.152 × 10-6 M s-1, respectively. Additionally, a colorimetric detection platform based on the PtAuIr nanozyme was established and applied to detect o-phenylenediamine (OPD), with a detection limit as low as 0.076 µM. This study highlights the important role of the Ir content in Pt-based nanozymes and demonstrates that PtAuIr nanozymes have potential applications in environmental detection.

Structural engineering of Pt-on-Rh hollow nanorods with high-performance peroxidase-like specific activity for colorimetric detection.

The preparation of nanozymes with high specific activity is highly important for various applications. However, only a few nanozymes have specific activities comparable to natural enzymes. Herein, novel Pt-on-Rh hollow nanorods (PtRh HNRs) were developed, in which surface Pt exhibited adjustable dispersity and interior Rh served as the support. The optimized PtRh HNRs demonstrated high-performance peroxidase (POD)-like activity, with a specific activity as high as 1352 U mg-1, which was 3.86 times that of their monometallic Pt counterparts. Density functional theory (DFT) calculations illustrated that the presence of Rh decreased the energy barrier of the rate-determining step. When PtRh HNRs were used as nanozymes in the colorimetric detection of hydrogen peroxide (H2O2) and ascorbic acid (AA), the limits of detection (LODs) were as low as 9.97 µM and 0.039 µM, respectively. The current work highlights a facile and powerful strategy for manufacturing nanozymes with high specific activity and demonstrates that the prepared PtRh HNRs have the potential for analysis and determination.

Galvanic replacement synthesis of PtPdAu hollow nanorods as peroxidase mimic with high specific activity for colorimetric detection.

Noble metal nanomaterials have been widely demonstrated to possess intrinsic enzyme-like properties and have been increasingly applied in the fields of analysis and biomedicine. However, current exploration of high-activity noble metal nanozymes is still far from adequate. The construction of hollow structures and adjustment of their elemental composition are effective ways to improve the specific activity (SA) of nanozymes. In this study, trimetallic PtPdAu hollow nanorods (HNRs) were developed using a galvanic replacement reaction and Kirkendall effect. The catalytic experiment showed that the PtPdAu HNRs possessed outstanding peroxidase-like performance and their SA value was up to 563.71 U mg-1, which is remarkable among various previously reported nanozymes and higher than that of monometallic or bimetallic counterparts with similar structure and size prepared in this study. Electron paramagnetic resonance (EPR)measurements showed that the PtPdAu HNRs could contribute to the formation of hydroxyl radicals (˙OH) in catalyzing hydrogen peroxide. When using PtPdAu HNRs as a nanozyme in the colorimetric detection of H2O2 and ascorbic acid (AA), the limits of detection were as low as 1.8 µM and 0.068 µM, respectively. This study demonstrates that PtPdAu HNRs are high-activity nanozymes and have the potential to be applied in the field of analysis.

Identification of Salt Stress-Responsive Proteins in Maize (Zea may) Seedlings Using iTRAQ-Based Proteomic Technique.

BACKGROUND: Soil salinity is a major abiotic stress that limits plant growth and yield worldwide. OBJECTIVE: To better understand the mechanism of salt stress adaptation in maize (Zea may), proteomic analysis of maize responses to salt stress were analyzed in seedling. MATERIALS AND METHODS: Taking maize seedlings untreated and treated with NaCl for 24 h as material, isobaric tags for relative and absolute quantitation (iTRAQ) were used to analyze the protein expression profile of maize seedlings after salt stress. RESULTS: The result showed that 270 differentially expression proteins (DEPs) were identified in maize seedlings after salt stress. The majority proteins had functions related to translation, ribosomal structure and biogenesis (15%), posttranslational modification, protein turnover, chaperones (14%) and others metabolism. Quantitative real-time PCR analysis showed that the EF-Tu, peroxiredoxin, FoF1-type ATP synthase, glutamate dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase, Acetyl-CoA acetyltransferase and nucleoside diphosphate kinase genes were up-regulated in the adaptation of maize to salt stress. CONCLUSIONS: The coped with salt stress of maize seedlings might be included nitrogen and glutamate (Glu) metabolism and energy homeostasis, nucleotide transport and metabolism, soluble sugar, fatty acid and nucleoside triphosphates synthesis. Moreover, the enhancement of plant to scavenge ROS, such as peroxiredoxin, might play significant roles in the adaptation of maize to salt stress.Taken together, these proteins might have important roles in defense mechanisms against salt stress in maize.We hope that this study provides valuable information for the further utilization and study on the molecular mechanisms of defense mechanisms in maize.

Cloning and Expression Analysis of ZmERD3 Gene From Zea mays.

BACKGROUND: Stresses (such as drought, salt, viruses, and others) seriously affect plant productivity. To cope with these threats, plants express a large number of genes, including several members of ERD (early responsive to dehydration) genes to synthesize and assemble adaptive molecules. But, the function of ERD3 gene hasn't been known so far. OBJECTIVES: The purpose of the present study was to clone the stress-resistance gene: ZmERD3, and to analyze its expression pattern in the maize plant organs at different stages and under various stress treatments. MATERIALS AND METHODS: MaizeGDB database search together with the bioinformatics analysis led to the identification of ZmERD3 gene in Zea mays. The cDNA sequence and promoter of ZmERD3 gene were obtained through PCR. Bioinformatics analysis was performed through online tools. The tissue-specific expression profile of the ZmERD3 gene in maize plant was carried out using the quantitative real time PCR (qRT-PCR) technique and its expression pattern in response to stress treatments (such as PEG, NaCl, ABA, and low temperature) was also analyzed through qRT-PCR method. RESULTS: Based on the homology alignment with AtERD3 (XP_002867953) in MaizeGDB (http://www. maizegdb.org/), the cDNA sequence and promoter region of the ZmERD3 gene were obtained. The bioinformatic analysis showed that ZmERD3 protein has one specific hit of methyltransferase and a high probability of location in the cytoplasm, and there are many cis-regulatory elements responsive to light, heat, cold, dehydration, as well as other stresses in its promoter sequence. Expression analysis revealed that the amount of ZmERD3 mRNA is different in all indicated organs of the maize plant. In addition, the ZmERD3 expression could be induced by abiotic stress treatments. Compared to the control, treatment with NaCl or PEG-6000 could significantly enhance the expression ability of ZmERD3 gene. As well, its expression level was increased about 20 times above the control after exposure to NaCl and PEG-6000 treatments for 3-6 h. CONCLUSIONS: One putative methyltransferase gene, ZmERD3 was cloned. ZmERD3 expression exhibited an obvious tissue-specificity, and its expression could make a significant response to NaCl and PEG-6000 treatments.

Bioinformatics Analysis of NBS-LRR Encoding Resistance Genes in Setaria italica.

In plants, resistance (R) genes are involved in pathogen recognition and subsequent activation of innate immune responses. The nucleotide-binding site-leucine-rich repeat (NBS-LRR) genes family forms the largest R-gene family among plant genomes and play an important role in plant disease resistance. In this paper, comprehensive analysis of NBS-encoding genes is performed in the whole Setaria italica genome. A total of 96 NBS-LRR genes are identified, and comprehensive overview of the NBS-LRR genes is undertaken, including phylogenetic analysis, chromosome locations, conserved motifs of proteins, and gene expression. Based on the domain, these genes are divided into two groups and distributed in all Setaria italica chromosomes. Most NBS-LRR genes are located at the distal tip of the long arms of the chromosomes. Setaria italica NBS-LRR proteins share at least one nucleotide-biding domain and one leucine-rich repeat domain. Our results also show the duplication of NBS-LRR genes in Setaria italica is related to their gene structure.

Characterization and functional analysis of a B3 domain factor from Zea mays.

In this study, we isolated a full-length cDNA and named ZmBDF from zea mays. ZmBDF encoded a protein of 356 amino acids and phylogenetic analysis showed that it belongs to a closely related subgroup with B3 domain factors in plants. The transcript level of ZmBDF could be induced by ABA, MeJA, salt or drought treatments. To further investigated the function of ZmBDF, ZmBDF over-expression transgenic lines were got by transforming it into Arabidopsis thaliana. ZmBDF over-expression transgenic plants in Arabidopsis could increase drought and salt tolerant in germination assay. Under drought condition, net photosynthetic rates (PN), stomatal conductance (gs), and internal leaf CO2 concentration (Ci) were less affected in transgenic plants compared with wild type. Besides, the chlorophyll a and chlorophyll b (chl a/chl b) ratio decreased in WT plants than the transgenic plants and total carotenoid content show opposite trends. Moreover, transgenic plants could also reduce the stomatal density and changed the stomatal shape. Taken together, our data suggested that ZmBDF could improve stress tolerance to drought and salt in maize.