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Mesocotyl elongation is a key trait influencing seedling emergence and establishment in direct-seeding rice cultivation. The phytohormone gibberellin (GA) has positive effects on mesocotyl elongation in rice. However, the physiological and molecular basis underlying the regulation of mesocotyl elongation mediated by GA priming under deep-sowing conditions remains largely unclear. In the present study, we performed a physiological and comprehensive transcriptomic analysis of the function of GA priming in mesocotyl elongation and seedling emergence using a direct-seeding japonica rice cultivar ZH10 at a 5-cm sowing depth. Physiological experiments indicated that GA priming significantly improved rice seedling emergence by increasing the activity of starch-metabolizing enzymes and compatible solute content to supply the energy essential for subsequent development. Transcriptomic analysis revealed 7074 differentially expressed genes (false discovery rate of

In China, aflatoxin B1 (AFB1) and sterigmatocystin (STC) have been detected in rice but there is no published information on the mycobiota in toxin-contaminated rice samples. Occurrence of AFB1 and STC was evaluated in 100 rice samples. Out of 78 samples of polished rice, 12 and 23 samples had detectable levels of AFB1 and STC, respectively, at mean levels of 0.14 μg/kg and 0.39 μg/kg, respectively. The highest level of STC in polished rice was 2.76 μg/kg in a sample from Hubei province; out of 22 samples of unhusked rice, STC was detected in 12 samples at a mean level of 0.91 μg/kg; however, only one sample contained detectable amounts of AFB1 at a level of 0.2 μg/kg. Seven samples that were positive for both AFB1 and STC were selected and evaluated for the presence of mycobiota; species of Aspergillus and Penicillium predominated. Twelve species of Penicillium and fifteen species of Aspergillus were isolated, of which P. fellutanum and A. candidus were the most frequently found. Further studies are now required to determine which of these species produce AFB1 and STC.

Leaf size is an important agronomic trait directly affecting yield in rice, and thus understanding the genes determining leaf size is important in breeding. In this study, one Leaf Mutant 7 (lm7) with small leaf size was isolated using ethyl methane sulphonate (EMS) mutagenesis from the japonica Zhenggeng 1925. MutMap by whole genome resequencing of phenotypic bulks revealed that LM7 is likely located in the 133 kb region on chromosome 7 using F2 population from a cross between lm7 and wild-type (WT) Zhenggeng 1925. The candidate gene encoding heat shock protein OsHSP40 for LM7 was functionally validated. Disruption of this gene in Oshsp40 mutants significantly reduced the leaf size compared with that of WT in rice. Microscopic examination showed that OsHSP40 modulated leaf size via regulating the veins formation and cell size/cell number. Nucleotide diversity analysis indicated that a single nucleotide polymorphism (SNP) variation of C to T in the coding region of OsHSP40 may cause small leaves among rice accessions. Therefore, the natural variation of OsHSP40 contributing to leaf size might be useful for rice breeding.

Nitrogen (N) speciation could influence the efficiency of Cd accumulation by plants grown in Cd-contaminated areas. However, limited information has been reported on how the application of N speciation to rice affects the Cd accumulation. Here, we investigated the physiological and genetic mechanisms involved in Cd uptake by roots, xylem translocation and subsequent Cd accumulation in rice (Oryza sativa L.) affected by different NO3−/NH4+ ratios under low-and-high Cd stress. Results showed that both N speciation and Cd stress affected plant growth, with high NH4+-N ratios treatments having higher tissue biomass, and high Cd treatment reducing tissue biomass. The Cd concentrations in shoots and roots were reduced with the increasing NH4+-N ratios (except for the full NO3−-N treatment), but did not affect the Cd translocation factor (TF). The total Cd accumulation of the whole plant were also reduced with the high NH4+-N ratios (NO3−/NH4+, 1:2 and 0:1) on the low Cd treatment due to the decline both in the Cd accumulation of shoots and roots. A scanning ion-selective electrode technique (SIET) showed that the net Cd2+ influxes at the root hair zone were inhibited with the increasing NH4+-N ratios in absence or pretreatment with different NO3−/NH4+ ratios. Additionally, the Cd concentrations in xylem sap were also displayed a decline trend with the increasing NH4+-N ratios under two dose Cd treatments. Furthermore, the gene expression related to Cd uptake (OsIRT1 and OsNRAPM5) and transport (OsHMA2) in roots showed the familiar tendencies with those of Cd uptake and transport at the physiological level treated with different NO3−/NH4+ ratios under two dose Cd treatments. It is concluded that increasing ammonium nutrition contributes to the inhibition of Cd uptake, xylem transport and subsequent accumulation in rice.

Organoarsenic arsanilic acid (ASA) contamination of paddy soil is a serious but less concerned hazard to agriculture and health of people consuming rice as staple food, for rice is one major pathway of arsenic (As) exposure to human food. To date little research has studied the effect of ASA on biochemical process of rice. Silicon (Si) application is able to reduce the toxicities of heavy metals in numerous plants, but little information about ASA. This work investigated whether and how Si influenced alleviation of ASA toxicity in rice at biochemical level to have a better understanding of defense mechanism by Si against ASA stress. Results showed that ASA reduced rice growth, disturbed protein metabolism, increased lipid peroxidation but decreased the efficiencies of antioxidant activities compared to control plants, more severe in roots than in shoots. The addition of Si in ASA-stressed rice plants noticeably increased growth and development as well as soluble protein contents, but decreased malondialdehyde (MDA) contents in ASA-stressed rice plants, suggesting that Si did have critical roles in ASA detoxification in rice. Furthermore, increased superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activities along with elevated glutathione (GSH) and ascorbic acid (AsA) contents implied the active involvement of ROS scavenging and played, at least in part, to Si-mediated alleviation of ASA toxicity in rice, and these changes were related to rice genotypes and tissues. The study provided physio-chemical mechanistic evidence on the beneficial effect of Si on organoarsenic ASA toxicity in rice seedlings.

Clausena lansium (Lour.) Skeels (Rutaceae) is a natural bioactive plant. Its roots, stems, leaves, and seeds are widely used in Chinese traditional and folk medicine. Although the characterization and functional analysis of bioactive components in Clausena lansium (Lour.) Skeels has been widely reported, the spatial distribution of these compounds within the main plant tissues remains undefined. Here, we adopted matrix-assisted laser desorption/ionization-mass spectrometry imaging (MALDI-MSI) to reveal the spatial distribution of active alkaloids, coumarins, sugars and organic acids in C. lansium. Using a combined wet and dry matrix covering method to enhance sensitivity, we detected alkaloids throughout the fruit including 3-methylcarbazole and murrastinine which were especially rich in the kernel tissues but were restricted to the stem xylem and medulla and in the leaf epidermal region. Interestingly, murrayanine and heptaphylline were mainly found in pulp tissues with very low content in the stems and leaves while girinimbine was only distributed within the outer kernel skin. Coumarins were mainly distributed in the fruit pericarp and leaf vein tissues but with no clear spatial specificity in stems. Lastly, hexoses were mainly evident in the fruit pulp, although sucrose was also found in the pericarp, pulp, and pulp fibers with citric acid being distributed throughout the fruit. The accurate spatial and chemical information obtained provides new insights into the specific accumulation of metabolites in individual tissues.

Arsenic (As) is ubiquitously present in the environment. The toxicity of As is related to its forms. This study was designed to compare the translocation and transformation of four As species from soil to rice, and metabolism in rats for four arsenic species. A set of 26550 data was obtained from pot experiments of rice plants grown in soil fortified with four As species, and 4050 data were obtained from rat experiments in which 81 rats were administered with the four As species. The total As in grain from the methyl arsenate fortified soil was 6.1, 4.9, and 5.2 times that from As(III), As(V), and dimethyl arsenate fortified soil, respectively. The total As in husk was 1.2-7.8 times greater than that in grain. After oral administration of each As species to rats, 83-96% was accumulatively excreted via feces and urine, while 0.1-16% was detected in blood. The translocation, transformation, and metabolism of different forms of arsenic vary greatly.

Silicon (Si) and selenium (Se) are generally considered as contributing elements for plant resistance to abiotic stresses, especially for those in heavy-metal stressed environments. However, the mechanisms underlying the different roles of Si and Se in mitigating cadmium (Cd) stress in flowering Chinese cabbage ( Brassica campestris L. ssp. chinensis var. utilis ) are still poorly understood. Here, we investigated the comparative responses to Si and Se in relation to antioxidant enzyme system and the glutathione-ascorbate cycle in flowering Chinese cabbage plants under Cd stress. Addition of Si and/or Se at equivalent concentrations alleviated Cd toxicity as demonstrated by increasing plant tissue (shoots and roots) biomass and reducing plant tissue (leaves and roots) concentrations of malondialdehyde (MDA) and hydrogen peroxide (H 2 O 2 ) in plants exposed to high Cd stress. Additionally, in comparison with the high Cd-alone treatment, the application of Si and/or Se significantly increased the activities of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX), while no differences in the size of these effects between Si and Se were observed at equal concentrations, suggesting that these three antioxidant enzymes were not the key factors involved in differences of Cd detoxification between Si and Se. Furthermore, the single addition of Se or in combined with Si markedly stimulated the efficiency of the GSH-AsA cycle by increasing the concentrations of glutathione (GSH) and ascorbate (AsA) as well as the activities of glutathione reductase (GR) and dehydroascorbate reductase (DHAR) in plant tissues (leaves and roots), especially at high dose, while little changes were observed in the Si-alone treatment, indicating that Se has the greater ability of increasing the efficiency of GSH-AsA cycle rather than of Si exposed to Cd stress. Overall, our results reveal that Se-mediated alleviation of Cd toxicity is due to increasing antioxidant enzyme activities and the GSH-AsA cycle efficiency. However, Si mitigation may involve other mechanisms apart from increasing antioxidant enzyme activities.

Silicon (Si) and selenium (Se) are generally considered as beneficial elements for the growth of higher plants, especially for those grown in heavy-metal stressed environments. However, the mechanisms underlying the roles of Si and Se in mitigating cadmium (Cd) stress in flowering Chinese cabbage (Brassica campestris L. ssp. chinensis var. utilis) are still poorly understood. Here, we investigated the comparative responses to Si and Se in relation to Cd uptake, compartmentation in roots, and xylem transport in flowering Chinese cabbage plants under Cd stress. Addition of Si or/and Se efficaciously alleviated the toxicity of Cd as demonstrated by increasing of tissue (shoots and roots) biomass of plants exposed to high Cd stress, especially for their coupling treatments with high doses. In compare with the Cd-alone treatment, the application of Si alone or in combination with Se greatly decreased plant shoot Cd concentrations as well as its translocation factor (TF), though the Cd concentrations in roots and the total Cd accumulation of whole plants showed increasing trends (especially for the treatments of high Si or coupling with Se), while no marked differences were found in plants exposed to the Se-alone treatment. Additionally, the application of Si alone or in combination with Se considerably reduced the Cd concentrations and its proportions in symplast and apoplast root saps and increased them in cell wall fragments, while little changes were observed for the Se-alone treatment. Furthermore, a greatly decreased tendency was also displayed for the Cd concentrations in xylem saps exposed to the treatments containing Si alone or in combination with Se. Overall, our results reveal that Si-mediated alleviation of Cd toxicity may be due to decreasing Cd concentrations and its proportions in symplasts and apoplasts, enhancing adsorption of Cd on cell walls, and restriction root-to-shoot Cd translocation. However, Se mitigation may involve other mechanisms.

Antimony (Sb) excess accumulation in edible parts of crops causes potential risks to human health. However, knowledge about the mechanisms of its accumulation within vegetable plants is still not well known. Here, we investigated the physiological processes of Sb involved in symplastic and apoplastic absorption, compartmentation by roots, and translocation in xylem in Brassica parachinensis L. exposed to antimonate (SbV) and antimonite (SbIII) forms. The results showed that plants treated with SbIII emerged to be more toxic than SbV as proved by the lower biomass and the higher concentrations of malonaldehyde (MDA) and hydrogen peroxide (H2O2) in plant tissues, especially at high dosages. The Sb concentration showed more in shoots but less in roots treated with SbV than with SbIII. The total Sb accumulation was higher under the SbV treatment than the SbIII treatment, mainly due to the higher accumulation in shoots. Additionally, the Sb concentration in symplastic flow of roots was higher exposed to SbV than SbIII, while no differences were found for the Sb concentration in apoplastic flow between them. Moreover, the Sb concentration in cell walls of roots was higher exposed to SbIII than SbV, especially at high levels. Furthermore, the Sb concentration in xylem was higher exposed to SbV than SbIII, and a greatly positive correlation was observed between the Sb concentrations in xylem and shoots. Overall, these findings revealed that vegetable plants accumulated more SbV than SbIII in edible parts mainly due to xylem translocation rather than root absorption.

Silicon (Si) and selenium (Se) are beneficial for many higher plants when grown on stress conditions. However, the mechanisms underlying the differential effects between foliar Si and Se in alleviation of plant toxicity exposed to cadmium (Cd) stress are remained unclear. In this study, we investigated the discrepant mechanisms of foliar Si and Se on Cd absorption and compartmentation by roots, its translocation in xylem, and the antioxidant system within Chinese flowering cabbage (Brassica campestris L. ssp. chinensis var. utilis) under low and high Cd stress. Results showed that plant growth was significantly enhanced by foliar additions of Si or/and Se according to an increased plant tissue biomass at high Cd exposure. In addition, the foliar coupled addition of Si and Se showed little effects on the concentrations of Si or Se in plant tissues in comparison with the single addition of foliar Si or Se respectively. The foliar Si alone or combined with Se markedly reduced the Cd concentrations in plant shoots under two Cd treatments. This might be explained by the lower Cd concentrations in symplast and apoplast and the higher Cd concentrations in cell walls of plant roots, and the lower Cd concentrations in xylem sap. However, no great changes in these values were observed under the treatments of foliar Se alone. Moreover, the foliar additions of Si or/and Se all increased the antioxidant enzyme activities of SOD, CAT and APX in plant tissues, especially at high Cd dosage. No significant differences in the increasing degrees of these three antioxidant enzymes were found between the foliar Si and Se treatments. However, only the foliar Se alone or combined with Si markedly promoted the antioxidant enzyme activities of GR and DHAR in plant tissues. Our findings demonstrate that the alleviation of Cd toxicity by foliar Si maybe mainly responsible for inhibition of Cd absorption and its translocation to plant shoots, reinforcing its compartmentation into root cell walls, whilst enhancing the antioxidant enzyme system may be employed by foliar Se.

Arsenic speciation in paddy rice is of considerable interest due to its impact on the food safety and human health. In this study, a simple methodology was developed to simultaneously extract and analyze As species in rice from China. Arsenic species, including arsenite (As(III)), arsenate (As(V)), dimethylarsinic acid (DMA), and monomethylarsonic acid (MMA), were extracted by methanol-water (50:50, v/v) containing 0.02 mol L−1 nitric acid with a microwave-assisted procedure, and then determined by high performance liquid chromatography–hydride generation-atomic fluorescence spectrometry (HPLC–HG-AFS). The results showed that the method has good efficiency (>90%) for rice, indicating that there were no significant losses or transformations of arsenic during sample treatment and analysis. The limits of quantification (LOQ) of the method were 8.0, 20, 12, and 12 ng g−1 for As(III), As(V), DMA, and MMA, respectively. When this method was applied to the analysis of rice, As(III) had the highest concentration,...

In previous studies, inorganic arsenic and total arsenic concentrations in rice bran have been much higher than those in polished rice obtained from the same whole paddy rice. However, the arsenic species distribution between rice and bran is still unknown, especially for arsenite (AsIII) and arsenate (AsV). To characterize the arsenic species in rice and bran and explain the elevated concentrations of inorganic arsenic and total arsenic, four arsenic species, AsIII, AsV, dimethylarsinic acid, and monomethylarsonic acid, were evaluated. Rice and bran samples (n = 108) purchased from local markets in the People's Republic of China were analyzed using high-performance liquid chromatography with hydride generation and atomic fluorescence spectrometry and then microwave extraction. As expected, most of the arsenic was found in bran, with bran/rice ratios of 6.8 for total arsenic species and 6.4 for inorganic arsenic. Among four arsenic species, the maximum bran/rice ratio was 104.7 (335/3.2 μg kg(-1)) for AsV followed by 1.2 (69.2/56.1) for AsIII, 1.3 (6.7/5.2) for dimethylarsinic acid, and 4.0 (0.8/0.2) for monomethylarsonic acid. Thus, the large difference in arsenic concentration between rice and bran was mostly due to the difference in the AsV concentration, which account for 96 and 95 % of the difference for total arsenic species and inorganic arsenic, respectively. Therefore, the possibility of AsV contamination in rice bran and its by-products needs more study. This study is the first in which concentrations of AsIII and AsV in rice and bran have been documented, revealing that a higher percentage of AsV occurs in bran than in rice.

P-arsanilic acid (AsA) is a emerging but less concerned contaminant used in animal feeding operations, for it can be degraded to more toxic metabolites after being excreted by animals. Rice is the staple food in many parts of the world, and also more efficient in accumulating arsenic (As) compared to other cereals. However, the uptake and transformation of AsA by rice is unclear. This study aimed to evaluate the potential risk of using AsA as a feed additive and using the AsA contaminated animal manure as a fertilizer. Five rice cultivars were grown in soil containing 100mg AsA/kg soil, after harvest, As species and their concentrations in different tissues were determined. Total As concentration of the hybrid rice cultivar was more than conventional rice cultivars for whole rice plant. For rice organs, the highest As concentration was found in roots. AsA could be absorbed by rice, partly degraded and converted to arsenite, monomethylarsonic acid, dimethylarsinic acid, arsenate. The number of As species and their concentrations in each cultivar were related to their genotypes. The soil containing 100mg AsA/kg or more is unsuitable for growing rice. The use of AsA and the disposal of animal manure requires detailed attention.

This study investigates the dissipation and residue of a metalaxyl and dimethomorph mixed formulation in grape and soil. A high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) analytical method was developed to determine the residue of metalaxyl and dimethomorph in grape and soil. The results showed that the average recoveries are in the range of 86.84 percent to 97.30 percent. The dissipation rate of metalaxyl in grape (with half life of 4.9 days) was faster than in soil (with half life of 8.7 days). The dissipation rates of E- and Z-isomers of dimethomorph in grape were almost the same (with half lives of 9.0 and 9.8 days, respectively). However, the dissipation rate of the E-isomer in soil was much faster than that of the Z-isomer (with half lives of 10.3 and 31.5 days, respectively). Moreover, the terminal residue of metalaxyl and dimethomorph were significantly below the available maximum residue limits (MRL). However, a difference was observed between the concentration of the Z- and E-isomers either in grape or soil. The ratio of E-isomer to Z-isomer in grape was higher than in soil, which may due to the different water solubilities and polarities of the two isomers.

A residue analytical method to detect pyrimethanil in tomatoes and soil was developed by using high-performance liquid chromatography with a diode array detector. The dissipation and residue level of pyrimethanil in tomatoes and soil were also investigated. Results showed that the average recoveries are in the range of 87.2 to 90.0 % with a relative standard difference of 2.22 to 7.61 % in tomatoes and soil. In Guangdong, Shandong, and Yunnan, the half-lives of pyrimethanil in tomatoes were 1.8, 3.6, and 4.2 days and those in soil were 4.0, 3.3, and 3.9 days, respectively. The dissipation rate of pyrimethanil in tomatoes and soil was affected by temperature, precipitation, and soil type. The terminal residue results showed that when pesticide pyrimethanil was used under the experiment design, all the results were far below the available maximum residue limits. Low residues in tomatoes and soil suggest that this pesticide is safe to use under the recommended dosage.

A method was developed for simultaneously determination of four arsenic speciation including trivalent arsenic (As (III)), pentavalent arsenic (As (V)), monomethylarsinic acid (MMA) and dimethylarsinic acid (DMA) in fruits and vegetables. Arsenic speciation in samples were extracted with methanol/water (50/50, v/v) after samples were dried at 105°C, and then detected by high performance liquid chromatography-hydride generation-atomic fluorescence spectrometry (HPLC-HG-AFS). The recoveries of four arsenic speciation were 81.7%∼103.9% with RSD of 0.88%∼5.03%, and detection limits were 0.8∼2.0 µg/kg. This indicates that the developed method has good accuracy and high sensitivity. The method was then applied to detect eleven types of fruits and vegetables samples randomly purchased from supermarkets. The analytical results showed that the main arsenic speciation were As (III) and As (V) in vegetables and As (III) in fruits. The concentrations of As (III) in vegetables were obviously higher than those in fruits.