Ryegrass uptake behavior and forage risk assessment after exposing to soil with combined polycyclic aromatic hydrocarbons and cadmium.

Internalization of chemicals and the forage risks of ryegrass under the combined exposure to PAHs and Cd at environmental concentrations were studied here. The effect of soil pH was also concerned due to the widely occurred soil acidification and general alkali remediation for acidification soil. Unexpectedly, as same as the acid-treated group (pH 6.77), the alkali-treatment (pH 8.83) increased Cd uptake compared with original soil pH group (pH 7.92) for the reason of CdOH+ and CdHCO3+ formed in alkali-treated group. Co-exposure to PAHs induced more oxidative stress than Cd exposure alone due to PAHs aggregated in young root regions, such as root tips, and consequently, affecting the expression of Cd-transporters, destroying the basic structure of plant cells, inhibiting the energy supply for the transporters, even triggering programmed cell death, and finally resulting in decreased Cd uptake. Even under environmental concentrations, combined exposure caused potential risks derived from both PAHs and Cd. Especially, ryegrass grown in alkali-treated soil experienced an increased forage risks despite the soil meeting the national standards for Cd at safe levels. These comprehensive results reveal the mechanism of PAHs inhibiting Cd uptake, improve the understanding of bioavailability of Cd based on different forms, provide a theoretical basis to formulate the safety criteria, and guide the application of actual soil management.

Sorghum SbGhd7 is a major regulator of floral transition and directly represses genes crucial for flowering activation.

Molecular genetic understanding of flowering time regulation is crucial for sorghum development. GRAIN NUMBER, PLANT HEIGHT AND HEADING DATE 7 (SbGhd7) is one of the six classical loci conferring photoperiod sensitivity of sorghum flowering. However, its functions remain poorly studied. The molecular functions of SbGhd7 were characterized. The gene regulatory network controlled by SbGhd7 was constructed and validated. The biological roles of SbGhd7 and its major targets were studied. SbGhd7 overexpression (OE) completely prevented sorghum flowering. Additionally, we show that SbGhd7 is a major negative regulator of flowering, binding to the promoter motif TGAATG(A/T)(A/T/C) and repressing transcription of the major florigen FLOWERING LOCUS T 10 (SbFT10) and floral activators EARLY HEADING DATE (SbEhd1), FLAVIN-BINDING, KELCH REPEAT, F-BOX1 (SbFKF1) and EARLY FLOWERING 3 (SbELF3). Reinforcing the direct effect of SbGhd7, SbEhd1 OE activated the promoters of three functional florigens (SbFT1, SbFT8 and SbFT10), dramatically accelerating flowering. Our studies demonstrate that SbGhd7 is a major repressor of sorghum flowering by directly and indirectly targeting genes for flowering activation. The mechanism appears ancient. Our study extends the current model of floral transition regulation in sorghum and provides a framework for a comprehensive understanding of sorghum photoperiod response.

Rice Seedlings and Microorganisms Mediate Biotransformation of Se in CdSe/ZnS Quantum Dots to Volatile Alkyl Selenides.

Quantum dots (QDs) are widely applied and inevitably released into the environment. The biotransformation of Se in typical CdSe/ZnS QDs coated with glutathione (CdSe/ZnS-GSH) to volatile alkyl selenides and the fate of alkyl selenides in the hydroponically grown rice system were investigated herein. After a 10-day exposure to CdSe/ZnS-GSH (100 nmol L-1), seven alkyl selenides, dimethyl selenide (DMSe), dimethyl diselenide (DMDSe), methyl selenol (MSeH), ethylmethyl selenide (EMSe), ethylmethyl diselenide (EMDSe), dimethyl selenenyl sulfide (DMSeS), and ethylmethyl selenenyl sulfide (EMSeS), were detected in the exposure system using the suspect screening strategy. CdSe/ZnS-GSH was first biotransformed to DMSe and DMDSe by plant and microorganisms. The generated DMSe was volatilized to the gas phase, adsorbed and absorbed by leaves and stems, downward transported, and released into the hydroponic solution, whereas DMDSe tended to be adsorbed/absorbed by roots and upward transported to stems. The airborne DMSe and DMDSe also partitioned from the gas phase to the hydroponic solution. DMSe and DMDSe in the exposure system were further transformed to DMSeS, EMSeS, EMSe, EMDSe, and MSeH. This study gives a comprehensive understanding on the behaviors of Se in CdSe/ZnS-GSH in a rice plant system and provides new insights into the environmental fate of CdSe/ZnS QDs.

Discussion: Prioritize perennial grain development for sustainable food production and environmental benefits.

Perennial grains have potential to contribute to ecological intensification of food production by enabling the direct harvest of human-edible crops without requiring annual cycles of disturbance and replanting. Studies of prototype perennial grains and other herbaceous perennials point to the ability of agroecosystems including these crops to protect water quality, enhance wildlife habitat, build soil quality, and sequester soil carbon. However, genetic improvement of perennial grain candidates has been hindered by limited investment due to uncertainty about whether the approach is viable. As efforts to develop perennial grain crops have expanded in past decades, critiques of the approach have arisen. With a recent report of perennial rice producing yields equivalent to those of annual rice over eight consecutive harvests, many theoretical concerns have been alleviated. Some valid questions remain over the timeline for new crop development, but we argue these may be mitigated by implementation of recent technological advances in crop breeding and genetics such as low-cost genotyping, genomic selection, and genome editing. With aggressive research investment in the development of new perennial grain crops, they can be developed and deployed to provide atmospheric greenhouse gas reductions.

Accumulation, translocation, and transformation of two CdSe/ZnS quantum dots in rice and pumpkin plants.

As a widely applied semiconductor nanomaterial, quantum dots (QDs) have drawn considerable interest. In this study, pumpkin and rice seedlings were hydroponically exposed to two core/shell CdSe/ZnS QDs coated with cysteamine (CdSe/ZnS-CA) and polyethylene glycol-carboxy (CdSe/ZnS-PEG-COOH) for 10 days to analyze their time-varying uptake, translocation, and transformation behaviors in plants. Both QDs were mainly adsorbed/absorbed by the roots in the particulate state, and more CdSe/ZnS-CA accumulated than CdSe/ZnS-PEG-COOH. For CdSe/ZnS-CA-treated plants, the Se and Cd concentrations (CSe and CCd) associated with the roots were 561 ± 75 and 580 ± 73 µg/g (dw) for rice and 474 ± 49 and 546 ± 53 µg/g (dw) for pumpkin, respectively, on day 10. For CdSe/ZnS-PEG-COOH-treated plants, the concentrations of Se and Cd associated with roots were 392 ± 56 and 453 ± 56 µg/g (dw) for rice and 363 ± 52 and 417 ± 52 µg/g (dw) for pumpkin, respectively. The surface charges and coatings significantly affected the accumulation of QDs at the beginning of exposure; however, the impaction decreased with time. The ratios between the Cd and Se concentrations (CCd/CSe) in the stems and leaves varied from those of the QD standards, indicating the transformation of the QDs in the exposure system. Se and Cd were more likely to translocate in CdSe/ZnS-PEG-COOH-treated plants than in CdSe/ZnS-CA-treated plants. The vertical translocation of Se was greater than that of Cd. Rice showed greater abilities of accumulation and translocation of Se and Cd from both QDs than pumpkin. These findings improve our understanding of the interference of QDs with plants and their environmental fate.

Bromophenol Induced Multiple Stress Responses in Rice Plants: Impact of Doses and Congener Structures.

Bromophenols (BPs) have both natural and artificial sources in the environment and are frequently detected in plants. Herein, the ubiquitous 2,4,6-TriBP was hydroponically exposed to rice seedlings at two concentrations (0.2 and 2.0 mg/L) to characterize the dose-dependent abiotic stress responses of rice plants to BPs. The 2,4,6-TriBP induced oxidative damage to rice roots and subsequently inhibited plant transpiration and growth at the end of exposure in both concentrations. Moreover, the gene expression of OsUGT72B1 and the activity of glycosyltransferases of exposed rice roots were 2.36-to-4.41-fold and 1.23-to-1.72-fold higher than that of the blank controls after 24 h, following the formation of glycoconjugates in response to 2,4,6-TriBP exposure. It was notable that the glycosylation rates also showed a dose-effect relationship in rice roots. One and six glycoconjugates of 2,4,6-TriBP were detected in 0.2 and 2.0 mg/L exposure groups, respectively. Considering the detected species of glycoconjugates for four other types of BPs, the numbers of bromine atoms were found to dramatically affect their glycosylation process in rice plants. These results improve our fundamental understanding of the impact of congener structures and exposure concentrations of organic contaminants on the glycosylation process in response to phytotoxicity.

Two Typical Glycosylated Metabolites of Tetrabromobisphenol A Formed in Plants: Excretion and Deglycosylation in Plant Root Zones.

The glycosylation process was investigated for the common brominated flame retardant tetrabromobisphenol A (TBBPA) in hydroponic exposure systems with pumpkin seedlings. Two typical glycosylation metabolites of TBBPA formed in pumpkin seedlings, TBBPA mono-ß-d-glucopyranoside (TBBPA MG) and TBBPA di-ß-d-glucopyranoside (TBBPA DG), increasing their mass early in the exposure (reaching maximum masses of 608 ± 53 and 3806 ± 1570 pmol at 12 h, respectively) and then falling throughout exposure. These two metabolites were released from roots to rhizosphere solutions, where they also exhibited initial increases followed by decreasing trends (reaching maximum masses of 595 ± 272 pmol at 3 h and 77.1 ± 36.0 pmol at 6 h, respectively). However, a (pseudo)zero-order deglycosylation of TBBPA MG and TBBPA DG (during the first 1.5 h) back to TBBPA was unexpectedly detected in the hydroponic solutions containing pumpkin exudates and microorganisms. The function of microorganisms in the solutions was further investigated, revealing that the microorganisms were main contributors to deglycosylation. Plant detoxification through glycosylation and excretion, followed by deglycosylation of metabolites back to the toxic parent compound (TBBPA) in hydroponic solutions, provides new insight into the uptake, transformation, and environmental fate of TBBPA and its glycosylated metabolites in plant/microbial systems.

Comparative evolution of vegetative branching in sorghum.

Tillering and secondary branching are two plastic traits with high agronomic importance, especially in terms of the ability of plants to adapt to changing environments. We describe a quantitative trait analysis of tillering and secondary branching in two novel BC1F2 populations totaling 246 genotypes derived from backcrossing two Sorghum bicolor x S. halepense F1 plants to a tetraploidized S. bicolor. A two-year, two-environment phenotypic evaluation in Bogart, GA and Salina, KS permitted us to identify major effect and environment specific QTLs. Significant correlation between tillering and secondary branching followed by discovery of overlapping sets of QTLs continue to support the developmental relationship between these two organs and suggest the possibility of pleiotropy. Comparisons with two other populations sharing S. bicolor BTx623 as a common parent but sampling the breadth of the Sorghum genus, increase confidence in QTL detected for these two plastic traits and provide insight into the evolution of morphological diversity in the Eusorghum clade. Correspondence between flowering time and vegetative branching supports other evidence in suggesting a pleiotropic effect of flowering genes. We propose a model to predict biomass weight from plant architecture related traits, quantifying contribution of each trait to biomass and providing guidance for future breeding experiments.

Compartmentalization and Excretion of 2,4,6-Tribromophenol Sulfation and Glycosylation Conjugates in Rice Plants.

The most environmentally abundant bromophenol congener, 2,4,6-tribromophenol (2,4,6-TBP, 6.06 µmol/L), was exposed to rice for 5 d both in vivo (intact seedling) and in vitro (suspension cell) to systematically characterize the fate of its sulfation and glycosylation conjugates in rice. The 2,4,6-TBP was rapidly transformed to produce 6 [rice cells (3 h)] and 8 [rice seedlings (24 h)] sulfated and glycosylated conjugates. The predominant sulfation conjugate (TP408, 93.0-96.7%) and glycosylation conjugate (TP490, 77.1-90.2%) were excreted into the hydroponic solution after their formation in rice roots. However, the sulfation and glycosylation conjugates presented different translocation and compartmentalization behaviors during the subsequent Phase III metabolism. Specifically, the sulfated conjugate could be vertically transported into the leaf sheath and leaf, while the glycosylation conjugates were sequestered in cell vacuoles and walls, which resulted in exclusive compartmentalization within the rice roots. These results showed the micromechanisms of the different compartmentalization behaviors of 2,4,6-TBP conjugates in Phase III metabolism. Glycosylation and sulfation of the phenolic hydroxyl groups orchestrated by plant excretion and Phase III metabolism may reduce the accumulation of 2,4,6-TBP and its conjugates in rice plants.

Quantitative trait mapping of plant architecture in two BC1F2 populations of Sorghum Bicolor × S. halepense and comparisons to two other sorghum populations.

KEY MESSAGE: Comparing populations derived, respectively, from polyploid Sorghum halepense and its progenitors improved knowledge of plant architecture and showed that S. halepense harbors genetic novelty of potential value for sorghum improvement Vegetative growth and the timing of the vegetative-to-reproductive transition are critical to a plant's fitness, directly and indirectly determining when and how a plant lives, grows and reproduces. We describe quantitative trait analysis of plant height and flowering time in the naturally occurring tetraploid Sorghum halepense, using two novel BC1F2 populations totaling 246 genotypes derived from backcrossing two tetraploid Sorghum bicolor x S. halepense F1 plants to a tetraploidized S. bicolor. Phenotyping for two years each in Bogart, GA and Salina, KS allowed us to dissect variance into narrow-sense genetic (QTLs) and environmental components. In crosses with a common S. bicolor BTx623 parent, comparison of QTLs in S. halepense, its rhizomatous progenitor S. propinquum and S. bicolor race guinea which is highly divergent from BTx623 permit inferences of loci at which new alleles have been associated with improvement of elite sorghums. The relative abundance of QTLs unique to the S. halepense populations may reflect its polyploidy and subsequent 'diploidization' processes often associated with the formation of genetic novelty, a possibility further supported by a high level of QTL polymorphism within sibling lines derived from a common S. halepense parent. An intriguing hypothesis for further investigation is that polyploidy of S. halepense following 96 million years of abstinence, coupled with natural selection during its spread to diverse environments across six continents, may provide a rich collection of novel alleles that offer potential opportunities for sorghum improvement.

Genetic Analysis of Stem Diameter and Water Contents To Improve Sorghum Bioenergy Efficiency.

Biofuel made from agricultural products has the potential in contribute to a stable supply of fuel for growing energy demands. Some salient plant traits, such as stem diameter and water content, and their relationship to other important biomass-related traits are so far poorly understood. Here, we performed QTL mapping for three stem diameter and two water content traits in a S. bicolor BTx623 x IS3620c recombinant inbred line population of 399 genotypes, and validated the genomic regions identified using genome-wide association studies (GWAS) in a diversity panel of 354 accessions. The discovery of both co-localized and non-overlapping loci affecting stem diameter traits suggests that stem widths at different heights share some common genetic control, but also have some distinct genetic influences. Co-localizations of stem diameter and water content traits with other biomass traits including plant height, flowering time and the 'dry' trait, suggest that their inheritance may be linked functionally (pleiotropy) or physically (linkage disequilibrium). Water content QTL in homeologous regions resulting from an ancient duplication event may have been retained and continue to have related functions for an estimated 96 million years. Integration of QTL and GWAS data advanced knowledge of the genetic basis of stem diameter and water content components in sorghum, which may lead to tools and strategies for either enhancing or suppressing these traits, supporting advances toward improved quality of plant-based biomass for biofuel production.

Metabolism of SCCPs and MCCPs in Suspension Rice Cells Based on Paired Mass Distance (PMD) Analysis.

Short-chain and medium-chain chlorinated paraffins (SCCPs and MCCPs) are mixtures of complex chemical compounds with intensive usage. They are frequently detected in various environmental samples. However, the interaction between CPs and plants, especially the biotransformation behaviors of CPs within plants, is poorly understood. In this study, 1,2,5,6,9,10-hexachlorodecane (CP-4, a typical standard of individual SCCP congeners) and 52%-MCCP (a commercial mixture standard of MCCPs with 52% chlorine content by mass) were selected as representative chemicals to explore the metabolic behaviors of SCCPs and MCCPs using suspension rice cell culture exposure systems. Both 79.53% and 40.70% of CP-4 and 52%-MCCP were metabolized by suspension rice cells, respectively. A complementary suspected screening strategy based on the pair mass distances (PMD) analysis algorithm was used to study the metabolism of CPs mediated by the plant cells. Forty and 25 metabolic products for CP-4 and 52%-MCCP, respectively, were identified, including (multi-) hydroxylation, dechlorination, -HCl- elimination metabolites, (hydroxylation-) sulfation, and glycosylation conjugates. Here, we propose a comprehensive metabolic molecular network and provide insight on degradation pathways of SCCPs and MCCPs in plants for the first time, aiding in further understanding of the transformation behaviors of CPs.

Uptake, phytovolatilization, and interconversion of 2,4-dibromophenol and 2,4-dibromoanisole in rice plants.

The structural analogs, 2,4-dibromophenol (2,4-DBP) and 2,4-dibromoanisole (2,4-DBA), have both natural and artificial sources and are frequently detected in environmental matrices. Their environmental fates, especially volatilization, including both direct volatilization from cultivation solution and phytovolatilization through rice plants were evaluated using hydroponic exposure experiments. Results showed that 2,4-DBA displayed stronger volatilization tendency and more bioaccumulation in aboveground rice tissues. Total volatilized 2,4-DBA accounted for 4.74% of its initial mass and was 3.43 times greater than 2,4-DBP. Phytovolatilization of 2,4-DBA and 2,4-DBP contributed to 6.78% and 41.7% of their total volatilization, enhancing the emission of these two contaminants from hydroponic solution into atmosphere. In this study, the interconversion processes between 2,4-DBP and 2,4-DBA were first characterized in rice plants. The demethylation ratio of 2,4-DBA was 12.0%, 32.0 times higher than methylation of 2,4-DBP. Formation of corresponding metabolites through methylation and demethylation processes also contributed to the volatilization of 2,4-DBP and 2,4-DBA from hydroponic solution into the air phase. Methylation and demethylation processes increased phytovolatilization by 12.1% and 36.9% for 2,4-DBP and 2,4-DBA. Results indicate that phytovolatilization and interconversion processes in rice plants serve as important pathways for the global cycles of bromophenols and bromoanisoles.

The Evolution of an Invasive Plant, Sorghum halepense L. ('Johnsongrass').

From noble beginnings as a prospective forage, polyploid Sorghum halepense ('Johnsongrass') is both an invasive species and one of the world's worst agricultural weeds. Formed by S. bicolor x S. propinquum hybridization, we show S. halepense to have S. bicolor-enriched allele composition and striking mutations in 5,957 genes that differentiate it from representatives of its progenitor species and an outgroup. The spread of S. halepense may have been facilitated by introgression from closely-related cultivated sorghum near genetic loci affecting rhizome development, seed size, and levels of lutein, a photochemical protectant and abscisic acid precursor. Rhizomes, subterranean stems that store carbohydrates and spawn clonal propagules, have growth correlated with reproductive rather than other vegetative tissues, and increase survival of both temperate cold seasons and tropical dry seasons. Rhizomes of S. halepense are more extensive than those of its rhizomatous progenitor S. propinquum, with gene expression including many alleles from its non-rhizomatous S. bicolor progenitor. The first surviving polyploid in its lineage in ∼96 million years, its post-Columbian spread across six continents carried rich genetic diversity that in the United States has facilitated transition from agricultural to non-agricultural niches. Projected to spread another 200-600 km northward in the coming century, despite its drawbacks S. halepense may offer novel alleles and traits of value to improvement of sorghum.

Transmission Genetics of a Sorghum bicolor × S. halepense Backcross Populations.

Despite a "ploidy barrier," interspecific crosses to wild and/or cultivated sorghum (Sorghum bicolor, 2n = 2x = 20) may have aided the spread across six continents of Sorghum halepense, also exemplifying risks of "transgene escape" from crops that could make weeds more difficult to control. Genetic maps of two BC1F1 populations derived from crosses of S. bicolor (sorghum) and S. halepense with totals of 722 and 795 single nucleotide polymorphism (SNP) markers span 37 and 35 linkage groups, with 2-6 for each of the 10 basic sorghum chromosomes due to fragments covering different chromosomal portions or independent segregation from different S. halepense homologs. Segregation distortion favored S. halepense alleles on chromosomes 2 (1.06-4.68 Mb, near a fertility restoration gene), 7 (1.20-6.16 Mb), 8 (1.81-5.33 Mb, associated with gene conversion), and 9 (47.5-50.1 Mb); and S. bicolor alleles on chromosome 6 (0-40 Mb), which contains both a large heterochromatin block and the Ma1 gene. Regions of the S. halepense genome that are recalcitrant to gene flow from sorghum might be exploited as part a multi-component system to reduce the likelihood of spread of transgenes or other modified genes. Its SNP profile suggests that chromosome segments from its respective progenitors S. bicolor and Sorghum propinquum have extensively recombined in S. halepense. This study reveals genomic regions that might discourage crop-to-weed gene escape, and provides a foundation for marker-trait association analysis to determine the genetic control of traits contributing to weediness, invasiveness, and perenniality of S. halepense.

Transformation of 1,1,1,3,8,10,10,10-octachlorodecane in air phase increased by phytogenic volatile organic compounds of pumpkin seedlings.

Short chain chlorinated paraffins (SCCPs) are widely distributed persistent organic pollutants (POPs). Airborne chlorodecanes were hypothesized to be transformed by reactive phytogenic volatile organic compounds (PVOCs) in our previous work. To test this hypothesis, PVOCs of pumpkin (Cucurbita maxima x C. moschata) were collected and reacted with 1,1,1,3,8,10,10,10-octachlorodecane in the air phase of a sealed glass bottle under illumination for 10 days (reaction system I, simulating atmospheric reaction conditions with PVOCs). The reaction control group (reaction system II) was set at the same conditions but only had chlorodecane (without PVOCs) inside the bottle. Transformation of SCCPs in the air phase of reaction control group was unexpectedly found. Results showed that 1,1,1,3,8,10,10,10-octachlorodecane was transformed to a great extent to C10Cl5-8, C9Cl6-8, and C8Cl7-8 in the air phase after 10-d illumination in both with and without the presence of PVOCs, which is explained by carbon chain decomposition, dechlorination and chlorine rearrangement products of the parent SCCP. Those transformation processes were increased to some extent by the PVOCs from pumpkin seedlings. This study provides the first experimental data on atmospheric transformation of SCCPs and also the first evidence that plant emissions (PVOCs) can increase the transformation of SCCPs in air under light and experimental conditions. It provides new insight into the potential transformation and fate of CPs in the environment.

Occurrences of perfluoroalkyl and polyfluoroalkyl substances in tree bark: Interspecies variability related to chain length.

Occurrences of perfluoroalkyl and polyfluoroalkyl substances (PFASs) in tree bark from four species were investigated. Species-dependent congener distribution patterns were firstly reported for perfluorocarboxylic acids (PFCAs) and perfluoroalkyl sulfonic acids (PFSAs). The majority of PFSAs and PFCAs in Chinese red pine bark were C5-C7 PFSAs and perfluorohexanoic acid (PFHxA, containing six carbon atoms, C6), whereas perfluorobutanesulfonic acid (PFBS, C4) and longer chain congeners (PFCAs: C ≥ 7; PFSAs: C ≥ 8) took a larger proportion in the fissured bark from Canadian poplar, Chinese scholartree and weeping willow. The species-dependent congener profiles depended on the structures and chemical compositions of tree bark, as well as the translocation of PFASs within plants. Different tree bark characteristics caused different retention abilities for particle-bound and gaseous PFASs. Particle-bound PFASs retained in the rougher structures of fissured bark led to preferential retention of long chain congeners (the major fraction in the particle phase), while lipid-rich Chinese red pine bark retained more gaseous PFASs (mainly short chain congeners). Besides, the abundance of short chain PFASs in red pine bark was consistent with the chain length-dependent translocation behaviors of PFASs in various plants, suggesting that translocation of PFASs within plants to tree bark may be invovled.

Multiple Metabolic Pathways of 2,4,6-Tribromophenol in Rice Plants.

Bromophenols occur naturally and are used globally as man-made additives in various industrial products. They are decomposition products of many emerging organic pollutants, such as tetrabromobisphenol A, polybrominated dibenzo- p-dioxin (PBDD), polybrominated diphenyl ethers (PBDE), and others. To characterize their biotransformation pathways, bromophenol congener 2,4,6-tribromophenol, being used most frequently in the synthesis of brominated flame retardants and having the greatest environmental abundance, was selected to hydroponically expose rice plants. After exposure for 5 days, 99.2% of 2,4,6-tribromophenol was metabolized by rice. Because of the lack of relative reference standards, an effective screening strategy was used to screen for potential metabolites that were further qualitatively identified by gas and liquid chromatography combined with high-resolution mass spectrometry. Forty transformation products were confirmed or tentatively identified at different confidence levels, including 9 phase I and 31 phase II metabolites. A large number of metabolites (39) were found in rice root, and 10 of them could be translocated and detected in rice stems or leaves. Many transformation pathways were proposed, including debromination, hydroxylation, methylation, coupling reactions, sulfation, and glycosylation. It was remarkable that a total of seven hydrophobic, persistent, and toxic OH-PBDEs and PBDD/Fs were found, indicating the biotic dimeric reactions of 2,4,6-tribromophenol that occurred in the rice plants. These results improve our understanding of the transformation and environmental fates of bromophenols, and they indicate new potential sources for OH-PBDEs and PBDD/Fs in the environment, especially in food chains.

Abiotic Methylation of Tetrabromobisphenol A (TBBPA) with the Occurrence of Methyl Iodide in Aqueous Environments.

Tetrabromobisphenol A (TBBPA) is the most widely used brominated flame retardant in the world. Its biotic methylation products, tetrabromobisphenol A mono- and dimethyl ether (TBBPA MME and TBBPA DME, respectively), are frequently detected in the environment, but the importance of abiotic methylation reactions of TBBPA in the environment is not known. In this study, the methylation of TBBPA mediated by methyl iodide (CH3I), a ubiquitous compound in aqueous environments, was investigated in simulated waters in the laboratory. It was found that abiotic methylation occurred under both light and dark conditions and was strongly affected by the pH, temperature, and natural organic matter concentration of the water. Abiotic methylation was further verified in natural river water, and the yield of TBBPA MME mediated abiotically by CH3I was much greater than that of biotic methylation. According to our calculations and by comparison of the activation energies (E a) for the abiotic methylation of TBBPA and the other four typical phenolic contaminants and/or metabolites (bisphenol A, triclosan, 5-OH-BDE-47, and 4'-OH-CB-61) mediated by CH3I, those phenolic compounds all show great methylation potentials. The results indicate a new abiotic pathway for generating TBBPA MME and TBBPA DME from TBBPA, and they also confirm the potentials for abiotic methylation of other phenolic contaminants in aqueous environments.

Heritability of the aged glutathione phenotype is dependent on tissue of origin.

Glutathione is a ubiquitous antioxidant that protects cells against reactive oxygen species and other chemical stressors. Despite its functional importance, the impact of genetics on the glutathione system has yet to be fully appreciated. Here, we investigated the heritability of glutathione levels and redox status in a disease-relevant condition: advanced age. We assembled a panel of 18-21-month-old mice representing 19 inbred strains and quantified the levels of reduced and oxidized glutathione, and their sums and ratios, in liver, kidney, heart, pancreas, cerebral cortex, and striatum. Heritability values were calculated for each phenotype and the results varied by tissue of origin. Cardiac glutathione phenotypes exhibited the highest heritabilities (G2 = 0.44-0.67), while striatal glutathione was least heritable (G2 = 0.11-0.29). Statistical relationships between tissues were evaluated, and the emergence of significant correlations suggested that despite tissue-specific heritabilities, at least some shared regulatory mechanisms may exist. Overall, these data highlight another mechanism by which genetic background determines antioxidant protection and stress resistance.