Uptake, biotransformation and physiological response of TBBPA in mangrove plants after hydroponics exposure

A review of occurrence, bioaccumulation, and fate of novel brominated flame retardants in aquatic environments: A comparison with legacy brominated flame retardants

Novel brominated flame retardants (NBFRs) have been developed as replacements for legacy brominated flame retardants (BFRs) such as polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecanes (HBCDs). The prevalence of NBFRs in aquatic environments has initiated intense concerns that they resemble to BFRs. To comprehensively elucidate the fate of NBFRs in aquatic environments, this review summarizes the physico-chemical properties, distribution, bioaccumulation, and fates in aquatic environments. 1,2-bis(2,3,4,5,6-pentabromophenyl) ethane (DBDPE) as the major substitute for PBDEs is the primary NBFR. The release from industrial point sources such as e-waste recycling stations is the dominant way for NBFRs to enter the environment, which results in significant differences in the regional distribution of NBFRs. Sediment is the major sink of NBFRs attributed to the high hydrophobicity. Significantly, there is no decreasing trend of NBFRs concentrations, while PBDEs achieved the peak value in 1970-2000 and decreased gradually. The bioaccumulation of NBFRs is reported in both field studies and laboratory studies, which is regulated by the active area, lipid contents, trophic level of aquatic organisms, and the log KOW of NBFRs. The biotransformation of NBFRs showed similar metabolism patterns to that of BFRs, including debromination, hydroxylation, methoxylation, hydrolysis, and glycosylation. In addition, NBFRs show great potential in trophic magnification along the aquatic food chain, which could pose a higher risk to high trophic-level species. The passive uptake by roots dominates the plant uptake of NBFRs, followed by acropetal and basipetal bidirectional transportation between roots and leaves in plants. This review will provide the support to understand the current pollution characteristics of NBFRs and highlight perspectives for future research.

Toxicity and tolerance mechanism of binary zinc oxide nanoparticles and tetrabromobisphenol A regulated by humic acid in Chlorella vulgaris

Recent studies have reported that nanoparticles (NPs) released into the aquatic environment may interact with persistent organic pollutants such as brominated flame retardants, whereas the environmental processes and toxicological impacts induced by such binary NPs require further specification. This study investigated the ultrastructural damage of Chlorella vulgaris triggered by exposure to zinc oxide (ZnO) NPs, tetrabromobisphenol A (TBBPA), ZnO-TBBPA, and ZnO-TBBPA-humic acid (HA), clarified the uptake and distribution of ZnO NPs in cells, and explored the physiological toxicity and tolerance mechanism. The results demonstrated that ZnO NPs induced irregular morphology in algal cells, and the disruption of the cellular ultrastructure by binary ZnO-TBBPA was also extremely severe due to the excessive uptake of ZnO NPs, which resulted in strong oxidative stress responses. In particular, the accumulation of reactive oxygen species further exacerbated the reduction of total chlorophyll content and algal density. Moreover, the cluster heat map and correlation analysis revealed that superoxide dismutase activity played a critical role in alleviating lipid peroxidation damage and enhancing the tolerance of algal cells to the stress of binary ZnO NPs. More notably, the existence of HA intensified the dispersion stability of NP suspensions and significantly mitigated the synergistic toxicity of binary ZnO-TBBPA. This study provides new insights into the environmental behavior and biological impacts of binary NPs in the natural environment.

Exogenous IAA application affects the specific characteristics of fluoranthene distribution in Arabidopsis

Indole-3-acetic acid (IAA) is a crucial growth regulator involved in the accumulation of polycyclic aromatic hydrocarbons (PAHs). However, the precise physiological and molecular mechanisms underlying IAA-mediated plant growth and PAH accumulation are not yet fully understood. In this study, two distinct IAA-sensitive genotypes of Arabidopsis thaliana (wild type and Axr5 mutant) were chosen to investigate the mechanisms of fluoranthene (Flu) uptake and accumulation in plant tissues (roots and leaves) through physiological and molecular analyses. The results revealed that the Flu concentration in Axr5 leaves was significantly higher than that in wild-type (WT) leaves. In roots, the Flu content decreased significantly with increasing IAA treatment, while no significant changes were observed with lower IAA treatment. Principal component analysis demonstrated that Flu accumulation in Arabidopsis roots was associated with IAA concentrations, whereas Flu accumulation in leaves was dependent on the genotype. Moreover, Flu accumulation showed a positive correlation with the activity of glutathione S-transferase (GST) and root length and a positive correlation with catalase (CAT) and peroxidase (POD) activity in the leaves. Transcriptome analysis confirmed that the expression of the ethylene-related gene ATERF6 and GST-related genes ATGSTF14 and ATGSTU27 in roots, as well as the POD-related genes AtPRX9 and AtPRX25 and CAT-related gene AtCAT3 in leaves, played a role in Flu accumulation. Furthermore, WRKY transcription factors (TFs) in roots and NAC TFs in leaves were identified as important regulators of Flu accumulation. Understanding the mechanisms of Flu uptake and accumulation in A. thaliana provides valuable insights for regulating PAH accumulation in plants.

Transcriptomic, epigenomic and physiological comparisons reveal key factors for different manganese tolerances in three Chenopodium ambrosioides L. populations

Chenopodium ambrosioides is a manganese (Mn) hyperaccumulator that can be used for Mn-polluted soil phytoremediation. However, the mechanism of Mn tolerance of C. ambrosioides remains largely unknown. In this study, the key factors for Mn tolerance of C. ambrosioides was investigated from the aspects of DNA methylation pattern, gene expression regulation and physiological function. We found that the two genotypes of C. ambrosioides populations have differentiated tolerance to Mn stress (Mn-tolerant: CS and XC, Mn-sensitive: WH). Although there was no difference in Mn accumulation between two types under excess Mn, the biomass and photosynthetic systems were more severely inhibited in Mn-sensitive type, as well as suffering more serious oxidative damage. More differentially expressed genes (DEGs) were downregulated in the Mn-tolerant type, indicating that the Mn-tolerant type tends to inhibit gene expression to cope with Mn stress. DEGs related to metal transport, antioxidant system, phytohormone and transcription factors contribute to the tolerance of C. ambrosioides to Mn, and account for difference in Mn stress sensitivities between the Mn-sensitive and tolerant types. We also found that DNA methylation variation may help to cope with Mn stress. The global DNA methylation level in C. ambrosioides increased under Mn stress, especially in the Mn-sensitive type. Dozens of methylated loci were significantly associated with the Mn accumulation trait of C. ambrosioides, and some critical DEGs were regulated by DNA methylation. Our study comprehensively demonstrated the Mn tolerance mechanism of C. ambrosioides for the first time, and highlighted the roles of epigenetic modification in C. ambrosioides response to Mn stress. Our findings may contribute to elucidating the adaptation mechanism of hyperaccumulator to the heavy metal toxicity.

Analysis of tetrabromobisphenol A and bisphenol A in plant sample-method optimization and identification of the derivatives

Tetrabromobisphenol A (TBBPA) is the most abundant brominated flame retardant and bisphenol A (BPA) is often identified as the metabolic product of TBBPA. Both of them are highly bioconcentrated and show serious biological toxicity. In this study, an analytical method was optimized to simultaneously determine TBBPA and BPA in plant samples. Moreover, the uptake and metabolism of TBBPA in maize were investigated through hydroponic exposure experiment. The whole analysis procedure included ultrasonic extraction, lipid removal, purification by solid-phase extraction cartridge, derivatization, and detection by GC/MS. Optimizations were conducted for each pretreatment step above. After improvement, methyl tert-butyl ether (MTBE) was chosen as the extraction solvent; the lipid removal was conducted by repartition between organic solvent and alkaline solution. The best suitable pH condition is 2-2.5 for the inorganic solvent before used for further purification by HLB and silica column with the optimized elute solvent of acetone and mixtures of acetone and hexane (1:1), respectively. The recoveries of TBBPA and BPA spiked in maize samples were 69±4% and 66±4% with the relative standard deviation less than 5%, respectively, for the entire treatment procedure. Limits of detections were 4.10 ng/g and 0.13 ng/g for TBBPA and BPA in plant samples, respectively. In the hydroponic exposure experiment (100 μg/L, 15 d), the concentrations of TBBPA in maize cultivated in pH 5.8 and pH 7.0 Hoagland solutions were 1.45 and 0.89 μg/g in roots and 8.45 and 6.34 ng/g in stems, while they were all below the detection limit for leaves, respectively. The distribution of TBBPA in different tissues was as the following order: root>>stem>leaf, illustrating the accumulation in the root and the translocation to the stem. The uptake variations under different pH conditions were attributed to the change of TBBPA species, now that it shows greater hydrophobicity at lower pH condition as a kind of ionic organic contaminant. Monobromobisphenol A and dibromobisphenol A were identified as metabolisms products of TBBPA in maize. The efficiency and simplicity of the method that we proposed characterize its potential application as a screening tool for environmental monitoring and contribute to a comprehensive study of the environmental behavior of TBBPA.

Abscisic acid plays a key role in the mechanism of photosynthetic and physiological response effect of Tetrabromobisphenol A on tobacco

The toxicity of bromide to animals and microorganisms has been widely studied, but the mechanism by which bromide toxicity affects plants is rarely studied. This study used the bromophenol compound Tetrabromobisphenol A (TBBPA) as a representative of bromide to explore the physiological and molecular response mechanism of tobacco leaves to TBBPA. In addition, physiological determination, transcriptomics, weighted gene co-expression network analysis (WGCNA) analysis, and random forest prediction model were conducted. The findings from this study indicated that TBBPA limited the photoreaction process by destroying the light-catching antenna protein of tobacco leaves, the activity of the photosystem reaction centers (PSII and PSI), and the linear electron transport efficiency. TBBPA also reduced the rate of the Calvin-Benson cycle by inhibiting the activities of gene such as Rubisco, PGK, and TPI, and finally destroyed the photosynthesis process. Although cyclic electron transport was enhanced under stress conditions, it could not reverse the damage caused by TBBPA on photosynthesis. TBBPA exposure resulted in the accumulation of reactive oxygen species (ROS) in tobacco leaves, and the activities of Superoxide dismutase (SOD), Ascorbate peroxidase (APX), and Glutathione peroxidase (GPX) and their coding genes were significantly down-regulated. Although POD activity and proline (Pro) content were increased, they were insufficient to remove excess O₂^·- free radicals to relieve ROS stress. WCGNA and random forest models predicted that the damage of TBBPA to the above processes in tobacco was closely related to the increase in abscisic acid (ABA) content. TBBPA affects the Calvin cycle by inducing ABA signal transduction and stomatal closure, which leads to a series of chain reactions, such as electron transport chain obstruction, excess of ROS, decrease in chlorophyll synthesis, and photosystem reaction center damage.

Physiological and Biochemical Responses of Kandelia obovata to Upwelling Stress

Mangroves growing in intertidal areas are faced with various stresses caused by coastal human activities and oceanic and atmospheric sources. Although the study of the physiological and biochemical characteristics of mangroves has been developing over the past four decades, the effect of upwelling on mangroves in plants stress resistance has seldom been investigated. Here, changes in the physiological and biochemical characteristics of the leaves of Kandelia obovata seedlings in response to upwelling were investigated (air temperature: 25 °C; water temperature: control 25 °C, 13 °C, and 5 °C; salinity: 10‰). The results revealed that upwelling treatment caused an increase in chlorophyll content but a decrease in photosynthetic fluorescence parameters. Hydrogen peroxide (H2O2) production and malondialdehyde activity (MDA) increased with the decrease in upwelling temperature. The proline content increased under upwelling stress, whereas the soluble sugar content decreased. Further, the activities of antioxidant enzymes, such as superoxide dismutase activity (SOD) and peroxidase activity (POD), showed an increasing trend during the treatment, while catalase activity (CAT) decreased. It was evidenced that upwelling stress triggered the physiological and biochemical responses of Kandelia obovata seedlings. This effect became more intense as the upwelling temperature decreased, and all these indicators showed different responses to upwelling stress. Through synthesizing more energy and regulating enzyme activity and osmotic pressure, the leaves of K. obovata formed a resistance mechanism to short-term upwelling.

Characteristics of zooplankton community structure and its relationship with environmental factors in the South Yellow Sea

A total of 91 species of zooplankton were sampled from the South Yellow Sea in the summer and autumn of 2019. Copepods were the predominant arthropods. The summer sample (81) contained higher species diversity than the autumn (70). In both seasons, Calanus sinicus, Sagitta enflata, S. crassa, Doliolum denticulatum, and Macrura larva were dominant species. The average abundance of zooplankton in summer and autumn was 424.9 and 52.6 ind./m³, respectively, and the biomass was 207.7 and 107.6 mg/m³, respectively. The Shannon-Wiener index (H') in summer was higher than that in autumn, while the Pielou index (J') and Margalef index (D') were lower than those in autumn. BIOENV showed that water temperature (ST), dissolved oxygen (DO), turbidity (Tur), and tetrabromobisphenol A (TBBPA) affected the zooplankton community structure in the South Yellow Sea. The concentration of TBBPA increased from offshore to nearshore, with a significant negative impact on diversity in summer.

Copper and zinc differentially affect root glutathione accumulation and phytochelatin synthase gene expression of Rhizophora mucronata seedlings: Implications for mechanisms underlying trace metal tolerance

Mangroves are susceptible to contamination due to their proximity to shores and human activities. Exposure to excessive trace metals can disturb their physiological functions and may eventually lead to death. Rhizophora mucronata is a common species growing in the mangrove forests of Thailand. Previous studies have shown that seedlings of R. mucronata are tolerant of trace metal and that they accumulate a large metal content in their root tissue. However, knowledge of their tolerance mechanisms is still lacking. To elicit the role of metal detoxification and sequestration by phytochelatins (PC) in the roots of R. mucronata seedlings, the impacts of Cu and Zn exposure were assessed on 1) physiological characteristics 2) the concentration of glutathione (GSH), a precursor of PC and 3) the level of the transcripts encoding phytochelatin synthase (PCS), the key enzyme for PC biosynthesis. Seedlings of R. mucronata were exposed to Cu and Zn in a hydroponic experiment (200 mg Cu or Zn/L in 1/4× Hoagland solution containing 8‰ NaCl, single addition). We found that both trace metals were largely accumulated in the roots. Only Cu-treated seedlings showed a decrease in the photosynthetic efficiency, in line with observed toxicity symptoms (i.e. bent stems and slight wilting of leaves). Metal accumulation, however, did not induce oxidative stress in the roots as indicated by similar level of total reactive species and lipid peroxidation across treatments. The GSH content in the roots exposed to Cu was significantly reduced while no change was observed in Zn-exposed roots. Coordinated semi-quantitative PCR and RT-qPCR revealed pcs down-regulation in Cu-treated roots, whereas Zn-treated roots showed a down-regulation on day 1 and a subsequent recovery on day 5. Failure of detoxification and sequestration of excess Cu due to GSH limitation and down-regulation of pcs may lead to the phytotoxic effects observed in Cu-treated plants. Our results suggest that both GSH and PC play an important role in trace metal tolerance in R. mucronata seedlings.