Nitric oxide (NO) is an important phytohormone for plant adaptation to mercury (Hg) stress. The effect of Hg on lignin synthesis, NO production in leaf, sheath and root and their relationship were investigated in two members of the grass family - wheat and maize. Hg stress decreased growth and lignin contents, significantly affected phenylpropanoid and monolignol pathways (PAL, phenylalanine ammonia-lyase; 4-coumarate: CoA ligase, 4CL; cinnamyl alcohol dehydrogenase, CAD), with maize identified to be more sensitive to Hg stress than wheat. Among the tissue types, sheath encountered severe damage compared to leaves and roots. Hg translocation in maize was about twice that in wheat. Interestingly, total NO produced under Hg stress was significantly decreased compared to control, with maximum reduction of 43.4% and 42.9% in wheat and maize sheath, respectively. Regression analysis between lignin and NO contents or the activities of three enzymes including CAD, 4CL and PAL displayed the importance of NO contents, CAD, 4CL and PAL for lignin synthesis. Further, the gene expression profiles encoding CAD, 4CL and PAL provided support for the damaging effect of Hg on wheat sheath, and maize shoot. To validate NO potential to mitigate Hg toxicity in maize and wheat, NO donor and NO synthase inhibitor were supplemented along with Hg. The resulting phenotype, histochemical analysis and lignin contents showed that NO mitigated Hg toxicity by improving growth and lignin synthesis and accumulation. In summary, Hg sensitivity was higher in maize seedlings compared to wheat, which was associated with the lower lignin contents and reduced NO contents. External supplementation of NO is proposed as a sustainable approach to mitigate Hg toxicity in maize and wheat.

Arsenic (As) is a highly toxic metalloid adversely affecting the environment, human health, and crop productivity. The present study assessed the synergistic effects of salinity and As on photosynthetic attributes, stomatal regulations, and metabolomics responses of the xero-halophyte Salvadora persica to decipher the As-salinity cross-tolerance mechanisms and to identify the potential metabolites/metabolic pathways involved in cross-tolerance of As with salinity. Salinity and As stress-induced significant stomatal closure in S. persica suggests an adaptive response to decrease water loss through transpiration. NaCl supplementation improved the net photosynthetic rate (by +39%), stomatal conductance (by +190%), water use efficiency (by +55%), photochemical quenching (by +37%), and electron transfer rate (54%) under As stress as compared to solitary As treatment. Our results imply that both stomatal and non-stomatal factors account for a reduction in photosynthesis under high salinity and As stress conditions. A total of 64 metabolites were identified in S. persica under salinity and/or As stress, and up-regulation of various metabolites support early As-salinity stress tolerance in S. persica by improving antioxidative defense and ROS detoxification. The primary metabolites such as polyphenols (caffeic acid, catechin, gallic acid, coumaric acid, rosmarinic acid, and cinnamic acid), amino acids (glutamic acid, cysteine, glycine, lysine, phenylalanine, and tyrosine), citrate cycle intermediates (malic acid, oxalic acid, and α-ketoglutaric acid), and most of the phytohormones accumulated at higher levels under combined treatment of As + NaCl compared to solitary treatment of As. Moreover, exogenous salinity increased glutamate, glycine, and cysteine, which may induce higher synthesis of GSH-PCs in S. persica. The metabolic pathways that were significantly affected in response to salinity and/or As include inositol phosphate metabolism, citrate cycle, glyoxylate and dicarboxylate metabolism, amino acid metabolism, and glutathione metabolism. Our findings indicate that inflections of various metabolites and metabolic pathways facilitate S. persica to withstand and grow optimally even under high salinity and As conditions. Moreover, the addition of salt enhanced the arsenic tolerance proficiency of this halophyte.

Arsenic (As) is recognized as a toxic metalloid and a severe threat to biodiversity due to its contamination. Soil and groundwater contamination with this metalloid has become a major concern. Large fractions of cultivable lands are becoming infertile gradually due to the irrigation of As contaminated water released from various sources. The toxicity of As causes the generation of free radicals, which are harmful to cellular metabolism and functions of plants. It alters the growth, metabolic, physiological, and molecular functions of the plants due to oxidative burst. Plants employ different signaling mechanisms to face the As toxicity like phosphate cascade, MAPK (Mitogen-Activated Protein Kinase), Ca-calmodulin, hormones, and ROS-signaling. The toxicity of As may significantly be reduced through various remediation techniques. Among them, the microbial-assisted remediation technique is cost-effective and eco-friendly. It breaks down the metalloid into less harmful species through various processes viz. biovolatilization, biomethylation, and transformation. Moreover, the adaptation strategies towards As toxicity are vacuolar sequestration, involvement of plant defense mechanism, and restricting its uptake from plant roots to above-ground parts. The speciation, uptake, transport, metabolism, ion dynamics, signaling pathways, crosstalk with phytohormones and gaseous molecules, as well as harmful impacts of the As on physiological processes, overall development of plants and remediation techniques are summarized in this review.

Brassinosteroids (BRs), a group of steroid phytohormones, are involved in multiple aspects of plant growth, development and stress responses. Despite recent studies on BRs-promoted pesticide metabolism in plants, the underlying mechanisms remain poorly understood. Here, we showed that 24-epibrassinolide (EBR) significantly enhanced the expression of RESPIRATORY BURST OXIDASE HOMOLOG1 (RBOH1) and H2O2 accumulation in the apoplast of chlorothalonil (CHT, a broad spectrum nonsystemic fungicide)-treated tomato plants. Silencing of RBOH1 significantly decreased the efficiency of EBR-induced CHT metabolism. Moreover, the EBR-induced upregulation in the transcripts of glutaredoxin gene GRXS16 was suppressed in RBOH1-silenced plants. Further studies indicated that silencing of GRXS16 compromised EBR-induced increases in glutathione content, activity of glutathione S-transferase (GST) and transcript of GST1, leading to an increase in CHT residue. By contrast, overexpression of tomato GRXS16 enhanced the basal levels of glutathione content and GST activity that eventually decreased CHT residues in transgenic plants. Our results reveal that BR-mediated induction of a modest oxidative burst is essential for the acceleration of glutathione-dependent pesticide metabolism via redox modulators, such as GRXS16. These findings shed new light on the mechanisms of BR-induced pesticide metabolism and thus have important implication in reducing pesticide residues in agricultural products.

Among emerging organic contaminants (EOCs), triclosan (TCS) is an antibacterial agent and frequently detected in sludge. In this study, RNA sequencing (RNA-seq) was used to obtain the first transcriptomic profile of tobacco with TCS treatment in comparison with control. The results of transcriptome profiling indicated that salicylic acid (SA) signalling pathway actively participated in the tobacco’s response to TCS treatment. The accumulation of endogenous SA in transgene tobacco lines transformed with a homologous gene of SA binding protein (LcSABP) was significantly enhanced. The resistance of transgenic tobacco lines to TCS was markedly enhanced revealed by morphological and physiological indexes while the total Chl level and Pₙ of transgenic individuals showed about 180% and 250% higher than that of WT on average, and the accumulation of H₂O₂ and O₂⁻ induced by TCS in SABP overexpressing tobacco was 35.3%–37.3% and 53.0%–56.0% lower than that of WT. In order to further explore the mechanism of TCS tolerance in transgenic plants, RNA-seq was then performed to obtain the second transcriptomic profile between wild type and transgenic samples with TCS exposure. The results indicated that differentially expressed genes (DEGs) were most highly enriched in MAPK signalling pathway, amino acid synthesis pathway and plant hormone transduction pathway. Especially, genes encoding key proteins such as cytochrome P450, laccase, peroxidase, glycosyl transferase, glutathione S-transferase and ATP-binding cassette were considered to be related to the increased tolerance ability of transgenic tobacco to the treatment of TCS stress. This research will likely provide novel insights into the molecular mechanism of SA-mediated amelioration of TCS stress on tobacco.

Sewage sludge applied to soil may be a valuable fertiliser but can also introduce poorly degradable and highly adsorptive wastewater-born residues of pharmaceuticals and personal care products (PPCPs) to the soil, posing a potential risk to the receiving environment. Three azole antimycotics (climbazole, ketoconazole and fluconazole), and one quaternary ammonium compound (benzyldimethyldodecylammonium chloride, BDDA) that are frequently detected in municipal sewage sludge and/or treated wastewater were therefore characterised in their toxicity toward terrestrial (Brassica napus) and aquatic (Lemna minor) plants. Fluconazole and climbazole showed the greatest toxicity to B. napus, while toxicity of ketoconazole and BDDA was by one to two orders of magnitude lower. Sludge amendment to soil at an agriculturally realistic rate of 5 t/ha significantly reduced the bioconcentration of BDDA in B. napus shoots compared to tests without sludge amendment, although not significantly reducing phytotoxicity. Ketoconazole, fluconazole and BDDA proved to be very toxic to L. minor with median effective concentrations ranging from 55.7 μg/L to 969 μg/L. In aquatic as well as terrestrial plants, the investigated azoles exhibited growth-retarding symptoms presumably related to an interference with phytohormone synthesis as known for structurally similar fungicides used in agriculture. While all four substances exhibited considerable phytotoxicity, the effective concentrations were at least one order of magnitude higher than concentrations measured in sewage sludge and effluent. Based on preliminary hazard quotients, BDDA and climbazole appeared to be of greater environmental concern than the two pharmaceuticals fluconazole and ketoconazole.

PURPOSE OF REVIEW: Livestock wastewater is a valuable vein of resources for the production of reused water, renewable energy, and fertilizers. This review aims to provide a comprehensive understanding on the opportunities and challenges to anaerobic membrane bioreactors (AnMBRs) for livestock wastewater treatment and resource recovery. RECENT FINDINGS: AnMBRs that integrates a membrane filtration process with anaerobic digestion exhibit high promise for livestock wastewater treatment and resource recovery. Organic matter in livestock wastewater can be biodegraded for the production of methane-rich biogas and bioactive substances, such as phytohormones, free amino acids, vitamins, and inorganic nutrients (e.g. ammonium and phosphate). Thus, the AnMBR effluent from livestock wastewater treatment can be potentially used for direct irrigation and processed for nutrient capture, for example, by struvite crystallization. Nevertheless, there remain several technical challenges to AnMBR development for livestock wastewater treatment. These mainly include digester susceptibility to inhibitory substances, low removal of antibiotics and heavy metals, and membrane fouling. Thus, recent studies have proposed several potential approaches to address these challenges to accelerate AnMBR development. These approaches can be largely classified as wastewater regulation, microbial acclimatization, process optimization, and amender addition. In this paper, we critically reviewed the performance of AnMBR for livestock wastewater treatment with respective to biogas production and contaminant removal. Key technical challenges and their potential countermeasures were delineated to shed light on further development of AnMBR in the field.

In this study, Gonium sp. was investigated for possible usage in dye-containing wastewater treatment. Trials were performed in media including triacontanol hormone, Reactive Orange 14, Reactive Red 120, Reactive Black 5, Remazol Brilliant Blue R (RBBR), and also hormone against the controls. Algae could remove RBBR with the highest dye removal percentage (56%) among the tested dyes. The optimum pH was 9 in removing 50 mg L−1 RBBR at a dye removal percentage of 47.1%. The role of laccase activity of Gonium sp. was also investigated. This first attempt in the literature showed the involvement of the enzyme in the algal growth and bioremoval process. In the presence of the plant growth hormone in the culture, the activity showed a steady and significant increase up to nearly sixfold between 5th and 14th days of incubation.

One of the main herbicides used in the agricultural environments is 2,4-dichlorophenoxyacetic acid (2,4-D). It is a synthetic plant hormone auxin employed in many crops including rice, wheat, sorghum, sugar cane, and corn to control wide leaf weeds. The indiscriminate use of pesticides can produce numerous damages to the environment. Therefore, this review has the objective to provide an overview on the main characteristics of the herbicides based on 2,4-D, mostly on the role of microorganisms in its degradation and its main degradation metabolite, 2,4- dichlorophenol (2,4-DCP). The remediation processes carried out by microorganisms are advantageous to avoid the pollution of the environment as well as to safeguard the population health.

This work was conducted to evaluate and compare the responses of Phaseolus vulgaris to three types of composts and vermicomposts derived from municipal solid waste (MSW). Different amendment rates were used and evaluated for their effect on germination, growth, and marketable yield. MSW-derived vermicomposts and composts were substituted into mineral brown-earth soil, applied at rates of 0 (control), 10, 20, 30, 40, 50, and 100% (v/v) in plastic pots of 7.2-L capacity. Green beans which are grown in 40% vermicompost/soil mixtures and compost/soil mixtures yielded 78.3–89.5% higher fruit weights as compared to control. Results showed that MSW vermicomposts consistently outperformed equivalent quantities of composts in terms of fruit yield, shoot, and root dry weights, which can be attributed to the contributions of physicochemical properties and nutrients content (N, P, and K) in the potting experiments. Consequently, it seemed likely that MSW vermicompost provided other biological inputs such as plant growth regulators (PGRs) and plant growth hormones (PGHs), which could have a considerably positive effect on the growth and yields of P. vulgaris as compared to composts. More in-depth scientific investigation is required in order to identify the distinctive effects and the exact mechanisms of these PGRs in MSW vermicomposts which influenced plant growth responses.