Enantioselective Response of Wheat Seedlings to Imazethapyr: From the Perspective of Fe and the Secondary Metabolite DIMBOA

Bensulfuron methyl induced multiple stress responses in the field wheat plants: Microbial community and metabolic network disturbance

Sulfonylurea (SU) herbicides are widely used and often detected in environmental matrices and have toxic effects on ecosystems and plant development. However, the interaction between SU and soil-plant metabolism during the whole wheat growth cycle remains poorly investigated. Field trials demonstrated that bensulfuron methyl exposure reduced wheat height and a thousand grains' weight, disrupting the critical metabolic pathways, including linoleic acid and amino acid metabolism in the maturity stage. During different growth processes, bensulfuron methyl exposure decreases wheat soil and plants' defense-related indole alkaloid compounds, such as benzoxazinoids and melatonin. Microbial sequencing results showed that bensulfuron methyl treated decreased the abundance of beneficial microorganisms (Gammaproteobacteria, Bacteroidia, and Blastocatella) in the rhizosphere soil, which positively correlated with the inhibition of soil enzyme activity and the secretion of allelopathic substances (benzoxazinoids and melatonin). Molecular docking further confirmed that bensulfuron methyl affects protein molecular structure by establishing hydrogen bonds, which disequilibrate wheat benzoxazinoids and melatonin metabolism. Therefore, bensulfuron methyl exposure disrupted the interaction between soil microorganisms and indole alkaloid metabolism, hindering plant development. This study provides constructive insights into the environmental risks of herbicides and agricultural product safety throughout wheat development.

Dual-Mediated Roles of H+-ATPase in Alleviating the Phytotoxicity of Imazethapyr to Nontarget Wheat

The regulation solutions and mechanisms of reducing pesticide phytotoxicity to nontarget plants are not well-defined and detailed. Here, we have proposed a new detoxification strategy to control the toxic effects of herbicide imazethapyr (IM) induced in wheat seedlings from the perspective of the plasma membrane (PM) H+-ATPase. We found that the changes in PM H+-ATPase activity have a regulatory effect on the phytotoxic effects induced by IM in plants. Treatment with PM H+-ATPase activators restored the reduced auxin content and photosynthetic efficiency caused by IM, thereby promoting plant growth. Application of a PM H+-ATPase inhibitor further reduced phosphorus content and significantly increased 2,4-dihydroxy-7-methoxy-2H,1,4-benzoxazin-3(4H)one (DIMBOA) and jasmonic acid levels. These effects indicate that auxin and DIMBOA may regulate plant growth trends and detoxification effects mediated by PM H+-ATPase. This work opens a new strategy for regulating herbicide toxicity to nontarget plants from the PM H+-ATPase.

Regulatory potential of secondary metabolite DIMBOA and baicalein to imazethapyr-induced toxicity in wheat seedlings

Controlling and mitigating the toxicity of herbicides to non-target plants is of significant importance in reducing ecological risks. The development of green and natural herbicide control technologies has become an urgent necessity. In this paper, how 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazine-3(4H)-one (DIMBOA) and baicalein alleviated oxidative stress induced by imazethapyr (IM) in wheat seedlings was investigated. We found that DIMBOA and baicalein enhanced the antioxidant enzyme activities in wheat seedlings exposed to IM and reduced the excessive reactive oxygen species due to IM stress by 21.3% and 23.5%, respectively. DIMBOA and baicalein also restored the iron content reduced by IM and effectively mitigated Fe2+ overload by alleviating the response of heme oxygenase 1 to IM stress. The antioxidant and iron homeostatic maintenance properties of DIMBOA and baicalein enhanced the defenses of wheat seedlings against IM stress. Our results highlight the potential implication of secondary metabolites as natural products to modulate herbicide toxicity to non-target plants.

Plasma Membrane (PM) H+-ATPase Mediates Rhizosphere Acidification and Regulates Herbicide Imazethapyr Toxicity in Wheat

The plasma membrane (PM) H+-ATPase is crucial for a plant defense system. However, there is currently no consensus on whether the PM H+-ATPase plays a role in alleviating the toxic effects of herbicides on nontarget plants. We found that under the herbicide imazethapyr (IM) exposure, PM H+-ATPase activity in wheat roots increased by approximately 69.53%, leading to rhizosphere acidification. When PM H+-ATPase activity is inhibited, the toxicity of IM significantly increases: When exposed to IM alone, the total Fe content of wheat roots decreased by 29.07%, the relative Fe2+ content increased by 27.75%, and the ROS content increased by 27.74%. When the PM H+-ATPase activity was inhibited, the corresponding data under IM exposure were 37.36%, 215%, and 57.68%, respectively. This work delves into the role of PM H+-ATPase in mediating the detoxification mechanism in plants exposed to herbicides, offering new insights into enhancing crop resistance against herbicides.

Transcriptomic and metabolomic analysis provides insight into imazethapyr toxicity to non-target plants

Imazethapyr is a widely used imidazolinone herbicide worldwide, and its potential adverse effects on non-target plants have raised concerns. Understanding the mechanisms of imazethapyr phytotoxicity is crucial for its agro-ecological risk assessment. Here, the comprehensive molecular responses and metabolic alterations of Arabidopsis in response to imazethapyr were investigated. Our results showed that root exposure to imazethapyr inhibited shoot growth, reduced chlorophyll contents, induced photoinhibition and decreased photosynthetic activity. By non-target metabolomic analysis, we identified 75 metabolites that were significantly changed after imazethapyr exposure, and they are mainly enriched in carbohydrate, lipid and amino acid metabolism. Transcriptomic analysis confirmed that imazethapyr significantly downregulated the genes involved in photosynthetic electron transport and the carbon cycle. In detail, 48 genes in the photosynthetic lightreaction and 11 genes in Calvin cycle were downregulated. Additionally, the downregulation of genes related to electron transport in mitochondria provides strong evidence for imazethapyr inhibiting photosynthetic carbon fixation and cellular energy metabolism as one of mechanisms of toxicity. These results revealed the molecular and metabolic basis of imazethapyr toxicity on non-target plants, contributing to environmental risk assessment and mitigate negative impact of imazethapyr residues in agricultural soils.

Mechanisms Underlying Allelopathic Disturbance of Herbicide Imazethapyr on Wheat and Its Neighboring Ryegrass (Lolium perenne)

As representatives of allelopathy, weeds consistently coexist with crops, exhibiting mutual growth inhibition. At the same time, herbicides are usually employed to control weeds. However, few studies have investigated how herbicides will affect allelopathy between crops and their neighboring weeds. Our findings suggested that allelopathic-induced phenotypic variations in ryegrass were reduced in the presence of the herbicide imazethapyr (IM), consistent with the antioxidant system analysis results. Additionally, IM affected the levels of allelochemical hydroxamic acid (Hx) in both plants. Hydroponic experiments revealed that this impact was due to the accelerated transportation of Hx from wheat to ryegrass, driven by ryegrass-secreted jasmonic acid. This study holds paramount significance for comprehending the effects of herbicides on the allelopathic interactions between nontargeted crops and neighboring weeds, contributing to an enhanced understanding of herbicides on plant species interactions.

Stereoselectivity of paclobutrazol enantiomers to oxidative stress in wheat

Chiral pesticides have the special chiral structures, so enantioselective biological effects are usually observed in living organisms. Current study used paclobutrazol as a case study and explored the enantioselective degradation and oxidative stress effect on wheat. The results demonstrated that the degradation of R-paclobutrazol was faster than S-paclobutrazol significantly and improved the content of MDA and O2 - in wheat plants, which proved that the R-paclobutrazol induced oxidative damage in wheat, showing selective biological effects, and S-paclobutrazol was friendly to wheat. This study provided a theoretical basis for the selective activity of chiral pesticides and the development of chiral pesticide monomers.

Phytotoxicity alleviation of imazethapyr to non-target plant wheat: active regulation between auxin and DIMBOA

Effectively controlling target organisms while reducing the adverse effects of pesticides on non-target organisms is a crucial scientific inquiry and challenge in pesticide ecotoxicology research. Here, we studied the alleviation of herbicide (R)-imazethapyr [(R)-IM] to non-target plant wheat by active regulation between auxin and secondary metabolite 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazine-3(4H)-one (DIMBOA). We found (R)-IM reduced 32.4% auxin content in wheat leaves and induced 40.7% DIMBOA accumulation compared to the control group, which effortlessly disrupted the balance between wheat growth and defense. Transcriptomic results indicated that restoration of the auxin level in plants promoted the up-regulation of growth-related genes and the accumulation of DIMBOA up-regulated the expression of defense-related genes. Auxin and DIMBOA alleviated herbicide stress primarily through effects in the two directions of wheat growth and defense, respectively. Additionally, as a common precursor of auxin and DIMBOA, indole adopted a combined growth and defense strategy in response to (R)-IM toxicity, i.e., restoring growth development and enhancing the defense system. Future regulation of auxin and DIMBOA levels in plants may be possible through appropriate methods, thus regulating the plant growth-defense balance under herbicide stress. Our insight into the interference mechanism of herbicides to the plant growth-defense system will facilitate the design of improved strategies for herbicide detoxification.

Imazethapyr disrupts plant phosphorus homeostasis and acquisition strategies

The deficiency of essential mineral nutrients caused by xenobiotics often results in plant mortality or an inability to complete its life cycle. Imazethapyr, a widely utilized imidazolinone herbicide, has a long-lasting presence in the soil-plant system and can induce toxicity in non-target plants. However, the effects of imazethapyr on mineral nutrient homeostasis remain poorly comprehended. In this study, Arabidopsis seedlings exposed to concentrations of 4 and 10 μg/L imazethapyr showed noticeable reductions in shoot development and displayed a distinct dark purple color, which is commonly associated with phosphorus (P) deficiency in crops. Additionally, the total P content in both the shoots and roots of Arabidopsis significantly decreased following imazethapyr treatment when compared to the control groups. Through the complementary use of physiological and molecular analyses, we discovered that imazethapyr hinders the abundance and functionality of inorganic phosphorus (Pi) transporters and acid phosphatase. Furthermore, imazethapyr impairs the plant's Pi-deficiency adaptation strategies, such as inhibiting Pi transporter activities and impeding root hair development, which ultimately exacerbate P starvation. These results provide compelling evidence that residues of imazethapyr have the potential to disrupt plant P homeostasis and acquisition strategies. These findings offer valuable insights for risk assessment and highlight the need to reconsider the indiscriminate use of imazethapyr, particularly under specific scenarios such as nutrient deficiency.

Role of Heme Oxygenase-1 in Dual Stress Response of Herbicide and Micronutrient Fe in Arabidopsis thaliana

Increasingly intensive agricultural practices are leading not only to herbicide contamination but also to nutritional stress on nontarget plants. This study evaluated the role of heme oxygenase-1 (HO-1) in the dual stress response of herbicide dichlorprop and micronutrient Fe in Arabidopsis thaliana. Our results revealed that co-treatment with 20 μM zinc protoporphyrin (a specific inhibitor of HO-1) reduced the activity of HO-1 by 21.6%, Fe²⁺ content by 19.8%, and MDA content by 20.0%, reducing abnormal iron aggregation and oxidative stress in response to the herbicide compared to treatment with (R)-dichloroprop alone, which has herbicidal activity. Thus, free Fe²⁺ released from HO-1 mediated dichlorprop-induced oxidative stress in the Fenton reaction and affected aberrant Fe aggregation, which also had an enantioselective effect. This study contributes to an in-depth understanding of the toxicity mechanism of herbicides under nutrient stresses, thus providing new strategies to control the environmental risks of herbicides.