Methylglyoxal detoxification pathway - Explored first time for imazethapyr tolerance in lentil (Lens culinaris L.)

Selenium and its nanoparticles modulate the metabolism of reactive oxygen species and morpho-physiology of wheat (Triticum aestivum L.) to combat oxidative stress under water deficit conditions

BACKGROUND

Wheat (Triticum aestivum L.) is one of the most important cereal crop species worldwide, but its growth and development are adversely influenced by drought stress. However, the application of trace elements is known to improve plant physiology under water-limited conditions. In this study, the effects of drought stress on wheat plants were investigated, with a focus on potential mitigation by foliar application of selenium nanoparticles (Se(np)) and sodium selenate (Na2SeO4). The experiment was conducted in a net house using a completely randomized design with four replications. The treatments involved three levels of drought stress (mild, moderate, and severe) started at 30 days after sowing (DAS), with foliar sprays of Se(np) and Se (both 25 µM) initiated at 27 DAS and repeated 4 times at 7-day intervals until 55 DAS.

RESULTS

Drought stress significantly reduced plant growth, whereas Se(np) and Se sprays enhanced it. Drought stress induced chlorophyll degradation, increased malondialdehyde and hydrogen peroxide levels, impaired membrane stability, and caused electrolyte leakage. Severe drought stress reduced the levels of antioxidants (e.g., proline, ascorbate, and glutathione by 4.18-fold, 80%, and 45%) and the activities of antioxidant enzymes (ascorbate peroxidase, dehydroascorbate reductase, and others). Conversely, treatment with Se(np) and Se restored these parameters, for example, 1.23-fold higher total chlorophyll content with Se(np) treatment, 26% higher APX activity with Se treatment, 15% lower electrolyte leakage with Se treatment in wheat plants under severe drought stress. This Se-associated enhancement facilitated rapid scavenging of reactive oxygen species and reduced methylglyoxal toxicity, thereby diminishing oxidative stress and positively affecting the morphophysiological and biochemical responses of the plants under drought.

CONCLUSIONS

Drought-stressed wheat plants exhibited reductions in physiological processes, including water uptake and photosynthetic activity. However, Se(np) and Se applied at 25 µM mitigated the detrimental effects of drought. The application of Se(np) was notably more effective than the application of Se in mitigating drought stress, indicating the potential of the application of Se(np) as a sustainable agricultural practice under water-limited conditions.

Methylglyoxal detoxifying gene families in tomato: Genome-wide identification, evolution, functional prediction, and transcript profiling

Methylglyoxal (MG) is a highly cytotoxic molecule produced in all biological systems, which could be converted into non-toxic D-lactate by an evolutionarily conserved glyoxalase pathway. Glutathione-dependent glyoxalase I (GLYI) and glyoxalase II (GLYII) are responsible for the detoxification of MG into D-lactate in sequential reactions, while DJ-1 domain containing glyoxalase III (GLYIII) catalyzes the same reaction in a single step without glutathione dependency. Afterwards, D-lactate dehydrogenase (D-LDH) converts D-lactate into pyruvate, a metabolically usable intermediate. In the study, a comprehensive genome-wide investigation has been performed in one of the important vegetable plants, tomato to identify 13 putative GLYI, 4 GLYII, 3 GLYIII (DJ-1), and 4 D-LDH genes. Expression pattern analysis using microarray data confirmed their ubiquitous presence in different tissues and developmental stages. Moreover, stress treatment of tomato seedlings and subsequent qRT-PCR demonstrated upregulation of SlGLYI-2, SlGLYI-3, SlGLYI-6A, SlGLYII-1A, SlGLYII-3B, SlDJ-1A, SlDLDH-1 and SlDLDH-4 in response to different abiotic stresses, whereas SlGLYI-6B, SlGLYII-1B, SlGLYII-3A, SlDJ-1D and SlDLDH-2 were downregulated. Expression data also revealed SlGLYII-1B, SlGLYI-1A, SlGLYI-2, SlDJ-1D, and SlDLDH-4 were upregulated in response to various pathogenic infections, indicating the role of MG detoxifying enzymes in both plant defence and stress modulation. The functional characterization of each of these members could lay the foundation for the development of stress and disease-resistant plants promoting sustainable agriculture and production.

Exploration of the biodegradation pathway and enhanced removal of imazethapyr from soil by immobilized Bacillus marcorestinctum YN1

Excessive or inappropriate applications of imazethapyr cause severe ecological deteriorations and health risks in human. A novel bacterial strain, i.e., Bacillus marcorestinctum YN1, was isolated to efficiently degrade imazethapyr, with the degradation pathways and intermediates predicted. Protein mass spectrometry analysis identified enzymes in strain YN1 potentially involved in imazethapyr biodegradation, including methylenetetrahydrofolate dehydrogenase, carbon-nitrogen family hydrolase, heme degrading monooxygenase, and cytochrome P450. The strain YN1 was further immobilized with biochar (BC600) prepared from mushroom waste (i.e., spent mushroom substrate) by pyrolysis at 600 °C to evaluate its degrading characteristics of imazethapyr. Scanning electron microscope observation showed that strain YN1 was adsorbed in the rich pore structure of BC600 and the adsorption efficiency reached the maximum level of 88.02% in 6 h. Both energy dispersive X-ray and Fourier transform infrared spectroscopy analyses showed that BC600 contained many elements and functional groups. The results of liquid chromatography showed that biochar-immobilized strain YN1 (IBC-YN1) improved the degradation rate of imazethapyr from 79.2% to 87.4%. The degradation rate of imazethapyr by IBC-YN1 could still reach 81.0% in the third recycle, while the bacterial survival rate was 67.73% after 180 d storage at 4 °C. The treatment of IBC-YN1 significantly shortened the half-life of imazethapyr in non-sterilized soil from 35.51 to 11.36 d, and the vegetative growth of imazethapyr sensitive crop plant (i.e., Cucumis sativus L.) was significantly increased in soil remediated, showing that the inhibition rate of root length and fresh weight were decreased by 12.45% and 38.49% respectively. This study exhanced our understanding of microbial catabolism of imazethapyr, and provided a potential in situ remediation strategy for improving the soil environment polluted by imazethapyr.

Evaluating the imazethapyr herbicide mediated regulation of phenol and glutathione metabolism and antioxidant activity in lentil seedlings

The imidazolinone group of herbicides generally work for controlling weeds by limiting the synthesis of the aceto-hydroxy-acid enzyme, which is linked to the biosynthesis of branched-chain amino acids in plant cells. The herbicide imazethapyr is from the class and the active ingredient of this herbicide is the same as other herbicides Contour, Hammer, Overtop, Passport, Pivot, Pursuit, Pursuit Plus, and Resolve. It is commonly used for controlling weeds in soybeans, alfalfa hay, corn, rice, peanuts, etc. Generally, the herbicide imazethapyr is safe and non-toxic for target crops and environmentally friendly when it is used at low concentration levels. Even though crops are extremely susceptible to herbicide treatment at the seedling stage, there have been no observations of its higher dose on lentils (Lens culinaris Medik.) at that stage. The current study reports the consequence of imazethapyr treatment on phenolic acid and flavonoid contents along with the antioxidant activity of the phenolic extract. Imazethapyr treatment significantly increased the activities of several antioxidant enzymes, including phenylalanine ammonia lyase (PAL), phenol oxidase (POD), glutathione reductase (GR), and glutathione-s-transferase (GST), in lentil seedlings at doses of 0 RFD, 0.5 RFD, 1 RFD, 1.25 RFD, 1.5 RFD, and 2 RFD. Application of imazethapyr resulted in the 3.2 to 26.31 and 4.57-27.85% increase in mean phenolic acid and flavonoid content, respectively, over control. However, the consequent fold increase in mean antioxidant activity under 2, 2- diphenylpicrylhdrazyl (DPPH) and ferric reducing antioxidant power (FRAP) assay system was in the range of 1.17-1.85 and 1.47-2.03%. Mean PAL and POD activities increased by 1.63 to 3.66 and 1.71 to 3.35-fold, respectively, in agreement with the rise in phenolic compounds, indicating that these enzyme's activities were modulated in response to herbicide treatment. Following herbicide treatments, the mean thiol content also increased significantly in corroboration with the enhancement in GR activity in a dose-dependent approach. A similar increase in GST activity was also observed with increasing herbicide dose.

Application of biochar and humic acid improves the physiological and biochemical processes of rice (Oryza sativa L.) in conferring plant tolerance to arsenic-induced oxidative stress

Biochar (BC) and humic acid (HA) are well-documented in metal/metalloid detoxification, but their regulatory role in conferring plant oxidative stress under arsenic (As) stress is poorly understood. Therefore, we aimed at investigating the role of BC and HA (0.2 and 0.4 g kg-1 soil) in the detoxification of As (0.25 mM sodium arsenate) toxicity in rice (Oryza sativa L. cv. BRRI dhan75). Arsenic exhibited an increased lipid peroxidation, hydrogen peroxide, electrolyte leakage, and proline content which were 32, 30, 9, and 89% higher compared to control. In addition, the antioxidant defense system of rice consisting of non-enzyme antioxidants (18 and 43% decrease in ascorbate and glutathione content) and enzyme activities (23-50% reduction over control) was decreased as a result of As toxicity. The damaging effect of As was prominent in plant height, biomass acquisition, tiller number, and relative water content. Furthermore, chlorophyll and leaf area also exhibited a decreasing trend due to toxicity. Arsenic exposure also disrupted the glyoxalase system (23 and 33% decrease in glyoxalase I and glyoxalase II activities). However, the application of BC and HA recovered the reactive oxygen species-induced damages in plants, upregulated the effectiveness of the ascorbate-glutathione pool, and accelerated the activities of antioxidant defense and glyoxalase enzymes. These positive roles of BC and HA ultimately resulted in improved plant characteristics with better plant-water status and regulated proline content that conferred As stress tolerance in rice. So, it can be concluded that BC and HA effectively mitigated As-induced physiology and oxidative damage in rice plants. Therefore, BC and HA could be used as potential soil amendments in As-contaminated rice fields.

Methylglyoxal metabolism is altered during defence response in pigeonpea (Cajanus cajan (L.) Millsp.) against the spotted pod borer (Maruca vitrata)

Pigeonpea (Cajanus cajan ) production can be affected by the spotted pod borer (Maruca vitrata ). Here, we identified biochemical changes in plant parts of pigeonpea after M. vitrata infestation. Two pigeonpea genotypes (AL 1747, moderately resistant; and MN 1, susceptible) were compared for glyoxalase and non-glyoxalase enzyme systems responsible for methylglyoxal (MG) detoxification, γ-glutamylcysteine synthetase (γ-GCS), glutathione-S-transferase (GST) and glutathione content in leaves, flowers and pods under control and insect-infested conditions. MN 1 had major damage due to M. vitrata infestation compared to AL 1747. Lower accumulation of MG in AL 1747 was due to higher activities of enzymes of GSH-dependent (glyoxylase I, glyoxylase II), GSH-independent (glyoxalase III) pathway, and enzyme of non-glyoxalase pathway (methylglyoxal reductase, MGR), which convert MG to lactate. Decreased glyoxylase enzymes and MGR activities in MN 1 resulted in higher accumulation of MG. Higher lactate dehydrogenase (LDH) activity in AL 1747 indicates utilisation of MG detoxification pathway. Higher glutathione content in AL 1747 genotype might be responsible for efficient working of MG detoxification pathway under insect infestation. Higher activity of γ-GCS in AL 1747 maintains the glutathione pool, necessary for the functioning of glyoxylase pathway to carry out the detoxification of MG. Higher activities of GST and GPX in AL 1747 might be responsible for detoxification of toxic products that accumulates following insect infestation, and elevated activities of glyoxylase and non-glyoxylase enzyme systems in AL 1747 after infestation might be responsible for reducing reactive cabanoyl stress. Our investigation will help the future development of resistant cultivars.

Proline-mediated activation of glyoxalase II improve methylglyoxal detoxification in Oryza sativa L. under chromium injury: Clarification via vector analysis of enzymatic activities and gene expression

Environmental factors affect plants in several ways including the excessive accumulation of methylglyoxal (MG), resulting in dysfunctions of many biological processes. Exogenous proline (Pro) application is one of the successful strategies to increase plant tolerance against various environmental stresses, including chromium (Cr). This study highlights the alleviation role of exogenous Pro on MG detoxification in rice plants induced by Cr(Vl) through modifying the expression of glyoxalase I (Gly I)- and glyoxalase II (Gly II)-related genes. The MG content in rice roots was significantly reduced by Pro application under Cr(VI) stress, however, there was little effect on the MG content in shoots. In this connection, the vector analysis was used to compare the involvement of Gly l and Gly II on MG detoxification in 'Cr(VI)' and 'Pro+Cr(VI)' treatments. Results exhibited that vector strength in rice roots increased with an increase in Cr concentrations, while there was a negligible difference in the shoots. The comparative analysis demonstrated that the vector strengths in roots under 'Pro+Cr(VI)' treatments were higher than 'Cr(VI)' treatments, suggesting that Pro improved Gly II activity more efficiently to reduce MG content in roots. Calculation of the gene expression variation factors (GEFs) indicated a positive effect of Pro application on the expression of Gly I and Gly ll-related genes, wherein a stronger impact was in roots than the shoots. Together, the vector analysis and gene expression data reveal that exogenous Pro chiefly improved Gly ll activity in rice roots which subsequently enhanced MG detoxification under Cr(VI) stress.

Insight into the physiological and biochemical mechanisms of biostimulating effect of Ascophyllum nodosum and Moringa oleifera extracts to minimize cadmium-induced oxidative stress in rice

Cadmium (Cd) is a serious threat for environmental sustainability as it can be taken up quickly by plants and transported to the food chain of living organisms. It alters plants' metabolic and physiological activities and causes yield loss, thereby, enhancing plant tolerance to Cd stress is of utmost essential. Therefore, an experiment was executed to investigate the potential role of Ascophyllum nodosum extract (ANE) and moringa (Moringa oleifera) leaf extract (MLE) to confer Cd tolerance in rice (Oryza sativa cv. BRRI dhan89). Thirty-five-day-old seedling was subjected to Cd stress (50 mg kg-1 CdCl2) alone and in a combination of ANE (0.25%) or MLE (0.5%) in a semi-controlled net house. Exposure to Cd resulted in accelerated production of reactive oxygen species, enhanced lipid peroxidation, and disrupted antioxidant defense and glyoxalase system, thus retarded plant growth, biomass production, and yield attributes of rice. On the contrary, the supplementation of ANE or MLE enhanced the contents of ascorbate and glutathione, and the activities of antioxidant enzymes such as ascorbate peroxidase, dehydroascorbate reductase, monodehydroascorbate reductase, glutathione reductase, glutathione peroxidase, and catalase. Moreover, supplementation of ANE and MLE enhanced the activities of glyoxalase I and glyoxalase II which prevented the overgeneration of methylglyoxal in Cd stressed rice plants. Thus, because of ANE and MLE addition Cd-induced rice plants showed a noticeable declination in membrane lipid peroxidation, hydrogen peroxide generation, and electrolyte leakage, whereas improved water balance. Furthermore, the growth and yield attributes of Cd-affected rice plants were improved with the supplementation of ANE and MLE. All the studied parameters indicates the potential role of ANE and MLE in mitigating Cd stress in rice plants through improving the physiological attributes, modulating antioxidant defense and glyoxalase system.

Effect of herbicide stress on synchronization of carbon and nitrogen metabolism in lentil (Lens culinaris Medik.)

Weed invasion causes significant yield losses in lentil. Imazethapyr (IM), a broad-spectrum herbicide inhibits the biosynthesis of branched chain amino acids necessary for plant growth. Plant growth depends upon translocation of photo-assimilates and their partitioning regulated by carbon and nitrogen metabolism. This study aimed to investigate the impact of imazethapyr spray on carbon and nitrogen metabolism in tolerant (LL1397 and LL1612) and susceptible (FLIP2004-7L and PL07) lentil genotypes during vegetative and reproductive development. Significantly higher activities of invertases and sucrose synthase (cleavage) in leaves and in podwall and seeds during early phase of development in tolerant genotypes were observed as compared to susceptible genotypes under herbicide stress that might be responsible for providing hexoses required for their growth. Activities of sucrose synthesizing enzymes, sucrose phosphate synthase and sucrose synthase (synthesis) increased significantly in podwalls and seeds of LL1397 and LL1612 genotypes during later phase of development towards maturity while the activities decreased in FLIP2004-7L and PL07 genotypes under herbicide stress. Activities of nitrate and nitrite reductase, glutamine 2-oxoglutarate aminotransferase, glutamine synthetase and glutamate dehydrogenase were increased in leaves, podwalls and seeds of LL1397 and LL1612 under herbicide stress. A proper synchronization of carbon and nitrogen metabolism in tolerant lentil genotypes during vegetative and reproductive phase might be one of the mechanisms for their recovery from herbicide stress. This first ever comprehensive information will provide a basis for future studies on the molecular mechanism of source sink relationship in lentil under herbicide stress and will be utilized in breeding programmes.