Jasmonic acid-mediated enhanced regulation of oxidative, glyoxalase defense system and reduced chromium uptake contributes to alleviation of chromium (VI) toxicity in choysum (Brassica parachinensis L.)

Glycine betaine enhances tolerance of low temperature combined with low light in pepper (Capsicum annuum L.) by improving the antioxidant capacity and regulating GB metabolism

Glycine betaine (GB) is commonly used as an osmotic regulator and a donor to facilitate changes in methylation in plants and animals, thereby enhancing stress resistance. However, low temperature combined with low light stress represent the most prevalent stresses during pepper growth period in northwest China, and limited studies have focused on the potential stress-mitigating effects of GB. Therefore, to examine the regulatory mechanism of GB-induced tolerance to LL stress, pepper seedlings were pretreated with 20 mmol L-1 GB and 60 μmol L-1 3-Deazaneplanocin A hydrochloride at a temperature of 10/5 °C and illumination of 100 μmol m-2 s-1. The results demonstrated that GB significantly alleviated the detrimental effects of low temperature combined with low light stress on growth of primary and lateral roots and increased the roots absorption of mineral nutrients (N, P, Ca, Fe, and Zn). In addition, GB induced the expression of the genes for CaSOD, CaPOD, CaCAT, CaGR1, and CaDHAR, improved osmotic regulation, and increased the activities of enzymatic (superoxide dismutase, peroxidase, catalase, glutathione reductase, and dehydroascorbate reductase) and non-enzymatic antioxidants (ascorbate and glutathione). This resulted in enhanced scavenging of reactive oxygen species, thereby maintaining a balanced oxidation-reduction within the cells. Furthermore, GB substituted S-adenosylmethionine, a partial methylation donor, during the methyl group metabolism process, altering the m6A methylation level and increasing the resistance of pepper seedlings to LL stress. Overall, exogenous GB pretreatment could be used as a potential strategy for enhancing the LL tolerance of plants.

Mitigating effects of Methyl Jasmonate on photosynthetic inhibition and oxidative stress of pepper (Capsicum annuum L) seedlings under low temperature combined with low light

Low temperature combined with low light (LL) is a critical abiotic stress that restricting plant growth and yield of pepper (Capsicum annuum L.). Methyl jasmonate (MeJA) is considered with potential benefits for improving plant stress resistance; however, the physiological mechanisms underlying the adaptation of pepper to LL stress have not been explored. This study aimed to investigate the potential mitigating effects of foliar MeJA (200 μmol L-1) application on pepper seedlings subjected to LL stress (10/5 °C, 100 μmol m-2 s-1) for 168 h. Our results indicated that the application of exogenous MeJA reduced the negative effect on growth inhibition of pepper seedlings caused by LL stress, significantly increased chlorophyll contents and photosynthetic capacity as a result of improved photosynthesis rate. In addition, MeJA reduced the accumulation of reactive oxygen species and malondialdehyde contents induced by LL stress, while enhancing the activities of superoxide dismutase, peroxidase, catalase, ascorbate peroxidase, dehydroascorbate reductase, and monodehydroascorbate reductase as a result of upregulated expression levels of antioxidant enzyme genes (CaSOD, CaPOD, CaCAT, CaAPX, CaGR, CaDHAR, and CaMDHAR). Additionally, it increased the ascorbic acid and reduced glutathione content, while reducing oxidized glutathione content, thereby preventing membrane lipid peroxidation and protecting plants from oxidative damage under LL stress. Furthermore, seedlings treated with MeJA exhibited significantly enhanced soluble sugar and soluble protein contents in leaves. Taken together, present findings indicate that MeJA application may serve as an effective strategy for mitigating LL-induced oxidative stress by maintaining plant growth, enhancing chlorophyll fluorescence, upregulating the antioxidant defence system, optimizing ascorbate-glutathione cycle, and osmotic adjustment.

Combined application of earthworms and plant growth promoting rhizobacteria improve metal uptake, photosynthetic efficiency and modulate secondary metabolites levels under chromium metal toxicity in Brassica juncea L

Chromium (Cr) toxicity impairs essential morphological and metabolic activities in plants. The present investigation was carried out to evaluate the beneficial role of plant growth promoting rhizobacterial strains namely Pseudomonas aeruginosa (M1), Burkholderia gladioli (M2) and earthworms (Eisenia fetida) in alleviating Cr toxicity in 10 days old Brassica juncea L. The findings delineated that addition of earthworms and PGPR restored growth, boosted Cr uptake and showed upregulation of metal transporter genes (SULTR 1-4). Supplementation of rhizospheric amendments reinstated Cr induced impairment in photosynthetic attributes. Gaseous exchange attributes, the efficiency of PS II, the content of total phenols, anthocyanin and flavonoids was enhanced with application of earthworms along with PGPR. Confocal imaging of primary photosynthetic pigment (chlorophyll), accessory photosynthetic pigment (carotenoids) and total phenols showed maximum fluorescence with combined inoculation of earthworms and both microbial strains (M1M2). The gene expression analysis revealed that Phyotene synthase (PSY), Photosystem II core protein psb A, psb B were down regulated in Cr stressed seedlings which upon supplementation with earthworms and PGPR were upregulated. Further, Phenylalanine ammonialyase (PAL), chalcone synthase (CHS) were upregulated with addition of earthworms and PGPR. Increased nitric oxide content, enhanced activity and upregulation of nitrate reductase (NR) gene was observed with addition of PGPR and earthworms.

Antioxidant Responses in Chromium-Stressed Maize as Influenced by Foliar and Root Applications of Fulvic Acid

Maize (Zea mays L.) faces significant challenges to its growth and productivity from heavy metal stress, particularly Chromium (Cr) stress, which induces reactive oxygen species (ROS) generation and damages photosynthetic tissues. This study aimed to investigate the effects of fulvic acid (FA) application, via foliar spray or root irrigation, on mitigating chromium stress in maize by evaluating its impact on antioxidant activity and growth parameters. Two maize varieties, P3939 and 30Y87, were subjected to chromium stress (CrCl3·6H2O) at concentrations of 300 µM and 100 µM for a duration of 5 weeks. The experiment was conducted in a wire house under natural environmental conditions at the Seed Centre, Institute of Botany, University of the Punjab, Lahore, Pakistan. Physiological assessments included electrolyte leakage, chlorophyll pigment content, malondialdehyde (MDA) levels, and activities of antioxidant enzymes such as catalase (CAT), ascorbate peroxidase (APX), and guaiacol peroxidase (GPX) in maize leaves. Growth parameters were also monitored. The results revealed that chromium stress significantly reduced chlorophyll content and increased oxidative stress, as evidenced by elevated MDA levels and electrolyte leakage. However, FA application notably mitigated these effects: chlorophyll content improved by 15%, and MDA levels decreased significantly. Irrigation with FA was particularly effective, reducing MDA levels by 40% compared to the 300 µM chromium treatment. Furthermore, while chromium stress enhanced antioxidant enzyme activities, FA application further boosted total soluble protein levels and antioxidant enzyme activities under stress conditions. In conclusion, FA application demonstrates potential in improving maize tolerance to heavy metal stress by enhancing the antioxidant defense system and preserving photosynthetic pigments. These findings highlight FA's promise as a practical strategy for mitigating the negative impacts of chromium stress on maize, promoting sustainable agricultural practices in contaminated environments.

Chromium uptake and its impact on antioxidant level, photosynthetic machinery, and related gene expression in Brassica napus cultivars

The development of heavy metals, particularly chromium (Cr)-tolerant crop cultivars, is hampered due to lack of understanding of the mechanisms behind Cr stress tolerance. In this study, two Brassica napus cultivars, ZS758 and ZD622, were compared for Cr stress resistance by using the chlorophyll a fluorescence technique and biochemical characteristics. In both cultivars, Cr stress dramatically decreased PSII and PSI efficiency, biomass accumulation, and antioxidant enzyme levels. Although, cultivar ZS758 showed reduction in oxidative stress by decreasing the production of reactive oxygen species (ROS) in terms of reduced H2O2 and MDA content and increased enzymatic activities of key antioxidants enzymes including SOD, APX, CAT, and POD activities that play a crucial role in the regulation of numerous transcriptional pathways involved in oxidative stress responses. Higher non-photochemical quenching (NPQ) and QY were found in tolerant ZS758 cultivar under Cr stress, indicating that tolerant cultivar had a greater capacity to preserve PSII activity under Cr stress by enhancing heat dissipation as a photo-protective component of NPQ. Lower PSI activity and electron transfer from PSII were confirmed by lower PSI efficiency and higher donor end limitation of PSI in both rapeseed cultivars. The Cr concentration was greater in the ZD622 as compared to ZS758, which affected the mineral nutrients profile and damaged the cellular ultrastructure and related gene expression levels. However, current study suggest that cultivar ZS758 is more resistant to Cr stress than ZD622 due to improved metabolism and structural integrity and Cr stress tolerance that is linked with the increased PSII activity, NPQ, and antioxidant potential; these physiological characteristics can be exploited to select cultivars for Cr stress tolerance.

Leveraging plant-based remediation technologies against chromite mining toxicity

The release of hazardous hexavalent chromium from chromite mining seriously threatens habitats and human health by contaminating water, air, and soil. Vulnerability to hexavalent chromium can result in significant health risks, viz, respiratory issues, gastrointestinal illnesses, skin problems in humans, and a plethora of toxic effects in animals. Moreover, Cr(VI) toxicity can adversely affect plant physiology by inhibiting seed germination, nutrient uptake, cell division, and root development, ultimately impairing growth and vitality. Fortunately, innovative techniques such as phytoremediation and nanotechnology have been developed to address heavy metal contamination, offering a promising solution, mainly through the use of hyperaccumulating plants. Biochar derived from plant waste is widely used and is emerging as a sustainable strategy for remediating Cr(VI) contamination. Biochar is rich in carbon and highly influential in removing Cr(VI) from contaminated soils. This approach addresses immediate challenges while providing a sustainable pathway for environmental rehabilitation in chromium mining. Integrating innovative technologies with nature-based solutions offers a holistic approach to reducing the harmful effects of chromium mining, thus protecting both human well-being and ecosystems. This review highlights the impact of Cr(VI) on different living biotas and further emphasizes the use of plants and plant-based materials for the sustainable remediation of chromite mining regions.

Synergistic effects of melatonin and glycine betaine on seed germination, seedling growth, and biochemical attributes of maize under salinity stress

Salinity stress represents a major threat to crop production by inhibiting seed germination, growth of seedlings, and final yield and, therefore, to the social and economic prosperity of developing countries. Recently, plant growth-promoting substances have been widely used as a chemical strategy for improving plant resilience towards abiotic stresses. This study aimed to determine whether melatonin (MT) and glycine betaine (GB) alone or in combination could alleviate the salinity-induced impacts on seed germination and growth of maize seedlings. Increasing NaCl concentration from 100 to 200 mM declined seed germination rate (4.6-37.7%), germination potential (24.5-46.7%), radical length (7.7-40.0%), plumule length (2.2-35.6%), seedling fresh (1.7-41.3%) and dry weight (23.0-56.1%) compared to control (CN) plants. However, MT and GB treatments lessened the adverse effects of 100 and 150 mM NaCl and enhanced germination comparable to control plants. In addition, results from the pot experiments show that 200 mM NaCl stress disrupted the osmotic balance and persuaded oxidative stress, presented by higher electrolyte leakage, hydrogen peroxide, superoxide radicals, and malondialdehyde compared to control plants. However, compared to the NaCl treatment, NaCl+MT+GB treatment decreased the accumulation of malondialdehyde (24.2-42.1%), hydrogen peroxide (36.2-44.0%), and superoxide radicals (20.1-50.9%) by up-regulating the activity of superoxide dismutase (28.4-51.2%), catalase (82.2-111.5%), ascorbate peroxidase (40.3-59.2%), and peroxidase (62.2-117.9%), and by enhancing osmolytes accumulation, thereby reducing NaCl-induced oxidative damages. Based on these findings, the application of MT+GB is an efficient chemical strategy for improving seed germination and growth of seedlings by improving the physiological and biochemical attributes of maize under 200 mM NaCl stress.

Isolation and characterization of chromium-resistant bacteria and their effects on germination, growth, and Cr accumulation in Capsicum annum (L.) under Cr stress

Chromium (Cr) is a well-known environmental pollutant while less information is available on the role of Cr-resistant bacteria in the alleviation of Cr-stress in chili (Capsicum annum L.) plants. Effect of Cr-resistant bacterial strains on growth and Cr uptake by chili plants was investigated. The results revealed that Cr-stress showed a negative effect on germination, photosynthesis, and relative water content but the inoculation ameliorated the plant stress. Chromium-resistant bacterial strains enhanced the shoot and root growth (33% SL, 19.7% RL), shoot and root dry weight (35%, 32.9%), relative water content (32.25%), membrane stability index (46.52%) SPAD value (50.76%), Cr concentration in shoots and roots (19.87 and 18.52 mg kg-1), bioaccumulation and translocation factor (0.396 mgkg-1), and seedling vigor index (40.8%) of plants. Chromium-resistant bacterial strains enhanced the NPK uptake while reduced Cr uptake by plants. The morphological and biochemical examination of rhizobacterial strains (and NM28) resistant to Cr-stress revealed smooth, off-white colonies of bacteria composed of rod-shaped cells which are Gram positive in reaction while negative in catalase activity. High quantities of malic acid were produced by bacterial strains under study i.e. NM8 (926.12 μgmL-2) and NM28 (992.25 μgmL-2). These strains were identified as Bacillus cereus strain NM8 and Bacillus subtilis strain NM28 through 16S rRNA sequencing. Results showed that B. cereus strain NM28 is more effective than B. cereus strain NM8 in promoting the growth of Cr-stressed Chili that might be suitable to develop biofertilizer for sustainable production of vegetables under metal stress.

Enhancing cauliflower growth under cadmium stress: synergistic effects of Cd-tolerant Klebsiella strains and jasmonic acid foliar application

The pollution of heavy metals (HMs) is a major environmental concern for agricultural farming communities due to water scarcity, which forces farmers to use wastewater for irrigation purposes in Pakistan. Vegetables grown around the cities are irrigated with domestic and industrial wastewater from areas near mining, paint, and ceramic industries that pollute edible parts of crops with various HMs. Cadmium (Cd) is an extremely toxic metal in arable soil that enters the food chain and damages the native biota, ultimately causing a reduction in plant growth and development. However, the use of microbes and growth regulators enhances plant growth and development as well as HM immobilization into the cell wall and hinders their entry into the food chain. Thus, the integrated use of bacterial consortium along with exogenously applied jasmonic acid (JA) mitigates the adverse effect of metal stress, ultimately reducing the metal mobility into roots by soil. Therefore, the current study was conducted to check the impact of Cd-tolerant bacteria and JA on the growth, nutrient status, and uptake of Cd in the cauliflower (Brassica oleracea). Our results demonstrated that increasing concentrations of Cd negatively affect growth, physiological, and biochemical attributes, while the use of a bacterial consortium (SS7 + SS8) with JA (40 μmol L-1) significantly improved chlorophyll contents, stem fresh and dry biomass (19.7, 12.7, and 17.3%), root length and root fresh and dry weights (28.8, 15.2, and 23.0%), and curd fresh and dry weights and curd diameter (18.7, 12.6, and 15.1%). However, the maximum reduction in soil Cd, roots, and curd uptake was observed by 8, 11, and 9.3%, respectively, under integrated treatment as compared to the control. Moreover, integrating bacterial consortium and JA improves superoxide dismutase (SOD) (16.79%), peroxidase dismutase (POD) (26.96%), peroxidase (POX) (26.13%), and catalase (CAT) (26.86%). The plant nitrogen, phosphorus, and potassium contents were significantly increased in soil, roots, and curd up to 8, 11, and 9.3%, respectively. Hence, a consortium of Klebsiella strains in combination with JA is a potential phytostabilizer and it reduces the uptake of Cd from soil to roots to alleviate the adverse impact on cauliflower's growth and productivity.

Phosphorus and selenium compounding mitigates Cr stress in peanut seedlings by enhancing growth homeostasis and antioxidant properties

Peanut is an economically important crop, but it is susceptible to Cr contamination. In this study, we used peanut as experimental material to investigate the effects of exogenous P, Se interacting with Cr on the nutrient growth and antioxidant system of peanut seedlings by simulating Cr (0 μM, 50 μM, and 100 μM) stress environment. The results showed that exogenous P, Se supply could mitigate irreversible damage to peanut seedlings by altering the distribution of Cr in roots and aboveground, changing root conformation, and repairing damaged cells to promote growth. When the Cr concentration is 100 μM, it exhibits the highest toxicity. Compared to the control group P and Se (0 MM), the treatment with simultaneous addition of P + Se (0.5 + 6.0) resulted in a significant increase in root length and root tip number by 248.7% and 127.4%, respectively. Additionally, there was a 46.9% increase in chlorophyll content, a 190.2% increase in total surface area of the seedlings, and a respective increase of 149.1% and 180.3% in soluble protein content in the shoot and roots. In addition, by restricting the absorption of Cr and reducing the synthesis of superoxide dismutase SOD (Superoxide dismutase), CAT (Catalase), POD (Peroxidase), and MDA (Malonaldehyde), it effectively alleviates the oxidative stress on the antioxidant system. Therefore, the exogenous addition of P (0.5 MM) and Se (6.0 MM) prevented the optimal concentration of chromium toxicity to peanuts. Our research provides strong evidence that the exogenous combination of P and Se reduces the risk of peanut poisoning by Cr, while also exploring the optimal concentration of exogenous P and Se under laboratory conditions, providing a basis for further field experiments.

Methyl jasmonate enhances the safe production ability of Cd-stressed wheat by regulating the antioxidant capacity, Cd absorption, and distribution in wheat

Identifying green and effective measures for reducing wheat Cd toxicity and grain Cd accumulation is crucial. This study used seedling sand culture and full-grown pot experiments of wheat cultivars 'Luomai23' (LM) and 'Zhongyu10' (ZY). The purpose was to determine the effects of exogenous MeJA on the phenotype, photosynthesis, antioxidant system, Cd accumulation and distribution, transporter gene expression, and cell wall properties of Cd-stressed wheat. Compared with Cd treatment alone, the plant height and maximum root length treated with 0.001 μM MeJA increased by more than 6.3% and 16.6%, respectively. Under 5 mg⋅kg-1 Cd treatment, spraying 10 μM MeJA increased the photosynthetic rate of LM and ZY by 23.5% and 35.8% at the filling stage, respectively. Methyl jasmonate significantly reduced the H2O2 and MDA contents by increasing the activities of POD, DHAR, MDHAR, and GR and the contents of AsA and GSH. Applicating MeJA increased the content of chelate substances, cell wall polysaccharides, and cell wall functional groups. Besides, MeJA regulated the expression of Cd transporter genes, with shoot and root Cd content decreasing by 46.7% and 27.9% in LM, respectively. Spraying 10 μM MeJA reduced Cd absorption and translocation from vegetative organs to grains, thus reducing the grain Cd content of LM and ZY by 36.1 and 39.9% under 5 mg⋅kg-1 Cd treatment, respectively. Overexpressing TaJMT significantly increased the MeJA content and Cd tolerance of Arabidopsis. These results have improved the understanding of the mechanism through which MeJA alleviates Cd toxicity and reduces Cd accumulation in wheat.

Salicylic acid and jasmonic acid-mediated different fate of nickel phytoremediation in two populations of Alyssum inflatum Nyár

This study investigates Ni phytoremediation and accumulation potential in the presence of salicylic acid (SA) (0, 50 and 200 μM) and jasmonic acid (JA) (0, 5 and 10 μM) in two populations of Alyssum inflatum under various nickel (Ni) doses (0, 100 and 400 μM). By measuring Ni levels in the shoots and roots, values of bioaccumulation coefficient (BAC), biological concentration factor (BCF) and translocation factor (TF) were calculated to quantify Ni accumulation and translocation between plant organs. Additionally, the amounts of histidine (His), citric acid (CA) and malic acid (MA) were explored. The results showed that plant dry weight (DW) [in shoot (29.8%, 8.74%) and in root (21.6%, 24.4%)] and chlorophyll [a (17.1%, 32.5%), b (10.1%, 30.9%)] declined in M and NM populations respectively, when exposed to Ni (400 μM). Conversely, the levels of MA [in shoot (37.0%, 32.0%) and in root (25.5%, 21.2%)], CA [in shoot (17.0%, 10.0%) and in root (47.9%, 37.2%)] and His [in shoot (by 1.59- and 1.34-fold) and in root (by 1.24- and 1.18-fold)] increased. Also, in the presence 400 μM Ni, the highest accumulation of Ni was observed in shoots of M (1392 μg/g DW) and NM (1382 μg/g DW). However, the application of SA and JA (especially in Ni 400 μM + SA 200 μM + JA 5 and 10 μM treatments) mitigated the harmful impact of Ni on physiological parameters. Also, a decreasing trend was observed in the contents of MA, CA, and His. The reduction of these compounds as important chelators of Ni caused a decrease in root-to-shoot Ni transfer and reducing accumulation in the shoots of both populations. The values of phytoremediation indices in both populations exposed to Ni (400 μM) were above one. In presence of the SA and JA, these indices showed a decreasing trend, although the values remained above one (BAC, BCF and TF > 1). Overall, the results indicated that SA and JA can reduce phytoremediation potential of the two populations through different mechanisms.

Characteristics and numerical simulation of chromium transportation, migration and transformation in soil-groundwater system

Understanding chromium (Cr) migration and dispersion patterns in the soil-groundwater system is critical for the control and remediation of subsurface Cr contamination. In this study, a typical Cr-contaminated site from the Pearl River Delta (PRD) in China was simulated with a three-dimensional (3D) sandbox experiment to investigate the migration and transformation behavior of Cr. Results revealed that under the combined influence of rainfall and groundwater flow, a complex flow field favorable for 3D migration and solute dispersion was formed. The flow field characteristics were influenced by water-table depth, which in turn affected Cr behavior in the system. Moreover, downward flow field expansion under low water-table conditions led to Cr vertical migration range expansion, causing greater contamination in the deep soil. The migration process was accompanied with Cr(VI) reduction, during which approximately 75 % of the total Cr was immobilized in soils. The reactive transport model achieved a good fit for Cr retention and morphological distribution in the solid phase. The model indicates that Cr is more readily transported and dispersed with groundwater, and Cr migrated and spread downstream by 15 m during the eighth year. Therefore, managing water-table depth could be a strategy to minimize the Cr vertical migration and contamination.

Effects of Jasmonic Acid on Stress Response and Quality Formation in Vegetable Crops and Their Underlying Molecular Mechanisms

The plant hormone jasmonic acid plays an important role in plant growth and development, participating in many physiological processes, such as plant disease resistance, stress resistance, organ development, root growth, and flowering. With the improvement in living standards, people have higher requirements regarding the quality of vegetables. However, during the growth process of vegetables, they are often attacked by pests and diseases and undergo abiotic stresses, resulting in their growth restriction and decreases in their yield and quality. Therefore, people have found many ways to regulate the growth and quality of vegetable crops. In recent years, in addition to the role that JA plays in stress response and resistance, it has been found to have a regulatory effect on crop quality. Therefore, this study aims to review the jasmonic acid accumulation patterns during various physiological processes and its potential role in vegetable development and quality formation, as well as the underlying molecular mechanisms. The information provided in this manuscript sheds new light on the improvements in vegetable yield and quality.

Role of methylglyoxal and glyoxalase in the regulation of plant response to heavy metal stress

KEY MESSAGE

Methylglyoxal and glyoxalase function a significant role in plant response to heavy metal stress. We update and discuss the most recent developments of methylglyoxal and glyoxalase in regulating plant response to heavy metal stress. Methylglyoxal (MG), a by-product of several metabolic processes, is created by both enzymatic and non-enzymatic mechanisms. It plays an important role in plant growth and development, signal transduction, and response to heavy metal stress (HMS). Changes in MG content and glyoxalase (GLY) activity under HMS imply that they may be potential biomarkers of plant stress resistance. In this review, we summarize recent advances in research on the mechanisms of MG and GLY in the regulation of plant responses to HMS. It has been discovered that appropriate concentrations of MG assist plants in maintaining a balance between growth and development and survival defense, therefore shielding them from heavy metal harm. MG and GLY regulate plant physiological processes by remodeling cellular redox homeostasis, regulating stomatal movement, and crosstalking with other signaling molecules (including abscisic acid, gibberellic acid, jasmonic acid, cytokinin, salicylic acid, melatonin, ethylene, hydrogen sulfide, and nitric oxide). We also discuss the involvement of MG and GLY in the regulation of plant responses to HMS at the transcriptional, translational, and metabolic levels. Lastly, considering the current state of research, we present a perspective on the future direction of MG research to elucidate the MG anti-stress mechanism and offer a theoretical foundation and useful advice for the remediation of heavy metal-contaminated environments in the future.

Physio-anatomical modifications and element allocation pattern in Alternanthera tenella Colla. associated with phytoextraction of chromium

Intensive industrial activities have elevated chromium (Cr) concentrations in the environment, particularly in soil and water, posing a significant threat due to its cytotoxic and carcinogenic properties. Phytoremediation has emerged as a sustainable and economical alternative for detoxifying pollutants. In this context, an attempt has been made to assess the efficacy of Cr remediation by the invasive plant Alternanthera tenella Colla. The study investigated morphological, anatomical, and physiological adaptations in plant tissues in response to 240 µM of K2Cr2O7, considering elemental distribution patterns and bioaccumulation potential. Growth parameter assessments revealed a notable 50% reduction in root elongation and biomass content; however, the plant exhibited a comparatively higher tolerance index (47%) under Cr stress. Chromium significantly influenced macro and micro-elemental distribution in plant tissues, particularly in roots and leaves. Structural modifications, including changes in the thickness and diameter of xylem walls in the root, stem, and leaf tissues of Cr-treated A. tenella, were observed. Distinct cell structural distortions and Cr deposit inclusions in the xylem wall and inner parenchyma cells were distinct. Under Cr stress, there was a reduction in pigment content and metabolites such as proteins and soluble sugars, while proline, phenol, and malondialdehyde showed a twofold increase. The concentration of Cr was higher in the shoots of A. tenella (185.7 mg/kg DW) than in the roots (179.625 mg/kg DW). With a high BCFroot value (16.23) and TF > 1, coupled with effective mechanisms to cope with metal stress, A. tenella emerges as an ideal candidate for chromium phytoextraction.

Exploring the potential role of hydrogen sulfide and jasmonic acid in plants during heavy metal stress

In plants, hydrogen sulfide (H2S) is mainly considered as a gaseous transmitter or signaling molecule that has long been recognized as an essential component of numerous plant cellular and physiological processes. Several subcellular compartments in plants use both enzymatic and non-enzymatic mechanisms to generate H2S. Under normal and stress full conditions exogenous administration of H2S supports a variety of plant developmental processes, including growth and germination, senescence, defense, maturation and antioxidant machinery in plants. Due to their gaseous nature, they are efficiently disseminated to various areas of the cell to balance antioxidant pools and supply sulphur to the cells. Numerous studies have also been reported regarding H2S ability to reduce heavy metal toxicity when combined with other signaling molecules like nitric oxide (NO), abscisic acid (ABA), calcium ion (Ca2+), hydrogen peroxide (H2O2), salicylic acid (SA), ethylene (ETH), jasmonic acid (JA), proline (Pro), and melatonin. The current study focuses on multiple pathways for JA and H2S production as well as their signaling functions in plant cells under varied circumstances, more specifically under heavy metal, which also covers role of H2S and Jasmonic acid during heavy metal stress and interaction of hydrogen sulfide with Jasmonic acid.

Ameliorative effects of Si-SNP synergy to mitigate chromium induced stress in Brassica juncea

Hyperaccumulation of heavy metal in agricultural land has hampered yield of important crops globally. It has consequently deepened concerns regarding the burning issue of food security in the world. Among heavy metals, Chromium (Cr) is not needed for plant growth and found to pose detrimental effects on plants. Present study highlights the role of exogenous application of sodium nitroprusside (SNP, exogenous donor of NO) and silicon (Si) in alleviating detrimental ramification of Cr toxicity in Brassica juncea. The exposure of B. juncea to Cr (100 μM) under hydroponic system hampered the morphological parameters of plant growth like length and biomass and physiological parameters like carotenoid and chlorophyll contents. It also resulted in oxidative stress by disrupting the equilibrium between ROS production and antioxidant quenching leading to accumulation of ROS such as hydrogen peroxide (H2O2) and superoxide (O2•‾) radicle which causes lipid peroxidation. However, application of Si and SNP both individually and in combination counteracted oxidative stress due to Cr by regulating ROS accumulation and enhancing antioxidant metabolism by upregulation of antioxidant genes of DHAR, MDHAR, APX and GR. As the alleviatory effects were more pronounced in plants treated with combined application of Si and SNP; therefore, our findings suggest that dual application of these two alleviators can be used to mitigate Cr stress.

Titanium dioxide nanoparticles potentially regulate the mechanism(s) for photosynthetic attributes, genotoxicity, antioxidants defense machinery, and phytochelatins synthesis in relation to hexavalent chromium toxicity in Helianthus annuus L

Chromium (VI) is one of the hazardous heavy metal, heavily discharged into the soil and severely hampers the plants yield. The TiO₂ NPs was selected due to its potential to alleviate the heavy metals toxicity. This manuscript unravels the mechanisms for Cr(VI) induced toxicity and how foliar application of TiO₂ NP_S potentially ameliorate the toxicity by regulating the photosynthetic attributes, DNA damage, antioxidants defense machinery, and phytochelatins synthesis in Helianthus annuus L. Plants were exposed to Cr(VI) concentrations [0, 15, 30, and 60 mg Cr(VI) kg^-1 of soil], and TiO₂ NP_S (15 mg L^-1, 25 nm size₎ were foliar sprayed thrice to the plants at three days interval. The maximum accumulation of total chromium was recorded in root (12.53 µg g^-1 DW) followed by shoot (5.67 µg g^-1 DW) at 60 mg Cr(VI) treatment. The presence and localization of TiO₂ NPs inside the plant leaf cells were confirmed by TEM-EDS analysis. The results revealed that Cr(VI) exposure had a dose-dependent inhibitory effects on photosynthetic attributes, structure of guard and epidermal cells, photosynthetic pigments; inducing impacts on H₂O₂ and MDA productions, DNA damage, AsA-GSH cycle, and most importantly on PC₂, and PC₃ synthesis which is rarely reported. However, TiO₂ NPs exposure minimized Cr(VI) induced toxicity through reduction of total chromium accumulation, H₂O₂ and MDA productions, thereby reducing DNA damage reported first time under combined treatment of Cr(VI)+ TiO₂ NPs as evidenced through comet assay. It also positively regulate the photosynthetic pigments, AsA-GSH cycle, and modulates PC₂ and PC₃ synthesis which have crucial impacts on ROS quenching and Cr(VI) detoxification, respectively, and in turn, minimizes Cr(VI) toxicity in H. annuus L. Besides, this study strengthens the less acknowledged report that Cr(VI) is an inducer of PCs synthesis and also confirms that TiO₂ NPs potentially counteract Cr(VI) toxicity.

Effect of jasmonic acid on the phytoremediation of dinitrophenol from wastewater by Solanum nigrum L. and Atriplex lentiformis (Torr.) S. Watson

Phytoremediation is one of the best methods for cleaning up natural resources like water because plants are eco-friendly and safe for the ecosystem. Hyperaccumulators, e.g., Solanum nigrum L. and Atriplex lentiformis (Torr.) S. Watson, have been used to remove toxic metals from soil and water through phytoremediation techniques, but it is unknown if they can remove hazardous chemicals such as dinitrophenol (DNP), from wastewater. A hydroponic experiment was conducted to study the efficiency of S. nigrum and A. lentiformis in removing DNP from wastewater. Jasmonic acid (JAC) was applied to the tested plants in two doses, 0.25 and 0.50 mmol, in an effort to better understand how it affects phytoremediation effectiveness. The growth of S. nigrum and A. lentiformis improved significantly (p < 0.05) by the foliar application of JAC. The applications of JAC1 and JAC2 significantly (p < 0.05) increased nutrient uptake and chlorophyll concentrations in S. nigrum and A. lentiformis plants. The foliar spraying of S. nigrum and A. lentiformis with JAC significantly (p < 0.05) increased the antioxidant enzymes activity, i.e., SOD and POD. The levels of osmoregulatory substances like proline and carbohydrates significantly (p < 0.05) increased after JAC was sprayed on S. nigrum and A. lentiformis plants. In the case of S. nigrum, the efficiency of DNP removal varied between 53 and 69%, with an average of 63%, while in the case of A. lentiformis, it varied between 47 and 62%, with an average of 56%. The removal efficiency of DNP reached 67 and 69% when S. nigrum was sprayed with JAC1 and JAC2. When JAC1 and JAC2 were sprayed on A. lentiformis, DNP removal efficiency rose from 47 to 60 and from 47 to 62%, respectively. S. nigrum and A. lentiformis plants can be grown normally and survive in dinitrophenol-contaminated water without showing any toxic symptoms. S. nigrum and A. lentiformis have a powerful antioxidant system and the ability to produce vital compounds that alleviate the stress caused by DNP toxicity. The findings are crucial for cleaning up polluted water and protecting the ecosystem's health from dangerous pollutants.

Hydrogen sulfide alleviates chromium toxicity by promoting chromium sequestration and re-establishing redox homeostasis in Zea mays L

Hydrogen sulfide (H₂S) is a multifunctional gaseous signaling molecule involved in the regulation of Cr stress responses. In the present study, we combined transcriptomic and physiological analyses to elucidate the mechanism underlying the mitigation of Cr toxicity by H₂S in maize (Zea mays L.). We showed that treatment with sodium hydrosulfide (NaHS, a donor of H₂S) partially alleviated Cr-induced growth inhibition. However, Cr uptake was not affected. RNA sequencing suggested that H₂S regulates the expression of many genes involved in pectin biosynthesis, glutathione metabolism, and redox homeostasis. Under Cr stress, NaHS treatment significantly increased pectin content and pectin methylesterase activity; thus, more Cr was retained in the cell wall. NaHS application also increased the content of glutathione and phytochelatin, which chelate Cr and transport it into vacuoles for sequestration. Furthermore, NaHS treatment mitigated Cr-induced oxidative stress by enhancing the capacity of enzymatic and non-enzymatic antioxidants. Overall, our results strongly support that H₂S alleviates Cr toxicity in maize by promoting Cr sequestration and re-establishing redox homeostasis rather than by reducing Cr uptake from the environment.

Exogenous hydrogen sulfide alleviates chromium toxicity by modulating chromium, nutrients and reactive oxygen species accumulation, and antioxidant defence system in mungbean (Vigna radiata L.) seedlings

Chromium (Cr), a highly toxic redox-active metal cation in soil, seriously threatens global agriculture by affecting nutrient uptake and disturbing various physio-biochemical processes in plants, thereby reducing yields. Here, we examined the effects of different concentrations of Cr alone and in combination with hydrogen sulfide (H₂S) application on the growth and physio-biochemical performance of two mungbeans (Vigna radiata L.) varieties, viz. Pusa Vishal (PV; Cr tolerant) and Pusa Ratna (PR; Cr sensitive), growing in a pot in hydroponics. Plants were grown in the pot experiment to examine their growth, enzymatic and non-enzymatic antioxidant levels, electrolyte balance, and plasma membrane (PM) H⁺-ATPase activity. Furthermore, root anatomy and cell death were analysed 15 days after sowing both varieties in hydroponic systems. The Cr-induced accumulation of reactive oxygen species caused cell death and affected the root anatomy and growth of both varieties. However, the extent of alteration in anatomical features was less in PV than in PR. Exogenous application of H₂S promoted plant growth, thereby improving plant antioxidant activities and reducing cell death by suppressing Cr accumulation and translocation. Seedlings of both cultivars treated with H₂S exhibited enhanced photosynthesis, ion uptake, glutathione, and proline levels and reduced oxidative stress. Interestingly, H₂S restricted the translocation of Cr to aerial parts of plants by improving the nutrient profile and viability of root cells, thereby relieving plants from oxidative bursts by activating the antioxidant machinery through triggering the ascorbate-glutathione cycle. Overall, H₂S application improved the nutrient profile and ionic homeostasis of Cr-stressed mungbean plants. These results highlight the importance of H₂S application in protecting crops against Cr toxicity. Our findings can be utilised to develop management strategies to improve heavy metal tolerance among crops.

Biogeochemical behaviour and toxicology of chromium in the soil-water-human nexus: A review

Chromium (Cr) affects human health if it accumulates in organs to elevated concentrations. The toxicity risk of Cr in the ecosphere depends upon the dominant Cr species and their bioavailability in the lithosphere, hydrosphere, and biosphere. However, the soil-water-human nexus that controls the biogeochemical behaviour of Cr and its potential toxicity is not fully understood. This paper synthesizes information on different dimensions of Cr ecotoxicological hazards in the soil and water and their subsequent effects on human health. The various routes of environmental exposure of Cr to humans and other organisms are also discussed. Human exposure to Cr(VI) causes both carcinogenic and non-carcinogenic health effects via complicated reactions that include oxidative stress, chromosomal and DNA damage, and mutagenesis. Chromium (VI) inhalation can cause lung cancer; however, incidences of other types of cancer following Cr(VI) exposure are low but probable. The non-carcinogenic health consequences of Cr(VI) exposure are primarily respiratory and cutaneous. Research on the biogeochemical behaviour of Cr and its toxicological hazards on human and other biological routes is therefore urgently needed to develop a holistic approach to understanding the soil-water-human nexus that controls the toxicological hazards of Cr and its detoxification.

Chromium Toxicity in Plants: Signaling, Mitigation, and Future Perspectives

Plants are very often confronted by different heavy metal (HM) stressors that adversely impair their growth and productivity. Among HMs, chromium (Cr) is one of the most prevalent toxic trace metals found in agricultural soils because of anthropogenic activities, lack of efficient treatment, and unregulated disposal. It has a huge detrimental impact on the physiological, biochemical, and molecular traits of crops, in addition to being carcinogenic to humans. In soil, Cr exists in different forms, including Cr (III) "trivalent" and Cr (VI) "hexavalent", but the most pervasive and severely hazardous form to the biota is Cr (VI). Despite extensive research on the effects of Cr stress, the exact molecular mechanisms of Cr sensing, uptake, translocation, phytotoxicity, transcript processing, translation, post-translational protein modifications, as well as plant defensive responses are still largely unknown. Even though plants lack a Cr transporter system, it is efficiently accumulated and transported by other essential ion transporters, hence posing a serious challenge to the development of Cr-tolerant cultivars. In this review, we discuss Cr toxicity in plants, signaling perception, and transduction. Further, we highlight various mitigation processes for Cr toxicity in plants, such as microbial, chemical, and nano-based priming. We also discuss the biotechnological advancements in mitigating Cr toxicity in plants using plant and microbiome engineering approaches. Additionally, we also highlight the role of molecular breeding in mitigating Cr toxicity in sustainable agriculture. Finally, some conclusions are drawn along with potential directions for future research in order to better comprehend Cr signaling pathways and its mitigation in sustainable agriculture.

5-Aminolevulinic Acid Induces Chromium [Cr(VI)] Tolerance in Tomatoes by Alleviating Oxidative Damage and Protecting Photosystem II: A Mechanistic Approach

Chromium [Cr(VI)] pollution is a major environmental risk, reducing crop yields. 5-Aminolevunic acid (5-ALA) considerably improves plant abiotic stress tolerance by inducing hydrogen peroxide (H2O2) and nitric oxide (NO) signalling. Our investigation aimed to uncover the mechanism of tomato tolerance to Cr(VI) toxicity through the foliar application of 5-ALA for three days, fifteen days before Cr treatment. Chromium alone decreased plant biomass and photosynthetic pigments, but increased oxidative stress markers, i.e., H2O2 and lipid peroxidation (as MDA equivalent). Electrolyte leakage (EL), NO, nitrate reductase (NR), phytochelatins (PCs), glutathione (GSH), and enzymatic and non-enzymatic antioxidants were also increased. Foliar application of 5-ALA before Cr treatment improved plant growth and photosynthetic pigments, diminished H2O2, MDA content, and EL, and resulted in additional enhancements of enzymatic and non-enzymatic antioxidants, NR activity, and NO synthesis. In Cr-treated tomato seedlings, 5-ALA enhanced GSH and PCs, which modulated Cr sequestration to make it nontoxic. 5-ALA-induced Cr tolerance was further enhanced by sodium nitroprusside (SNP), a NO donor. When sodium tungstate (ST), a NR inhibitor, was supplied together with 5-ALA to Cr-treated plants, it eliminated the beneficial effects of 5-ALA by decreasing NR activity and NO synthesis, while the addition of SNP inverted the adverse effects of ST. We conclude that the mechanism by which 5-ALA induced Cr tolerance in tomato seedlings is mediated by NR-generated NO. Thus, NR and NO are twin players, reducing Cr toxicity in tomato plants via antioxidant signalling cascades.

Chemical characterization and the intrusion through elicitation and Agrobacterium rhizogenes mediated hairy root transformation in Saussurea costus C.B. Clarke

Saussurea costus (Asteraceae) commonly known as kuth, is an important medicinal plant with a rich repository of medicinally valuable compounds. During the present study, pharmacologically important sesquiterpene lactones namely costunolide, dehydrocostus lactone, betulinic acid and syringin were isolated from different plant extracts. Furthermore, the elicitation effect of jasmonic acid (JA) and different light regiments on the accumulation of secondary metabolites (costunolide and dehydrocostus lactone) was evaluated using HPLC. There was an increase in amount of costunolide and dehydrocostus lactone compared to control after 96 h of treatment with JA and continuous light. The amount of costunolide after 96 h was maximum 6.47 mg/g DW in response to JA as compared to control which was found to be 1.7 mg/g DW. Similarly, the concentration of dehydrocostus lactone after 96 h showed maximum accumulation of compound 4.7 mg/g DW in response to continuous light. The in vitro response in MS medium augmented with BAP (4 mg/l) produces friable and creamish coloured callus, however, number of days increased from 10 to 22 days with 70% culture response. Also, Agrobacterium rhizogenes strain LBA9402 was found to be most effective strain for the establishment of hairy root cultures among all the strains used. The genomic DNA was used as template in PCR to amplify rolB gene which confirmed the efficient transformation of the roots. Additionally, total metabolite content of in vitro raised hairy roots of S. costus was significantly higher than the field grown plants. The production of secondary metabolites through elicitation and hairy roots can serve as a potential tool for the conservation action programme in S. costus.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-022-01270-9.

The regulation of glutathione s-transferases by gibberellic acid application in salt treated maize leaves

Plant hormones and antioxidant system changes occur during plants' exposure to stress conditions. Although the interactions of some plant hormones (abscisic acid, salicylic acid, jasmonic acid, nitric oxide, and ethylene) with the glutathione s-transferase (GST) enzyme, which is one of the antioxidant enzymes, have already been reported, the influence of gibberellic acid (GA3) on this enzyme under saline conditions has not yet been reported. Plant material for the experiments was obtained from M14G144 cultivar of maize (Zea mays L.) plants grown as a soil culture in growth chambers at 22 °C, 65-70% moisture, 16-h light/8-h dark conditions, and with full strength Hoagland solution for 8 days under controlled growth conditions. Then, the plants were exposed to salt stress (350 mM NaCl and 100, 300, and 500 ppm GA3) simultaneously. In maize leaves, GA3 treatment alleviated the physiological parameters under salt stress. Specifically, the treatments with 100 and 500 ppm of GA3 were able to trigger GST enzyme and isoenzyme activities as well as hydrogen sulfide accumulation and anthocyanin content, although the lowest malondialdehyde, hydrogen peroxide, and superoxide radical content were under the treatment of 300 ppm of GA3. Besides this, GST gene expression levels were found to be upregulated between 1.5 and fourfold higher in all the plants treated with GA3 at different concentrations in proportion to salt stress. These results first indicated that the reason for the changes in GA3-treated plants was the stimulating role of this hormone to maintain GST regulation in maize plants.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-022-01269-2.

Hexavalent-Chromium-Induced Oxidative Stress and the Protective Role of Antioxidants against Cellular Toxicity

Hexavalent chromium is a highly soluble environmental contaminant. It is a widespread anthropogenic chromium species that is 100 times more toxic than trivalent chromium. Leather, chrome plating, coal mining and paint industries are the major sources of hexavalent chromium in water. Hexavalent chromium is widely recognised as a carcinogen and mutagen in humans and other animals. It is also responsible for multiorgan damage, such as kidney damage, liver failure, heart failure, skin disease and lung dysfunction. The fate of the toxicity of hexavalent chromium depends on its oxidation state. The reduction of Cr (VI) to Cr (III) is responsible for the generation of reactive oxygen species (ROS) and chromium intermediate species, such as Cr (V) and Cr (IV). Reactive oxygen species (ROS) are responsible for oxidative tissue damage and the disruption of cell organelles, such as mitochondria, DNA, RNA and protein molecules. Cr (VI)-induced oxidative stress can be neutralised by the antioxidant system in human and animal cells. In this review, the authors summarise the Cr (VI) source, toxicity and antioxidant defence mechanism against Cr (VI)-induced reactive oxygen species (ROS).

Chromium in plant growth and development: Toxicity, tolerance and hormesis

Research over the last three decades showed that chromium, particularly the oxyanion chromate Cr(VI) behaves as a toxic environmental pollutant that strongly damages plants due to oxidative stress, disruption of nutrient uptake, photosynthesis and metabolism, and ultimately, represses growth and development. However, mild Cr(VI) concentrations promote growth, induce adventitious root formation, reinforce the root cap, and produce twin roots from single root meristems under conditions that compromise cell viability, indicating its important role as a driver for root organogenesis. In recent years, considerable advance has been made towards deciphering the molecular mechanisms for root sensing of chromate, including the identification of regulatory proteins such as SOLITARY ROOT and MEDIATOR 18 that orchestrate the multilevel dynamics of the oxyanion. Cr(VI) decreases the expression of several glutamate receptors, whereas amino acids such as glutamate, cysteine and proline confer protection to plants from hexavalent chromium stress. The crosstalk between plant hormones, including auxin, ethylene, and jasmonic acid enables tissues to balance growth and defense under Cr(VI)-induced oxidative damage, which may be useful to better adapt crops to biotic and abiotic challenges. The highly contrasting responses of plants manifested at the transcriptional and translational levels depend on the concentration of chromate in the media, and fit well with the concept of hormesis, an adaptive mechanism that primes plants for resistance to environmental challenges, toxins or pollutants. Here, we review the contrasting facets of Cr(VI) in plants including the cellular, hormonal and molecular aspects that mechanistically separate its toxic effects from biostimulant outputs.

Plant hormones and neurotransmitter interactions mediate antioxidant defenses under induced oxidative stress in plants

Due to global climate change, abiotic stresses are affecting plant growth, productivity, and the quality of cultivated crops. Stressful conditions disrupt physiological activities and suppress defensive mechanisms, resulting in stress-sensitive plants. Consequently, plants implement various endogenous strategies, including plant hormone biosynthesis (e.g., abscisic acid, jasmonic acid, salicylic acid, brassinosteroids, indole-3-acetic acid, cytokinins, ethylene, gibberellic acid, and strigolactones) to withstand stress conditions. Combined or single abiotic stress disrupts the normal transportation of solutes, causes electron leakage, and triggers reactive oxygen species (ROS) production, creating oxidative stress in plants. Several enzymatic and non-enzymatic defense systems marshal a plant's antioxidant defenses. While stress responses and the protective role of the antioxidant defense system have been well-documented in recent investigations, the interrelationships among plant hormones, plant neurotransmitters (NTs, such as serotonin, melatonin, dopamine, acetylcholine, and γ-aminobutyric acid), and antioxidant defenses are not well explained. Thus, this review discusses recent advances in plant hormones, transgenic and metabolic developments, and the potential interaction of plant hormones with NTs in plant stress response and tolerance mechanisms. Furthermore, we discuss current challenges and future directions (transgenic breeding and genome editing) for metabolic improvement in plants using modern molecular tools. The interaction of plant hormones and NTs involved in regulating antioxidant defense systems, molecular hormone networks, and abiotic-induced oxidative stress tolerance in plants are also discussed.

Application of zinc oxide nanoparticles as fertilizer boosts growth in rice plant and alleviates chromium stress by regulating genes involved in oxidative stress

Chromium toxicity impairs the productivity of rice crops and raises a major concern worldwide and thus, it calls for unconventional and sustainable means of crop production. In this study, we identified the implication of zinc oxide nanoparticles (ZnO NPs) in promoting plant growth and ameliorating chromium-induced stress in seedlings of rice (Oryza sativa). This investigation demonstrates that the exogenous supplementation of ZnO NPs at 25 μM activates defense mechanisms conferring rice seedlings significant tolerance against stress imposed by the exposure of 100 μM Cr(VI). Further, supplementation of this nanofertilizer reversed the inhibitory effects of Cr(VI) on growth and photosynthetic efficiency. The growth promotion was primarily associated with the function of ZnO NPs in inducing activity of antioxidative enzymes i.e. APX, DHAR, MDHAR and GR belonging to the ascorbate-glutathione cycle in the Cr-exposed seedlings, exceeding the levels in control. The overexpression of these antioxidative genes correlated concomitantly with the decrease of oxidants including SOR and H₂O₂ and the increase in the levels of non-enzymatic antioxidants: AsA and GSH.

Seed Priming with Spermine Mitigates Chromium Stress in Rice by Modifying the Ion Homeostasis, Cellular Ultrastructure and Phytohormones Balance

Chromium (Cr) is an important environmental constraint effecting crop productivity. Spermine (SPM) is a polyamine compound regulating plant responses to abiotic stresses. However, SPM-mediated tolerance mechanisms against Cr stress are less commonly explored in plants. Thus, current research was conducted to explore the protective mechanisms of SPM (0.01 mM) against Cr (100 µM) toxicity in two rice cultivars, CY927 (sensitive) and YLY689 (tolerant) at the seedling stage. Our results revealed that, alone, Cr exposure significantly reduced seed germination, biomass and photosynthetic related parameters, caused nutrient and hormonal imbalance, desynchronized antioxidant enzymes, and triggered oxidative damage by over-accretion of reactive oxygen species (ROS), malondialdehyde (MDA) and electrolyte leakage in both rice varieties, with greater impairments in CY927 than YLY689. However, seed priming with SPM notably improved or reversed the above-mentioned parameters, especially in YLY689. Besides, SPM stimulated the stress-responsive genes of endogenous phytohormones, especially salicylic acid (SA), as confirmed by the pronounced transcript levels of SA-related genes (OsPR1, OsPR2 and OsNPR1). Our findings specified that SPM enhanced rice tolerance against Cr toxicity via decreasing accumulation of Cr and markers of oxidative damage (H2O2, O2•- and MDA), improving antioxidant defense enzymes, photosynthetic apparatus, nutrients and phytohormone balance.

Beneficial role of methyl jasmonate on morphological, physiological and phytochemical responses of Calendula officinalis L. under Chromium toxicity

Contamination of soil with chromium (Cr) is a rising problem in terms of agricultural sustainability and food safety. Here, the effects of methyl jasmonate (MJ; 0, 5, and 10 µM) on alleviating Cr stress (0, 100, and 200 µM) were surveyed in pot marigold (Calendula officinalis L.). The results showed that Cr stress significantly reduced photosynthetic pigments and leaf accumulation of total soluble sugars, total starch, and mineral nutrients and, consequently, lowered the height and biomass of pot marigold plants. Chromium toxicity also increased the leaf levels of oxidative stress markers and induced oxidative stress, which was associated with damage to bio-membranes and increased levels of malondialdehyde. However, MJ supplementation reduced the leaf accumulation of Cr, increased the content of photosynthetic pigments, and improved the performance of the photosynthetic machinery in Cr-stressed plants. MJ supplementation boosted the antioxidant defense system by upregulating antioxidant enzymes, glyoxalase enzymes, and the ascorbate-glutathione (AsA-GSH) pool redox, which significantly diminished Cr-induced oxidative stress. Hence, MJ supplementation might be a practicable approach for reducing Cr absorption and its negative impacts on pot marigold plants growing under Cr-contaminated conditions. Clinical trials registration Not applicable.

Jasmonic acid alleviates cadmium toxicity through regulating the antioxidant response and enhancing the chelation of cadmium in rice (Oryza sativa L.)

Cadmium (Cd) is a potentially hazardous element with substantial biological toxicity, adversely affecting plant growth and physiological metabolism. Therefore, it is necessary to explore practical and environment-friendly approaches to reduce toxicity. Jasmonic acid (JA) is an endogenous growth regulator which helps plants defend against biological and abiotic stresses. To determine how JA help relieve Cd toxicity in rice, both laboratory and field experiments were implemented. In the seedling stage, the role of JA in mediating rice Cd tolerance was investigated via a fluorescent probe in vivo localization, Fourier Transform Infrared Spectroscopy (FTIR), and colorimetry. At the mature growth stage of rice, field experiments were implemented to research the effects of JA on the Cd uptake and translocation in rice. In the seedling stage of rice, we found that JA application increased the cell wall compartmentalization of Cd by promoting the Cd combination on chelated-soluble pectin of rice roots and inhibited Cd movement into protoplasts, thereby reducing the Cd content in the roots by 30.5% and in the shoots by 53.3%, respectively. Application of JA reduced H2O2 content and helped relieve Cd-induced peroxidation damage of membrane lipid by increasing the level of catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), and glutathione (GSH), but had no significant effect on the superoxide dismutase (SOD) activity. Additionally, field experiments showed that foliar spraying of JA inhibited rice Cd transport from the stalk and root to the grain and reduced Cd concentration in grain by 29.7% in the high-Cd fields and 28.0% in the low-Cd fields. These results improve our understanding of how JA contributes to resistance against Cd toxicity in rice plants and reduces the accumulation of Cd in rice kernels.

Methyl jasmonate increases aluminum tolerance in rice by augmenting the antioxidant defense system, maintaining ion homeostasis, and increasing nonprotein thiol compounds

Aluminum (Al) stress is known as a serious threat to the growth and production of crops in acidic soils. Here, the effects of different concentrations of methyl jasmonate (MJ, 0.5 and 1 µM) on rice plants were investigated hydroponically under different concentrations of Al (0.5 and 1 mM). Aluminum treatments injured membrane lipids and photosynthetic apparatus by reducing the leaf contents of mineral nutrients and increasing the accumulation of free radicals (hydrogen peroxide, methylglyoxal, and superoxide anion), resulting in reduced growth and biomass of rice. In comparison to control plants, 0.5 and 1 μM Al treatments lowered height by 21 and 37% and total dry weight by 24 and 41%, respectively. Exogenously added methyl diminished the inhibitory effects of Al stress on growth and photosynthetic apparatus by restoring ion homeostasis and improving chlorophyll metabolism. The application of MJ, by inducing the activity of antioxidant enzymes and the glyoxalase cycle, lessened the levels of the toxic compounds hydrogen peroxide, methylglyoxal, and superoxide anion and, as a result, dwindled the toxic Al-induced oxidative stress. Methyl jasmonate enhanced the leaf accumulation of nonprotein thiol compounds and improved plant tolerance under Al stress by increasing the activity of enzymes involved in the synthesis of thiol compounds. Methyl jasmonate increased the leaf accumulation of glutathione and phytochelatins in Al-stressed plants by increasing the expression of GSH1, PCS, and ABCC1, which reduced the toxicity of toxic Al accumulated in leaves by sequestering toxic Al in vacuoles. Together, the results revealed that MJ increased the tolerance of rice under Al toxicity by maintaining ion homeostasis, improving the activity of antioxidant enzymes and the glyoxalase system, and increasing the level of non-protein thiol compounds. This research adds to our understanding of how MJ may be used in the future to improve Al stress tolerance in sustainable agriculture.

Increasing Heavy Metal Tolerance by the Exogenous Application of Organic Acids

Several metals belong to a group of non-biodegradable inorganic constituents that, at low concentrations, play fundamental roles as essential micronutrients for the growth and development of plants. However, in high concentrations they can have toxic and/or mutagenic effects, which can be counteracted by natural chemical compounds called chelators. Chelators have a diversity of chemical structures; many are organic acids, including carboxylic acids and cyclic phenolic acids. The exogenous application of such compounds is a non-genetic approach, which is proving to be a successful strategy to reduce damage caused by heavy metal toxicity. In this review, we will present the latest literature on the exogenous addition of both carboxylic acids, including the Kreb's Cycle intermediates citric and malic acid, as well as oxalic acid, lipoic acid, and phenolic acids (gallic and caffeic acid). The use of two non-traditional organic acids, the phytohormones jasmonic and salicylic acids, is also discussed. We place particular emphasis on physiological and molecular responses, and their impact in increasing heavy metal tolerance, especially in crop species.

Iron Oxide and Silicon Nanoparticles Modulate Mineral Nutrient Homeostasis and Metabolism in Cadmium-Stressed Phaseolus vulgaris

The application of nanoparticles (NPs) has been proved as an efficient and promising technique for mitigating a wide range of stressors in plants. The present study elucidates the synergistic effect of iron oxide nanoparticles (IONPs) and silicon nanoparticles (SiNPs) in the attenuation of Cd toxicity in Phaseolus vulgaris. Seeds of P. vulgaris were treated with IONPs (10 mg/L) and SiNPs (20 mg/L). Seedlings of uniform size were transplanted to pots for 40 days. The results demonstrated that nanoparticles (NPs) enhanced growth, net photosynthetic rate, and gas exchange attributes in P. vulgaris plants grown in Cd-contaminated soil. Synergistic application of IONPs and SiNPs raised not only K+ content, but also biosynthesis of polyamines (PAs), which alleviated Cd stress in P. vulgaris seedlings. Additionally, NPs decreased malondialdehyde (MDA) content and electrolyte leakage (EL) in P. vulgaris plants exposed to Cd stress. These findings suggest that stress alleviation was mainly attributed to the enhanced accumulation of K+ content, improved antioxidant defense system, and higher spermidine (Spd) and putrescine (Put) levels. It is suggested that various forms of NPs can be applied synergistically to minimize heavy metal stress, thus increasing crop production under stressed conditions.

Association of jasmonic acid priming with multiple defense mechanisms in wheat plants under high salt stress

Salinity is a global conundrum that negatively affects various biometrics of agricultural crops. Jasmonic acid (JA) is a phytohormone that reinforces multilayered defense strategies against abiotic stress, including salinity. This study investigated the effect of JA (60 μM) on two wheat cultivars, namely ZM9 and YM25, exposed to NaCl (14.50 dSm^-1) during two consecutive growing seasons. Morphologically, plants primed with JA enhanced the vegetative growth and yield components. The improvement of growth by JA priming is associated with increased photosynthetic pigments, stomatal conductance, intercellular CO₂, maximal photosystem II efficiency, and transpiration rate of the stressed plants. Furthermore, wheat cultivars primed with JA showed a reduction in the swelling of the chloroplast, recovery of the disintegrated thylakoids grana, and increased plastoglobuli numbers compared to saline-treated plants. JA prevented dehydration of leaves by increasing relative water content and water use efficiency via reducing water and osmotic potential using proline as an osmoticum. There was a reduction in sodium (Na⁺) and increased potassium (K⁺) contents, indicating a significant role of JA priming in ionic homeostasis, which was associated with induction of the transporters, viz., SOS1, NHX2, and HVP1. Exogenously applied JA mitigated the inhibitory effect of salt stress in plants by increasing the endogenous levels of cytokinins and indole acetic acid, and reducing the abscisic acid (ABA) contents. In addition, the oxidative stress caused by increasing hydrogen peroxide in salt-stressed plants was restrained by JA, which was associated with increased α-tocopherol, phenolics, and flavonoids levels and triggered the activities of superoxide dismutase and ascorbate peroxidase activity. This increase in phenolics and flavonoids could be explained by the induction of phenylalanine ammonia-lyase activity. The results suggest that JA plays a key role at the morphological, biochemical, and genetic levels of stressed and non-stressed wheat plants which is reflected in yield attributes. Hierarchical cluster analysis and principal component analyses showed that salt sensitivity was associated with the increments of Na⁺, hydrogen peroxide, and ABA contents. The regulatory role of JA under salinity stress was interlinked with increased JA level which consequentially improved ion transporting, osmoregulation, and antioxidant defense.

Proline-mediated regulation on jasmonate signals repressed anthocyanin accumulation through the MYB-bHLH-WDR complex in rice under chromium exposure

Toxic metal-induced overaccumulation of anthocyanin (ATH) in plants can oxidize proteins and break DNA. Herein, the role of exogenous proline (Pro) on the repression of ATH accumulation in rice seedlings during hexavalent chromium [Cr(VI)] exposure was studied. Results indicated that exogenous Pro-mediated regulation of jasmonate signals activated the MYB-bHLH-WDR complex to repress ATH accumulation in rice tissues under Cr(VI) stress. Biochemical and transcript analysis indicated that exogenous Pro promoted the synthesis of jasmonic acid (JA) and its molecularly active metabolite jasmonic acid isoleucine (JA-Ile) in rice tissues under Cr(VI) stress. Increment in the endogenous level of jasmonates positively triggered the expression of genes responsible for the JA signaling pathway and activated the MYB-bHLH-WDR complex, eventually repressing the glycosylation of anthocyanidin to form ATH in rice tissues. In conclusion, exogenous proline-mediated regulation on jasmonate signals was tissue-specific under Cr(VI) stress and a more positive effect was detected in shoots rather than roots.

Amelioration potential of β-pinene on Cr(VI)-induced toxicity on morphology, physiology and ultrastructure of maize

Heavy metals' amassment in the soil environment is a threat to crop and agricultural sustainability and consequentially the global food security. For achieving enhancement of crop productivity in parallel to reducing chromium (Cr) load onto food chain demands continuous investigation and efforts to develop cost-effective strategies for maximizing crop yield and quality. In this context, we investigated the amelioration of Cr(VI) toxicity through β-pinene in experimental dome simulating natural field conditions. The protective role of β-pinene was determined on physiology, morphology and ultrastructure in Zea mays under Cr(VI) stress (250 and 500 μM). Results exhibited a marked reduction in the overall growth (shoot and root length and dry matter) of Z. mays plants subjected to Cr(VI) stress. Photosynthetic pigments (chlorophyll and carotenoids) were evidently reduced, and there was a loss of membrane integrity. Supplementation of β-pinene (100 μM), however, declined the toxicity induced by Cr(VI). Interestingly, Cr-tolerant abilities were improved in relation to plant growth, photosynthetic pigments and membrane integrity with the combined treatment of Cr(VI) and β-pinene. β-Pinene also reduced the root-mediated uptake of Cr(VI) and translocation to shoots. Moreover, significant ultrastructural damages recorded in roots and shoots under Cr(VI) stress were partially reverted upon addition of β-pinene. Our analyses revealed that β-pinene mitigates Cr(VI) toxicity in Z. mays, either by membrane stabilization or serving as a barrier to the uptake of Cr from soil. Thus, exogenous supply of β-pinene can be an effective alternative to mitigate Cr toxicity in soil. However, it is deemed essential to investigate further the responses throughout the life cycle of the plant on β-pinene supplementation under natural conditions.

Stress amelioration response of glycine betaine and Arbuscular mycorrhizal fungi in sorghum under Cr toxicity

Chromium toxicity is a major problem in agricultural soils that negatively affects a plant’s metabolic activities. It reduces biochemical and antioxidant defence system’s activities. In search of the solution to this problem a two-year pot experiment (completely randomized design with three replications), in three genetically different varieties of sorghum (SSG 59–3, HJ 513 and HJ 541) under Cr toxicity (2 and 4 ppm) was conducted to determine the effect of glycine betaine (50 and 100mM) and Arbuscular mycorrhizal fungi (AMF) on the antioxidant system (enzymes viz. superoxide dismutase, ascorbate peroxidase, catalase, glutathione reductase, peroxidase and metabolites viz. glutathione, ascorbate, proline, β-carotene) along with Cr accumulation and indices of oxidative stress parameters (polyphenol oxidase, hydrogen peroxide and malondialdehyde) at two growth stages (vegetative and grain filling). According to results; Cr stress (2 & 4 ppm) increased its accumulation and indices of oxidative stresses significantly (p≤0.05) in all varieties of sorghum at both growth stages. However, soil application of glycine betaine (GB) and AMF decreased Cr accumulation and indices of oxidative stress by increasing antioxidant enzymes and metabolites activities at both growth stages in all varieties. The combination of 100mM GB with AMF was observed most significant (p≤0.05) in decreasing oxidative stress and improved the antioxidant system’s activities. The SSG 59–3 cultivar showed the lowest Cr accumulation (1.60 and 8.61 ppm), indices of oxidative stress and highest antioxidant system’s activity among these three cultivars at both growth stages. Thus, SSG 59–3 was found most tolerant cultivars followed by HJ 513 and then HJ 541. These findings suggest that both GB and AMF, either individually or combined can play a positive role to reduce oxidative stress and increased antioxidant attributes under Cr toxicity in sorghum.

Deriving Soil Quality Criteria of Chromium Based on Species Sensitivity Distribution Methodology

Chromium (Cr) is one of the most severe heavy metal contaminants in soil, and it seriously threatens ecosystems and human health through the food chain. It is fundamental to collect toxicity data of Cr before developing soil quality criteria/standards in order to efficiently prevent health risks. In this work, the short-term toxic effects of Cr(VI) and Cr(III) on the root growth of eleven terrestrial plants were investigated. The corresponding fifth percentile hazardous concentrations (HC₅) by the best fitting species sensitivity distribution (SSD) curves based on the tenth percentile effect concentrations (EC₁₀) were determined to be 0.60 and 4.51 mg/kg for Cr (VI) and Cr (III), respectively. Compared to the screening level values worldwide, the HC₅ values in this study were higher for Cr(VI) and lower for Cr(III) to some extent. The results provide useful toxicity data for deriving national or local soil quality criteria for trivalent and hexavalent Cr.

Chromium (VI)-Induced Alterations in Physio-Chemical Parameters, Yield, and Yield Characteristics in Two Cultivars of Mungbean (Vigna radiata L.)

Chromium (Cr) presently used in various major industries and its residues possess a potent environmental threat. Contamination of soil and water resources due to Cr ions and its toxicity has adversely affected plant growth and crop productivity. Here, deleterious effects of different levels of Cr (VI) treatments i.e., 0, 30, 60, 90, and 120 μM on two mungbean cultivars, Pusa Vishal (PV) and Pusa Ratna (PR), in hydroponic and pot conditions were evaluated. Germination, seedling growth, biomass production, antioxidant enzyme, electrolytic leakage, oxidative stress (hydrogen peroxide and malondialdehyde), and proline content were determined to evaluate the performance of both cultivars under hydroponic conditions for 15 days. The hydroponic results were further compared with the growth and seed yield attributes of both the genotypes in pot experiments performed over 2 years. Seedling growth, biomass production, total chlorophyll (Chl), Chl-a, Chl-b, nitrogen content, plant height, seed protein, and seed yield decreased significantly under the 120 μM Cr stress level. Activities of antioxidant enzymes superoxide dismutase, catalase, ascorbate peroxidase and peroxidase increased in the leaves following Cr exposure at 60-90 μM but declined at 120 μM. Cr-induced reductions in growth and seed yield attributes were more in the sensitive than in the tolerant cultivar. Cr accumulation in the roots, stems, leaves, and seeds increased with an increase in Cr concentrations in the pot conditions. Furthermore, for both cultivars, there were significant negative correlations in morpho-physiological characteristics under high Cr concentrations. Overall results suggest that (PR) is more sensitive to Cr stress (PV) at the seedling stage and in pot conditions. Furthermore, (PV) can be utilized to study the mechanisms of Cr tolerance and in breeding programs to develop Cr-resistant varieties.