Arsenic Stress Research Articles

Isolation and Characterization of Arsenic-Tolerable Bacteria from Groundwater and Their Implementation on Rice Seedling's Shoot and Root Enhancement.

Arsenic exerts detrimental impacts on primary metabolism in plants, leading to reduced crop yield. Some arsenic-resistant plant growth-promoting bacteria (PGPB) help plants by providing some plant hormones to sustain their growth and development under arsenic stress. Here, seven different species of Bacillus were isolated from arsenic-contaminated groundwater of West Bengal, India. Those species were capable of growing in the presence of > 3.12g/L arsenate (AsV) and > 0.65g/L arsenite (AsIII) salts and also resist different heavy metals like Cu2+, Fe2+, Co2+, Zn2+, Pb2+, etc. They were susceptible to multiple groups of antibiotics like beta-lactam, aminoglycosides, etc. All species were capable of detoxifying arsenite and influenced rice seedlings' growth in the presence of arsenic salts by their capabilities likenitrogen-fixing ability, phosphate solubilization, indole 3-acetic acid (IAA), gibberellic acid (GA), proline production, etc. Most species helped enhance root and shoot lengths under arsenic stress. These primary findings suggest that those Bacillus spp. could be used as potential bio-fertilizers in arsenic-contaminated agricultural fields.

Arsenic Stress Mitigation Using a Novel Plant Growth-Promoting Bacterial Strain Bacillus mycoides NR5 in Spinach Plant (Spinacia oleracea L.).

Present study aimed to identify arsenic (As)-resistant bacterial strains that can be used to mitigate arsenic stress. A bacterium Bacillus mycoides NR5 having As tolerance limit of 1100 mg L-1 was isolated from Nag River, Maharashtra, India. It was also equipped with plant growth-promoting (PGP) attributes like phosphate solubilization, siderophores, ammonia, and nitrate reduction, with added antibiotic tolerance. Furthermore, scanning electron microscopy (SEM) and transmission electron micrograph (TEM) suggested biosorption as possible mechanisms of arsenic tolerance. A strong peak in FTIR spectra at 3379.0 corresponding to amine in As-treated NR5 also indicated metal interaction with cell surface protein. Amplification of arsenic reductase gene in NR5 further suggested intracellular transformation of As speciation. Moreover, As tolerance capability of NR5 was shown in spinach plants in which the bacterium effectively mitigated 25 ppm As by producing defense-related proline molecules. Evidence from SEM, TEM, and FTIR, concluded biosorption possibly the primary mechanism of As tolerance in NR5 along with the transformation of arsenic. B. mycoides NR5 with PGP attributes, high As tolerance, and antibiotic resistance mediated enhanced As tolerance in spinach plants advocated that the strain can be a better choice for As bioremediation in contaminated agricultural soil and water.

Efficacy of two different forms of selenium towards reduction of arsenic toxicity and accumulation in Cicer arietinum L.

Arsenic migration from soil to crop plants and subsequently human consumption of contaminated foodstuffs is a serious threat for society. In the present study, two oxidation states of selenium [Se(0) and Se(VI)] were used to check their efficacy towards amelioration of arsenic toxicity in chickpeas (Cicer arietinum L.). Three different concentrations (1, 5, and 10 mg/L) of both oxidation states of selenium were applied separately and in combination against a fixed dose (10 mg/L) of arsenic [(As(V)] treatment on chickpea seedlings. Further, seed germination and seedling growth attributes, oxidative stress, and antioxidant defense under different treatments were analyzed. The changes in anatomical structures and arsenic accumulation in different parts of seedlings were also studied. Results revealed that increased generation of oxidative stress affected physiobiochemical parameters of seedlings and diminished plant growth and deformation in vascular bundles under arsenic stress. However, the combined application of Se with As showed overall improvement in seedling growth, reduced oxidative stress, and organized vascular bundles of chickpea seedlings as compared to arsenic stress alone. The arsenic uptake and accumulation in chickpea seedlings were also reduced upon supplementation of Se. The highest reduction of arsenic accumulation by 42 and 56 % in roots, while 47 and 58 % in shoots were recorded by the application of 10 mg/L of Se(0) and Se (VI) under As stress, respectively. Overall, Se(VI) showed much better performance towards the minimization of arsenic-induced phytotoxicity and arsenic accumulation as compared to Se(0). Therefore, this study explored the efficacy of different forms of selenium towards the mitigation of arsenic toxicity in plants.

Effects of Phosphorus Sources on Arsenic Stress Mitigation in Wheat via Proline and Antioxidant Pathways

Effects of Phosphorus Sources on Arsenic Stress Mitigation in Wheat via Proline and Antioxidant Pathways

Interactions between arsenic and nitrogen regulate nitrogen availability and arsenic mobility in flooded paddy soils

In paddy soils, arsenic (As) stress influences nitrogen (N) transformation while application of N fertilizers during rice cropping affects As transformation. However, specific interactive effects between As and N in flooded paddy soils on As mobility and N availability were unclear. Here, we examined N and As dynamics in flooded paddy soils treated with four As levels (0, 30, 80 and 150 mg kg−1) and three urea additions (0, 4 and 8 mmol N kg−1). Arsenic contamination inhibited diazotrophs (nifH) and fungi but promoted AOA and denitrification genes (narG, nirK, nirS), decreasing dissolved organic N, NH4+-N and NO3–-N. Besides, urea application stimulated As- and Fe-reducing bacteria (arrA and Geo) coupled with anammox. On Day 28, the addition of 8 mmol N kg–1 increased total As concentrations in solutions of soils treated with 30 and 80 mg As kg−1 by 2.4 and 1.8 times compared with the nil-N control. In contrast, at 150 mg As kg−1, it decreased the total As concentration in soil solution by 63 % through facilitating As(III) oxidation coupled with NO3–-N reduction. These results indicate that As contamination decreases N availability, but urea application affects As mobility, depending on As contamination level.

Alleviating arsenic stress affecting the growth of Vigna radiata through the application of Klebsiella strain ASBT-KP1 isolated from wastewater.

Arsenic contamination of soil and water is a major environmental issue. Bioremediation through plant growth-promoting bacteria is viable, cost-effective, and sustainable. Along with arsenic removal, it also improves plant productivity under stressful conditions. A crucial aspect of such a strategy is the selection of bacterial inoculum. The described study demonstrates that the indigenous wastewater isolate, ASBT-KP1, could be a promising candidate. Identified as Klebsiella pneumoniae, ASBT-KP1 harbors genes associated with heavy metal and oxidative stress resistance, production of antimicrobial compounds and growth-promotion activity. The isolate efficiently accumulated 30 μg/g bacterial dry mass of arsenic. Tolerance toward arsenate and arsenite was 120 mM and 70 mM, respectively. Plant biomass content of Vigna radiata improved by 13% when grown in arsenic-free soil under laboratory conditions in the presence of the isolate. The increase became even more significant under the same conditions in the presence of arsenic, recording a 37% increase. The phylogenetic analysis assigned ASBT-KP1 to the clade of Klebsiella strains that promote plant growth. Similar results were also observed in Oryza sativa, employed to assess the ability of the strain to promote growth, in plants other than V. radiata. This study identifies a prospective candidate in ASBT-KP1 that could be employed as a plant growth-promoting rhizoinoculant in agricultural practices.

Pseudochrobactrum asaccharolyticum mitigates arsenic induced oxidative stress of maize plant by enhancing water status and antioxidant defense system

BackgroundOxidative stress mediated by reactive oxygen species (ROS) is a common denominator in arsenic toxicity. Arsenic stress in soil affects the water absorption, decrease stomatal conductance, reduction in osmotic, and leaf water potential, which restrict water uptake and osmotic stress in plants. Arsenic-induced osmotic stress triggers the overproduction of ROS, which causes a number of germination, physiological, biochemical, and antioxidant alterations. Antioxidants with potential to reduce ROS levels ameliorate the arsenic-induced lesions. Plant growth promoting rhizobacteria (PGPR) increase the total soluble sugars and proline, which scavenging OH radicals thereby prevent the oxidative damages cause by ROS. The main objective of this study was to evaluate the potential role of Arsenic resistant PGPR in growth of maize by mitigating arsenic stress.MethodologyArsenic tolerant PGPR strain MD3 (Pseudochrobactrum asaccharolyticum) was used to dismiss the ‘As’ induced oxidative stress in maize grown at concentrations of 50 and 100 mg/kg. Previously isolated arsenic tolerant bacterial strain MD3 “Pseudochrobactrum asaccharolyticum was used for this experiment. Further, growth promoting potential of MD3 was done by germination and physio-biochemical analysis of maize seeds. Experimental units were arranged in Completely Randomized Design (CRD). A total of 6 sets of treatments viz., control, arsenic treated (50 & 100 mg/kg), bacterial inoculated (MD3), and arsenic stress plus bacterial inoculated with three replicates were used for Petri plates and pot experiments. After treating with this MD3 strain, seeds of corn were grown in pots filled with or without 50 mg/kg and 100 mg/kg sodium arsenate.ResultsThe plants under arsenic stress (100 mg/kg) decreased the osmotic potential (0.8 MPa) as compared to control indicated the osmotic stress, which caused the reduction in growth, physiological parameters, proline accumulation, alteration in antioxidant enzymes (Superoxide dismutase-SOD, catalase-CAT, peroxidase-POD), increased MDA content, and H2O2 in maize plants. As-tolerant Pseudochrobactrum asaccharolyticum improved the plant growth by reducing the oxidation stress and antioxidant enzymes by proline accumulation. PCA analysis revealed that all six treatments scattered differently across the PC1 and PC2, having 85.51% and 9.72% data variance, respectively. This indicating the efficiency of As-tolerant strains. The heatmap supported the As-tolerant strains were positively correlated with growth parameters and physiological activities of the maize plants.ConclusionThis study concluded that Pseudochrobactrum asaccharolyticum reduced the ‘As’ toxicity in maize plant through the augmentation of the antioxidant defense system. Thus, MD3 (Pseudochrobactrum asaccharolyticum) strain can be considered as bio-fertilizer.

Phosphorous accumulation associated with mitochondrial PHT3-mediated enhanced arsenate tolerance in Chlamydomonas reinhardtii

Arsenate is a highly toxic element and excessive accumulation of arsenic in the aquatic environment easily triggers a problem threatening the ecological health. Phytoremediation has been widely explored as a method to alleviate As contamination. Here, the green algae, Chlamydomonas reinhardtii was investigated by profiling the accumulation of arsenate and phosphorus, which share the same uptake pathway, in response to arsenic stress. Both C. reinhardtii wild type C30 and the Crpht3 mutant were cultured under arsenic stress, and demonstrated a similar growth phenotype under limited phosphate supply. Sufficient phosphate obviously increased the uptake of polyphosphate and intercellular phosphate in the Crpht3 mutant, which increased the arsenic tolerance of the Crpht3 mutant under stress from 500 µmol L−1 As(V). Upregulation of the PHT3 gene in the Crpht3 mutant increased accumulation of phosphate in the cytoplasm under arsenate stress, which triggered a regulatory role for the differentially expressed genes that mediated improvement of the glutathione redox cycle, antioxidant activity and detoxification. While the wild type C30 showed weak arsenate tolerance because of little phosphate accumulation. These results suggest that the enhanced arsenic tolerance of the Crpht3 mutant is regulated by the PHT3 gene mediation. This study provides insight onto the responsive mechanisms of the PHT3 gene-mediated in alleviating arsenic toxicity in plants.

Evaluation of interaction among arsenic and Brevibacterium sp. strain CS2 and its proteins profiling

In this study, Brevibacterium sp. strain CS2 was used to evaluate the mechanisms of arsenic interaction with the bacterium and its enzymatic and protein profiling under arsenic stress. The bacterium was capable to resist the arsenate 280 mM and arsenite 40 mM as per MIC. The whole genome, available on NCBI, was analyzed for genes associated with arsenic, which confirmed the genes for both arsenic oxidation (aioB) and arsenic reduction arsR, arsC, ACR3, and arsB. The sharpening and shifting of FTIR spectra in the ranges of 3278–2851 cm−1 are due to hydroxyl and amide stretching. SEM analysis showed no significant changes in morphology in arsenic stress while EDX analysis proved the arsenite interaction by showing arsenic peaks in the graph. Both glutathione and non-protein thiol showed different responses in the absence and presence of arsenic stress. Protein bands such as 25, 30, 32, 37, 42, 48, and 100 kDa were expressed more in arsenic-treated samples as compared to the control one. The presence of arsenic oxidizing genes, the ability to resist arsenic, and the varied response of enzymes and proteins in arsenic stress make the bacterium a suitable agent for arsenic eradication from contaminated sites.

Evaluation of Response of Rice Varieties Differing in Phosphorus Use Efficiency Under Arsenic Stress

Evaluation of Response of Rice Varieties Differing in Phosphorus Use Efficiency Under Arsenic Stress

Regulation of arsenate stress by nitric oxide and hydrogen sulfide in Oryza sativa seedlings: Implication of sulfur assimilation, glutathione biosynthesis, and the ascorbate-glutathione cycle and its genes

Seed priming by nitric oxide (NO) and hydrogen sulphide (H2S) in combating against abiotic stress in plants is well documented. However, knowledge of fundamental mechanisms of their crosstalk is scrambled. Therefore, the reported study examined the probable role of NO and H2S in the mitigation of arsenate toxicity (As(V)) in rice seedlings and whether their potential signalling routes crossover. Results report that As(V) toxicity limited shoot and root length growth with more As accumulation in roots. As(V) further caused elevated reactive oxygen species levels, inhibited ascorbate-glutathione cycle enzymes and relative gene expression of its enzymes and thus, causing lipid and protein oxidation. These results correlate with reduced nitric oxide synthase-like and L–cysteine desulfhydrase activity along with endogenous NO and H2S. While, L-NAME or PAG augmented As(V) toxicity, and addition of SNP or NaHS effectively reversed their respective effects. Furthermore, SNP under PAG or NaHS under L-NAME were able to pacify As(V) stress, implicating that endogenous NO and H2S efficiently ameliorate As(V) toxicity but without their shared signaling in rice seedlings.

Assessment of rice genotypes through the lens of morpho-physiological and biochemical traits in response to arsenic stress

Rice is a globally important food crop which is sensitive to the presence of a metalloid, arsenic (As). There is limited research pertaining to identifying relevant As-tolerant rice germplasm in adaptive breeding research initiatives, despite the fact that As contamination in rice has long been known. This study served to identify the growth performance of different rice genotypes under high levels of As. Rice seed germination analysis (germination percentage, GP) was performed to categorize the eight different rice genotypes and growing under varying As levels including As25, 25 μM and As50, 50 μM. The Zhenong 41 was identified as the highly tolerant genotypes with lowest decrease in GP by 87 %, plant height (PH) by 26 %, and dry weight (DW) by 16 %; while 9311 was observed to be the most sensitive genotype with highest reduction in GP by 44 %, PH by 48 % and DW by 54 % under As25 stress conditions, compared to control treatment. The higher As50 stress treatment delivered more adverse growth inhibitory effects than the rice plants cultivated under As25. Specifically, the As-sensitive rice genotype 9311 showed significantly higher decrease in foliar chlorophyll contents relative to the other genotypes, especially Zhenong 41 (As-tolerant). During exposure to high As levels, the rice genotype 9311 significantly modulated and augmented the production of MDA and H2O2 by stimulating the activities of POD, SOD, and CAT. This study revealed interesting insights into the responses of rice genotypes to variable As stresses throughout the various growth stages. Overall, the findings of this study could be harnessed to support any ongoing As-tolerant rice breeding agendas for cultivation in As-polluted environments.

Alleviation of arsenic stress in pakchoi by foliar spraying of engineered nanomaterials.

Addressing heavy metal contamination in leafy vegetables is critically important due to its adverse effects on human health. In this study, we investigated the inhibitory effects of foliar spraying with four nanoparticles (CeO2, ZnO, SiO2, and S NPs) on arsenic (As) stress in pakchoi (Brassica rapa var. Chinensis). The findings reveal that foliar application of ZnO NPs at 1 ~ 2.5 mg plant-1 and CeO2 NPs at 5 mg plant-1 significantly reduces As in shoots by 40.9 ~ 47.3% and 39.4%, respectively. Moreover, 5 mg plant-1 CeO2 NPs increased plant height by 6.06% and chlorophyll a (Chla) content by 30.2% under As stress. Foliar spraying of CeO2 NPs at 0.2-5 mg plant-1 also significantly enhanced superoxide dismutase (SOD) activity in shoots by 9.4 ~ 13.9%, lowered H2O2 content by 42.4 ~ 53.25%, and increased root protein contents by 79 ~ 109.2%. CeO2 NPs regulate the As(III)/As(V) ratio, aiding in As efflux from roots and thereby reducing As toxicity to plants. In vitro digestion experiments reveal that the consumption of CeO2 NPs carries the lowest health risk of As. In addition, foliar spraying of ZnO NPs at 1 ~ 2.5 mg plant-1 can suppress plant As uptake by modulating enzyme activity, reducing leaf damage, and enhancing chlorophyll content. The study demonstrates that high CeO2 NP concentrations and suitable ZnO NP concentrations can alleviate As toxicity in pakchoi, consequently reducing human health risks.

Application of CuNPs and AMF alleviates arsenic stress by encompassing reduced arsenic uptake through metabolomics and ionomics alterations in Elymus sibiricus

Recent studies have exhibited a very promising role of copper nanoparticles (CuNPs) in mitigation of abiotic stresses in plants. Arbuscular mycorrhizae fungi (AMF) assisted plants to trigger their defense mechanism against abiotic stresses. Arsenic (As) is a non-essential and injurious heavy-metal contaminant. Current research work was designed to elucidate role of CuNPs (100, 200 and 300 mM) and a commercial inoculum of Glomus species (Clonex® Root Maximizer) either alone or in combination (CuNPs + Clonex) on physiology, growth, and stress alleviation mechanisms of E. sibiricus growing in As spiked soils (0, 50, and 100 mg Kg− 1 soil). Arsenic induced oxidative stress, enhanced biosynthesis of hydrogen peroxide, lipid peroxidation and methylglyoxal (MG) in E. sibiricus. Moreover, As-phytotoxicity reduced photosynthetic activities and growth of plants. Results showed that individual and combined treatments, CuNPs (100 mM) as well as soil inoculation of AMF significantly enhanced root growth and shoot growth by declining As content in root tissues and shoot tissues in As polluted soils. E. sibiricus plants treated with CuNPs (100 mM) and/or AMF alleviated As induced phytotoxicity through upregulating the activity of antioxidative enzymes such as catalase (CAT) and superoxide dismutase (SOD) besides the biosynthesis of non-enzymatic antioxidants including phytochelatin (PC) and glutathione (GSH). In brief, supplementation of CuNPs (100 mM) alone or in combination with AMF reduced As uptake and alleviated the As-phytotoxicity in E. sibiricus by inducing stress tolerance mechanism resulting in the improvement of the plant growth parameters.

Determining arsenic stress tolerance genes in rice (Oryza sativa L.) via genomic insights and QTL mapping with double haploid lines

Arsenic, a hazardous heavy metal with potent carcinogenic properties, significantly affects key rice-producing regions worldwide. In this study, we present a quantitative trait locus (QTL) mapping investigation designed to identify candidate genes responsible for conferring tolerance to arsenic toxicity in rice (Oryza sativa L.) during the seedling stage. This study identified 17 QTLs on different chromosomes, including qCHC-1 and qCHC-3 on chromosome 1 and 3 related to chlorophyll content and qRFW-12 on chromosome 12 related to root fresh weight. Gene expression analysis revealed eight candidate genes exhibited significant upregulation in the resistant lines, OsGRL1, OsDjB1, OsZIP2, OsMATE12, OsTRX29, OsMADS33, OsABCG29, and OsENODL24. These genes display sequence alignment and phylogenetic tree similarities with other species and engaging in protein-protein interactions with significant proteins. Advanced gene-editing techniques such as CRISPR-Cas9 to precisely target and modify the candidate genes responsible for arsenic tolerance will be explore. This approach may expedite the development of arsenic-resistant rice cultivars, which are essential for ensuring food security in regions affected by arsenic-contaminated soil and water.

Melatonin differentially refines the metabolome to improve seed formation during grain developmental stages and enhances yield in two contrasting rice cultivars, grown in arsenic-contaminated soil

The manuscript revealed the ameliorative effects of exogenous melatonin in two distinct reproductive stages, i.e., developing grains (20 days after pollination) and matured grains (40 days after pollination) in two contrasting indica rice genotypes, viz., Khitish (arsenic-susceptible) and Muktashri (arsenic-tolerant), irrigated with arsenic-contaminated water throughout their life-cycle. Melatonin administration improved yield-related parameters like rachis length, primary and secondary branch length, number of grains per panicle, number of filled and empty grains per panicle, grain length and breadth and 1000-grain per weight. Expression of GW2, which negatively regulates grain development, was suppressed, along with concomitant induction of positive regulators like GIF1, DEP1 and SPL14 in both Khitish and Muktashri. Melatonin lowered arsenic bioaccumulation in grains and tissue biomass, more effectively in Khitish. Unregulated production of reactive oxygen species, leading to cellular necrosis caused by arsenic, was reversed in presence of melatonin. Endogenous melatonin level was stimulated due to up-regulation of the key biosynthetic genes, SNAT and ASMT. Melatonin enhanced the production of diverse antioxidants like anthocyanins, flavonoids, total phenolics and ascorbic acid and also heightened the production of thiol-metabolites (cysteine, reduced glutathione, non-protein thiols and phytochelatin), ensuring effective chelation and arsenic detoxification. Altogether, our observation, supported by principal component analysis, proved that melatonin re-programs the antioxidative metabolome to enhance plant resilience against arsenic stress to mitigate oxidative damages and reduce arsenic translocation from the soil to tissue biomass and edible grains.

Staphylococcus arlettae mediated defense mechanisms and metabolite modulation against arsenic stress in Helianthus annuus.

Arsenate, a metalloid, acting as an analog to phosphate, has a tendency to accumulate more readily in plant species, leading to adverse effects. In the current study, sunflower seedlings were exposed to 25, 50 and 100 ppm of the arsenic. Likewise, a notable reduction (p<0.05) was observed in the relative growth rate (RGR) by 4-folds and net assimilation rate (NAR) by 75% of Helianthus annuus when subjected to arsenic (As) stress. Nevertheless, the presence of Staphylococcus arlettae, a plant growth-promoting rhizobacterium with As tolerance, yielded an escalation in the growth of H. annuus within As-contaminated media. S. arlettae facilitated the conversion of As into a form accessible to plants, thereby, increasing its uptake and subsequent accumulation in plant tissues. S. arlettae encouraged the enzymatic antioxidant systems (Superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX) and catalase (CAT)) and non-enzymatic antioxidants (flavonoids, phenolics, and glutathione) in H. annuus seedlings following substantial As accumulation. The strain also induced the host plant to produce osmolytes like proline and sugars, mitigating water loss and maintaining cellular osmotic balance under As-induced stress. S. arlettae rectified imbalances in lignin content, reduced high malonaldehyde (MDA) levels, and minimized electrolyte leakage, thus counteracting the toxic impacts of the metal. The strain exhibited the capability to concurrently encourage plant growth and remediate Ascontaminated growth media through 2-folds rate of biotransformation and bio-mobilization.

Exploring the transporters and mechanisms of arsenic detoxification in plants and potential role of nanoparticles in alleviating arsenic stress

Exploring the transporters and mechanisms of arsenic detoxification in plants and potential role of nanoparticles in alleviating arsenic stress

Enhanced arsenic stress tolerance in landrace and improved rice cultivars through modulation of gibberellic acid (GA3) synthesis and antioxidant metabolism via phosphorus and silicon supplementation

Arsenic (As), an environmental pollutant, imposes toxic impacts on plant health. In recent years, researchers have focused on comprehending the As-induced intrusion in growth and metabolic components. However, the interactions between phosphorus (P) and silicon (Si) remain elusive, specifically in rice (Oryza sativa) cultivars. Therefore, the present study investigated the effects of P and Si on the defense mechanisms, nutrients accumulation, carbohydrate metabolism, gibberellic acid (GA3) synthesis, and growth responses in Indica rice cultivars (landrace and improved) under As stress. With this focus, our study potentially indicated that As stress (150 µM) negatively impacted the underlying physiological and growth traits, with more pronounced effects on the improved cultivar compared to the landrace. However, P (30 mg kg−1 soil) and/ or Si (1 mM) treatments have prominently reduced oxidative stress with improved defense mechanisms and GA synthesis. Modulation of enzymatic defense system increased in both cultivars but more pronounced in landrace, including superoxide dismutase (+36.47%, +24.43%), ascorbate peroxidase (+95.11%, +78.26%), along with non-enzymatic antioxidants such as ascorbate (+29.43%, +21.48%), and reduced glutathione (+75.45%, +62.34%) concentrations, respectively. Notably, GA concentration (+23.78%, +16.48%) was substantially increased by the cumulative application of P and Si under As stress in both cultivars but more conspicuous in the landrace, respectively. Further, employing GA biosynthesis inhibitor, paclobutrazol (PBZ; 10 µM), substantiated the input of GA-mediated As tolerance, wherein, PBZ reversed the impacts of P and Si on the endogenous GA concentration and defense metabolism. In summation, landrace outperformed improved cultivar leading to As tolerance. This implies that the landrace could be used for future breeding programs permitting in-depth considerations of P and Si-mediated GA3 synthesis under As stress conditions.

Synergistic impact of Serendipita indica and Zhihengliuella sp. ISTPL4 on the mitigation of arsenic stress in rice.

Arsenic (As) is a highly toxic metal that interferes with plant growth and disrupts various biochemical and molecular processes in plants. In this study, the harmful effects of As on rice were mitigated using combined inoculation of a root endophyte Serendipita indica and an actinobacterium Zhihengliuella sp. ISTPL4. A randomized experiment was conducted, in which rice plants were grown under controlled conditions and As-stressed conditions. The control and treatment groups consisted of untreated and non-stressed plants (C1), treated and non-stressed plants (C2), stressed and untreated plants (T1), and stressed and treated plants (T2). Various phenotypic characteristics such as shoot length (SL), root length (RL), shoot fresh weight (SFW), root fresh weight (RFW), shoot dry weight (SDW), and root dry weight (RDW) and biochemical parameters such as chlorophyll content, protein content, and antioxidant enzymatic activities were evaluated. The activity of various antioxidant enzymes was increased in T2 followed by T1 plants. Furthermore, high concentrations of phytohormones such as ethylene (ET), gibberellic acid (GA), and cytokinin (CK) were found at 4.11 μmol mg-1, 2.53 μmol mg-1, and 3.62 μmol mg-1 of FW of plant, respectively. The results of AAS indicated an increased As accumulation in roots of T2 plants (131.5 mg kg-1) than in roots of T1 plants (120 mg kg-1). It showed that there was an increased As accumulation and sequestration in roots of microbial-treated plants (T2) than in uninoculated plants (T1). Our data suggest that this microbial combination can be used to reduce the toxic effects of As in plants by increasing the activity of antioxidant enzymes such as SOD, CAT, PAL, PPO and POD. Furthermore, rice plants can withstand As stress owing to the active synthesis of phytohormones in the presence of microbial combinations.