The mechanism of arsenic (As) tolerance was investigated on two contrasting rice (Oryza sativa L.) genotypes, selected for As tolerance and accumulation. One tolerant (Triguna) and one sensitive ...(IET-4786) variety were exposed to various arsenate (0–50μM) levels for 7d for biochemical analyses. Arsenic induced oxidative stress was more pronounced in IET-4786 than Triguna especially in terms of reactive oxygen species, lipid peroxidation, EC and pro-oxidant enzymes (NADPH oxidase and ascorbate oxidase). However, Triguna tolerated As stress through the enhanced enzymes activities particularly pertaining to thiol metabolism such as serine acetyl transferase (SAT), cysteine synthase (CS), γ-glutamyl cysteine synthase (γ-ECS), γ-glutamyl transpeptidase (γ-GT), and glutathione-S-transferase (GST) as well as arsenate reductase (AR). Besides maintaining the ratio of redox couples GSH/GSSG and ASC/DHA, the level of phytochelatins (PCs) and phytochelatin synthase (PCS) activity were more pronounced in Triguna, in which harmonized responses of thiol metabolism was responsible for As tolerance in contrast to IET-4786 showing its susceptible nature towards As exposure.
► Rice varieties Triguna and IET-4786 showed differential phytotoxic responses and As accumulation. ► Arsenic induced oxidative stress and pro-oxidant enzymes activities were higher in IET-4786 than Triguna. ► Triguna tolerated stress through maintenance of thiol metabolic pathway & ASC/DHA & GSH/GSSG balance. ► PC species & PCS activity were more pronounced in Triguna than IET-4786. ► Contrastingly, IET-4786 is very sensitive to As exposure due to reduction of sulphate assimilation pathway.
Arsenic (As) is posing serious health concerns in South East Asia where rice, an efficient accumulator of As, is prominent crop. Salicylic acid (SA) is an important signaling molecule and plays a ...crucial role in resistance against biotic and abiotic stress in plants. In present study, ameliorative effect of SA against arsenate (As(V)) toxicity has been investigated in rice (Oryza sativa L.). Arsenate stress hampered the plant growth in terms of root, shoots length, and biomass as well as it enhanced the level of H2O2 and MDA in dose dependent manner in shoot. Exogenous application of SA, reverted the growth, and oxidative stress caused by As(V) and significantly decreased As translocation to the shoots. Level of As in shoot was positively correlated with the expression of OsLsi2, efflux transporter responsible for root to shoot translocation of As in the form of arsenite (As(III)). SA also overcame As(V) induced oxidative stress and modulated the activities of antioxidant enzymes in a differential manner in shoots. As treatment hampered the translocation of Fe in the shoot which was compensated by the SA treatment. The level of Fe in root and shoot was positively correlated with the transcript level of transporters responsible for the accumulation of Fe, OsNRAMP5, and OsFRDL1, in the root and shoot, respectively. Co-application of SA was more effective than pre-treatment for reducing As accumulation as well as imposed toxicity.
Irrigation of paddy fields to arsenic (As) containing groundwater leads to As accumulation in rice grains and causes serious health risk to the people worldwide. To reduce As intake via consumption ...of contaminated rice grain, identification of the mechanisms for As accumulation and detoxification in rice is a prerequisite. Herein, we report involvement of a member of rice NRAMP (Natural Resistance‐Associated Macrophage Protein) transporter, OsNRAMP1, in As, in addition to cadmium (Cd), accumulation through expression in yeast and Arabidopsis. Expression of OsNRAMP1 in yeast mutant (fet3fet4) rescued iron (Fe) uptake and exhibited enhanced accumulation of As and Cd. Expression of OsNRAMP1 in Arabidopsis provided tolerance with enhanced As and Cd accumulation in root and shoot. Cellular localization revealed that OsNRAMP1 resides on plasma membrane of endodermis and pericycle cells and may assist in xylem loading for root to shoot mobilization. This is the first report demonstrating role of NRAMP in xylem mediated loading and enhanced accumulation of As and Cd in plants. We propose that genetic modification of OsNRAMP1 in rice might be helpful in developing rice with low As and Cd content in grain and minimize the risk of food chain contamination to these toxic metals.
Arsenic (As) is a highly toxic environmental pollutant which accumulates in rice grain and causes chronic and epidemic effects on human health. We report role of rice NRAMP (Natural Resistance‐Associated Macrophage Protein) transporter, OsNRAMP1, in As, in addition to cadmium (Cd), accumulation through expression in yeast and Arabidopsis. Cellular localization revealed that OsNRAMP1 resides on plasma membrane of endodermis and pericycle cells and may assist in xylem loading for root to shoot mobilization. This is the first report demonstrating role of NRAMP in xylem mediated loading and enhanced accumulation of As and Cd in plants.
Arsenic (As), a naturally occurring metallic element, is a dreadful health hazard to millions of people across the globe. Arsenic is present in low amount in the environment and originates from ...anthropogenic impact and geogenic sources. The presence of As in groundwater used for irrigation is a worldwide problem as it affects crop productivity, accumulates to different tissues and contaminates food chain. The consumption of As contaminated water or food products leads to several diseases and even death. Recently, studies have been carried out to explore the biochemical and molecular mechanisms which contribute to As toxicity, accumulation, detoxification and tolerance acquisition in plants. This information has led to the development of the biotechnological tools for developing plants with modulated As tolerance and detoxification to safeguard cellular and genetic integrity as well as to minimize food chain contamination. This review aims to provide current updates about the biochemical and molecular networks involved in As uptake by plants and the recent developments in the area of functional genomics in terms of developing As tolerant and low As accumulating plants.
•Arsenic affects plant growth and human health due to food chain contamination.•Omics can be an important tool to identify arsenic associated molecular networks.•Biotechnological interventions can modulate arsenic response in plants.•This review updates gene mining and approaches to develop altered arsenic response.
Nitric oxide (NO) is a gaseous signaling molecule and has a profound impact on plant growth and development. It is reported to serve as pro oxidant as well as antioxidant in plant system. In the ...present study, we evaluated the protective role of NO against arsenate (As(V)) toxicity in rice plants. As(V) exposure has hampered the plant growth, reduced the chlorophyll content, and enhanced the oxidative stress, while the exogenous NO supplementation has reverted these symptoms. NO supplementation has reduced the arsenic (As) accumulation in root as well as shoot. NO supplementation to As(V) exposed plants has reduced the gene expression level of OsLsi1 and OsLsi2. As(V) stress significantly impacted thiol metabolism, it reduced GSH content and GSH/GSSG ratio, and enhanced the level of PCs. NO supplementation maintained the GSH/GSSG ratio and reduced the level of PCs. NO supplementation reverted As(V) induced iron deficiency in shoot and had significant impact of gene expression level of various iron transporters (OsYSL2, OsFRDL1, OsIRT1, and OsIRO2). Conclusively, exogenous application of NO could be advantageous against As(V) toxicity and could confer the tolerance to As(V) stress in rice.
Rice is the most consumed food crop and essential determinant in global food security program. Currently, arsenic (As) accumulation in rice is a critical concern in terms of both crop productivity ...and grain quality; therefore, it is an urgent need to reduce As accumulation. Here, we selected a glutaredoxin (OsGrx_C7) gene that plays an essential role in AsIII tolerance in rice. To explore the mechanism, we raised OsGrx_C7 overexpression (OE) rice lines, which showed improved plant AsIII tolerance and lowered its accumulation in grains. Arsenic accumulation in husk, unpolished, and polished rice reduced by ca. 65%, 67%, and 85%, respectively, in OE lines, compared to wild-type (WT) plants. To know the rationale, expression of AsIII transporters (aquaporins) in root and shoot tissues were examined, and revealed that OsGrx_C7 regulates the expression of these genes, which ultimately reduces root to shoot AsIII translocation. Additionally, OsGrx_C7 improves root growth by regulating the expression of oxidative stress-induced root expansion related genes, promote root growth and plant health. Overall, current study suggested that AsIII induced OsGrx_C7 markedly enhanced tolerance to AsIII with reduced accumulation in grains by regulating root expansion and controlling root to shoot As transport by altered expression of AsIII aquaporins.
•Studied a novel role of rice glutaredoxin (OsGrx_C7) in facilitating root adaptation to AsIII toxicity.•Rice glutaredoxin regulate the expression of AsIII transporters (Aquaporins).•OsGrx_C7 control root to shoot arsenic translocation and reduces arsenic accumulation in grains.
Glutaredoxins (Grxs) are a family of small multifunctional proteins involved in various cellular functions, including redox regulation and protection under oxidative stress. Despite the high number ...of Grx genes in plant genomes (48 Grxs in rice), the biological functions and physiological roles of most of them remain unknown. Here, the functional characterization of the two arsenic-responsive rice Grx family proteins, OsGrx_C7 and OsGrx_C2.1 are reported. Over-expression of OsGrx_C7 and OsGrx_C2.1 in transgenic Arabidopsis thaliana conferred arsenic (As) tolerance as reflected by germination, root growth assay, and whole plant growth. Also, the transgenic expression of OsGrxs displayed significantly reduced As accumulation in A. thaliana seeds and shoot tissues compared to WT plants during both AsIII and AsV stress. Thus, OsGrx_C7 and OsGrx_C2.1 seem to be an important determinant of As-stress response in plants. OsGrx_C7 and OsGrx_C2.1 transgenic showed to maintain intracellular GSH pool and involved in lowering AsIII accumulation either by extrusion or reducing uptake by altering the transcript of A. thaliana AtNIPs. Overall, OsGrx_C7 and OsGrx_C2.1 may represent a Grx family protein involved in As stress response and may allow a better understanding of the As induced stress pathways and the design of strategies for the improvement of stress tolerance as well as decreased As content in crops.
Fifteen fungal strains were isolated from arsenic contaminated (range 9.45–15.63
mg
kg
−
1
) agricultural soils from the state of West Bengal, India. Five fungal strains were belonged to the
...Aspergillus and
Trichoderma group each, however, remaining five were identified as the
Neocosmospora,
Sordaria,
Rhizopus,
Penicillium and sterile mycelial strain. All these fungal strains were cultivated on medium supplemented with 100, 500, 1000, 5000 and 10,000
mg
l
−
1
of sodium arsenate. After 30-day cultivation under laboratory conditions, radial growth of these strains was determined and compared with control. Toxicity and tolerance of these strains to arsenate were evaluated on the basis of tolerance index. Out of fifteen, only five fungal strains were found resistant and survived with tolerance index pattern as 0.956 (sterile mycelial strain)
>
0.311 (
Rhizopus sp.)
>
0.306 (
Neocosmospora sp.)
>
0.212 (
Penicillium sp.)
>
0.189 (
Aspergillus sp.) at 10,000
mg
l
−
1
of arsenate. The arsenic removal efficacy of ten fungal strains, tolerant to 5000
mg
l
−
1
arsenate, was also assayed under laboratory conditions for 21
days. All these strains were cultivated individually on mycological broth enriched with 10
mg
l
−
1
of arsenic. The initial and final pH of cultivating medium, fungal biomass and removal of arsenic by each fungal strain were evaluated. Fungal biomass of ten strains removed arsenic biologically from the medium which were ranged from 10.92 to 65.81% depending on fungal species. The flux of biovolatilized arsenic was determined indirectly by estimating the sum of arsenic content in fungal biomass and medium. The mean percent removal as flux of biovolatilized arsenic ranged from 3.71 to 29.86%. The most effective removal of arsenic was observed in the
Trichoderma sp., sterile mycelial strain,
Neocosmospora sp. and
Rhizopus sp. fungal strains. These fungal strains can be effectively used for the bioremediation of arsenic-contaminated agricultural soils.
► Biological removal of arsenic by different fungal strains. ► Fungal strains isolated from arsenic contaminated soils. ► Five fungal strains resistant at 10,000
mg
l
−
1
of arsenate. ► Flux of biovolatilized arsenic ranged from 3.71 to 29.86%. ► Fungal strains can be effectively used for the bioremediation of arsenic-contaminated agricultural soils.
•Microbial consortium of P. putida and C. vulgaris improved the growth and reduced arsenic induced oxidative stress in rice.•The consortium reduced the accumulation of arsenic and also improved the ...level of nutrient elements in rice.•Reduced arsenic in rice due to the consortium alleviated the requirement of thiols and antioxidant enzymes.
In the present study, arsenic (As) toxicity amelioration potential of a consortium of plant growth promoting rhizobacterium (Pseudomonas putida) and alga (Chlorella vulgaris) was evaluated during arsenate (AsV) exposure to rice (Oryza sativa) plants for 15 d. The consortium mediated amelioration of As toxicity was evident through improved growth of rice plants (root and shoot length and biomass) and reduced oxidative stress as level of superoxide radicals (O2−), hydrogen peroxide (H2O2) and membrane damage. The positive responses were attributable to a significant decline in As accumulation in root (94 mg kg−1 dw) and shoot (51 mg kg−1 dw) in consortium (P. putida + C. vulgaris) inoculated seedlings as compared to As alone exposed plants (156 and 98 mg kg−1 dw, respectively). There were also significant changes in the level of various nutrient elements (Mn, Fe, Co, Zn, Mo and Cu), thiols and in the activities of antioxidant and thiol metabolism enzymes in the consortium inoculated seedlings that allowed the plants to tolerate As stress effectively and achieve better growth. The study demonstrated that consortium of P. putida and C. vulgaris may alleviate As stress and improve growth of rice seedlings along with reduction in As levels.
Arsenic is commonly present in subsoil and is a carcinogen in humans. Rice takes up arsenic and it accumulates in different plant parts, including grains, at levels several-fold higher than the soil. ...In high arsenic regions, rice can contribute substantially to arsenic intake by the human population. Arsenic in rice grains is present in the carcinogenic inorganic or the relatively safer organic (methylated) form. A wide variation is noticed in different rice genotypes with respect to the proportion of arsenic in these forms in grains. Mechanisms involved in arsenic uptake, efflux from roots, loading into xylem, transport, partitioning, arsenate reduction, arsenic sequestration in vacuoles, volatilization from leaves, accumulation in grains etc. are poorly understood. Selection of cultivars accumulating low inorganic arsenic is an important trait to be used by breeders to develop rice varieties safer for cultivation in arsenic-contaminated regions. Systematic efforts have not been made to screen rice genotypes for mining the genes involved in arsenic uptake, transport and accumulation in grains. Identification of rice germplasm with varying arsenic uptake and partitioning, and development of mapping populations with contrasting grain arsenic, are required for association studies and QTL mapping for accelerating rice improvement. Efforts on gene expression profiling, deep transcriptome sequencing, high throughput metabolomics and phenotyping of contrasting arsenic accumulating lines need to be increased to develop strategies for design of safer rice varieties. Network research projects need to be developed along these approaches to accelerate the development of crop varieties safer for farming in arsenic-contaminated environments.
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