Oxidative Stress In Rice Research Articles

Utilizing Arthrospira platensis for the fabrication of zinc oxide nanoparticles: Analysis and assessment for enhancing drought tolerance in Sub1A QTL bearing rice seedlings

In the present study, the underlying pathways for zinc oxide nanoparticles (ZnO-NPs) mediated modulation of oxidative stress under drought were evaluated in rice seedlings. Principally, rice cultivar (cv. Swarna Sub1) was used to assess the potential of the Sub1A QTL for its drought sensitivity in response to bio-fabricated ZnO-NPs. ZnO-NPs were synthesized from algal (Arthrospira platensis) extract and characterized for their opto-physical properties, confirming size (54 nm), hydrodynamicity (-18.54), amorphous-cubic shape and others features. Fifteen-day-old rice seedlings were primed with 25 ppm ZnO-NPs and exposed to 12 % polyethylene glycol (PEG) mediated drought stress (DS) for 7-days under laboratory conditions. Primarily, Sub1A QTL responded to drought-induced anoxic stress with a significant increase in the activities of alcohol dehydrogenase (447.41 %) and pyruvate decarboxylase (96.51 %) through ZnO-NPs sensitization. Plants recorded a significant reduction in root growth, which regained 89.25 % with ZnO-NPs treatments. ZnO-NPs also recovered relative water content (49 %), proline (99.2 %), and improved chlorophyll fluorescence (90.9 %) under stress. Furthermore, drought-induced membrane leakage was stabilized by reducing ionic conductivity through the distribution of wall-bound polyamines. A characteristic feature of fluorescence also reinforced the sustenance of photosynthetic activities by ZnO-NPs under drought. Alternatively, rice seedlings showed regulation of oxidative stress, where lipid peroxidation and protein carbonylation were reduced by 270 % and 178.2 %, respectively. This was observed with the minimization of superoxide and hydrogen peroxide concentrations by regulating apoplastic oxidase activity (117.64 %) with distinct polymorphisms in proteins. These observations suggest that ZnO-NPs can ameliorate drought-induced oxidative stress in rice, providing insights for improved nano-fertigation.

Mitigating Pb-induced oxidative stress in rice plants by cerium oxide and iron oxide nanoparticles

Nanotechnology offers creative and effective solutions for addressing various environmental issues, such as heavy metals (HM). The rapidly increasing HM concentrations in agricultural land have drawn considerable attention. Nanoparticles (NPs) have special physiochemical features that help reduce stress. This study assessed the viability of applying CeO2NPs and FeONPs to rice plants at a concentration of 25 mg/L to effectively remove the detrimental effects of lead (Pb) by using various concentrations (100 and 200 ppm) on plant development and growth. To achieve the desired concentrations, a Pb solution was prepared by dissolving lead nitrate in distilled water and added to the soil. Interestingly, the application of CeO2NPs and FeONPs resulted in a notable increase in plant growth, biomass, gas exchange characteristics, antioxidant enzymatic activity (SOD, POD, APX, and CAT), their gene expressions, as well as other antioxidants (phenols, prolines, amino acids, flavonoids, anthocyanins, and ascorbic acids) while simultaneously reducing oxidative stress (MDA, H2O2, and electrolyte leakage) and Pb uptake in rice. Conversely, Pb elevation in the soil increased oxidative damage and organic acid exudation pattern in the rice. At 200 ppm, a significant rise in Pb content (416.67 % and 380 %) was found in the roots and leaves of rice plants. According to our findings, rice growth can be bio-stimulated by CeO2NPs and FeONPs. Subsequent investigations should focus on the persistent ecological consequences and molecular mechanisms associated with the application of cerium oxide and iron oxide nanoparticles in agriculture to reduce Pb-induced oxidative stress.

Zinc finger protein ZFP36 and pyruvate dehydrogenase kinase PDK1 function in ABA-mediated aluminum tolerance in rice

Aluminum (Al) toxicity poses a significant constraint on field crop yields in acid soils. Zinc finger protein 36 (ZFP36) is well-documented for its pivotal role in enhancing tolerance to both drought and oxidative stress in rice. This study unveils a novel function of ZFP36 modulated by abscisic acid (ABA)-dependent mechanisms, specifically aimed at alleviating Al toxicity in rice. Under Al stress, the expression of ZFP36 significantly increased through an ABA-dependent pathway. Knocking down ZFP36 heightened Al sensitivity, while overexpressing ZFP36 conferred increased resistance to Al stress. Additionally, our investigations revealed a physical interaction between ZFP36 and pyruvate dehydrogenase kinase 1 in rice (OsPDK1). Biochemical assays further elucidated that OsPDK1 phosphorylates ZFP36 at the amino acid site 73–161. Subsequent experiments demonstrated that ZFP36 positively regulates the expression of ascorbate peroxidases (OsAPX1) and OsALS1 by binding to specific elements in their upstream segments in rice. Through genetic and phenotypic analyses, we unveiled that OsPDK1 influences ABA-triggered antioxidant defense to alleviate Al toxicity by interacting with ZFP36. In summary, our study underscores that pyruvate dehydrogenase kinase 1 (OsPDK1) phosphorylates ZFP36 to modulate the activities of antioxidant enzymes via an ABA-dependent pathway, influencing tolerance of rice to soil Al toxicity.

Heat shock combined with salinity impairs photosynthesis but stimulates antioxidant defense in rice plants

The interactive mechanisms that occur between heat shock and salt stress and their reflexes on photosynthesis and redox metabolism in plants are little understood yet. We tested the hypothesis that heat shock negatively interacts with salt stress, affecting most intensely K+/Na+ homeostasis, stomatal closure, and CO2 assimilation, in comparison to PSII activity and oxidative stress in rice leaves. 31-day old rice plants were previously exposed to 0 and 100 mM NaCl for eight days at 27 °C and afterwards two groups were transferred to high temperature (42 °C, heat shock) for 10 hours (heat and heat + salt) whereas two other groups remained at 27 °C (control and single salt treatments). Heat-salinity interaction greatly stimulated Na+ accumulation in leaves causing intense decrease in K+/Na+ ratios, inducing significant osmotic and ionic alterations. Stomata were closed intensely causing drastic impairment in CO2 assimilation and decrease in water use efficiency. In contrast, the PSII activity was much lesser affected, corroborated by a low increase in the fraction of closed reaction centers of PSII and slight decrease in electron transport rates. Despite that unbalance in photosynthesis, combined stress partially favored oxidative protection as indicated by a reduction in the levels of H2O2 and lipid peroxidation associated with reduction in the contents of reduced forms of ascorbate and glutathione. These favorable antioxidant responses were accompanied by increases in the activities of ascorbate peroxidases, superoxide dismutases, glutathione peroxidases, and phenol peroxidases whereas catalases and glycolate oxidases decreased. These antioxidant responses were not enough to mitigate overall physiological damages caused by combined stress, as indicated by drastic increase in membrane damage and decrease in relative water content in leaves. Heat shock drastically aggravates the negative effects caused by salt stress on the photosynthetic efficiency, especially CO2 assimilation, despite the heat – salinity interaction has partially favored the antioxidant defense.

A novelmicronutrients and methyl jasmonate cocktail of elicitors via seed priming improves drought tolerance by mitigating oxidative stress in rice (Oryza sativaL.).

Drought is a major limiting factor for rice (Oryza sativa L.) production globally, and a cost-effective seed priming technique using bio-elicitors has been found to have stress mitigating effects. Till date, mostly phytohormones have been preferred as bio-elicitors, but the present study is a novel attempt to demonstrate the favorable role of micronutrients-phytohormone cocktail, i.e., iron (Fe), zinc (Zn), and methyl jasmonate (MJ) via seed priming method in mitigating the deleterious impacts of drought stress through physio-biochemical and molecular manifestations. The effect of cocktail/priming was studied on the relative water content, chlorophyll a/b and carotenoid contents, proline content, abscisic acid (ABA) content, and on the activities of ascorbate peroxidase (APX), superoxide dismutase (SOD), NADPH oxidase (Nox), and catalase (CAT). The expressions of drought-responsive genes OsZn-SOD, OsFe-SOD, and Nox1 were found to be modulated under drought stress in contrasting rice genotypes -N-22 (Nagina-22, drought-tolerant) and PS-5 (Pusa Sugandh-5, drought-sensitive). A progressive rise in carotenoids (10-19%), ABA (18-50%), proline (60-80%), activities of SOD (27-62%), APX (46-61%), CAT (50-80%), Nox (16-30%), and upregulated (0.9-1.6-fold) expressions of OsZn-SOD, OsFe-SOD, and Nox1 genes were found in the primed plants under drought condition. This cocktail would serve as a potential supplement in modern agricultural practices utilizing seed priming technique to mitigate drought stress-induced oxidative burst in food crops.

OsCPK12 phosphorylates OsCATA and OsCATC to regulate H2O2 homeostasis and improve oxidative stress tolerance in rice

Calcium-dependent protein kinases (CPKs), the best-characterized calcium sensors in plants, regulate many aspects of plant growth and development as well as plant adaptation to biotic and abiotic stresses. However, how CPKs regulate the antioxidant defense system remains largely unknown. We previously found that impaired function of OsCPK12 leads to oxidative stress in rice, with more H2O2, lower catalase (CAT) activity, and lower yield. Here, we explored the roles of OsCPK12 in oxidative stress tolerance in rice. Our results show that OsCPK12 interacts with and phosphorylates OsCATA and OsCATC at Ser11. Knockout of either OsCATA or OsCATC leads to an oxidative stress phenotype accompanied by higher accumulation of H2O2. Overexpression of the phosphomimetic proteins OsCATAS11D and OsCATCS11D in oscpk12-cr reduced the level of H2O2 accumulation. Moreover, OsCATAS11D and OsCATCS11D showed enhanced catalase activity in vivo and in vitro. OsCPK12-overexpressing plants exhibited higher CAT activity as well as higher tolerance to oxidative stress. Our findings demonstrate that OsCPK12 affects CAT enzyme activity by phosphorylating OsCATA and OsCATC at Ser11 to regulate H2O2 homeostasis, thereby mediating oxidative stress tolerance in rice.

Graphene oxide influences transfer of plasmid-mediated antibiotic resistance genes into plants

As an emerging contaminant, antibiotic resistance genes (ARGs) are raising concerns about its significant threat to public health. Meanwhile, graphene oxide (GO), which also has a potential ecological damage with increasingly entering the environment, has a great influence on the transfer of ARGs. However, little is known about the effects mechanisms of GO on the migration of antibiotic resistance genes (ARGs) from bacteria into plants. In this study, we investigated the influence of GO on the transfer of ARGs carried by RP4 plasmids from Bacillus subtilis into rice plants. Our results showed that the presence of GO at concentrations ranging from 0 to 400 mg L−1 significantly reduced the transfer of ARGs into rice roots by 13–71 %. Moreover, the migration of RP4 from the roots to aboveground parts was significantly impaired by GO. These effects may be attributed to several factors. First, higher GO concentrations led to low pH in the culture solution, resulting in a substantial decrease in the number of antibiotic-resistant bacteria. Second, GO induced oxidative stress in rice, as indicated by enhanced Evans blue dye staining, and elevated levels of malondialdehyde, nitric oxide, and phenylalanine ammonia-lyase activity. The oxidative stress negatively affected plant growth, as demonstrated by the reduced fresh weight and altered lignin content in the rice. Microscopic observations confirmed the entry of GO into root cells but not leaf mesophyll cells. Furthermore, potential recipients of RP4 plasmid strains in rice after co-cultivation experiments were identified, including Bacillus subtilis, Bacillus amyloliquefaciens, and Bacillus cereus. These findings clarify the influence of GO on ARGs in the bacteria–plant system and emphasize the need to consider its potential ecological risks.

Fluorescence probes evaluated the hydrogen peroxide level in rice roots under cadmium ion stress

Abiotic stress and oxidative stress are closely related to the health status of plants. Plants will produce oxidative stress under abiotic stress, induce mitochondrial dysfunction, cause programmed cell death, and decrease plant survival rate. It is well known that rice is an essential crop for humans, but its cadmium tolerance is poor. Therefore, it is crucial to determine whether cadmium stress causes oxidative stress in rice in order to guide rice cultivation. Hydrogen peroxide (H2O2), a highly reactive oxygen species (ROS), is one of the most critical signals in corps under oxidative stress. In this work, we adopted a near-infrared (NIR) H2O2 fluorescent probe YFE-1 and a cadmium ion (Cd2+) fluorescent probe SCP to observe the fluctuation of H2O2 in rice roots under Cd2+ co-incubation conditions. Due to the advantages of fast response (within 2 min), a large Stokes shift (181 nm), good selectivity, and a low detection limit (LOD:26.4 nM), YFE-1 achieved the visualization of H2O2 produced by Cd2+ stress in rice roots. This study provides a new idea for assessing the risk of oxidative stress of Cd2+ in rice roots. It is expected to guide the control of Cd2+ in the rice planting industry to improve rice yield.

Micro/nanoscale bone char alleviates cadmium toxicity and boosts rice growth via positively altering the rhizosphere and endophytic microbial community

This present study investigated pork bone-derived biochar as a promising amendment to reduce Cd accumulation and alleviate Cd-induced oxidative stress in rice. Micro/nanoscale bone char (MNBC) pyrolyzed at 400 °C and 600 °C was synthesized and characterized before use. The application rates for MNBCs were set at 5 and 25 g·kg−1 and the Cd exposure concentration was 15 mg·kg−1. MNBCs increased rice biomass by 15.3–26.0% as compared to the Cd-alone treatment. Both types of MNBCs decreased the bioavailable Cd content by 27.4–54.8%; additionally, the acid-soluble Cd fraction decreased by 10.0–12.3% relative to the Cd alone treatment. MNBC significantly reduced the cell wall Cd content by 50.4–80.2% relative to the Cd-alone treatment. TEM images confirm the toxicity of Cd to rice cells and that MNBCs alleviated Cd-induced damage to the chloroplast ultrastructure. Importantly, the addition of MNBCs decreased the abundance of heavy metal tolerant bacteria, Acidobacteria and Chloroflexi, by 29.6–41.1% in the rhizosphere but had less impact on the endophytic microbial community. Overall, our findings demonstrate the significant potential of MNBC as both a soil amendment for heavy metal-contaminated soil remediation and for crop nutrition in sustainable agriculture.

Supplementation with Ascophyllum nodosum extracts mitigates arsenic toxicity by modulating reactive oxygen species metabolism and reducing oxidative stress in rice

Ascophyllum nodosum extract (ANE) is considered as an effective source of biostimulants that have the potential of ameliorating the negative impact of different abiotic stresses in plants. Considering the growth-promoting ability and other regulatory roles of ANE, the present investigation was executed to evaluate the role of ANE in conferring arsenic (As) tolerance in rice (Oryza sativa L. cv. BRRI dhan89). Rice seedlings (35-d-old) were exposed to two doses of sodium arsenate (As1 − 50 mg As kg–1 soil; As2 − 100 mg As kg–1 soil) at 25 days after transplanting through irrigation, whereas only water was applied to the control. Foliar application of 0.1% ANE was also supplemented under control as well as As-stressed conditions at 7 days intervals for 5 times. Arsenic-induced oxidative stress was evident through a sharp increase in lipid peroxidation, hydrogen peroxide, methylglyoxal, and electrolyte leakage in the As-treated plants. As a consequence, plant growth and biomass, leaf relative water content, as well as yield attributes were reduced noticeably. On the other hand, ANE supplemented plants accumulated enhanced levels of ascorbate and glutathione, their redox balance, and the activities of antioxidant and glyoxalase enzymes viz. ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, glutathione reductase, catalase, glutathione peroxidase, and activities of glyoxalase I and glyoxalase II, respectively. Furthermore, relative water content, plant growth, yield attributes and yield were increased in the As-treated rice plants with ANE supplementation. The results reflected that foliar spray with ANE alleviated As-induced oxidative stress in rice plants by modulating the antioxidative defense and glyoxalase system.

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

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

​Antioxidant Responses of Arsenite-induced Oxidative Stress in Rice (Oryza sativa L.) and its Modulation by Eugenol (Extracted from Ocimum sanctum)

Background: Irrigation with arsenic-contaminated groundwater is leading to high arsenic-laden rice seeds and lower yields. In the present study, the effect of exogenous treatment of eugenol (extracted from Ocimum sanctum L. leaf) on hydroponically grown rice seedlings was examined by investigating the antioxidant system under arsenic stress. Methods: In the experiment 7 day old rice seedlings (IR-64) were exposed to 10,50,100 µM of arsenite separately and co-treatment with 10,50,100 µM eugenol in a hydroponic medium for 7 days. The activity of antioxidant enzymes such as superoxide dismutase, ascorbate peroxidase, glutathione peroxidase, catalase and lipid peroxidation (malondialdehyde) in root and shoot tissues were determined separately by standard protocol. Result: Under arsenic treatment oxidative stress was induced by overproduction of reactive oxygen species (ROS) and disruption of antioxidant defense system measured in terms of increased activity of antioxidant enzymes and lipid peroxidation (malondialdehyde) in root and shoot tissues separately. Eugenol-treated seedlings along with arsenic exposure substantially decreased the level of arsenic uptake in plants resulting in a substantial reduction in ROS overproduction and MDA content. SOD, CAT, GPX activities perform an influential role in arsenic stress acclimatization and eugenol treated seedlings with arsenic exposures indicated substantial changes in all variables evaluated as compared to arsenic treatment only. This study suggests that oxidative stress caused by arsenic was ameliorated by eugenol.

Beneficial effects of endophytic Pantoea ananatis with ability to promote rice growth under saline stress.

Soil salinization severely inhibits plant growth, leading to a low crop yield. The aim of the current study was to isolate endophytic bacteria with the ability to promote rice growth under saline conditions. We isolated eight salt-tolerant endophytic bacteria from rice roots. An isolated strain D1 was selected due to its ability to stimulate rice seed germination in the presence of NaCl, which was identified as Pantoea ananatis D1. It exhibited multiple plant growth-promoting traits including phosphate solubilization, production of indole-3-acetic acid, 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase and siderophore. Inoculation of P. ananatis D1 obviously enhanced the rice root and shoot growth under normal and saline conditions. It also significantly increased the contents of chlorophyll, total soluble protein, and proline in salt-stressed rice seedlings. Moreover P. ananatis D1 could ameliorate the oxidative stress in rice induced by NaCl and Na2 CO3 treatment. The malondialdehyde content and various antioxidant enzyme activities were decreased by P. ananatis D1 inoculation in salt-affected rice. In addition, P. ananatis D1 showed a positive potential for limiting the Na+ accumulation and enhancing the K+ uptake, leading to an increase of 1·2-1·7 fold in K+ /Na+ ratio under saline environment. Pantoea ananatis D1 has the ability to improve the salt tolerance of rice seedlings. The application of plant growth-promoting bacteria (PGPB) is an eco-friendly strategy to improve plant tolerance towards abiotic stresses. We demonstrated that P. ananatis D1 could be used as an effective halotolerant PGPB to enhance rice growth in different salt-affected soils.

Nitric Oxide Enhances Photosynthetic Nitrogen and Sulfur-Use Efficiency and Activity of Ascorbate-Glutathione Cycle to Reduce High Temperature Stress-Induced Oxidative Stress in Rice (Oryza sativa L.) Plants.

The effects of nitric oxide (NO) as 100 µM sodium nitroprusside (SNP, NO donor) on photosynthetic-nitrogen use efficiency (NUE), photosynthetic-sulfur use efficiency (SUE), photosynthesis, growth and agronomic traits of rice (Oryza sativa L.) cultivars, Taipie-309 (high photosynthetic-N and SUE) and Rasi (low photosynthetic-N and SUE) were investigated under high temperature stress (40 °C for 6 h). Plants exposed to high temperature stress caused significant reduction in photosynthetic activity, use efficiency of N and S, and increment in H2O2 and thiobarbituric acid reactive substance (TBARS) content. The drastic effects of high temperature stress were more pronounced in cultivar Rasi than Taipie-309. However, foliar spray of SNP decreased the high temperature induced H2O2 and TBARS content and increased accumulation of proline and activity of ascorbate–glutathione cycle that collectively improved tolerance to high temperature stress more effectively in Taipie-309. Exogenously applied SNP alleviated the high temperature induced decrease in photosynthesis through maintaining higher photosynthetic-NUE and photosynthetic-SUE, activity of ribulose 1,5 bisphosphate carboxylase/oxygenase (Rubisco), and synthesis of reduced glutathione (GSH). The use of 2-4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxy-3-oxide (cPTIO, NO scavenger) substantiated the study that in the absence of NO oxidative stress increased, while NO increased photosynthetic-NUE and photosynthetic-SUE, net photosynthesis and plant dry mass. Taken together, the present investigation reveals that NO increased heat stress tolerance and minimized high temperature stress adversaries more effectively in cultivar Taipie-309 than Rasi by enhancing photosynthetic-NUE and SUE and strengthening the antioxidant defense system.

Goethite-modified biochar ameliorates the growth of rice (Oryza sativa L.) plants by suppressing Cd and As-induced oxidative stress in Cd and As co-contaminated paddy soil

Co-contamination of soils with cadmium (Cd) and arsenic (As) in rice growing areas is a serious threat to environment and human health. Increase in soil Cd and As levels curtail the growth and development of rice plants by causing oxidative stress and reduction in photosynthetic activity. Therefore, it is necessary to formulate and evaluate different strategies for minimizing the Cd and As uptake in rice plant. We modified biochar (BC) with goethite and assessed the effects of goethite-modified biochar (GB) application on mitigating Cd and As stress in rice plant. Although BC supply to rice plants enhanced their performance in contaminated soil but application of different GB levels i.e.1.5% GB to the soil resulted in prominent improvements in physiological and biochemical attributes of rice plants grown in Cd and As co-contaminated paddy soil. It was observed that soil amendment with GB increased the plant growth, biomass, photosynthetic pigments, gas exchange attribute of rice plant and suppressed the oxidative stress in rice leaves and roots by increased antioxidant enzymes activities. Supplementing the soil with 1.5% GB incremented the iron plaque (Fe-plaque) formation and enhanced the Cd and As sequestration by Fe-plaque. Application of GB (1.5%) significantly improved the Fe content of Fe-plaque by 68.7%. Maximum Cd (1.57 mg kg−1) and As (0.85 mg kg−1) sequestration by Fe-plaque was observed with 1.5% GB treatment. Compared to the control, 1.5% GB treatment application prominently reduced the Cd content in the rice roots and shoots by 42.9%, and 56.7%, respectively and As content in the rice roots and shoots declined by 32.2%, 46.6%, respectively, compared to the control. These findings demonstrate that amending the soil with 1.5% GB can be a potential remediation strategy for checking Cd and As accumulation, reducing oxidative stress and increasing the growth of rice plant.

Role of exogenous signaling molecules in alleviating salt-induced oxidative stress in rice (Oryza sativa L.): a comparative study

Intensified salt stress is an acute hindrance to crop cultivation, whereas plant signaling molecules can efficiently prompt salinity tolerance. Therefore, this study was accomplished to explore the potential salinity stress-mitigating effect of different signaling molecules in rice. The rice (cv. BRRI dhan29) seeds were immersed in 20 mM KNO3, 0.15 mM H2O2, 0.8 mM AsA (ascorbic acid) and 10 mM CaCl2 solutions for 24 h. Eventually, primed seeds were exposed to 75 mM NaCl in Petri dishes during germination. Moreover, 14-day-old rice seedlings were pretreated with different agents, viz., KNO3, H2O2, AsA and CaCl2 (concentrations were same as previous), for 2 days. Primed and non-primed seedlings were grown for 4 days under 75 mM NaCl stress condition. The result revealed that salt stress caused reduced germination indices and pre-seedling and seedling growth inhibition and impaired photosynthetic capacity, whereas catalase (CAT), ascorbate peroxidase (APX) and peroxidase (POX) activities were decreased in salt-treated plants. However, application of the four signaling molecules promoted the germination indices and growth and resisted chlorosis. Pretreatment with CaCl2 and AsA was observed to be relatively more efficient in conferring salinity tolerance of rice as reflected from the significant enhanced germination and growth in the saline medium by increasing reactive oxygen species (ROS) scavenging capacity, both at germination and seedling stage. All the selected signaling molecules significantly detoxified excess ROS, i.e., H2O2 and $${\text{O}}_{2}^{ \cdot - }$$ and reduced lipid peroxidation by up-regulating the enzymes, CAT, APX and POX. Moreover, H2O2 and KNO3 pretreatment also mitigated salt-imposed oxidative stress and enhanced growth performance of rice seedlings. Overall, the study confirms that CaCl2 and AsA pretreatment were more effective than H2O2 and KNO3 priming to improve salt tolerance in rice.

Silicon-induced antioxidant defense and methylglyoxal detoxification works coordinately in alleviating nickel toxicity in Oryza sativa L.

Nickel (Ni), an essential nutrient of plant but very toxic to plant at supra-optimal concentration that causes inhibition of seed germination emergence and growth of plants as a consequence of physiological disorders. Hence, the present study investigates the possible mechanisms of Ni tolerance in rice seedlings by exogenous application of silicon (Si). Thirteen-day-old hydroponically grown rice (Oryza sativa L. cv. BRRI dhan54) were treated with Ni (NiSO4.7H2O, 0.25 and 0.5 mM) sole or in combination with 0.50 mM Na2SiO3 for a period of 3 days to investigate the effect of Si supply for revoking the Ni stress. Nickel toxicity gave rise to reactive oxygen species (ROS) and cytotoxic methylglyoxal (MG), accordingly, initiated oxidative stress in rice leaves, and accelerated peroxidation of lipids and consequent damage to membranes. Reduced growth, biomass accumulation, chlorophyll (chl) content, and water balance under Ni-stress were also found. However, free proline (Pro) content increased in Ni-exposed plants. In contrast, the Ni-stressed seedlings fed with supplemental Si reclaimed the seedlings from chlorosis, water retrenchment, growth inhibition, and oxidative stress. Silicon up-regulated most of the antioxidant defense components as well as glyoxalase systems, which helped to improve ROS scavenging and MG detoxification. Hence, these results suggest that the exogenous Si application can improve rice seedlings' tolerance to Ni-toxicity.

Protective Role of Mentha arvensis Aqueous Extract against Manganese Induced Toxicity by Reducing Mn Translocation and Promoting Antioxidative Defense in growing Indica Rice Seedlings

Mentha arvensis L. (Ma) leaf extract, a wide source of natural antioxidants is widely used to protect animal cells against oxidative stress. In the current study, we have studied the ameliorative effects of Ma leaf extract on Mn induced oxidative stress in rice (Oryza sativa L.) seedlings. Hydroponically grown rice seedlings treated with 1.5 mM MnCl2 showed a decline in vigour and contents of photosynthetic pigments, increased production of reactive oxygen species (O2˙‾, H2O2, and.OH), lipid peroxidation, protein thiol and carbonyl contents along with increased activity of antioxidative enzymes- superoxide dismutase (SOD), guaiacol peroxidase (GPX) and ascorbate peroxidase (APX). The activity of catalase (CAT), however, declined in the seedlings after prolonged Mn treatment of 8 days. Interestingly exogenous application of Ma leaf extract (638.4 mg ml-1) effectively restored the Mn-induced decline in seedling vigour, photosynthetic pigments, increased levels of H2O2, lipid peroxides and altered activities of antioxidative enzymes. The results indicate that exogenous application of Ma leaf extract significantly lowers the toxic effects of Mn in rice seedlings by modulating Mn translocation and reducing oxidative stress.

Residual impact of biochar on cadmium uptake by rice (Oryza sativa L.) grown in Cd-contaminated soil

Cadmium (Cd) is the family member of toxic heavy metals, and its accumulation in food crops has become a global environmental constraint. Biochar potentially minimizes the metal contents in plants, but limited work has been reported on its residual effect on subsequent crops. The residual effect of various biochar levels (0, 1.5, 3.0, and 5.0% w/w) on Cd accumulation in rice has been investigated in this study. Biochar treatments enhanced the rice growth, photosynthesis, and antioxidant enzymes, whereas diminished the Cd contents and oxidative stress in rice. Cadmium concentration in shoots decreased by 24.4, 36.6, and 57.5% in 1.5, 3.0, and 5.0% biochar treatments over the control. Biochar supply enhanced the soil pH and electrical conductivity, whereas diminished the soil bioavailable Cd. Overall, the results depicted a significant residual impact of rice straw biochar on rice growth attributes and Cd uptake. However, studies are still needed to explore the long-term sustainability of biochars prepared from different feedstocks on bioavailability of toxic metals in soils and uptake by food crops under field conditions.

Ascorbic acid toxicity is related to oxidative stress and enhanced by high light and knockdown of chloroplast ascorbate peroxidases in rice plants

Toxicity caused by high concentrations of ascorbic acid (AA) has been widely reported in animal cells but is scarcely described in plants. In this study, rice plants deficient (knockdown) in two chloroplast ascorbate peroxidases (APX7/8) and non-transformed (NT) were exposed to wide exogenous AA concentrations in the presence of low light and high light (HL). Reduced (ASC) and oxidized (DHA) ascorbate reached much higher concentrations in symplast compared to the apoplastic space, and high redox states were found in both cellular compartments. Exogenous AA concentrations above 30 mM caused strong cellular and oxidative damage indicated by decreased cell integrity and increased lipid peroxidation in leaves. These toxic effects were strongly enhanced by HL and, to a small extent, by deficiency of both chloroplastic proteins APX7/8. The combination of HL and high AA concentration induced a strong increase in H2O2, associated with decrease in the content of chlorophylls and carotenoids. High AA concentrations strongly induced stomatal closure and impairment in CO2 assimilation, in combination with decreased quantum efficiency of photosystem II (PSII) and PSI. We postulate that oxidative stress caused by AA toxicity in the presence of HL was induced by over-production of reactive oxygen species due to an imbalance between excess energy in the photosystems and low CO2 assimilation, which was related closely to strong decrease in stomatal conductance. In addition, high ASC levels might have acted as a pro-oxidant in the presence of high H2O2 concentrations, stimulating the Fenton reaction and contributing to the intensification of oxidative stress in rice leaves.