Silver nanoparticles in plant health: Physiological response to phytotoxicity and oxidative stress.

Silver nanoparticles (AgNPs) have gained significant attention in various fields due to their unique properties, but their release into the environment has raised concerns about their environmental and biological impacts. Silver nanoparticles can enter plants following their exposure to roots or via stomata following foliar exposure. Upon penetrating the plant cells, AgNPs interact with cellular components and alter physiological and biochemical processes. One of the key concerns associated with plant exposure to AgNPs is the potential of these materials to induce oxidative stress. Silver nanoparticles can also suppress plant growth and development by disrupting essential plant physiological processes, such as photosynthesis, nutrient uptake, water transport, and hormonal regulation. In crop plants, these disruptions may, in turn, affect the productivity and quality of the harvested components and therefore represent a potential threat to agricultural productivity and ecosystem stability. Understanding the phytotoxic effects of AgNPs is crucial for assessing their environmental implications and guiding the development of safe nanomaterials. By delving into the phytotoxic effects of AgNPs, this review contributes to the existing knowledge regarding their environmental risks and promotes the advancement of sustainable nanotechnological practices.

CmoPIP1-4 confers drought tolerance in pumpkin by altering hydrogen sulfide signaling.

Drought is a major limiting factor for the growth and development of pumpkins. Plasma membrane intrinsic proteins (PIPs) are major water channels that play a crucial role in the regulation of cellular water status and solute trafficking during drought conditions. CmoPIP1-4 is a plasma membrane-localized protein that is significantly upregulated in roots and leaves under drought-stress conditions. In this study, the overexpression of CmoPIP1-4 enhances drought resistance in yeast. In contrast, CRISPR-mediated CmoPIP1-4 knockout in pumpkin roots increased drought sensitivity. This increased drought sensitivity of CmoPIP1-4 knockout plants is associated with a decline in the levels of hydrogen sulfide (H2S) and abscisic acid (ABA), accompanied by an increase in water loss caused by greater levels of transpiration and stomatal conductance. In addition, the sensitivity of CmoPIP1-4 CRISPR plants is further aggravated by reduced antioxidative enzyme activity, decreased proline and sugar contents, and extensive root damage. Furthermore, expression profiles of genes such as CmoHSP70s, CmoNCED3, CmoNCED4, and others involved in metabolic activities were markedly reduced in CmoPIP1-4 CRISPR plants. Moreover, we also discovered an interaction between the drought-responsive gene CmoDCD and CmoPIP1-4, indicating their potential role in activating H2S-mediated signaling in pumpkin, which could confer drought tolerance. The findings of our study collectively demonstrate CmoPIP1-4 plays a crucial role in the regulation of H2S-mediated signaling, influencing stomatal density and aperture in pumpkin plants, and thereby enhancing their drought tolerance.

Decreased Photosynthetic Efficiency in Nicotiana tabacum L. under Transient Heat Stress.

Heat stress is an abiotic factor that affects the photosynthetic parameters of plants. In this study, we examined the photosynthetic mechanisms underlying the rapid response of tobacco plants to heat stress in a controlled environment. To evaluate transient heat stress conditions, changes in photochemical, carboxylative, and fluorescence efficiencies were measured using an infrared gas analyser (IRGA Licor 6800) coupled with chlorophyll a fluorescence measurements. Our findings indicated that significant disruptions in the photosynthetic machinery occurred at 45 °C for 6 h following transient heat treatment, as explained by 76.2% in the principal component analysis. The photosynthetic mechanism analysis revealed that the dark respiration rate (Rd and Rd*CO2) increased, indicating a reduced potential for carbon fixation during plant growth and development. When the light compensation point (LCP) increased as the light saturation point (LSP) decreased, this indicated potential damage to the photosystem membrane of the thylakoids. Other photosynthetic parameters, such as AMAX, VCMAX, JMAX, and ΦCO2, also decreased, compromising both photochemical and carboxylative efficiencies in the Calvin-Benson cycle. The energy dissipation mechanism, as indicated by the NPQ, qN, and thermal values, suggested that a photoprotective strategy may have been employed. However, the observed transitory damage was a result of disruption of the electron transport rate (ETR) between the PSII and PSI photosystems, which was initially caused by high temperatures. Our study highlights the impact of rapid temperature changes on plant physiology and the potential acclimatisation mechanisms under rapid heat stress. Future research should focus on exploring the adaptive mechanisms involved in distinguishing mutants to improve crop resilience against environmental stressors.

Predicting and optimizing reactive oxygen species metabolism in Punica granatum L. through machine learning: role of exogenous GABA on antioxidant enzyme activity under drought and salinity stress.

BACKGROUND: Drought and salinity stress have been proposed as the main environmental factors threatening food security, as they adversely affect crops' agricultural productivity. As a potential solution, the application of plant growth regulators to enhance drought and salinity tolerance has gained considerable attention. γ-aminobutyric acid (GABA) is a four-carbon non-protein amino acid that accumulates in plants as a response to stressful conditions. This study focused on a comparative assessment of several machine learning (ML) regression models, including radial basis function, generalized regression neural network (GRNN), random forest (RF), and support vector regression (SVR) to develop predictive models for assessing the effect of different concentrations of GABA (0, 10, 20, and 40 mM) on various physio-biochemical traits during periods of drought, salinity, and combined stress conditions. The physio-biochemical traits included antioxidant enzyme activities (superoxide dismutase, SOD; peroxidase, POD; catalase, CAT; and ascorbate peroxidase, APX), protein content, malondialdehyde (MDA) levels, and hydrogen peroxide (H2O2) levels. The non­dominated sorting genetic algorithm­II (NSGA­II) was employed for optimizing the superior prediction model. RESULTS: The GRNN model outperformed the other ML algorithms and was therefore selected for optimization by NSGA-II. The GRNN-NSGA-II model revealed that treatment with GABA at concentrations of 20.90 mM and 20.54 mM, under combined drought and salinity stress conditions at 20.86 and 20.72 days post-treatment, respectively, could result in the maximum values for protein content (by 0.80 and 0.69), APX activity (by 50.63 and 51.51), SOD activity (by 0.54 and 0.53), POD activity (by 1.53 and 1.72), CAT activity (by 4.42 and 5.66), as well as lower MDA levels (by 0.12 and 0.15) and H2O2 levels (by 0.44 and 0.55), respectively, in the 'Atabaki' and 'Rabab' cultivars. CONCLUSIONS: This study demonstrates that the GRNN-NSGA-II model, as an advanced ML algorithm with a strong predictive ability for outcomes in combined stressful environmental conditions, provides valuable insights into the significant factors influencing such multifactorial processes.

Unlocking the potential of co-application of steel slag and biochar in mitigation of arsenic-induced oxidative stress by modulating antioxidant and glyoxalase system in Abelmoschus esculentus L.

This study investigates our hypothesis that how effect of arsenic stress on okra (Abelmoschus esculentus L.) can be alleviated through the use of waste materials such as steel slag (SS) and corncob biochar (BC). Different growth variables, biochemical parameters, oxidative stress markers, enzymatic and non-enzymatic antioxidants and glyoxylase enzyme activities were assessed. When okra was exposed to As, there was a noticeable decrease in seedling length, biomass, relative water content, various biochemical attributes, however, electrolyte leakage and lipid peroxidation in okra were enhanced. The supplementation of SS and BC-either individually or in combination-improved the growth parameters and reduced oxidative stress markers. Application of SS and BC also lowered As accumulation in roots and shoots of okra mitigating adverse effects of As exposure. Additionally, the activities of antioxidant and glyoxalase enzyme increased when SS and BC were present, concurrently reducing methylglyoxal content. Arsenic-induced stress led to oxidative damage, an enhancement in both enzymatic and non-enzymatic antioxidants, induced the synthesis of thiol and phytochelatins in roots and shoots. These may play a vital function in alleviating oxidative stress induced by As. Superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase activities were significantly enhanced in As-treated plants. These enhancement were further amplified when SS and BC were amended to As-treated okra. Therefore, synergistic application of SS and BC effectively protects okra against oxidative stress induced by As by increasing both antioxidant defense and glyoxalase systems. Both SS, an industrial byproduct, and BC, generated from agricultural waste, are cost-effective, environmentally friendly, safe, and non-toxic materials which can be used for crop production in As contaminated soil.

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

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

Modulation of plant photosynthetic processes during metal and metalloid stress, and strategies for manipulating photosynthesis-related traits.

Metals constitute vital elements for plant metabolism and survival, acting as essential co-factors in cellular processes which are indispensable for plant growth and survival. Excess or deficient provision of metal/metalloids puts plant's life and survival at risk, thus considered a potent stress for plants. Chloroplasts as an organelle with a high metal demand form a pivotal site within the metal homeostasis network. Therefore, the metal-mediated electron transport chain (ETC) in chloroplasts is a primary target site of metal/metalloid-induced stresses. Both excess and deficient availability of metal/metalloids threatens plant's photosynthesis in several ways. Energy demands from the photosynthetic carbon reactions should be in balance with energy output of ETC. Malfunctioning of ETC components as a result of metal/metalloid stress initiates photoinhiition. A feedback inhibition from carbon fixation process also impedes the ETC. Metal stress impairs antioxidant enzyme activity, pigment biosynthesis, and stomatal function. However, genetic manipulations, nutrient management, keeping photostasis, and application of phytohormones are among strategies for coping with metal stress. Consequently, a comprehensive understanding of the underlying mechanisms of metal/metalloid stress, as well as the exploration of potential strategies to mitigate its impact on plants are imperative. This review offers a mechanistic insight into the disruption of photosynthesis regulation by metal/metalloids and highlights adaptive approaches to ameliorate their effects on plants. Focus was made on photostasis, nutrient interactions, phytohormones, and genetic interventions for mitigating metal/metalloid stresses.

2,4-D mediated moderation of aluminum tolerance in Salvinia molesta D. Mitch. with regards to bioexclusion and related physiological and metabolic changes.

We examined the efficacy of 2,4-dichlorophenoxy acetic acid (2,4-D; 500 µM) in enhancing the potential of Salvinia species for tolerance to aluminum (Al) toxicity (240 and 480 µM, seven days). Salvinia showed better efficacy in removal of toxicity of Al by sorption mechanism with changes of bond energy shifting on cell wall residues and surface structure. Plants recorded tolerance to Al concentration (480 µM) when pretreated with 2,4-D through adjustment of relative water content, proline content, osmotic potential, and improved the pigment fluorescence for energy utilization under Al stress. Photosynthetic activities with regards to NADP-malic enzyme and malic dehydrogenase and sugar metabolism with wall and cytosolic invertase activities were strongly correlated with compatible solutes. A less membrane peroxidation and protein carbonylation had reduced ionic loss over the membrane that was studied with reduced electrolyte leakage with 2,4-D pretreated plants. Membrane stabilization was also recorded with higher ratio of K+ to Na+, thereby suggesting roles of 2,4-D in ionic balance. Better sustenance of enzymatic antioxidation with peroxidase and glutathione metabolism reduced reactive oxygen species accumulation and save the plant for oxidative damages. Moreover, gene polymorphism for antioxidant, induced by 2,4-D varied through Al concentrations would suggest an improved biomarker for tolerance. Collectively, analysis and discussion of plant's responses assumed that auxin herbicide could be a potential phytoprotectant for Salvinia as well as improving the stability to Al toxicity and its bioremediation efficacy.

In previous reports, aquatic weeds, particularly, from pteridophytic flora have been exercised, however, in less frequent. Aluminum (Al) toxicity, being a major problem, specifically with respect to cultivated crops like rice and vegetables, is a serious issue in alkaline soil. In context to growth of Salvinia in the areas of low lands where few important crops like rice are frequently cultivated. Therefore, Al toxicity with regards to rice cultivation in low land conditions, which is habitat for Salvinia, could be interesting. Thus, decontamination of low land for salinity with aquatic environment can be remediated with biological materials where Salvinia would be a choice. This would be something new in studies for the aquatic weeds over the existing database. Moreover, 2,4-dichlorophenoxy acetic acid (2,4-D) being a common herbicide in agricultural field that becomes more problematic with metal toxicity is another focus for physiological responses with Salvinia. The adoption and sustainability of Salvinia against 2,4-D may highlight insights for physiological activities would be the biomarker for herbicide toxicity.

Plant Responses and Tolerance to Salt Stress: Physiological and Molecular Interventions 2.0.

Environmental problems are pervasive and significantly impact a variety of plant species, which are affected by two broad types of conditions: abiotic and biotic stress [...].

Exogenous Allantoin Confers Rapeseed (Brassica campestris) Tolerance to Simulated Drought by Improving Antioxidant Metabolism and Physiology.

Allantoin is an emerging plant metabolite, but its role in conferring drought-induced oxidative stress is still elusive. Therefore, an experiment was devised to explore the role of allantoin (0.5 and 1.0 mM; foliar spray) in rapeseed (Brassica campestris cv. BARI Sarisha-17) under drought. Seedlings at fifteen days of age were subjected to drought, maintaining soil moisture levels at 50% and 25% field capacities, while well-irrigated plants served as the control group. Drought-stressed plants exhibited increased levels of lipid peroxidation and hydrogen peroxide, electrolyte leakage, and impaired glyoxalase systems. Thus, the growth, biomass, and yield attributes of rapeseed were significantly impaired under drought. However, the allantoin-supplemented plants showed a notable increase in their contents of ascorbate and glutathione and decreased dehydroascorbate and glutathione disulfide contents under drought. Moreover, the activity of antioxidant enzymes such as ascorbate peroxidase, dehydroascorbate reductase, glutathione reductase, glutathione peroxidase, and catalase were accelerated with the allantoin spray and the glyoxalase system was also enhanced under drought. Moreover, the improvement in water balance with reduction in proline and potassium ion contents was also observed when allantoin was applied to the plants. Overall, the beneficial effects of allantoin supplementation resulted in the improved plant growth, biomass, and yield of rapeseed under drought conditions. These findings suggest that allantoin acts as an efficient metabolite in mitigating the oxidative stress caused by reactive oxygen species by enhancing antioxidant defense mechanisms and the glyoxalase system.

Abscisic acid priming confers salt tolerance in maize seedlings by modulating osmotic adjustment, bond energies, ROS homeostasis, and organic acid metabolism.

This study aimed at investigating the influence of exogenous abscisic acid (ABA) on salt homeostasis under 100 mM NaCl stress in maize (Zea mays L. cv. Kaveri 50) through 3 and 5 days of exposure. The ratio of Na+ to K+, hydrogen peroxide (H2O2) and superoxide (O2•‒) accumulation, electrolyte leakage were the major determinants for salt sensitivity. Pretreatment with ABA [ABA (+)] had altered the salt sensitivity of plants maximally through 5 days of treatment. Plants controlled well for endogenous ABA level (92% increase) and bond energy minimization of cell wall residues to support salt tolerance proportionately to ABA (+). Salt stress was mitigated through maintenance of relative water content (RWC) (16%), glycine betaine (GB) (26%), proline (28%) and proline biosynthesis enzyme (ΔP5CS) (26%) under the application of ABA (+). Minimization of lipid peroxides (6% decrease), carbonyl content (9% decrease), acid, alkaline phosphatase activities were more tolerated under 100 mM salinity at 5 days duration. Malate metabolism for salt tolerance was dependent on the activity of the malic enzyme, malate dehydrogenase through transcript abundance in real-time manner as a function of ABA (+). Establishment of oxidative stress through days under salinity recorded by NADPH-oxidase activity (39% increase) following ROS generation as detected in tissue specific level. The ABA (+) significantly altered redox homeostasis through ratio of AsA to DHA (21% increase), GSH to GSSG (12% increase) by dehydroascorbate reductase and glutathione reductase respectively, and other enzymes like guaiacol peroxidase, catalase, glutathione reductase activities. The ABA in priming was substantially explained in stress metabolism as biomarker for salinity stress with reference to maize.

Biochemical Compounds, Antioxidant Capacity, Leaf Color Profile and Yield of Basil (Ocimum sp.) Microgreens in Floating System.

Basil is a great source of phytochemicals such as polyphenols, vitamin C, anthocyanin, and flavonoids. In this work, the biochemical compounds, antioxidant capacity, leaf color profile, and yield of 21 cultivars and genotypes of basil microgreen were investigated. Results showed that the highest antioxidant potential composite index (APCI) was measured in Persian Ablagh genotype (70.30). Twenty-one basil genotypes were classified into four clusters, including cluster 1 (lowest antioxidant capacity and total phenolic compounds), cluster 2 (lowest anthocyanin, vitamin C and APCI index), cluster 3 (highest vitamin C, total phenolic compounds, antioxidant capacity and APCI index), and cluster 4 (highest levels of anthocyanin). The principal components analysis (PCA) of basil genotypes showed diversity in terms of phytochemical components, and F1, F2, F3, and F4 explained the variation at the rate of 78.12%. The average annual temperature of the origin of basil seeds plays an important role in the synthesis of antioxidant content. Most of the seeds with moderate origin had a higher APCI index. The Persian Ablagh genotype, Violeto, and Kapoor cultivars can be recommended, according to their APCI index and yield. These cultivars can be used individually or in different ratios to produce different biochemical substances with different concentrations for various purposes.

Potential of Halophytes as Sustainable Fodder Production by Using Saline Resources: A Review of Current Knowledge and Future Directions.

Good quality water and arable land are required for both domestic and agricultural uses. Increasing population leads to urbanization and industrialization increasing the need to share these resources and creating threats to the food supply. Higher meat consumption requires mitigation strategies to protect food and mitigate economic crises, especially in developing nations. The production of food crops for energy purposes and lower yield due to climate change increase food prices as well as have a negative impact on the economy. Thus, an alternative food source is required featuring high forage components to reduce grazing periods and to prevent rangeland degradation. Halophytes can tolerate high salinity and can be easily grown for fodder in coastal areas where fodder is a problem. Varied climate conditions offer opportunities to grow suitable halophytes for specific purposes. One important feature is their use as fodder. To reduce food shortages, saline areas could be used to grow nutritive and productive halophytic forage. Wild plants have undesirable metabolites produced in harsh conditions which may be harmful for ruminant health. Halophytes have moderate amounts of these metabolites which are nontoxic. Halophytes can be grown without intruding on agricultural lands and freshwater resources and could promote livestock production which may improve the socio-economic conditions of poor farmers in a sustainable and ecofriendly manner.

Regulation of NADP-Malic Enzyme Activity in Maize (Zea mays L.) under Salinity with Reference to Light and Darkness.

We revealed the functional characterization of C4-NADP-malic enzyme (NADP-ME), extracted and partially purified from maize (Zea mays L. cv. Kaveri 50). The leaf discs were previously activated under 1000-1200 µE m-2 s-1, incubated in bicarbonate (2.0 mM) solution, and subjected to salt stress (100 mM NaCl). Initially, salt stress was evident from the accumulations of proline, chlorophyll content, carbohydrate profile, and Hill activity influencing the C4 enzyme. Primarily, in illuminated tissues, the activity of the enzyme recorded a reduced trend through salinity irrespective of light and darkness compared to the control. On illumination, the kinetic parameters such as Vmax of the enzyme increased by 1.36-fold compared to in the dark under salinity whereas Km was decreased by 20% under the same condition. The extent of light induction was proportionate to limiting (0.01 mM) and saturated (4.0 mM) malate concentrations for enzyme activity. Moreover, the catalytic properties of the enzyme were also tested on concomitant responses to activator (citrate and succinate) and inhibitor (oxalate and pyruvate) residues. The sensitivity to light and dark effects was also tested for reducing agents such as dithiothreitol, suggesting the effect of the changes in redox on the regulatory properties of the enzyme. The ratio of enzyme activity under light and darkness in the presence or absence of a reducing agent was concomitantly increased with varying malate concentrations. At the molecular level, protein polymorphism of the enzyme represented minor variations in band intensities, however, not in numbers through salinity subjected to light and darkness. Therefore, salinity-induced changes in the decarboxylation reaction, evident by NADP-ME activity, may be based on the redox property of regulatory sites and sensitivity to light and darkness.

Primary plant nutrients modulate the reactive oxygen species metabolism and mitigate the impact of cold stress in overseeded perennial ryegrass.

Overseeded perennial ryegrass (Lolium perenne L.) turf on dormant bermudagrass (Cynodon dactylon Pers. L) in transitional climatic zones (TCZ) experience a severe reduction in its growth due to cold stress. Primary plant nutrients play an important role in the cold stress tolerance of plants. To better understand the cold stress tolerance of overseeded perennial ryegrass under TCZ, a three-factor and five-level central composite rotatable design (CCRD) with a regression model was used to study the interactive effects of nitrogen (N), phosphorus (P), and potassium (K) fertilization on lipid peroxidation, electrolyte leakage, reactive oxygen species (ROS) production, and their detoxification by the photosynthetic pigments, enzymatic and non-enzymatic antioxidants. The study demonstrated substantial effects of N, P, and K fertilization on ROS production and their detoxification through enzymatic and non-enzymatic pathways in overseeded perennial ryegrass under cold stress. Our results demonstrated that the cold stress significantly enhanced malondialdehyde, electrolyte leakage, and hydrogen peroxide contents, while simultaneously decreasing ROS-scavenging enzymes, antioxidants, and photosynthetic pigments in overseeded perennial ryegrass. However, N, P, and K application mitigated cold stress-provoked adversities by enhancing soluble protein, superoxide dismutase, peroxide dismutase, catalase, and proline contents as compared to the control conditions. Moreover, N, P, and, K application enhanced chlorophyll a, chlorophyll b, total chlorophyll, and carotenoids in overseeded perennial ryegrass under cold stress as compared to the control treatments. Collectively, this 2-years study indicated that N, P, and K fertilization mitigated cold stress by activating enzymatic and non-enzymatic antioxidants defense systems, thereby concluding that efficient nutrient management is the key to enhanced cold stress tolerance of overseeded perennial ryegrass in a transitional climate. These findings revealed that turfgrass management will not only rely on breeding new varieties but also on the development of nutrient management strategies for coping cold stress.

Insight into the biochemical and physiological mechanisms of nanoparticles-induced arsenic tolerance in bamboo.

Introduction: Arsenic (As) contamination in soil, sediments, and water poses a significant threat to the growth of bamboo plants. However, nanoparticles with high metal absorbance capacity can play a key role in the reduction of heavy metals toxicity in plants as well as maintaining their growth under toxicity. Methods: Hence, an in vitro experiment was conducted to determine the influence of three types of nanoparticles: 150 µM silicon nanoparticles (SiO2 NPs), 150 µM titanium nanoparticles (TiO2 NPs), and 150 µM zinc oxide nanoparticles (ZnO NPs) on As (150 µM and 250 µM) tolerance enhancement of a one-year-old bamboo species (Pleioblastus pygmaeus). Results and discussion: The results showed that while As at 150 µM and 250 µM significantly disrupted the plant growth by excessive generation of reactive oxygen species (ROS) components, and inducing cell membrane peroxidation, the addition of NPs increased both enzymatic and non-enzymatic antioxidant activities, upregulated glyoxalase defense system, and improved gas exchange parameters and photosynthetic pigments content, leading to the enhanced plant shoot and root dry weight. These were achieved by lowering levels of ROS, electrolyte leakage (EL), malondialdehyde (MDA), hydrogen peroxide (H2O2) and the superoxide radical ( O 2 • - ), as well as decreasing As accumulation in the plant organs. Thus, it might be concluded that ZnO NPs, SiO2NPs, and TiO2NPS alone or in combination can significantly increase the bamboo plant tolerance to As toxicity via key mechanisms, including induction of various antioxidants and glyoxalase defense systems, scavenging of ROS and methylglyoxal (MG), increasing phytochelatins production, reduction of As accumulation and translocation, and improving photosynthetic pigments under As toxicity. Additionally, the results showed that the combined application of 150 µM ZnO NPs, SiO2 NPs, and TiO2 NPs had the greatest effect on enhancing the plant tolerance to As at 150 µM and 250 µM.

Silencing of PpNRAMP5 improves manganese toxicity tolerance in peach (Prunus persica) seedlings.

The natural resistance-associated macrophage protein (NRAMP) gene family assists in the transport of metal ions in plants. However, the role and underlying physiological mechanism of NRAMP genes under heavy metal toxicity in perennial trees remain to be elucidated. In Prunus persica, five NRAMP family genes were identified and named according to their predicted phylogenetic relationships. The expression profiling analysis indicated that PpNRAMPs were significantly induced by excess manganese (Mn), iron, zinc, and cadmium treatments, suggesting their potential role in heavy metal uptake and transportation. Notably, the expression of PpNRAMP5 was tremendously increased under Mn toxicity stress. Heterologous expression of PpNRAMP5 in yeast cells also confirmed Mn transport. Suppression of PpNRAMP5 through virus-induced gene silencing enhanced Mn tolerance, which was compromised when PpNRAMP5 was overexpressed in peach. The silencing of PpNRAMP5 mitigated Mn toxicity by dramatically reducing Mn contents in roots, and effectively reduced the chlorophyll degradation and improved the photosynthetic apparatus under Mn toxicity stress. Therefore, PpNRAMP5-silenced plants were less damaged by oxidative stress, as signified by lowered H2O2 contents and O2•- staining intensity, also altered the reactive oxygen species (ROS) homeostasis by activating enzymatic antioxidants. Consistently, these physiological changes showed an opposite trend in the PpNRAMP5-overexpressed peach plants. Altogether, our findings suggest that downregulation of PpNRAMP5 markedly reduces the uptake and transportation of Mn, thus activating enzymatic antioxidants to strengthen ROS scavenging capacity and photosynthesis activity, thereby mitigating Mn toxicity in peach plants.

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

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

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.