Addressing lanthanum toxicity in plants: Sources, uptake, accumulation, and mitigation strategies.

Lanthanum (La), the second most abundant rare earth element (REE) is emerging as an environmental issue, with the potential to impact ecosystems and human health. Major sources of soil contamination by La include agricultural, and industrial activities. Lanthanum is non-essential for plant growth but accumulates in various plant parts. The uptake of La by plants is intricately influenced by various factors such as soil pH, redox potential, cation exchange capacity, presence of organic acids and rhizosphere composition. These factors significantly impact the availability and absorption of La ions. Lanthanum impact on plants depends on soil characteristics, cultivated species, developmental stage, La concentration, treatment period, and growth conditions. Excessive La concentrations affect cell division, DNA structure, nutrient uptake, and photosynthesis and induce toxicity symptoms. Plants employ detoxification mechanisms like vacuolar sequestration, osmolyte synthesis, and antioxidant defense system. However, higher concentrations of La can overwhelm these defense mechanisms, leading to adverse effects on plant growth and development. Further, accumulation of La in plants increases the risk for human exposure. Strategies to mitigate La toxicity are, therefore, vital for ecosystem protection. The application of phytoremediation, supplementation, chelation, amendments, and biosorption techniques contributes to the mitigation of La toxicity. This review provides insights into La sources, uptake, toxicity, and alleviation strategies in plants. Identifying research gaps and discussing advancements aims to foster a holistic understanding and develop effective strategies for protecting plant health and ecosystem resilience against La contamination.

The efficient applications of native flora for phytorestoration of mine tailings: a pan-global survey.

Mine tailings are the discarded materials resulting from mining processes after minerals have been extracted. They consist of leftover mineral fragments, excavated land masses, and disrupted ecosystems. The uncontrolled handling or discharge of tailings from abandoned mine lands (AMLs) poses a threat to the surrounding environment. Numerous untreated mine tailings have been abandoned globally, necessitating immediate reclamation and restoration efforts. The limited feasibility of conventional reclamation methods, such as cost and acceptability, presents challenges in reclaiming tailings around AMLs. This study focuses on phytorestoration as a sustainable method for treating mine tailings. Phytorestoration utilizes existing native plants on the mine sites while applying advanced principles of environmental biotechnology. These approaches can remediate toxic elements and simultaneously improve soil quality. The current study provides a global overview of phytorestoration methods, emphasizing the specifics of mine tailings and the research on native plant species to enhance restoration ecosystem services.

Nanowonders in agriculture: Unveiling the potential of nanoparticles to boost crop resilience to salinity stress.

Soil salinization significantly affects crop production by reducing crop quality and decreasing yields. Climate change can intensify salinity-related challenges, making the task of achieving global food security more complex. To address the problem of elevated salinity stress in crops, nanoparticles (NPs) have emerged as a promising solution. NPs, characterized by their small size and extensive surface area, exhibit remarkable functionality and reactivity. Various types of NPs, including metal and metal oxide NPs, carbon-based NPs, polymer-based NPs, and modified NPs, have displayed potential for mitigating salinity stress in plants. However, the effectiveness of NPs application in alleviating plant stress is dependent upon multiple factors, such as NPs size, exposure duration, plant species, particle composition, and prevailing environmental conditions. Moreover, alterations to NPs surfaces through functionalization and coating also play a role in influencing plant tolerance to salinity stress. NPs can influence cellular processes by impacting signal transduction and gene expression. They counteract reactive oxygen species (ROS), regulate the water balance, enhance photosynthesis and nutrient uptake and promote plant growth and yield. The objective of this review is to discuss the positive impacts of diverse NPs on alleviating salinity stress within plants. The intricate mechanisms through which NPs accomplish this mitigation are also discussed. Furthermore, this review addresses existing research gaps, recent breakthroughs, and prospective avenues for utilizing NPs to combat salinity stress.

Mitigating cadmium accumulation and toxicity in plants: The promising role of nanoparticles.

Cadmium (Cd) is a highly toxic heavy metal that adversely affects humans, animals, and plants, even at low concentrations. It is widely distributed and has both natural and anthropogenic sources. Plants readily absorb and distribute Cd in different parts. It may subsequently enter the food chain posing a risk to human health as it is known to be carcinogenic. Cd has a long half-life, resulting in its persistence in plants and animals. Cd toxicity disrupts crucial physiological and biochemical processes in plants, including reactive oxygen species (ROS) homeostasis, enzyme activities, photosynthesis, and nutrient uptake, leading to stunted growth and reduced biomass. Although plants have developed defense mechanisms to mitigate these damages, they are often inadequate to combat high Cd concentrations, resulting in yield losses. Nanoparticles (NPs), typically smaller than 100 nm, possess unique properties such as a large surface area and small size, making them highly reactive compared to their larger counterparts. NPs from diverse sources have shown potential for various agricultural applications, including their use as fertilizers, pesticides, and stress alleviators. Recently, NPs have emerged as a promising strategy to mitigate heavy metal stress, including Cd toxicity. They offer advantages, such as efficient absorption by crop plants, the reduction of Cd uptake, and the enhancement of mineral nutrition, antioxidant defenses, photosynthetic parameters, anatomical structure, and agronomic traits in Cd-stressed plants. The complex interaction of NPs with calcium ions (Ca2+), intracellular ROS, nitric oxide (NO), and phytohormones likely plays a significant role in alleviating Cd stress. This review aims to explore the positive impacts of diverse NPs in reducing Cd accumulation and toxicity while investigating their underlying mechanisms of action. Additionally, it discusses research gaps, recent advancements, and future prospects of utilizing NPs to alleviate Cd-induced stress, ultimately promoting improved plant growth and yield.

Alleviation of chromium stress in plants using metal and metal oxide nanoparticles.

Chromium (Cr), one of the hazardous pollutants, exists predominantly as Cr(VI) and Cr(III) in the environment. Cr(VI) is more toxic than Cr(III) due to its high mobility and solubility. Elevated levels of Cr in agricultural soil due to various anthropogenic activities cause Cr accumulation in plants, resulting in a significant reduction in plant yield and quality due to Cr-induced physiological, biochemical and molecular alterations. It can infiltrate the food chain through crop plants and cause harmful effects in humans via biomagnification. Cr(VI) is linked to cancer in humans. Therefore, mitigation strategies are required to remediate Cr-polluted soils and limit its accumulation in plants for safe food production. Recent research on metal and metal oxide nanoparticles (NPs) has shown that they can effectively reduce Cr accumulation and phytotoxicity. The effects of these NPs are influenced by their type and dose, exposure method, plant species and experimental settings. In this review, we present an up-to-date compilation and comprehensive analysis of the existing literature regarding the process of uptake and distribution of Cr and impact and potential mechanisms of metal and metal oxide nanoparticles led mitigation of Cr-induced stress in plants. We have also discussed recent developments, existing research gaps and future research directions in the field of Cr stress mitigation by NPs in plants. Overall, this review can provide valuable insights in reducing Cr accumulation and toxicity using metal and metal oxide nanoparticles, thereby promoting safe and sustainable cultivation of food and phytostabilization of Cr-polluted soil.

Failure of methanol detoxification in pests confers broad spectrum insect resistance in PME overexpressing transgenic cotton.

Methanol is noxious to insect pests, but most plants do not make enough of it to shield themselves from encroaching insects. Methanol emission is known to increase in the instance of herbivory. In the current study, we showed that Aspergillus niger pectin methylesterase over-expression increases methanol emission and confers resistance to polyphagous insect pests on transgenic cotton plants by impeding the possible methanol detoxification pathways. Transgenic plants emitted ∼11 fold higher methanol displaying insect mortality of 96% and 93% in Helicoverpa armigera and Spodoptera litura, respectively. The larvae were unable to survive and finish their life cycle and the surviving larvae exhibited severe growth retardation. Insects try to detoxify methanol via catalase, carboxylesterase and cytochrome P450 monooxygenase enzymes, amongst which cytochrome P450 plays a major role in oxidizing methanol to formaldehyde and formaldehyde to formic acid, which is broken down into carbon dioxide and water. In our study, catalase and esterase enzymes were found to be upregulated, but cytochrome P450 monooxygenase levels were not much affected. Leaf disc assays and In-planta bioassays also showed 50-60% population reduction in the sap sucking pests, such as Bemisia tabaci and Phenacoccus solenopsis. These findings imply that elevated methanol emissions confer resistance in plants against chewing and sap-sucking pests by tampering the methanol detoxification pathways. Such mechanism will be useful in imparting expansive resistance against pests in plants.

Distinct defensive activity of phenolics and phenylpropanoid pathway genes in different cotton varieties toward chewing pests.

Identifying the maximum level of inherent defense against harmful insects in natural variation among wild lineages of crop plants may result in high yield tolerant varieties and reducing use of chemical insecticides. However, knowledge of natural cotton genotypes with high insect-resistance is still indistinguishable at the biochemical or molecular level. In the present study, different cultivated Gossypium hirsutum varieties were evaluated for their inherent insect-tolerance against two major cottons chewing pests. The insect bio-assay identified two tolerant and one susceptible cotton varieties. The study demonstrates difference in phenolic acids, proanthocyanidin and tannin accumulation in tolerant and susceptible varieties. The post-infestation of chewing pests increases transcript level of the phenylpropanoid pathway genes were detected in tolerant varieties as compared to the susceptible varieties. Altogether, chewing pest-tolerance level in cotton varieties is the cumulative effect of enhanced phenylpropanoid pathway genes expression and secondary metabolite leading to defense responses to conventional host plant.

Azadirachta indica and Ocimum sanctum leaf extracts alleviate arsenic toxicity by reducing arsenic uptake and improving antioxidant system in rice seedlings.

In the present study the potentials of aqueous extracts of the two plants, neem (Azadirachta indica) and Tulsi (Ocimum sanctum) were examined in alleviating arsenic toxicity in rice (Oryza sativa L.) plants grown in hydroponics. Seedlings of rice grown for 8 days in nutrient solution containing 50 µM sodium arsenite showed decline in growth, reduced biomass, altered membrane permeability and increased production of superoxide anion (O2 ·-), H2O2 and hydroxyl radicals (·OH). Increased lipid peroxidation marked by elevated TBARS (thiobarbituric acid reactive substances) level, increased protein carbonylation, alterated levels of ascorbate, glutathione and increased activities of enzymes SOD (superoxide dismutase), CAT (catalase), APX (ascorbate peroxidase) and GPX (glutathione peroxidase) were noted in the seedlings on As treatment. Exogenously added leaf aqueous extracts of Azadirachta indica (0.75 mg mL-1, w/v) and Ocimum sanctum (0.87 mg mL-1, w/v) in the growth medium considerably alleviated As toxicity effects in the seedlings, marked by reduced As uptake, restoration of membrane integrity, reduced production of ROS, lowering oxidative damage and restoring the levels of ascorbate, glutathione and activity levels of antioxidative enzymes. Arsenic uptake in the seedlings declined by 72.5% in roots and 72.8% in shoots, when A. indica extract was present in the As treatment medium whereas with O. sanctum extract, the uptake declined by 67.2% in roots and 70.01% in shoots. Results suggest that both A. indica and O. sanctum aqueous extracts have potentials to alleviate arsenic toxicity in rice plants and that A. indica can serve as better As toxicity alleviator compared to O. sanctum.

Comprehensive analysis of regulatory elements of the promoters of rice sulfate transporter gene family and functional characterization of OsSul1;1 promoter under different metal stress.

Adverse environmental conditions including heavy metal stress impose severe effects on the plant growth and development limiting productivity and yield. Studies demonstrated that changes in genome-wide expression modulate various biochemical processes and molecular components in response to heavy metal stress in plants. Some of the key components involved in such a regulation are the transcription initiation machinery, nucleotide sequence of promoters and presence of cis-acting elements. Therefore, identification of the putative cis-acting DNA sequences involved in gene regulation and functional characterization of promoters are important steps in understanding response of plants to heavy metal stress. In this study, comprehensive analysis of the proximal promoters of members of rice sulfate transporter gene family which is an essential component of stress response has been carried out. Analysis suggests presence of various common stress related cis-acting elements in the promoters of members of this gene family. In addition, transcriptional regulation of the arsenic-responsive high affinity sulfate transporter, OsSul1;1, has been studied through development of Arabidopsis transgenic lines expressing reporter gene encoding ß-glucuronidase under the control of OsSul1;1 promoter. Analysis of the transgenic lines suggests differential response of the OsSul1;1 promoter to various heavy metals as well as other abiotic stresses.

Omics and biotechnology of arsenic stress and detoxification in plants: current updates and prospective.

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.

Expression of a rice Lambda class of glutathione S-transferase, OsGSTL2, in Arabidopsis provides tolerance to heavy metal and other abiotic stresses.

Global industrial growth has contaminated the soil and water with many hazardous compounds, including heavy metals. These heavy metals are not only toxic to plants but also cause severe human health hazards when leach out into food chain. One of the approaches employed for the decontamination of environment includes identification and overexpression of genes involved in the detoxification mechanism of plants. Glutathione S-transferases (GSTs) are a superfamily of enzymes, principally known for their role in detoxification reactions. Different classes of GSTs have been used to develop plants with improved detoxification mechanism, but not much information is available for Lambda class of GSTs. Here, we studied expression of OsGSTLs in different rice genotypes under arsenic stress. The study suggests differential expression of these genes in arsenic sensitive and tolerant genotypes. Further, the role of one member of Lambda class OsGSTL2 was studied by expressing in heterologous system, Arabidopsis. Transgenic lines developed were analysed for their response to different abiotic stresses including heavy metals. Analysis suggests that OsGSTL2 provides tolerance for heavy metals and other abiotic stresses like cold, osmotic stress and salt. We conclude that OsGSTLs can be utilized for developing plant varieties tolerant to different abiotic stresses including heavy metals.

Inhibition of ribonuclease and protease activities in arsenic exposed rice seedlings: role of proline as enzyme protectant.

When seedlings of two rice (Oryza sativa L.) cvs. Malviya-36 and Pant-12 were raised under 25 and 50 microM As2O3 in the medium an increase in the level of RNA, proteins and proline accompanied with a decline in the level of free amino acid pool was observed under arsenic supplementation compared to controls. In situ As3+ treatment caused a marked inhibition in activities of ribonuclease (RNase, EC 3.1.27.1), protease and leucine aminopeptidase (LAP, EC 3.4.11.1) whereas the activity level of carboxypeptidase (EC 3.4.16.5) was enhanced. In vitro supply of As2O3 in the enzyme assay medium beyond 400 microM resulted in gradual inhibition of RNase and beyond 5 microM inhibition of LAP activities. Addition of 1M proline in the assay medium significantly restored the loss in RNase activity due to in vitro arsenic treatment or due to osmotic stress created by incorporation of polyethylene glycol (PEG). Isoform pattern of RNase extracted from As3+ -exposed seedlings showed a significant alteration compared to its pattern in unexposed seedlings. Results suggest that arsenic exposure impairs hydrolysis of RNA and proteins in rice seedlings due to inhibition of RNase and proteases activities and that proline accumulating under As3+ toxicity appears to serve as enzyme protectant.

Modulation of nitrate reductase activity in rice seedlings under aluminium toxicity and water stress: role of osmolytes as enzyme protectant.

Nitrate reductase (NR) activity in the presence of Mg2+ (NR act) representing the non-phosphorylated NR state and the activity in the presence of EDTA (NR max) representing maximum NR activity was measured in roots and shoots of 15 d grown aluminium and water stressed rice seedlings to examine changes in NR activation state due to these stresses. Seedlings subjected to a moderate water stress level of -0.5 MPa for 24 h or grown in presence of 80 microM Al3+showed decreased level of NR max but resulted in higher NR act and NR activation state. However, seedlings grown in presence of a higher level of 160 microM Al3+ showed a decline in NR act as well as NR max. With a higher water stress Level of -2.0MPa a marked decline in the levels of both NR act and NR max was observed, whereas NR activation state remained almost unaltered with severe water stress. NR activity appeared to be sensitive to H2O2, PEG-6000, NaCl and various metal salts. Incorporation of these components in the enzyme assay medium led to decreased affinity of enzyme towards its substrate with increase in Km and decrease in Vmax values. Addition of each of the osmolytes i.e. 1 mol/L proline, 1 mol/L glycine betaine or 1 mol/L sucrose in the enzyme assay medium caused a considerable protection to the enzyme against the damaging effects of stressful components. An enhanced level of proline and glycine betaine was observed in Al-stressed seedlings and sucrose in Al as well as water stressed seedlings. Results suggest that Al toxicity and water stress decrease total amount of functional NR in rice seedlings and the osmolytes proline, glycine betaine and sucrose appear to have a direct protective action on enzyme NR under stressful conditions

Purification and characterization of two isoforms of glucose 6-phosphate dehydrogenase (G6PDH) from Chlorella vulgaris C-27.

Two kinds of isoforms of glucose 6-phosphate dehydrogenase (G6PDH) were purified from cells of a freezing-tolerant strain, Chlorella vulgaris C-27, by sequential steps of chromatography on five kinds of columns, including a HiTrap Blue column which showed excellent separation of the isoforms from each other. The two isoforms (G6PDH1 and G6PDH2) were purified up to 109-fold and 197-fold with specific activity of 14.4 and 26.0 U/mg-protein, respectively. G6PDH1 showed an apparent Mr of 200,000 with a subunit Mr of about 58,000, whereas G6PDH2 showed an apparent Mr of 450,000 with a subunit Mr of about 52,000. The kinetic parameters were measured and several enzymatic features of the isoforms, such as effects of metal ions on the enzyme activity, were clarified, which showed that the two isoforms were different from each other in many respects. Among the effective ions, Cd2+ showed marked stimulating effects on both isoforms. G6PDH1 and G6PDH2 seem to be a cytosolic and a chloroplastic type, respectively, as judged by their sensitivity to DTT, and also from the results of sequence similarity searches using their N-terminal and internal amino acid sequences.