Glutathione: A key player in metal chelation, nutrient homeostasis, cell cycle regulation and the DNA damage response in cadmium-exposed Arabidopsis thaliana

Peptides Used for Heavy Metal Remediation: A Promising Approach

In recent years, heavy metal pollution has become increasingly prominent, severely damaging ecosystems and biodiversity, and posing a serious threat to human health. However, the results of current methods for heavy metal restoration are not satisfactory, so it is urgent to find a new and effective method. Peptides are the units that make up proteins, with small molecular weights and strong biological activities. They can effectively repair proteins by forming complexes, reducing heavy metal ions, activating the plant's antioxidant defense system, and promoting the growth and metabolism of microorganisms. Peptides show great potential for the remediation of heavy metal contamination due to their special structure and properties. This paper reviews the research progress in recent years on the use of peptides to remediate heavy metal pollution, describes the mechanisms and applications of remediation, and provides references for the remediation of heavy metal pollution.

Role of glutathione S-transferases in the mode of action of herbicides that inhibit amino acid synthesis in Amaranthus palmeri

Acetolactate synthase inhibitors (ALS inhibitors) and glyphosate are two classes of herbicides that act by inhibiting an enzyme in the biosynthetic pathway of branched-chain or aromatic amino acids, respectively. Besides amino acid synthesis inhibition, both herbicides trigger similar physiological effects in plants. The main aim of this study was to evaluate the role of glutathione metabolism, with special emphasis on glutathione S-transferases (GSTs), in the mode of action of glyphosate and ALS inhibitors in Amaranthus palmeri. For that purpose, plants belonging to a glyphosate-sensitive (GLS) and a glyphosate-resistant (GLR) population were treated with different doses of glyphosate, and plants belonging to an ALS-inhibitor sensitive (AIS) and an ALS-inhibitor resistant (AIR) population were treated with different doses of the ALS inhibitor nicosulfuron. Glutathione-related contents, GST activity, and related gene expressions (glutamate-cysteine ligase, glutathione reductase, Phi GST and Tau GST) were analysed in leaves. According to the results of the analytical determinations, there were virtually no basal differences between GLS and GLR plants or between AIS and AIR plants. Glutathione synthesis and turnover did not follow a clear pattern in response to herbicides, but GST activity and gene expression (especially Phi GSTs) increased with both herbicides in treated sensitive plants, possibly related to the rocketing H2O2 accumulation. As GSTs offered the clearest results, these were further investigated with a multiple resistant (MR) population, compressing target-site resistance to both glyphosate and the ALS inhibitor pyrithiobac. As in single-resistant plants, measured parameters in the MR population were unaffected by herbicides, meaning that the increase in GST activity and expression occurs due to herbicide interactions with the target enzymes.

Comparing cadmium-induced effects on the regulation of the DNA damage response and cell cycle progression between entire rosettes and individual leaves of Arabidopsis thaliana

Cadmium (Cd) activates the DNA damage response (DDR) and inhibits the cell cycle in Arabidopsis thaliana through the transcription factor SUPPRESSOR OF GAMMA RESPONSE 1. The aim of this study was to investigate which individual leaf best reflects the Cd-induced effects on the regulation of the DDR and cell cycle progression in rosettes, enabling a more profound interpretation of the rosette data since detailed information, provided by the individual leaf responses, is lost when studying the whole rosette. Wild-type A. thaliana plants were cultivated in hydroponics and exposed to different Cd concentrations. Studied individual leaves were leaf 1 and 2, which emerged before Cd exposure, and leaf 3, which emerged upon Cd exposure. The DDR and cell cycle regulation were studied in rosettes as well as individual leaves after several days of Cd exposure. Varying concentration-dependent response patterns were observed between the entire rosette and individual leaves. Gene expression of selected DDR and cell cycle regulators showed higher similarity in their response between the rosette and the individual leaf emerged during Cd exposure than between both individual leaves. The same pattern was observed for plant growth and cell cycle-related parameters. We conclude that Cd-induced effects on the regulation of the DDR and cell cycle progression in the leaf that emerged during Cd exposure, resemble those observed in the rosette the most, which contributes to the interpretation of the rosette data in the framework of plant development and after exposure to Cd.

B2 O3 nanoparticles alleviate salt stress in maize leaf growth zones by enhancing photosynthesis and maintaining mineral and redox status

Salt stress induces significant loss in crop yield worldwide. Although the growth-stimulating effects of micronutrient nanoparticles (NPs) application under salinity have been studied, the molecular and biochemical mechanisms underlying these effects are poorly understood. The large size of maize leaf growth zones provides an ideal model system to sample and investigate the molecular and physiological bases of growth at subzonal resolution. Using kinematic analysis, our study indicated that salinity at 150 mM inhibited maize leaf growth by decreasing cell division and expansion in the meristem and elongation zones. Consistently, salinity downregulated cell cycle gene expression (wee1, mcm4, and cyclin-B2-4). B2 O3 NP (BNP) mitigated the stress-induced growth inhibition by reducing the decrease in cell division and expansion. BNP also enhanced the photosynthesis-related parameters. Simultaneously, chlorophyll, phosphoenolpyruvate carboxylase and ribulose-1,5-bisphosphate carboxylase/oxygenase were stimulated in the mature zone. Concomitant with growth stimulation by BNP, mineral homeostasis, particularly for B and Ca, was monitored. BNP reduced oxidative stress (e.g., lessened H2 O2 generation along the leaf zones and reduced lipid peroxidation in the mature zone) induced by salinity. This resulted from better maintenance of the redox status, that is, increased the glutathione-ascorbate cycle in the meristem and elongation zones, and flavonoids and tocopherol levels in the mature zone. Our study has important implications for assessing the salinity stress impact mitigated by BNP on maize growth, providing a basis to improve the resilience of crop species under salinity stress conditions.

Heavy Metals, Their Phytotoxicity, and the Role of Phenolic Antioxidants in Plant Stress Responses with Focus on Cadmium: Review

The current state of heavy metal (HM) environmental pollution problems was considered in the review: the effects of HMs on the vital activity of plants and the functioning of their antioxidant system, including phenolic antioxidants. The latter performs an important function in the distribution and binding of metals, as well as HM detoxification in the plant organism. Much attention was focused on cadmium (Cd) ions as one of the most toxic elements for plants. The data on the accumulation of HMs, including Cd in the soil, the entry into plants, and the effect on their various physiological and biochemical processes (photosynthesis, respiration, transpiration, and water regime) were analyzed. Some aspects of HMs, including Cd, inactivation in plant tissues, and cell compartments, are considered, as well as the functioning of various metabolic pathways at the stage of the stress reaction of plant cells under the action of pollutants. The data on the effect of HMs on the antioxidant system of plants, the accumulation of low molecular weight phenolic bioantioxidants, and their role as ligand inactivators were summarized. The issues of polyphenol biosynthesis regulation under cadmium stress were considered. Understanding the physiological and biochemical role of low molecular antioxidants of phenolic nature under metal-induced stress is important in assessing the effect/aftereffect of Cd on various plant objects-the producers of these secondary metabolites are widely used for the health saving of the world's population. This review reflects the latest achievements in the field of studying the influence of HMs, including Cd, on various physiological and biochemical processes of the plant organism and enriches our knowledge about the multifunctional role of polyphenols, as one of the most common secondary metabolites, in the formation of plant resistance and adaptation.

Manganese and copper additions differently reduced cadmium uptake and accumulation in dwarf Polish wheat (Triticum polonicum L.)

This study investigated the effects of manganese (Mn) and copper (Cu) on dwarf Polish wheat under cadmium (Cd) stress by evaluating plant growth, Cd uptake, translocation, accumulation, subcellular distribution, and chemical forms, and the expression of genes participating in cell wall synthesis, metal chelation, and metal transport. Compared with the control, Mn deficiency and Cu deficiency increased Cd uptake and accumulation in roots, and Cd levels in root cell wall and soluble fractions, but inhibited Cd translocation to shoots. Mn addition reduced Cd uptake and accumulation in roots, and Cd level in root soluble fraction. Cu addition did not affect Cd uptake and accumulation in roots, while it caused a decrease and an increase of Cd levels in root cell wall and soluble fractions, respectively. The main Cd chemical forms (water-soluble Cd, pectates and protein integrated Cd, and undissolved Cd phosphate) in roots were differently changed. Furthermore, all treatments distinctly regulated several core genes that control the main component of root cell walls. Several Cd absorber (COPT, HIPP, NRAMP, and IRT) and exporter genes (ABCB, ABCG, ZIP, CAX, OPT, and YSL) were differently regulated to mediate Cd uptake, translocation, and accumulation. Overall, Mn and Cu differently influenced Cd uptake and accumulation; Mn addition is an effective treatment for reducing Cd accumulation in wheat.

Cadmium-induced oxidative stress responses and acclimation in plants require fine-tuning of redox biology at subcellular level

Cadmium (Cd) is one of the most toxic compounds released into our environment and is harmful to human health, urging the need to remediate Cd-polluted soils. To this end, it is important to increase our insight into the molecular mechanisms underlying Cd stress responses in plants, ultimately leading to acclimation, and to develop novel strategies for economic validation of these soils. Albeit its non-redox-active nature, Cd causes a cellular oxidative challenge, which is a crucial determinant in the onset of diverse signalling cascades required for long-term acclimation and survival of Cd-exposed plants. Although it is well known that Cd affects reactive oxygen species (ROS) production and scavenging, the contribution of individual organelles to Cd-induced oxidative stress responses is less well studied. Here, we provide an overview of the current information on Cd-induced organellar responses with special attention to redox biology. We propose that an integration of organellar ROS signals with other signalling pathways is essential to finetune plant acclimation to Cd stress.

Phytochelatins: Sulfur-Containing Metal(loid)-Chelating Ligands in Plants

Phytochelatins (PCs) are small cysteine-rich peptides capable of binding metal(loid)s via SH-groups. Although the biosynthesis of PCs can be induced in vivo by various metal(loid)s, PCs are mainly involved in the detoxification of cadmium and arsenic (III), as well as mercury, zinc, lead, and copper ions, which have high affinities for S-containing ligands. The present review provides a comprehensive account of the recent data on PC biosynthesis, structure, and role in metal(loid) transport and sequestration in the vacuoles of plant cells. A comparative analysis of PC accumulation in hyperaccumulator plants, which accumulate metal(loid)s in their shoots, and in the excluders, which accumulate metal(loid)s in their roots, investigates the question of whether the endogenous PC concentration determines a plant's tolerance to metal(loid)s. Summarizing the available data, it can be concluded that PCs are not involved in metal(loid) hyperaccumulation machinery, though they play a key role in metal(loid) homeostasis. Unraveling the physiological role of metal(loid)-binding ligands is a fundamental problem of modern molecular biology, plant physiology, ionomics, and toxicology, and is important for the development of technologies used in phytoremediation, biofortification, and phytomining.

Role of oxidative stress in the physiology of sensitive and resistant Amaranthus palmeri populations treated with herbicides inhibiting acetolactate synthase

The aim of the present study was to elucidate the role of oxidative stress in the mode of action of acetolactate synthase (ALS) inhibiting herbicides. Two populations of Amaranthus palmeri S. Watson from Spain (sensitive and resistant to nicosulfuron, due to mutated ALS) were grown hydroponically and treated with different rates of the ALS inhibitor nicosulfuron (one time and three times the field recommended rate). Seven days later, various oxidative stress markers were measured in the leaves: H₂O₂, MDA, ascorbate and glutathione contents, antioxidant enzyme activities and gene expression levels. Under control conditions, most of the analysed parameters were very similar between sensitive and resistant plants, meaning that resistance is not accompanied by a different basal oxidative metabolism. Nicosulfuron-treated sensitive plants died after a few weeks, while the resistant ones survived, independently of the rate. Seven days after herbicide application, the sensitive plants that had received the highest nicosulfuron rate showed an increase in H₂O₂ content, lipid peroxidation and antioxidant enzymatic activities, while resistant plants did not show these responses, meaning that oxidative stress is linked to ALS inhibition. A supralethal nicosulfuron rate was needed to induce a significant oxidative stress response in the sensitive population, providing evidence that the lethality elicited by ALS inhibitors is not entirely dependent on oxidative stress.

Physiological and transcription level responses of microalgae Auxenochlorella protothecoides to cold and heat induced oxidative stress

Temperature is a crucial factor affecting microalgae CO₂ capture and utilization. However, an in-depth understanding of how microalgae respond to temperature stress is still unclear. In particular, the regulation mechanism under opposite temperature (heat and cold) stress had not yet been reported. In this study, the physicochemical properties and transcription level of related genes of microalgae Auxenochlorella protothecoides UTEX 2341 under heat and cold stress were investigated. Heat stress (Hs) caused a drastic increase of reactive oxygen species (ROS) in UTEX 2341. As key elements responded to Hs, superoxide dismutase (SOD) enzyme increased by 150%, 70%, and 30% in activity, and nitric oxide (NO) grew by 409.6%, 212.5%, and 990.4% in content compared with the control at 48 h, 96 h, 168 h. Under cold stress (Cs), ROS increased in the early stage and decreased in the later stage. As key factors responded to Cs, proline (Pro) increased respectively by 285%, 383%, and 81% in content, and heat shock transcriptional factor HSFA1d increased respectively by 161%, 71%, and 204% in transcript level compared with the control at 48 h, 96 h, 168 h. Furthermore, the transcript level of antioxidant enzymes or antioxidant coding genes was consistent with the changing trend of enzymes activity or antioxidant content. Notably, both glutathione (GSH) and heat shock protein 97 (hsp 97) were up-regulated in response to Hs and Cs. In conclusion, GSH and hsp 97 were the core elements of UTEX 2341 in response to both Hs and Cs. SOD and NO were the key elements that responded to Hs, while proline and HSFA1d were the key elements that responded to Cs. This study provided a basis for the understanding of the response mechanism of microalgae under temperature stress and the improvement of the microalgae tolerance to temperature stress.

The Response of Thiols to Cadmium Stress in Spinach (Spinacia Oleracea L.)

The aim of this study is to examine the thiol species for the high cadmium (Cd) tolerance of spinach and provide information for the improvement of soil utilization. The spinach was cultured in aqueous solution with concentrations of Cd ranging from 1 to 9 mg/L. The time responses of glutathione (GSH) and phytochelatins (PCs, PC2-PC4) in the tissues of spinach were monitored via HPLC−MS/MS, and the concentrations of Cd in the roots, shoots and leaves were detected by ICP−OES. Data were analyzed via one-way ANOVA and Spearman correlation to assess the relationships among the types of thiols and the changes between types of thiols and Cd. As Cd stress increased, Cd concentrations in tissues also increased. The total thiol contents responded to Cd stresses with correlations r ranging from 0.394 (root), 0.520 (shoot) to 0.771 (leaf) (p < 0.01). GSH and PC3 were dominant on most of the days under Cd stress. The correlation r between improvements in GSH and increments of Cd concentration in roots was −0.808 (p < 0.01), and r between changes in PC3 and changes in Cd concentrations in leaves was −0.503 (p < 0.01). No correlation can be found between GSH and the subtypes of PCs in shoots, but strong positive correlations within the subtypes of PCs. Thiols can be produced in different tissues of spinach, while the shoots are only a transport tissue for GSH.

Transcriptome sequencing of Brassica napus highlights the complex issues with soil supplementation with sewage sludge

The soil supplementation with sewage sludge (SS) has become a widespread method to improve soil quality, but its long-term possible consequences are still relatively unknown. SS may contain several groups of contaminants to which the biological responses of the organisms are still poorly understood mainly due to the mixture toxicity. In this context, RNA-seq has been used to assess the impact of the exposure to sewage sludge supplemented soil at the whole-transcriptome level in the Brassica napus (B. napus). Although the municipal sewage sludge passed all safety regulations set by the EU commission (86/278/EEC), soil supplementation with SS caused a significant (p < 0.05) increase in the content of lead (by 68.8%, 71.4% in plant shoots and roots, respectively), zinc (by 22.4% and 31.2%), nickel (by 67.0% and 30.2%), and copper (by 33.1% and 39.2%). The de-novo assembled transcriptome of B. napus identified 555 differently expressed genes (DEGs) in a response to sewage sludge supplementation at the false detection rate below 0.001 (FDR <0.001). Among them, 313 genes were up-regulated and 242 genes were down-regulated. The gene ontology analysis (GO) had shown, that significantly enriched GO groups included genes involved in photosynthesis, carbohydrate metabolism and photosystems repair (41 genes), response to oxidative stress (50 genes), response to pathogens (36 genes), response to xenobiotics (15 genes), and heavy metals (41 genes), cell death (8 genes), cell wall structure (15 genes). These results suggest a significant impact of contaminants in sewage sludge on plants transcriptome. The transcriptomic approach facilitated a better understanding of the molecular level of the potential toxicity of sewage sludge in B. napus. RNA-seq allowed for the identification of potential novel early-warning molecular markers of environmental contamination. This work highlights the crucial necessity for rapid legislation change concerning the allowable levels of contaminants in sewage sludge applied on land, to mitigate the possible adverse outcomes in the ecosystem after its use as a fertilizer.

MYB43 as a novel substrate for CRL4PRL1 E3 ligases negatively regulates cadmium tolerance through transcriptional inhibition of HMAs in Arabidopsis

Controlled stability of proteins is a highly efficient mechanism to direct diverse processes in plants. A key regulatory system for protein stability is given by the CULLIN-RING E3 ligases (CRLs). In this work, MYB43 is identified as a novel target of a CUL4-DDB1-PRL1 (PLEIOTROPIC REGULATORY LOCUS 1)-RING E3 ligase (CRL4^PRL1 E3 ligase). Its stability depends on the presence of PRL1, a WD40-containing protein functioning as a substrate receptor of the CRL4 E3 ligases. Genetic studies have indicated that MYB43 is a negative regulator of cadmium (Cd) tolerance in Arabidopsis by transcriptional inhibition of important Cd transporters (HMA2, HMA3 and HMA4), while PRL1 and CUL4 positively regulate Cd tolerance. Expression of CUL4 and PRL1 was enhanced in response to Cd stress, and PRL1 can interact with and target MYB43 for degradation depending on assembly of CRL4^PRL1 E3 ligase, and consequently increase the expression of HMA2, HMA3 and HMA4 through attenuating the transcriptional inhibition. HMA2 and HMA4 are shown to transport cadmium ion (Cd²⁺ ) from the roots of plants to the shoots through the xylem, ultimately increasing the plants' tolerance to Cd stress.

Subtoxic levels of some heavy metals cause differential root-shoot structure, morphology and auxins levels in Arabidopsis thaliana

Contamination of soil by heavy metals severely affects plant growth and causes soil pollution. While effects on plant growth have been investigated for metals taken individually or in groups, less is known about their comparative effects. In this study Arabidopsis thaliana seedlings were grown for 14 days in Petri dishes containing medium contaminated by six common heavy metals (Hg, Cd, Pb, Cu, Ni and Zn), at the minimum concentrations defined as toxic by the most recent EU legislation on contamination of agricultural soils. (a) Root structure and morphology, (b) metal composition and translocation, and (c) the levels of indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA) were analyzed. Metals accumulated more in roots than in shoots, with concentrations that differed by several orders of magnitude depending on the metal: Cd (ca. 700 × and ca. 450 × in roots and shoots, respectively), Hg (150 × , 80 × ), Ni (50 × , 20 × ), Cu (48 × , 20 × ), Zn (23 × , 6 × ), and Pb (9 × , 4 × ). Responses were significant for at least nine of the ten root parameters (with the exception of Hg), and five of the six shoot parameters (with the exception of Zn). Cu and Zn induced respectively the strongest responses in root hormonal (up to ca. 240% the control values for IBA, 190% for IAA) and structural parameters (up to 210% for main root length, 330% for total lateral root length, 220% for number of root tips, 600% for total root surface, and from 2.5° to 26.0° of root growth angle). Regarding the shoots, the largest changes occurred for shoot height (down to 60% for Ni), rosette diameter (down to 45% for Hg), leaf number (up to 230% for Zn) and IBA (up to 240% for Pb and Cu). A microscope analysis revealed that shape and conformation of root hairs were strongly inhibited after Cd exposure, and enhanced under Hg and Pb. The results could have positive applications such as for defining toxicity thresholds (in phytoremediation) and acceptable concentration levels (for policies) for some of the most common heavy metals in agricultural soils.

Metal tolerance in plants: Molecular and physicochemical interface determines the "not so heavy effect" of heavy metals

An increase in technological interventions and ruthless urbanization in the name of development has deteriorated our environment over time and caused the buildup of heavy metals (HMs) in the soil and water resources. These heavy metals are gaining increased access into our food chain through the plant and/or animal-based products, to adversely impact human health. The issue of how to restrict the entry of HMs or modulate their response in event of their ingress into the plant system is worrisome. The current knowledge on the interactive-regulatory role and contribution of different physical, biophysical, biochemical, physiological, and molecular factors that determine the heavy metal availability-uptake-partitioning dynamics in the soil-plant-environment needs to be updated. The present review critically analyses the interactive overlaps between different adaptation and tolerance strategies that may be causally related to their cellular localization, conjugation and homeostasis, a relative affinity for the transporters, rhizosphere modifications, activation of efflux pumps and vacuolar sequestration that singly or collectively determine a plant's response to HM stress. Recently postulated role of gaseous pollutants such as SO₂ and other secondary metabolites in heavy metal tolerance, which may be regulated at the whole plant and/or tissue/cell is discussed to delineate and work towards a "not so heavy" response of plants to heavy metals present in the contaminated soils.

Glutathione Is Required for the Early Alert Response and Subsequent Acclimation in Cadmium-Exposed Arabidopsis thaliana Plants

Pollution by cadmium (Cd) is a worldwide problem, posing risks to human health and impacting crop yield and quality. Cadmium-induced phytotoxicity arises from an imbalance between antioxidants and pro-oxidants in favour of the latter. The Cd-induced depletion of the major antioxidant glutathione (GSH) strongly contributes to this imbalance. Rather than being merely an adverse effect of Cd exposure, the rapid depletion of root GSH levels was proposed to serve as an alert response. This alarm phase is crucial for an optimal stress response, which defines acclimation later on. To obtain a better understanding on the importance of GSH in the course of these responses and how these are defined by the rapid GSH depletion, analyses were performed in the GSH-deficient cadmium-sensitive 2-1 (cad2-1) mutant. Cadmium-induced root and leaf responses related to oxidative challenge, hydrogen peroxide (H2O2), GSH, ethylene, and 1-aminocyclopropane-1-carboxylic acid (ACC) were compared between wild-type (WT) and mutant Arabidopsis thaliana plants. Although the cad2-1 mutant has significantly lower GSH levels, root GSH depletion still occurred, suggesting that the chelating capacity of GSH is prioritised over its antioxidative function. We demonstrated that responses related to GSH metabolism and ACC production were accelerated in mutant roots and that stress persisted due to suboptimal acclimation. In general, the redox imbalance in cad2-1 mutant plants and the lack of proper transient ethylene signalling contributed to this suboptimal acclimation, resulting in a more pronounced Cd effect.

Genes involved in mRNA surveillance are induced in Brachypodium distachyon under cadmium toxicity

BACKGROUND

Cd accumulation in plant cells results in dramatic problems including oxidative stress and inhibition of vital enzymes. It also affects mineral uptakes by disrupting membrane permeability. Interaction among Cd and other plant nutrient elements changes the nutritional contents of crops and reduces their yield.

METHODS AND RESULTS

In the present study, Cd stress in Brachypodium distachyon led to the upregulation of some heavy metal transport genes (influx or efflux) encoding cation-efflux proteins, heavy metal-associated proteins and NRAMP proteins. The Arabidopsis orthologs of the differentially expressed B. distachyon genes (DEGs) under Cd toxicity were identified, which exhibited Bradi4g26905 was an ortholog of AtALY1-2. Detailed co-expression network and gene ontology analyses found the potential involvement of the mRNA surveillance pathway in Cd tolerance in B. distachyon. These genes were shown to be downregulated by sulfur (S) deficiency.

CONCLUSIONS

This is the first transcriptomic study investigating the effect of Cd toxicity in B. distachyon, a model plant for genomic studies in Poaceae (Gramineae) species. The results are expected to provide valuable information for more comprehensive research related to heavy metal toxicity in plants.

MdATG5a induces drought tolerance by improving the antioxidant defenses and promoting starch degradation in apple

Drought occurrence seriously affects the productivity and quality of apple crop worldwide. Autophagy, a conserved process for the degradation and recycling of unwanted cellular components, is considered to positively regulate the tolerance of various abiotic stresses in plants. In the current study, we isolated two ATG5 homologs genes, namely, MdATG5a and MdATG5b, from apple, demonstrating their responsiveness to drought and oxidative stresses. In addition to having the same cellular localization in the nucleus and cytoplasm, both MdATG5a and MdATG5b could interact with MdATG12. Transgenic apple plants overexpressing MdATG5a exhibited an improved drought tolerance, as indicated by less drought-related damage and higher photosynthetic capacities compared to wild-type (WT) plants under drought stress. The overexpression of MdATG5a improved antioxidant defenses in apple when exposed to drought via elevating both antioxidant enzyme activities and the levels of beneficial antioxidants. Furthermore, under drought stress, the overexpression of MdATG5a promoted the mobilization of starch to accumulate greater levels of soluble sugars, contributing to osmotic adjustments and supporting carbon skeletons for proline synthesis. Such changes in physiological responses may be associated with increased autophagic activities in the transgenic plants upon exposure to drought. Our results demonstrate that MdATG5a-mediated autophagy enhances drought tolerance of apple plants via improving antioxidant defenses and metabolic adjustments.

Influence of foliar glutathione and putrescine on metabolism and mineral status of genetically diverse rapeseed cultivars under hexavalent chromium stress

We studied the physio-biochemical involvement of exogenous signaling compounds, glutathione and putrescine (alone and in combination), on three contrasting genotypes (cvs. Shiralee, Rainbow, and Dunkled) of canola (Brassica napus L.) of plants exposed to chromium stress. Seeds were germinated in Cr-contaminated soil (0 and 50 μg/g Cr⁶⁺), and both signaling compounds were applied as a foliar spray to 20-day-old plants. Changes in root, stem, and leaf nitro-oxidative metabolism, endogenous GSH level, secondary metabolites, and mineral nutrients were investigated from 60-day-old plants. Exposure to Cr⁶⁺ increased stem GSH and NO concentrations in all cultivars. Maximum root Cr⁶⁺ bioaccumulation was recorded in cv. Rainbow and the least in cv. Shiralee. Also, Cr⁶⁺ stress decreased number and weight of seeds and pod length. Disturbances in root and shoot mineral profile were evident; however, its magnitude varied in all cultivars. The exogenous GSH improved root and shoot P, Fe, S, and Zn concentrations; however, the effect was cultivar specific. Leaf endogenous GSH was increased by exogenous GSH while NO levels remained unaffected. The GSH application also promoted shoot Cr⁶⁺ bioaccumulation while PUT application caused a recovery in seed number and seed weight. Both PUT and GSH differentially affected tissue-specific secondary metabolite profile. Overall, the exogenous GSH was much more effective in alleviating the Cr⁺⁶ toxicity in canola.

Silicon reduces cadmium absorption and increases root-to-shoot translocation without impacting growth in young plants of hemp (Cannabis sativa L.) on a short-term basis

Textile hemp (Cannabis sativa L.) is a non-edible multipurpose crop suitable for fiber production and/or phytoremediation on moderately heavy metal-contaminated soils. Experiments were conducted in nutrient solution to assess the short-term impact of silicon (Si), a well-known beneficial element, on plants exposed to 20 μM cadmium (Cd) in nutrient solution. Cd decreased plant growth and affected photosynthesis through non-stomatal effects. Cd translocation factor was higher than 1, confirming the interest of hemp for phytoextraction purposes. Additional Si did not improve plant growth after 1 week of treatment but decreased Cd accumulation in all organs and improved water use efficiency through a decrease in transpiration rate. Si had only marginal impact on Cd distribution among organs. It increased glutathione and phytochelatin synthesis allowing the plants to efficiently cope with oxidative stress through the improvement of Cd sequestration on thiol groups in the roots. Si may thus have a fast impact on the plant behavior before the occurrence of plant growth stimulation.

Singlet Oxygen Generation in Dark-Hypoxia by Catalytic Microenvironment-Tailored Nanoreactors for NIR-II Fluorescence-Monitored Chemodynamic Therapy

Singlet oxygen (¹ O₂ ) has a potent anticancer effect, but photosensitized generation of ¹ O₂ is inhibited by tumor hypoxia and limited light penetration depth. Despite the potential of chemodynamic therapy (CDT) to circumvent these issues by exploration of ¹ O₂ -producing catalysts, engineering efficient CDT agents is still a formidable challenge since most catalysts require specific pH to function and become inactivated upon chelation by glutathione (GSH). Herein, we present a catalytic microenvironment-tailored nanoreactor (CMTN), constructed by encapsulating MoO₄ ^2- catalyst and alkaline sodium carbonate within liposomes, which offers a favorable pH condition for MoO₄ ^2- -catalyzed generation of ¹ O₂ from H₂ O₂ and protects MoO₄ ^2- from GSH chelation owing to the impermeability of liposomal lipid membrane to ions and GSH. H₂ O₂ and ¹ O₂ can freely cross the liposomal membrane, allowing CMTN with a built-in NIR-II ratiometric fluorescent ¹ O₂ sensor to achieve monitored tumor CDT.

Validation and uncertainty estimation of analytical method for quantification of phytochelatins in aquatic plants by UPLC-MS

Phytochelatins (PCs) are peptides that play an important role in homeostasis and detoxification of heavy metal in plants. Furthermore, they have been proposed as earlier potential biomarkers of aquatic pollution by heavy metals. Nowadays, several researchers have reported on current methods for quantification of glutathione (GSH) and the PCs (phytochelatin 2, phytochelatin 3, phytochelatin 4) quantification in plants. However, no method has reported the uncertainty of the measurement, which helps to improve the accuracy and quality assurance in the PC quantification. In this work, a new methodology using ultra-high-performance liquid chromatography coupled to mass spectrometry (UPLC-MS) to measure with high precision and accuracy the PCs in aquatic plants, was validated. Selectivity, linearity, limit of detection, limit of quantification, precision, trueness and uncertainty estimation were examined as parts of the method validation. The described method shows excellent linearity in different ranges for all analytes with coefficients of determination higher than 0.99. The relative standard deviation for intra-day precision was <3% and for inter-day <10%. All LOD and LOQ analytes ranged from 0.02 to 0.08 μg ml^-1, and from 0.03 to 0.09 μg ml^-1, respectively. The recoveries varied from 61% to 89%. In order to obtain an interval of results with the highest confidence levels, the uncertainty associated with the measurements was evaluated. The calibration curve (>50%) and recovery (19-44%) were the most important contributors to the total uncertainty. The proposed method was applied to quantify GSH and PCs in the aquatic plants Lemna gibba L., Myriophyllum heterophyllum Michx., Arenaria paludicola and Hydrocotyle ranunculoides L. fil., showing statistical differences in the mass fraction of the analytes.

Potential risks of nicotine on the germination, growth, and nutritional properties of broad bean

This study evaluated the allelopathy, uptake and accumulation, and potential agricultural and food safety risks of nicotine in broad bean (Vicia faba L.) during seed germination and seedling growth. Nicotine stress has an allelopathic inhibitory effect on seeds and a hormesis effect on germinated seeds and seedlings, which has an enhancement effect (<50 mg kg^-1) and an inhibition effect (>100 mg kg^-1) on the germinated seeds and an enhancement effect (<100 mg kg^-1) and an inhibition effect (>200 mg kg^-1) on the seedlings. Exogenous nicotine can be absorbed by broad bean roots from nicotine-contaminated soil and accumulated in the main organs of the seedlings, especially the leaves, which exceeded the maximum residue level (0.03 mg kg^-1 DW) at 50 mg kg^-1. Moreover, nicotine resulted in a bitter taste in the edible broad bean leaves, disrupting the balance of basic nutritional properties, decreasing sucrose, and increasing bitter substances such as choline and procyanidin. These results demonstrated that residual nicotine in the soil not only poses potential risks to sustainable agricultural development but also a food safety risk for consumers. The present study provides insight into the potential risks of nicotine in agroecosystems.

Sulfur Homeostasis in Plants

Sulfur (S) is an essential macronutrient for plant growth and development. S is majorly absorbed as sulfate from soil, and is then translocated to plastids in leaves, where it is assimilated into organic products. Cysteine (Cys) is the first organic product generated from S, and it is used as a precursor to synthesize many S-containing metabolites with important biological functions, such as glutathione (GSH) and methionine (Met). The reduction of sulfate takes place in a two-step reaction involving a variety of enzymes. Sulfate transporters (SULTRs) are responsible for the absorption of SO42- from the soil and the transport of SO42- in plants. There are 12-16 members in the S transporter family, which is divided into five categories based on coding sequence homology and biochemical functions. When exposed to S deficiency, plants will alter a series of morphological and physiological processes. Adaptive strategies, including cis-acting elements, transcription factors, non-coding microRNAs, and phytohormones, have evolved in plants to respond to S deficiency. In addition, there is crosstalk between S and other nutrients in plants. In this review, we summarize the recent progress in understanding the mechanisms underlying S homeostasis in plants.

Eukaryotic and Prokaryotic Phytochelatin Synthases Differ Less in Functional Terms Than Previously Thought: A Comparative Analysis of Marchantia polymorpha and Geitlerinema sp. PCC 7407

This paper reports functional studies on the enzyme phytochelatin synthase in the liverwort Marchantia polymorpha and the cyanobacterium Geitlerinema sp. strain PCC 7407. In vitro activity assays in control samples (cadmium-untreated) showed that phytochelatin synthase was constitutively expressed in both organisms. In the presence of 100 µM cadmium, in both the liverwort and the cyanobacterium, the enzyme was promptly activated in vitro, and produced phytochelatins up to the oligomer PC₄. Likewise, in vivo exposure to 10–36 µM cadmium for 6-120 h induced in both organisms phytochelatin synthesis up to PC₄. Furthermore, the glutathione (GSH) levels in M. polymorpha were constitutively low (compared with the average content in higher plants), but increased considerably under cadmium stress. Conversely, the GSH levels in Geitlerinema sp. PCC 7407 were constitutively high, but were halved under metal treatments. At odds with former papers, our results demonstrate that, as in M. polymorpha and other plants, the cyanobacterial phytochelatin synthase exposed to cadmium possesses manifest transpeptidasic activity, being able to synthesize phytochelatins with a degree of oligomerization higher than PC₂. Therefore, prokaryotic and eukaryotic phytochelatin synthases differ less in functional terms than previously thought.