Cadmium-induced changes in pigments, total phenolics, and phenylalanine ammonia-lyase activity in fronds of Azolla imbricata

Pervasive influence of heavy metals on metabolic pathways is potentially relieved by hesperidin to enhance the phytoremediation efficiency of Bassia scoparia

Hesperidin (HSP), a flavonoid, is a potent antioxidant, metal chelator, mediator of signaling pathways, and regulator of metal uptake in plants. The study examined the ameliorative effects of HSP (100 μM) on Bassia scoparia grown under excessive levels of heavy metals (zinc (500 mg kg-1), copper (400 mg kg-1), cadmium (100 mg kg-1), and chromium (100 mg kg-1)). The study clarifies the underlying mechanisms by which HSP lessens metabolic mayhem to enhance metal stress tolerance and phytoremediation efficiency of Bassia scoparia. Plants manifested diminished growth because of a drop in chlorophyll content and nutrient acquisition, along with exacerbated deterioration of cellular membranes reflected in elevated reactive oxygen species (ROS) production, lipid peroxidation, and relative membrane permeability. Besides the colossal production of cytotoxic methylglyoxal, the activity of lipoxygenase was also higher in plants under metal toxicity. Conversely, hesperidin suppressed the production of cytotoxic ROS and methylglyoxal. Hesperidin improved oxidative defense that protected membrane integrity. Hesperidin caused a more significant accumulation of osmolytes, non-protein thiols, and phytochelatins, thereby rendering metal ions non-toxic. Hydrogen sulfide and nitric oxide endogenous levels were intricately maintained higher in plants treated with HSP. Hesperidin increased metal accumulation in Bassia scoparia and thereby had the potential to promote the reclamation of metal-contaminated soils.

Impact of High Light Intensity and Low Temperature on the Growth and Phenylpropanoid Profile of Azolla filiculoides

Exposure to high light intensity (HL) and cold treatment (CT) induces reddish pigmentation in Azolla filiculoides, an aquatic fern. Nevertheless, how these conditions, alone or in combination, influence Azolla growth and pigment synthesis remains to be fully elucidated. Likewise, the regulatory network underpinning the accumulation of flavonoids in ferns is still unclear. Here, we grew A. filiculoides under HL and/or CT conditions for 20 days and evaluated the biomass doubling time, relative growth rate, photosynthetic and non-photosynthetic pigment contents, and photosynthetic efficiency by chlorophyll fluorescence measurements. Furthermore, from the A. filiculoides genome, we mined the homologs of MYB, bHLH, and WDR genes, which form the MBW flavonoid regulatory complex in higher plants, to investigate their expression by qRT-PCR. We report that A. filiculoides optimizes photosynthesis at lower light intensities, regardless of the temperature. In addition, we show that CT does not severely hamper Azolla growth, although it causes the onset of photoinhibition. Coupling CT with HL stimulates the accumulation of flavonoids, which likely prevents irreversible photoinhibition-induced damage. Although our data do not support the formation of MBW complexes, we identified candidate MYB and bHLH regulators of flavonoids. Overall, the present findings are of fundamental and pragmatic relevance to Azolla's biology.

Exogenously applied melatonin enhanced the tolerance of Brassica napus against cobalt toxicity by modulating antioxidant defense, osmotic adjustment, and expression of stress response genes

The excessive accumulation of cobalt (Co) in plant tissues severely impairs plant growth that ultimately reduces the yield. However, melatonin (MT) has been known to mediate the abiotic stress tolerance in plants. The present study aimed at investigating the protective mechanisms of exogenously applied MT (0, 50 and 100 μM) under Co (0, 100, 200 and 300 μM) stress by focusing on morpho-physiological, biochemical and cellular characterizations of Brassica napus plants. Cobalt (300 μM) alone treatment drastically inhibited the stomatal conductance, plant height (45%), leaf area (30%), free amino acid (139%), relative electrolyte leakage (109%), and total soluble sugars (71%), compared with the control. However, the exogenous supply of MT notably minimized the oxidative damage, lipid peroxidation and maintained the membrane integrity under Co-toxicity by restricting the overproduction of ROS (H₂O₂ and O₂^•), and MDA in leaves and roots. Melatonin significantly enhanced the activities of ROS-scavenging antioxidant enzymes, secondary metabolism-related phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO), stress-responsive genes (heat shock protein as HSP-90, methyl transferase as MT) and regulated the Co-transporters, especially in roots. These findings indicated that an exogenous supply of MT improve the plant morphology, photosynthetic apparatus, osmotic adjustments, and antioxidant defense systems by enhancing the Co-detoxification in B. napus plants.

Effect of Glomus mosseae, cadmium, and elevated air temperature on main flavonoids and phenolic acids contents in alfalfa

Global warming and heavy metal-contaminated soils co-occur in natural ecosystems. Flavonoids and phenolic acids in plants have significant antioxidant activity and free radical scavenging ability, which can quickly increase under adverse environments. Arbuscular mycorrhizal fungi (AMF) colonization can affect the synthesis of flavonoids and phenolic acids in host plants. This study focused on the main effect of Glomus mosseae, cadmium (Cd, 8 mg kg^-1 dry soils), and elevated temperature (ET, + 3 °C) on main flavonoids and phenolic acids in 120-d Medicago sativa L. (alfalfa). Elevated temperature decreased G. mosseae colonization ratio by 49.5% under Cd exposure. Except for p-hydroxybenzoic acid, flavonoids and phenolic acids content in shoots increased (p < 0.05) under G. mosseae + Cd relative to Cd only. G. mosseae and Cd showed significant effects on rutin, quercetin, apigenin, liquiritigenin, gallic acid, p-hydroxybenzoic acid, p-coumaric acid, and ferulic acid, and G. mosseae colonization led to increases in these compounds by 41.7%, 35.4%, 32.2%, 267.8%, 84.7%, 33.5%, 102.8%, and 89.4%, respectively, under ET + Cd. Carbon, N, and Cd in alfalfa and G. mosseae colonization rate were significant factors on flavonoids and phenolic acids accumulation. Additionally, P content in shoots significantly influenced flavonoids content. G. mosseae inoculation significantly stimulated the synthesis of main flavonoids and phenolic acids in alfalfa shoots under ET + Cd, which was helpful to understand the regulation of AMF on non-enzyme antioxidant system of plants grown in heavy metal-contaminated soils under global change scenarios.

Application of duckweed (Lemna sp.) and water fern (Azolla sp.) in the removal of pharmaceutical residues in water: State of art focus on antibiotics

In recent decades, antibiotic residues in the environment have increased, affecting components of biological communities, from bacteria to plants and animals. Different methods have been used to remove these compounds, including phytoremediation with floating aquatic species such as duckweed and aquatic fern, with positive results. This study analyses information about the removal efficiency of drugs, with a focus on antibiotics, using Lemna and Azolla, which will allow a better understanding of phytoremediation processes from the perspective of plant physiology. The physiological processes of macrophytes in an environment with this type of pollutant and the phytotoxic effects on plants at high concentrations are also analysed. The metabolization of toxic compounds occurs in three phases: phase I begins with the absorption of antibiotics and the secretion of reactive oxygen species (ROS); in phase II, the effects of ROS are neutralized and minimized by conjugation with enzymes such as glutathione transferase or metabolites such as glutathione; and phase III culminates with the storage of the assimilated compounds in the vacuoles, apoplast and cell wall. In this way, plants contribute to the removal of toxic compounds. In summary, there is sufficient scientific evidence on the efficiency of the elimination of pharmaceutical compounds by these floating macrophytes at the laboratory scale, which indicates that their application under real conditions can have good results.

Transcriptional, secondary metabolic, and antioxidative investigations elucidate the rapid response mechanism of Pontederia cordata to cadmium

Pontederia cordata is previously demonstrated a cadmium (Cd) tolerant plant, and also a candidate for the phytoremediation of heavy-metal-contaminated wetlands. A hydroponic experiment was used to investigate variations in photosynthetic gas exchange parameters, antioxidative activities, chlorophyll and secondary metabolite contents, and transcriptome in leaves of the plant exposed to 0.44 mM Cd²⁺ for 0 h, 24 h, and 48 h. Under Cd²⁺ exposure for 24 h, the plant presented a favorable photosynthesis by maintaining relatively higher antioxidant activity. Cd²⁺ exposure for 48 h accelerated membrane peroxidation, declined photosynthetic pigment content, and increased polyphenol oxidase activity, thus interfering with photosynthesis. The phenylpropane pathway served as a chemical rather than physical defense against Cd²⁺ in the plant leaves. A total of 20,998, 4743, and 4413 differentially expressed genes (DEGs) were identified in the groups of 0 h vs 24 h, 0 h vs 48 h, and 24 h vs 48 h, respectively. The primary metabolic pathways of the DEGs were mainly enriched in nitrogen metabolism, starch and sucrose metabolism, fructose and mannose metabolism, as well as pentose-phosphate pathway, contributing to a stable cell structure and function. Flavonoid biosynthesis directly or indirectly played an antioxidative role against Cd²⁺ in the leaves. Forty-nine transcription factor (TF) families were identified, and 8 TF families were shared among the three groups. The present study provides a theoretical foundation for investigating tolerance mechanisms of wetland plants to Cd stress in terms of secondary metabolism and transcriptional regulation.

Modulation of the toxic effects of zinc oxide nanoparticles by exogenous salicylic acid pretreatment in Chenopodium murale L

Due to many uses of zinc oxide nanoparticles (ZnO NPs) in various industries, the release of these particles in the environment and their effects on living organisms is inevitable. In this study, the role of salicylic acid (SA) pretreatments in modulating the toxicity of ZnO NPs was investigated using a hydroponic system. After pretreatment with different concentrations of SA (0, 25, 75, and 150 μM), Chenopodium murale plants were exposed to ZnO NPs (50 mg L^-1). The results showed that exogenous SA increased the length, weight, chlorophyll, proline, starch, and soluble sugars in the plants. Besides, SA pretreatments improved water status in the plants treated with ZnO NPs. In SA-pretreated plants, increased activity of catalase (CAT), guaiacol peroxidase (GPX), and superoxide dismutase (SOD) was associated with a decline in electrolyte leakage (EL %) and membrane peroxidation. Under NPs stress, SA pretreatments increased the content of phenolic compounds by increasing the activity of phenylalanine ammonia-lyase (PAL). Exogenous SA reduced the translocation of larger amounts of Zn to the shoots, with more accumulation in the roots. This result can be used to produce healthy food from plants grown in environments contaminated with nanoparticles. It seems that all concentrations of SA reduced the symptoms of ZnO NPs toxicity in the plant by strengthening the function of the antioxidant system and increasing the content of some metabolites. Findings also suggest that SA pretreatment can compensate for the growth reduction caused by ZnO NPs.

Morphological and biochemical responses of Macrotyloma uniflorum (Lam.) Verdc. to allelopathic effects of Mikania micrantha Kunth extracts

Yield loss due to noxious weeds is one among several reasons for the reduced economy for the developing countries. Impacts of one such weed i.e. Mikania micrantha were investigated on the rate of seed germination, growth, biomass, photosynthetic pigments, total soluble protein, phenolics and proline content of leaves of Macrotylama uniflorum (an important pulse). In a completely randomized setup, control and four concentrations (10 mg/ml, 50 mg/ml, 100 mg/ml and 200 mg/ml) of the aqueous leaf extracts of M. micrantha were tested on the seeds of M. uniflorum. The extracts inhibited germination, growth, biomass, chlorophyll, carotenoid and protein contents. The protein content of M. uniflorum decreased to 8.48 mg/g at 200 mg/ml. Similarly, shoot length and root length were also decreased up to 5.11 cm and 0.85 cm respectively and water content increased with the increasing concentration of weed extracts. The leaf extracts resulted in an increase in the phenolics (19.66 mg) and proline (24.49 mg) content of the crop plant. The preliminary study indicated that the aqueous leaf extracts of weed plant resulted in negative or detrimental impact on growth and physiology of the plant and this might be due to the release of secondary metabolites. The present investigation may further lead to the identification of certain secondary metabolites or allelo-chemicals that may have an important agricultural application for sustainability and may enhance the level of crop protection against several other harmful plant species.

A review on in vivo and in vitro nanotoxicological studies in plants: A headlight for future targets

Owing to the unique properties and useful applications in numerous fields, nanomaterials (NMs) received a great attention. The mass production of NMs has raised major concern for the environment. Recently, some altered growth patterns in plants have been reported due to the plant-NMs interactions. However, for NMs safe applications in agriculture and medicine, a comprehensive understanding of bio-nano interactions is crucial. The main goal of this review article is to summarize the results of the toxicological studies that have shown the in vitro and in vivo interactions of NMs with plants. The toxicity mechanisms are briefly discussed in plants as the defense mechanism works to overcome the stress caused by NMs implications. Indeed, the impact of NMs on plants varies significantly with many factors including physicochemical properties of NMs, culture media, and plant species. To investigate the impacts, dose metrics is an important analysis for assaying toxicity and is discussed in the present article to broadly open up different aspects of nanotoxicological investigations. To access reliable quantification and measurement in laboratories, standardized methodologies are crucial for precise dose delivery of NMs to plants during exposure. Altogether, the information is significant to researchers to describe restrictions and future perspectives.

Genome-wide identification and characterization of long non-coding RNAs conferring resistance to Colletotrichum gloeosporioides in walnut (Juglans regia)

BACKGROUND

Walnut anthracnose caused by Colletotrichum gloeosporioides (Penz.) Penz. and Sacc. is an important walnut production problem in China. Although the long non-coding RNAs (lncRNAs) are important for plant disease resistance, the molecular mechanisms underlying resistance to C. gloeosporioides in walnut remain poorly understood.

RESULTS

The anthracnose-resistant F26 fruits from the B26 clone and the anthracnose-susceptible F423 fruits from the 4-23 clone of walnut were used as the test materials. Specifically, we performed a comparative transcriptome analysis of F26 and F423 fruit bracts to identify differentially expressed LncRNAs (DELs) at five time-points (tissues at 0 hpi, pathological tissues at 24 hpi, 48 hpi, 72 hpi, and distal uninoculated tissues at 120 hpi). Compared with F423, a total of 14,525 DELs were identified, including 10,645 upregulated lncRNAs and 3846 downregulated lncRNAs in F26. The number of upregulated lncRNAs in F26 compared to in F423 was significantly higher at the early stages of C. gloeosporioides infection. A total of 5 modules related to disease resistance were screened by WGCNA and the target genes of lncRNAs were obtained. Bioinformatic analysis showed that the target genes of upregulated lncRNAs were enriched in immune-related processes during the infection of C. gloeosporioides, such as activation of innate immune response, defense response to bacterium, incompatible interaction and immune system process, and enriched in plant hormone signal transduction, phenylpropanoid biosynthesis and other pathways. And 124 known target genes for 96 hub lncRNAs were predicted, including 10 known resistance genes. The expression of 5 lncRNAs and 5 target genes was confirmed by qPCR, which was consistent with the RNA-seq data.

CONCLUSIONS

The results of this study provide the basis for future functional characterizations of lncRNAs regarding the C. gloeosporioides resistance of walnut fruit bracts.

Alleviation of cadmium-induced phytotoxicity and growth improvement by exogenous melatonin pretreatment in mallow (Malva parviflora) plants

The present work was aimed to study the effect of melatonin pretreatments on growth, oxidative stress modulation, cadmium (Cd) accumulation, and tolerance in mallow (Malva parviflora, Malvaceae) plants under the hydroponic system. Application of substances that can modulate the harmful effects of Cd on plant yield and reduce its accumulation in the edible parts is of particular importance. Therefore, the mallow plants pretreated with 15, 50, and 100 µM of melatonin were exposed to 50 µM Cd. Our results showed that melatonin, especially at 15 and 50 µM, led to positive effects on Cd tolerance, including a significant increase in growth, photosynthetic pigments, and soluble protein content. Exogenous melatonin could improve relative water content (RWC) and stomatal conductance in the plants treated with Cd, probably through an increase in proline. Further, lower concentrations of melatonin led to a decrease in Cd translocation to the shoots. Based on the results, melatonin considerably increased catalase (CAT), superoxide dismutase (SOD), and guaiacol peroxidase (GPX) activities as well as the production of phenols. The increased activity of antioxidant enzymes led to a decrease in electrolyte leakage (EL), lipid peroxidation, and H₂O₂ content in the plants exposed to Cd stress. Under Cd stress, the increased phenols content in melatonin-pretreated plants could be due to the induction of phenylalanine ammonia-lyase (PAL) activity and an increase in shoot soluble carbohydrates. The results showed that the use of melatonin could reduce oxidative stress and improve biomass in the plants exposed to Cd. At least in our experimental conditions, this information appears to be useful for healthy food production.

Differential Production of Phenolics, Lipids, Carbohydrates and Proteins in Stressed and Unstressed Aquatic Plants, Azolla filiculoides and Azolla pinnata

The metabolic plasticity of shikimate and phenylpropanoid pathways redirects carbon flow to different sink products in order to protect sessile plants from environmental stresses. This study assessed the biochemical responses of two Azolla species, A. filiculoides and A. pinnata, to the combined effects of environmental and nutritional stresses experienced while growing outdoors under Australian summer conditions. These stresses triggered a more than 2-fold increase in the production of total phenols and their representatives, anthocyanins (up to 18-fold), flavonoids (up to 4.7-fold), and condensed tannins (up to 2.7-fold), which led to intense red coloration of the leaves. These changes were also associated with an increase in the concentration of carbohydrates and a decrease in concentrations of lipids and total proteins. Changes in lipid biosynthesis did not cause significant changes in concentrations of palmitoleic acid (C16:0), linolenic acid (C18:3), and linoleic acid (C18:2), the fatty acid signatures of Azolla species. However, a reduction in protein production triggered changes in biosynthesis of alanine, arginine, leucine, tyrosine, threonine, valine, and methionine amino acids. Stress-triggered changes in key nutritional components, phenolics, lipids, proteins, and carbohydrates could have a significant impact on the nutritional value of both Azolla species, which are widely used as a sustainable food supplement for livestock, poultry, and fish industries.

High accumulation of phenolics and amino acids confers tolerance to the combined stress of cobalt and copper in barley (Hordeum vulagare)

Cobalt (Co) and copper (Cu) co-exist in the metal contaminated soils and cause the serious toxicity to crops, while their interactive effect on plant growth and development is still poorly understood. In this work, a hydroponic experiment was carried out to reveal the interactive effect of Co and Cu on photosynthesis and metabolite profiles of two barley genotypes differing in metal tolerance. The results showed that both single and combined treatments of Co and Cu caused a significant reduction in chlorophyll content and photosynthetic rate of the two barley (Hordeum vulgare) genotypes, with the effect being greater for the combined treatment and the sensitive genotype (Ea52) being more affected than the tolerant genotype (Yan66). Compared to Cu or Co treatment alone, the combined treatment significantly increased the levels of phenolic components, including cinnamic derivatives (caffeic, chlorogenic, ferullic, p-coumaric); benzoic derivatives (p-hydroxybenzoic, vanillic, syringic, sallicilic, protocatechuic acid) as well as free amino acids, with Yan66 having more accumulation than Ea52. Meanwhile, under the combined treatment, the phenylalanine ammonialyase-related gene (HvPAL) was highly regulated along with the genes involved in the synthesis of malate (HvMDH) and citrate (HvCSY), with Ya66 showing the higher expression of these genes than Ea52. It can be concluded that higher Cu and Co stress tolerance in Yan66 is attributed to more accumulation of the metabolites including phenolics and amino acids.

Identification of volatile active components in Acori Tatarinowii Rhizome essential oil from different regions in China by C6 glioma cells

Background

Acori Tatarinowii Rhizome (ATR) is a well-recognized Chinese herbal medicine prescribed to treat neurological disorders. The essential oil (ATEO) is considered as the active fraction of ATR and the content of ATEO is used as the only indicator for ATR content determination. The quality of ATEO varies widely due to region difference; however, little is known about how to study ATEO quality chemically and biologically in response to region difference. Thus, it is of great importance to identify volatile active components in ATEO to conduct quality study. In this study, we analyzed ATEO from different regions in China using chemical component analysis combined with biological activity evaluation.

Methods

GC-MS was used to obtain different volatile component profiles of ATEO and significantly changed volatile components were screened out. The neuroprotective activities of ATEO, including anti-oxidation, anti-inflammation and neurotrophic functions, were revealed in C6 glioma cells. The correlation study between the bioactivities and the components was performed.

Results

57 volatile components, including terpenoids, phenylpropanoids, aromatic compounds, and other aliphatic compounds, were identified. 8 volatile components (β-asarone, cis-methyl isoeugenol, γ-asarone, methyleugenol, calarene, longifolene, β-caryophyllene and caryophyllene oxide) from ATEO were significantly changed due to region difference and 2 of them (β-asarone and γ-asarone) showed strong correlation with neuroprotective activities.

Conclusions

Our results reveal that ATEO from different regions in China show great changes in chemical composition and biological activity. Moreover, phenylpropanoids (β-asarone and γ-asarone) present strong correlation with the bioactivities, which are considered as volatile active components in ATEO. The findings will be useful for the development of quality study of ATEO.

Plants' genetic variation approach applied to zinc contamination: secondary metabolites and enzymes of the antioxidant system in Pfaffia glomerata accessions

Zinc (Zn) is a micronutrient, but its excessive concentration can impair plant growth and development. Fertilizers, liming materials, pesticides and fungicides containing Zn have contributed to increase its concentration in agricultural soils. The aim of the present study is to evaluate the effect of Zn excess on the non-enzymatic (anthocyanin and β-ecdysone) and enzymatic (superoxide dismutase-SOD and guaiacol peroxidase-GPX) antioxidant system of two P. glomerata accessions (JB and GD) grown in hydroponic system and soil, under short- and long-term exposure times. Three Zn levels (2, 100 and 200 μM) and two short-term exposure times (7 and 14 d) were tested in the hydroponic experiment. Three Zn levels (2, 100 and 200 mg kg^-1) and two long-term exposure times (34 and 74 d) were tested in the soil experiment. The effects of Zn excess on P. glomerata accessions depended on the growth system and exposure time. Zinc excess in both tested growth systems resulted in significant change in the tissue oxidative process (MDA concentration) in both accessions, as well as broadened the antioxidant system response, which was based on antioxidant enzymes (SOD and GPX) and secondary metabolites (anthocyanins and β-ecdysone). The highest anthocyanin concentration was observed in accession JB, which was grown in hydroponics, but tissue anthocyanin concentration increased in both accessions, regardless of growth medium and exposure time. The β-ecdysone concentration in the roots increased in both accessions, but accession GD was more responsive to Zn excess. There was significant physiological variation in P.glomerata accessions in response to Zn excess.

Oxidative Stress Responses of Some Endemic Plants to High Altitudes by Intensifying Antioxidants and Secondary Metabolites Content

Most endemic plant species have limited altitudinal ranges. At higher altitudes, they are subjected to various environmental stresses. However, these plants use unique defense mechanisms at high altitudes as a convenient survival strategy. The changes in antioxidant defense system and accumulation of different secondary metabolites (SMs) were investigated as depending on altitude in five endemic endangered species (Nepeta septemcrenata, Origanum syriacum subsp. Sinaicum, Phlomis aurea, Rosa arabica, and Silene schimperiana) naturally growing in Saint Katherine protectorate (SKP). Leaves were collected from different sites between 1600 and 2200 m above sea level to assess the biochemical and physiological variations in response to high altitudes. At higher altitudes, the soil pH and micronutrient soil content decreased, which can be attributed to lower mineralization processes at lower pH. Total phenols, ascorbic acid, proline, flavonoids, and tannins increased in response to different altitudes. SMs progressively increased in the studied species, associated with a significant decrease in the levels of antioxidant enzyme activity. R. arabica, as the most threatened plant, showed the maximum response compared with other species. There was an increase in photosynthetic pigments, which was attained via the increase in chlorophyll a, chlorophyll b, and carotenoid contents. There was a significant increase in total soluble sugars and total soluble protein content in response to different altitudes. SDS-PAGE of leaf proteins showed alteration in the protein profile between different species and the same species grown at a different altitude. These five species can adapt to high-altitude habitats by various physiological mechanisms, which can provide a theoretical basis for the future conservation of these endangered endemic species in SKP.

Resemblance and Difference of Seedling Metabolic and Transporter Gene Expression in High Tolerance Wheat and Barley Cultivars in Response to Salinity Stress

To elucidate inter-specific similarity and difference of tolerance mechanism against salinity stress between wheat and barley, high tolerant wheat cv. Suntop and sensitive cv. Sunmate and tolerant barley cv. CM72 were hydroponically grown in a greenhouse with 100 mM NaCl. Glutathione, secondary metabolites, and genes associated with Na+ transport, defense, and detoxification were examined to discriminate the species/cultivar difference in response to salinity stress. Suntop and CM72 displayed damage to a lesser extent than in Sunmate. Compared to Sunmate, both Suntop and CM72 recorded lower electrolyte leakage and reactive oxygen species (ROS) production, higher leaf relative water content, and higher activity of PAL (phenylalanine ammonia-lyase), CAD (cinnamyl alcohol dehydrogenase), PPO (polyphenol oxidase), SKDH (shikimate dehydrogenase), and more abundance of their mRNA under salinity stress. The expression of HKT1, HKT2, salt overly sensitive (SOS)1, AKT1, and NHX1 was upregulated in CM72 and Suntop, while downregulated in Sunmate. The transcription factor WRKY 10 was significantly induced in Suntop but suppressed in CM72 and Sunmate. Higher oxidized glutathione (GSSG) content was accumulated in cv. CM72 and Sunmate, but increased glutathione (GSH) content and the ratio of GSH/GSSG were observed in leaves and roots of Suntop under salinity stress. In conclusion, glutathione homeostasis and upregulation of the TaWRKY10 transcription factor played a more important role in wheat salt-tolerant cv. Suntop, which was different from barley cv. CM72 tolerance to salinity stress. This new finding could help in developing salinity tolerance in wheat and barley cultivars.

Multi-Component Antioxidative System and Robust Carbohydrate Status, the Essence of Plant Arsenic Tolerance

Arsenic (As) contaminates the food chain and decreases agricultural production through impairing plants, particularly due to oxidative stress. To better understand the As tolerance mechanisms, two contrasting tobacco genotypes: As-sensitive Nicotiana sylvestris and As-tolerant N.tabacum, cv. 'Wisconsin' were analyzed. The most meaningful differences were found in the carbohydrate status, neglected so far in the As context. In the tolerant genotype, contrary to the sensitive one, net photosynthesis rates and saccharide levels were unaffected by As exposure. Importantly, the total antioxidant capacity was far stronger in the As-tolerant genotype, based on higher antioxidants levels (e.g., phenolics, ascorbate, glutathione) and activities and/or appropriate localizations of antioxidative enzymes, manifested as reverse root/shoot activities in the selected genotypes. Accordingly, malondialdehyde levels, a lipid peroxidation marker, increased only in sensitive tobacco, indicating efficient membrane protection in As-tolerant species. We bring new evidence of the orchestrated action of a broad spectrum of both antioxidant enzymes and molecules essential for As stress coping. For the first time, we propose robust carbohydrate metabolism based on undisturbed photosynthesis to be crucial not only for subsidizing C and energy for defense but also for participating in direct reactive oxygen species (ROS) quenching. The collected data and suggestions can serve as a basis for the selection of plant As phytoremediators or for targeted breeding of tolerant crops.

Genotypic variation for cadmium tolerance in common bean (Phaseolus vulgaris L.)

Given the limitation of crop production in Cd-polluted areas, the identification and selection of plant genotypes tolerant to Cd stress are of great significance. In the present work, we show the existence of genotypic variation for Cd tolerance in common bean. The laboratory screening of 25 bean genotypes indicated a significant positive correlation of the mean productivity (MP) and the geometric mean productivity (GMP) with plant fresh weight both in control and Cd-treated plants. A principal component analysis further confirmed this variation and, together with other analyses, led to the selection of genotypes G-11867, Taylor, Emerson, and D-81083 as tolerant genotypes. A total of six bean genotypes with different degrees of Cd tolerance were selected, and their long-term physiological responses to Cd (0, 45, and 90 mg/kg soil) were evaluated. Increasing Cd concentrations led to higher Cd accumulation both in roots and shoots, and to significant rises in the levels of the oxidative stress biomarkers malondialdehyde (MDA), dityrosine (D-T), and 8-hydroxy-2'-deoxyguanosine (8-OH-2'-dG). Remarkable reductions in plant hormone levels and chlorophyll contents, as well as in dry and fresh weight, were observed in Cd-treated plants. Among the examined genotypes, Emerson, Taylor, and G-11867 were found to be more tolerant to Cd owing to lower Cd accumulation and lower oxidative stress levels, as well as higher chlorophyll and hormone contents. Our results contribute to the understanding of the physiological and biochemical basis of Cd tolerance in bean plants and may therefore, be useful for breeding programs directed towards obtaining bean varieties showing low Cd accumulation.

Transcriptome profiling of Fagopyrum tataricum leaves in response to lead stress

BACKGROUND

Lead (Pb) pollution is a widespread environmental problem that is harmful to living organisms. Tartary buckwheat (Fagopyrum tataricum), a member of the family Polygonaceae, exhibits short growth cycles and abundant biomass production, could be an ideal plant for phytoremediation due to its high Pb tolerance. Here, we aimed to explore the molecular basis underlying the responses of this plant to Pb stress.

RESULTS

In our study, ultrastructural localization assays revealed that Pb ions primarily accumulate in leaf vacuoles. RNA deep sequencing (RNA-Seq) of tartary buckwheat leaves was performed on two Pb-treated samples, named Pb1 (2000 mg/kg Pb (NO₃)₂) and Pb2 (10,000 mg/kg Pb (NO₃)₂), and a control (CK). A total of 88,977 assembled unigenes with 125,203,555 bases were obtained. In total, 2400 up-regulated and 3413 down-regulated differentially expressed genes (DEGs) were identified between CK and Pb1, and 2948 up-regulated DEGs and 3834 down-regulated DEGs were generated between CK and Pb2, respectively. Gene Ontology (GO) and pathway enrichment analyses showed that these DEGs were primarily associated with 'cell wall', 'binding', 'transport', and 'lipid and energy' metabolism. The results of quantitative real-time PCR (qRT-PCR) analyses of 15 randomly selected candidate DEGs and 6 regulated genes were consistent with the results of the transcriptome analysis. Heterologous expression assays in the yeast strain Δycf1 indicated that overexpressing CCCH-type zinc finger protein 14 (ZFP14) enhanced sensitivity to Pb²⁺, while 5 other genes, namely, metal transporter protein C2 (MTPC2), phytochelatin synthetase-like family protein (PCSL), vacuolar cation/proton exchanger 1a (VCE1a), natural resistance-associated macrophage protein 3 (Nramp3), and phytochelatin synthetase (PCS), enhanced the Pb tolerance of the mutant strain.

CONCLUSION

Combining our findings with those of previous studies, we generated a schematic model that shows the metabolic processes of tartary buckwheat under Pb stress. This study provides important data for further genomic analyses of the biological and molecular mechanisms of Pb tolerance and accumulation in tartary buckwheat.

Modification of oxidative stress through changes in some indicators related to phenolic metabolism in Malva parviflora exposed to cadmium

This study was conducted to investigate the role of phenolic compounds in the antioxidant defense system in Malva parviflora L. plants treated with cadmium (Cd). After surface sterilization, the seeds were sown on seedling trays. Forty-day-old plants were then transferred to hydroponic cultures with Cd (40 μM) or without Cd (control). Some biochemical and physiological parameters were assayed on the sixth day after Cd treatment. Based on the results, the plants showed an increase in leaf soluble carbohydrates, total phenolic compounds, total flavonoids, and phenylalanine ammonia-lyase (PAL) activity at the end of the exposure period. However, length, fresh weight, chlorophyll (Chl) b, total Chl, stomatal conductance and starch content decreased under Cd treatment. There was no significant difference between the plants exposed to Cd and the control group for Chl a, SPAD index, carotenoids, and anthocyanins as well as the H₂O₂ content six days after treatment. The Cd content in the roots was considerably higher than that in the shoots. In assessing the antioxidant capacity of plant extracts, different results were observed using 1, 1-diphenyl-2-picryl-hydrazyl (DPPH) test and beta-carotene/linoleic acid bleaching assay. According to the results of this study, it seems that increased activity of PAL enzyme leads to an increase in biosynthesis of phenolic compounds in M. parviflora. This mechanism probably increases the antioxidant capacity of the plant to suppress Cd-induced toxicity and oxidative stress.

Toxicity of cadmium selenide nanoparticles on the green microalgaChlorella vulgaris: inducing antioxidative defense response

Green algae are dominant primary producers in aquatic environments. Thus, assessing the influences of pollutants such as nanoparticles on the algae is of high ecological significance. In the current study, cadmium selenide nanoparticles (CdSe NPs) were synthesized using the hydrothermal method and their characteristics were determined by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and Fourier-transform infrared spectroscopy (FT-IR) techniques. Subsequently, the toxicity of synthesized nanoparticles on the green microalga Chlorella vulgaris was investigated. The observations by SEM confirmed that exposure to CdSe NPs had severe impacts on the algal morphology. Furthermore, the obtained results revealed the toxic effect of CdSe NPs by a decrease in the number of cells. Measurement of antioxidant enzymes activity showed an increase in the activity of catalase, and a decrease in the activity of superoxide dismutase (SOD) at high concentrations of CdSe NPs. The exposure of C. vulgaris to CdSe NPs resulted also in a change in algal pigments as well as total phenol content. Taken together, CdSe NPs appeared to have significant cytotoxic effects on C. vulgaris in the applied concentrations.

The Effect of Cadmium on the Activity of Stress-Related Enzymes and the Ultrastructure of Pea Roots

The analysis of the effects of cadmium (Cd) on plant cells is crucial to understand defense mechanisms and adaptation strategies of plants against Cd toxicity. In this study, we examined stress-related enzyme activities after one and seven days of Cd application and the ultrastructure of roots of Pisum sativum L. after seven days of Cd treatment (10, 50, 100, and 200 μM CdSO4). Our results showed that phenylalanine ammonia-lyase (PAL) activity and the amount of Cd accumulated in the roots were significantly positively correlated with the Cd concentration used in our experiment. However, Cd caused a decrease of all studied antioxidative enzyme activities (i.e., catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GPX)). The analysis of the ultrastructure (TEM) showed various responses to Cd, depending on Cd concentrations. In general, lower Cd concentrations (50 and 100 μM CdSO4) mostly resulted in increased amounts of oil bodies, plastolysomes and the accumulation of starch granules in plastids. Meanwhile, roots treated with a higher concentration of Cd (200 μM CdSO4) additionally triggered protective responses such as an increased deposition of suberin lamellae in the endodermal cell walls. This indicates that Cd induces a complex defense response in root tissues.

TiO2 nanoparticles may alleviate cadmium toxicity in co-treatment experiments on the model hydrophyte Azolla filiculoides

The hydrophyte Azolla filiculoides can be a useful model to assess if TiO₂ NPs may in some way alleviate the Cd injuries and improve the ability of the plant to cope with this metal. With this mechanistic hypothesis, after a pre-treatment with TiO₂ NPs, A. filiculoides plants were transferred to cadmium-contaminated water with or without TiO₂ nanoparticles. After 5 days of treatment, cadmium uptake, morpho-anatomical, and physiological aspects were studied in plants. The continuous presence of TiO₂ nanoparticles, though not increasing the uptake of cadmium in comparison with a priming treatment, induced a higher translocation of this heavy metal to the aerial portion. Despite the translocation factor was always well below 1, cadmium contents in the fronds, generally greater than 100 ppm, ranked A. filiculoides as a good cadmium accumulator. Higher cadmium contents in leaves did not induce damages to the photosynthetic machinery, probably thanks to a compartmentalization strategy aimed at confining most of this pollutant to less metabolically active peripheral cells. The permanence of NPs in growth medium ensured a better efficiency of the antioxidant apparatus (proline and glutathione peroxidase and catalase activities) and induced a decrease in H₂O₂ content, but did not suppress TBARS level.

Plant-lead interactions: Transport, toxicity, tolerance, and detoxification mechanisms

Natural and human activities introduced an excess level of toxic lead (Pb) to the environment. Pb has no known biological significance and its interactions with plants lead to the production of reactive oxygen species (ROS). Pb and/or ROS have the potential to cause phytotoxicity by damaging the tissue ultrastructure, cellular components, and biomolecules. These damaging effects may possibly result in the inhibition of normal cellular functioning, physiological reactions, and overall plant performances. ROS play a dual role and act as a signaling molecule in plant defense system. This system encircles enzymatic and non-enzymatic antioxidative mechanisms. Catalase, superoxide dismutase, peroxidase, and enzymes from the ascorbate-glutathione cycle are the major enzymatic antioxidants, while non-enzymatic antioxidants include phenols, flavonoids, ascorbic acid, and glutathione. Pb removal from contaminated sites using plants depend on the plant's Pb accumulation capacity, Pb-induced phytotoxicity, and tolerance and detoxification mechanisms plants adopted to combat against this phytotoxicity. However, the consolidated information discussing Pb-plant interaction including Pb uptake and its translocation within tissues, Pb-mediated phytotoxic symptoms, antioxidative mechanisms, cellular, and protein metabolisms are rather limited. Thus, we aimed to present a consolidated information and critical discussions focusing on the recent studies related to the Pb-induced toxicity and oxidative stress situations in different plants. The important functions of different antioxidants in plants during Pb stress have been reviewed. Additionally, tolerance responses and detoxification mechanisms in the plant through the regulation of gene expression, and glutathione and protein metabolisms to compete against Pb-induced phytotoxicity are also briefly discussed herein.

Physiological and anthocyanin biosynthesis genes response induced by vanadium stress in mustard genotypes with distinct photosynthetic activity

The present study aimed to elucidate the photosynthetic performance, antioxidant enzyme activities, anthocyanin contents, anthocyanin biosynthetic gene expression, and vanadium uptake in mustard genotypes (purple and green) that differ in photosynthetic capacity under vanadium stress. The results indicated that vanadium significantly reduced photosynthetic activity in both genotypes. The activities of the antioxidant enzymes were increased significantly in response to vanadium in both genotypes, although the purple exhibited higher. The anthocyanin contents were also reduced under vanadium stress. The anthocyanin biosynthetic genes were highly expressed in the purple genotype, notably the genes TT8, F3H, and MYBL2 under vanadium stress. The results indicate that induction of TT8, F3H, and MYBL2 genes was associated with upregulation of the biosynthetic genes required for higher anthocyanin biosynthesis in purple compared with the green mustard. The roots accumulated higher vanadium than shoots in both mustard genotypes. The results indicate that the purple mustard had higher vanadium tolerance.

Phytoextraction potential of water fern (Azolla pinnata) in the removal of a hazardous dye, methyl violet 2B: Artificial neural network modelling

This study investigated the potential of Azolla pinnata (AP) in the removal of toxic methyl violet 2B (MV) dye wastewater using the phytoextraction approach with the inclusion of an Artificial Neural Network (ANN) modelling. Parameters examined included the effects of dye concentration, pH and plant dosage. The highest removal efficiency was 93% which was achieved at a plant dosage of 0.8 g (dye volume = 200 mL, initial pH = 6.0, initial dye concentration = 10 mg L^-1). A significant decrease in relative frond number (RFN), a growth rate estimator, observed at a dye concentration of 20 mg L^-1 MV indicated some toxicity, which coincided with the plant pigments studies where the chlorophyll a content was lower than the control. There were little differences in the plant pigment contents between the control and those in the presence of dye (5 to 15 mg L^-1) indicating the tolerance of AP to MV at lower concentrations. A three-layer ANN model was optimized (6 neurons in the hidden layer) and successfully predicted the phytoextraction of MV (R = 0.9989, RMSE = 0.0098). In conclusion, AP proved to be a suitable plant that could be used for the phytoextraction of MV while the ANN modelling has shown to be a reliable method for the modelling of phytoextraction of MV using AP.

Leaf defense system of Robinia pseudoacacia L. seedlings exposed to 3years of elevated atmospheric CO2 and Cd-contaminated soils

Short-term exposure to elevated CO₂ increases cadmium (Cd) uptake in some plant species (wheat, poplars, and willows), which triggers an increase in antioxidative system activity to deal with additional reactive oxygen species that are generated. Here, we examined leaf defenses in Robinia pseudoacacia L. seedlings exposed to elevated CO₂+Cd for 3years. Three years of elevated CO₂ decreased Cd uptake into leaves and the Cd content in soils and increased the pH of rhizosphere soil relative to ambient CO₂. In plants exposed to Cd stress, leaf chlorophyll content was greater under elevated CO₂ than under ambient CO₂. Superoxide dismutase, peroxidase, and catalase activity increased, glutathione content increased, and malondialdehyde and phytochelatins contents decreased under elevated CO₂+Cd relative to Cd alone. Proline, soluble sugars, flavonoids, saponins, and phenolic acids contents were greater under elevated CO₂+Cd than under Cd alone, and condensed tannin content was lower. Overall, long-term elevation of CO₂ enhanced the leaf defense system of R. pseudoacacia exposed to Cd by stimulating antioxidant enzyme activity, osmotic adjustment, and the production of glutathione, flavonoids and phenolic acids. Future research should focus on understanding the mechanisms involved in the decrease in Cd uptake into leaves and Cd content in soils and the increase in rhizosphere soil pH under long-term exposure to elevated CO₂.

Biochemical and Genetical Responses of Phoenix dactylifera L. to Cadmium Stress

The cadmium (Cd), a heavy metal, causes toxicity, which leads to hampering the growth and development of the plant. The molecular and biochemical approaches were used for the investigation of antioxidant system response and genotoxicity in date palm (Phoenix dactylifera L.) cv. Sagai in pot experiment having Cd. The root length was more affected than the shoot length as more accumulation of Cd occurs in roots. Fresh weights of root and shoot were reduced significantly in treated plants as compared to the control. The proline content was increased at low concentration of Cd (300 µM-CdCl2) than the medium and high concentrations (600 and 900 µM-CdCl2), respectively. The thiobarbituric acid reactive substances (TBARS) content was increased at 600 and 900 µM-CdCl2 compared to the plants treated at 300 µM-CdCl2 and controls. Antioxidant enzymatic assay was performed under Cd stress and compared with control plants. The catalase (CAT) and superoxide dismutase (SOD) activities were found to be high in plants treated with CdCl2 at 300 µM compared to at 600 and 900 µM-CdCl2, respectively. The genotoxicity of Cd was assessed using the inter-simple sequence repeat (ISSR) marker where all treated and control plants were clustered into three main groups based on genetic similarity. P. dactylifera plants were found to be more divergent at high Cd stress as compared to control and plants treated at low concentration of Cd.

Response of phenolic metabolism to cadmium and phenanthrene and its influence on pollutant translocations in the mangrove plant Aegiceras corniculatum (L.) Blanco (Ac)

Polyphenolic compounds are abundant in mangrove plants, playing a pivotal role in the detoxification of pollutants extruded from surrounding environments into plant tissues. The present study aimed to examine the variations of phenolic compounds, namely total polyphenolics, soluble tannins, condensed tannins and lignin, in the mangrove plant Aegiceras corniculatum (L.) due to the presence of exogenous cadmium and phenanthrene and to explore the influence of phenolic metabolism on biological translocation of these pollutants from roots to leaves. After a 6-week exposure to cadmium and phenanthrene, significant accumulations of both pollutants were observed. All determined phenolic compounds in both leaves and roots at high dosage levels were enhanced compared to the uncontaminated plant. Elevations of polyphenols in both treatments are possibly a result of stimulation in the activity of phenylalanine ammonia-lyase (PAL) and the enrichment of soluble sugar. Additionally, a significantly positive dosage relationship between polyphenolic metabolism intensity and phenanthrene contamination levels was found, while the trend observed in cadmium treatment was weak since cadmium at high levels inhibited phenolic production. The enrichment of polyphenols led to a decline in the biological translocation of these pollutants from roots to leaves. The immobilization of pollutants in the plant roots is possibly linked to the adsorption potential of polyphenols. These results will improve the understanding of the tolerance of mangrove plants to exogenous pollutants and will guide the selection of plants in phytoremediation because of the variability of polyphenol concentrations among species.

Response of Leptospermum scoparium, Kunzea robusta and Pinus radiata to contrasting biowastes

The myrtaceae family has a cosmopolitan distribution and includes the Australasian native species Leptospermum scoparium (mānuka) and Kunzea robusta (kānuka), which are of economic interest for the production of high-value honey and essential oils. Potentially, these species could be established on low-fertility or degraded soils that have been amended with biowastes, including biosolids and sawdust. We aimed to determine the effect of these biowastes on nitrate leaching and the growth and chemical composition of these plant species compared to Pinus radiata (pine), a common forestry species. The addition of biosolids (1250kgNha^-1 equiv.) increased the total dry biomass of mānuka, kānuka, and pine by 117, 90, and 86% respectively. Mixing sawdust with biosolids stimulated growth of mānuka (52%), kānuka (121%) but not pine. Biosolids increased plant uptake of N, P, and trace elements, but not to levels of concern. Nitrate leaching from all treatments was negligible (<2kgha^-1).

Effect of cadmium on phenolic compounds, antioxidant enzyme activity and oxidative stress in blueberry (Vaccinium corymbosum L.) plantlets grown in vitro

Cadmium (Cd(2+)) can affect plant growth due to its mobility and toxicity. We evaluated the effects of Cd(2+) on the production of phenolic compounds and antioxidant response of Vaccinium corymbosum L. Plantlets were exposed to Cd(2+) at 50 and 100µM for 7, 14 and 21 days. Accumulation of malondialdehyde (MDA), hydrogen peroxide (H2O2) and the antioxidant enzyme SOD was determined. The profile of phenolic compounds was evaluated using LC-MS. The antioxidant activity was measured using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and the ferric reducing antioxidant power test (FRAP). Cd(2+) increased the content of MDA, with the highest increase at 14 days. The presence of Cd(2+) resulted in changes in phenolic compounds. The main phenolic compound found in blueberry plantlets was chlorogenic acid, whose abundance increased with the addition of Cd(2+) to the medium. The changes in the composition of phenolic compounds showed a positive correlation with the antioxidant activity measured using FRAP. Our results suggest that blueberry plantlets produced phenolic compounds with reducing capacity as a selective mechanism triggered by the highest activity of Cd(2+).

Elevated CO2 affects secondary metabolites in Robinia pseudoacacia L. seedlings in Cd- and Pb-contaminated soils

Secondary metabolites play important roles in plant interactions with the environment. The co-occurrence of heavy metal contamination of soils and rising atmospheric CO2 has important effects on plant. It is important to explore the ways in which production of plant secondary metabolites is affected by heavy metals under elevated atmospheric CO2. We examined the effects of elevated CO2 on secondary metabolite contents in Robinia pseudoacacia seedlings grown in Cd- and lead (Pb)-contaminated soils. The increase in secondary metabolites was greater under Cd + Pb exposure than under exposure to individual metals regardless of elevated CO2 with the exception of condensed tannins in leaves and total alkaloids in stems. Except for phenolic compounds and condensed tannins, elevated CO2 was associated with increased secondary metabolite contents in leaves and stems of plants exposed to Cd, Pb, and Cd + Pb compared to plants exposed to ambient CO2 + metals. Changes in saponins in leaves and alkaloids in stems were greater than changes in the other secondary metabolites. Significant interactive effects of CO2, Cd, and Pb on secondary metabolites were observed. Saponins in leaves and alkaloids in stems were more sensitive than other secondary metabolites to elevated CO2 + Cd + Pb. Elevated CO2 could modulate plant protection and defense mechanisms in R. pseudoacacia seedlings exposed to heavy metals by altering the production of secondary metabolites. The increased Cd and Pb uptake under elevated CO2 suggested that R. pseudoacacia may be used in the phytoremediation of heavy metal-contaminated soils under global environmental scenarios.

Growth under elevated air temperature alters secondary metabolites in Robinia pseudoacacia L. seedlings in Cd- and Pb-contaminated soils

Plant secondary metabolites play a pivotal role in growth regulation, antioxidant activity, pigment development, and other processes. As the global climate changes, increasing atmospheric temperatures and contamination of soil by heavy metals co-occur in natural ecosystems, which alters the pH of rhizosphere soil and influences the bioavailability and mobility of metals. Elevated temperatures in combination with heavy metals are expected to affect plant secondary metabolites, but this issue has not been extensively examined. Here, we investigated secondary metabolites in Robiniapseudoacacia seedlings exposed to elevated temperatures using a passive warming device in combination with Cd- and Pb-contaminated soils. Heavy metals significantly stimulated the accumulation of saponins, phenolic compounds, and flavonoids in leaves and stems; alkaloid compounds increased in leaves and decreased in stems, and condensed tannins fluctuated. Elevated temperatures, alone and in combination with Cd and Pb, caused increases in secondary metabolites in the plant tissues. Phenolic compounds showed the greatest changes among the secondary metabolites and significant interactive effects of temperature and metals were observed. These results suggest that slightly elevated temperature could enhance protective and defense mechanisms of Robinia pseudoacacia seedlings exposed to heavy metals by stimulating the production of secondary metabolites.

Methyl Jasmonate Regulates Antioxidant Defense and Suppresses Arsenic Uptake in Brassica napus L

Methyl jasmonate (MJ) is an important plant growth regulator, involved in plant defense against abiotic stresses, however, its possible function in response to metal stress is poorly understood. In the present study, the effect of MJ on physiological and biochemical changes of the plants exposed to arsenic (As) stress were investigated in two Brassica napus L. cultivars (ZS 758 - a black seed type, and Zheda 622 - a yellow seed type). The As treatment at 200 μM was more phytotoxic, however, its combined application with MJ resulted in significant increase in leaf chlorophyll fluorescence, biomass production and reduced malondialdehyde content compared with As stressed plants. The application of MJ minimized the oxidative stress, as revealed via a lower level of reactive oxygen species (ROS) synthesis (H2O2 and OH(-)) in leaves and the maintenance of high redox states of glutathione and ascorbate. Enhanced enzymatic activities and gene expression of important antioxidants (SOD, APX, CAT, POD), secondary metabolites (PAL, PPO, CAD) and induction of lypoxygenase gene suggest that MJ plays an effective role in the regulation of multiple transcriptional pathways which were involved in oxidative stress responses. The content of As was higher in yellow seeded plants (cv. Zheda 622) as compared to black seeded plants (ZS 758). The application of MJ significantly reduced the As content in leaves and roots of both cultivars. Findings of the present study reveal that MJ improves ROS scavenging through enhanced antioxidant defense system, secondary metabolite and reduced As contents in both the cultivars.

Influence of combined use of iodide and compost on Hg accumulation by Lepidium sativum L

This study focuses on the influence of adding iodide (KI) and compost in different soil/compost ratios on the efficiency of Hg phytoextraction by Lepidium sativum L. Plant growth and non-enzymatic antioxidants are studied to understand metabolic plant adaptations to Hg stress during soil reclamation and their relations to Hg accumulation. Due to the use of relatively high chelant dosages in current plant-based soil remediation techniques and associated environmental risks, it is necessary to explore alternative approaches to the phytoextraction of Hg from contaminated soils. The results show a coordinated increase in non-enzymatic antioxidants in plants cultivated in growing media containing polluted soil, compost and KI. This indicates that the non-enzymatic antioxidative defence system of L. sativum L. is involved in its strategy to survive conditions of mercury-induced stress. Adding compost and iodide to Hg polluted soil also increases the total accumulation of Hg by L. sativum L. and the translocation of pollutants to aerial plant tissues. Simultaneous application of compost and KI promoted the Hg accumulation by L. sativum L. in a pot experiment.

Uptake and toxicity of arsenic, copper, and silicon in Azolla caroliniana and Lemna minor

Here we report on the analysis of two aquatic plant species, Azolla caroliniana and Lemna minor, with respect to tolerance and uptake of co-occurring arsenic, copper, and silicon for use in engineered wetlands. Plants were cultured in nutrient solution that was amended with arsenic (0 or 20 microM), copper (2 or 78 microM), and silicon (0 or 1.8 mM) either singly or in combination. We hypothesized that arsenic and copper would negatively affect the uptake of metals, growth, and pigmentation and that silicon would mitigate those stresses. Tolerance was assessed by measuring growth of biomass and concentrations of chlorophyll and anthocyanins. Both plant species accumulated arsenic, copper, and silicon; L. minor generally had higher levels on a per biomass basis. Arsenic negatively impacted A. caroliniana, causing a 30% decrease in biomass production and an increase in the concentration of anthocyanin. Copper negatively impacted L. minor, causing a 60% decrease in biomass production and a 45% decrease in chlorophyll content. Silicon augmented the impact of arsenic on biomass production in A. caroliniana but mitigated the effect of copper on L. minor. Our results suggest that mixtures of plant species may be needed to maximize uptake of multiple contaminants in engineered wetlands.

Short term exposure of Lemna minor and Lemna gibba to mercury, cadmium and chromium

The effects of mercury (Hg), cadmium (Cd) and chromium (Cr) in concentrations ranging from 0.02 to 20 mg L−1 applied for 24 h were assessed in Lemna minor and Lemna gibba by measuring changes in protein concentration, ascorbic acid, phenolics, malondialdehyde (MDA), hydrogen peroxide (H2O2), the activity of guaiacol peroxidase (G-POX) and catalase (CAT). Ascorbic acid, phenolics, catalase and guaiacol peroxidase played a key role in the antioxidative response of L. gibba. Inadequate activity of antioxidant enzymes in the L. minor resulted in MDA and H2O2 accumulation. In both used species, Hg treatment decreased protein content and increased CAT and G-POX activity, but decreased MDA and H2O2 levels. Cadmium and chromium had opposite impacts on two used Lemna species on almost all observed parameters. Enhanced antioxidative responses of L. gibba to lower concentrations of Hg, Cd and Cr indicated greater abiotic stress tolerance than L. minor.

The effect of pre-incubation of Allium cepa L. roots in the ATH-rich extract on Pb uptake and localization

The positive influence of anthocyanin (ATH) on toxic metal-treated plant material is well documented; however, it is still not explained if it is caused by changes in element absorption and distribution. Therefore, detailed analysis of the effect of the ATH-rich extract from red cabbage leaves on Pb uptake and localization at morphological, anatomical and ultrastructural level was the goal of this study. Two-day-old adventitious roots of Allium cepa L. (cv. Polanowska) were treated for 2 h with the aqueous solution of Pb(NO3)2 at the concentration of 100 μM with or without preliminary incubation in the anthocyanin-rich extract from Brassica oleracea L. var. capitata rubra leaves (250 μM, 3 h). The red cabbage extract did not change the total Pb uptake but it enhanced the translocation of accumulated metal from roots to shoots. Within the pretreated roots, more Pb was deposited in their basal part and definitely smaller amount of the metal was bound in the apoplast of the outer layers of cortex cells. The ultrastructural analysis (transmission electron microscopy and X-ray microanalysis) revealed that the ATH-rich extract lowered the number of Pb deposits in intracellular spaces, cell wall and cytoplasm of root meristematic cells as well as in such organelles important to cell metabolism as mitochondria, plastids and nucleus. The Pb deposits were preferably localised in those vacuoles where ATH also occurred. This sequestration of Pb in vacuoles is probably responsible for reduction of metal cytotoxicity and consequently could lead to better plant growth.

Lead toxicity, defense strategies and associated indicative biomarkers in Talinum triangulare grown hydroponically

Talinum species have been used to investigate a variety of environmental problems for e.g. determination of metal pollution index and total petroleum hydrocarbons in roadside soils, stabilization and reclamation of heavy metals (HMs) in dump sites, removal of HMs from storm water-runoff and green roof leachates. Species of Talinum are popular leaf vegetables having nutrient antinutrient properties. In this study, Talinum triangulare (Jacq.) Willd (Ceylon spinach) grown hydroponically were exposed to different concentrations of lead (Pb) (0, 0.25, 0.5, 0.75, 1.0 and 1.25 mM) to investigate the biomarkers of toxicity and tolerance mechanisms. Relative water content, cell death, photosynthetic pigments, sulphoquinovosyldiacylglycerol (SQDG), anthocyanins, α-tocopherol, malondialdehyde (MDA), reactive oxygen species (ROS) glutathione (GSH and GSSG) and elemental analysis have been investigated. The results showed that Pb in roots and shoots gradually increased as the function of Pb exposure; however Pb concentration in leaves was below detectable level. Chlorophylls and SQDG contents increased at 0.25 mM of Pb treatment in comparison to control at all treated durations, thereafter decreased. Levels of carotenoid, anthocyanins, α-tocopherol, and lipid peroxidation increased in Pb treated plants compared to control. Water content, cells death and elemental analysis suggested the damage of transport system interfering with nutrient transport causing cell death. The present study also explained that Pb imposed indirect oxidative stress in leaves is characterized by decreases in GSH/GSSG ratio with increased doses of Pb treatment. Lead-induced oxidative stress was alleviated by carotenoids, anthocyanins, α-tocopherol and glutathione suggesting that these defense responses as potential biomarkers for detecting Pb toxicity.

Molecular mechanism for cadmium-induced anthocyanin accumulation in Azolla imbricata

Anthocyanins inducibly synthesized by Cd treatment showed high antioxidant activity and might be involved in internal detoxification mechanisms of Azolla imbricata against Cd toxicity. In order to understand anthocyanin biosynthesis mechanism during Cd stress, the cDNAs encoding chalcone synthase (CHS) and dihydroflavonol reductase (DFR), two key enzymes in the anthocyanin synthesis pathway, were isolated from A. imbricata. Deduced amino acid sequences of the cDNAs showed high homology to the sequences from other plants. Expression of AiDFR, and to a lesser extent AiCHS, was significantly induced in Cd treatment plant in comparison with the control. CHS and DFR enzymatic activities showed similar pattern changes with these genes expression during Cd stress. These results strongly indicate that Cd induced anthocyanin accumulation is probably mediated by up-regulation of structural genes including CHS and DFR, which might further increase the activities of enzymes encoded by these structural genes that control the anthocyanin biosynthetic steps.

Phytoremediation potential of aquatic macrophyte, Azolla

Aquatic macrophytes play an important role in the structural and functional aspects of aquatic ecosystems by altering water movement regimes, providing shelter to fish and aquatic invertebrates, serving as a food source, and altering water quality by regulating oxygen balance, nutrient cycles, and accumulating heavy metals. The ability to hyperaccumulate heavy metals makes them interesting research candidates, especially for the treatment of industrial effluents and sewage waste water. The use of aquatic macrophytes, such as Azolla with hyper accumulating ability is known to be an environmentally friendly option to restore polluted aquatic resources. The present review highlights the phytoaccumulation potential of macrophytes with emphasis on utilization of Azolla as a promising candidate for phytoremediation. The impact of uptake of heavy metals on morphology and metabolic processes of Azolla has also been discussed for a better understanding and utilization of this symbiotic association in the field of phytoremediation.

Diadenosine polyphosphates (Ap3A and Ap4A) behave as alarmones triggering the synthesis of enzymes of the phenylpropanoid pathway in Arabidopsis thaliana

It is known that cells under stress accumulate various dinucleoside polyphosphates, compounds suggested to function as alarmones. In plants, the phenylpropanoid pathways yield metabolites protecting these organisms against various types of stress. Observations reported in this communication link these two phenomena and provide an example of a metabolic "addressee" for an "alarm" signaled by diadenosine triphosphate (Ap3A) or diadenosine tetraphosphate (Ap4A). In response to added Ap3A or Ap4A, seedlings of Arabidopsis thaliana incubated in full nutrition medium increased both the expression of the genes for and the specific activity of phenylalanine ammonia-lyase and 4-coumarate:coenzyme A ligase, enzymes that control the beginning of the phenylpropanoid pathway. Neither adenine mononucleotides (AMP, ADP or ATP) nor adenosine evoked such effects. Reactions catalyzed in vitro by these enzymes were not affected by Ap3A or Ap4A.

Cd, Fe, and light sensitivity: interrelationships in Cd-treated populus

Cadmium is a toxic heavy metal causing iron deficiency in the shoot and light sensitivity of photosynthetic tissues that leads to decreased photosynthetic performance and biomass production. Light intensity had strong impact on both photosynthetic activity and metal accumulation of cadmium-treated plants. At elevated irradiation, cadmium accumulation increased due to the higher dry mass of plants, but its allocation hardly changed. A considerable amount of iron accumulated in the roots, and iron concentration was higher in leaves developed at moderate rather than low irradiation. At the same time, the higher the irradiation the lower the maximal photochemical quantum efficiency. The decreased photochemical efficiency, however, started to recover after a week of Cd treatment at moderate light without substantial change in metal concentrations but following the accumulation of green fluorescent compounds. Both cadmium treatment and higher light caused the accumulation of flavonoids in leaf mesophyll vacuoles/chloroplasts, but accumulation of flavonols, fluorescing at 510 nm, was characteristic to cadmium stress. Therefore, flavonoids, which may act by scavenging reactive radicals, chelating Cd, and shielding against excess irradiation, play an important part in Cd stress tolerance of Populus, and may have special impact on its phytoremediation capacity.

Effects of Pb stress on nutrient uptake and secondary metabolism in submerged macrophyte Vallisneria natans

For better understanding the metabolic adaptations to Pb stress in submerged plants, the alterations in mineral elements uptake and in secondary metabolism were studied in leaves of Vallisneria natans (Lour.) Hara exposed to 0-100μM Pb for 0-7d. Pb content increased in leaves in a dose-dependent way. The increase of calcium, magnesium and iron content and the decrease of phosphorus, potassium and manganese content were detected in leaves of V. natans under Pb stress, while no significant changes were detected in copper and zinc concentration. Meanwhile, there was an increase in the concentrations of total phenolic and flavonoids. Pb treatment caused an increase in the catalytic activities of shikimate dehydrogenase, phenylalanine ammonialyase and polyphenol oxidase. The results suggest that nutrient uptake and secondary metabolism were actively regulated by V. natans plants in response to Pb stress.

Tolerance of Silene vulgaris to copper: population-related comparison of selected physiological parameters

Tolerance of three Slovak populations of Silene vulgaris [from the localities "Harmanec" (total soil Cu 34.1 mg kg⁻¹), "Lubietová"; (total soil Cu 831.6 mg kg⁻¹) and "Špania dolina" (total soil Cu 1368.7 mg kg⁻¹) referred as SV1, SV2, and SV3, respectively] and Silene dioica (SD; from the locality "Špania dolina") exposed to 60 μM Cu for 7 days has been studied. Respective controls with 0.21 μM Cu were also cultured. SV3 and SD contained higher total shoot Cu than SV1. Methanol-soluble shoot Cu represented 60, 59, 59, and 55% from total shoot Cu and roots contained 16.7-, 20.4-, 9.9- and 28.9-fold more Cu than shoots in SV1, SV2, SV3, and SD, respectively. Soluble proteins were the least affected in SV3 and SD when Cu-exposed and control plants were compared. Root hydrogen peroxide and superoxide showed similar trend and were correlated with enhancement of ascorbate- and guaiacol-peroxidase activities. Malondialdehyde accumulation increased in SV1 and SV2. Phenylalanine ammonia-lyase activity and total soluble phenols were higher in SV3 Cu-exposed plants compared to SV1 and SV2. Shikimate dehydrogenase activity was enhanced in all Cu-exposed populations. Cinnamyl alcohol dehydrogenase activity and root lignin content were not affected and polyphenol oxidase activity was not detected. Within 14 detected free amino acids, majority of them decreased preferentially in the roots. Only serine increased in shoots and decreased in roots of all populations. Potassium content was not affected in SV3. Na, Ca, and Fe increased in roots of Cu-exposed plants of all populations, while Mg was the least affected and Zn increased in SV2 and SV3 shoots and roots. This study revealed the highest tolerance in population from the locality with the highest soil Cu content. Present findings as complex metabolic responses to Cu stress with special emphasis on phenolic metabolism are discussed.

The contents of risk elements, arsenic speciation, and possible interactions of elements and betalains in beetroot (Beta vulgaris, L.) growing in contaminated soil

The effect of enhanced soil risk element contents on the uptake of As, Cd, Pb, and Zn was determined in two pot experiments. Simultaneously, transformation of arsenic and its compounds in beetroot (Beta vulgaris L.) plants was investigated. The mobile fractions of elements were determined in 0.05 mol L−1 (NH4)2SO4 extracts and did not exceed 2% of total soil arsenic, 9% of total cadmium, 3% of total lead, and 8% of total zinc, respectively. Although the soils were extremely contaminated the mobile portions of the elements represented only a small fragment of the total element content. Arsenic contents in beet plants reached up to 25 mg As kg−1 in roots and 48 mg As kg−1 in leaves in the soil characterized by the highest mobile arsenic portion. Arsenic portions extractable with water and phosphate buffer from the beetroot samples did not show significant differences between the extraction agents but the extractability was affected by the arsenic concentration. Arsenic was almost quantitatively extractable from the samples with the lowest total arsenic concentration, whereas in the samples with the highest total arsenic concentration less than 25% was extractable. Arsenate was the dominant arsenic compound in the extracts (70% in phosphate buffer, 50% in water extracts). A small portion of dimethylarsinic acid, not exceeding 0.5%, was detected only in the sample growing in the soil with the highest arsenic concentration. The role of betalains (betanin, isobetanin, vulgaxanthin I and vulgaxanthin II) in transformation/detoxification of arsenic in plants was not confirmed in this experiment because the plants were able to grow in the contaminated soil without any symptoms of arsenic toxicity.

Seasonal variability of physiological and biochemical aspects of chromium accumulation in outdoor-grown Salvinia minima

Seasonal variations in physiological and biochemical parameters of the aquatic fern Salvinia minima exposed to different Cr(VI) concentrations were studied. Growth, photosynthetic pigments, soluble carbohydrates, sucrose-related enzymes, lipid peroxidation, phenolics, and Cr accumulation in floating and submerged leaves were analyzed. Cr content was lower in winter than in summer, indicating that active metabolic events occurred in metal uptake. Leaf number and metal concentration factor were higher in summer than in winter. Relative growth rate (R(n)) indicated that growth was more affected by Cr in winter than in summer. Biochemical parameters showed great seasonal variations under increasing Cr. Hexose, starch, malondialdehyde and phenolic contents were greatest in winter, but R(n) and protein values were lowest. Sucrose content was highest in summer floating leaves. A great seasonal variability was observed in sucrose-related enzymes with the highest activities occurring in winter lipoxygenase was much higher in winter than in summer, indicating a strong lipid peroxidation. Results indicate that in Salvinia Cr causes seasonal perturbations in carbohydrate metabolism and oxidative stress by altering both sucrose-related enzymes and lipoxygenase activities. Variability in physiological and biochemical parameters seems to indicate that in outdoor conditions different mechanisms, in terms of Cr accumulation and tolerance, may occur in S. minima during summer and winter.

Recent developments in the application of proteomics to the analysis of plant responses to heavy metals

Pollution of soils by heavy metals is an ever-growing problem throughout the world, and is the result of human activities as well as geochemical weathering of rocks and other environmental causes such as volcanic eruptions, acid rain and continental dusts. Plants everywhere are continuously exposed to metal-contaminated soils. The uptake of heavy metals not only constrains crop yields, but can also be a major hazard to the health of humans and to the entire ecosystem. Although analysis of gene expression at the mRNA level has enhanced our understanding of the response of plants to heavy metals, many questions regarding the functional translated portions of plant genomes under metal stress remain unanswered. Proteomics offers a new platform for studying complex biological functions involving large numbers and networks of proteins, and can serve as a key tool for revealing the molecular mechanisms that are involved in interactions between toxic metals and plant species. This review focuses on recent developments in the applications of proteomics to the analysis of the responses of plants to heavy metals; such studies provide a deeper understanding of protein responses and the interactions among the possible pathways that are involved in detoxification of toxic metals in plant cells. In addition, the challenges faced by proteomics in understanding the responses of plants to toxic metal are discussed, and some possible future strategies for meeting these challenges are proposed.