Nickel accumulation and its effect on growth, physiological and biochemical parameters in millets and oats

Elevated CO2 differentially attenuates beryllium-induced oxidative stress in oat and alfalfa

Elevated CO2 (eCO2 ) is one of the climate changes that may benefit plant growth under emerging soil contaminants such as heavy metals. In this regard, the morpho-physiological mechanisms underlying the mitigating impact of eCO2 on beryllium (Be) phytotoxicity are poorly known. Hence, we investigated eCO2 and Be interactive effects on the growth and metabolism of two species from different groups: cereal (oat) and legume (alfalfa). Be stress significantly reduced the growth and photosynthetic attributes in both species, but alfalfa was more susceptible to Be toxicity. Be stress induced reactive oxygen species (ROS) accumulation by increasing photorespiration, subsequently resulting in increased lipid and protein oxidation. However, the growth inhibition and oxidative stress induced by Be stress were mitigated by eCO2 . This could be explained, at least partially, by the increase in organic acids (e.g., citric acid) released into the soil, which subsequently reduced Be uptake. Additionally, eCO2 reduced cellular oxidative damage by reducing photorespiration, which was more significant in alfalfa plants. Furthermore, eCO2 improved the redox status and detoxification processes, including phytochelatins, total glutathione and metallothioneins levels, and glutathione-S-transferase activity in both species, but to a greater extend in alfalfa. In this context, eCO2 also stimulated anthocyanin biosynthesis by accumulating its precursors (phenylalanine, coumaric acid, cinnamic acid, and naringenin) and key biosynthetic enzymes (phenylalanine ammonia-lyase, cinnamate hydroxylase, and coumarate:CoA ligase) mainly in alfalfa plants. Overall, this study explored the mechanistic approach by which eCO2 alleviates the harmful effects of Be. Alfalfa was more sensitive to Be stress than oats; however, the alleviating impact of eCO2 on Be stress was more pronounced in alfalfa.

Geranium robertianum L. tolerates various soil types burdened with heavy metals

Many heavy metals (HMs) are essential micronutrients for the growth and development of plants. However, human activities such as mining, smelting, waste disposal, and industrial processes have led to toxic levels of HMs in soil. Fortunately, many plant species have developed incredible adaptive mechanisms to survive and thrive in such harsh environments. As a widespread and ruderal species, Geranium robertianum L. inhabits versatile soil types, both polluted and unpolluted. Considering the ubiquity of G. robertianum, the study aimed to determine whether geographically distant populations can tolerate HMs. We collected soil and plant samples from serpentine, an anthropogenic heavy metal contaminated, and a non-metalliferous site to study the physiological state of G. robertianum. HMs in soil and plants were determined using flame atomic absorption spectrometry. Spectrophotometric methods were used to measure the total content of chlorophylls a and b, total phenolics, phenolic acids, flavonoids, and proline. Principal component analysis (PCA) was used to investigate the potential correlation between HMs concentrations gathered from various soil types and plant samples and biochemical data acquired for plant material. A statistically significant difference was observed for all localities regarding secondary metabolite parameters. A positive correlation between Ni and Zn in soil and Ni and Zn in plant matter was observed (p<0.0005) indicating higher absorption. Regardless of high concentrations of heavy metals in investigated soils, G. robertianum displayed resilience and was capable of thriving. These results may be ascribed to several protective mechanisms that allow G. robertianum to express normal growth and development and act as a pioneer species.

Modulation in the enzymatic antioxidants, MDA level and elicitation in conessine biomolecule in Holarrhena pubescens (medicinal tree) cultures exposed to different heavy metals: Ni, Co, Cr and As

Nodal explants of Holarrhena pubescens, an important medicinal tree, were cultured on Murashige and Skoog's medium (MS) containing 15 µM BA (control) alone and on medium supplemented with different concentrations (0, 1, 5, 25, 50, 100 and 200 mg/L) of heavy metals such as NiCl2, CoCl2, As2O3 and CrO3 to study their toxic effect. After 28 days of treatments, the nodal segments were harvested to assess the average number of shoots per explants, average shoot length, malondialdehyde content, proline content, conessine accumulation and antioxidant enzymatic activity. Among all the metals tried, best morphogenic response was achieved at 5 mg/L CrO3 where 80% culture differentiated an average of 3.21 ± 0.08 shoots per explant having 0.95 ± 0.018 cm average shoot length. Highest concentration (200 mg/L) of all the heavy metals proved lethal for morphogenesis. Maximum inhibition in average shoot number and average shoot length was observed in nodal explants treated with 25 mg/L As2O3 where an average of 0.49 ± 0.047 shoots having an average shoot length of 0.3 ± 0.02 cm. Contrarily, addition of heavy metals in culture medium proved strong elicitors, exhibiting significant enhancement in the biosynthesis of conessine, an important bioactive compound. HPLC analysis of the crude extract of in vitro grown untreated nodal cultures revealed an average of 117.06 ± 2.59 µg/g d. w. of conessine, whereas those treated with 100 mg/L of CoCl2 accounted for 297.1 ± 7.76 µg/g d. w. (an increase of 156% over control). Among the heavy metals tried, CoCl2 proved to be the best for conessine enhancement which was in the order of CoCl2 > Cr2O3 > NiCl2 > As2O3 in the nodal explants. Concomitantly, MDA content, the antioxidant enzymes activities of catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GR) and ascorbate peroxidase (APX) were also observed to be differentially expressed with the increase in the heavy metals concentration from 1 to 200 mg/L. Free proline, too, increased up to 3.5-fold over control. The results obtained during the present investigation revealed that the overall response of the nodal explants in terms of morphogenesis, conessine content and antioxidant enzyme activities was metal specific as well as dose dependent.

Hormetic dose responses induced by nickel oxide nanoparticles (NiONPs) on growth, biochemical, and antioxidant defense systems of Dracocephalum kotschyi

The application of nickel oxide nanoparticles (NiONPs) in various fields leads to their release into soil and water and, consequently, interaction with plants. Unlike its bulk counterpart, the phytotoxic potential of NiONPs is relatively less studied, particularly in a hormesis framework. Hormesis is an interesting phenomenon characterized by low-dose stimulation and high-dose inhibition. Therefore, this study demonstrates the stimulatory and inhibitory effects of NiONPs on Dracocephalum kotschyi Boiss as a medicinal plant cultivated in a pot experiment carried out in a greenhouse for 3 weeks. High bioaccumulation of nickel (Ni) in roots of treated plants relative to shoots indicates higher oxidative damage. NiONPs induced hormetic effects on photosynthetic pigments, as at low concentration of 50 mg/L stimulated chlorophyll (2.8-46.7%), carotenoid (16%), and anthocyanin (5.9%) contents and at higher concentrations inhibited the content of these pigments. A hormetic response was observed in growth parameters, i.e., NiONPs induced shoot height (7.2%) and weight (33%) at 100 mg/L, while inhibited shoot and root length (14.5-16.1% and 28.7-42.7%) and weight (46.8-48.1% and 37-40.6%), respectively, at 1000 and 2500 mg/L. The treated plants declined the toxic effects and oxidative stress caused by NiONPs by activating non-enzymatic antioxidants (phenolic compounds and proline) and enzymatic antioxidants, i.e., increasing the levels of SOD, POD, CAT, and APX. Therefore, the present study investigated for the first time the different mechanisms and responses of D. kotschyi plants to NiONPs in a wide range of concentrations. The results suggest that NiONPs may act as an elicitor at lower concentrations in medicinal plants according to specific conditions. However, these NPs at higher concentrations induce oxidative stress and harmful effects on plants, so their use poses serious risks to human health and the environment.

Nickel (Ni) phytotoxicity and detoxification mechanisms: A review

Scientists studying the environment, physiology, and biology have been particularly interested in nickel (Ni) because of its dual effects (essentiality and toxicity) on terrestrial biota. It has been reported in some studies that without an adequate supply of Ni, plants are unable to finish their life cycle. The safest Ni limit for plants is 1.5 μg g^-1, while the limit for soil is between 75 and 150 μg g^-1. Ni at lethal levels harms plants by interfering with a variety of physiological functions, including enzyme activity, root development, photosynthesis, and mineral uptake. This review focuses on the occurrence and phytotoxicity of Ni with respect to growth, physiological and biochemical aspects. It also delves into advanced Ni detoxification mechanisms such as cellular modifications, organic acids, and chelation of Ni by plant roots, and emphasizes the role of genes involved in Ni detoxification. The discussion has been carried out on the current state of using soil amendments and plant-microbe interactions to successfully remediate Ni from contaminated sites. This review has identified potential drawbacks and difficulties of various strategies for Ni remediation, discussed the importance of these findings for environmental authorities and decision-makers, and concluded by noting the sustainability concerns and future research needs regarding Ni remediation.

Positive Tetrahydrocurcumin-Associated Brain-Related Metabolomic Implications

Tetrahydrocurcumin (THC) is a metabolite of curcumin (CUR). It shares many of CUR's beneficial biological activities in addition to being more water-soluble, chemically stable, and bioavailable compared to CUR. However, its mechanisms of action have not been fully elucidated. This paper addresses the preventive role of THC on various brain dysfunctions as well as its effects on brain redox processes, traumatic brain injury, ischemia-reperfusion injury, Alzheimer's disease, and Parkinson's disease in various animal or cell culture models. In addition to its strong antioxidant properties, the effects of THC on the reduction of amyloid β aggregates are also well documented. The therapeutic potential of THC to treat patterns of mitochondrial brain dysmorphic dysfunction is also addressed and thoroughly reviewed, as is evidence from experimental studies about the mechanism of mitochondrial failure during cerebral ischemia/reperfusion injury. THC treatment also results in a dose-dependent decrease in ERK-mediated phosphorylation of GRASP65, which prevents further compartmentalization of the Golgi apparatus. The PI3K/AKT signaling pathway is possibly the most involved mechanism in the anti-apoptotic effect of THC. Overall, studies in various animal models of different brain disorders suggest that THC can be used as a dietary supplement to protect against traumatic brain injury and even improve brain function in Alzheimer's and Parkinson's diseases. We suggest further preclinical studies be conducted to demonstrate the brain-protective, anti-amyloid, and anti-Parkinson effects of THC. Application of the methods used in the currently reviewed studies would be useful and should help define doses and methods of THC administration in different disease conditions.

Toxicity and tolerance of nickel in sunflower (Helianthus annuus L.)

This study aimed at exploration of nickel (Ni) application (0, 10, 20, 30, and 40 mg L^-1) on physiological and biochemical attributes of sunflower cultivars (Hysun-33 and SF-187) grown in sand culture. Results revealed a significant decrease in vegetative parameters in both sunflower cultivars by increasing Ni concentration, although low levels of Ni (10 mg L^-1) improved growth attributes to some extent. Among photosynthetic attributes, 30 and 40 mg L^-1 Ni application severely reduced the photosynthetic rate (A), stomatal conductance (g_s), water use efficiency (WUE), and Ci/Ca ratio but improved the transpiration rate (E) in both sunflower cultivars. The same level of Ni application also reduced leaf water potential, osmotic potentials, and relative water contents but increased leaf turgor potential and membrane permeability. At low level (10 and 20 mg L^-1), Ni improved the soluble proteins, while high Ni concentration decreased it. The opposite was true for total free amino acids and soluble sugars. To conclude, the high Ni concentration in various plant organs had a strong impact with the changes in vegetative growth, physiological and biochemical attributes. A positive correlation of growth, physiological, water relations, and gas exchange parameters at low levels of Ni and negative correlation at higher Ni level confirmed that the supplementation of low Ni levels greatly modulated studied attributes. Based on observed attributes, Hysun-33 showed high tolerance to Ni stress as compared to SF-187.

Comparative assessment of the heavy metal phytoextraction potential of vegetables from agricultural soils: A field experiment

A field study was established to determine the phytoextraction potential of six vegetable species, namely Amaranthus viridis L., Basella alba L., Brassica chinensis var. Parachinensis, Brassica rapa L., Capsicum frutescens L., and Ocimum tenuiflorum L.. These edible plants were selected for their short growth cycles and high biomass production, which are some traits for efficient phytoremediation. Following acid digestion of the soil and vegetable samples using the USEPA 3050B acid digestion method, the extracts were analyzed for Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn using ICP-OES. Results in soil samples showed that the concentrations of both beneficial and essential heavy metals, and non-essential heavy metals are below the WHO, USEPA, and CCME soil quality guidelines. Al is one of the highest concentrations found in the soil samples but it tends to accumulate in the root part of all vegetable species compared to the aboveground parts. In general, B. rapa L. accumulated the highest level of Cd (0.4 mg/kg) and Pb (5.71 mg/kg), while B. alba L. accumulated the highest Cr (2.62 mg/kg) in all plant parts. The findings in this study indicated that Co, Cu, Fe, Mn and Zn were mostly accumulated in leaves of A. viridis L. (Co, Cu, Fe, Mn and Zn), B. alba L. (Co, Fe and Mn), B. chinensis (Mn and Zn) and O. tenuiflorum L. (Mn), and roots of C. frutescens L. (Co, Cu, Fe and Mn), B. alba L. (Co, Cu and Zn), A. viridis L. and B. chinensis (Cu and Fe) and B. rapa L. (Fe). Cr, Pb and Ni were significantly greater in B. alba L. (Cr) And B. rapa L. (Ni and Pb) roots. MTF >1 was observed in the roots of all species for Co, Cd, Zn, and Ni. BTC values varied between the different vegetable species with A. viridis L. having the greatest heavy metal mobility between its plant parts and the best heavy metal phytoextraction potential among other species. The PCA biplots showed that heavy metals were partitioned differently between various plant parts of the vegetable species and can be explained by the first two components (PC1 and PC2) which were associated with the root and/or leaf parts for most vegetable species.

A Multi-Method Approach for Impact Assessment of Some Heavy Metals on Lactuca sativa L

Heavy metals represent a large category of pollutants. Heavy metals are the focus of researchers around the world, mainly due to their harmful effects on plants. In this paper, the influence of copper, cadmium, manganese, nickel, zinc and lead, present in soil in different concentrations (below the permissible limit, the maximum permissible concentration and a concentration higher than the maximum permissible limit) on lettuce (Lactuca sativa L.) was evaluated. For this purpose, the authors analyzed the variation of photosynthetic pigments, total polyphenols, antioxidant activity and the elemental content in the studied plants. The experimental results showed that the variation of the content of biologically active compounds, elemental content and the antioxidant activity in the plants grown in contaminated soil, compared to the control plants, depends on the type and concentration of the metal added to the soil. The biggest decrease was recorded for plants grown in soil treated with Ni I (-42.38%) for chlorophyll a, Zn II (-32.92%) for chlorophyll b, Ni I (-40.46%) for carotenoids, Pb I (-40.95%) for polyphenols and Cu III (-29.42%) for DPPH. On the other hand, the largest increase regarding the amount of biologically active compounds was registered for Mn I (88.24%) in the case of the chlorophyll a, Mn I (65.56%) for chlorophyll b, Pb I (116.03%) for carotenoids, Ni III (1351.23%) for polyphenols and Ni III (1149.35%) for DPPH.

Application of nickel chitosan nanoconjugate as an antifungal agent for combating Fusarium rot of wheat

Agro-researchers are endlessly trying to derive a potential biomolecule having antifungal properties in order to replace the application of synthetic fungicides on agricultural fields. Rot disease often caused by Fusarium solani made severe loss of wheat crops every year. Chitosan and its metallic nano-derivatives hold a broad-spectrum antifungal property. Our interdisciplinary study deals with the application of nickel chitosan nanoconjugate (NiCNC) against Fusarium rot of wheat, in comparison with chitosan nanoparticles (CNPs) and commercial fungicide Mancozeb. CNPs and NiCNC were characterized on the basis of UV–Vis spectrophotometry, HR-TEM, FESEM, EDXS and FT-IR. Both CNPs and NiCNC were found effective against the fungal growth, of which NiCNC at 0.04 mg/mL showed complete termination of F. solani grown in suitable medium. Ultrastructural analysis of F. solani conidia treated with NiCNC revealed pronounced damages and disruption of the membrane surface. Fluorescence microscopic study revealed generation of oxidative stress in the fungal system upon NiCNC exposure. Moreover, NiCNC showed reduction in rot disease incidence by 83.33% of wheat seedlings which was further confirmed through the observation of anatomical sections of the stem. NiCNC application helps the seedling to overcome the adverse effect of pathogen, which was evaluated through stress indices attributes.

Algal consortia based metal detoxification of municipal wastewater: Implication on photosynthetic performance, lipid production, and defense responses

The present investigation was carried out to assess the competence of artificially engineered microalgal consortia i.e. consortia 1 (Scenedesmus vacuolatus + Chlorococcum humicola), consortia 2 (Tetradesmus sp. + Scenedesmus vacuolatus), and consortia 3 (Chlorococcum humicola + Scenedesmus vacuolatus + Tetradesmus sp.) for municipal wastewater treatment and lipid production under laboratory conditions. The purpose of the present study was to screen the competent microalgae consortia based on wastewater remediation, photosynthetic performance, and antioxidant defense responses. The outcome based on nutrient reutilization (78.98-98%), metal detoxification (50-94%), and biomass production (1.43-1.65 folds) reflected greater adaptability and tolerance of consortia 2 against different concentrations of wastewater. The photosynthetic performance parameters such as active photosystem II reaction centre, the quantum yield, and photosynthetic performance index were increased by 1.20-2.35 folds in consortia 2 after treatment with different concentrations of wastewater. Additionally, Fourier transform infrared spectroscopy peak showed at 1750 cm^-1 confirmed neutral lipid accumulation in consortia 2 at 100% concentration of wastewater. The measurement of oxidative stress markers such as thiobarbituric acid reactive species and hydrogen peroxide showed considerable decline in consortia 2 as compared to consortia 1 and 3. Interestingly, increased non-enzymatic (1.02-2.44 folds) and enzymatic antioxidant (1.05-4.14 folds) activity in consortia 2 reflected that oxidative stress was attenuated by the amplified activity of ascorbic acid, proline, cysteine, superoxide dismutase, catalase, and glutathione reductase. Overall, photosynthetic performance, lipid production, and antioxidants activity represented that the consortia 2 can be effectively used for sustainable wastewater treatment and lipid production. Thus, the synergistic association of two microalgae may be the superior and neoteric paradigm with multilevel benefits such as sustainable nutrient resource utilization, metal detoxification, and lipid production.

Arbuscular Mycorrhizal Fungi Are an Influential Factor in Improving the Phytoremediation of Arsenic, Cadmium, Lead, and Chromium

The increasing expansion of mines, factories, and agricultural lands has caused many changes and pollution in soils and water of several parts of the world. In recent years, metal(loid)s are one of the most dangerous environmental pollutants, which directly and indirectly enters the food cycle of humans and animals, resulting in irreparable damage to their health and even causing their death. One of the most important missions of ecologists and environmental scientists is to find suitable solutions to reduce metal(loid)s pollution and prevent their spread and penetration in soil and groundwater. In recent years, phytoremediation was considered a cheap and effective solution to reducing metal(loid)s pollution in soil and water. Additionally, the effect of soil microorganisms on increasing phytoremediation was given special attention; therefore, this study attempted to investigate the role of arbuscular mycorrhizal fungus in the phytoremediation system and in reducing contamination by some metal(loid)s in order to put a straightforward path in front of other researchers.

Physiological and Gene Expression Responses of Six Annual Ryegrass Cultivars to Cobalt, Lead, and Nickel Stresses

Heavy metals negatively affect soil quality and crop growth. In this study, we compared the tolerance of six ryegrass cultivars to cobalt (Co²⁺), lead (Pb²⁺), and nickel (Ni²⁺) stresses by analyzing their physiological indexes and transcript levels of genes encoding metal transporters. Compared with the other cultivars, the cultivar Lm1 showed higher germination rates and better growth under Co²⁺, Pb²⁺, or Ni²⁺ treatments. After 48 h of Co²⁺ treatment, the total antioxidant capacity of all six ryegrass cultivars was significantly increased, especially that of Lm1. In contrast, under Pb²⁺ stress, total antioxidant capacity of five cultivars was significantly decreased, but that of Lm1 was unaffected at 24 h. Staining with Evans blue dye showed that the roots of Lm1 were less injured than were roots of the other five ryegrass cultivars by Co²⁺, Pb²⁺, and Ni²⁺. Lm1 translocated and accumulated lesser Co²⁺, Pb²⁺, and Ni²⁺ than other cultivars. In Lm1, genes encoding heavy metal transporters were differentially expressed between the shoots and roots in response to Co²⁺, Pb²⁺, and Ni²⁺. The aim of these researches could help find potential resource for phytoremediation of heavy metal contamination soil. The identified genes related to resistance will be useful targets for molecular breeding.

Accumulation and Effect of Heavy Metals on the Germination and Growth of Salsola vermiculata L. Seedlings

The influence of different concentrations of heavy metals (Cu, Mn, Ni, Zn) was analyzed in the Salsola vermiculata germination pattern, seedling development, and accumulation in seedlings. The responses to different metals were dissimilar. Germination was only significantly reduced at Cu and Zn 4000 μM but Zn induced radicle growth at lower concentrations. Without damage, the species acted as a good accumulator and tolerant for Mn, Ni, and Cu. In seedlings, accumulation increased following two patterns: Mn and Ni, induced an arithmetic increase in content in tissue, to the point where the content reached a maximum; with Cu and Ni, the pattern was linear, in which the accumulation in tissue was directly related to the metal concentration in the medium. Compared to other Chenopodiaceae halophyte species, S. vermiculata seems to be more tolerant of metals and is proposed for the phytoremediation of soils contaminated by heavy metals.

Nickel stress-tolerance in plant-bacterial associations

Nickel (Ni) is an essential element for plant growth and is a constituent of several metalloenzymes, such as urease, Ni-Fe hydrogenase, Ni-superoxide dismutase. However, in high concentrations, Ni is toxic and hazardous to plants, humans and animals. High levels of Ni inhibit plant germination, reduce chlorophyll content, and cause osmotic imbalance and oxidative stress. Sustainable plant-bacterial native associations are formed under Ni-stress, such as Ni hyperaccumulator plants and rhizobacteria showed tolerance to high levels of Ni. Both partners (plants and bacteria) are capable to reduce the Ni toxicity and developed different mechanisms and strategies which they manifest in plant-bacterial associations. In addition to physical barriers, such as plants cell walls, thick cuticles and trichomes, which reduce the elevated levels of Ni entrance, plants are mitigating the Ni toxicity using their own antioxidant defense mechanisms including enzymes and other antioxidants. Bacteria in its turn effectively protect plants from Ni stress and can be used in phytoremediation. PGPR (plant growth promotion rhizobacteria) possess various mechanisms of biological protection of plants at both whole population and single cell levels. In this review, we highlighted the current understanding of the bacterial induced protective mechanisms in plant-bacterial associations under Ni stress.

Effect of silicon on the young maize plants exposed to nickel stress

Nickel (Ni) is involved in several physiological processes in plants but its excess in environment has many phytotoxic effects. Silicon (Si), an element required for optimal plant performance, has been shown to have beneficial effects for plants coping with various types of stresses. Here we studied the alleviative potential of Si (2.5 mM) added to hydroponically grown maize (Zea mays L.) plants under Ni (100 μM) stress. Ni decreased most of the growth parameters, total chlorophyll (Chl) and leaf relative water content (RWC), and catalase (CAT; EC 1.11.1.6) activity, while leaf water loss (LWL), contents of proline (Pro), hydrogen peroxide (H₂O₂) and ascorbate (AsA), membrane lipid peroxidation and activities of peroxidase (POX; EC 1.11.1.7) and superoxide dismutase (SOD; EC 1.15.1.1) were increased. Supplementation of Si to Ni-treated plants enhanced the leaf area, Chl content, RWC, CAT and POX (only in younger leaf) activities and decreased LWL, the contents of Pro (in younger leaf), H₂O₂ (roots) and AsA, lipid peroxidation and POX and SOD activities. We may conclude that Si mitigated the Ni-induced stress in maize by amelioration of the leaf water deficient status (Pro, RWC, LWL), enhancing membrane stability (MDA) and influencing enzymatic (SOD, POX, CAT) and non-enzymatic (Pro, AsA) defence systems. The increased Chl content and leaf area improve overall plant performance.

Multiple effects of silicon on alleviation of nickel toxicity in young maize roots

Although beneficial metalloid silicon (Si) has been shown to alleviate the toxicity of various heavy metals, there is a lack of knowledge about the role of Si in possible alleviation of phytotoxicity caused by excess of essential nickel (Ni). In the present study we investigated the growth and biomass production, reactive oxygen species (ROS) formation and activities of selected antioxidants, as well as combined effect of Ni and Si on the integrity of cell membranes and electrolyte leakage in young maize roots treated for 24, 48 and 72 h with excess of Ni and/or Si. By histochemical methods we also visualized Ni distribution in root tissues and compared the uptake of Ni and Si with the development of root apoplasmic barriers. Ni enhanced the root lignification and suberization and shifted the development of apoplasmic barriers towards the root tip. Similarly, localization of Ni correlated with lignin and suberin deposition in root endodermis, further supporting the barrier role of this tissue in Ni uptake. Si reversed the negative impact of Ni on root anatomy. Additionally, improved cell membrane integrity, and enhanced ascorbate-based antioxidant system might be the mechanisms how Si partially mitigates the deleterious effects of Ni excess in maize plants.

Exploring the genetic variability and diversity of pearl millet core collection germplasm for grain nutritional traits improvement

Improving essential nutrient content in staple food crops through biofortification breeding can overcome the micronutrient malnutrition problem. Genetic improvement depends on the availability of genetic variability in the primary gene pool. This study was aimed to ascertain the magnitude of variability in a core germplasm collection of diverse origin and predict pearl millet biofortification prospects for essential micronutrients. Germplasm accessions were evaluated in field trials at ICRISAT, India. The accessions differed significantly for all micronutrients with over two-fold variation for Fe (34-90 mg kg^-1), Zn (30-74 mg kg^-1), and Ca (85-249 mg kg^-1). High estimates of heritability (> 0.81) were observed for Fe, Zn, Ca, P, Mo, and Mg. The lower magnitude of genotype (G) × environment (E) interaction observed for most of the traits implies strong genetic control for grain nutrients. The top-10 accessions for each nutrient and 15 accessions, from five countries for multiple nutrients were identified. For Fe and Zn, 39 accessions, including 15 with multiple nutrients, exceeded the Indian cultivars and 17 of them exceeded the biofortification breeding target for Fe (72 mg kg^-1). These 39 accessions were grouped into 5 clusters. Most of these nutrients were positively and significantly associated among themselves and with days to 50% flowering and 1000-grain weight (TGW) indicating the possibility of their simultaneous improvement in superior agronomic background. The identified core collection accessions rich in specific and multiple-nutrients would be useful as the key genetic resources for developing biofortified and agronomically superior cultivars.

Vermicompost improves maize, millet and sorghum growth in iron mine tailings

The Fundão dam was designed to store iron mine tailings in the region of Mariana, MG, Brazil. When it ruptured, the tailings overflowed. These tailings affected the soil due to the formation of a thick crust as a result of drying (compaction) and hindered the natural revegetation process. In this context, the use of organic fertilizers, including vermicompost, is method of reducing the physical limitations on root growth caused by soil properties and changing soil-metal interactions. For this reason, vermicompost was added to iron mine tailings, and its morphological and physiological effects on maize, millet and sorghum plants were studied. The experiment was conducted in a greenhouse using 6 dm³ pots. The plants were subjected to three treatments: mine tailings, mine tailings + vermicompost, and a reference soil. From the V3 stage onwards, biweekly growth, leaf gas exchange and chlorophyll fluorescence evaluations were performed. At the end of the experiment, dry biomass and metal, macro- and micronutrient contents were quantified, and the root morphology was evaluated. The tailings created physical limitations on root growth and had low nutrient content as well as high concentrations of chromium, iron and manganese. The addition of vermicompost favored increases in shoot and root dry biomass, increases in root length, volume, surface area and diameter, and the absorption of macro- and micronutrients, which was reflected in the growth of the studied species. In addition, vermicompost led to greater investment in thick and very thick roots, and in general, the plants showed no symptoms of metal toxicity. Considering the characteristics of the studied tailings, it can be concluded that vermicompost favors the growth of plant species and may be a viable method for beginning the recovery process in areas containing iron mine tailings.

Ethephon mitigates nickel stress by modulating antioxidant system, glyoxalase system and proline metabolism in Indian mustard

The role of ethylene (through application of ethephon) in the regulation of nickel (Ni) stress tolerance was investigated in this study. Ethephon at concentration of 200 µl l^-1 was applied to mustard (Brassica juncea) plants grown without and with 200 mg kg^-1 soil Ni to study the increased growth traits, biochemical attributes, photosynthetic efficiency, nutrients content, activities of antioxidants such as superoxide dismutase, ascorbate peroxidase, glutathione reductase, and glutathione peroxidase, glyoxalase systems and enhanced the proline metabolism. In the absence of ethephon, Ni increased oxidative stress with a concomitant decrease in photosynthesis, growth and nutrients content. However, application of ethephon positively increased growth traits, photosynthetic parameters, nutrients content and also elevated the generation of antioxidants enzymes and glyoxalase systems, proline production to combat oxidative stress. Plants water relations and cellular homeostasis were maintained through increased photosynthetic efficiency and proline production. This signifies the role of ethylene in mediating Ni tolerance via regulating proline production and photosynthetic capacity. Ethephon can be used as an exogenous supplement on plants to confer Ni tolerance. The results can be exploited to develop tolerance in plants via gene editing technology encoding enzymes responsible for proline synthesis, antioxidant defence, glyoxalase systems and photosynthetic effectiveness.

Assessing chromium pollution and natural stabilization processes in agricultural soils by bulk and micro X-ray analyses

A combined approach based on multiple X-ray analytical techniques and conventional methods was adopted to investigate the distribution and speciation of Cr in a polluted agricultural soil, from the bulk-scale down to the (sub)micro-level. Soil samples were collected from two different points, together with a control sample taken from a nearby unpolluted site. The bulk characterization revealed that the polluted soils contained much higher concentrations of organic matter (OM) and potentially toxic elements (PTE) than the control. Chromium was the most abundant PTE (up to 5160 g kg^-1), and was present only as Cr(III), as its oxidation to Cr(VI) was hindered by the high OM content. According to sequential extractions, Cr was mainly associated to the soil oxidisable fraction (74%) and to the residual fraction (25%). The amount of Cr potentially bioavailable for plant uptake (DTPA-extractable) was negligible. Characterization of soil thin sections by micro X-ray fluorescence (μXRF) and field emission scanning electron microscopy coupled with microanalysis (FEGSEM-EDX) showed that Cr was mainly distributed in aggregates ranging from tens micrometres to few millimetres in size. These aggregates were coated with an aluminosilicate layer and contained, in the inner part, Cr, Ca, Zn, P, S and Fe. Hyperspectral elaboration of μXRF data revealed that polluted soils were characterised by an exogenous organic-rich fraction containing Cr (not present in the control), and an endogenous aluminosilicate fraction (present also in the control), coating the Cr-containing aggregates. Analyses by high-resolution micro X-ray computed tomography (μCT) revealed a different morphology of the soil aggregates in polluted soils compared with the control. The finding of microscopic leather residues, combined with the results of bulk- and micro-characterizations, suggested that Cr pollution was likely ascribable to soil amendment with tannery waste-derived matrices. However, over the years, a natural process of Cr stabilization occurred in the soil thus reducing the environmental risks.

Structural Adaptation and Physiological Mechanisms in the Leaves of Anthyllis vulneraria L. from Metallicolous and Non-Metallicolous Populations

Calamine wastes highly contaminated with trace metals (TMs) are spontaneously inhabited by a legume plant Anthyllis vulneraria L. This study determined an adaptation strategy of metallicolous (M) A. vulneraria and compared it with that of the non-metallicolous (NM) ecotype. We hypothesized that TMs may lead to (i) leaf apoplast modifications and (ii) changes in the antioxidant machinery efficiency that facilitate plant growth under severe contamination. To verify our hypothesis, we implemented immunolabelling, transmission electron microscopy and biochemical measurements. NM leaves were larger and thicker compared to the M ecotype. Microscopic analysis of M leaves showed a lack of dysfunctions in mesophyll cells exposed to TMs. However, changes in apoplast composition and thickening of the mesophyll and epidermal cell walls in these plants were observed. Thick walls were abundant in xyloglucan, pectins, arabinan, arabinogalactan protein and extensin. The tested ecotypes differed also in their physiological responses. The metallicolous ecotype featured greater accumulation of photosynthetic pigments, enhanced activity of superoxide dismutase and increased content of specific phenol groups in comparison with the NM one. Despite this, radical scavenging activity at the level of 20% was similar in M and NM ecotypes, which may implicate effective reduction of oxidative stress in M plants. In summary, our results confirmed hypotheses and suggest that TMs induced cell wall modifications of leaves, which may play a role in metal stress avoidance in Anthyllis species. However, when TMs reach the protoplast, activation of antioxidant machinery may significantly strengthen the status of plants naturally growing in TM-polluted environment.

A multivariate analysis of comparative effects of heavy metals on cellular biomarkers of phytoremediation using Brassica oleracea

The biochemical/physiological variations in plant responses to heavy metals stress govern plant's ability to phytoremediate/tolerate metals. So, the comparative effects of different types of heavy metals on various plant responses can better elucidate the mechanisms of metal toxicity and detoxification. This study compared the physiological modifications, photosynthetic performance and detoxification potential of Brassica oleracea under different levels of chromium (Cr), nickel (Ni) and selenium (Se). All the heavy metals induced a severe phytotoxicity to B. oleracea in terms of chlorophyll contents, Ni being the most toxic (76% decrease). Brassica oleracea showed high lipid oxidation: 87% and 273%, respectively in leaves and roots. Furthermore, all the metals increased the activities of catalase and peroxidase, while decreased superoxide dismutase and ascorbate peroxidase. Interestingly, heavy metals decreased hydrogen peroxide contents perhaps due to their possible transformation to another form of reactive oxygen species such as hydroxyl radical. Among the three metals, Ni was more phytotoxic than Cr and Se. Moreover, the phytoremediation/tolerance potential of B. oleracea to Ni, Cr and Se stress varied with the type of metal, their applied levels, response variables and plant organ type (root/shoot). The multivariate analysis separated different plant response variables and heavy metal treatments into different groups based on their correlations.

Salicylic acid enhances nickel stress tolerance by up-regulating antioxidant defense and glyoxalase systems in mustard plants

The present study identified inverse relationships between nickel (Ni) levels and growth, photosynthesis and physio-biochemical attributes, but increasing levels of Ni stress enhanced methylglyoxal, electrolyte leakage, hydrogen peroxide, and lipid peroxidation content. Exogenous application of salicylic acid (SA) (10^-5 M) ameliorated the ill-effects of Ni by restoring growth, photosynthesis and physio-biochemical attributes and increasing the activities of enzymes associated with antioxidant systems, especially the ascorbate-glutathione (AsA-GSH) cycle and glyoxalase system. In addition, SA application to Ni-stressed plants had an additive effect on the activities of the ascorbate and glutathione pools, and the AsA-GSH cycle enzymes (ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, glutathione reductase), superoxide dismutase, catalase, glutathione S-transferase, and osmolyte biosynthesis). This trend also follows in glyoxalase system viz. glyoxalase I and glyoxalase II enzymes. Nevertheless, exogenous SA supplementation restored mineral nutrient contents. Principal component analysis showed that growth, photosynthesis, and mineral nutrient parameters were positively correlated with each other and negatively correlated with antioxidant enzymes and oxidative stress biomarkers. Hence, SA is an alternative compound with potential application in the phytoremediation of Ni.

Nickel Carcinogenesis Mechanism: DNA Damage

Nickel (Ni) is known to be a major carcinogenic heavy metal. Occupational and environmental exposure to Ni has been implicated in human lung and nasal cancers. Currently, the molecular mechanisms of Ni carcinogenicity remain unclear, but studies have shown that Ni-caused DNA damage is an important carcinogenic mechanism. Therefore, we conducted a literature search of DNA damage associated with Ni exposure and summarized known Ni-caused DNA damage effects. In vitro and vivo studies demonstrated that Ni can induce DNA damage through direct DNA binding and reactive oxygen species (ROS) stimulation. Ni can also repress the DNA damage repair systems, including direct reversal, nucleotide repair (NER), base excision repair (BER), mismatch repair (MMR), homologous-recombination repair (HR), and nonhomologous end-joining (NHEJ) repair pathways. The repression of DNA repair is through direct enzyme inhibition and the downregulation of DNA repair molecule expression. Up to now, the exact mechanisms of DNA damage caused by Ni and Ni compounds remain unclear. Revealing the mechanisms of DNA damage from Ni exposure may contribute to the development of preventive strategies in Ni carcinogenicity.

The potential of an energy crop "Conocarpus erectus" for lead phytoextraction and phytostabilization of chromium, nickel, and cadmium: An excellent option for the management of multi-metal contaminated soils

Past studies have thoroughly explored the phytoextraction/phytostabilization potentials of different plant species for particular metals. However, none of the plants was able to tackle the problem of multi-metal in contaminated soils. We report herewith the potential of Conocarpus erectus to extract lead (Pb) while having the capability to stabilize chromium (Cr), nickel (Ni) and cadmium (Cd) in polluted soil. The C. erectus was subjected to grow for 120 days in a soil spiked with four different levels of each metal i.e. Pb (0, 600, 1200 and 2400 mg kg^-1), Ni (0, 50, 100 and 200 mg kg^-1), Cr (0, 150, 300 and 600 mg kg^-1) and Cd (0, 20, 40 and 80 mg kg^-1). Data related to plant growth, physiology, biochemistry and antioxidants activities revealed that forenamed parameters were significantly reduced with increasing spiking levels. Contrarily, metal speciation in plant parts (metal concentrations in shoots and roots, and metal contents in these corresponding plant parts), metal removal per pot, and DTPA-extractable metals from the soil were significantly increased with increasing spiking level upon the termination of the experiment. Curiously, each spiking level demonstrated elevated Pb concentrations in shoots than roots, while the concentrations of other metals (Cr, Ni, and Cd) were found higher in roots than in the shoots. Likewise, at each spiking level, C. erectus showed both bioconcentration factor (BCF) and translocation factor (TF) values greater than 1 for Pb, while these values were ever lower than 1 for Cr, Ni, and Cd. Moreover, the percentages of Pb removal were ever higher than other metals at each spiking level. Outcomes of our experiment suggest that C. erectus has immense potential for the phytoextraction of Pb and phytostabilization of Cr, Ni, and Cd in polluted soil. It is suggested that this plant can be used to tackle the problem of multi-metal pollution in soils.

Evaluation of the protective role of exogenous growth regulators against Ni toxicity in woody shrub Daphne jasminea

The results provide a significant verification of the activity of exogenously applied phytohormones: gibberellic acid, jasmonic acid, and brassinolide in the modulation of the plant's response to nickel treatment. The study investigated nickel accumulation and its toxicity to Daphne jasminea shoots cultured in vitro with or without exogenous supplementation with phytohormones: gibberellic acid (GA3), jasmonic acid (JA), and brassinolide (BL). The aim was to verify the modulatory effect of exogenous plant growth regulators (PGRs) on plant reaction to Ni excess. The combined action of Ni and PGRs was evaluated at the anatomical, ultrastructural, and biochemical levels. Nickel toxicity was manifested in decreased biomass accretion and growth tolerance index (83-53.6%), attributed to enhanced synthesis of growth inhibitors, mainly abscisic acid. As a defence reaction, endogenous gibberellins accumulated. Exogenous GA3 ameliorated the plant reaction to Ni stress, inducing proliferation and growth rate. Ni tolerance in the presence of GA3 was attributed to peroxisomal reactions that stimulated the synthesis of endogenous JA. In contrast, the application of BL caused enhanced Ni accumulation. Plants suffered from pronounced stress due to massive oxidation. The defence strategy of plants subjected to Ni and BL involved cell wall rearrangements. Exogenous JA stimulated the synthesis of active auxins and salicylic acid, contributing to enhanced mitotic activity within explants. However, JA disturbed the integrity of chloroplasts and lamellar compartments. Our study revealed that an action of exogenous PGRs may either enhance tolerance to Ni or increase metal toxicity in D. jasminea. Particularly in in vitro culture, where explants are subjected to external phytohormonal stimuli, the combined effects of supplemental PGRs may enhance stress and substantially affect plant development. Our results provide a significant verification of exogenous PGRs activity in the modulation of plant response to nickel.

Identification of suitable internal control genes for transcriptional studies in Eleusine coracana under different abiotic stress conditions

Finger millet [Eleusine coracana (L.) Gaertn] is an excellent food and forage crop of arid and semiarid areas in Africa and Asia. It is well adapted to drought, heat, high salinity, poor soil fertility and low pH with an efficient C₄ carbon fixation mechanism for high yield potential. To normalize the target gene expression data, the identification of suitable reference genes is essential. Ten candidate reference genes were selected and their expression stability was analyzed in various samples treated with different abiotic stress conditions. Five different statistical algorithms: geNorm, NormFinder, BestKeeper, ΔCt, and RefFinder were used to determine the stability of these genes. Our results revealed GAPDH, EEF1a, ACT and CYC as highly stable reference genes and PP2A and eIF4A as least stable reference genes across all the samples and suggesting that these genes could be used for accurate transcript normalization under abiotic stress. To the best of our knowledge, this is the first report on identification of suitable reference genes for accurate transcript normalization using qRT-PCR in finger millet under abiotic stress.

Arbuscular mycorrhizal fungi alleviate the heavy metal toxicity on sunflower (Helianthus annuus L.) plants cultivated on a heavily contaminated field soil at a WEEE-recycling site

An 8-week pot experiment was conducted to investigate the growth and responses of sunflower (Helianthus annuus L.) to arbuscular mycorrhizal (AM) fungal inoculations on a heavily heavy metal (HM)-contaminated (H) soil and a lightly HM-enriched (L) soil, both of which were collected from a waste electrical and electronic equipment (WEEE)-recycling site. Compared with the L soil, the H soil induced significantly larger (P<0.05) concentrations of Cd, Cu, Pb, Cr, Zn and Ni in sunflower (except for root Cr and shoot Ni), which impaired the thylakoid lamellar folds in leaves. The biomasses and P concentrations of shoots and roots, as well as the total P acquisitions per pot were all significantly decreased (P<0.05). Both Funneliformis mosseae (Fm) and F. caledonium (Fc) inoculation significantly increased (P<0.05) root mycorrhizal colonization. For the L soil, AM fungal inoculations had no significant effects on the soil-plant system, except for a decrease of soil pH and increases of soil available P and DTPA-extractable Zn concentrations with the Fm-inoculated treatment. For the H soil, however, AM fungal inoculations significantly increased (P<0.05) the biomasses and P concentrations of shoots and roots, as well as the total P acquisitions per pot, and significantly reduced (P<0.05) the concentrations of HMs in shoots (except for Cu and Pb with Fm- and Fc- inoculated treatments, respectively) and alleviated the toxicity symptoms of HMs in thylakoid structure of leaves. AM fungal inoculations in the H soil also significantly increased (P<0.05) the shoot uptake of HMs (except for Cr), and tended to decrease the total concentrations of HMs in soils. This suggests the potential application of AM fungi for both reducing HM stress and promoting phytoextraction of HM-contaminated soils caused by WEEE recycling.

Tetrahydrocurcumin Provides Neuroprotection in Experimental Traumatic Brain Injury and the Nrf2 Signaling Pathway as a Potential Mechanism

The protective effect of tetrahydrocurcumin (THC) after experimental traumatic brain injury (TBI) has been demonstrated, as demonstrated by the inhibition of oxidative stress, mitochondrial dysfunction, and apoptosis. However, the mechanisms underlying this effect are still not well understood. This study was to investigate the neuroprotective effects of THC, and its potential mechanisms, in a rat model of TBI. To this end, rats were divided into 4 groups: the sham group, the TBI group, the TBI + vehicle (V) group, and the TBI + THC group. THC or V was administered via intraperitoneal injection to rats in the TBI + V and TBI + THC groups 30 min after TBI. After euthanasia (24 h after TBI), neurological scores, brain water content, and neuronal cell death in the cerebral cortex were recorded. Brain samples were collected after neurological scoring for further analysis. THC treatment alleviated brain edema, attenuated TBI-induced neuronal cell apoptosis, and improved neurobehavioral function. In addition, NFE2-related factor 2 (Nrf2) expression was upregulated following TBI. These results suggest that THC improves neurological outcome after TBI, possibly by activating the Nrf2 signaling pathway.