Influence of nickel stress on growth and some important physiological/biochemical attributes in some diverse canola (Brassica napus L.) cultivars

Salicylic acid and jasmonic acid-mediated different fate of nickel phytoremediation in two populations of Alyssum inflatum Nyár

This study investigates Ni phytoremediation and accumulation potential in the presence of salicylic acid (SA) (0, 50 and 200 μM) and jasmonic acid (JA) (0, 5 and 10 μM) in two populations of Alyssum inflatum under various nickel (Ni) doses (0, 100 and 400 μM). By measuring Ni levels in the shoots and roots, values of bioaccumulation coefficient (BAC), biological concentration factor (BCF) and translocation factor (TF) were calculated to quantify Ni accumulation and translocation between plant organs. Additionally, the amounts of histidine (His), citric acid (CA) and malic acid (MA) were explored. The results showed that plant dry weight (DW) [in shoot (29.8%, 8.74%) and in root (21.6%, 24.4%)] and chlorophyll [a (17.1%, 32.5%), b (10.1%, 30.9%)] declined in M and NM populations respectively, when exposed to Ni (400 μM). Conversely, the levels of MA [in shoot (37.0%, 32.0%) and in root (25.5%, 21.2%)], CA [in shoot (17.0%, 10.0%) and in root (47.9%, 37.2%)] and His [in shoot (by 1.59- and 1.34-fold) and in root (by 1.24- and 1.18-fold)] increased. Also, in the presence 400 μM Ni, the highest accumulation of Ni was observed in shoots of M (1392 μg/g DW) and NM (1382 μg/g DW). However, the application of SA and JA (especially in Ni 400 μM + SA 200 μM + JA 5 and 10 μM treatments) mitigated the harmful impact of Ni on physiological parameters. Also, a decreasing trend was observed in the contents of MA, CA, and His. The reduction of these compounds as important chelators of Ni caused a decrease in root-to-shoot Ni transfer and reducing accumulation in the shoots of both populations. The values of phytoremediation indices in both populations exposed to Ni (400 μM) were above one. In presence of the SA and JA, these indices showed a decreasing trend, although the values remained above one (BAC, BCF and TF > 1). Overall, the results indicated that SA and JA can reduce phytoremediation potential of the two populations through different mechanisms.

Genetic architecture of tuber-bound free amino acids in potato and effect of growing environment on the amino acid content

Free amino acids in potato tubers contribute to their nutritional value and processing quality. Exploring the natural variation in their accumulation in tubers across diverse genetic backgrounds is critical to potato breeding programs aiming to enhance or partition their distribution effectively. This study assessed variation in the tuber-bound free amino acids in a diversity panel of tetraploid potato clones developed and maintained by the Texas A&M Potato Breeding Program to explore their genetic basis and to obtain genomic-estimated breeding values for applied breeding purposes. Free amino acids content was evaluated in tubers of 217 tetraploid potato clones collected from Dalhart, Texas in 2019 and 2020, and Springlake, Texas in 2020. Most tuber amino acids were not affected by growing location, except histidine and proline, which were significantly lower (- 59.0%) and higher (+ 129.0%), respectively, at Springlake, Texas (a location that regularly suffers from abiotic stresses, mainly high-temperature stress). Single nucleotide polymorphism markers were used for genome-wide association studies and genomic selection of clones based on amino acid content. Most amino acids showed significant variations among potato clones and moderate to high heritabilities. Principal component analysis separated fresh from processing potato market classes based on amino acids distribution patterns. Genome-wide association studies discovered 33 QTL associated with 13 free amino acids. Genomic-estimated breeding values were calculated and are recommended for practical potato breeding applications to select parents and advance clones with the desired free amino acid content.

Effect of exogenous taurine on growth, oxidative defense, and nickel (Ni) uptake in canola (Brassica napus L.) under Ni stress

Nickel (Ni) contamination and its associated hazardous effects on human health and plant growth are ironclad. However, the potential remedial effects of taurine (TAU) on Ni-induced stress in plants remain obscure. Therefore, the present study was undertaken to examine the effect of TAU seed priming (100 and 150 mg L‒1) as an alleviative strategy to circumvent the phytotoxic effects of Ni (150 mg kg‒1) on two canola cultivars (Ni-tolerant cv. Shiralee and Ni-sensitive cv. Dunkeld). Our results manifested an apparent decline in growth, biomass, photosynthetic pigments, leaf relative water content, DPPH free radical scavenging activity, total soluble proteins, nitrate reductase activity, and nutrient acquisition (N, P, K, Ca) under Ni toxicity. Further, Ni toxicity led to a substantial increase in oxidative stress reflected as higher levels of superoxide radicals (O2•‒) and hydrogen peroxide (H2O2) alongside increased relative membrane permeability, lipoxygenase (LOX) activity, and Ni accumulation in leaves and roots. However, TAU protected canola plants from Ni-induced oxidative damage through the amplification of hydrogen sulfide (H2S) production that intensified the antioxidant system to avert O2•‒, H2O2, and malondialdehyde (MDA) production. Further, TAU-mediated increase in H2S levels maintained membrane integrity that might have improved ionomics and bettered plant growth under Ni toxicity.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01359-9.

Mixing tannery effluent had fertilizing effect on growth, nutrient accumulation, and photosynthetic capacity of some cucurbitaceous vegetables: A little help from foe

Tannery effluent contains a number of organic and inorganic elements as pollutants which reduce plant growth. To overcome shortage of water, use of diluted industrial wastewater such as tannery effluent can be a viable strategy for improving crop growth and yield. A pot experiment was conducted to determine the effects of tannery effluent and its various dilutions on physiological and biochemical characteristics of five cucurbitaceous vegetables. Tannery effluent was applied 0, 25, 50, 75 and 100% to 3-week-old plants of five cucurbitaceous vegetables (Cucurbita maxima, Luffa cylindrica, Citrullus vulgaris, Cucumis melo, and Praecitrullus fistulosus) for 4 weeks. Tannery effluent reduced the growth of all five cucrbitaceous vegetables. Diluted tannery effluent (25%) improved the growth of Cucurbita maxima, Citrullus vulgaris, and Cucumis melo. Moderately diluted (50%) did not affect the growth of Citrullus vulgaris and Cucumis melo. Toxic effects of tannery effluent were associated with high accumulation of heavy metals Cr, Cd, Mn, and Fe in leaves and roots. High accumulation of heavy metals in leaves reduced the accumulation of nutrients in leaves (N, P, K) and reduced photosynthetic pigments and photosynthetic rate. Changes in photosynthetic rates of all vegetable species due to tannery effluent were not associated with stomatal limitations (stomatal conductance, transpiration rate, internal CO₂). Toxic effects of tannery effluent on plants also include changes in N-metabolism (amino acid and protein). However, extent of these adverse effects of tannery effluent on vegetables was species specific. It is suggested that Cucurbita maxima can be grown by supplying 25% tannery effluent, whereas Citrullus vulgaris and Cucumis melo can be grown with moderately diluted (50%) tannery effluent.

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.

Assessing the effects of nickel on, e.g., Medicago sativa L. nodules using multidisciplinary approach

Industrial wastes and fertilizers can introduce excessive levels of nickel (Ni) into the environment, potentially causing threats to plants, animals, as well as human beings. However, the number of studies on the effects of Ni toxicity on nodules is fairly limited. To address this issue, the effects of increasing Ni concentration on alfalfa nodules were assessed at chemical, biochemical, and transcriptomic levels. For this purpose, plants were grown in soils supplied with Ni (control, 0 mg/kg; C1, 50 mg/kg; C2, 150 mg/kg; C3, 250 mg/kg; and C4, 500 mg/kg) for 90 days. Ni loads in leaves, roots, and nodules were monitored after the exposure period. A set of biochemical biomarkers of oxidative stress was determined in nodules including antioxidants and metal homeostasis as well as lipid peroxidation. Gene expression levels of the main targets involved in oxidative stress and metal homeostasis were assessed. Our data indicated a high concentration of Ni in leaves, roots, and nodules where values reached 25.64 ± 3.04 mg/kg, 83.23 ± 5.16 mg/kg, and 125.71 ± 4.53 mg/kg in dry weight, respectively. Moreover, a significant increase in nodule biomass was observed in plants exposed to C4 in comparison to control treatment and percentage increased by 63%. Then, lipid peroxidation increased with a rate of 95% in nodules exposed to C4. Enzymatic activities were enhanced remarkably, suggesting the occurrence of oxidative stress, with increased superoxide dismutase (SOD), glutathione reductase (GR), and ascorbate peroxidase (APX). Our results showed also a significant upregulation of SOD, GR and APX genes in nodules. Nodule homoglutathione (HGSH) levels increased with the different Ni concentrations, with a remarkable decrease of glutathione S-transferase (GST) activity and glutathione (GSH) content for the highest Ni concentration with 43% and 52% reduction, respectively. The phytochelatin (PC) and metallothionein (MT) concentrations increased in nodules, which implied the triggering of a cellular protection mechanism for coping with Ni toxicity. The results suggested that Ni promotes a drastic oxidative stress in alfalfa nodules, yet the expression of MT and PC to reduce Ni toxicity could be used as Ni stress bioindicators. Our findings provide new insights into the central role of alfalfa nodules in limiting the harmful effects of soil pollution. Therefore, nodules co-expressing antioxidant enzymes may have high phytoremediation potential.

Interaction between zinc and selenium bio-fortification and toxic metals (loid) accumulation in food crops

Biofortification is the supply of micronutrients required for humans and livestock by various methods in the field, which include both farming and breeding methods and are referred to as short-term and long-term solutions, respectively. The presence of essential and non-essential elements in the atmosphere, soil, and water in large quantities can cause serious problems for living organisms. Knowledge about plant interactions with toxic metals such as cadmium (Cd), mercury (Hg), nickel (Ni), and lead (Pb), is not only important for a healthy environment, but also for reducing the risks of metals entering the food chain. Biofortification of zinc (Zn) and selenium (Se) is very significant in reducing the effects of toxic metals, especially on major food chain products such as wheat and rice. The findings show that Zn- biofortification by transgenic technique has reduced the accumulation of Cd in shoots and grains of rice, and also increased Se levels lead to the formation of insoluble complexes with Hg and Cd. We have highlighted the role of Se and Zn in the reaction to toxic metals and the importance of modifying their levels in improving dietary micronutrients. In addition, cultivar selection is an essential step that should be considered not only to maintain but also to improve the efficiency of Zn and Se use, which should be considered more climate, soil type, organic matter content, and inherent soil fertility. Also, in this review, the role of medicinal plants in the accumulation of heavy metals has been mentioned, and these plants can be considered in line with programs to improve biological enrichment, on the other hand, metallothioneins genes can be used in the program biofortification as grantors of resistance to heavy metals.

Brassica Species in Phytoextractions: Real Potentials and Challenges

The genus Brassica is recognized for including species with phytoaccumulation potential and a large amount of research has been carried out in this area under a variety of conditions, from laboratory experiments to field trials, with spiked or naturally contaminated soils, using one- or multi-element contaminated soil, generating various and sometimes contradictory results with limited practical applications. To date, the actual field potential of Brassica species and the feasibility of a complete phytoextraction process have not been fully evaluated. Therefore, the aim of this study was to summarize the results of the experiments that have been performed with a view to analyzing real potentials and limitations. The reduced biomass and low metal mobility in the soil have been addressed by the development of chemically or biologically assisted phytoremediation technologies, the use of soil amendments, and the application of crop management strategies. Certain issues, such as the fate of harvested biomass or the performance of species in multi-metal-contaminated soils, remain to be solved by future research. Potential improvements to current experimental settings include testing species grown to full maturity, using a greater amount of soil in experiments, conducting more trials under real field conditions, developing improved crop management systems, and optimizing solutions for harvested biomass disposal.

Organic and inorganic amendments for the remediation of nickel contaminated soil and its improvement on Brassica napus growth and oxidative defense

In-situ stabilization has been considered an effective way to remediate metal contaminated soil. Thus, pot experiments were undertaken to investigate the effectiveness of multiple stabilization agents such as biochar (BC), mussel shell (MS), zeolite (ZE) and limestone (LS) on the immobilization of Ni, physicochemical features and enzyme activities in polluted soil. Results showed that the sole application of Ni adversely affected the rapeseed growth, photosynthetic pigments, and antioxidative defense. However, the addition of amendments to the contaminated soil significantly reduced Ni bioavailability. The XRD analysis confirmed the formation of Ni related ligands and FTIR showed the presence of hydroxyl, carboxyl and sulfur functional groups, as well as complexation and adsorption of Ni on amendments. Among multiple amendments, biochar significantly enhanced plant biomass attributes and total chlorophyll content. Moreover, addition of amendments also strengthened the antioxidant defense by decreasing Ni induced oxidative stress (H₂O₂ and O₂^.-), increased macronutrient availability, reduced Ni uptake and improved soil health. The qPCR analysis showed that the Ni transporters were significantly suppressed by amendments, which is correlated with the lower accumulation of Ni in rapeseed. The present study showed that immobilizing agents, especially biochar, is an effective amendment to immobilize Ni in soil, which restricts its entry into the food chain.

Cadmium, chromium, nickel and nitrate accumulation in wheat (Triticum aestivum L.) using wastewater irrigation and health risks assessment

The wastewater utilization for irrigation purposes is common practice in peri-urban areas located in vicinity of developed cities. This water contains elements like chromium (Cr), nickel (Ni), cadmium (Cd) and nitrate (NO₃-N) that poses health risk when exposed to human. In this study effect of wastewater irrigation from Chakara wastewater plant, Faisalabad on growth of wheat and health risks was assessed. Pot experiment was conducted at Institute of Soil and Environmental, University of Agriculture, Faisalabad using different concentration of wastewater as treatment 100% tap water, 25% wastewater + 75% tap water, 50% wastewater + 50% tap water, 75% wastewater + 25% tap water, 100% wastewater. The results indicated that the wastewater irrigation negatively effects the plant growth and physiological parameters. The minimum plant height, grain weight, spike length, osmotic potential and SPAD values were recorded 50.33 cm, 1.47 g plant^-1, 7.00 cm, 423 and 38.91 respectively in 100% wastewater irrigation. The risk quotient (RQ _TEs) for each toxic element and cumulative risk index (RI _TEs) values were calculated. The cadmium risk quotient (Cd _RQ) for adults was on margin and value was >1 for in 75% wastewater + 25% tap water and 100% wastewater irrigation, while the RQ for Ni and Cr was <1. Maximum RI _TEs values calculated in 100% wastewater irrigation 0.424 and 0.294 for children and adults respectively. Hence it was concluded that wastewater irrigation significantly increased the accumulation rate of metals and nitrate in wheat and cause potential health risks for children and adults.

Metabolic modifications to Ni excess in L. minor: Role of organic-, amino- and fatty acid profiles

In this study, the effects of excess nickel (Ni) (100 μM and 200 μM) on growth, antioxidant production, fatty acid, organic and amino acids profiles were examined in Lemna minor L. After 7 days of Ni treatment, chlorosis, growth inhibition and ROS overproduction were observed, accompanied by Ni accumulation. Interestingly, decreased malondialdehyde (MDA) levels were recorded in fronds upon Ni exposure. Fatty acid profiles in Ni-treated L. minor were characterized by increases in saturated- and decreases in unsaturated fatty acids. Ni excess increased the activities of antioxidant enzymes such as superoxide dismutase (SOD), guiacol peroxidase (GPX), and glutathione reductase (GR), and non-enzymatic antioxidants such as glutathione (GSH) and ascorbic acid (AsA); however, deactivation of ascorbate peroxidase (APX) and catalase (CAT) activities were also observed. Disruption of amino acid metabolism in Ni-exposed fronds was evidenced by the accumulation of cysteine, arginine, threonine, valine, isoleucine, leucine, lysine and phenylalanine, as well as reduced levels of tyrosine, alanine, aspartate and proline. Approximately 299%-396%, 139%-254% and 56%-97% concentration increments in citric, malic and oxalic acids, respectively, were concomitantly observed with significant decreases in tartaric, acetic, and fumaric acids in fronds subjected to Ni stress. Taken together, these results indicated that Ni stress induced negative effects on plant physiological, biochemical and morphological processes; however, it is likely that the coordination of metabolites and antioxidants may ameliorate the damaging effects of Ni accumulation.

Nickel toxicity in plants: reasons, toxic effects, tolerance mechanisms, and remediation possibilities-a review

Nickel (Ni) is a naturally occurring metal, but anthropogenic activities such as industrialization, use of fertilizers, chemicals, and sewage sludge have increased its concentration in the environment up to undesirable levels. Ni is considered to be essential for plant growth at low concentration; however, Ni pollution is increasing in the environment, and therefore, it is important to understand its functional roles and toxic effects on plants. This review emphasizes the environmental sources of Ni, its essentiality, effects, tolerance mechanisms, possible remediation approaches, and research direction that may help in interdisciplinary studies to assess the significance of Ni toxicity. Briefly, Ni affects plant growth both positively and negatively, depending on the concentration present in the growth medium. On the positive side, Ni is essential for normal growth, enzymatic activities (e.g., urease), nitrogen metabolism, iron uptake, and specific metabolic reactions. On the negative side, Ni reduces seed germination, root and shoot growth, biomass accumulation, and final production. Moreover, Ni toxicity also causes chlorosis and necrosis and inhibits various physiological processes (photosynthesis, transpiration) and cause oxidative damage in plants. The threat associated with Ni is increased as Ni concentration increases day by day in the environment, particularly in soils; therefore, it would be hazardous for crop production in the near future. Additionally, the lack of information regarding the mechanisms of Ni tolerance in plants further intensifies this situation. Therefore, future research should be focused on approachable and prominent solutions in order to minimize the entry of Ni into our ecosystems.

Physiological response and mineral elements accumulation pattern in Sesuvium portulacastrum L. subjected in vitro to nickel

Sesuvium portulacastrum, a halophyte with high tolerance to heavy metals like Cd, Pb and Ni is considered for phytoremediation of metal contaminated saline soils. The tolerance to a selected metal ion could, by hypothesis, be stimulated through in vitro adaptation and regeneration of the plant. Seedlings obtained by in vitro micro-propagation, were exposed to 0, 25 and 50 μM Ni, as NiCl₂, in agar-based medium for 30 days. Growth parameters, plant water content, the concentration of photosynthetic pigments, proline and malondialdehyde (MDA) concentrations were determined. Nickel and nutrients distribution in leaves was studied by micro-Proton-Induced-X-ray-Emission (μ-PIXE). The results showed that Ni was mainly accumulated in vascular bundles, next in water storage tissues and chlorenchyma. Ni concentrations in chlorenchyma increased with increasing Ni in culturing medium, in direct relation to decrease of photosynthetic pigments and increase of oxidative stress. As compared to control plants, Ni induced substantial increase in MDA and proline accumulation. Plants exposed to 50 μM Ni accumulated up to 650 μg g^-1 of Ni in the shoots, exhibiting chlorosis and necrosis and a drastically reduced plant growth. Perturbations in uptake and distribution of nutrients were observed, inducing mineral deficiency, probably through membrane leakage. The mineral nutrient disturbances induced by Ni could be highly implicated in the restriction of S. portulacastrum development under the acute 50 μM Ni level.

Soil Enzymatic Activities as Influenced by Lead and Nickel Concentrations in a Vertisol of Central India

A pot-culture was conducted in Completely Randomized Design with three replicates to study the effect of Pb and Ni on enzymatic activities in a Vertisols. Results indicated that increasing in the levels of Pb from 0, 100, 150 and 300 mg kg^-1 soil significantly reduced the dehydrogenase activity (DHA) 38.9, 32.1, 30.9, 18.1 µg triphenylformazan g^-1 soil 24 h^-1; acid phosphatase activities 73, 61, 58, 55 µg PNP g^-1 soil h^-1 and alkaline phosphatase activities 80.7, 69.4, 66.2 and 64.0 µg PNP g^-1 soil h^-1, respectively. Application of Ni up to 100 mg kg^-1 had significantly improved the soil enzymatic activities and thereafter there was no such change up to the highest level (300 mg Ni kg^-1). Among soil enzymatic activities, DHA was more sensitive to Pb application. The findings generated through this study can be useful for managing waste water for safe disposal as well as sustainable crop production.

Improvement in productivity, nutritional quality, and antioxidative defense mechanisms of sunflower (Helianthus annuus L.) and maize (Zea mays L.) in nickel contaminated soil amended with different biochar and zeolite ratios

Nickel (Ni) contaminated soils pose a potential ecological risk to the environment, soil health, and quality of food produced on them. We hypothesized that application of miscanthus biochar (BC) and cationic zeolite (ZE) at various proportions into a Ni contaminated soil can efficiently immobilize Ni and reduce its bioavailability to sunflower (Helianthus annuus L.) and maize (Zea mays L.). An electroplating effluent contaminated soil was amended with BC and ZE, as sole treatments (2% w/w) and their combinations of various ratios (BC, ZE, BC25%ZE75%, BC50%ZE50% and BC75%ZE25%) for immobilization of Ni in the soil. Furthermore, the associated effects of these treatments on residual and DTPA-extractable Ni from the soil; concentrations of Ni in shoots, roots, and grain; growth, physiology, biochemistry and the antioxidant defence mechanisms of sunflower and maize were investigated. Results revealed that BC50%ZE50% treatment efficiently reduced DTPA-extractable Ni in the soil, Ni concentrations in shoots, roots, and grain, while improved selective parameters of both plants. Interestingly, the BC75%ZE25% treatment significantly improved the biomass, grain yield, physiology, biochemistry and antioxidant defense machinery, while decreased Ni oxidative stress in both sunflower and maize, compared to rest of the treatments. The results demonstrate that the BC50%ZE50% treatment can efficiently reduce Ni concentrations in the roots, shoots and grain of both sunflower and maize whereas, an improvement in biomass, grain yield, physiological, biochemical, and antioxidant defense machinery of both crops can only be achieved with the application of BC75%ZE25% treatment in a Ni contaminated soil.

Microwave irradiation and citric acid assisted seed germination and phytoextraction of nickel (Ni) by Brassica napus L.: morpho-physiological and biochemical alterations under Ni stress

The complex bio-geochemistry of soil allows pollutant to persist for a longer period of time which further decreased the fertility and natural composition of land. Nickel, an inorganic pollutant, coming from a wide range of industrial and manufacturing units possesses serious threat to soil degradation and crop productivity around the world. The present study was carried to evaluate the combined role of microwave irradiation (MR) and citric acid (CA) on the phytoextraction potential of Brassica napus L. under Ni stress. An initial seed germination test was conducted to select effective time scale of MR exposure. Highest seed germination was observed at exposure of 2.45 GHz frequency for 30 s. Healthy seeds of B. napus L. genotype Faisal Canola (RBN-03060) treated with MR at 2.45 GHz for 30 s were sown in plastic pots filled with 5 kg of soil. Nickel and CA applied exogenously in solution form with different combinations to both MR-treated and untreated B. napus plants. The MR-treated plants showed higher growth, biomass, photosynthetic pigments (Chl a, b, total, and carotenoids) and activities of antioxidant enzymes (SOD, POD, APX, CAT) as compared to untreated plants who showed higher reactive oxygen species (MDA, H₂O₂) and electrolyte leakage. Increasing Ni concentration significantly decreased the physiological and biochemical attributes of B. napus both in MR-treated and untreated plants. The addition of CA alleviated Ni-induced toxic effects in both MR-treated and untreated plants by improving antioxidant defense system. The degree of Ni stress mitigation was higher in MR-treated plants. The Ni concentration was higher in root, stem, and leaves of MR-treated plants under CA application as compared to untreated plants. The present study concluded that seeds treated with MR before sowing showed higher accumulation and concentration of Ni from soil, and this phenomenon boosted with the application of CA.

Nickel tolerance, accumulation and subcellular distribution in the halophytes Sesuvium portulacastrum and Cakile maritima

It has been shown that halophytes are able to successfully cope with heavy metal toxicity, suggesting their possible use for remediation of metal contaminated soils. In this work, Ni tolerance and accumulation in two halophytes, Sesuvium portulacastrum (L.) L. and Cakile maritima Scop. was investigated. Seedlings of both species were subjected hydroponically during 21 days to 0, 25, 50, and 100 μM of NiCl₂. The growth and photosynthesis parameters revealed that S. portulacastrum tolerates Ni better than C. maritima. The photosynthesis activity, chlorophyll content and photosystem II integrity were less impacted in Ni-treated S. portulacastrum as compared to C. maritima, although, Ni accumulated in higher concentrations in the shoots of S. portulacastrum (1050 μg g^-1 DW) than in those of C. maritima (550 μg g^-1 DW). The subcellular fractionation of Ni in the shoots of both species showed that C. maritima accumulated about 65% of Ni in the soluble fraction, while 28% was associated with the cell walls. In S. portulacastrum 44% of the total cellular Ni was seen in the soluble fraction and 43% was bound to the cell walls. It can be concluded that S. portulacastrum tolerates Ni better than C. maritima, most probably due to a better ability to sequester Ni in the cell walls, restricting its accumulation in the soluble fraction.

Judicious use of kinetin to improve growth and yield of rice in nickel contaminated soil

The present study was conducted to evaluate the effect of kinetin on growth and yield of rice in the presence and absence of nickel contamination. Rice seedlings were dipped in kinetin solution (10(-3), 10(-4) and 10 M(-5)) for 2 hours and transplanted in pots having soil contaminated with nickel sulfate @ 130 mg kg(-1). Experiment was laid out according to completely randomized design with four replications. Results revealed that kinetin significantly improved growth and yield of rice grown in nickel contamination. Kinetin @ 10(-4) M showed maximum improvement in plant height, paddy yield, 1000 grain weight, number of tillers and panicles up to 9.76, 15.72, 11.77, 11.87, and 10.90%, respectively, as compared to plants grown in contaminated soil without kinetin. Kinetin also improved the uptake of nutrients (NPK) in straw and grain of plants grown in Ni contaminated soil. Plants treated with kinetin had more concentration of Ni in shoot but less in grain compared to plants grown in Ni contaminated soil without application of kinetin. The application of kinetin can reduce stress effect on plants through improvement in the biomass of plant. This strategy could be used to increase the phytoextraction of Ni from the contaminated soil.

Genotypic variation in phytoremediation potential of Indian mustard exposed to nickel stress: a hydroponic study

Ten Indian mustard (Brassica juncea L.) genotypes were screened for their nickel (Ni) phytoremediation potential under controlled environmental conditions. All ten genotypes were grown hydroponically in aqueous solution containing Ni concentrations (as nickel chloride) ranging from 0 to 50 μM and changes in plant growth, biomass and total Ni uptake were evaluated. Of the ten genotypes (viz. Agrini, BTO, Kranti, Pusa Basant, Pusa Jai Kisan, Pusa Bahar, Pusa Bold, Vardhan, Varuna, and Vaibhav), Pusa Jai Kisan was the most Ni tolerant genotype accumulating up to 1.7 μg Ni g(-1) dry weight (DW) in its aerial parts. Thus Pusa Jai Kisan had the greatest potential to become a viable candidate in the development of practical phytoremediation technologies for Ni contaminated sites.

Feedstock quality and growth of bioenergy crops fertilized with sewage sludge

Sewage sludge is rich in essential plant nutrients, but its use is restricted for crop production due to the pollutants it contains, such as metalloids and heavy metals. Sludge is also very sticky and compact. Therefore, the objectives of this work were to evaluate (1) the impact of various amounts of sludge on bioenergy crop productivity and quality and (2) the use of peat as an adjuvant to reduce the stickiness, density and nutrient richness of the sludge. Three different applications of sludge were examined, high, low (50% of high) and low mixed with an equal volume of peat. The sludge-peat mix increased significantly leaf area and biomass accumulation of maize and hemp. High sludge and sludge-peat mix applications increased significantly the leaf area and biomass accumulation as well as the net photosynthesis of oilseed rape. High sludge application resulted in the highest heavy metal and metalloid accumulation in maize and hemp. Sludge-peat mix resulted in the highest heavy metal and metalloid accumulation in oilseed rape. However, the sludge-peat mix application provided the best feedstock quality in all three crops, since chloride, silicon and sulfur concentrations and ash content in plant material were the lowest of the three sludge treatments.

Inoculation of endophytic bacteria on host and non-host plants--effects on plant growth and Ni uptake

Among a collection of Ni resistant endophytes isolated from the tissues of Alyssum serpyllifolium, four plant growth promoting endophytic bacteria (PGPE) were selected based on their ability to promote seedling growth in roll towel assay. Further, the PGPE screened showed the potential to produce plant growth promoting (PGP) substances and plant polymer hydrolyzing enzymes. These isolates were further screened for their PGP activity on A. serpyllifolium and Brassica juncea under Ni stress using a phytagar assay. None of the four isolates produced any disease symptoms in either plant. Further, strain A3R3 induced a maximum increase in biomass and Ni content of plants. Based on the PGP potential in phytagar assay, strain A3R3 was chosen for studying its PGP effect on A. serpyllifolium and B. juncea in Ni contaminated soil. Inoculation with A3R3 significantly increased the biomass (B. juncea) and Ni content (A. serpyllifolium) of plants grown in Ni contaminated soil. The strain also showed high level of colonization in tissue interior of both plants. By 16S rRNA gene sequencing analysis, A3R3 was identified as Pseudomonas sp. Successful colonization and subsequent PGP potentiality of Pseudomonas sp. A3R3 indicate that the inoculation with PGPE might have significant potential to improve heavy metal phytoremediation.

Significance of phenols in cadmium and nickel uptake

The effects of 2-aminoindane-2-phosphonic acid (AIP), a potent phenylalanine ammonia-lyase (PAL) inhibitor, on the accumulation of cadmium and nickel in chamomile (Matricaria chamomilla) were examined in this study. In vitro assay of AIP effect showed a 90% reduction in PAL activity. In plants cultured for 7 days in Cd or Ni solutions with AIP, PAL activity was higher in both shoots and roots (in comparison with metals without AIP), and was correlated with changes in free phenylalanine content. Individual amino acids were both positively and negatively affected by AIP, with the accumulation of tyrosine and proline showing increases in some variants. Contents of soluble phenols and flavonoids were not considerably affected, while amounts of coumarin-related compounds, cell wall-bound phenols and phenolic acids were substantially reduced in AIP-treated variants. Lignin accumulation decreased in controls and increased in Cd variants in response to AIP. Shoot Cd content was depleted, but shoot Ni was elevated by AIP. Total root content of Cd and Ni decreased in +AIP variants. AIP also caused more expressive changes in hydrogen peroxide and superoxide content in Cd than in Ni variants. Our results indicate that phenols have important roles in the uptake of Cd and Ni. The present findings are discussed in the context of available data regarding AIP's effect on phenols.

Phytotoxic effects of nickel on yield and concentration of macro- and micro-nutrients in sunflower (Helianthus annuus L.) achenes

The phytotoxic effects of varying levels of nickel (0, 10, 20, 30, and 40 mg L(-1)) on growth, yield and accumulation of macro- and micro-nutrients in leaves and achenes of sunflower (Helianthus annuus L.) were appraised in this study. A marked reduction in root and shoot fresh biomass was recorded at higher Ni levels. Nickel stress also caused a substantial decrease in all macro- and micro-nutrients in leaves and achenes. The lower level of Ni (10 mg L(-1)) had a non-significant effect on various yield attributes, but higher Ni levels considerably decreased these parameters. Higher Ni levels decreased the concentrations of Ca, Mn and Fe in achenes. In contrast, achene N, K, Zn, Mn and Cu decreased consistently with increasing level of Ni, even at lower level (10 mg L(-1)). Sunflower hybrid Hysun-33 had better yield and higher most of the nutrients in achenes as compared with SF-187. The maximum reduction in all parameters was observed at the maximum level of nickel (40 mg L(-1)) where almost all parameters were reduced more than 50% of those of control plants. In conclusion, the pattern of uptake and accumulation of different nutrients in sunflower plants were nutrient- and cultivar-specific under Ni-stress.

Essential roles and hazardous effects of nickel in plants

With the world's ever increasing human population, the issues related to environmental degradation of toxicant chemicals are becoming more serious. Humans have accelerated the emission to the environment of many organic and inorganic pollutants such as pesticides, salts, petroleum products, acids, heavy metals, etc. Among different environmental heavy-metal pollutants, Ni has gained considerable attention in recent years, because of its rapidly increasing concentrations in soil, air, and water in different parts of the world. The main mechanisms by which Ni is taken up by plants are passive diffusion and active transport. Soluble Ni compounds are preferably absorbed by plants passively, through a cation transport system; chelated Ni compounds are taken up through secondary, active-transport-mediated means, using transport proteins such as permeases. Insoluble Ni compounds primarily enter plant root cells through endocytosis. Once absorbed by roots, Ni is easily transported to shoots via the xylem through the transpiration stream and can accumulate in neonatal parts such as buds, fruits, and seeds. The Ni transport and retranslocation processes are strongly regulated by metal-ligand complexes (such as nicotianamine, histidine, and organic acids) and by some proteins that specifically bind and transport Ni. Nickel, in low concentrations, fulfills a variety of essential roles in plants, bacteria, and fungi. Therefore, Ni deficiency produces an array of effects on growth and metabolism of plants, including reduced growth, and induction of senescence, leaf and meristem chlorosis, alterations in N metabolism, and reduced Fe uptake. In addition, Ni is a constituent of several metallo-enzymes such as urease, superoxide dismutase, NiFe hydrogenases, methyl coenzyme M reductase, carbon monoxide dehydrogenase, acetyl coenzyme-A synthase, hydrogenases, and RNase-A. Therefore, Ni deficiencies in plants reduce urease activity, disturb N assimilation, and reduce scavenging of superoxide free radical. In bacteria, Ni participates in several important metabolic reactions such as hydrogen metabolism, methane biogenesis, and acetogenesis. Although Ni is metabolically important in plants, it is toxic to most plant species when present at excessive amounts in soil and in nutrient solution. High Ni concentrations in growth media severely retards seed germinability of many crops. This effect of Ni is a direct one on the activities of amylases, proteases, and ribonucleases, thereby affecting the digestion and mobilization of food reserves in germinating seeds. At vegetative stages, high Ni concentrations retard shoot and root growth, affect branching development, deform various plant parts, produce abnormal flower shape, decrease biomass production, induce leaf spotting, disturb mitotic root tips, and produce Fe deficiency that leads to chlorosis and foliar necrosis. Additionally, excess Ni also affects nutrient absorption by roots, impairs plant metabolism, inhibits photosynthesis and transpiration, and causes ultrastructural modifications. Ultimately, all of these altered processes produce reduced yields of agricultural crops when such crops encounter excessive Ni exposures.