Response of wheat seedlings to ni stress: effects of supplemental calcium

Bio-stimulating effect of endophytic Aspergillus flavus AUMC 16068 and its respective ex-polysaccharides in lead stress tolerance of Triticum aestivum plant

Heavy metal accumulation is one of the major agronomic challenges that has seriously threatened food safety. As a result, metal-induced phytotoxicity concerns require quick and urgent action to retain and maintain the physiological activities of microorganisms, the nitrogen pool of soils, and the continuous yields of wheat in a constantly worsening environment. The current study was conducted to evaluate the plant growth-promoting endophytic Aspergillus flavus AUMC 16,068 and its EPS for improvement of plant growth, phytoremediation capacity, and physiological consequences on wheat plants (Triticum aestivum) under lead stress. After 60 days of planting, the heading stage of wheat plants, data on growth metrics, physiological properties, minerals content, and lead content in wheat root, shoot, and grains were recorded. Results evoked that lead pollution reduced wheat plants' physiological traits as well as growth at all lead stress concentrations; however, inoculation with lead tolerant endophytic A. flavus AUMC 16,068 and its respective EPS alleviated the detrimental impact of lead on the plants and promoted the growth and physiological characteristics of wheat in lead-contaminated conditions and also lowering oxidative stress through decreasing (CAT, POD, and MDA), in contrast to plants growing in the un-inoculated lead polluted dealings. In conclusion, endophytic A. flavus AUMC 16,068 spores and its EPS are regarded as eco-friendly, safe, and powerful inducers of wheat plants versus contamination with heavy metals, with a view of protecting plant, soil, and human health.

A Hormetic Spatiotemporal Photosystem II Response Mechanism of Salvia to Excess Zinc Exposure

Exposure of Salvia sclarea plants to excess Zn for 8 days resulted in increased Ca, Fe, Mn, and Zn concentrations, but decreased Mg, in the aboveground tissues. The significant increase in the aboveground tissues of Mn, which is vital in the oxygen-evolving complex (OEC) of photosystem II (PSII), contributed to the higher efficiency of the OEC, and together with the increased Fe, which has a fundamental role as a component of the enzymes involved in the electron transport process, resulted in an increased electron transport rate (ETR). The decreased Mg content in the aboveground tissues contributed to decreased chlorophyll content that reduced excess absorption of sunlight and operated to improve PSII photochemistry (Φ_PSII), decreasing excess energy at PSII and lowering the degree of photoinhibition, as judged from the increased maximum efficiency of PSII photochemistry (Fv/Fm). The molecular mechanism by which Zn-treated leaves displayed an improved PSII photochemistry was the increased fraction of open PSII reaction centers (qp) and, mainly, the increased efficiency of the reaction centers (Fv′/Fm′) that enhanced ETR. Elemental bioimaging of Zn and Ca by laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) revealed their co-localization in the mid-leaf veins. The high Zn concentration was located in the mid-leaf-vein area, while mesophyll cells accumulated small amounts of Zn, thus resembling a spatiotemporal heterogenous response and suggesting an adaptive strategy. These findings contribute to our understanding of how exposure to excess Zn triggered a hormetic response of PSII photochemistry. Exposure of aromatic and medicinal plants to excess Zn in hydroponics can be regarded as an economical approach to ameliorate the deficiency of Fe and Zn, which are essential micronutrients for human health.

Biogeochemical Behavior of Lead and Nickel as Influenced by Phosphatic Fertilizer Applied to Rice (Oryza sativa L.) Cultivars Grown under City Effluent Irrigation

The hydrology of arid to semi-arid regions is substantially different from that in humid regions due to scarce hydrological data distributions with dry climates and strong evapo-transpirative conditions. In the perspective of global water shortage, food security for all of the living beings has become a matter of great concern. Efficient use of water resources both in urban and rural environments and application of non-conventional water resources for irrigation are becoming increasingly important. In order to sustain crop production, the re-use of treated wastewater for irrigation of crops could be a good option. A pot experiment was set up to evaluate effects of different doses of di-ammonium phosphate (DAP) fertilizer on lead (Pb) and nickel (Ni) phyto-availability by two cultivars of rice irrigated with city effluent. Experiment was conducted in a completely randomized design (CRD) each with three replications. The results showed effective immobilization of Pb with applied phosphatic fertilizer. Among all of the tested treatments, the most effective treatment to reduce phyto-availability of Pb was T4 (248 kg P ha−1) due to antagonistic interaction. While Ni showed inconsistent behavior with both synergistic and antagonistic interaction (biphasic) to applied phosphorus (P) rates. Data regarding various growth parameters such as plant height, number of tillers, shoot and root dry weights, straw and grain yields, and physiological attributes such as total chlorophyll contents, photosynthetic and transpiration rates showed significant (p ≤ 0.05) responses to P application. An increasing trend was revealed in determined parameters with increased P application rates, with the exception of decreased plant height. The conclusion of the present remedial approach indicated that addition of P can significantly reduce the risks of rice grown under city effluent irrigation containing high Pb and Ni contents.

Toxicity of Cadmium and nickel in the context of applied activated carbon biochar for improvement in soil fertility

Toxicity induced by heavy metals deteriorates soil fertility status. It also adversely affects the growth and yield of crops. These heavy metals become part of the food chain when crops are cultivated in areas where heavy metals are beyond threshold limits. Cadmium (Cd) and nickel (Ni) are considered the most notorious ones among different heavy metals. The high water solubility of Cd made it a potential toxin for plants and their consumers. Accumulation of Ni in plants, leaves, and fruits also deteriorates their quality and causes cancer in humans when such a Ni-contaminated diet is used regularly. Both Cd and Ni also compete with essential nutrients of plants, making the fertility status of soil poor. To overcome this problem, the use of activated carbon biochar can play a milestone role. In the recent past application of activated carbon biochar is gaining more and more attention. Biochar sorb the Cd and Ni and releases essential micronutrients that are part of its structure. Many micropores and high cation exchange capacity make it the most acceptable organic amendment to improve soil fertility and immobilize Cd and Ni. In addition to improving water and nutrients, soil better microbial proliferation enhances the soil rhizosphere ecosystem and nutrient cycling. This review has covered Cd and Ni harmful effects on crop yield and their immobilization by activated carbon biochar. The focus was made to elaborate on the positive effects of biochar on crop yield and soil health.

Improvement of alfalfa resistance against Cd stress through rhizobia and arbuscular mycorrhiza fungi co-inoculation in Cd-contaminated soil

Rhizobia and arbuscular mycorrhiza fungi (AMF) are important symbiotic microbes that are advantageous to plants growing in metal-contaminated soil. However, it remains unclear how inoculated microbes affect rhizosphere microbial communities or whether subsequent changes in rhizosphere microbiomes contribute to improving plant resistance under metal stress. This study investigated the effects of rhizobia and AMF inoculation on alfalfa resistance to Cd stress. The response of rhizosphere microbial communities to inoculation and its role in increasing alfalfa' ability to cope with stress were further analyzed using high-throughput sequencing of 16S and ITS rRNA genes. Results showed that single rhizobia or AMF inoculation significantly improved alfalfa resistance to Cd stress, while their co-inoculation resulted in the greatest overall improvement. Improved resistance was reflected by the significant mitigation of Cd-induced lipid peroxidation and reactive oxygen species (ROS) stress caused by increases in antioxidant enzyme activities along with co-inoculation. Furthermore, co-inoculation significantly altered the rhizosphere microbial community structure by decreasing fungal community diversity and increasing bacterial community diversity. Results of partial least squares path modeling (PLS-PM) and variation partitioning analysis (VPA) showed that the rhizosphere bacterial community predominated over the fungal community with respected to improvements in resistance to Cd stress under the co-inoculation treatments. This improvement was specifically seen in the enrichment of certain key bacterial taxa (including Proteobacteria, Actinobacteria, Acidobacteria, and Chloroflexi) induced by the rhizobia and AMF co-inoculation, enhancing alfalfa' ability to uptake rhizosphere nutrients and reduce its release of photosynthetically-derived carbon (C) into soil. Our findings revealed that the co-inoculation of multiple symbiotic microbes can assist plants to effectively cope with Cd stress, providing a greater understanding of rhizosphere bacterial taxa in the microbe-induced phytomanagement.

Response of Three Greek Populations of Aegilops triuncialis (Crop Wild Relative) to Serpentine Soil

A common garden experiment was established to investigate the effects of serpentine soil on the photosynthetic and biochemical traits of plants from three Greek populations of Aegilops triuncialis. We measured photosynthetic and chlorophyll fluorescence parameters, proline content, and nutrient uptake of the above plants growing in serpentine and non-serpentine soil. The photochemical activity of PSII was inhibited in plants growing in the serpentine soil regardless of the population; however, this inhibition was lower in the Aetolia-Acarnania population. The uptake and the allocation of Ni, as well as that of some other essential nutrient elements (Ca, Mg, Fe, Mn), to upper parts were decreased with the lower decrease recorded in the Aetolia-Acarnania population. Our results showed that excess Ni significantly increased the synthesis of proline, an antioxidant compound that plays an important role in the protection against oxidative stress. We conclude that the reduction in the photosynthetic performance is most probably due to reduced nutrient supply to the upper plant parts. Moreover, nickel accumulation in the roots recorded in plants from all three populations seems to be a mechanism to alleviate the detrimental effects of the serpentine soil stress. In addition, our data suggest that the population from Aetolia-Acarnania could be categorized among the nickel excluders.

Impact of urban sewage sludge on soil physico-chemical properties and phytotoxicity as influenced by soil texture and reuse conditions

Urban sewage sludge (USS) is increasingly applied to agricultural soils, but mixed results have been reported because of variations in reuse conditions. Most field trials have been conducted in cropping systems, which conceal intrinsic soil responses to sludge amendments due to the rhizosphere effect and farming practices. Therefore, the current field study highlights long-term changes in bare soil properties in strict relationship with soil texture and USS dose. Two agricultural soils (loamy sand [LS] and sandy [S]) were amended annually with increasing sludge rates up to 120 t ha-1 yr-1 for 5 yr under unvegetated conditions. Outcomes showed a USS dose-dependent variation of all studied parameters in topsoil samples. Soil salinization was the most significant risk related to excessive USS doses. Total dissolved salts (TDS) in saturated paste extracts reached the highest concentrations of 37.2 and 43.1 g L-1 in S soil and LS soil, respectively, treated with 120 t USS ha-1 yr-1 . This was also reflected by electrical conductivity of the saturated paste extract (ECe ) exceeding 4,000 µS cm-1 in both treatments. As observed for TDS, fertility indicators and bioavailable metals varied with soil texture due to the greater retention capacity of LS soil owing to higher fine fraction content. Soil phytotoxicity was estimated by the seed germination index (GI) calculated for lettuce, alfalfa, oat, and durum wheat. The GI was species dependent, indicating different degrees of sensitivity or tolerance to increasing USS rates. Lettuce germination was significantly affected by changes in soil conditions showing negative correlations with ECe and soluble metals. In contrast, treatment with USS enhanced the GI of wheat, reflecting higher salinity tolerance and a positive effect of sludge on abiotic conditions that control germination in soil. Therefore, the choice of adapted plant species is the key factor for successful cropping trials in sludge-amended soils.

Biological approaches of fluoride remediation: potential for environmental clean-up

Fluoride (F), anion of fluorine which is naturally present in soil and water, behaves as toxic inorganic pollutant even at lower concentration and needs immediate attention. Its interaction with flora, fauna and other forms of life, such as microbes, adversely affect various physiochemical parameters by interfering with several metabolic pathways. Conventional methods of F remediation are time-consuming, laborious and cost intensive, which renders them uneconomical for sustainable agriculture. The solution lies in cracking down this environmental contaminant by adopting economic, eco-friendly, cost-effective and modern technologies. Biological processes, viz. bioremediation involving the use of bacteria, fungi, algae and higher plants that holds promising alternative to manage F pollution, recover contaminated soil and improve vegetation. The efficiency of indigenous natural agents may be enhanced, improved and selected over the hazardous chemicals in sustainable agriculture. This review article emphasizes on various biological approaches for the remediation of F-contaminated environment, and exploring their potential applications in environmental clean-up. It further focuses on thorough systemic study of modern biotechnological approaches such as gene editing and gene manipulation techniques for enhancing the plant-microbe interactions for F degradation, drawing attention towards latest progresses in the field of microbial assisted treatment of F-contaminated ecosystems. Future research and understanding of the molecular mechanisms of F bioremediation would add on to the possibilities of the application of more competent strains showing striking results under diverse ecological conditions.

Seed Priming Improved Antioxidant Defense System and Alleviated Ni-Induced Adversities in Rice Seedlings Under N, P, or K Deprivation

Excess nickel (Ni) concentration in the growing medium severely hampers the plant growth by disturbing oxidative metabolism and nutrient status. The present study was carried out to investigate the individual and interactive effects of Ni toxicity (0.25 mM NiSO4.6H2O) and nutrient deprivation (no-N, no-P, or no-K) on growth, oxidative metabolism, and nutrient uptake in primed and non-primed rice seedlings. Rice seed was primed with distilled water (hydropriming), selenium (5 mg L^-1), or salicylic acid (100 mg L^-1). The Ni toxicity and deprivation of N, P, or K posed negative effects on the establishment of rice seedlings. The shoot length and fresh biomass were severely reduced by Ni toxicity and nutrient stresses; the minimum shoot growth was recorded for rice seedlings grown under Ni toxicity and no-N stress. The Ni toxicity reduced the root fresh biomass but did not significantly affect the root length of N-deprived seedlings. The rice seedlings with no-P or no-K recorded similar root fresh biomass compared with those grown with sufficient nutrient supply. The Ni toxicity alone or in combination with nutrient stresses triggered the production of reactive oxygen species (ROS) and caused lipid peroxidation in rice seedlings. Among antioxidants, only glutathione reductase and vitamin E were significantly increased by Ni toxicity under different nutrient stress treatments. The Ni toxicity also reduced the concentrations of N particularly in shoot of rice seedlings. The N-deprived (no-N) seedlings recorded maximum Ni concentration in shoot, while K-deprived (no-K) seedlings showed higher Ni concentrations in root. Seed priming with selenium or salicylic acid was effective to alleviate the detrimental effects of Ni toxicity and/or nutrient stresses on rice seedlings. The better growth and greater stress tolerance of primed seedlings was coordinately attributed to lower ROS production, higher membrane stability, strong antioxidative defense system, and maintenance of mineral nutrient status.

Are Fungal Endophytes Merely Mycorrhizal Copycats? The Role of Fungal Endophytes in the Adaptation of Plants to Metal Toxicity

The contamination of soil with toxic metals is a worldwide problem, resulting in the disruption of plant vegetation and subsequent crop production. Thus, remediation techniques for contaminated soil and water remain a constant interest of researchers. Phytoremediation, which utilizes plants to remove or stabilize contaminants, is perceived to be a promising strategy. However, phytoremediation's use to date is limited because of constraints associated with such factors as slow plant growth rates or metal toxicity. Microbial-assisted phytoremediation serves as an alternative solution, since the impact of the microbial symbionts on plant growth and stress tolerance has frequently been described. Endophytic fungi occur in almost every plant in the natural environment and contribute to plant growth and tolerance to environmental stress conditions. Although this group of symbiotic fungi was found to form association with a wide range of hosts, including the non-mycorrhizal Brassicaceae metallophytes, their role in the response of plants to metal toxicity has not been thoroughly elucidated to date. This review summarizes the current knowledge regarding the role of endophytic fungi in the tolerance of plants to toxic metals and highlights the similarities and differences between this group of symbiotic fungi and mycorrhizal associations in terms of the survival of the plant during heavy metal stress.

Assessment of toxic impact of metals on proline, antioxidant enzymes, and biological characteristics of Pseudomonas aeruginosa inoculated Cicer arietinum grown in chromium and nickel-stressed sandy clay loam soils

Considering the heavy metal risk to soil microbiota and agro-ecosystems, the study was designed to determine metal toxicity to bacteria and to find metal tolerant bacteria carrying multifarious plant growth promoting activities and to assess their impact on chickpea cultivated in stressed soils. Metal tolerant strain SFP1 recognized as Pseudomonas aeruginosa employing 16S rRNA gene sequence determination showed maximum tolerance to Cr (400 μg/ml) and Ni (800 μg/ml) and produced variable amounts of indole acetic acid, HCN, NH₃, and ACC deaminase and could solubilize insoluble phosphates even under Cr (VI) and Ni stress. Metal tolerant P. aeruginosa reduced toxicity of Cr (VI) and Ni and concomitantly enhanced the performance of chickpea grown under stressed and conventional soils. At 144 mg Cr kg^-1, the measured parameters of a bacterial strain was significantly enhanced, but it was lower compared to those recorded at 660 mg Ni kg^-1. The strain SFP1 demonstrated maximum increase in seed yield (81%) and grain protein (16%) at 660 mg Ni kg^-1 over uninoculated and untreated control. Stressed plants had more proline, antioxidant enzymes, and metal concentrations in plant tissues. P. aeruginosa, however, remarkably declined the level of stress markers (proline and APX, SOD, CAT, and GR), as well as with Cr (VI) and Ni uptake by chickpea. Conclusively, P. aeruginosa strain SFP1 due to its dual metal tolerant ability, capacity to secrete plant growth promoting regulators even under metal stress and potential to mitigate metal toxicity, could be developed as microbial inoculant for enhancing chickpea production in Cr and Ni contaminated soils.

Bacterial mediated alleviation of heavy metal stress and decreased accumulation of metals in plant tissues: Mechanisms and future prospects

Heavy metal pollution of agricultural soils is one of main concerns causing some of the different ecological and environmental problems. Excess accumulation of these metals in soil has changed microbial community (e.g., structure, function, and diversity), deteriorated soil, decreased the growth and yield of plant, and entered into the food chain. Plants' tolerance to heavy metal stress needs to be improved in order to allow growth of crops with minimum or no accumulation of heavy metals in edible parts of plant that satisfy safe food demands for the world's rapidly increasing population. It is well known that PGPRs (plant growth-promoting rhizobacteria) enhance crop productivity and plant resistance to heavy metal stress. Many recent reports describe the application of heavy metal resistant-PGPRs to enhance agricultural yields without accumulation of metal in plant tissues. This review provides information about the mechanisms possessed by heavy metal resistant-PGPRs that ameliorate heavy metal stress to plants and decrease the accumulation of these metals in plant, and finally gives some perspectives for research on these bacteria in agriculture in the future.

Advances in microbe-assisted reclamation of heavy metal contaminated soils over the last decade: A review

Contamination of agricultural soils with trace metals present lethal consequences in terms of diverse ecological and environmental problems that entail entry of metal in food chain, soil deterioration, plant growth suppression, yield reduction and alteration in microbial community. Metal polluted soils have become a major concern for scientists around the globe. Phytoremediation involves the hyperaccumulation of metals in different plant parts. Phytoremediation of metals from polluted soils could be enhanced through inoculation with metal resistant plant growth promoting (PGP) bacteria. These PGP bacteria not only promote plant growth but also enhance metal uptake by plants. There are a number of reports in the literature where PGP bacterial inoculation improves metal accumulation in different plant parts without influencing plant growth. Therefore, there is a need to select PGP bacterial strains which possess the potential to improve plant growth as well as expedite the phytoremediation of metals. In this review, we have discussed the mechanisms possessed by PGP bacteria to promote plant growth and phytoremediation of metals. The central part of this review deals with the recent advances in microbial assisted-phytoremediation of metals.

Isolation of plant-growth-promoting and metal-resistant cultivable bacteria from Arthrocnemum macrostachyum in the Odiel marshes with potential use in phytoremediation

Arthrocnemum macrostachyum is a halophyte naturally growing in southwest coasts of Spain that can tolerate and accumulate heavy metals. A total of 48 bacteria (30 endophytes and 18 from the rhizosphere) were isolated from A. macrostachyum growing in the Odiel River marshes, an ecosystem with high levels of contamination. All the isolates exhibited plant-growth-promoting (PGP) properties and most of them were multiresistant to heavy metals. Although the presence of heavy metals reduced the capability of the isolates to exhibit PGP properties, several strains were able to maintain their properties or even enhance them in the presence of concrete metals. Two bacterial consortia with the best-performing endophytic or rhizospheric strains were selected for further experiments. Bacterial inoculation accelerated germination of A. macrostachyum seeds in both the absence and presence of heavy metals. These results suggest that inoculation of A. macrostachyum with the selected bacteria could ameliorate plant establishment and growth in contaminated marshes.

Effect of different amendments on rice (Oryza sativa L.) growth, yield, nutrient uptake and grain quality in Ni-contaminated soil

Rice ( Oryza sativa L.) is one of the main staple food crops which is inherently low in micronutrients, especially iron (Fe), and can lead to severe Fe deficiency in populations having higher consumption of rice. Soils polluted with nickel (Ni) can cause toxicity to rice and decreased Fe uptake by rice plants. We investigated the potential role of biochar (BC) and gravel sludge (GS), alone and in combination, for in situ immobilization of Ni in an industrially Ni-contaminated soil at original and sulfur-amended altered soil pH. Our further aim was to increase Fe bioavailability to rice plants by the exogenous application of ferrous sulfate to the Ni-immobilized soil. Application of the mixture of both amendments reduced grain Ni concentration, phytate, Phytate/Fe, Phyt/Zn molar ratios, and soil DTPA-extractable Ni. In addition, the amendment mixture increased 70 % Fe and 229 % ferritin concentrations in rice grains grown in the soil at original pH. The Fe and ferritin concentrations in S-treated soil was increased up to 113 and 383 % relative to control respectively. This enhanced Fe concentration and corresponding ferritin in rice grains can be attributed to Ni/Fe antagonism where Ni has been immobilized by GS and BC mixture. This proposed technique can be used to enhance growth, yield, and Fe biofortification in rice by reducing soil pH while in parallel in situ immobilizing Ni in polluted soil.

Assessment of Coriolopsis gallica-treated olive mill wastewater phytotoxicity on tomato plants

The aim of the present study was to evaluate the phytotoxicity of olive mill wastewater (OMW) after being treated by the white-rot fungus Coriolopsis gallica. For this, the effect of irrigation with treated OMW (TOMW) and untreated OMW (UOMW) on tomato plants (Lycopersicon esculentum) for 3 weeks was studied. The control plants were irrigated with distilled water. Agronomic tests were performed in pot experiments in a greenhouse using the randomized complete block (RCB) experimental design. The relative leaf height (RLH), as a morphological parameter, and the content of total phenols in the roots and total chlorophyll [Cha + Chb] and reducing sugars in the leaves, as physiological parameters, were selected as responses of the experimental design. The results obtained showed that [Cha + Chb] in the leaves of tomato growth under TOMW was enhanced by 36.3 and 19.4 % compared to the plant growth under UOMW and to the controls, respectively. Also, reducing sugar concentrations were closed to those of the control plants, ranging from 0.424 to 0.678 g/L for the different dilutions tested. However, the plants irrigated with UOMW showed lower reducing sugar concentrations ranging from 0.042 to 0.297g/L. The optimum RLH (0.537) was observed in the plants irrigated with TOMW diluted at (1:4), this value being higher than that observed in the controls (0.438). Our study proved that the irrigation with TOMW significantly improved tomato growth and photosynthesis activity over those irrigated with UOMW. Optimization of TOMW as a fertilizer was obtained for a dilution of 1:4. From the obtained results, it can be concluded that OMW treated by C. gallica holds potential to be used as a fertilizer for tomato plants. Graphical Abstract ᅟ Please provide a caption for the graphical abstract.The graphical abstract is improved and sent as attachment Please replace it.

The impact of Ni on the physiology of a Mediterranean Ni-hyperaccumulating plant

High nickel (Ni) levels exert toxic effects on plant growth and plant water content, thus affecting photosynthesis. In a pot experiment, we investigated the effect of the Ni concentration on the physiological characteristics of the Ni hyperaccumulator Alyssoides utriculata when grown on a vermiculite substrate in the presence of different external Ni concentrations (0-500 mg Ni L(-1)). The results showed that the Ni concentration was higher in leaves than in roots, as evidenced by a translocation factor = 3 and a bioconcentration factor = 10. At the highest concentration tested (500 mg Ni L(-1)), A. utriculata accumulated 1100 mg Ni per kilogram in its leaves, without an effects on its biomass. Plant water content increased significantly with Ni accumulation. Ni treatment did not, or only slightly, affected chlorophyll fluorescence parameters. The photosynthetic efficiency (FV/FM) of A. utriculata was stable between Ni treatments (always ≥ 0.8) and the photosynthetic performance of the plant under Ni stress remained high (performance index = 1.5). These findings support that A. utriculata has several mechanisms to avoid severe damage to its photosynthetic apparatus, confirming the tolerance of this species to Ni under hyperaccumulation.

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.

An analytical deterministic model for simultaneous phytoremediation of Ni and Cd from contaminated soils

Soil contamination by heavy metals, due to human activities, is not often limited to a single contaminant. The objective of this study was to develop a simple model for phytoextracting separate and combined Ni and Cd from contaminated soils. The study was further aimed to study phytoextraction potential of ornamental kale and land cress grown in soils contaminated with separate and combined Ni and Cd metals. The results indicated that elevated Ni and Cd concentrations in soil inhibit growth of both ornamental kale and land cress plants. In Ni + Cd treatments, growth and development of both plants were more affected than in either Ni or Cd treatments. Further, in Ni + Cd treatments, Ni concentration in tissues of both plants was increased by increasing soil Ni concentration under various Cd concentrations. At constant Ni concentration, addition of Cd did not appreciably changed Ni content of plant tissues. Land cress demonstrated higher tolerance to soil contamination by Ni and Cd compared to ornamental kale. It also demonstrated higher phytoextraction potential for soil Cd than ornamental kale. Enhanced bioavailability of Ni and Cd ions, due to competitive adsorption and desorption reactions, had no reasonable effect on metal ion accumulation in plant tissues. This indicates that at relatively high soil contamination, metal ion adsorption is no longer a limiting factor for phytoremediation. The newly proposed model, which assumes that metal uptake rate inversely depends on total soil metal ion concentration, reasonably well predicted the cleanup time of Ni, Cd, and Ni at the presence of Cd from the contaminated soils. The model also predicts that phytoremediation process takes much longer time when soil is contaminated by multi-metal ions.

Comparative Ni tolerance and accumulation potentials between Mesembryanthemum crystallinum (halophyte) and Brassica juncea: Metal accumulation, nutrient status and photosynthetic activity

Saline soils often constitute sites of accumulation of industrial and urban wastes contaminated by heavy metals. Halophytes, i.e. native salt-tolerant species, could be more suitable for heavy metal phytoextraction from saline areas than glycophytes, most frequently used so far. In the framework of this approach, we assess here the Ni phytoextraction potential in the halophyte Mesembryanthemum crystallinum compared with the model species Brassica juncea. Plants were hydroponically maintained for 21 days at 0, 25, 50, and 100μM NiCl2. Nickel addition significantly restricted the growth activity of both species, and to a higher extent in M. crystallinum, which did not, however, show Ni-related toxicity symptoms on leaves. Interestingly, photosynthesis activity, chlorophyll content and photosystem II integrity assessed by chlorophyll fluorescence were less impacted in Ni-treated M. crystallinum as compared to B. juncea. The plant mineral nutrition was differently affected by NiCl2 exposure depending on the element, the species investigated and even the organ. In both species, roots were the preferential sites of Ni(2+) accumulation, but the fraction translocated to shoots was higher in B. juncea than in M. crystallinum. The relatively good tolerance of M. crystallinum to Ni suggests that this halophyte species could be used in the phytoextraction of moderately polluted saline soils.

Implications for food safety of the uptake by tomato of 25 trace-elements from a phosphogypsum amended soil from SW Spain

Phosphogypsum (PG) has been usually applied as Ca-amendment to reclaim sodic soils such as those in the marshland area of Lebrija (SW Spain). This work aimed at the effects of PG amendments on the uptake of trace-elements by tomato and its implications for food safety. A completely randomized experiment was performed using a representative soil from Lebrija in a greenhouse involving six replicates and four PG treatments equivalent to 0, 20, 60, and 200 Mg ha(-1). Soil-to-plant transfer factors (TFs) were determined for Be, B, Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Sr, Mo, Ag, Cd, Sb, Cs, Ba, Tl, Pb, Th and U. The highest TF in shoots was observed for Cd (4.0; 1.5 in fruits), its concentration being increased with increasing PG doses due to its content in this metal (2.1 mg Cd kg(-1)PG). Phosphogypsum applying decreased the concentrations of Mn, Co and Cu in shoots; and of B, Cu, Sb, Cs, Ba, Tl and Th in fruits, however enhanced the accumulation of Se in fruits. Although Cd concentrations in tomato were below the maximum allowed levels in control pots (0 Mg PG ha(-1)), PG amendments above 60 Mg ha(-1) exceeded such limits.

Serpentine bacteria influence metal translocation and bioconcentration of Brassica juncea and Ricinus communis grown in multi-metal polluted soils

The aim of this study was to assess the effects of inoculation of rhizosphere or endophytic bacteria (Psychrobacter sp. SRS8 and Pseudomonas sp. A3R3, respectively) isolated from a serpentine environment on the plant growth and the translocation and accumulation of Ni, Zn, and Fe by Brassica juncea and Ricinus communis on a multi-metal polluted serpentine soil (SS). Field collected SS was diluted to 0, 25, 50, and 75% with pristine soil in order to obtain a range of heavy metal concentrations and used in microcosm experiments. Regardless of inoculation with bacteria, the biomass of both plant species decreased with increase of the proportion of SS. Inoculation of plants with bacteria significantly increased the plant biomass and the heavy metal accumulation compared with non-inoculated control in the presence of different proportion of SS, which was attributed to the production of plant growth promoting and/or metal mobilizing metabolites by bacteria. However, SRS8 showed a maximum increase in the biomass of the test plants grown even in the treatment of 75% SS. In turn, A3R3 showed maximum effects on the accumulation of heavy metals in both plants. Regardless of inoculation of bacteria and proportion of SS, both plant species exhibited low values of bioconcentration factor (<1) for Ni and Fe. The inoculation of both bacterial strains significantly increased the translocation factor (TF) of Ni while decreasing the TF of Zn in both plant species. Besides this contrasting effect, the TFs of all metals were <1, indicating that all studied bacteria-plant combinations are suitable for phytostabilization. This study demonstrates that the bacterial isolates A3R3 and SRS8 improved the growth of B. juncea and R. communis in SS soils and have a great potential to be used as inoculants in phytostabilization scenarios of multi-metal contaminated soils.

Excess Ca(2+) does not alleviate but increases the toxicity of Hg(2+) to photosystem II in Synechocystis sp. (Cyanophyta)

This study demonstrated that excess Ca(2+) increased the toxicity of Hg(2+) to PSII of cyanobacterium Synechocystis sp. using fast rise chlorophyll fluorescence test. Excess Ca(2+) increased the inhibitory effect of Hg(2+) on O2 evolution. Exposure to Hg(2+) caused increase in functional antenna size (ABS/RC), trapping rate of reaction center (TR0/RC), dissipated energy flux per reaction center (DI0/RC) and maximum quantum yield of non-photochemical deexcitation ( [Formula: see text] ), indicating that some reaction centers were transformed to dissipation sinks under Hg(2+) stress. Hg(2+) stress slowed down electron transport on both donor side and acceptor side and caused accumulation of P680(+). Excess Ca(2+) intensified all the Hg(2+) toxic effects on PSII function and led to dysfunction of PSII. The number of reaction centers that were transformed into dissipation sinks increased with increasing Ca(2+) concentration.

High light intensity augments mercury toxicity in cyanobacterium Nostoc muscorum

The present study is aimed at investigating the role of growth irradiance in determining the extent of mercury (Hg) toxicity on various physiological parameters viz. growth, pigment contents, photosynthesis, respiration, (14)CO(2) fixation, photosynthetic electron transport, photorespiration and enzyme activity of cyanobacterium Nostoc muscorum. A general decline was observed in all these parameters with increasing concentration of Hg except for carotenoids content and respiratory activity which exhibited significant enhancement. This effect was more pronounced in high light (130 μmol photon m(-2) s(-1)) exposed cells as compared to normal (70 μmol photon m(-2) s(-1)) and low (10 μmol photon m(-2) s(-1)) light exposed cells. Among the photosynthetic electron transport activities, whole chain was found to be more sensitive than photosystem II (PSII) and photosystem I (PSI). (14)CO(2) fixation was more affected as compared to O(2) evolution when exposed to Hg and different light intensities. Photorespiratory activity, which is an index of protecting organisms from light-induced damage, also showed a similar declining trend. Enzyme assay revealed that among the carboxylating enzymes, activity of RUBISCO was more severely inhibited than PEPCase. Thus, these results suggest that Hg itself was toxic at all tested concentrations and high light intensity augmented its toxicity in N. muscorum inhibiting the growth, pigment contents and photosynthetic activity of the organism.

Nickel and ultraviolet-B stresses induce differential growth and photosynthetic responses in Pisum sativum L. seedlings

Enhanced level of UV-B radiation and heavy metals in irrigated soils due to anthropogenic activities are deteriorating the environmental conditions necessary for growth and development of plants. The present study was undertaken to study the individual and interactive effects of heavy metal nickel (NiCl(2)·6H(2)O; 0.01, 0.1, 1.0 mM) and UV-B exposure (0.4 W m(-2); 45 min corresponds to 1.08 KJ m(-2)) on growth performance and photosynthetic activity of pea (Pisum sativum L.) seedlings. Ni treatment at high doses (0.1 and 1.0 mM Ni) and UV-B alone reduced chlorophyll content and photosynthetic activity (oxygen yield, carbon fixation, photorespiration, and PSI, PSII, and whole chain electron transport activities), and declining trends continued with combined doses. In contrast to this, Ni at 0.01 mM appeared to be stimulatory for photosynthetic pigments and photosynthetic activity, thereby enhanced biomass was observed at this concentration. However, combined dose (UV-B + 0.01 mM Ni) caused inhibitory effects. Carotenoids showed different responses to each stress. Nickel at high doses strongly inhibited PSII activity and the inhibition was further intensified when chloroplasts were simultaneously exposed to UV-B radiation. PSI activity appeared to be more resistant to each stress. High doses of Ni (0.1 and 1.0 mM) and UV-B alone interrupted electron flow at the oxygen evolving complex. Similar damaging effects were caused by 0.01 and 0.1 mM Ni together with UV-B, but the damage extended to PSII reaction center in case of 1.0 mM Ni in combination with UV-B. In conclusion, the results demonstrate that low dose of Ni stimulated the growth performance of pea seedlings in contrast to its inhibitory role at high doses. However, UV-B alone and together with low as well as high doses of Ni proved to be toxic for P. sativum L.

Evaluation of olive oil mill wastewater toxicity on spinach

BACKGROUND, AIM, AND SCOPE

Olive oil mill wastewater (OMW), a by-product of the olive oil extraction process, is annually produced in huge amounts in olive-growing areas and represents a significant environmental problem in Mediterranean areas. We studied the impact of OMW dilutions (1:20 and 1:10) on spinach plants in order to evaluate OMW dilutions as a low-cost alternative method for the disposal of this waste.

MATERIALS AND METHODS

The effects of OMW dilutions were evaluated on seed germination, shoot and root elongation, biomass production, nutrient uptake and translocation, ascorbic acid content, polyphenols, photosynthetic pigments, and photosynthetic performance of spinach.

RESULTS

Plant biomass was more affected than plant height and total chlorophyll; carotenoid and ascorbic acid content progressively decreased with decreasing OMW dilution. Exposure to both OMW dilutions resulted in overaccumulation of total polyphenols, which were negatively correlated to plant biomass and nutrients. Nutrient (Fe, Ca, and Mg) content was insufficient leading to reduced growth. Water use efficiency decreased mainly due to decreased CO(2) assimilation rate rather than to a decline of transpiration rate. Disturbances in photosystem II (PSII) photochemical efficiency could be better envisaged by the ratio between variable fluorescence and initial fluorescence (Fv/Fo), which showed much greater amplitude than the maximal photochemical efficiency of PSII photochemistry (Fv/Fm).

CONCLUSIONS

From the data obtained, it is suggested that 1:20 OMW dilutions are still phytotoxic and that higher OMW dilutions should be used in order to use this waste for the irrigation of spinach plants.

Toxicity effects of olive-mill wastewater on growth, photosynthesis and pollen morphology of spinach plants

Olive mill-wastewater (OMW), a by-product of the olive oil extraction process, represents a significant environmental problem in Mediterranean areas. We studied the impact of OMW dilutions (1:10 and 1:20) on growth, photosynthesis, proline and sugar accumulation as well as on pollen morphology of spinach (Spinacia oleracea L.) plants, to evaluate the application of OMW dilutions as pretreatment technique, prior to land disposal. Biomass, height, total chlorophyll and leaf area of spinach declined progressively with decreasing OMW dilution. Since fatty acids and phenolic compounds (present in the OMW) are considered precursors in the polymerization of sporopollenin, we suggest that under OMW treatment spinach plants seem to 'direct' the excess of these substances in the production and formation of increased pollen grains. Proline did not accumulate under OMW stress, but decreased possible due to transport to pollens in response to increased demand to over-production of pollens. Both OMW dilutions resulted in a decreased efficiency of PSII functioning and an increased excitation pressure (1-q(p)). It is concluded that, higher than 1:20 OMW dilutions should be used, and/or additional treatment should be applied before use of the OMW in the environment.

Perspectives of plant-associated microbes in heavy metal phytoremediation

"Phytoremediation" know-how to do-how is rapidly expanding and is being commercialized by harnessing the phyto-microbial diversity. This technology employs biodiversity to remove/contain pollutants from the air, soil and water. In recent years, there has been a considerable knowledge explosion in understanding plant-microbes-heavy metals interactions. Novel applications of plant-associated microbes have opened up promising areas of research in the field of phytoremediation technology. Various metabolites (e.g., 1-aminocyclopropane-1-carboxylic acid deaminase, indole-3-acetic acid, siderophores, organic acids, etc.) produced by plant-associated microbes (e.g., plant growth promoting bacteria, mycorrhizae) have been proposed to be involved in many biogeochemical processes operating in the rhizosphere. The salient functions include nutrient acquisition, cell elongation, metal detoxification and alleviation of biotic/abiotic stress in plants. Rhizosphere microbes accelerate metal mobility, or immobilization. Plants and associated microbes release inorganic and organic compounds possessing acidifying, chelating and/or reductive power. These functions are implicated to play an essential role in plant metal uptake. Overall the plant-associated beneficial microbes enhance the efficiency of phytoremediation process directly by altering the metal accumulation in plant tissues and indirectly by promoting the shoot and root biomass production. The present work aims to provide a comprehensive review of some of the promising processes mediated by plant-associated microbes and to illustrate how such processes influence heavy metal uptake through various biogeochemical processes including translocation, transformation, chelation, immobilization, solubilization, precipitation, volatilization and complexation of heavy metals ultimately facilitating phytoremediation.

Raw and fungal-treated olive-mill wastewater effects on selected parameters of lettuce (Lactuca sativa L.) growth--the role of proline

Olive-mill wastewater (OMW) constitutes a major agricultural waste stream for which disposal is associated with significant environmental repercussions. No data are available on the effects of biotreated OMW and of the protective role of exogenously provided proline on plant physiology. In the present study, OMW was administered, either raw or previously treated by the white-rot fungus Pleurotus ostreatus, with or without proline amendment, to lettuce plants growing in sterilized sand. Biotreated OMW and proline addition resulted in significant moderation of OMW adverse effects on plant biomass production and ascorbic acid content, while their synergistic action alleviated the severe negative impact on net photosynthetic rate, water use efficiency and photosynthetic activity (Fv/Fo) invoked by the effluent. Moreover, biotreated OMW supplemented with proline, moderated the decrease in chlorophylls exerted by raw OMW, but it did not contribute at restoring carotenoids content. Restoration of plant transpiration was complete when biotreated OMW was used (with or without proline); proline alone mitigated the negative impact of OMW on photosynthetic efficiency (Fv/Fm and Fv'/Fm'). It seems that key photosynthetic parameters could be exploited as suitable evaluators of wastewater-induced plant toxicity, while plant fertigation with biotreated and/or supplemented OMW could be an interesting prospect in valorizing this effluent.

Changes in photosynthesis, mesophyll conductance to CO2, and isoprenoid emissions in Populus nigra plants exposed to excess nickel

Poplar (Populus nigra) plants were grown hydroponically with 30 and 200 μM Ni (Ni30 and Ni200). Photosynthesis limitations and isoprenoid emissions were investigated in two leaf types (mature and developing). Ni stress significantly decreased photosynthesis, and this effect depended on the leaf Ni content, which was lower in mature than in developing leaves. The main limitations to photosynthesis were attributed to mesophyll conductance and metabolism impairment. In Ni-stressed developing leaves, isoprene emission was significantly stimulated. We attribute such stimulation to the lower chloroplastic [CO2] than in control leaves. However chloroplastic [CO2] did not control isoprene emission in mature leaves. Ni stress induced the emission of cis-β-ocimene in mature leaves, and of linalool in both leaf types. Induced biosynthesis and emission of isoprenoids reveal the onset of antioxidant processes that may also contribute to reduce Ni stress, especially in mature poplar leaves.

Responses of Cynara cardunculus L. to single and combined cadmium and nickel treatment conditions

A greenhouse pot experiment was carried out to study the responses of Cynara cardunculus L. (cardoon) to cadmium and nickel. Three groups of 12 pots each were planted with cardoon plants and spiked with single and combined cadmium and nickel aqueous solutions. The bioavailable metal concentrations, measured in soil, ranged widely and were up to 246.7 mg kg⁻¹ for Cd and 61.1 mg kg⁻¹ for Ni. Under Cd treatment, cardoon growth remained unaffected, while increased Ni soil concentrations inhibited plant growth and were lethal to the highly treated plants. In the combined Cd and Ni treatments, an antagonistic effect was observed between the two metals. Cadmium and nickel concentrations in cardoon tissues rose with increasing metal concentrations in the soil. Cadmium and nickel contents in shoots reached 169.3 and 342.3 mg kg⁻¹ in the single treatments while, under the combined Cd and Ni treatments, they were up to 235.0 and 440.7 mg kg⁻¹, respectively. Generally, mean contents of both metals in the shoots were higher than in the roots and the translocation factor was greater than 1. A possible enhancing effect of nickel on cadmium uptake was observed. Cardoon showed characteristics of a Cd accumulator.

Inoculation of Ni-resistant plant growth promoting bacterium Psychrobacter sp. strain SRS8 for the improvement of nickel phytoextraction by energy crops

This study was conducted to elucidate effects of inoculating plant growth-promoting bacterium Psychrobacter sp. SRS8 on the growth and phytoextraction potential of energy crops Ricinus communis and Helianthus annuus in artificially Ni contaminated soils. The toxicity symptom in plants under Ni stress expressed as chlorophyll, protein content, growth inhibition, and Fe, P concentrations were studied, and the possible relationship among them were also discussed. The PGPB SRS8 was found capable of stimulating plant growth and Ni accumulation in both plant species. Further, the stimulation effect on plant biomass, chlorophyll, and protein content was concomitant with increased Fe and P assimilation from soil to plants. Further, the induction of catalase and peroxidase activities was also involved in the ability of SRS8 to increase the tolerance in both plant species under Ni stress. The findings suggest that strain SRS8 play an important role in promoting the growth and phytoextraction efficiency of R. communis and H. annuus, which may be used for remediation of metal contaminated sites.

Interference of nickel with the photosynthetic apparatus of Zea mays

Photosynthetic capacity of plants in heavy metals-polluted environment depends on growth stage of plants. Previously, Ni effect on the process of photosynthesis was studied in fully developed plants. The objective of our studies was the response of the developing photosynthetic apparatus to Ni. Changes in chlorophyll a fluorescence induction kinetics: t(1/2), F(v), F(m), F(0), F(v)/F(m), the content of chlorophyll a, b and carotenoids (x+c), as well as the ratios of chlorophyll (a+b) to the total carotenoids [(a+b)/(x+c)] and chlorophyll a/b (Chl a/b) were followed in leaves of 3 day old seedlings of Zea mays exposed to 0, 100 and 200 microNi for 8 and 13 days. The values of t(1/2), F(v), F(m) markedly declined in seedlings treated with 200 microM Ni for both periods, while the F(v)/F(m) ratio decreased in those exposed to 200 microM Ni for 13 days. The content of (x+c) declined gradually with time of plant exposure to the metal. The (a+b)/(x+c) ratio was reduced under Ni treatment, particularly after 8 days. The Chl a/b ratio increased in seedlings treated with the metal for 8 days, but decreased after 13-day-exposure, indicating different response of Chl b to Ni depending on the exposure time. During growth under Ni stress maize invested primarily in Cars and the reaction centre pigment-Chl a. The protective mechanisms in the Ni stressed plant are discussed.

Growth and mineral composition of nickel-stressed plants under conditions of supplementation with excessive amounts of calcium and iron

This study investigated the effectiveness of excessive calcium (Ca) and iron (Fe) supplement nutrition in spinach Markiza F(1) cv. and sweet corn Zlota Karlowa cv. to alleviate nickel (Ni)-induced phytotoxicity. The following doses of the pollutant Ni were introduced: 0 (control), 40, or 60 mg Ni/kg growth medium. Two levels of calcium (Ca), 270 (basic) and 400 mg/kg (intensive), as well as two levels of iron (Fe), 10 (basic) and 20 mg/kg (intensive), respectively, were used. Intensive nutrition supplementation of Ni-stressed test plants species with Ca or Fe was beneficial as manifested by significantly increased maize shoots and roots biomass, lowered content of Ni in spinach and maize in above-ground parts, and decreased concentration of the pollutant in roots of intensive Ca-supplied maize plants grown in the environment containing 60 mg Ni/kg. Moreover there was significantly elevated Fe content in highly fertilized with iron spinach plants grown in the presence of 60 mg Ni/kg and in shoots of Ni-treated maize plants intensively supplied with Ca or Fe. Generally, high content of Ca or Fe in the growth medium significantly raised the content of free and bound Ca in shoots of Ni-stressed spinach plants. The same phenomenon was found in roots, but only in the presence of 60 mg Ni. Intensive nutrition supplementation of Ni-treated maize plants with Fe or Ca generally did not change the concentration of free Ca in plant organs, but elevated bound Ca levels in roots was observed. Increased bound Ca content was also found in leaves of maize plants intensive supplied with Ca. Thus, intensive Ca or Fe nutrition presents a promising potential for use in the conditions of Ni contamination by increasing plant growth, reducing Ni translocation from roots to shoots and raising the nutritive value of above-ground parts of spinach and maize plants.

Ni2+ toxicity in rice: effect on membrane functionality and plant water content

The heavy metal nickel is an essential mineral trace nutrient found at low concentrations in most natural soils. However, it may reach toxic levels in certain areas and affect a number of biochemical and physiological processes in plants. Wilting and leaf necrosis have been described as typical visible symptoms of Ni(2+) toxicity. The plasma membrane (PM) of root cells constitutes the first barrier for the entry of heavy metals but also a target of their toxic action. This work studies the relationship between disturbances of membrane functionality and the development of the typical symptoms of Ni(2+) toxicity. Rice plants (Oryza sativa L. cv. Bahia) grown in nutrient medium containing 0.5mM Ni(2+) showed a significant decrease in water content as a consequence of the stress. Addition of Ni(2+) to the solution bathing the roots induced a concentration-dependent PM depolarization but the activity of the PM-H(+)-ATPase was not inhibited by the presence of Ni(2+) and the initial resting potential recovered in less than 1h. In the short term (hours), membrane permeability of root cells was not significantly affected by Ni(2+) treatments. However, in the long term (days) a drastic loss of K(+) was measured in roots and shoots, which should be responsible for the changes in the water content measured, since stomatal conductance and the transpiration rate remained unaffected by Ni(2+) treatment. The effects induced by Ni(2+) were not permanent and could be reverted, at least in part, by transferring the plants to a medium without Ni(2+).