Effect of copper and lead on photosynthesis and plant pigments in black gram [Vigna mungo (L.) Hepper]

Root development in Leucaena leucocephala (Lam.) de Wit enhances copper accumulation

Potentially toxic elements (PTE) in soil like copper (Cu) have been common in agricultural and mining areas worldwide. The sustainable remediation of these areas has been shown to have high socio-environmental relevance and phytoremediation is one of the green technologies to be considered. The challenge is to identify species that are tolerant to PTE, and to assess their phytoremediation potential. The objective of this study was to evaluate the physiological response of Leucaena leucocephala (Lam.) de Wit and to determine the species tolerance and phytoremediation potential to concentrations of Cu in the soil (100, 200, 300, 400 and 500 mg/dm3). The photosynthetic rate was not affected, while the content of chlorophylls decreased as Cu concentrations increased. There was an increased in stomatal conductance and water use efficiency from the treatment of 300. The root biomass and the length were bigger than the shoots, in the treatments above 300. Cu accumulation was greater in the roots than in the shoot of the plants, thus, the Cu translocation index to the shoot was lower. The ability to absorb and accumulate, mainly, Cu in the roots, allowed the development and growth of plants, since the parameters of photosynthesis and biomass accumulation were not affected by the Cu excess. This accumulation in the roots is characterized as a strategy for the phytostabilization of Cu. Therefore, L. leucocephala is tolerant to the Cu concentrations evaluated and has a potential phytoremediation of Cu in the soil.

Effects of Heavy Metals on Stomata in Plants: A Review

Stomata are one of the important structures for plants to alleviate metal stress and improve plant resistance. Therefore, a study on the effects and mechanisms of heavy metal toxicity to stomata is indispensable in clarifying the adaptation mechanism of plants to heavy metals. With the rapid pace of industrialization and urbanization, heavy metal pollution has been an environmental issue of global concern. Stomata, a special physiological structure of plants, play an important role in maintaining plant physiological and ecological functions. Recent studies have shown that heavy metals can affect the structure and function of stomata, leading to changes in plant physiology and ecology. However, although the scientific community has accumulated some data on the effects of heavy metals on plant stomata, the systematic understanding of the effects of heavy metals on plant stomata remains limited. Therefore, in this review, we present the sources and migration pathways of heavy metals in plant stomata, analyze systematically the physiological and ecological responses of stomata on heavy metal exposure, and summarize the current mechanisms of heavy metal toxicity on stomata. Finally, the future research perspectives of the effects of heavy metals on plant stomata are identified. This paper can serve as a reference for the ecological assessment of heavy metals and the protection of plant resources.

Potential of vermicompost and limestone in reducing copper toxicity in young grapevines grown in Cu-contaminated vineyard soil

Foliar fungicide application in grapevines increases the content of heavy metals such as copper (Cu) in vineyard soils, which may reach phytotoxic levels. The application of soil amendments such as limestone and vermicompost may reduce Cu availability and phytotoxicity. The study aimed to assess growth, physiological status and changes in root morphology in young grapevines grown for 12 months in Cu-contaminated soil with and without the application of soil amendments. Samples of a Typic Hapludalf soil were collected in a vineyard with more than 30 years of cultivation. The following treatments were used: 1) control (without amendment), 2) application of organic vermicompost (86.7 g kg^-1) and 3) application of limestone (3 Mg ha^-1). Grapevines (Paulsen 1103 rootstock) were transplanted and grown for 12 months in PVC soil columns. We assessed parameters of growth, photosynthesis and root morphology. Grapevines grown in soil treated with limestone showed increased growth, dry matter yield and photosynthetic efficiency. The highest Cu concentrations in root tissue were found in grapevines grown in control soil. The application of vermicompost in this study did not alleviate Cu toxicity. Grapevines grown in soil treated with vermicompost showed high manganese (Mn) concentration in shoots before the winter pruning, reflecting the high Mn concentrations in soil solution that caused Mn phytotoxicity, resulting in plant death after the winter pruning. The vermicompost used in this study is not suitable for agronomic use. The use of limestone was an effective strategy to reduce Cu availability and phytotoxicity.

Chromium(VI) Toxicity in Legume Plants: Modulation Effects of Rhizobial Symbiosis

Most legume species have the ability to establish a symbiotic relationship with soil nitrogen-fixing rhizobacteria that promote plant growth and productivity. There is an increasing evidence of reactive oxygen species (ROS) important role in formation of legume-rhizobium symbiosis and nodule functioning. Environmental pollutants such as chromium compounds can cause damage to rhizobia, legumes, and their symbiosis. In plants, toxic effects of chromium(VI) compounds are associated with the increased production of ROS and oxidative stress development as well as with inhibition of pigment synthesis and modification of virtually all cellular components. These metabolic changes result in inhibition of seed germination and seedling development as well as reduction of plant biomass and crop yield. However, if plants establish symbiosis with rhizobia, heavy metals are accumulated preferentially in nodules decreasing the toxicity of metals to the host plant. This review summarizes data on toxic effects of chromium on legume plants and legume-rhizobium symbiosis. In addition, we discussed the role of oxidative stress in both chromium toxicity and formation of rhizobial symbiosis and use of nodule bacteria for minimizing toxic effects of chromium on plants.

Urea increased nickel and copper accumulation in the leaves of Egeria densa (Planch.) Casp. and Ceratophyllum demersum L. during short-term exposure

In the present study, two fresh water plant species Egeria densa (Planch.) Casp. and Ceratophyllum demersum L. were subjected to separate and combined action of urea (2mМ) and metals (Ni and Cu, 10μM) to investigate the phytoremediation potential of these two submerged macrophytes during short-term experiments (48h). Both submerged macrophytes demonstrated high accumulative potential for Ni and Cu (average bioconcentration factors were 2505 for Ni and 3778 for Cu). The urea (2 mM) was not significantly toxic for studied plant species. Futhermore, urea worked as an additional source of nitrogen and stimulated some metabolic processes such as the synthesis of photosynthetic pigments, soluble proteins, non-enzymatic antioxidants, and activated some enzymes. Adding urea to the metals increased their accumulation in both macrophytes (on average by 35% for Ni and 15% for Cu). Combined action of urea and Ni did not have a significant effect on antioxidant response, but caused a sharp increase of urease activity (4 folds on an average) in both plants. The copper exerted a stronger toxic effect on both studied macrophytes compared to nickel. Adding urea to copper in some cases diminished the toxic action of this metal. Study concludes that the responses of E. densa and C. demersum to urea and metal action (separate and combined) were depended on the type of pollutant and the activity of antioxidant defence system. Therefore, the studied aquatic macrophytes found to be potential phytoremediators of water bodies, the addition of an organic nitrogen source in the form of urea in environmentally relevant concentration will increase the efficiency of phytoextraction of metals.

Changes in subcellular distribution and antioxidant compounds involved in Pb accumulation and detoxification in Neyraudia reynaudiana

The effects of increasing concentrations of lead (Pb) on Pb accumulation, subcellular distribution, ultrastructure, photosynthetic characteristics, antioxidative enzyme activity, malondialdehyde content, and phytochelatin contents were investigated in Neyraudia reynaudiana seedlings after a 21-day exposure. A Pb analysis at the subcellular level showed that the majority of Pb in the roots was associated with the cell wall fraction, followed by the soluble fraction. In contrast, the majority of the Pb in the leaves was located in the soluble fraction based on transmission electron microscopy and energy dispersive X-ray analyses. Furthermore, high Pb concentrations adversely affected N. reynaudiana cellular structure. The changes in enzyme activity suggested that the antioxidant system plays an important role in eliminating or alleviating Pb toxicity, both in the roots and leaves of N. reynaudiana. Additionally, the phytochelatin contents in the roots and leaves differed significantly between Pb-spiked treatments and control plants. Our results provide strong evidence that cell walls restrict Pb uptake into the protoplasm and establish an important protective barrier. Subsequent vacuolar compartmentalization in leaves could isolate Pb from other substances in the cell and minimize Pb toxicity in other organelles over time. These results also demonstrated that the levels of antioxidant enzymes and phytochelatin in leaves and roots are correlated with Pb toxicity. These detoxification mechanisms promote Pb tolerance in N. reynaudiana.

Characterization of efficient plant-growth-promoting bacteria isolated from Sulla coronaria resistant to cadmium and to other heavy metals

The inoculation of plants with plant-growth-promoting rhizobacteria has become a priority in the phytoremediation of heavy-metal-contaminated soils. A total of 82 bacteria were isolated from Sulla coronaria root nodules cultivated on four soil samples differently contaminated by heavy metals. The phenotypic characterization of these isolates demonstrated an increased tolerance to cadmium reaching 4.1mM, and to other metals, including Zn, Cu and Ni. Polymerase Chain Reaction/Restriction Fragment Length Polymorphism (PCR/RFLP) analysis showed a large diversity represented by genera related to Agrobacterium sp., R. leguminosarum, Sinorhizobium sp., Pseudomonas sp., and Rhizobium sp. Their symbiotic effectiveness was evaluated by nodulation tests. Taking into consideration efficiency and cadmium tolerance, four isolates were chosen; their 16SrRNA gene sequence showed that they belonged to Pseudomonas sp. and the Rhizobium sullae. The selected consortium of soil bacteria had the ability to produce plant-growth-promoting substances such as indole acetic acid and siderophore. The intracellular Cd accumulation was enhanced by increasing the time of incubation of the four soil bacteria cultivated in a medium supplemented with 0.1mM Cd. The existence of a cadmium-resistant gene was confirmed by PCR. These results suggested that Sulla coronaria in symbiosis with the consortium of plant-growth-promoting rhizobacteria (PGPR) could be useful in the phytoremediation of cadmium-contaminated soils.

In situ phytostabilisation capacity of three legumes and their associated Plant Growth Promoting Bacteria (PGPBs) in mine tailings of northern Tunisia

PGPBs-legumes associations represent an alternative procedure for phytostabilisation of heavy metals polluted soils mainly generated by industrial and agricultural practices. In this study we evaluated the capacity of Vicia faba, Lens culinaris and Sulla coronaria, inoculated in situ by specific heavy metals resistant inocula, for the phytostabilisation of copper, lead and cadmium respectively. The experimentation was performed in mine tailings of northern Tunisia. Results proved that inoculation enhanced roots and shoots biomass production of faba bean by 14% and 12%, respectively, and significantly improved pods yield by 91%. In lentil, the inoculation ameliorated shoot biomass up to 27%. The highest nitrogen fixation was recorded by Sulla coronaria. The three symbioses accumulated heavy metals essentially in roots, and poorly in shoots. In addition, cadmium accumulation in roots of inoculated sulla was enhanced by 39%. Furthermore, inoculations decreased heavy metals availability in the soil up to -10% of Cu and -47% of Pb respectively in roots of faba bean and lentil. Our results suggested a positive effect of co-inoculation of legumes by appropriate heavy metals resistant PGPBs for the phytostabilisation of mine tailings. Elsewhere, the enhancement in the antioxidant enzymes activities demonstrated the role of the three inocula to alleviate the heavy metals induced stress.

Lead tolerance mechanism in Conyza canadensis: subcellular distribution, ultrastructure, antioxidative defense system, and phytochelatins

We used hydroponic experiments to examine the effects of different concentrations of lead (Pb) on the performance of the Pb-tolerable plant Conyza canadensis. In these experiments, most of the Pb was accumulated in the roots; there was very little Pb accumulated in stems and leaves. C. canadensis is able to take up significant amounts of Pb whilst greatly restricting its transportation to specific parts of the aboveground biomass. High Pb concentrations inhibited plant growth, increased membrane permeability, elevated antioxidant enzyme activity in roots, and caused a significant increase in root H2O2 and malondialdehyde content. Analysis of Pb content at the subcellular level showed that most Pb was associated with the cell wall fraction, followed by the nucleus-rich fraction, and with a minority present in the mitochondrial and soluble fractions. Furthermore, transmission electron microscopy and energy dispersive X-ray analysis of root cells revealed that the cell wall and intercellular space in C. canadensis roots are the main locations of Pb accumulation. Additionally, high Pb concentrations adversely affected the cellular structure of C. canadensis roots. The increased enzyme activity suggests that the antioxidant system may play an important role in eliminating or alleviating Pb toxicity in C. canadensis roots. However, the levels of non-protein sulfhydryl compounds, glutathione, and phytochelatin did not significantly change in either the roots or leaves under Pb-contaminated treatments. Our results provide strong evidence that cell walls restrict Pb uptake into the root and act as an important barrier protecting root cells, while demonstrating that antioxidant enzyme levels are correlated with Pb exposure. These findings demonstrate the roles played by these detoxification mechanisms in supporting Pb tolerance in C. canadensis.

The uptake and bioaccumulation of heavy metals by food plants, their effects on plants nutrients, and associated health risk: a review

Heavy metal contamination is a globally recognized environmental issue, threatening human life very seriously. Increasing population and high demand for food resulted in release of various contaminants into environment that finally contaminate the food chain. Edible plants are the major source of diet, and their contamination with toxic metals may result in catastrophic health hazards. Heavy metals affect the human health directly and/or indirectly; one of the indirect effects is the change in plant nutritional values. Previously, a number of review papers have been published on different aspects of heavy metal contamination. However, no related information is available about the effects of heavy metals on the nutritional status of food plants. This review paper is focused upon heavy metal sources, accumulation, transfer, health risk, and effects on protein, amino acids, carbohydrates, fats, and vitamins in plants. The literature about heavy metals in food plants shows that both leafy and nonleafy vegetables are good accumulators of heavy metals. In nonleafy vegetables, the bioaccumulation pattern was leaf > root ≈ stem > tuber. Heavy metals have strong influence on nutritional values; therefore, plants grown on metal-contaminated soil were nutrient deficient and consumption of such vegetables may lead to nutritional deficiency in the population particularly living in developing countries which are already facing the malnutrition problems.

Photosynthesis light-independent reactions are sensitive biomarkers to monitor lead phytotoxicity in a Pb-tolerant Pisum sativum cultivar

Lead (Pb) environmental contamination remains prevalent. Pisum sativum L. plants have been used in ecotoxicological studies, but some cultivars showed to tolerate and accumulate some levels of Pb, opening new perspectives to their use in phytoremediation approaches. However, the putative use of pea plants in phytoremediation requires reliable toxicity endpoints. Here, we evaluated the sensitivity of a large number of photosynthesis-related biomarkers in Pb-exposed pea plants. Plants (cv. "Corne de Bélier") were exposed to Pb concentrations up to 1,000 mg kg(-1) soil during 28 days. The photosynthetic potential biomarkers that were analyzed included pigments, chlorophyll (Chl) a fluorescence, gas exchange, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) activity, and carbohydrates. Flow cytometry (FCM) was also used to assess the morpho-functional status of chloroplasts. Finally, Pb-induced nutrient disorders were also evaluated. Net CO2 assimilation rate (A) and RuBisCO activity decreased strongly in Pb-exposed plants. Plant dry mass (DM) accumulation, however, was only reduced in the higher Pb concentrations tested (500 and 1,000 mg kg(-1) soil). Pigment contents increased solely in plants exposed to the largest Pb concentration, and in addition, the parameters related to the light-dependent reactions of photosynthesis, Fv/Fm and ΦPSII, were not affected by Pb exposure. In contrast to this, carbohydrates showed an overall tendency to increase in Pb-exposed plants. The morphological status of chloroplasts was affected by Pb exposure, with a general trend of volume decrease and granularity increase. These results point the endpoints related to the light-independent reactions of photosynthesis as more sensitive predictors of Pb-toxicity than the light-dependent reactions ones. Among the endpoints related to the light-independent photosynthesis reactions, RuBisCO activity and A were found to be the most sensitive. We discuss here the advantages of using these parameters as biomarkers for Pb toxicity in plants. Finally, we report that, despite showing physiological disorders, these cultivar plants survived and accumulated high doses of Pb, and their use in environmental/decontamination studies is open to debate.

Effects of copper sulfate on growth and physiological responses of Limoniastrum monopetalum

A glasshouse study of the coastal shrub Limoniastrum monopetalum was carried out to evaluate its tolerance and capacity to accumulate copper. We investigate the effects of Cu from 0 to 60 mmol l(-1) on the growth, photosynthetic apparatus, and nutrient uptake of L. monopetalum, by measuring gas exchange, chlorophyll fluorescence parameters, photosynthetic pigments, and total copper, nitrogen, phosphorus, sulfur, calcium, and magnesium content in the plant tissues. Although L. monopetalum did not survive at 60 mmol l(-1) Cu, the species demonstrated a high tolerance to Cu-induced stress, since all plants survived external Cu concentrations of up to 35 mmol l(-1) and displayed similar growth in the Cu-enriched medium as in the control treatment of up to the external level of 15 mmol Cu l(-1) (1,000 mg Cu l(-1)). The reduced growth registered in plants exposed to 35 mmol Cu l(-1) can be attributed to reduced photosynthetic carbon assimilation associated with the adverse effect of the metal on the photochemical apparatus and a reduction in the absorption of essential nutrients. Copper tolerance was associated with the capacity of the plant to accumulate the metal in its roots and effectively prevent its translocation to photosynthetic tissues. L. monopetalum has the characteristics of a Cu-excluder plant and could be used in the revegetation of Cu-contaminated soils.

Influence of cadmium on the symbiotic interaction established between peanut (Arachis hypogaea L.) and sensitive or tolerant bradyrhizobial strains

Heavy metals in soil are known to affect rhizobia-legume interaction reducing not only rhizobia viability, but also nitrogen fixation. In this work, we have compared the response of the symbiotic interaction established between the peanut (Arachis hypogaea L.) and a sensitive (Bradyrhizobium sp. SEMIA6144) or a tolerant (Bradyrhizobium sp. NLH25) strain to Cd under exposure to this metal. The addition of 10 μM Cd reduced nodulation and nitrogen content in both symbiotic associations, being the interaction established with the sensitive strain more affected than that with the tolerant one. Plants inoculated with the sensitive strain accumulated more Cd than those inoculated with the tolerant strain. Nodules showed an increase in reactive oxygen species (ROS) production when exposed to Cd. The histological structure of the nodules exposed to Cd revealed a deposit of unknown material on the cortex and a significant reduction in the infection zone diameter in both strains, and a greater number of uninfected cells in those nodules occupied by the sensitive strain. In conclusion, Cd negatively impacts on peanut-bradyrhizobia interaction, irrespective of the tolerance of the strains to this metal. However, the inoculation of peanut with Bradyrhizobium sp. NLH25 results in a better symbiotic interaction suggesting that the tolerance observed in this strain could limit Cd accumulation by the plant.

Growth and photosynthetic responses to copper in wild grapevine

The present study evaluates the tolerance and accumulation potential of Vitis vinifera ssp. sylvestris under moderate and high external Cu levels. A greenhouse experiment was conducted in order to investigate the effects of a range of external Cu concentrations (0-23mmolL(-1)) on growth and photosynthetic performance by measuring gas exchange, chlorophyll fluorescence parameters and photosynthetic pigments. We also measured the total copper, nitrogen, phosphorus, sulphur, calcium, magnesium, iron, potassium and sodium concentrations in the plant tissues. All the experimental plants survived even with external Cu concentrations as high as 23mmolL(-1) (1500mg Cu L(-1)), although the excess of metal resulted in a biomass reduction of 35%. The effects of Cu on growth were linked to a reduction in net photosynthesis, which may be related to the effect of the high concentration of the metal on photosynthetic electron transport. V. vinifera ssp. sylvestris survived with leaf Cu concentrations as high as 80mgkg(-1) DW and growth parameters were unaffected by leaf tissue concentrations of 35mg Cu kg(-1) DW. The results of our study indicate that plants of V. vinifera ssp. sylvestris from the studied population are more tolerant to Cu than the commercial varieties of grapevine that have been studied in the literature, and could constitute a basis for the genetic improvement of Cu tolerance in grapevine.

Nickel detoxification and plant growth promotion by multi metal resistant plant growth promoting Rhizobium species RL9

Pollution of the biosphere by heavy metals is a global threat that has accelerated dramatically since the beginning of industrial revolution. The aim of the study is to check the resistance of RL9 towards the metals and to observe the effect of Rhizobium species on growth, pigment content, protein and nickel uptake by lentil in the presence and absence of nickel. The multi metal tolerant and plant growth promoting Rhizobium strain RL9 was isolated from the nodules of lentil. The strain not only tolerated nickel but was also tolerant o cadmium, chromium, nickel, lead, zinc and copper. The strain tolerated nickel 500 μg/mL, cadmium 300 μg/mL, chromium 400 μg/mL, lead 1,400 μg/mL, zinc 1,000 μg/mL and copper 300 μg/mL, produced good amount of indole acetic acid and was also positive for siderophore, hydrogen cyanide and ammonia. The strain RL9 was further assessed with increasing concentrations of nickel when lentil was used as a test crop. The strain RL9 significantly increased growth, nodulation, chlorophyll, leghaemoglobin, nitrogen content, seed protein and seed yield compared to plants grown in the absence of bioinoculant but amended with nickel The strain RL9 decreased uptake of nickel in lentil compared to plants grown in the absence of bio-inoculant. Due to these intrinsic abilities strain RL9 could be utilized for growth promotion as well as for the remediation of nickel in nickel contaminated soil.

Tolerance and accumulation of copper in the salt-marsh shrub Halimione portulacoides

The present study evaluated the tolerance and accumulation potential in the salt-marsh shrub Halimione portulacoides under moderate and high external Cu levels. A greenhouse experiment was conducted in order to investigate the effects of a range of external Cu concentrations (0 to 60 mmol l(-1)) on growth and photosynthetic performance by measuring gas exchange, chlorophyll fluorescence parameters and photosynthetic pigments. We also determined total copper, nitrogen, phosphorus and sulfur concentrations in the plant tissues. H. portulacoides survived with external Cu concentrations of up to 35 mmol Cu l(-1), although the excess of metal resulted in a biomass reduction of 48%. The effects of Cu on growth were linked to a drastic reduction in net photosynthesis. However, H. portulacoides tolerated Cu levels of up to 15 mmol Cu l(-1) without suffering adverse physiological effects. Our results indicate that this species could play an important role in the restoration of Cu-contaminated soils.

Sub-tropical urban environment affecting content and composition of non-structural carbohydrates of Lolium multiflorum ssp. italicum cv. Lema

This study analyzed the relationship between environmental factors, especially air pollution and climatic conditions, and non-structural carbohydrates (NSC) in plants of Lolium multiflorum exposed during 10 consecutive periods of 28 days at a polluted site (Congonhas) and at a reference site in São Paulo city (Brazil). After exposure, NSC composition and leaf concentrations of Al, Fe, Cu, Zn, Pb and Cd were measured. The seasonal pattern of NSC accumulation was quite similar in both sites, but plants at Congonhas showed higher concentrations of these compounds, especially fructans of low and medium degree of polymerization. Regression analysis showed that NSC in plants growing at the polluted site were explained by variations on temperature and leaf concentration of Fe (positive effect), as well as relative humidity and particulate material (negative effect). NSC in the standardized grass culture, in addition to heavy metal accumulation, may indicate stressing conditions in a sub-tropical polluted environment.

Effects of heavy metal toxicity on growth, symbiosis, seed yield and metal uptake in pea grown in metal amended soil

Soils contaminated with heavy metals present a major threat to sustainable agriculture. Understanding the effects of these metals on pea productivity will be useful. We studied the effects of cadmium, chromium and copper used both separately and as mixtures, on over all growth of pea plants inoculated with Rhizobium sp. Among the metals, copper was most toxic for pea plants and decreased the seed yield by 15% at 1,338 mg kg(-1) compared to control plants whereas cadmium and chromium in general, increased the measured parameters. The metal accumulation in roots and shoots at 90 d and in grains at 120 d differed among treatments.

Effect of metal-tolerant plant growth-promoting Rhizobium on the performance of pea grown in metal-amended soil

The nickel- and zinc-tolerant plant growth-promoting (PGP) Rhizobium sp. RP5 was isolated from nodules of pea, grown in metal-contaminated Indian soils. The PGP potentials of strain RP5 was assessed under in vitro conditions. Strain RP5 displayed a high level of tolerance to nickel (350 microg ml(-1)) and zinc (1500 microg ml(-1)) and showed PGP activity under in vitro conditions. The PGP activity of this strain was further assessed with increasing concentrations of nickel and zinc, using pea as a test crop. The bio-inoculant enhanced the dry matter, nodule numbers, root N, shoot N, leghemoglobin, seed yield, and grain protein (GP) by 19%, 23%, 26%, 47%, 112%, 26%, and 8%, respectively, at 290 mg Ni kg(-1) while at 4890 mg Zn kg(-1) soil, it increased the dry matter, nodule numbers, leghemoglobin, seed yield, GP, and root and shoot N by 18%, 23%, 78%, 26%, 7%, 25%, and 42%, respectively, compared to plants grown in soil amended with metal only. The bio-inoculant increased the glutathione reductase activity of roots and nodules by 46% and 65% at 580 mg Ni kg(-1) and 47% and 54% at 9780 mg Zn kg(-1) soil, respectively, compared to uninoculated plants. The inoculated strain decreased the concentration of nickel and zinc in plant organs. The intrinsic abilities of nitrogen fixation, growth promotion, and the ability to reduce the toxicity of nickel and zinc of the tested strain could be of practical importance in augmenting the growth and yield of pea, in nickel- and zinc-polluted soils.

Effect of metal tolerant plant growth promoting Bradyrhizobium sp. (vigna) on growth, symbiosis, seed yield and metal uptake by greengram plants

The nickel and zinc tolerant plant growth promoting Bradyrhizobium sp. (vigna) RM8 was isolated from nodules of greengram, grown in metal contaminated Indian soils. The plant growth promoting (PGP) potentials of strain RM8 was assessed both in the presence and absence of nickel and zinc under in vitro conditions. Strain RM8 tolerated a high level of nickel (300 microg ml(-1)) and zinc (1400 microg ml(-1)) on yeast extract mannitol agar medium. Bradyrhizobium sp. (vigna) strain RM8 produced 13.3 microg ml(-1) of indole acetic acid in Luria Bertani broth at 100 microg ml(-1) of tryptophan which increased to 13.6 microg ml(-1) at 50 microg Ni ml(-1) and 13.5 microg ml(-1) at 300 microg Zn ml(-1). Strain RM8 was positive for siderophore, HCN and ammonia both in the absence and presence of nickel and zinc. The PGP activity of this strain was further evaluated with increasing concentrations of nickel and zinc using greengram as a test crop. The bioinoculant enhanced the nodule numbers by 82%, leghaemoglobin by 120%, seed yield by 34%, grain protein by 13%, root N by 41% and shoot N by 37% at 290 mg Ni kg(-1) soil. At 4890 mg Zn kg(-1) soil, the bioinoculant increased the nodule numbers by 50%, leghaemoglobin by 100%, seed yield by 36%, grain protein by 13%, root N by 47% and shoot N by 42%. The bioinoculant strain RM8 reduced the uptake of nickel and zinc by plant organs compared to plants grown in the absence of bioinoculant. This study suggested that the bioinoculant due to its intrinsic abilities of growth promotion and attenuation of the toxic effects of nickel and zinc could be exploited for remediation of metal from nickel and zinc contaminated sites.

Accumulation, speciation and cellular localization of copper in Sesbania drummondii

Growth, accumulation and intracellular speciation and distribution of copper (Cu) in Sesbania drummondii was studied using scanning-electron microscopy (SEM), X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). The growth of seedlings was assessed in terms of biomass accumulation. The growth of the seedling was enhanced by 73.5% at a low Cu concentration (50 mg l-1) compared to the control treatment. Additionally, seedling growth was inhibited by 18% at 300 mg l-1 Cu with respect to the control. Copper concentration in roots and shoots was increased with increasing Cu concentration in the growth solution. The accumulation of Cu was found to be higher in roots than in the shoots. At a concentration of 300 mg l-1 Cu, the roots accumulated 27,440 mg Cu kg-1 dry weight (dw) while shoots accumulated 1282 mg Cu kg-1 dw. Seedlings were assessed for photosynthetic activity by measuring chlorophyll a fluorescence parameters: Fv/Fm and Fv/F0 values. Photosynthetic integrity was not affected by any of the Cu treatments. The X-ray absorption spectroscopic (XAS) studies showed that Cu was predominantly present as Cu(II) in Sesbania tissue. In addition, from the XAS studies it was shown that the Cu exists in a mixture of different coordination states consisting of Cu bound to sugars and small organic acids with some possible precipitated copper oxide. From the EXAFS studies, the coordination of Cu was determined to have four equatorial oxygen(nitrogen) ligands at 1.96 A and two axial oxygen ligands at 2.31 A. Scanning-electron microscopy studies revealed the distribution of Cu within the seedlings tissues, predominantly accumulated in the cortical and vascular (xylem) regions of root tissues. In the stem, most of the Cu was found within the xylem tissue. However, the deposition of Cu within the leaf tissues was in the parenchyma. The present study demonstrates the mechanisms employed by S. drummondii for Cu uptake and its biotransformation.

Impact of heavy metal toxicity on plant growth, symbiosis, seed yield and nitrogen and metal uptake in chickpea

Experiments were conducted to investigate the phytotoxic effects of heavy metals on chickpea, grown in unsterilised soils. Cadmium at 23 mg/kg soil, when used alone or in combination with other metals, was found to be the most toxic and significantly (P ≤ 0.05) reduced the plant growth, nodulation, chlorophyll content, and root and shoot N contents. Cadmium (23 mg/kg soil) and lead (390 mg/kg soil) reduced the number of nodules by 69.2 and 13.7%, respectively. Cadmium at 5.75 and 11.5 mg/kg soil decreased the seed yield by 14 and 19%, respectively, compared with the control. In contrast, lead at 97.5 and 195 mg/kg soil increased the seed yield by 12.3 and 8.8%, respectively, above the control. Generally, the chlorophyll content decreased with increasing rates of each metal. The root and shoot N content decreased by 33.3 and 30.7% at 23 mg/kg of cadmium, whereas lead at 390 mg/kg soil increased the root and shoot N content by 10 and 3%, respectively, above the control. The grain protein decreased gradually with increasing rates of each metal. An average maximum reduction (27%) in grain protein was observed with mixtures of 23 mg cadmium + 135 mg chromium + 580.2 mg nickel per kg soil. Flowering in chickpea plants was delayed following metal application. The degree of toxicity of heavy metals on the measured parameters decreased in the following order: cadmium, zinc, nickel, copper, chromium, then lead. Accumulation of heavy metals was higher in the roots relative to the shoots of chickpea and was significantly correlated with the concentration of the metals added to the soil.