Differential antioxidative responses to cadmium in roots and leaves of pea (Pisum sativum L. cv. Azad)

Regulation of Phytosiderophore Release and Antioxidant Defense in Roots Driven by Shoot-Based Auxin Signaling Confers Tolerance to Excess Iron in Wheat

Iron (Fe) is essential but harmful for plants at toxic level. However, how wheat plants tolerate excess Fe remains vague. This study aims at elucidating the mechanisms underlying tolerance to excess Fe in wheat. Higher Fe concentration caused morpho-physiological retardation in BR 26 (sensitive) but not in BR 27 (tolerant). Phytosiderophore and 2-deoxymugineic acid showed no changes in BR 27 but significantly increased in BR 26 due to excess Fe. Further, expression of TaSAMS. TaDMAS1, and TaYSL15 significantly downregulated in BR 27 roots, while these were upregulated in BR 26 under excess Fe. It confirms that inhibition of phytosiderophore directs less Fe accumulation in BR 27. However, phytochelatin and expression of TaPCS1 and TaMT1 showed no significant induction in response to excess Fe. Furthermore, excess Fe showed increased catalase, peroxidase, and glutathione reductase activities along with glutathione, cysteine, and proline accumulation in roots in BR 27. Interestingly, BR 27 self-grafts and plants having BR 26 rootstock attached to BR 27 scion had no Fe-toxicity induced adverse effect on morphology but showed BR 27 type expressions, confirming that shoot-derived signal triggering Fe-toxicity tolerance in roots. Finally, auxin inhibitor applied with higher Fe concentration caused a significant decline in morpho-physiological parameters along with increased TaSAMS and TaDMAS1 expression in roots of BR 27, revealing the involvement of auxin signaling in response to excess Fe. These findings propose that tolerance to excess Fe in wheat is attributed to the regulation of phytosiderophore limiting Fe acquisition along with increased antioxidant defense in roots driven by shoot-derived auxin signaling.

Physiological and proteomic analysis of selenium-mediated tolerance to Cd stress in cucumber (Cucumis sativus L.)

Selenium can mitigate cadmium toxicity in plants. However, the mechanism of this alleviation has not been fully understood. In the present study, the role of Se in inducing tolerance to Cd stress in cucumber was elucidated. Results showed that Se significantly alleviated Cd-induced growth inhibition, reduced Cd concentration, increased SPAD value and improved photosynthetic performance. Through proteomic analysis by two-dimensional gel electrophoresis (2-DE) coupled with mass spectrometry, 26 protein spots were identified, which were significantly influenced by Cd stress and/or Se application. Among these proteins, the abundance of 21 spots (10 in leaves and 11 in roots) were repressed in Cd-treated and up-accumulated or no-changed in Cd+Se-treated cucumber. These altered proteins were involved in the response to stress, metabolism, photosynthesis and storage, they were including glutathione S-transferase F8, heat shock protein STI-like, peroxidase, ascorbate oxidase, fructose-bisphosphate aldolase 2, NiR, Rieske type ion sulfur subunit and PsbP domain-containing protein 6. Furthermore, we identified five proteins with an increase in relative abundance after Cd treatment, they were involved in the functional groups active in response to stress and transport. The present study provided novel insights into Se-mediated tolerance of cucumber seedlings against Cd toxicity at the proteome level.

Expression of Echmr gene from Eichhornia offers multiple stress tolerance to Cd sensitive Escherichia coli Δgsh mutants

The detoxification of heavy metals frequently involves conjugation to glutathione prior to compartmentalization and eflux in higher plants. We have expressed a heavy metal stress responsive (Echmr) gene from water hyacinth, which conferred tolerance to Cd sensitive Escherichia coli Δgsh mutants against heavy metals and abiotic stresses. The recombinant E. coli Δgsh mutant cells showed better growth recovery and survival than control cells under Cd (200 μM), Pb(200 μM), heat shock (50 °C), cold stress at 4 °C for 4 h, and UV-B (20 min) exposure. The enhanced expression of Echmr gene revealed by northern analysis during above stresses further advocates its role in multi-stress tolerance. Heterologous expression of EcHMR from Eichhornia rescued Cd(2+) sensitive E. coli mutants from Cd(2+) toxicity and induced better recovery post abiotic stresses. This may suggests a possible role of Echmr in Cd(II) and desiccation tolerance in plants for enhanced stress response.

Performance of rose scented geranium (Pelargonium graveolens) in heavy metal polluted soil vis-à-vis phytoaccumulation of metals

An investigation was carried out to evaluate the effect of heavy metal toxicity on growth, herb, oil yield and quality and metal accumulation in rose scented geranium (Pelargonium graveolens) grown in heavy metal enriched soils. Four heavy metals (Cd, Ni, Cr, and Pb) each at two levels (10 and 20 mg kg-1 soil) were tested on geranium. Results indicated that Cr concentration in soil at 20 mg kg-1 reduced leaves, stem and root yield by 70, 83, and 45%, respectively, over control. Root growth was significantly affected in Cr stressed soil. Nickel, Cr, and Cd concentration and accumulation in plant increased with higher application of these metals. Chromium, nickel and cadmium uptake was observed to be higher in leaves than in stem and roots. Essential oil constituents were generally not significantly affected by heavy metals except Pb at 10 and 20 ppm, which significantly increased the content of citronellol and Ni at 20 ppm increased the content of geraniol. Looking in to the higher accumulation of toxic metals by geranium and the minimal impact of heavy metals on quality of essential oil, geranium can be commercially cultivated in heavy metal polluted soil for production of high value essential oil.

Cadmium toxicity investigated at the physiological and biophysical levels under environmentally relevant conditions using the aquatic model plant Ceratophyllum demersum

Cadmium (Cd) is an important environmental pollutant and is poisonous to most organisms. We aimed to unravel the mechanisms of Cd toxicity in the model water plant Ceratophyllum demersum exposed to low (nM) concentrations of Cd as are present in nature. Experiments were conducted under environmentally relevant conditions, including nature-like light and temperature cycles, and a low biomass to water ratio. We measured chlorophyll (Chl) fluorescence kinetics, oxygen exchange, the concentrations of reactive oxygen species and pigments, metal binding to proteins, and the accumulation of starch and metals. The inhibition threshold concentration for most parameters was 20 nM. Below this concentration, hardly any stress symptoms were observed. The first site of inhibition was photosynthetic light reactions (the maximal quantum yield of photosystem II (PSII) reaction centre measured as Fv /Fm , light-acclimated PSII activity ΦPSII , and total Chl). Trimers of the PSII light-harvesting complexes (LHCIIs) decreased more than LHC monomers and detection of Cd in the monomers suggested replacement of magnesium (Mg) by Cd in the Chl molecules. As a consequence of dysfunctional photosynthesis and energy dissipation, reactive oxygen species (superoxide and hydrogen peroxide) appeared. Cadmium had negative effects on macrophytes at much lower concentrations than reported previously, emphasizing the importance of studies applying environmentally relevant conditions. A chain of inhibition events could be established.

Antioxidant defense gene analysis in Brassica oleracea and Trifolium repens exposed to Cd and/or Pb

This study focused on the expression analysis of antioxidant defense genes in Brassica oleracea and in Trifolium repens. Plants were exposed for 3, 10, and 56 days in microcosms to a field-collected suburban soil spiked by low concentrations of cadmium and/or lead. In both species, metal accumulations and expression levels of genes encoding proteins involved and/or related to antioxidant defense systems (glutathione transferases, peroxidases, catalases, metallothioneins) were quantified in leaves in order to better understand the detoxification processes involved following exposure to metals. It appeared that strongest gene expression variations in T. repens were observed when plants are exposed to Cd (metallothionein and ascorbate peroxidase upregulations) whereas strongest variations in B. oleracea were observed in case of Cd/Pb co-exposures (metallothionein, glutathione transferase, and peroxidase upregulations). Results also suggest that there is a benefit to use complementary species in order to better apprehend the biological effects in ecotoxicology.

Adaptation and detoxification mechanisms of Vetiver grass (Chrysopogon zizanioides) growing on gold mine tailings

Vetiver grass (Chrysopogon zizanioides) was investigated for its potential use in the rehabilitation of gold mine tailings, its ability to extract and accumulate toxic metals from the tailings and its metal tolerant strategies. Vetiver grass was grown on gold mine tailings soil, in a hothouse, and monitored for sixteen weeks. The mine tailings were highly acidic and had high electrical conductivity. Vetiver grass was able to grow and adapt well on gold mine tailings. The results showed that Vetiver grass accumulated large amounts of metals in the roots and restricted their translocation to the shoots. This was confirmed by the bioconcentration factor of Zn, Cu, and Ni of >1 and the translocation factor of <1 for all the metals. This study revealed the defense mechanisms employed by Vetiver grass against metal stress that include: chelation of toxic metals by phenolics, glutathione S-tranferase, and low molecular weight thiols; sequestration and accumulation of metals within the cell wall that was revealed by the scanning electron microscopy that showed closure of stomata and thickened cell wall and was confirmed by high content of cell wall bound phenolics. Metal induced reactive oxygen species are reduced or eliminated by catalase, superoxide dismutase and peroxidase dismutase.

Selenium Supplementation Affects Physiological and Biochemical Processes to Improve Fodder Yield and Quality of Maize (Zea mays L.) under Water Deficit Conditions

Climate change is one of the most complex challenges that pose serious threats to livelihoods of poor people who rely heavily on agriculture and livestock particularly in climate-sensitive developing countries of the world. The negative effects of water scarcity, due to climate change, are not limited to productivity food crops but have far-reaching consequences on livestock feed production systems. Selenium (Se) is considered essential for animal health and has also been reported to counteract various abiotic stresses in plants, however, understanding of Se regulated mechanisms for improving nutritional status of fodder crops remains elusive. We report the effects of exogenous selenium supply on physiological and biochemical processes that may influence green fodder yield and quality of maize (Zea mays L.) under drought stress conditions. The plants were grown in lysimeter tanks under natural conditions and were subjected to normal (100% field capacity) and water stress (60% field capacity) conditions. Foliar spray of Se was carried out before the start of tasseling stage (65 days after sowing) and was repeated after 1 week, whereas, water spray was used as a control. Drought stress markedly reduced the water status, pigments and green fodder yield and resulted in low forage quality in water stressed maize plants. Nevertheless, exogenous Se application at 40 mg L^-1 resulted in less negative leaf water potential (41%) and enhanced relative water contents (30%), total chlorophyll (53%), carotenoid contents (60%), accumulation of total free amino acids (40%) and activities of superoxide dismutase (53%), catalase (30%), peroxidase (27%), and ascorbate peroxidase (27%) with respect to control under water deficit conditions. Consequently, Se regulated processes improved fodder yield (15%) and increased crude protein (47%), fiber (10%), nitrogen free extract (10%) and Se content (36%) but did not affect crude ash content in water stressed maize plants. We propose that Se foliar spray (40 mg L^-1) is a handy, feasible and cost-effective approach to improve maize fodder yield and quality in arid and semi-arid regions of the world facing acute shortage of water.

Arbuscular mycorrhizal fungal inoculation protects Miscanthus × giganteus against trace element toxicity in a highly metal-contaminated site

Arbuscular mycorrhizal fungus (AMF)-assisted phytoremediation could constitute an ecological and economic method in polluted soil rehabilitation programs. The aim of this work was to characterize the trace element (TE) phytoremediation potential of mycorrhizal Miscanthus × giganteus. To understand the mechanisms involved in arbuscular mycorrhizal symbiosis tolerance to TE toxicity, the fatty acid compositions and several stress oxidative biomarkers were compared in the roots and leaves of Miscanthus × giganteus cultivated under field conditions in either TE-contaminated or control soils. TEs were accumulated in greater amounts in roots, but the leaves were the organ most affected by TE contamination and were characterized by a strong decrease in fatty acid contents. TE-induced oxidative stress in leaves was confirmed by an increase in the lipid peroxidation biomarker malondialdehyde (MDA). TE contamination decreased the GSSG/GSH ratio in the leaves of exposed plants, while peroxidase (PO) and superoxide dismutase (SOD) activities were increased in leaves and in whole plants, respectively. AMF inoculation also increased root colonization in the presence of TE contamination. The mycorrhizal colonization determined a decrease in SOD activity in the whole plant and PO activities in leaves and induced a significant increase in the fatty acid content in leaves and a decrease in MDA formation in whole plants. These results suggested that mycorrhization is able to confer protection against oxidative stress induced by soil pollution. Our findings suggest that mycorrhizal inoculation could be used as a bioaugmentation technique, facilitating Miscanthus cultivation on highly TE-contaminated soil.

Hydrogen sulfide modulates cadmium-induced physiological and biochemical responses to alleviate cadmium toxicity in rice

We investigated the physiological and biochemical mechanisms by which H₂S mitigates the cadmium stress in rice. Results revealed that cadmium exposure resulted in growth inhibition and biomass reduction, which is correlated with the increased uptake of cadmium and depletion of the photosynthetic pigments, leaf water contents, essential minerals, water-soluble proteins, and enzymatic and non-enzymatic antioxidants. Excessive cadmium also potentiated its toxicity by inducing oxidative stress, as evidenced by increased levels of superoxide, hydrogen peroxide, methylglyoxal and malondialdehyde. However, elevating endogenous H₂S level improved physiological and biochemical attributes, which was clearly observed in the growth and phenotypes of H₂S-treated rice plants under cadmium stress. H₂S reduced cadmium-induced oxidative stress, particularly by enhancing redox status and the activities of reactive oxygen species and methylglyoxal detoxifying enzymes. Notably, H₂S maintained cadmium and mineral homeostases in roots and leaves of cadmium-stressed plants. By contrast, adding H₂S-scavenger hypotaurine abolished the beneficial effect of H₂S, further strengthening the clear role of H₂S in alleviating cadmium toxicity in rice. Collectively, our findings provide an insight into H₂S-induced protective mechanisms of rice exposed to cadmium stress, thus proposing H₂S as a potential candidate for managing toxicity of cadmium, and perhaps other heavy metals, in rice and other crops.

Profiling of rutin-mediated alleviation of cadmium-induced oxidative stress in Zygophyllum fabago

Zygophyllum fabago grows in arid, saline soil, or disturbed sites, such as former industrial or mining areas. This species is able to grow in coarse mineral substrates contaminated with heavy metals. To investigate the effects of the flavonoid rutin (Rtn) on certain heavy metal stress responses such as antioxidant defense systems and water status, seedlings were subjected to 100 and 200 μM CdCl2 treatment without or with 0.25 and 1 mM Rtn for 7 and 14 d (days). Cd stress decreased growth (RGR), water content (RWC), leaf osmotic potential (Ψ(Π)), and chlorophyll fluorescence, all of which could be partly alleviated by addition of Rtn. Activities of superoxide dismutase, peroxidase (POX), ascorbate peroxidase, and glutathione reductase increased within the first 7 d after exposure to Cd. However, failure of antioxidant defense in the scavenging of reactive oxygen species (ROS) was evidenced by an abnormal rise in superoxide anion radical ( O2(•-)) and hydrogen peroxide contents and a decline in hydroxyl radical (OH(•)) scavenging activity, resulting in enhancement of lipid peroxidation (TBARS) as a marker of Cd-induced oxidative stress. However, exogenously applied Rtn considerably improved the stress tolerance of plants via a reduction in Cd accumulation, modulation of POX activity, increase of proline (Pro) content, decrease in TBARS and ROS content and consequent lowering of oxidative damage of membrane. Overall, 0.25 and 1 mM Rtn could protect Z. fabago from the harmful effects of 100 μM Cd-induced oxidative stress throughout the experiment.

Contribution of glutathione to the control of cellular redox homeostasis under toxic metal and metalloid stress

The accumulation of toxic metals and metalloids, such as cadmium (Cd), mercury (Hg), or arsenic (As), as a consequence of various anthropogenic activities, poses a serious threat to the environment and human health. The ability of plants to take up mineral nutrients from the soil can be exploited to develop phytoremediation technologies able to alleviate the negative impact of toxic elements in terrestrial ecosystems. However, we must select plant species or populations capable of tolerating exposure to hazardous elements. The tolerance of plant cells to toxic elements is highly dependent on glutathione (GSH) metabolism. GSH is a biothiol tripeptide that plays a fundamental dual role: first, as an antioxidant to mitigate the redox imbalance caused by toxic metal(loid) accumulation, and second as a precursor of phytochelatins (PCs), ligand peptides that limit the free ion cellular concentration of those pollutants. The sulphur assimilation pathway, synthesis of GSH, and production of PCs are tightly regulated in order to alleviate the phytotoxicity of different hazardous elements, which might induce specific stress signatures. This review provides an update on mechanisms of tolerance that depend on biothiols in plant cells exposed to toxic elements, with a particular emphasis on the Hg-triggered responses, and considering the contribution of hormones to their regulation.

Physiological and proteomics analyses reveal the mechanism of Eichhornia crassipes tolerance to high-concentration cadmium stress compared with Pistia stratiotes

Cadmium (Cd) pollution is an environmental problem worldwide. Phytoremediation is a convenient method of removing Cd from both soil and water, but its efficiency is still low, especially in aquatic environments. Scientists have been trying to improve the ability of plants to absorb and accumulate Cd based on interactions between plants and Cd, especially the mechanism by which plants resist Cd. Eichhornia crassipes and Pistia stratiotes are aquatic plants commonly used in the phytoremediation of heavy metals. In the present study, we conducted physiological and biochemical analyses to compare the resistance of these two species to Cd stress at 100 mg/L. E. crassipes showed stronger resistance and was therefore used for subsequent comparative proteomics to explore the potential mechanism of E. crassipes tolerance to Cd stress at the protein level. The expression patterns of proteins in different functional categories revealed that the physiological activities and metabolic processes of E. crassipes were affected by exposure to Cd stress. However, when some proteins related to these processes were negatively inhibited, some analogous proteins were induced to compensate for the corresponding functions. As a result, E. crassipes could maintain more stable physiological parameters than P. stratiotes. Many stress-resistance substances and proteins, such as proline and heat shock proteins (HSPs) and post translational modifications, were found to be involved in the protection and repair of functional proteins. In addition, antioxidant enzymes played important roles in ROS detoxification. These findings will facilitate further understanding of the potential mechanism of plant response to Cd stress at the protein level.

Specific mechanisms of tolerance to copper and cadmium are compromised by a limited concentration of glutathione in alfalfa plants

The induction of oxidative stress is a characteristic symptom of metal phytotoxicity and is counteracted by antioxidants such as glutathione (GSH) or homoglutathione (hGSH). The depletion of GSH│hGSH in fifteen-day-old alfalfa (Medicago sativa) plants pre-incubated with 1mM buthionine sulfoximine (BSO) affected antioxidant responses in a metal-specific manner under exposure to copper (Cu; 0, 6, 30 and 100μM) or cadmium (Cd; 0, 6 and 30μM) for 7 days. The phytotoxic symptoms observed with excess Cu were accompanied by an inhibition of root glutathione reductase (GR) activity, a response that was augmented in Cd-treated plants but reverted when combined with BSO. The synthesis of phytochelatins (PCs) was induced by Cd, whereas the biothiol concentration decreased in Cu-treated plants, which did not accumulate PCs. The depletion of GSH│hGSH by BSO also produced a strong induction of oxidative stress under excess Cu stress, primarily due to impaired GSH│hGSH-dependent redox homeostasis. In addition, the synthesis of PCs was required for Cd detoxification, apparently also determining the distribution of Cd in plants, as less metal was translocated to the shoots in BSO-incubated plants. Therefore, specific GSH│hGSH-associated mechanisms of tolerance were triggered by stress due to each metal.

Antioxidant responses of Annelids, Brassicaceae and Fabaceae to pollutants: a review

Pollutants, such as Metal Trace Elements (MTEs) and organic compounds (polycyclic aromatic hydrocarbons, pesticides), can impact DNA structure of living organisms and thus generate damage. For instance, cadmium is a well-known genotoxic and mechanisms explaining its clastogenicity are mainly indirect: inhibition of DNA repair mechanisms and/or induction of Reactive Oxygen Species (ROS). Animal or vegetal cells use antioxidant defense systems to protect themselves against ROS produced during oxidative stress. Because tolerance of organisms depends, at least partially, on their ability to cope with ROS, the mechanisms of production and management of ROS were investigated a lot in Ecotoxicology as markers of biotic and abiotic stress. This was mainly done through the measurement of enzyme activities The present Review focuses on 3 test species living in close contact with soil that are often used in soil ecotoxicology: the worm Eisenia fetida, and two plant species, Trifolium repens (white clover) and Brassica oleracea (cabbage). E. fetida is a soil-dwelling organism commonly used for biomonitoring. T. repens is a symbiotic plant species which forms root nodule with soil bacteria, while B. oleracea is a non-symbiotic plant. In literature, some oxidative stress enzyme activities have already been measured in those species but such analyses do not allow distinction between individual enzyme involvements in oxidative stress. Gene expression studies would allow this distinction at the transcriptomic level. A literature review and a data search in molecular database were carried out on the basis of keywords in Scopus, in PubMed and in Genbank™ for each species. Molecular data regarding E. fetida were already available in databases, but a lack of data regarding oxidative stress related genes was observed for T. repens and B. oleracea. By exploiting the conservation observed between species and using molecular biology techniques, we partially cloned missing candidates involved in oxidative stress and in metal detoxification in E. fetida, T. repens and B. oleracea.

EDTA enhanced plant growth, antioxidant defense system, and phytoextraction of copper by Brassica napus L

Copper (Cu) is an essential micronutrient for normal plant growth and development, but in excess, it is also toxic to plants. The present study investigated the influence of ethylenediaminetetraacetic acid (EDTA) in enhancing Cu uptake and tolerance as well as the morphological and physiological responses of Brassica napus L. seedlings under Cu stress. Four-week-old seedlings were transferred to hydroponics containing Hoagland's nutrient solution. After 2 weeks of transplanting, three levels (0, 50, and 100 μM) of Cu were applied with or without application of 2.5 mM EDTA and plants were further grown for 8 weeks in culture media. Results showed that Cu alone significantly decreased plant growth, biomass, photosynthetic pigments, and gas exchange characteristics. Cu stress also reduced the activities of antioxidants, such as superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), and catalase (CAT) along with protein contents. Cu toxicity increased the concentration of reactive oxygen species (ROS) as indicated by the increased production of malondialdehyde (MDA) and hydrogen peroxide (H2O2) in both leaves and roots. The application of EDTA significantly alleviated Cu-induced toxic effects in B. napus, showing remarkable improvement in all these parameters. EDTA amendment increased the activity of antioxidant enzymes by decreasing the concentrations of MDA and H2O2 both in leaves and roots of B. napus. Although, EDTA amendment with Cu significantly increased Cu uptake in roots, stems, and leaves in decreasing order of concentration but increased the growth, photosynthetic parameters, and antioxidant enzymes. These results showed that the application of EDTA can be a useful strategy for phytoextraction of Cu by B. napus from contaminated soils.

Physiological Responses and Tolerance Mechanisms to Cadmium in Conyza canadensis

Experiments were conducted to examine the effects of different concentrations of Cd on the performance of the Cd accumulator Conyza canadensis. Cd accumulation in roots and leaves (roots>leaves) increased with increasing Cd concentration in soil. High Cd concentration inhibited plant growth, increased the membrane permeability of leaves, and caused a significant decline in plant height and chlorophyll [chlorophyll (Chl) a, Chl b, and total Chl] content. Leaf ultrastructural analysis of spongy mesophyllic cells revealed that excessive Cd concentrations cause adverse effects on the chloroplast and mitochondrion ultrastructures of C. canadensis. However, the activities of antioxidant enzymes, such as superoxide dismutase, catalase, peroxidase, total non-protein SH compounds, glutathione, and phytochelatin (PC) concentrations, showed an overall increase. Specifically, the increase in enzyme activities demonstrated that the antioxidant system may play an important role in eliminating or alleviating the toxicity of Cd in C. canadensis. Furthermore, results demonstrate that PC synthesis in plant cells is related to Cd concentration and that PC production levels in plants are related to the toxic effects caused by soil Cd level. These findings demonstrate the roles played by these compounds in supporting Cd tolerance in C. canadensis.

Drought degree constrains the beneficial effects of a fungal endophyte on Atractylodes lancea

AIMS

Plants, fungal endophytes (FEs) and the changing environment interact with each other forming an interlaced network. This study evaluates nonadditive and interactive effects of the FE Acremonium strictum and drought treatment on Atractylodes lancea plantlets.

METHODS AND RESULTS

By applying FEs (meristem cultures of At. lancea, fungal inoculation of Ac. strictum and plantlet acclimatization) and drought treatment (regular watering, mild drought, severe drought), a research system of At. lancea ramets under different treatments was established. During 12 days of drought treatment, the plantlets' physiological responses and basic growth traits were measured and analysed. Although drought and FE presence affected plantlet traits to differing degrees, the interactive effects of the two were more pronounced. In particular under mild drought treatment, the FE conferred drought tolerance to plantlets by enhancing leaf soluble sugars, proteins, proline and antioxidant enzyme activity; decreasing the degree of plasmalemma oxidation; and increasing the host's abscisic acid level and root:shoot ratio. When exposed to regular watering or severe drought, these effects were not significant.

CONCLUSIONS

Plant traits plasticity was conferred by dual effects of drought stress and FEs, and these factors are interactive. Although FEs can help plants cope with drought stress, the beneficial effects are strictly constrained by drought degree.

SIGNIFICANCE AND IMPACT OF THE STUDY

During finite environmental stress, FEs can benefit plants, and for this reason, they may alleviate the effects of climate change on plants. However, because the benefits of FEs are highly context dependent, the role of FEs in a changing background should be re-assessed.

Cadmium induces two waves of reactive oxygen species in Glycine max (L.) roots

Cadmium (Cd) is a non-essential heavy metal that may be toxic or even lethal to plants as it can be easily taken up by the roots and loaded into the xylem to the leaves. Using soybean roots (Glycine max L.) DM 4800, we have analysed various parameters related to reactive oxygen metabolism and nitric oxide (NO) during a 6 day Cd exposure. A rise in H(2)O(2) and NO, and to a lesser extent O(2)(·-) content was observed after 6 h exposure with a concomitant increase in lipid peroxidation and carbonyl group content. Both oxidative markers were significantly reduced after 24 h. A second, higher wave of O(2)(·-) production was also observed after 72 h of exposure followed by a reduction until the end of the treatment. NOX and glicolate oxidase activity might be involved in the initial Cd-induced reactive oxygen species (ROS) production and it appears that other sources may also participate. The analysis of antioxidative enzymes showed an increase in glutathione-S-transferase activity and in transcript levels and activity of enzymes involved in the ascorbate-glutathione cycle and the NADPH-generating enzymes. These results suggest that soybean is able to respond rapidly to oxidative stress imposed by Cd by improving the availability of NADPH necessary for the ascorbate-glutathione cycle.

Accumulation of heavy metals using Sorghum sp

The essential requirement for the effective phytoremediation is selection of a plant species which should be metal tolerant, with high biomass production and known agronomic techniques. The above mentioned criteria are met by crop plant sorghum (Sorghum bicolor). The response of hydroponically grown S. bicolor plants to cadmium and zinc stress was followed. The impact of metal application on physiological parameters, including changes in chlorophylls contents and antioxidative enzymes activities, was followed during the stress progression. Cadmium and zinc were accumulated primarily in the roots of sorghum plants. However, elevation of metal concentrations in the media promoted their transfer to the shoots. Toxic effects of metals applied at lower concentrations were less serious in the shoots in comparison with their influence to the roots. When applied at higher concentrations, transfer of the metals into the leaves increased, causing growth reduction and leading to Chl loss and metal-induced chlorosis. Moreover, higher metal levels in the roots overcame the quenching capacity of peroxidase and glutathione transferase, which was associated with reduction of their activities. Fortification of antioxidant system by addition of glutathione significantly increased the accumulation of cadmium in the roots as well as in the shoots at the highest cadmium concentration applied.

Hydrogen sulfide alleviates lead-induced photosynthetic and ultrastructural changes in oilseed rape

The role of hydrogen sulfide (H2S) in alleviating lead (Pb) induced stress in oilseed rape (Brassica napus L.) was studied under laboratory conditions. Plants were grown hydroponically in greenhouse conditions under three levels (0, 100, and 400 µM) of Pb and three levels (0, 100 and 200 µM) of H2S donor, sodium hydrosulfide (NaHS). Application of H2S significantly improved the plant growth, root morphology, chlorophyll contents and photosynthetic activity in leaves of B. napus under Pb stress. Moreover, exogenously applied H2S significantly lowered the Pb concentration in shoots and roots of plants under Pb stress. The microscopic examination indicated that application of exogenous H2S enabled a clean mesophyll cell having a well developed chloroplast with thylakoid membranes and starch grains. A number of modifications could be observed in root tip cell i.e. mature mitochondria, long endoplasmic reticulum and golgibodies under combined application of H2S and Pb. On the basis of these findings, it can be concluded that application of exogenous H2S has a protective role on plant growth, net photosynthesis rate and ultrastructural changes in B. napus plants under high Pb exposures.

The effects of cadmium-zinc interactions on biochemical responses in tobacco seedlings and adult plants

The objective of the present study was to investigate the effects of cadmium-zinc (Cd-Zn) interactions on their uptake, oxidative damage of cell macromolecules (lipids, proteins, DNA) and activities of antioxidative enzymes in tobacco seedlings as well as roots and leaves of adult plants. Seedlings and plants were exposed to Cd (10 µM and 15 µM) and Zn (25 µM and 50 µM) as well as their combinations (10 µM or 15 µM Cd with either 25 µM or 50 µM Zn). Measurement of metal accumulation exhibited that Zn had mostly positive effect on Cd uptake in roots and seedlings, while Cd had antagonistic effect on Zn uptake in leaves and roots. According to examined oxidative stress parameters, in seedlings and roots individual Cd treatments induced oxidative damage, which was less prominent in combined treatments, indicating that the presence of Zn alleviates oxidative stress. However, DNA damage found in seedlings, and lower glutathione reductase (GR) and superoxide dismutase (SOD) activity recorded in both seedlings and roots, after individual Zn treatments, indicate that Zn accumulation could impose toxic effects. In leaves, oxidative stress was found after exposure to Cd either alone or in combination with Zn, thus implying that in this tissue Zn did not have alleviating effects. In conclusion, results obtained in different tobacco tissues suggest tissue-dependent Cd-Zn interactions, which resulted in activation of different mechanisms involved in the protection against metal stress.

Impaired leaf CO2 diffusion mediates Cd-induced inhibition of photosynthesis in the Zn/Cd hyperaccumulator Picris divaricata

Mechanisms of cadmium (Cd)-induced inhibition of photosynthesis in the Zn/Cd hyperaccumulator Picris divaricata were investigated using photosynthesis limitation analysis. P. divaricata seedlings were grown in nutrient solution containing 0, 5, 10, 25, 50, or 75 μM Cd for 2 weeks. Total limitations to photosynthesis (TL) increased from 0% at 5 μM Cd to 68.8% at 75 μM Cd. CO2 diffusional limitation (DL) made the largest contribution to TL, accounting for 93-98% of TL in the three highest Cd treatments, compared to just 2-7% of TL attributable to biochemical limitation (BL). Microscopic imaging revealed significantly decreased stomatal density and mesophyll thickness in the three highest Cd treatments. Chlorophyll fluorescence parameters related to photosynthetic biochemistry (Fv/Fm, NPQ, ΦPSII, and qP) were not significantly decreased by increased Cd supply. Our results suggest that increased DL in leaves is the main cause of Cd-induced inhibition of photosynthesis in P. divaricata, possibly due to suppressed function of mesophyll and stomata. Analysis of chlorophyll fluorescence showed that Cd supply had little effect on photochemistry parameters, suggesting that the PSII reaction centers are not a main target of Cd inhibition of photosynthesis in P. divaricata.

Antimony toxicity in the lichen Xanthoria parietina (L.) Th. Fr

In this paper we tested if treating the lichen Xanthoria parietina with Sb-containing solutions causes Sb bioaccumulation as well as physiological and ultrastructural changes. Total and intracellular antimony content in Sb-treated samples increased progressively with increasing concentration in the treatment solutions. Incubation of X. parietina thalli with Sb at concentrations as low as 0.1mM caused a decrease in sample viability, measured as intensity of respiratory activity, and damage to cell membranes, expressed in terms of membrane lipid peroxidation, as well as ultrastructural changes such as plasmolysis, impairment of the thylakoid system of the alga and cytoplasmic lipid droplets. The photosynthetic system hardly responded, at least under the tested experimental conditions.

The negative effects of cadmium on Bermuda grass growth might be offset by submergence

Revegetation in the water-level-fluctuation zone (WLFZ) could stabilize riverbanks, maintain local biodiversity, and improve reservoir water quality in the Three Gorges Reservoir Region (TGRR). However, submergence and cadmium (Cd) may seriously affect the survival of transplantations. Bermuda grass (Cynodon dactylon) is a stoloniferous and rhizomatous prostrate weed displaying high growth rate. A previous study has demonstrated that Bermuda grass can tolerate deep submergence and Cd stress, respectively. In the present study, we further analyzed physiological responses of Bermuda grass induced by Cd-and-submergence stress. The ultimate goal was to explore the possibility of using Bermuda grass for revegetation in the WLFZ of China's TGRR and other riparian areas. The Cd-and-submergence-treated plants had higher malondialdehyde contents and peroxidase than control, and both increased with the Cd concentration increase. All treated plants catalase activity increased with the experimental duration increases, and their superoxide dismutase also gradually increased with the Cd concentration from 1 day to 15 days. Total biomass of the same Cd-and-submergence plants increased along the experimental duration as well. Plants exposed to Cd-and-submergence stress showed shoot elongation. The heights of all treated plants were taller than those of the control. Leaf chlorophyll contents, maximum leaf length, and soluble sugars contents of all the Cd-and-submergence-treated plants were more than those of the untreated control. Although Cd inhibits plants growth, decreases chlorophyll and biomass content, and with the submergence induced the leaf and shoot elongation, more part of the Cd-and-submergence stress plants appeared in the air, exhibited fast growth with maintenance of leaf color, which guaranteed the plants' photosynthesis, and ensured the total biomass and carbohydrate sustainability, further promoting Cd-and-submergence tolerance. The results imply that the negative effects of cadmium on Bermuda grass growth might be offset by submergence.

Mineral nutrient imbalance, total antioxidants level and DNA damage in common bean (Phaseolus vulgaris L.) exposed to heavy metals

The present study aimed to analyze the biological effects induced by bioaccumulation of metals in common bean (Phaseolus vulgaris L.). Effects of mineral nutrient imbalance, total antioxidants level and DNA damage induced by accumulation of heavy metals, were investigated in bean seedlings treated with two selected metal concentrations for 7 days. Metal content is analyzed by inductively coupled plasma - atomic emission spectrometer (ICP-AES), for total antioxidants level assessment the Ferric-Reducing Antioxidant Power (FRAP) assay is used and Random Amplified Polymorphic DNA (RAPD) method was applied for investigation of DNA damages. The increasing metal concentration in the treatment medium changed synchronously metal content in samples, and decreased total antioxidant activity in all samples with exception only for samples treated with Ni and Cd. The obtained "DNA fingerprints" demonstrated that the increasing metal concentrations induced changes in RAPD profiles (disappearance and/or appearance of bands in comparison with untreated control samples). The highest number of missing bands was observed in samples treated with zinc (total 4 bands) and nickel (total 4 bands) at both concentrations. These results suggested that mineral nutrient imbalance is involved in changes of antioxidant levels and DNA damages of the seedlings, which may help to understand the mechanism of metal toxicity in plants.

Glutathione peroxidase expression and activity in barley root tip after short-term treatment with cadmium, hydrogen peroxide and t-butyl hydroperoxide

The purpose of this study was to analyse the alterations of glutathione peroxidase (GPX) expression and activity during the recovery period after a short-term treatment of barley root tip with cadmium (Cd) and hydrogen peroxide (H(2)O(2)). The transcript level of GPX increased as early as 1 h and GPX activity 3 h after short-term treatment independently of Cd concentration. In 15 μM Cd-treated roots, its expression reached a peak within 2 h and sustained until 3 h, after which it gradually declined. After 6 h of short-term Cd treatment, the activity of GPX was the highest in the 15-μM Cd-treated roots. At higher Cd concentrations, the activity of GPX was lower than in 15 μM Cd-treated roots, but still higher than in control roots. A considerable increase in H(2)O(2) production was observed even after only 1 h of short-term exposure of roots to 30 and 60 μM Cd, while after 15 μM Cd exposure, its production increased 3 h after the treatment. Lipid peroxidation increased even 1 h after short-term treatment in a Cd concentration-dependent manner. A considerable decrease of GPX activity was observed after the exposure of roots to H(2)O(2) or t-butyl hydroperoxide in a concentration-dependent manner despite that its expression increased even 1 h after short-term treatment. Presumable, under high acute Cd stress, rapid accumulation of H(2)O(2) leads to the disturbance of basal metabolic processes affecting also GPX activity. In contrast, high GPX activity under moderate Cd stress maintains cell function despite the high rate of H(2)O(2) metabolism in root tip.

5-Aminolevulinic acid ameliorates cadmium-induced morphological, biochemical, and ultrastructural changes in seedlings of oilseed rape

Due to its prolific growth, oilseed rape (Brassica napus L.) can be grown successfully for phytoremediation of cadmium (Cd)-contaminated soils. Nowadays, use of plant growth regulators against heavy metals stress is one of the major objectives of researchers. The present study evaluates the ameliorate effects of 5-aminolevulinic acid (ALA, 0, 0.4, 2, and 10 mg/l) on the growth of oilseed rape (B. napus L. cv. ZS 758) seedlings under Cd stress (0, 100, and 500 μM). Results have shown that Cd stress hampered the seedling growth by decreasing the radical and hypocotyls length, shoot and root biomass, chlorophyll content, and antioxidants enzymes. On the other hand, Cd stress increased the level of malondialdehyde (MDA) and production of H2O2 and accumulation of Cd in the shoots. The microscopic study of leaf mesophyll cells showed that toxicity of Cd totally destroyed the whole cell structure, and accumulation of Cd also appeared in micrographs. Application of ALA at lower dosage (2 mg/l) enhanced the seedling growth and biomass. The results showed that 2 mg/l ALA significantly improved chlorophyll content under Cd stress and decreased the level of Cd contents in shoots. Application of ALA reduced the MDA and H2O2 levels in the cotyledons. The antioxidants enzymes (ascorbate peroxidase, peroxidase, catalase, glutathione reductase, and superoxide dismutase) enhanced their activities significantly with the application of 2 mg/l ALA under Cd stress. This study also indicated that higher dosage of ALA (10 mg/l) imposed the negative effect on the growth of oilseed rape. Microscopic study showed that application of ALA alleviated the toxic effects of Cd in the mesophyll cell and improved the cell structure. Use of 2 mg/l ALA under 500 μM Cd was found to be more effective, and under this dosage, cell structure was clear, with obvious cell wall and cell membrane as well as a big nucleus, which was found with well-developed two or more nucleoli. Chloroplast was almost round in shape and contained thylakoids membranes and grana, but starch grains were not found in chloroplast comparatively to other treatments. On the basis of our results, we can conclude that ALA has a promotive effect which could improve plant survival under Cd stress.

Influence of heavy metal stress on antioxidant status and DNA damage in Urtica dioica

Heavy metals have the potential to interact and induce several stress responses in the plants; thus, effects of heavy metal stress on DNA damages and total antioxidants level in Urtica dioica leaves and stems were investigated. The samples are sampled from areas with different metal exposition. Metal content was analyzed by Inductively Coupled Plasma-Atomic Emission Spectrometer (ICP-AES), for total antioxidants level assessment the Ferric-Reducing Antioxidant Power (FRAP) assay was used, and genomic DNA isolation from frozen plant samples was performed to obtain DNA fingerprints of investigated plant. It was found that heavy metal contents in stems generally changed synchronously with those in leaves of the plant, and extraneous metals led to imbalance of mineral nutrient elements. DNA damages were investigated by Random Amplified Polymorphic DNA (RAPD) technique, and the results demonstrated that the samples exposed to metals yielded a large number of new fragments (total 12) in comparison with the control sample. This study showed that DNA stability is highly affected by metal pollution which was identified by RAPD markers. Results suggested that heavy metal stress influences antioxidant status and also induces DNA damages in U. dioica which may help to understand the mechanisms of metals genotoxicity.

The fate of arsenic, cadmium and lead in Typha latifolia: a case study on the applicability of micro-PIXE in plant ionomics

Understanding the uptake, accumulation and distribution of toxic elements in plants is crucial to the design of effective phytoremediation strategies, especially in the case of complex multi-element pollution. Using micro-proton induced X-ray emission, the spatial distribution of Na, Mg, Al, Si, P, S, Cl, K, Ca, Mn, Fe, Zn, As, Br, Rb, Sr, Cd and Pb have been quantitatively resolved in roots and rhizomes of an obligate wetland plant species, Typha latifolia, treated with a mixture of 100 μM each of As, Cd and Pb, together. The highest concentrations of As, Cd and Pb were found in the roots of the T. latifolia, with tissue-specific distributions. The As was detected in the root rhizodermis, and in the rhizome the majority of the As was within the vascular tissues, which indicates the high mobility of As within T. latifolia. The Cd was detected in the root exodermis, and in the vascular bundle and epidermis of the rhizome. The highest Pb concentrations were detected in the root rhizodermis and exodermis, and in the epidermis of the rhizome. These data represent an essential step in the resolution of fundamental questions in plant ionomics.

Nitric oxide (NO) counteracts cadmium induced cytotoxic processes mediated by reactive oxygen species (ROS) in Brassica juncea: cross-talk between ROS, NO and antioxidant responses

Research on NO in plants has achieved huge attention in recent years mainly due to its function in plant growth and development under biotic and abiotic stresses. In the present study, we investigated Cd induced NO generation and its relationship to ROS and antioxidant regulation in Brassica juncea. Cd accumulated rapidly in roots and caused oxidative stress as indicated by increased level of lipid peroxidation and H2O2 thus, inhibiting the overall plant growth. It significantly decreased the root length, leaf water content and photosynthetic pigments. A rapid induction in intracellular NO was observed at initial exposures and low concentrations of Cd. A 2.74-fold increase in intracellular NO was recorded in roots treated with 25 μM Cd than control. NO effects on Malondialdehyde (MDA) content and on antioxidant system was investigated by using sodium nitroprusside (SNP), a NO donor and a scavenger, [2-(4-carboxy-2-phenyl)-4,4,5,5-tetramethylinidazoline-1-oxyl-3-oxide] (cPTIO). Roots pretreated with 5 mM SNP for 6 h when exposed to 25 μM Cd for 24 h reduced the level of proline, non-protein thiols, SOD, APX and CAT in comparison to only Cd treatments. However, this effect was almost blocked by 100 μM cPTIO pretreatment to roots for 1 h. This ameliorating effect of NO was specific because cPTIO completely reversed the effect in the presence of Cd. Thus, the present study report that NO strongly counteracts Cd induced ROS mediated cytotoxicity in B. juncea by controlling antioxidant metabolism as the related studies are not well reported in this species.

Effects of cadmium on enzymatic and non-enzymatic antioxidative defences of rice (Oryza sativa L.)

The effects of 60-d cadmium (Cd) exposure on enzymatic and non-enzymatic antioxidative system of Oryza sativa L. seedlings at tillering stage were studied using soil culture experiment. Research findings showed that chlorophyll content of Oryza sativa L. declined with the increase in soil metal concentration. Cd pollution induced the antioxidant stress by inducing O2(-1) and H2O2, which increased in plants; at the same time, MDA as the final product of peroxidation of membrane lipids, accumulated in plant. The antioxidant enzyme system was initiated under the Cd exposure, i.e. almost all the activities of superoxide dismutase (SOD), peroxidase, catalase, glutathione peroxidase, and ascorbate peroxidase were elevated both in leaves and roots. The non-protein thiols including phytochelatins and glutathione to scavenge toxic free radicals caused by Cd stress was also studied. The contents of phytochelatins and glutathione were about 3.12-6.65-fold and 3.27-10.73-fold in leaves, against control; and the corresponding values were about 3.53-9.37-fold and 1.41-5.11-fold in roots, accordingly.

Eriophorum angustifolium and Lolium perenne metabolic adaptations to metals- and metalloids-induced anomalies in the vicinity of a chemical industrial complex

As plants constitute the foundation of the food chain, concerns have been raised about the possibility of toxic concentrations of metals and metalloids being transported from plants to the higher food chain strata. In this perspective, the use of important phytotoxicity endpoints may be of utmost significance in assessing the hazardous nature of metals and metalloids and also in developing ecological soil screening levels. The current study aimed to investigate the role of glutathione (GSH) and its associated enzymes in the metabolic adaptation of two grass species namely Eriophorum angustifolium Honck. and Lolium perenne L. to metals and metalloids stress in the vicinity of a chemical industrial complex (Estarreja, Portugal). Soil and plant samples were collected from contaminated (C) and non-contaminated (reference, R) sites, respectively, near and away from the Estarreja Chemical Complex, Portugal. Soils (from 0 to 10 and 10 to 20 cm depths) were analyzed for pH, organic carbon, and metals and metalloids concentrations. Plant samples were processed fresh for physiological and biochemical estimations, while oven-dried plant samples were used for metals and metalloids determinations following standard methodologies. Both soils and plants from the industrial area exhibited differential concentrations of major metals and metalloids including As, Cu, Hg, Pb, and Zn. In particular, L. perenne shoot displayed significantly higher and lower concentrations of Pb and As, respectively at contaminated site (vs. E. angustifolium). Irrespective of sites, L. perenne shoot exhibited significantly higher total GSH pool, oxidized glutathione (GSSG) and oxidized protein (vs. E. angustifolium). Additionally, severe damages to photosynthetic pigments, proteins, cellular membrane integrity (in terms of electrolyte leakage), and lipid peroxidation were also perceptible in L. perenne shoot. Contrarily, irrespective of the sites, activities of catalase and GSH-regenerating enzyme, GSH reductase, and GSH-metabolizing enzymes such as GSH peroxidase and GSH sulfotransferase were significantly higher in shoot of E. angustifolium. Despite the higher total GSH content, L. perenne is vulnerable to multi-metals-induced stress in comparison to E. angustifolium as depicted by increased GSH- and protein oxidation, low reactive oxygen radical-processing potential (exhibited in terms of low catalase activity) and poor GSH pool utilization efficiency (in terms of lower GSH-associated enzymes activities). The outcome of the present study may be significant for understanding vital GSH-mediated metals and metalloids tolerance mechanisms in plants as well as their unsuitability for animal consumption due to higher metals and metalloids burdens.

Cadmium induced physio-biochemical and molecular response in Brassica juncea

Cadmium is a hazardous heavy metal; its presence in the agricultural soil constrains the crop productivity and restricts crop plants from reaching their full genetic potential. In the present study, two Brassica juncea cultivars (Pusa Bold and Pusa Jaikisan), were exposed to different concentrations of cadmium (Cd) as cadmium chloride (CdCl2) (50 microM, 100 microM, 150 microM, and 200 microM). The effect of cadmium on seed germination ratio, changes in the root and shoot length, plant dry weight, moisture content, metal tolerance index, antioxidant enzyme activity and lipid peroxidation were studied. The consequence of cadmium stress at the molecular level was studied using a key gene Phytochelatin Synthase (PCS). The results of our study suggested that, exposure of cadmium affected the seed germination, growth rate, biomass content and antioxidant enzyme activities in the root, shoot and leaves of both the cultivars. Transcript expression of PCS was increased with increasing CdCl2 concentration in both the cultivars. Based on the results, it was concluded that, Brassica juncea Cv Pusa Jaikisan is more tolerant to cadmium toxicity than the Pusa Bold. These findings could be used to develop heavy metal stress tolerant plants and more importantly, detoxification of heavy metals in the soil.

Comparative proteome analysis of high and low cadmium accumulating soybeans under cadmium stress

A comparative proteomic study was performed to unravel the protein networks involved in cadmium stress response in soybean. Ten-day-old seedlings of contrasting cadmium accumulating soybean cultivars-Harosoy (high cadmium accumulator), Fukuyutaka (low cadmium accumulator), and their recombinant inbred line CDH-80 (high cadmium accumulator) were exposed to 100 μM CdCl(2) treatment for 3 days. Root growth was found to be affected under cadmium stress in all. Varietal differences at root protein level were evaluated. NADP-dependent alkenal double bond reductase P1 was found to be more abundant in low cadmium accumulating Fukuyutaka. Leaf proteome analysis revealed that differentially expressed proteins were primarily involved in metabolism and energy production. The results indicate that both high and low cadmium accumulating cultivars and CDH-80 share some common defense strategies to cope with the cadmium stress. High abundance of enzymes involved in glycolysis and TCA cycle might help cadmium challenged cells to produce more energy necessary to meet the high energy demand. Moreover, enhanced expressions of photosynthesis related proteins indicate quick utilization of photoassimilates in energy generation. Increased abundance of glutamine synthetase in all might be involved in phytochelatin mediated detoxification of cadmium ions. In addition, increased abundance of antioxidant enzymes, namely superoxide dismutase, ascorbate peroxidase, catalase, ensures cellular protection from reactive oxygen species mediated damages under cadmium stress. Enhanced expression of molecular chaperones in high cadmium accumulating cultivar might be another additional defense mechanism for refolding of misfolded proteins and to stabilize protein structure and function, thus maintain cellular homeostasis.