Sodium chloride enhances cadmium tolerance through reducing cadmium accumulation and increasing anti-oxidative enzyme activity in tobacco

Variety-dependent responses of common tobacco with differential cadmium resistance: Cadmium uptake and distribution, antioxidative activity, and gene expression

Cadmium (Cd), which accumulates in tobacco leaves, enters the human body through inhalation of smoke, causing harmful effects on health. Therefore, identifying the pivotal factors that govern the absorption and resistance of Cd in tobacco is crucial for mitigating the harmful impact of Cd. In the present study, four different Cd-sensitive varieties, namely, ZhongChuan208 (ZC) with resistance, ZhongYan100 (ZY), K326 with moderate resistance, and YunYan87 (YY) with sensitivity, were cultivated in hydroponic with different Cd concentrations (20 µM, 40 µM, 60 µM and 80 µM). The results indicated that plant growth was significantly decreased by Cd. Irrespective of the Cd concentration, ZC exhibited the highest biomass, while YY had the lowest biomass; ZY and K326 showed intermediate levels. Enzymatic (APX, CAT, POD) and nonenzymatic antioxidant (Pro, GSH) systems showed notable variations among varieties. The multifactor analysis suggested that the ZC and ZY varieties, with higher levels of Pro and GSH content, contribute to a decrease in the levels of MDA and ROS. Among all the Cd concentrations, ZC exhibited the lowest Cd accumulation, while YY showed the highest. Additionally, there were significant differences observed in Cd distribution and translocation factors among the four different varieties. In terms of Cd distribution, cell wall Cd accounted for the highest proportion of total Cd, and organelles had the lowest proportion. Among the varieties, ZC showed lower Cd levels in the cell wall, soluble fraction, and organelles. Conversely, YY exhibited the highest Cd accumulation in all tissues; K326 and ZY had intermediate levels. Translocation factors (TF) varied among the varieties under Cd stress, with ZC and ZY showing lower TF compared to YY and K326. This phenomenon mainly attributed to regulation of the NtNramp3 and NtNramp5 genes, which are responsible for the absorption and transport of Cd. This study provides a theoretical foundation for the selection and breeding of tobacco varieties that are resistant to or accumulate less Cd.

Differential absorption of cadmium and zinc by tobacco plants: Role of apoplastic pathway

Cadmium (Cd) contamination presents a significant challenge in global agriculture. This study explores the efficacy of chemical induction, specifically using sodium chloride (NaCl), to limit Cd uptake in tobacco (Nicotiana tabacum) and assesses its impact on essential divalent metal ions (DMIs). We conducted a comprehensive analysis encompassing ion absorption, root histology, and biochemistry to understand the influence of this method. Our results revealed that NaCl induction led to a notable 30 % decrease in Cd absorption, while maintaining minimal impact on zinc (Zn) uptake. Intriguingly, the absence of essential DMIs, such as calcium (Ca), magnesium (Mg), and Zn, was found to diminish the plant's capacity to absorb Cd. Furthermore, moderate NaCl induction resulted in an increased diameter of the root stele and enhanced lignin content, indicating a restriction of Cd absorption through the apoplastic pathway. Conversely, a compensatory absorption mechanism via the symplastic pathway appeared to be activated in the absence of essential elements. These findings highlight the potential of chemical induction as a strategy to mitigate agricultural Cd risks, offering insights into the complex interplay between plant ion transport pathways and metal uptake regulation.

Effects of Soil Properties on Pb, Cd, and Cu Contents in Tobacco Leaves of Longyan, China, and Their Prediction Models

Longyan City in Fujian Province is one of China's top-quality tobacco-producing areas and plays an essential role in local economic development. To determine the correlation between heavy metal content in tobacco leaves and soil factors, soil physical and chemical properties and heavy metal contents of lead, cadmium, and copper in tobacco leaves were measured and analyzed by the correlation regression method. The content of lead, cadmium, and copper in soil was determined using hydrochloric acid extraction-AAS and graphite furnace atomic absorption spectrometry. Inductively coupled plasma-mass spectrometry was used to determine heavy metal in tobacco leaf. The findings revealed that the average concentrations of lead, cadmium, and copper in the soil were 12.1, 0.092, and 3.88 mg/kg, respectively. In contrast, the average levels of lead, cadmium, and copper in tobacco leaves were 2.33, 4.89, and 4.35 mg/kg, respectively. The cadmium enrichment coefficient of 54.3 was higher than lead and copper, indicating a greater health risk. Soil pH value was negatively correlated with lead content in tobacco leaf, while potassium and phosphorus nutrient levels were negatively correlated with copper content. In contrast, a positive correlation was established between the presence of organic matter with cadmium content in tobacco leaves. The prediction models of lead, cadmium, and copper in tobacco leaves can be expressed by the regression equation corresponding to each heavy metal as follows: YPb=2.33 - 0.005∗ XK+0.007∗XN  - 0.271∗XpH+0.065∗XPb (R2 = 0.787), YCd=1.55+0.012∗XOM - 0.014∗XCu+34.6∗XCd (R2 = 0.891), and YCu=4.64 - 0.029∗XP - 0.007∗XK+0.245∗XCu (R2 = 0.724), respectively. The prediction models above provide an effective predictive tool for assessing heavy metal risk in tobacco leaves using soil properties in the study area.

Changes in antioxidant system and sucrose metabolism in maize varieties exposed to Cd

Different maize varieties respond differentially to cadmium (Cd) stress. However, the physiological mechanisms that determine the response are not well defined. Antioxidant systems and sucrose metabolism help plants to cope with abiotic stresses, including Cd stress. The relationship of these two systems in the response to Cd stress is unclear. Seed is sensitive to Cd stress during germination. In this study, we investigated changes in the antioxidant system, sucrose metabolism, and abscisic acid and gibberellin concentrations in two maize varieties with low (FY9) or high (SY33) sensitivities to Cd under exposure to CdCl2 (20 mg L-1) at different stages of germination (3, 6, and 9 days).The seed germination and seedling growth were inhibited under Cd stress. The superoxide, malondialdehyde, and proline concentrations, and the superoxide dismutase, peroxidase, catalase, and lipoxygenase activities increased compared with those of the control (CK; without Cd). The expression levels of three genes (ZmOPR2, ZmOPR5, and ZmPP2C6) responsive to oxidative stress increased differentially in the two varieties under Cd stress. The activity of the antioxidant system and the transcript levels of oxidative stress-responsive genes were higher in the Cd-tolerant variety, FY9, than in the sensitive variety, SY33. Sucrose metabolism was increased under Cd stress compared with that of the CK and was more active in the Cd-sensitive variety, SY33. These results suggest that the antioxidant system is the first response to Cd stress in maize, and that sucrose metabolism is cooperative and complementary under exposure to Cd.

Research Advances in Cadmium Uptake, Transport and Resistance in Rice (Oryza sativa L.)

Rice (Oryza sativa L.) is one of the most important food crops, feeding half of the world’s population. However, rice production is affected by cadmium (Cd) toxicity. Due to an increase in Cd-contaminated soil and rice grains, and the serious harm to human health from Cd, research on Cd uptake, transport and resistance in rice has been widely conducted, and many important advances have been made. Rice plants absorb Cd mainly from soil through roots, which is mediated by Cd absorption-related transporters, including OsNramp5, OsNramp1, OsCd1, OsZIP3, OsHIR1, OsIRT1 and OsIRT2. Cd uptake is affected by soil’s environmental factors, such as the concentrations of Cd and some other ions in soil, soil properties, and other factors can affect the bioavailability of Cd in soil. Then, Cd is transported within rice plants mediated by OsZIP6, OsZIP7, OsLCD, OsHMA2, CAL1, OsCCX2, OsLCT1 and OsMTP1, from roots to shoots and from shoots to grains. To resist Cd toxicity, rice has evolved many resistance strategies, including the deposition of Cd in cell walls, vacuolar Cd sequestration, Cd chelation, antioxidation and Cd efflux. In addition, some unresolved scientific questions surrounding Cd uptake, transport and resistance in rice are proposed for further study.

Wheat TaPUB1 Regulates Cd Uptake and Tolerance by Promoting the Degradation of TaIRT1 and TaIAA17

Cadmium (Cd) accumulation in agricultural soils is an increasingly serious problem, as plants absorb Cd, which inhibits their growth and development. Nonetheless, the molecular mechanisms underlying Cd detoxification and accumulation in wheat (Triticum aestivum L.) are unclear. Here, we isolated the U-box E3 ligase TaPUB1 from wheat and reported the functional characterization of TaPUB1 in Cd uptake and tolerance in wheat. Under Cd stress, TaPUB1 overexpression lines displayed higher photosynthetic rates than the wild type; opposite results were observed in the TaPUB1-RNAi lines. In addition, TaPUB1 overexpression lines showed reduced Cd uptake and accumulation, whereas RNAi plants exhibited a significant increase in Cd accumulation after Cd treatment. We further found that TaPUB1 enhanced the resistance of wheat to Cd stress in three ways. First, TaPUB1 interacts with and ubiquitinates TaIRT1, resulting in the inhibition of Cd uptake. Second, TaPUB1 interacts directly with and ubiquitinates TaIAA17, facilitates its degradation, and results in primary root elongation by activating the Aux signaling pathway under Cd stress. Moreover, TaPUB1 decreases ROS accumulation by regulating antioxidant-related gene expression and antioxidant enzyme activity under Cd stress. Thus, a molecular mechanism by which TaPUB1 regulates Cd uptake and tolerance by modulating the stability of TaIRT1 and TaIAA17 proteins was revealed.

Foliar-Applied Glutathione Mitigates Cadmium-Induced Oxidative Stress by Modulating Antioxidant-Scavenging, Redox-Regulating, and Hormone-Balancing Systems in Brassica napus

The antioxidant glutathione (GSH) mitigates adverse physio-metabolic effects and defends against abiotic types of stress, such as cadmium (Cd) stress. However, its function and role in resisting Cd phytotoxicity by leveraging plant antioxidant-scavenging, redox-regulating, and hormone-balancing systems have not been comprehensively and systematically demonstrated in the Cd-hyperaccumulating plant Brassica napus L. cv. Tammi (oilseed rape). In this study, the effects of exogenously applied GSH to the leaves of B. napus seedlings exposed to Cd (10 μM) were investigated. As a result, Cd stress alone significantly inhibited growth and increased the levels of reactive oxygen species (ROS) and the bioaccumulation of Cd in the seedlings compared with those in unstressed controls. Furthermore, Cd stress induced an imbalance in plant stress hormone levels and decreases in endogenous GSH levels and GSH redox ratios, which were correlated with reductions in ascorbate (AsA) and/or nicotinamide adenine dinucleotide phosphate (NADPH) redox states. However, the exogenous application of GSH to Cd-stressed B. napus seedlings reduced Cd-induced ROS levels and enhanced antioxidant-scavenging defenses and redox regulation by both increasing seedling AsA, GSH, and NADPH concentrations and rebalancing stress hormones, thereby enhancing Cd uptake and accumulation. These results demonstrate that GSH improved plant redox status by upregulating the AsA-GSH-NADPH cycle and reestablishing normal hormonal balance. This indicates that exogenously applied GSH can mitigate Cd phytotoxicity in B. napus and possibly other plants. Therefore, GSH can potentially be applied to Cd-polluted soil for plant remediation.

Effects of cerium oxide on rice seedlings as affected by co-exposure of cadmium and salt

Effects of CeO₂ NPs (200 mg.L^-1) on rice (Oryza sativa L.) alone or co-exposure with cadmium (Cd) and salt (sodium chloride, NaCl) were investigated in hydroponic systems for two weeks. Physiological results show that rice biomass was significantly inhibited when NaCl or CdCl₂ added alone or in co-exposure treatment. CeO₂ NPs significantly relieve the chlorophyll damage under CdCl₂ environmental stress. The presence of CeO₂ NPs alleviated both stressors induced damages to rice as indicated by the reduced proline level. Additionally, CeO₂ NPs triggered the antioxidant defense systems to counteract the oxidative stress caused by NaCl and CdCl₂. The level of 8-OHdG, one of the most important indicators for genotoxicity, in rice suggest that the presence of CeO₂ NPs reduced the DNA damage in NaCl treated rice. Elemental analysis indicated that co-exposure to NaCl and CdCl₂ slightly decreased the Cd content as compared to the one in the CdCl₂ alone treatment, and this co-exposure also significantly reduced the Na content when comparing with the NaCl alone treatment. Taken together, our findings suggest that CeO₂ NPs could alleviate the CdCl₂ and NaCl stresses, but could not completely change the phenotype of both contaminants treated rice.

Cadmium stress increases antioxidant enzyme activities and decreases endogenous hormone concentrations more in Cd-tolerant than Cd-sensitive wheat varieties

The different wheat varieties have different tolerance to cadmium stress, while the mechanisms underlying the Cd tolerance are still poorly understood. A pot experiment was conducted to study the changes of antioxidant enzyme activities and endogenous hormones in wheat (Triticum aestivum) genotypes differing in cadmium (Cd) accumulation (low = Pingan 8 and high = Bainong 160) in different growth stages under Cd stress. The Cd treatment (3 mg/kg) increased the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) and concentrations of malondialdehyde (MDA) and abscisic acid (ABA); in contrast, it reduced the net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), intercellular carbon dioxide concentration (Ci) and the concentrations of gibberellin (GA₃), auxin (IAA) and zeatin nucleoside (ZR) in wheat leaves compared to the CK (without Cd). The antioxidant enzyme activities were higher in Bainong 160 than Pingan 8 under Cd stress. In addition, the changes in endogenous hormone concentration were smaller in Bainong 160 than Pingan 8 leaves. The correlation coefficients of Bainong 160 and Pingan 8 were 0.87 and 0.66, respectively. Our results suggest that high Cd accumulation (greater Cd tolerance) in Bainong 160 is associated with higher photosynthetic parameters, higher activities of antioxidant enzyme and higher concentration of hormones than Pingan 8.

Effect of salinity on cadmium tolerance, ionic homeostasis and oxidative stress responses in conocarpus exposed to cadmium stress: Implications for phytoremediation

Contamination of soil with salinity and Cd negatively affects growth and productivity of plants. The proposed study has been planned to explore the effects of salinity on Cd uptake, tolerance and phytoremediation potential of conocarpus (Conocarpus erectus L.). One-month-old uniform plants of conocarpus were exposed to 0, 8.9, 44.5, 89 and 178 µM Cd alone or in combination with 0, 100 and 200 mM NaCl in Hoagland's nutrient solution. Results revealed that shoot and root biomasses, leaf water content and pigment content decreased more in response to combination of Cd and salinity compared to Cd alone. The Na⁺ and Cl^- concentrations in shoot and root were not affected by Cd alone, but increased in Cd + salinity treatments. The K⁺ concentration decreased by Cd alone as well as Cd combination with salinity. Plant Cd uptake increased in the presence of salinity but its translocation from root to shoot remained unaffected. Exposure of plants to Cd alone and Cd + salinity caused oxidative stress via overproduction of H₂O₂ and inducing lipid peroxidation. The activities of antioxidant enzymes such as SOD, CAT, POD and APX increased to mitigate this oxidative stress. It is concluded that the tolerance of conocarpus against Cd stress is decreased in the presence of salinity due to increased uptake of toxic ions and intensification of oxidative stress. Moreover, the Cd uptake behavior of this tree indicates its suitability for phytostabilization of Cd contaminated saline and non-saline soils.

Salinity decreases Cd translocation by altering Cd speciation in the halophytic Cd-accumulator Carpobrotus rossii

BACKGROUND AND AIMS

Salt has been shown to affect Cd translocation and accumulation in plants but the associated mechanisms are unclear. This study examined the effects of salt type and concentration on Cd uptake, translocation and accumulation in Carpobrotus rossii.

METHODS

Plants were grown in nutrient solution with the same Cd concentration or Cd2+ activity in the presence of 25 mm NaNO3, 12.5 mm Na2SO4 or 25 mm NaCl for ≤10 d. Plant growth and Cd uptake were measured and the accumulation of peptides and organic acids, and Cd speciation in plant tissues were analysed.

KEY RESULTS

Salt addition decreased shoot Cd accumulation by >50 % due to decreased root-to-shoot translocation, irrespective of salt type. Synchrotron-based X-ray absorption spectroscopy revealed that, after 10 d, 61-94 % Cd was bound to S-containing ligands (Cd-S) in both roots and shoots, but its speciation was not affected by salt. In contrast, Cd in the xylem sap was present either as free Cd2+ or complexes with carboxyl groups (Cd-OH). When plants were exposed to Cd for ≤24 h, 70 % of the Cd in the roots was present as Cd-OH rather than Cd-S. However, NaCl addition decreased the proportion of Cd-OH in the roots within 24 h by forming Cd-Cl complexes and increasing the proportion of Cd-S. This increase in Cd-S complexes by salt was not due to changes in glutathione and phytochelatin synthesis.

CONCLUSIONS

Salt addition decreased shoot Cd accumulation by decreasing Cd root-to-shoot translocation due to the rapid formation of Cd-S complexes (low mobility) within the root, without changing the concentrations of glutathione and phytochelatins.

Sodium chloride decreases cadmium accumulation and changes the response of metabolites to cadmium stress in the halophyte Carpobrotus rossii

BACKGROUND AND AIMS

Salinity affects the bioavailability of cadmium (Cd) in soils and Cd accumulation in plants, but the associated mechanisms remain unclear. This study aimed to assess the metabolic response to NaCl and Cd and the relationship between metabolites and Cd accumulation in the halophyte Carpobrotus rossii, which has potential for Cd phytoextraction.

METHODS

Plants were grown in nutrient solution with 0-400 mm NaCl in the presence of 5 or 15 µm Cd, with varied or constant solution Cd2+ activity. Plant growth and Cd uptake were measured, and the accumulation of peptides, and organic and amino acids in plant tissues were assessed.

KEY RESULTS

The addition of NaCl to Cd-containing solutions improved plant growth along with 70-87 % less shoot Cd accumulation, resulting from decreases in Cd root uptake and root-to-shoot translocation irrespective of Cd2+ activity in solutions. Moreover, Cd exposure increased the concentration of phytochelatins, which correlated positively with Cd concentrations in plants regardless of NaCl addition. In comparison, Cd inhibited the synthesis of organic acids in shoots and roots in the absence of NaCl, but increased it in shoots in the presence of NaCl. While Cd increased the concentrations of amino acids in plant shoots, the effect of NaCl on the synthesis of amino acids was inconsistent.

CONCLUSIONS

Our data provide the first evidence that NaCl decreased Cd shoot accumulation in C. rossii by decreasing Cd root uptake and root-to-shoot translocation even under constant Cd2+ activity. The present study also supports the important role of peptides and organic acids, particular of phytochelatins, in Cd tolerance and accumulation although the changes of those metabolites was not the main reason for the decreased Cd accumulation.

Cadmium adsorption, chelation and compartmentalization limit root-to-shoot translocation of cadmium in rice (Oryza sativa L.)

Strategies to reduce cadmium (Cd) in rice grain, below concentrations that represent serious human health concerns, require that the mechanisms of Cd distribution and accumulation within rice plants be established. Here, a comprehensive hydroponic experiment was performed to investigate the differences in the Cd uptake, chelation and compartmentalization between high (D83B) and low (D62B) Cd-accumulation cultivars contrasting in Cd accumulation in order to establish the roles of these processes in limiting Cd translocation from root to shoot. D83B showed 3-fold higher Cd accumulation in the shoots than the cultivar D62B. However, a short-term Cd uptake experiment showed more Cd uptake by D62B than by D83B. The distribution of Cd in roots and shoots differed significantly. D83B translocated 38% of total Cd taken up to the shoots, whereas D62B retained most of the Cd in the roots. D62B had higher amounts of non-protein thiols (NPTs) and glutathione (GSH) than D83B. The NPT and Cd distribution ratio (CDR) in the anionic form in the roots of D62B increased gradually as Cd concentration increased. In D83B, in contrast, levels of CDR in the cationic form increased significantly from 22.10 to 43.37%, while NPT only increased slightly. Furthermore, the percentage of Cd ions retained in thiol-rich peptides, especially in the HMW complexes, was significantly higher in D62B compared with D83B. However, D83B possessed a greater proportion of potentially mobile (cationic) Cd in the roots and showed superior Cd translocation from root to shoot. Taken as a whole, the results presented in this study revealed that Cd chelation, compartmentalization and adsorption contribute to the Cd retention in roots.

Assessing toxic effects of [Omim]Cl and [Omim]BF4 in zebrafish adults using a biomarker approach

In the present study, the toxic effects of 1-octyl-3-methylimidazolium chloride ([Omim]Cl) and 1-octyl-3-methylimidazolium tetrafluoroborate ([Omim]BF4) on the zebrafish livers were studied at 0, 5, 10, 20, and 40 mg L(-1) on the 7th and 14th days. In addition, the concentrations of [Omim]Cl and [Omim]BF4 in the test water, the acute toxicity of the two ionic liquids (ILs), and the influence of anions on the toxicity of the ILs were evaluated. The acute toxicity test results showed 50 % lethal concentration (LC50) values of 152.3 ± 12.1 mg L(-1) for [Omim]Cl and 144.0 ± 11.4 mg L(-1) for [Omim]BF4. At the lowest concentration investigated (5 mg L(-1)), [Omim]Cl and [Omim]BF4 did not significantly affect zebrafish during the exposure period. However, the toxic effects of these substances were enhanced as dosing concentrations and exposure times were increased. Levels of reactive oxygen species (ROS) were significantly enhanced on the 7th day after 20 mg L(-1) and on the 14th day after 10 mg L(-1) of either substance was applied, resulting in oxidative damage, such as lipid peroxidation and DNA damage. The experimental results also indicated little effect of the anions on the toxicity of ILs and consistent toxic effects of [Omim]Cl and [Omim]BF4. Graphical Abstract The graphical abstract for the present study after exposure to [Omim]Cl and [Omim]BF4. The letter R represents the anions Cl(-) and BF4 (.)

Sulfur decreases cadmium translocation and enhances cadmium tolerance by promoting sulfur assimilation and glutathione metabolism in Brassica chinensis L

We investigated the ameliorative role of sulfur (S) in protecting plants against cadmium (Cd) toxicity by using two pakchoi (Brassica chinensis L.) cultivars with different Cd tolerance levels. The exposure of pakchoi seedlings to 100μM Cd inhibited plant growth, increased superoxide content, enhanced membrane lipid peroxidation, and induced Cd accumulation in the roots and shoots. Application of S to Cd-stressed plants alleviated Cd-induced oxidative stress by promoting the capacity of the ascorbate (AsA)-glutathione (GSH) cycle, enhanced S assimilation by increasing the activity of ATP sulfurylase (ATPS) and o-acetylserine(thiol)lyase (OASTL), and decreased Cd translocation from the roots to the shoots by enhancing phytochelatins (PCs) biosynthesis. Results suggested that S reversed Cd-induced growth inhibition and oxidative stress by restraining Cd translocation from the roots to the shoots and upregulating S assimilation and GSH metabolism, including the AsA-GSH cycle and PCs synthesis.

Isobolographic analysis of the interaction between cadmium (II) and sodium sulphate: toxicological consequences

Sulphate is an essential nutrient for autotrophic organisms and has been shown to have important implications in certain processes of tolerance to cadmium toxicity. Sodium sulphate is the main salt of sulphate in the natural environments. The concentration of this salt is increasing in the aquatic environments due to environmental pollution. The aim of this study was to investigate, using an analysis of isobolograms, the type and the degree of the interaction between Cd(II) and sodium sulphate in the freshwater microalga Chlamydomonas moewusii. Two blocks of experiments were performed, one at sub-optimal sodium sulphate concentrations (<14.2 mg/L) and the other at supra-optimal concentrations (>14.2 mg/L). Three fixed ratios (2:1, 1:1, and 1:2) of the individual EC50 for cadmium and sodium sulphate were used within each block. The isobolographic analysis of interaction at sub-optimal concentrations showed a stronger antagonistic effect with values of interaction index (γ) between 1.46 and 3.4. However, the isobologram with sodium sulphate at supra-optimal concentrations revealed a slight but significant synergistic effect between both chemicals with an interaction index between 0.54 and 0.64. This synergic effect resulted in the potentiation of the toxic effects of cadmium, synergy that was related to the increase of the ionic strength and of two species of cadmium, CdSO4 (aq), and Cd(SO4)2(2-) , in the medium. Results of the current study suggest that sodium sulphate is able to perform a dual antagonist/synergist effect on cadmium toxicity. This role was concentration dependent.

The effects of phosphate on arsenic uptake and toxicity alleviation in tobacco genotypes with differing arsenic tolerances

Phosphate (PO4 (3-) ) has been reported to suppress arsenate (As(v) ) uptake in plants. However, its effects on controlling the availability of As(v) in tobacco genotypes with different arsenic (As) tolerances has not been fully explored. In the present study, the effects of PO4 (3-) on As(v) uptake were investigated in a hydroponic culture using 2 tobacco (Nicotiana tabacum) genotypes (ZY90 and FSMY) that differed in As(v) tolerance. A total of 9 treatment combinations comprising As(v) treatments of 0 µM, 10 µM, and 100 µM and PO4 (3-) treatments of 0 µM, 50 µM, and 500 µM were used. The results showed that ZY90 had greater reductions in leaf photosynthetic parameters, root and shoot dry weight, length, and nutrient content than did FSMY when exposed to As(v) stress. The addition of 500 µM external PO4 (3-) significantly suppressed As(v) (100 µM) uptake in both FSMY and ZY90, with the effect being more pronounced in FSMY. Greater PO4 (3-) uptake in plants significantly reduced the influx of As(v) , causing an increase in photosynthesis and nutrient uptake. Phosphate supply increased superoxide dismutase activity, catalase activity, and malondialdehyde content. The present study showed that PO4 (3-) is an effective competitive inhibitor of As(v) , and it can be effectively used to control As(v) accumulation in tobacco plants.

Sodium chloride alleviates cadmium toxicity by reducing nitric oxide accumulation in tobacco

Nitric oxide (NO) is involved in regulating the response of plants to Cd toxicity. In this study, we examined possible involvement of NO in the alleviation of Cd toxicity by NaCl in tobacco plants. Two independent experiments were conducted to investigate the changes of NO accumulation and Cd concentration in tobacco plants after the addition of a NO donor, sodium nitroprusside dehydrate (SNP), or a NO inhibitor, nitro-l-arginine methyl ester (l-NAME) in the solution containing NaCl and Cd. NO accumulation in tobacco roots was enhanced when plants were exposed to Cd, but reduced in the treatments of NaCl or l-NAME. NO production was not enhanced even when SNP (NO donor) was added to the solution containing Cd and NaCl. Root number was reduced in plants exposed to Cd, and increased by the addition of NaCl and reduced by the addition of SNP. Addition of NaCl or l-NAME to the Cd-containing solution reduced Cd concentration in plant tissues, with l-NAME having a more dramatic effect. It can be concluded that alleviation of Cd toxicity by NaCl contributed to reduction of NO accumulation in plants.

Involvement of an antioxidant defense system in the adaptive response to cadmium in maize seedlings (Zea mays L.)

Chemical and biological analyses were used to investigate the growth response and antioxidant defense mechanism of maize seedlings (Zea mays L.) grown in soils with 0-100 mg kg(-1) Cd. Results showed that maize seedlings have strong abilities to accumulate and tolerate high concentrations of Cd. For soil with 50 mg kg(-1) Cd, the Cd contents in roots and shoots of maize seedlings are as large as 295.6 and 153.0 mg kg(-1) DW, respectively, without visible symptoms of toxicity. Lower soil Cd concentrations lead to a decrease in reduced glutathione (GSH) content in leaves of maize seedlings, whereas higher soil Cd concentrations resulted in an increase in the activities of superoxide dismutase, guaiacol peroxidase, catalase, and ascorbate peroxidase. Maize seedlings have strong capacities to adapt to low concentrations of Cd by consuming GSH and to develop an antioxidative enzyme system to defend against high-Cd stress.

The cytotoxic and genotoxic effects of metalaxy-M on earthworms (Eisenia fetida)

As the main optical isomer of metalaxyl, metalaxyl-M has been widely used worldwide in recent years because of its notable effect on the prevention and control of crop diseases. Together with the toxicity and degradation of metalaxyl-M, the chemical has attracted the attention of researchers. The present study examined the toxic effects of metalaxyl-M on earthworms at 0 mg kg(-1) , 0.1 mg kg(-1) , 1 mg kg(-1) , and 3 mg kg(-1) on days 7, 14, 21 and 28 after exposure. The results showed that metalaxyl-M could cause an obvious increase in the production of reactive oxygen species (ROS) when the concentration was higher than 0.1 mg kg(-1) , which led to lipid peroxidation in earthworms. Metalaxyl-M can induce DNA damage in earthworms, and the level of DNA damage markedly increased with increasing the concentration of metalaxyl-M. Metalaxyl-M also has a serious influence on the activities of antioxidant enzymes, which results in irreversible oxidative damage in cells. The changes of these indicators all indicated that metalaxyl-M may cause cytotoxic and genotoxic effects on earthworms.

Involvement of ethylene in alleviation of Cd toxicity by NaCl in tobacco plants

The possible involvement of ethylene in alleviating cadmium (Cd) toxicity by NaCl was investigated because our previous experiments showed that a low concentration of NaCl could alleviate Cd toxicity of tobacco plants. Tobacco plants exposed to the treatment of a combination of Cd-NaCl exhibited more vigorous growth than did those exposed to the treatment of Cd stress alone, as reflected by greater biomass, longer roots, taller shoots, larger SPAD values and higher photosynthetic rates. The results also indicated that it is Na(+), rather than Cl(-), that alleviates Cd toxicity. Cd-NaCl treatments enhanced and inhibited ethylene production in roots and in leaves, respectively, in comparison with the plants exposed to Cd alone. However, the exogenous application of ethylene did not improve root growth under Cd exposure, indicating that ethylene is not directly involved in the rooting process. It may be assumed that the addition of NaCl into the solution containing Cd regulates root growth by mediating ethylene synthesis.