Alleviate Cd Toxicity Research Articles

Nitric oxide can induce tolerance to oxidative stress of peanut seedlings under cadmium toxicity

To study the role of sodium nitroprusside (SNP, a donor of NO) in alleviating cadmium (Cd) toxicity in peanut (Arachis hypogaea L.), peanut seedlings exposed to 50, 100, or 200 µM Cd as CdCl2 were treated with 250 µM SNP. Cd exposure depressed plant growth, inhibited the photosynthesis, and resulted in oxidative stress. In roots, Cd was mostly trapped in the cell wall under low Cd stress, but most Cd was accumulated in the soluble fraction under high Cd concentrations. In leaves, a majority of Cd was accumulated in the cell wall regardless of Cd treatment level. Addition of SNP at 250 µM significantly alleviated Cd toxicity in peanut seedlings, including improved photosynthesis, up-regulated antioxidant system, and reduced Cd translocation from roots to shoots as evidenced by decreased Cd accumulation in stems and leaves. SNP application also changed the subcellular distribution of Cd in leaf and root tissues, by increasing Cd retention in root and leaf cell wall while reducing Cd accumulation in the soluble fractions and cell organelles. These results indicate that SNP has great application potential for improving the growth of plants under heavy metal stress such as Cd toxicity.

NaCl alleviates Cd toxicity by changing its chemical forms of accumulation in the halophyte Sesuvium portulacastrum.

It has previously been shown that certain halophytes can grow and produce biomass despite of the contamination of their saline biotopes with toxic metals. This suggests that these plants are able to cope with both salinity and heavy metal constraints. NaCl is well tolerated by halophytes and apparently can modulate their responses to Cd. However, the underlying mechanisms remain unclear. This study explores the impact of NaCl on growth, Cd accumulation, and Cd speciation in tissues of the halophyte Sesuvium portulacastrum. Seedlings of S. portulacastrum were exposed during 1 month to 0, 25, and 50 μM Cd combined with low salinity (LS, 0.09 mM NaCl) or high salinity (HS, 200 mM NaCl) levels. Growth parameters and total tissue Cd concentrations were determined, in leaves, stems, and root. Moreover, Cd speciation in these organs was assessed by specific extraction procedures. Results showed that, at LS, Cd induced chlorosis and necrosis and drastically reduced plant growth. However, addition of 200 mM NaCl to Cd containing medium alleviated significantly Cd toxicity symptoms and restored plant growth. NaCl reduced the concentration of Cd in the shoots; nevertheless, due to maintenance of higher biomass under HS, the quantity of accumulated Cd was not modified. NaCl modified the chemical form of Cd in the tissues by increasing the proportion of Cd bound to pectates, proteins, and chloride suggesting that this change in speciation is involved in the positive impact of NaCl on Cd tolerance. We concluded that the tolerance of S. portulacastrum to Cd was enhanced by NaCl. This effect is rather governed by the modification of the speciation of the accumulated Cd than by the reduction of Cd absorption and translocation.

IAA alleviates Cd toxicity on growth, photosynthesis and oxidative damages in eggplant seedlings

Plant growth regulator IAA (indole-3-acetic acid), besides its role in growth and development, is gaining increased attention because of its involvement in regulation of abiotic stresses. To ascertain this hypothesis, sand culture experiments were conducted to investigate the implication of IAA in regulation of Cd (cadmium) toxicity in eggplant (Solanum melongena L.) seedlings. Cd at tested doses (Cd1: 3 mg Cd kg−1 sand and Cd2: 9 mg Cd kg−1 sand) declined growth, pigment contents and photosynthesis, and increased the rate of dark respiratory oxygen uptake, and these effects were accompanied with Cd accumulation in tissues. Photochemistry of photosystem II (PS II) was analyzed by measuring chlorophyll a fluorescence kinetics-JIP test. Cd declined the efficiency of PS II in its concentration dependent manner which is evident from the decreased values of Fv/F0, Fv/Fm (ϕP0), Ψ0, ϕE0 and PIABS and increased values of F0/Fv and energy fluxes per reaction centre: ABS/RC, ET0/RC, TR0/RC and DI0/RC. Enhanced level of oxidants: superoxide radical and hydrogen peroxide under Cd stress stimulated the rate of lipid peroxidation and electrolyte leakage, despite of appreciable rise in activity of superoxide dismutase, peroxidase, catalase, glutathione-s-transferase and contents of non protein thiol and proline. Exogenous IAA application alleviated Cd induced toxicity on growth performance by improving the structural and functional attributes of photosynthetic apparatus i.e. pigment contents and photosynthetic activity. The ameliorating effect of exogenous IAA was due to (1) significant reduction in Cd uptake in roots and its translocation to leaves and (2) further rise in level/activity of antioxidants which brought the level of oxidants under control hence, minimized the oxidative damage in eggplant seedlings.

水稻根系响应镉胁迫的蛋白质差异表达分析

PDF HTML阅读 XML下载 导出引用 引用提醒 水稻根系响应镉胁迫的蛋白质差异表达 DOI: 10.5846/stxb201403230517 作者: 作者单位: 福建农林大学生命科学学院,福建农林大学,福建农林大学,福建农林大学生命科学学院,福建农林大学,福建农林大学,福建农林大学生命科学学院,福建农林大学,淮南师范学院生命科学系,福建农林大学生命科学学院,福建农林大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目(31070403);福建省自然科学基金项目(2009J01056,2013J01083);福建省教育厅基金项目(JA09084);福建省高校服务海西建设重点项目(0B08B005);福建农林大学重点项目建设专项(6112c0604) Analysis of the differently expressed proteins in rice roots in response to cadmium stress Author: Affiliation: School of life sciences, Fujian Agriculture and Forestry University,,,,,,School of life sciences, Fujian Agriculture and Forestry University,,,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为探讨水稻根系对镉胁迫的分子生理响应,以抗镉水稻PI312777和镉敏感水稻IR24为材料,设置Cd2+浓度为0、50和100 μmol/L的水培试验,处理7 d后分析了水稻根系的蛋白质差异表达。结果表明,在镉胁迫下水稻PI312777和IR24根系有18个蛋白质发生了差异表达,其中的12个得到MALDI-TOF/MS鉴定。这些鉴定的蛋白功能可分四类:(1)与活性氧(ROS)胁迫相关的过氧化物酶(POD)、蛋氨酸腺苷转移酶(MAT)、类萌发素蛋白前体;(2)与谷胱甘肽(GSH)合成相关的S-腺苷甲硫氨酸合成酶(SAMS)、谷氨酰胺合成酶(GS)和谷氨酸脱氢酶(GDH);(3)与逆境胁迫相关的ABA胁迫诱导蛋白含HVA22域蛋白、ABA-胁迫-成熟诱导蛋白5(ASR5);(4)与细胞分裂调控相关的GTP结合核蛋白Ran-2。镉胁迫下SAMS和GTP结合核蛋白Ran-2在两种水稻根系均发生上调表达;MAT、POD、类萌发素蛋白前体和GS发生下调表达;依赖NADP-GDH、GDH和磷酸甘油酸变位酶在IR24根部均发生下调表达,在PI312777根部仅在100 μmol/L Cd2+处理发生下调表达;含HVA22域蛋白在PI312777根部上调表达,在IR24根部发生下调表达;ASR5在PI312777根部上调表达,在IR24根部的表达无显著差异;100 μmol/L Cd2+胁迫下60S酸性核糖体蛋白P0在水稻PI312777根部表达下调,在IR24根部表达上调。可见,镉胁迫使水稻根部ROS增加,形成氧化胁迫反应,造成毒害作用,而水稻根通过调节SAMS和GS提高GSH合成降低镉毒害。ASR5和HVA22蛋白等逆境胁迫蛋白的表达差异则是水稻品种间抗性差异的重要原因之一。 Abstract:To investigate the molecular and physiological responses in rice roots to cadmium (Cd) stress, a set of hydroponic culture experiments treated with Cd2+ at 0, 50, and 100 μmol/L in the solutions were conducted to analyze the differentially expressed proteins in the roots of two rice (Oryza sativa L.) cultivars (Cd-tolerant rice PI312777 and Cd-sensitive rice IR24) 7 days after the treatments. The results showed that 18 proteins were differentially expressed in the roots of PI312777 and IR24 under Cd stress; 12 of them were identified by the MALDI-TOF/MS technique. The biological functions of these identified proteins were involved in four metabolic pathways, including (1) reactive oxygen species (ROS) stress: peroxidase (POD), methionine adenosyltransferase (MAT), and germin-like protein precursor; (2) glutathione (GSH) synthesis: S-adenosylmethionine synthetase (SAMS), glutamine synthetase (GS), and glutamate dehydrogenase (GDH); (3) stress response induced by abscisic acid (ABA): HVA22 and abscisic acid-stress-ripening-inducible 5 protein (ASR5); and (4) cell division regulation: GTP-binding nuclear protein Ran-2.Under Cd stress conditions, the expression of SAMS and GTP-binding nuclear protein Ran-2 were up-regulated and MAT, POD, the germin-like protein precursor, and GS were down-regulated in the roots of the two rice cultivars. The expression of NADP-GDH, GDH and phosphoglycerate mutase were down-regulated in the roots of rice IR24, but they were down-regulated in PI312777 only upon the treatment with 100 μmol/L Cd2+. The expression of protein with HVA22 domain was up-regulated in PI312777, but it was downregulated reversed in IR24. ASR5 was up-regulated in rice PI312777, but no significant change was found in IR24. The 60s acidic ribosomal protein P0 was down-regulated in PI312777, but up-regulated in IR24 at 100 μmol/L Cd2+condition. Our results suggest that Cd stress increases ROS and produces oxidative stress in rice roots, which lead to Cd toxicity in rice roots. To alleviate Cd toxicity, rice roots increase the GSH synthesis by up-regulation of SAMS and GS. Different expression patterns of stress-related proteins such as ASR5 and HVA22 are important in understanding the differences in Cd tolerance across rice cultivars. 参考文献 相似文献 引证文献

Effects of exogenous salicylic acid and nitric oxide on physiological characteristics of two peanut cultivars under cadmium stress

The interactive effects of salicylic acid (SA) and nitric oxide (NO) on alleviating cadmium (Cd) toxicity in peanut (Arachis hypogaea L.) were studied. Seedlings of two cultivars (Huayu 22 — a big seed type, and Xiaobaisha — a small seed type) were treated with 200 μM CdCl2 without or with 0.1 mM SA or 0.25 mM sodium nitroprusside (SNP, an NO donor). Results show that the Cd exposure depressed the plant growth of both the cultivars but more of Huayu 22 than of Xiaobaisha. Exogenous SA and NO alleviated Cd toxicity in both the peanut cultivars: they improved growth, chlorophyll content, photosynthesis, and mineral nutrition. Furthermore, exogenous SA or NO decreased oxidative stress by increasing activities of antioxidant enzymes and content of non-enzymatic antioxidants. Besides, in roots and leaves of both the cultivars, exogenous SA and NO increased Cd accumulation in the cell wall and decreased Cd distribution to organelles. In particular, the effect of SA+SNP was most obvious.

Cadmium-induced hydrogen sulfide synthesis is involved in cadmium tolerance in Medicago sativa by reestablishment of reduced (homo)glutathione and reactive oxygen species homeostases.

Until now, physiological mechanisms and downstream targets responsible for the cadmium (Cd) tolerance mediated by endogenous hydrogen sulfide (H2S) have been elusive. To address this gap, a combination of pharmacological, histochemical, biochemical and molecular approaches was applied. The perturbation of reduced (homo)glutathione homeostasis and increased H2S production as well as the activation of two H2S-synthetic enzymes activities, including L-cysteine desulfhydrase (LCD) and D-cysteine desulfhydrase (DCD), in alfalfa seedling roots were early responses to the exposure of Cd. The application of H2S donor sodium hydrosulfide (NaHS), not only mimicked intracellular H2S production triggered by Cd, but also alleviated Cd toxicity in a H2S-dependent fashion. By contrast, the inhibition of H2S production caused by the application of its synthetic inhibitor blocked NaHS-induced Cd tolerance, and destroyed reduced (homo)glutathione and reactive oxygen species (ROS) homeostases. Above mentioned inhibitory responses were further rescued by exogenously applied glutathione (GSH). Meanwhile, NaHS responses were sensitive to a (homo)glutathione synthetic inhibitor, but reversed by the cotreatment with GSH. The possible involvement of cyclic AMP (cAMP) signaling in NaHS responses was also suggested. In summary, LCD/DCD-mediated H2S might be an important signaling molecule in the enhancement of Cd toxicity in alfalfa seedlings mainly by governing reduced (homo)glutathione and ROS homeostases.

Effect of exogenous nitric oxide on antioxidative system and S-nitrosylation in leaves of Boehmeria nivea (L.) Gaud under cadmium stress.

Cadmium (Cd)-induced growth inhibition is one of the primary factors limiting phytoremediation effect of Boehmeria nivea (L.) Gaud in contaminated soil. Sodium nitroprusside (SNP), a donor of nitric oxide (NO), has been evidenced to alleviate Cd toxicity in many plants. However, as an important mechanism of NO in orchestrating cellular functions, S-nitrosylation is still poorly understood in its relation with Cd tolerance of plants. In this study, higher exogenous NO levels were found to coincide with higher S-nitrosylation level expressed as content of S-nitrosothiols (SNO). The addition of low concentration (100 μM) SNP increased the SNO content, and it simultaneously induced an alleviating effect against Cd toxicity by enhancing the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR) and reduced the accumulation of H2O2 as compared with Cd alone. Application of S-nitrosoglutathione reductase (GSNOR) inhibitors dodecanoic acid (DA) in 100 μM SNP group brought in an extra elevation in S-nitrosylation level and further reinforced the effect of SNP. While the additions of 400 μM SNP and 400 μM SNP + 50 μM DA further elevated the S-nitrosylation level, it markedly weakened the alleviating effect against Cd toxicity as compared with the addition of 100 μM SNP. This phenomenon could be owing to excess consumption of glutathione (GSH) to form SNO under high S-nitrosylation level. Therefore, the present study indicates that S-nitrosylation is involved in the ameliorating effect of SNP against Cd toxicity. This involvement exhibited a concentration-dependent property.

Foliar application with nano-silicon alleviates Cd toxicity in rice seedlings.

Nanofertilizers may be more effective than regular fertilizers in improving plant nutrition, enhancing nutrition use efficiency, and protecting plants from environmental stress. A hydroponic pot experiment was conducted to study the role of foliar application with 2.5 mM nano-silicon in alleviating Cd stress in rice seedlings (Oryza sativa L. cv Youyou 128) grown in solution added with or without 20 μM CdCl2. The results showed that Cd treatment decreased the growth and the contents of Mg, Fe, Zn, chlorophyll a, and glutathione (GSH), accompanied by a significant increase in Cd accumulation. However, foliar application with nano-Si improved the growth, Mg, Fe, and Zn nutrition, and the contents of chlorophyll a of the rice seedlings under Cd stress and decreased Cd accumulation and translocation of Cd from root to shoot. Cd treatment produced oxidative stress to rice seedlings indicated by a higher lipid peroxidation level (as malondialdehyde (MDA)) and higher activities of antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), and a lower GSH content. However, those nano-Si-treated plants had lower MDA but higher GSH content and different antioxidant enzyme activities, indicating a higher Cd tolerance in them. The results suggested that nano-Si application alleviated Cd toxicity in rice by decreasing Cd accumulation, Cd partitioning in shoot and MDA level and by increasing content of some mineral elements (Mg, Fe, and Zn) and antioxidant capacity.

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.

The alleviation of cadmium toxicity in oilseed rape (Brassica napus) by the application of salicylic acid

To assess the potential role of salicylic acid (SA) in plants under cadmium (Cd) stress, a study was conducted on three different oilseed rape (Brassica napus) genotypes. Gas exchange parameters, photosynthetic pigments, antioxidant enzymes activities, mineral nutrients concentration, and ultrastructural analysis were carried out for assessment. Interestingly, cadmium treatment reduced gas exchange parameters, photosynthetic pigments, mineral elements [calcium (Ca), magnesium (Mg), and iron] and the activity of catalase (CAT) enzyme. Whereas, a pronounced increase was observed in malondialdehyde content and antioxidant enzymes, cadmium and zinc accumulation. Impressively, SA played its role as an alleviatory agent by reducing the damage to all parameters caused by Cd except internal CO2 concentration which was further decreased by SA. Even more, Cd and SA showed synergistic effects by increasing superoxide dismutase, peroxidases, ascorbate peroxidase, guaiacol peroxidase, glutathione reductase and decreasing CAT. Apart from affecting the enzyme activities of oilseed rape, both Cd and SA had the same inhibitory effects on Ca and Mg concentrations. Damage caused by Cd to chloroplast and other internal organelles were almost rectified by SA. Effective role of SA, in alleviating Cd toxicity, could be attributed to the SA-induced improvement of photosynthetic activities, enhancement of antioxidant enzymes activities, reduction in lipid peroxidation and Cd uptake. These findings reflect the possible role of SA as a potential inhibitor of cadmium toxicity by strengthening the internal immunity in oilseed rape.

How does NaCl improve tolerance to cadmium in the halophyte Sesuvium portulacastrum?

Sesuvium portulacastrum is a halophyte with considerable Cd tolerance and accumulation, especially under high salinity. The species seems a good candidate for phytoremediation of Cd-contaminated, saline soils. However, the mechanisms sustaining salt-induced alleviation of Cd toxicity remain unknown. Seedlings of S. portulacastrum were submitted hydroponically to different Cd concentrations (0, 25 and 50μM Cd) in combination with low (0.09mM), or high (200mM) NaCl. Cadmium distribution within leaves and stems was assessed by total Cd, cell sap Cd, and Cd in different cell fractions. In plants with low salt supply (LS) Cd induced severe toxicity. The presence of 200mM NaCl (HS) significantly alleviated Cd toxicity symptoms. HS drastically reduced both Cd-induced H2O2 production and membrane damage. In HS plants the reduced Cd uptake was only in part responsible for the lower Cd toxicity. Even at equal internal leaf Cd concentrations less Cd toxicity was observed in HS than in LS plants. In HS plants proportionally more Cd was bound in cell walls and proportionally less accumulated in the soluble fraction than in LS plants. Our results show that NaCl improves plant performance under Cd stress by both a decrease of Cd2+ activity in the medium leading to less Cd uptake and a change of Cd speciation and compartmentation inside tissues. More efficient internal detoxification seems mainly brought about by preferential Cd binding to chloride and cell walls in plants treated with a high salt concentration.

Polyhydroxyfullerene binds cadmium ions and alleviates metal-induced oxidative stress in Saccharomyces cerevisiae.

The water-soluble polyhydroxyfullerene (PHF) is a functionalized carbon nanomaterial with several industrial and commercial applications. There have been controversial reports on the toxicity and/or antioxidant properties of fullerenes and their derivatives. Conversely, metals have been recognized as toxic mainly due to their ability to induce oxidative stress in living organisms. We investigated the interactive effects of PHF and cadmium ions (Cd) on the model yeast Saccharomyces cerevisiae by exposing cells to Cd (≤5 mg liter(-1)) in the absence or presence of PHF (≤500 mg liter(-1)) at different pHs (5.8 to 6.8). In the absence of Cd, PHF stimulated yeast growth up to 10.4%. Cd inhibited growth up to 79.7%, induced intracellular accumulation of reactive oxygen species (ROS), and promoted plasma membrane disruption in a dose- and pH-dependent manner. The negative effects of Cd on growth were attenuated by the presence of PHF, and maximum growth recovery (53.8%) was obtained at the highest PHF concentration and pH. The coexposure to Cd and PHF decreased ROS accumulation up to 36.7% and membrane disruption up to 30.7% in a dose- and pH-dependent manner. Two mechanisms helped to explain the role of PHF in alleviating Cd toxicity to yeasts: PHF decreased Cd-induced oxidative stress and bound significant amounts of Cd in the extracellular medium, reducing its bioavailability to the cells.

Growth, photosynthesis and oxidative responses of Solanum melongena L. seedlings to cadmium stress: Mechanism of toxicity amelioration by kinetin

The sand culture experiments were conducted to investigate whether the foliar application of kinetin (KN), a kind of cytokinins alleviates cadmium (Cd) toxicity in Solanum melongena L. seedlings. The Cd1 (3mgCdkg−1 soil) and Cd2 (9mgCdkg−1 soil) doses of Cd declined growth of S. melongena seedlings in concentration dependent manner which was due to accumulation of Cd in roots and shoots. Kinetin at 10μM alleviated Cd toxicity which was accompanied by appreciable decrease in Cd accumulation in seedlings. The photosynthetic pigments: Chlorophyll (Chl) a, b and carotenoids (Car) contents, and chlorophyll fluorescence parameters: Fm/F0, Fv/F0 (except Fv/Fm and qP) were decreased while NPQ was raised by Cd, however, with exogenous KN application the damaging effects on photosynthetic pigments and fluorescence parameters were significantly ameliorated. The oxidative stress markers such as superoxide radical, hydrogen peroxide and malondialdehyde (lipid peroxidation) contents were enhanced by both the doses of Cd; however, together with KN these oxidative indices were diminished significantly. Cadmium treatment increased antioxidative enzymes: superoxide dismutase, peroxidase, catalase and glutathione-S-transferase activity and the contents of non-enzymatic antioxidants: non protein thiol and proline as compared to control, and KN application further enhanced the antioxidant capacity in Cd treated and even untreated seedlings. The overall results suggest that foliar application of KN improved the growth performance of S. melongena seedlings even in presence of toxic level of Cd by strengthening the antioxidant system and photosynthetic capacity.

Protective role of selenium on pepper exposed to cadmium stress during reproductive stage.

The aim of the present study was to examine the effects of exogenous selenium (Se) supplementation on the tolerance of pepper (Capsicum annuum L.) cv. Suryamukhi Cluster plants to cadmium (Cd) phytotoxicity at the reproductive stage. The pepper plants were supplied with Cd (0, 0.25 or 0.50 mM) and Se (0, 3 or 7 μM), individually or simultaneously, three times during the experiment. The obtained results show that Cd had deleterious effect on pepper plants at the reproductive stage. However, Se supplementation improved the flower number, fruit number and fruit diameter in plants exposed to 0.50 mM Cd. Moreover, both Se concentrations used in 0.25 mM Cd-treated plants and 3 μM Se in 0.50 mM Cd-treated plants enhanced fruit yield per plant as compared to Cd-alone treatment. The chlorophyll concentrations significantly increased in the fruits of Cd-exposed plants after Se addition. However, Se supplementation reduced total carotenoids and total soluble solid (TSS) concentrations in the pepper fruits exposed to Cd. Selenium also generally enhanced the total antioxidant activity of pepper fruits subjected to Cd. Both Se concentrations used increased mean productivity (MP), stress tolerance index (STI) and yield stability index (YSI) in plants grown in the medium containing 0.25 mM Cd. At low concentration (3 μM), Se significantly increased geometric mean productivity (GMP), STI and YSI of plant exposed to 0.50 mM Cd. The highest Cd concentration in the fruits was achieved at 0.50 mM Cd and Se application significantly reduced Cd accumulation in the Cd-exposed plants. Our results indicate that application of Se can alleviate Cd toxicity in pepper plants at the reproductive stage by restricting Cd accumulation in fruits, enhancing their antioxidant activity and thus improving the reproductive and stress tolerance parameters.

Cellular Mechanisms in Higher Plants Governing Tolerance to Cadmium Toxicity

Cadmium (Cd) is an inorganic mineral in the earth's crust. Cadmium entry into the environment occurs through geogenic and anthropogenic sources. Industrial activities including mining, electroplating, iron and steel plants, and battery production employ Cd during their processes and often release Cd into the environment. When disseminated into soil, Cd can be detrimental to agro-ecosystems because it is relatively mobile and phytotoxic even at low concentrations. Cadmium's phytotoxicity is due to reductions in the rate of transpiration and photosynthesis and chlorophyll concentration resulting in retardation of plant growth, and an alteration in the nutrient concentration in roots and leaves. In response to Cd toxicity, plants have developed protective cellular mechanisms such as synthesis of phytochelatins and metallothioneins, metal compartmentalization in vacuoles, and the increased activity of antioxidant enzymes to neutralize Cd-induced toxicity. While these direct protective mechanisms can help alleviate Cd toxicity, other indirect mechanisms such as microelements (zinc, iron, manganese, and selenium) interfering with Cd uptake may decrease Cd concentration in plants. This comprehensive review encompasses the significance of Cd, portals of contamination and toxicity to plants, and implications for crop production. Various mitigation strategies with the beneficial effects of zinc, iron, manganese, and selenium in activating defence mechanisms against Cd stress are discussed. Furthermore, this review systematically identifies and summarises suitable strategies for mitigating Cd-induced toxicity in plants.

Citric acid assisted phytoremediation of cadmium by Brassica napus L

Phytoextraction is an eco-friendly and cost-effective technique for removal of toxins, especially heavy metals and metalloids from contaminated soils by the roots of high biomass producing plant species with subsequent transport to aerial parts. Lower metal bioavailability often limits the phytoextraction. Organic chelators can help to improve this biological technique by increasing metal solubility. The aim of the present study was to investigate the possibility of improving the phytoextraction of Cd by the application of citric acid. For this purpose, plants were grown in hydroponics under controlled conditions. Results indicated that Cd supply significantly decreased the plant growth, biomass, pigments, photosynthetic characteristics and protein contents which were accompanied by a significant increase in Cd concentration, hydrogen peroxide (H2O2), electrolyte leakage, malondialdehyde (MDA) accumulation and decrease in antioxidant capacity. The effects were dose dependent with obvious effects at higher Cd concentration. Application of CA significantly enhanced Cd uptake and its accumulation in plant roots, stems and leaves. Citric acid alleviated Cd toxicity by increasing plant biomass and photosynthetic and growth parameters alone and in combination with Cd and by reducing oxidative stress as observed by reduction in MDA and H2O2 production and decreased electrolyte leakage induced by Cd stress. Application of CA also enhanced the antioxidant enzymes activity alone and under Cd stress. Thus, the data indicate that exogenous CA application can increase Cd uptake and minimize Cd stress in plants and may be beneficial in accelerating the phytoextraction of Cd through hyper-accumulating plants such as Brassica napus L.

Ethylene production is associated with alleviation of cadmium-induced oxidative stress by sulfur in mustard types differing in ethylene sensitivity

We studied the response of ethylene-sensitive (Pusa Jai Kisan) and ethylene-insensitive (SS2) mustard (Brassica juncea) cultivars to 0, 0.5, 1.0 and 2.0mM SO42−, and the effect of 1.0mM SO42− was studied in the amelioration of 50µM cadmium (Cd). The Cd-induced oxidative stress and Cd accumulation were greater in SS2 than Pusa Jai Kisan, but sulfur (S) application alleviated Cd-induced oxidative stress more prominently in Pusa Jai Kisan by increasing S-metabolism and synthesis of reduced glutathione (GSH) and ethylene production; and promoted photosynthesis and plant dry mass under Cd stress. The ethylene-sensitive cultivar responded more to S treatment under Cd stress and showed increased activity of antioxidant system resulting in increased photosynthesis and growth. Cadmium treatment resulted in rapid increase in ethylene formation which adversely influenced photosynthesis and plant dry mass. However, S and ethephon application to Cd-treated plants lowered ethylene formation to optimal range responsible for maximal GSH synthesis and protection against Cd-induced oxidative stress. The similarity of the effectiveness of 1.0mM SO42− with 200µLL−1 ethylene source as ethephon in alleviation of 50µM Cd further verifies that differential alleviation of Cd toxicity in the two cultivars by S was dependent on ethylene production. The results suggest that ethylene production determines Cd stress alleviation by S via regulatory interaction with antioxidant metabolism. Thus, ethylene production and sensitivity bear a prominent role in alleviation of Cd stress by S and can be used as a criterion for developing Cd tolerant genotypes.

Expression of sulfur uptake assimilation-related genes in response to cadmium, bensulfuron-methyl and their co-contamination in rice roots

The responses of sulfur (S) uptake assimilation-related genes' expression in roots of two rice cultivars to cadmium (Cd), bensulfuron-methyl (BSM) and their co-contamination (Cd+BSM) were investigated by gene-chip microarray analysis and quantitative real-time PCR (QRT-PCR) technology. Treatments of Cd and Cd+BSM induced expression of sulfate transporter and permease genes, and promoted sulfate uptake in rice roots. Cd+BSM could alleviate Cd toxicity to cv. Fengmeizhan seedlings, probably due to Cd+BSM promoting greater S absorption by seedlings. Cd and Cd+BSM induced expression of sulfate assimilation-related genes, and thus activated the sulfur assimilation pathway. Cd and Cd+BSM induced expression of phytochelatin synthase and metallothionein genes, and induced expression of glutathione S-transferases (GSTs), glutathione synthase (GS) and S-containing antioxidation enzyme genes, which detoxified Cd2+. It is suggested that (to cope with the toxicity of Cd, BSM and their co-contamination) the S uptake and assimilation pathway was activated in rice roots by increased expression of related genes, thus enhancing the supply of organic S for synthesis of Cd or BSM resistance-related substances.

N-acetyl-cysteine alleviates Cd toxicity and reduces Cd uptake in the two barley genotypes differing in Cd tolerance

A hydroponic experiment was carried out to study the physiological mechanisms of N-acetyl cysteine (NAC) in mitigating cadmium (Cd) toxicity in two barley (Hordeum vulgare L.) genotypes, Dong 17 (Cd-sensitive) and Weisuobuzhi (Cd-tolerant). Addition of 200 μM NAC to a culture medium containing 5 μM Cd (Cd + NAC) markedly alleviated Cd-induced growth inhibition and toxicity, maintained root cell viability, and dramatically depressed O 2 ·− and ·OH, and malondialdehyde accumulation, significantly reduced Cd concentration in leaves and roots, especially in the sensitive genotype Dong 17. External NAC counteracted Cd-induced alterations of certain antioxidant enzymes, e.g., brought root superoxide dismutase and glutathione reductase, leaf/root peroxidase and glutathione peroxidase activities of the both genotypes down towards the control level, but elevated Cd-stress-depressed leaf catalase in Dong 17 and root ascorbate peroxidase activities in both genotypes. NAC counteracted Cd-induced alterations in amino acids and microelement contents. Furthermore, NAC significantly reduced Cd-induced damage to leaf/root ultrastructure, e.g. the shape of chloroplasts in plants treated with Cd + NAC was relatively normal with well-structured thylakoid membranes and parallel pattern of lamellae but less osmiophilic plastoglobuli compared with Cd alone treatment; nuclei of root cells were better formed and chromatin distributed more uniformly in both genotypes. These results suggested that under Cd stress, NAC may protects barley seedlings against Cd-induced damage by directly and indirectly scavenging reactive oxygen species and by maintaining stability and integrity of the subcellular structure.

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.