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1.
Pea (Pisum sativum L. cv. Azad) plants exposed to 4 and 40 microM of Cd for 7 d in hydroponic culture were analysed with reference to the distribution of metal, the accumulation of biomass and the metal's effects on antioxidants and antioxidative enzymes in roots and leaves. Cd-induced a decrease in plant biomass. The maximum accumulation of Cd occurred in roots followed by stems and leaves. An enhanced level of lipid peroxidation and an increased tissue concentration of hydrogen peroxide (H2O2) in both roots and leaves indicated that Cd caused oxidative stress in pea plants. Roots and leaves of pea plants responded differently to Cd with reference to the induction of enhanced activities of most of the enzymes monitored in the present study. These differential responses to Cd were further found to be associated with levels of Cd to which the plants were exposed. Cd-induced enhancement in superoxide dismutase (SOD) activity was more at 40 microM than at 4 microM in leaves. While catalase (CAT) prominently increased in leaves both at 4 and 40 microM Cd, ascorbate peroxidase (APX) showed maximum stimulation at 40 microM Cd in roots. Enhancement in glutathione reductase (GR) activity was also more at 40 microM than at 4 microM Cd in roots. While glutathione peroxidase (GPOX) activity decreased in roots and remained almost unmodified in leaves, glutathione S-transferase (GST) showed pronounced stimulation in both roots and leaves of pea plants exposed to 40 microM Cd. Increased activities of antioxidative enzymes in Cd-treated plants suggest that they have some additive function in the mechanism of metal tolerance in pea plants.  相似文献   

2.
The effects of cadmium (Cd) uptake on ultrastructure and lipid composition of chloroplasts were investigated in 28-day-old tomato plants (Lycopersicon esculentum var. Ibiza F1) grown for 10 days in the presence of various concentrations of CdCl2. Different growth parameters, lipid and fatty acid composition, lipid peroxidation, and lipoxygenase activity were measured in the leaves in order to assess the involvement of this metal in the generation of oxidative stress. We first observed that the accumulation of Cd increased with external metal concentration, and was considerably higher in roots than in leaves. Cadmium induced a significant inhibition of growth in both plant organs, as well as a reduction in the chlorophyll and carotenoid contents in the leaves. Ultrastructural investigations revealed that cadmium induced disorganization in leaf structure, essentially marked by a lowered mesophyll cell size, reduced intercellular spaces, as well as severe alterations in chloroplast fine structure, which exhibits disturbed shape and dilation of thylakoid membranes. High cadmium concentrations also affect the main lipid classes, leading to strong changes in their composition and fatty acid content. Thus, the exposure of tomato plants to cadmium caused a concentration-related decrease in the fatty acid content and a shift in the composition of fatty acids, resulting in a lower degree of fatty acid unsaturation in chloroplast membranes. The level of lipid peroxides and the activity of lipoxygenase were also significantly enhanced at high Cd concentrations. These biochemical and ultrastructural changes suggest that cadmium, through its effects on membrane structure and composition, induces premature senescence of leaves.  相似文献   

3.
The phytotoxicity imposed by cadmium (Cd) and its detoxifying responses of Bacopa monnieri L. have been investigated. Effect on biomass, photosynthetic pigments and protein level were evaluated as gross effect, while lipid peroxidation and electrolyte leakage reflected oxidative stress. Induction of phytochelatins and enzymatic and non-enzymatic antioxidants were monitored as plants primary and secondary metal detoxifying responses, respectively. Plants accumulated substantial amount of Cd in different plant parts (root, stem and leaf), the maximum being in roots (9240.11 microg g(-1) dw after 7 d at 100 microM). Cadmium induced oxidative stress, which was indicated by increase in lipid peroxidation and electrical conductivity with increase in metal concentration and exposure duration. Photosynthetic pigments showed progressive decline while protein showed slight increase at lower concentrations. Enzymes viz., superoxide dismutase (SOD, EC 1.15.1.1), guaiacol peroxidase (GPX, EC 1.11.1.7) ascorbate peroxidase (APX, EC 1.11.1.11) and glutathione reductase (GR, EC 1.6.4.2) showed stimulation except catalase (CAT, EC 1.11.1.6) which showed declining trend. Initially, an enhanced level of cysteine, glutathione and non-protein thiols was observed, which depleted with increase in exposure concentration and duration. Phytochelatins induced significantly at 10 microM Cd in roots and at 50 microM Cd in leaves. The phytochelatins decreased in roots at 50 microM Cd, which may be correlated with reduced level of GSH, probably due to reduced GR activity, which exerted increased oxidative stress as also evident by the phenotypic changes in the plant like browning of roots and slight yellowing of leaves. Thus, besides synthesis of phytochelatins, availability of GSH and concerted activity of GR seem to play a central role for Bacopa plants to combat oxidative stress caused by metal and to detoxify it. Plants ability to accumulate and tolerate high amount of Cd through enhanced level of PCs and various antioxidants suggest it to be a suitable candidate for phytoremediation.  相似文献   

4.
Cadmium accumulation and oxidative burst in garlic (Allium sativum)   总被引:13,自引:0,他引:13  
To investigate the temporal sequence of physiological reactions of garlic (Allium sativum) to cadmium (Cd) treatment, seedlings developed from cloves were grown in increasing concentrations of CdCl2, ranging from 1-10 mM, for up to 8 days in sand. Analysis of Cd uptake indicated that most Cd accumulated in roots, but some was also translocated and accumulated in leaves at longer exposure time (after 12h) and higher concentrations (5 and 10mM) of CdCl2. Changes in activities of antioxidative enzymes, including superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), were characterized in leaves of garlic seedlings. Cd (5 and 10 mM) initially inhibited the activities of SOD and CAT but thereafter recovered or even increased compared with control plants. POD activities at 5 and 10 mM of Cd increased more than 3-4 times over control plants within 12 h and then dropped, but were still higher than controls at the end of the experiment. Otherwise lipid peroxidation enhanced with the increasing of incubation time and concentrations of external Cd. Leaves exposed to 1 mM CdCl2 showed a less pronounced response and only a small reduction in shoot growth. These results suggested that in leaves of garlic seedlings challenged by CdCl2 at higher concentrations, induction of these various enzymes is part of a general defense strategy to cope with overproduction of reactive oxygen. The possible mechanism of antioxidative enzymes changing before Cd accumulation in leaves of garlic seedlings is discussed.  相似文献   

5.
The treatment of growing tomato (Lycopersicum esculentum) plants with CdCl2 (0, 1, 5, 10, 25 et 50 microM) on various plant physiological parameters and membrane lipids of primary and young leaves was studied. In leaves of tomato plants Cd produced a significant inhibition of growth, chlorophyll content and alteration of the nutrient status in both primary and young leaves. A decrease in lipid contents, specially galactolipids and phospholipids, was observed after Cd treatment.  相似文献   

6.
As reported previously, atmospheric nitrogen dioxide (NO2) at an ambient level increased plant size and the contents of cell constituents. We investigated this effect of atmospheric NO2 on decontamination of cadmium (Cd) by kenaf (Hibiscus cannabinus). Seventeen-day-old seedlings of kenaf were grown in air either with NO2 or without NO2. (Plants were exposed to 100 +/- 50 ppb NO2 for 10 d under irrigation of 0.1% Hyponex supplemented with 20 microM CdCl2.) Plants were then harvested and the biomass of stems, leaves, and roots, as well as the content of Cd in the organs, was determined. The stem and root biomass per plant were 1.25-1.27-fold greater in +NO2 plants than in -NO2 plants. The Cd content per stem was more than 30% greater in +NO2 plants than in -NO2 plants.  相似文献   

7.
The behavior of glutathione reductase (GR, EC 1.6.4.2) activity and isoforms were analyzed in wheat (Triticum aestivum L.) leaves and roots exposed to a chronic treatment with a toxic cadmium (Cd) concentration. A significant growth inhibition (up to 55%) was found in leaves at 7, 14 and 21 days, whereas roots were affected (51%) only after three weeks. Wheat plants grown in the presence of 100microM Cd showed a time-dependent accumulation of this metal, with Cd concentration being 10-fold higher in roots than in leaves. Nevertheless, lipid peroxidation was augmented in leaves in all experiments, but not in roots until 21 days. Cadmium treatment altered neither the GR activity nor the isoform pattern in the leaves. However, GR activity increased 111% and 200% in roots at 7 and 14 days, respectively, returning to control levels after 21 days. Three GR isoforms were found in roots of control and treated plants, two of which were enhanced by Cd treatment at 7 and 14 days, as assessed by activity staining on native gels. The changes in the isoform pattern modified the global kinetic properties of GR, thereby decreasing significantly (2.5-fold) the Michaelis constant (K(m)) value for oxidized glutathione. Isozyme induction was not associated with an enhancement of GR mRNA and protein expression, indicating that post-translational modification could occur. Our data demonstrated that up-regulation of GR activity by the induction of distinctive isoforms occurs as a defense mechanism against Cd-generated oxidative stress in roots.  相似文献   

8.
9.
Seedlings (2 weeks old) of pepper (Capsicum annum) were grown in nutrient solution with added CdCl(2) (10 or 50 microM) for 7 days. In Cd-treated plants, changes in acyl lipids and fatty acid composition were investigated. Cd particularly lowered the amount of monogalactosyldiacylglycerol (MGDG) and enhanced accumulation of phospholipids [phosphatidylcholine (PC), phosphatidylethanolamine and phosphatidylglycerol] in leaves. In contrast, content of PC and galactolipids (MGDG and digalactosyldiacylglycerol) decreased in roots. Fatty acid composition of leaves was also changed by Cd addition to external medium, but no important changes occurred in roots. Levels of leaf polyunsaturated fatty acids, especially 18:3 and 16:3, were reduced. Lipid and fatty acid composition changes in roots are discussed in relation to Cd tolerance in pepper.  相似文献   

10.
11.
BACKGROUND AND AIMS: To date, there are no crop mutants described in the literature that display both Cd accumulation and tolerance. In the present study a unique pea (Pisum sativum) mutant SGECd(t) with increased Cd tolerance and accumulation was isolated and characterized. METHODS: Ethylmethane sulfonate mutagenesis of the pea line SGE was used to obtain the mutant. Screening for Cd-tolerant seedlings in the M2 generation was performed using hydroponics in the presence of 6 microm CdCl2. Hybridological analysis was used to identify the inheritance of the mutant phenotype. Several physiological and biochemical characteristics of SGECd(t) were studied in hydroponic experiments in the presence of 3 microm CdCl2, and elemental analysis was conducted. KEY RESULTS: The mutant SGECd(t) was characterized as having a monogenic inheritance and a recessive phenotype. It showed increased Cd concentrations in roots and shoots but no obvious morphological defects, demonstrating its capability to cope well with increased Cd levels in its tissues. The enhanced Cd accumulation in the mutant was accompanied by maintenance of homeostasis of shoot Ca, Mg, Zn and Mn contents, and root Ca and Mg contents. Through the application of La(+3) and the exclusion of Ca from the nutrient solution, maintenance of nutrient homeostasis in Cd-stressed SGECd(t) was shown to contribute to the increased Cd tolerance. Control plants of the mutant (i.e. no Cd treatment) had elevated concentrations of glutathione (GSH) in the roots. Through measurements of chitinase and guaiacol-dependent peroxidase activities, as well as proline and non-protein thiol (NPT) levels, it was shown that there were lower levels of Cd stress both in roots and shoots of SGECd(t). Accumulation of phytochelatins [(PCcalculated) = (NPT)-(GSH)] could be excluded as a cause of the increased Cd tolerance in the mutant. CONCLUSIONS: The SGECd(t) mutant represents a novel and unique model to study adaptation of plants to toxic heavy metal concentrations.  相似文献   

12.
Cadmium (Cd)-induced oxidative stress and antioxidant defense mechanisms were analyzed in roots and leaves of Vigna mungo L. Seeds were germinated in perlite-vermiculite and irrigated with Hoagland nutrient solution. At day 6, seedlings were exposed to 40 μM Cd under semi-hydroponic conditions for a period of 12 days. Growth anomalies and abnormal chromatin condensation were observed in Cd-treated plants, in comparison with control ones. Cd accumulation was observed in roots of treated plants. The analyses of antioxidative defense and oxidative parameters in roots, stems and leaves showed different tissue-specific responses. Superoxide dismutase (SOD) and guaiacol peroxidase (GPx) activities and the level of lipid peroxidation (MDA content) decreased in roots. However, they increased in leaves. Catalase activity and chlorophyll content, on the other hand, decreased over exposure to Cd stress. Total glutathione, non-protein thiols, reduced glutathione (GSH) and phytochelatins increased significantly, while oxidized glutathione (GSSG) decreased, as compared with control plants. The present data suggest that the presence of Cd in soil and water can cause oxidative damage that may be detrimental for optimum production of nutritional mung.  相似文献   

13.
14.
The effect of treatment with benzothiadiazole (BTH) or l -2-oxothiazolidine-4-carboxylic acid (OTC), and their interaction with Plum pox virus (PPV) infection, on antioxidative metabolism of pea plants was studied at the subcellular level. PPV infection produced a 20% reduction in plant growth. Pre-treatment of pea plants with OTC or BTH afforded partial protection against PPV infection, measured as the percentage of leaves showing symptoms, but neither BTH nor OTC significantly reduced the virus content. PPV infection caused oxidative stress, as monitored by increases in lipid peroxidation and protein oxidation in soluble and chloroplastic fractions. In leaves of non-infected plants, OTC increased the content of reduced glutathione (GSH) and total glutathione; accordingly, an increase in the redox state of glutathione was observed. An increase in oxidized glutathione (GSSG) was found in symptomatic leaves from infected plants. A similar increase in GSSG was also observed in asymptomatic leaves from infected, untreated plants. However, no changes in GSSG occurred in asymptomatic leaves from infected plants treated with BTH and OTC and, accordingly, a higher redox state of GSH was recorded in those leaves, which could have had a role in the reduction of symptoms, as observed in asymptomatic leaves from infected plants treated with BTH or OTC. Treatment with BTH or OTC had some effect on antioxidant enzymes in soluble and chloroplastic fractions from infected pea leaves. An increase in antioxidative mechanisms, such as GSH-related enzymes (DHAR, GR and G6PDH), as well as APX and POX, at the subcellular level was observed, which could play a role in reducing the severity of cellular damage induced by Sharka in pea leaves.  相似文献   

15.
The present study investigated the possible mediatory role of salicylic acid (SA) in protecting plants from cadmium (Cd) toxicity. The exposure of pea plants to increasing Cd concentrations (0.5, 1.0, 2.0 and 5.0 μM) during early stages of their establishment, caused a gradual decrease in shoot and root fresh weight accumulation, the rate of CO2 fixation and the activity of ribulose-1,5-bisphosphate carboxylase (RuBPC, E.C. 4.1.1.39), the effect being most expressed at higher Cd concentrations. In vivo the excess of Cd-induced alterations in the redox cycling of oxygen-evolving centers and the assimilatory capacity of the pea leaves as revealed by changes in thermoluminescence emission after flash illumination. The levels of some important parameters associated with oxidative stress, namely lipid peroxidation, electrolyte leakage and proline production were increased. Seed pretreatment with SA alleviated the negative effect of Cd on growth, photosynthesis, carboxylation reactions, thermoluminescence characteristics and chlorophyll content, and led to decrease in oxidative injuries caused by Cd. The data suggest that the beneficial effect of SA during an earlier growth period could be related to avoidance of cumulative damage upon exposure to cadmium thus reducing the negative consequences of oxidative stress caused by heavy metal toxicity. In addition, the observed high endogenous levels of SA after treatment with Cd suggests that SA may act directly as an antioxidant to scavenge the reactive oxygen species and/or indirectly modulate redox balance through activation of antioxidant responses.Taken together these evidences could explain at some extend the protective role of SA on photochemical activity of chloroplast membranes and photosynthetic carboxylation reactions in Cd-stressed pea plants.  相似文献   

16.
Growth, cadmium accumulation and potassium and calcium status were studied in two halophytes from Aizoaceae family: Sesuvium portulacastrum and Mesembryanthemum crystallinum. After multiplication, the seedlings were cultivated on nutrient solution supplemented with NaCl (100mM) and CdCl2 (0, 50, 100, 200 and 300 microM). After 1 month of treatment, plants were harvested and the dry weight, as well as the Cd, K and Ca concentrations in tissues were determined. Results showed that S. portulacastrum, a perennial halophyte with slow growth, is significantly more tolerant to Cd than M. crystallinum, an annual plant. Cd severely inhibited Mesembryanthemum growth even at the lowest Cd concentration in culture medium (50 microM), and did not modify significantly that of Sesuvium. For both halophytes, Cd accumulation was significantly higher in the roots than in the shoots. However, Cd concentration reached 350-700 microg g(-1) DM in the shoots, values characteristic of Cd hyperaccumulator plants. The addition of Cd in the culture medium led to a disturbance of Ca and especially K nutrition, suggesting the possibility to improve plant growth and Cd phytoextraction of both halophytes by increasing nutrient availability in the culture medium.  相似文献   

17.
The role of salicylic acid (SA) in alleviating cadmium (Cd) toxicity was investigated in a hydroponic cultivation system. Short-term exposure of bean (Phaseolus vulgaris) plants to 20 μM Cd inhibited biomass production and intensively increased accumulation of Cd in both roots and leaves. At leaf level, Cd significantly decreased mineral ions, chlorophyll and carotenoids concentrations. Concomitantly, Cd enhanced electrolyte leakage, H2O2 content and lipid peroxidation as indicated by malondialdehyde (MDA) accumulation. SA pretreatment decreased the uptake and the transport of Cd, alleviated the Cd-induced inhibition of nutrient absorption and led to a significant increase of chlorophyll and carotenoid content. SA application alleviated the oxidative damages as evidenced by the lowered H2O2 and MDA content. SA particularly induced an increase in both CAT and APX activities accompanied by a significant reduction in SOD and POD activities. As important antioxidants, ascorbate and glutathione contents in bean leaves exposed to cadmium were significantly decreased by SA treatment. These results reveal the potentiating effect of salicylic acid in regulating cadmium induced oxidative stress in bean plants.  相似文献   

18.
The effects of cadmium (Cd) on cellular proteolytic responses were investigated in the roots and leaves of tomato (Solanum lycopersicum L., var Ibiza) plants. Three-week-old plants were grown for 3 and 10 days in the presence of 0.3–300 μM Cd and compared to control plants grown in the absence of Cd. Roots of Cd treated plants accumulated four to fivefold Cd as much as mature leaves. Although 10 days of culture at high Cd concentrations inhibited plant growth, tomato plants recovered and were still able to grow again after Cd removal. Tomato roots and leaves are not modified in their proteolytic response with low Cd concentrations (≤3 μM) in the incubation medium. At higher Cd concentration, protein oxidation state and protease activities are modified in roots and leaves although in different ways. The soluble protein content of leaves decreased and protein carbonylation level increased indicative of an oxidative stress. Conversely, protein content of roots increased from 30 to 50%, but the amount of oxidized proteins decreased by two to threefold. Proteolysis responded earlier in leaves than in root to Cd stress. Additionally, whereas cysteine- and metallo-endopeptidase activities, as well as proteasome chymotrypsin activity and subunit expression level, increased in roots and leaves, serine-endopeptidase activities increased only in leaves. This contrasted response between roots and leaves may reflect differences in Cd compartmentation and/or complexation, antioxidant responses and metabolic sensitivity to Cd between plant tissues. The up-regulation of the 20S proteasome gene expression and proteolytic activity argues in favor of the involvement of the 20S proteasome in the degradation of oxidized proteins in plants. This paper is dedicated to Nathalie Galtier (1964–2005), who was senior researcher at the INRA Research Center, Villenave d’Ornon, France.  相似文献   

19.
金属硫蛋白是一类小分子量的金属结合蛋白 ,有 β,α两个结构域 .用另一个 α结构域取代金属硫蛋白的 β结构域 ,得到突变体 αα.通过 PCR法在 αα- c DNA翻译起始密码子 ATG前加入植物偏爱的碱基组合 AACA,构建 Ca MV双 35S启动子驱动的 αα- c DNA植物表达载体 p GPTVd35S-αα,此载体以抗除草剂基因 ( bar)作为选择标记物 .用根癌农杆菌介导的叶盘法对栽培种烟草 NC89进行转化 .Southern和 Western印迹分析表明突变体αα- c DNA已整合进入烟草基因组并且可以正常表达 .Northern印迹结果显示突变体αα- c DNA在烟草根部的表达强于叶部 .烟草根、茎、叶Cd2 +含量分析表明 ,转基因植物与对照相比 ,Cd2 +更多地集中在根部 ,在一定程度上降低了叶片中的 Cd2 + 含量 .Cd2 + 抗性实验进一步证明突变体αα- c DNA的表达提高了转基因烟草对 Cd2 + 的抗性 :转基因烟草在 2 0 0μmol/L Cd Cl2 条件下生长正常 ,在 40 0μmol/Cd Cl2 培养基内也可以存活 .而 1 0 0μmol/L Cd Cl2 即成为对照烟草的致死剂量 .  相似文献   

20.
Beneficial effects of low-concentration chemical stressors have been investigated previously in different model systems. The symptoms of stimulation are known from earlier studies, but information about the mechanism is at an initial stage. In the present work, the mechanism of stimulation of low-concentration Cd (5 x 10(-8)M) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU, 10(-7)M) was investigated in barley seedlings. In treated plants, the amount of cytokinins increased in roots and, after being transported to the leaves, they caused stimulation there. To identify the signal transduction pathway(s) involved in the primary stimulation of cytokinin synthesis (and/or activation) in roots, specific phosphatidylinositol-4,5-bisphosphate-inositol-1,4,5-triphosphate/diacylglycerol (PIP(2)-IP(3)/DAG) and mitogen activated protein kinase (MAPK) signaling pathway inhibitors were added to the nutrient solution, and all proved to be effective, eliminating the stimulation by the stressors. Measurements of superoxide dismutase (SOD, EC 1.15.1.1) activity and the amount of malonyldialdehyde (MDA) showed that the increased amount of Cd did not cause oxidative stress in the roots, and no oxidative stress was found in the leaves, where Cd did not even accumulate. DCMU slightly increased the activity of SOD after 1 week in roots, but did not cause lipid peroxidation. In leaves, there was no oxidative stress upon treatment with DCMU. Thus, oxidative stress cannot be responsible for the stimulation with low-concentration stressors, as they changed the activity of SOD differently, while being equally stimulative for the plants.  相似文献   

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