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1.

Aims

Contamination of sunflower (Helianthus annuus L.) by cadmium (Cd) is a concern for food and feed safety as this species accumulates Cd to a greater extent than other crops. We examined the relationships between root architecture and Cd2+ uptake by roots.

Methods

We determined and mathematically modelled the longitudinal variation of Cd2+ influx in first order roots of sunflower grown in hydroponics by using short-term exposure to 109Cd-labelled solutions (0.8 to 500 nM). Thereafter, by taking into account the longitudinal variation of the influx, we simulated the uptake of Cd2+ for 24 h by cohorts of roots characterised by various architectural characteristics.

Results

Cd2+ influx at the root tip was on average 2.9 times that of the basal region close to the taproot. The simulations indicated that the total Cd2+ uptake by root cohorts mainly depends on 1/ the root diameter and the number of roots, 2/ the value of the Cd2+ influx at the basal region 3/ the stronger influx at the root tip.

Conclusion

Considering a higher Cd2+ influx at the root tip may be important to understand the relationship between root architecture and Cd2+ uptake by the root system.  相似文献   

2.

Aims

In a previous work, we observed a longitudinal decrease in Cd2+ influx starting from the root tip in first order lateral roots of sunflower (Helianthus annuus L.) grown in hydroponics. This variable influx was expected to impact the total Cd2+ uptake depending on the root system architecture and on how steep was the decrease of the influx. Here, we examined the influence of the culture substrate, of the age and order of lateral roots on the longitudinal variation of Cd2+ influx.

Methods

By using short-term exposures to 109Cd-labelled solution (5 to 200 nM), we compared the longitudinal variations in Cd2+ roots influx depending on the growth substrate (hydroponics or sand), on the root age and order.

Results

In second order laterals, Cd2+ influx decreased from the apex to the root base, as for first order laterals. For sand cultures compared to hydroponics, the mean Cd2+ influx was lower and decreased more steeply with the distance from the apex. The influx also decreased with increasing root age and order, markedly in hydroponics but less for sand cultures.

Conclusion

Results suggested that for a given root surface area, the Cd2+ uptake by a root system should increase with increasing number of root tips and decreasing individual root length.  相似文献   

3.
The Relationship between Salinity and Cadmium Stress in Barley   总被引:1,自引:0,他引:1  
Distribution of cadmium between roots and shoots of barley was manipulated by the cadmium concentration (0.01 and 0.005 mM Cd2+), pH (4.6 and 5.9) as well as treatment duration. The prolongation of treatment increased dry mass and content of cadmium in plants. The cadmium is accumulated mainly in roots. Presence of both, 0.005 mM Cd2+ and 100 mM NaCl in medium at pH 5.9 (Cd-NaCl plants) resulted in the most severe growth inhibition of plants, but about one half accumulation of cadmium in roots then in a case of only Cd-treated plants. In the Cd-NaCl plants, the net photosynthetic and transpiration rates were less reduced then in a case of only NaCl-treated plants. The treatments also influenced uptake of Ca, Cd, Cu, K, Mg, Na and Zn predominantly in roots. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

4.
Excess cadmium (Cd2+) in the soil environment is taken up by plants and can cause phytotoxicity. Elevated temperatures also lead to deleterious effects on plants. Plants are very often exposed to a combination of stresses rather than a single stress. The effect of Cd2+ and heat stress (HS) on the growth, root ultrastructure, lipid peroxidation (MDA), hydrogen peroxide accumulation and the activities of antioxidant enzymes peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) of rice roots from sensitive cv. DR-92 and tolerant cv. Bh-1 were investigated at 10 and 20 day of growth under controlled conditions. At day 10 under all Cd2+ treatments, the Cd2+ content between the two rice cultivars were almost similar. Application of 500 μM Cd2+ significantly increased metal concentrations at day 20 in the roots of rice seedlings resulting in a maximum accumulation of 44.25 μg Cd2+ g-1 dry wt in cv. DR-92 and 30 μg Cd2+ g-1 dry wt in cv. Bh-1 with a ~25 % decline in Relative Growth Index (RGI) in cv. DR-92. TEM studies revealed slight disorganization with cell wall ingrowths in root tissues from cv. DR-92 grown in 100 μM Cd2+ + HS. Uptake and accumulation of Cd2+ increased upon heat treatment in parenchyma, vacuoles and vascular cylinder of root tissues. Peroxidase primarily located in cell walls, the intensity being higher in sensitive cv. DR-92. Under Cd2+ stress alone, plants of sensitive cv. DR-92 significantly increased the H2O2 and MDA levels together with increased activities of the enzymes POD, CAT and APX at day 10 but remained almost stable at day 20. A strong increase in MDA levels was noted at day 20 in tolerant cv. Bh-1. Cd2+ + HS treatments in tolerant cv.Bh-1 led to a decreased H2O2 and MDA levels and decreased activities of the enzymes POD, CAT and APX. Results suggest stimulation of root antioxidant system under combination of two stresses and that heat stress seem to have a direct protective role by mitigating the effect of mild Cd2+ toxicity largely by enhanced Cd2+-MT formation contributing thereby towards the management of Cd2+ toxicity at cellular level that confers Cd2+ tolerance to rice cv. Bh-1.  相似文献   

5.
Despite intense research, the mechanism of Cd2+ toxicity on photosynthesis is still elusive because of the multiplicity of the inhibitory effects and different barriers in plants. The quick Cd2+ uptake in Synechocystis PCC 6803 permits the direct interaction of cadmium with the photosynthetic machinery and allows the distinction between primary and secondary effects. We show that the CO2‐dependent electron transport is rapidly inhibited upon exposing the cells to 40 µm Cd2+ (50% inhibition in ~15 min). However, during this time we observe only symptoms of photosystem I acceptor side limitation and a build of an excitation pressure on the reaction centres, as indicated by light‐induced P700 redox transients, O2 polarography and changes in chlorophyll a fluorescence parameters. Inhibitory effects on photosystem II electron transport and the degradation of the reaction centre protein D1 can only be observed after several hours, and only in the light, as revealed by chlorophyll a fluorescence transients, thermoluminescence and immunoblotting. Despite the marked differences in the manifestations of these short‐ and long‐term effects, they exhibit virtually the same Cd2+ concentration dependence. These data strongly suggest a cascade mechanism of the toxic effect, with a primary effect in the dark reactions.  相似文献   

6.
7.
We have calibrated the alkaline protocol of the plant comet (Single Cell Gel Electrophoresis) assay as a method for detecting the extent of induced DNA damage in potato plants (Solanum tuberosum L. cultivar Korela). After 2 and 24 h treatments of the rooted cuttings with the heavy metal cadmium (Cd2+), a dose–response increase in DNA damage was noted versus controls in root nuclei. With a 24 h recovery period, the Cd2+-induced DNA damage in roots increased significantly. No significant increase in DNA damage was demonstrated in leaf nuclei after 24 h Cd2+ treatments, but continuous Cd2+ treatments for 2 weeks resulted in an increase in leaf DNA damage. This increase may be however associated with necrotic and apoptotic DNA fragmentation, as the affected plants had inhibited growth and distorted yellowish leaves. For comparison, the monofunctional alkylating agent ethyl methanesulphonate, and γ-rays were assessed for induced DNA damage. Analysis of the accumulation of cadmium by inductively coupled plasma optical emission spectrometry demonstrates that roots accumulate almost 9-fold more cadmium than aboveground parts of the rooted potato cuttings. This may explain the absence of Cd2+ genotoxicity in leaves after short-term treatments.  相似文献   

8.
The effect of cadmium on the photosynthetic activity of Synechocystis PCC 6803 was monitored in this study. The oxygen evolving capacity of Synechocystis treated with 40 μM CdCl2 was depressed to 10% of the maximum in 15 min, indicating that Cd2+ penetrated rapidly into the cells and blocked the photosynthetic activity. However, neither photosystem II (PSII) nor photosystem I (PSI) activity showed a significant short-term decrease which would explain this fast decrease in the whole-chain electron transport. Thermoluminescence measurements have shown that the charge separation and stabilization in PSII remains essentially unchanged during the first few hours following the Cd2+ treatment. The electron flow through PSI was monitored by following the redox changes of the P700 reaction centers of PSI. Alterations in the oxidation kinetics of P700 in the Cd2+-treated cells indicated that Cd2+ treatment might affect the available electron acceptor pool of P700, including the CO2 reduction and accumulation in the cells. Perturbed angular correlation of γ-rays (PAC) using the radioactive 111mCd isotope was used to follow the Cd2+ uptake at a molecular level. The most plausible interpretation of the PAC data is that Cd2+ is taken up by one or more Zn proteins replacing Zn2+ in Synechocystis PCC 6803. Using the radioactive 109Cd isotope, a protein of approximately 30 kDa that binds Cd2+ could be observed in sodium dodecyl sulfate polyacrylamide gel electrophoresis. The results indicate that Cd2+ might inactivate different metal-containing enzymes, including carbonic anhydrase, by replacing the zinc ion, which would explain the rapid and almost full inhibition of the photosynthetic activity in cyanobacteria.  相似文献   

9.
He J  Qin J  Long L  Ma Y  Li H  Li K  Jiang X  Liu T  Polle A  Liang Z  Luo ZB 《Physiologia plantarum》2011,143(1):50-63
To characterize the dynamics of Cd2+ flux in the rhizosphere and to study cadmium (Cd) plant‐internal partitioning in roots, wood, bark and leaves in relation to energy metabolism, reactive oxygen species (ROS) formation and antioxidants, Populus × canescens plantlets were exposed to either 0 or 50 µM CdSO4 for up to 20 days in the nutrient solution. A strong net Cd2+ influx in root apex was observed after Cd exposure for 24 h, even if net Cd2+ influx decreased gradually in roots. A large amount of Cd was accumulated in roots. Cd ions were uploaded via the xylem to leaves and further transported to the phloem where significant accumulation was detected. Cd accumulation led to decreased photosynthetic carbon assimilation but not to the depletion in soluble carbohydrates. Increased levels of ROS were present in all tissues, except the bark of Cd‐exposed poplars. To combat Cd‐induced superoxide and hydrogen peroxide, P.×canescens appeared to rely mainly on the formation of soluble phenolics as these compounds showed the highest accumulation in the bark and the lowest in wood. Other potential radical scavengers such as proline, sugar alcohols and antioxidant enzymes showed tissue‐ and exposure time‐specific responses to Cd. These results indicate a complex pattern of internal Cd allocation in P.×canescens resulting in higher ROS stress in wood than in bark and intermediate responses in roots and leaves, probably because of differential capacities of these tissues for the production of protective phenolic compounds.  相似文献   

10.
In this study, we evaluated how cadmium inhibitory effect on photosystem II and I electron transport may affect light energy conversion into electron transport by photosystem II. To induce cadmium effect on the photosynthetic apparatus, we exposed Chlamydomonas reinhardtii 24 h to 0–4.62 μM Cd2+. By evaluating the half time of fluorescence transients O–J–I–P at different temperatures (20–30°C), we were able to determine the photosystem II apparent activation energies for different reduction steps of photosystem II, indicated by the O–J–I–P fluorescence transients. The decrease of the apparent activation energies for PSII electron transport was found to be strongly related to the cadmium-induced inhibition of photosynthetic electron transport. We found a strong correlation between the photosystem II apparent activation energies and photosystem II oxygen evolution rate and photosystem I activity. Different levels of cadmium inhibition at photosystem II water-splitting system and photosystem I activity showed that photosystem II apparent activation energies are strongly dependent to photosystem II donor and acceptor sides. Therefore, the oxido-reduction state of whole photosystem II and I electron transport chain affects the conversion of light energy from antenna complex to photosystem II electron transport.  相似文献   

11.
Trace element contamination of lands is a serious environmental problem that limits yield and threatens human health. To study the combined effect of high salinity and toxic levels of trace elements on halophytes, the performance of two marsh species, Atriplex halimus and Suaeda fruticosa, grown for 1 month with an irrigation solution supplemented with 200 mM NaCl and 400 μM Cd2+ or 400 μM Cu2+ was evaluated. The effect of the combined stress conditions on hormone signaling was also assessed. Biomass production and chlorophyll content decreased under Cd2+ stress in both species, whereas Cu2+ had a lower impact on plant performance. The different plant sensibilities to the two trace elements assayed indicate that each metal has a different effect on plants. Furthermore, the deleterious effect of metal toxicity was alleviated when NaCl was added to the irrigation solution, demonstrating that NaCl improves plant performance and tolerance of halophytic species to cope with trace element intoxication. Results show that both species accumulated important quantities of Cd2+ and Cu2+ in roots (Cd2+: 2,690–3,130 μg g?1 DW and Cu2+: 2,070–2,770 μg g?1 DW); this finding allows us to classify these species among the hyperaccumulator plants. Cd2+ and Cu2+ differently affected endogenous phytohormone contents in both species. Data suggest an essential involvement of roots on the regulation of tolerance to trace elements. Therefore, indole-3-acetic acid levels increased in roots of both species irrigated with high levels of Cd2+, which suggests that the auxin may stimulate root promotion and growth under these stress conditions. Other compounds, classically considered as “stress hormones” showed very different patterns of accumulation. Whereas, salicylic acid (SA) levels in roots and leaves increased in response to Cd2+, root contents of jasmonic acid (JA), and abscisic acid (ABA) decreased. In leaves, the rambling pattern of accumulation observed for JA and ABA suggested the lack of a specific role in regulation against trace element toxicity. Together, data suggest that SA could act as a specific signal that detects trace element toxicity, whereas JA and ABA promote general responses against abiotic stress.  相似文献   

12.
13.
Aquatic macrophytes play an important role in the removal of toxic metals from wastewater. Therefore, the induction of Fe plaque on the roots, and its consequences on Cd tolerance investigated in an aquatic macrophyte Pistia stratiotes L. The presence of Fe2+ ion but not Fe3+ resulted in Fe plaque formation. Induction of Fe plaque decreased Ca and increased K and Fe accumulations in the root. Plaque formed plants had accumulated less Cd until 50.0?µM CdCl2 treatments because plaque acted as a barrier to Cd exposure. However, at higher concentrations (500.0?µM CdCl2), plaque formed plants contained more Cd in the roots. Cadmium inducible ion leakage in the root and lowering of the photosynthetic pigment content were less in plants with a plaque. Stretching of aromatic carbonyl groups and alkyl groups among plaque formed plants upon Cd treatments indicated the putative role of phenolics in Cd detoxification.  相似文献   

14.
重金属镉(Cd)在植物体内的转运途径及其调控机制   总被引:19,自引:0,他引:19  
王晓娟  王文斌  杨龙  金樑  宋瑜  姜少俊  秦兰兰 《生态学报》2015,35(23):7921-7929
重金属镉(Cd)的毒害效应与其由土壤向植物地上部分运输有关,揭示Cd~(2+)转运途径及其调控机制可为提高植物抗镉性以及镉污染的植物修复提供依据。对Cd~(2+)在植物体内的转运途径,特别是限制Cd~(2+)移动的细胞结构和分子调控机制研究进展进行了回顾。Cd~(2+)通过共质体和质外体途径穿过根部皮层进入木质部的过程中,大部分在皮层细胞间沉积,少部分抵达中柱后转移到地上部分。为了免受Cd~(2+)的危害,植物体产生了多种限制Cd~(2+)吸收和转移的生理生化机制:1)环绕在内皮层径向壁和横向壁上的凯氏带阻止Cd~(2+)以质外体途径进入木质部;2)螯合剂与进入根的Cd~(2+)螯合形成稳定化合物并区隔在液泡中;3)通过H+/Cd~(2+)离子通道等将Cd~(2+)逆向转运出根部。植物共质体和质外体途径转运重金属镉的能力以及两条途径的串扰尚待进一步明晰和阐明。  相似文献   

15.
Given that Cd accumulates within plant tissues to levels that are toxic to animals, it is necessary to understand the role of plants in highly Cd-contaminated systems and their subsequent impact on the health of animals. A solution culture experiment was conducted to elucidate the effects of increasing Cd2+ activity ({Cd2+}) on growth of Rhodes grass (Chloris gayana Kunth.) and signal grass (Brachiaria decumbens Stapf.). The shoot and root fresh mass of both Rhodes grass and signal grass was reduced by 50% at ca. 0.5 µM {Cd2+}. Elevated {Cd2+} resulted in a significant decrease in the tissue Mn concentration for both the shoots and roots, and caused a chlorosis of the veins in the shoots. Root hair growth was prolific even at high {Cd2+}, thus root hair growth appeared to be less sensitive to elevated Cd than was root growth per se. The critical shoot tissue concentrations (50% reduction in growth), 230 µg g?1 for Rhodes grass and 80 µg g?1 for signal grass, exceeded the maximum level of Cd tolerated in the diet of animals (ca. 5 µg g?1). When assessing the risk associated with the revegetation of Cd-contaminated sites with Rhodes grass or signal grass, careful consideration must be given, therefore, to the transfer of toxic concentrations of Cd to grazing animals and through the wider food chain.  相似文献   

16.
17.
Enhanced phytoextraction uses soil chelators to increase the bioavailability of heavy metals. This study tested the effectiveness of ethylenediaminetetraacetic acid (EDTA) and citric acid in enhancing cadmium (Cd) phytoextraction and their effects on the growth, yield, and ionic uptake of maize (Zea mays). Maize seeds of two cultivars were sown in pots treated with 15 (Cd15) or 30 mg Cd kg?1 soil (Cd30). EDTA and citric acid at 0.5 g kg?1 each were applied 2 weeks after germination. Results demonstrated that the growth, yield per plant, and total grain weight were reduced by exposure to Cd. EDTA increased the uptake of Cd in shoots, roots, and grains of both maize varieties. Citric acid did not enhance the uptake of Cd, rather it ameliorated the toxicity of Cd, as shown by increased shoot and root length and biomass. Cadmium toxicity reduced the number of grains, rather than the grain size. The maize cultivar Sahiwal-2002 extracted 1.6% and 3.6% of Cd from soil in both Cd+ EDTA treatments. Hence, our study implies that maize can be used to successfully phytoremediate Cd from soil using EDTA, without reducing plant biomass or yield.  相似文献   

18.
The plasmalemma vesicles isolated from cucumber and maize roots were used to study the effect of Cu2+ and Cd2+ on the hydrolytic and proton pumping activities of ATPase. In vivo application of metal ions to the plant growth solutions resulted in stimulation of the proton transport in maize. In cucumber roots the action of metals was not the same: cadmium stimulated the H+ transport through plasmalemma whereas Cu2+ almost completely inhibited it. Copper ions decreased the hydrolytic activity of H+-ATPase in cucumber, without any effect on this activity in membranes isolated from maize roots. The effect of cadmium on the hydrolytic activities was opposite: ATP-hydrolysis activity in plasmalemma was not altered in cucumber, whereas in maize its stimulation was observed. The amount of accumulated metals was not the main reason of different influence of metals on H+-ATPase activity in tested plants. In in vitro experiments Cu2+ inhibited H+ transport in the cucumber, to a higher degree than Cd2+ and both metals did not change this H+-ATPase activity of plasmalemma isolated from corn roots. Cu2+ added into the incubation medium reduced the hydrolytic activity of ATPase in the plasma membrane isolated from cucumber as well as from corn roots. Cd2+ diminished the hydrolytic activity of ATPase in cucumber, and no effect of Cd2+ in the plasmalemma isolated from corn roots was found. Our results indicated different in vitro and in vivo action of both metals on H+-ATPase and different response of this enzyme to Cu2+ and Cd2+ in maize and cucumber.  相似文献   

19.
Tonoplast, ion antiport activities are critical to ion homeostasis and sequestration in plants. The biochemical properties of these activities, and the enzymes that catalyse them, are little characterized. Here we applied biochemical approaches to study some characteristics and to distinguish between Ca2+/H+ and Cd2+/H+ antiporter activities of tonoplast vesicles from non‐transformed, wild‐type plants. Solubilization and reconstitution of oat‐seedling (Avena sativa L.) root tonoplast vesicles resulted in about a 6‐fold loss of protein, about a 6‐fold enhancement of Cd2+/H+ antiport specific activity (at 10 µM Cd2+), and almost complete loss of Ca2+/H+ antiport activity. Similar results were found for vesicles from mature tobacco (Nicotiana tabacum) roots. Cd2+ concentration‐dependent proton efflux was similar and linear with both oat vesicles and proteoliposomes. In contrast, Ca2+ concentration‐dependent proton efflux of oat vesicles was easily observed while that with proteoliposomes was minimal and non‐linear. Cd2+ pre‐treatment of oat vesicles reduced verapamil inhibition of Cd2+/H+ activity and verapamil binding to vesicles, while Ca2+ pre‐treatment was much less protective of Ca2+/H+ activity and verapamil binding. Results show the usefulness of reconstitution, and also inhibitor/ion interaction assays for distinguishing between transporter activities in vitro, but they do not resolve the question of whether there are separate enzymes for Cd2+/H+ and Ca2+/H+. Our observation that solubilization and reconstitution have similar effects on both Cd2+/H+ and Ca2+/H+ activities of root tonoplast vesicles from immature oat and mature tobacco roots suggests that the transporters involved are similar in young and mature roots, and in roots of different species.  相似文献   

20.
We have investigated the influence of silicon on higher zinc concentration reducing the growth of aboveground parts by ca 50 % in young maize plants (hybrid Novania) grown in hydroponics. Eight different treatments were used: control, Zn (800 μM ZnSO4·7H2O), Si1/Si2.5/Si5 (1/2.5/5 mM Na2SiO7) and Zn+Si (combination of zinc and all silicon concentrations). The concentration of Zn and Si and their distribution in plants was determined. The growth parameters (length of primary seminal root, leaf area of first and second leaves, fresh and dry weight of below- and above-ground plant parts) of plants grown in various Zn+Si treatments were significantly decreased in comparison to all other treatments. Increasing concentration of Si in combination with Zn treatment and selected hybrid (Novania) resulted in increased physiological stress in comparison to Zn treatment. However, roots and shoots of all Zn+Si treated plants contained significantly lower amount of Zn than Zn treatment. The Si concentration in roots was the same in Si and Zn+Si plants. In general, higher amount of Si was observed in shoots than in roots of Si1- and Si2.5-treated plants and opposite was observed in Si5-treated plants. In spite of significantly decreased root and shoot accumulation of Zn in the presence of Si, no positive effect of Si on Zn toxicity in young maize plants under experimental conditions used in this work and used maize hybrid was observed.  相似文献   

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