Localization and toxic effects of cadmium, copper, and uranium in azolla

The storage and distribution of copper, cadmium, and uranium and their effects on ionic contents in roots and shoots of Azolla filiculoides has been studied by x-ray microanalysis. The relative content of copper was eightfold higher in the root than in the shoot, suggesting low mobility of this metal in Azolla plant. Cadmium relative content in the shoot was similar to its content in the root, hence its mobility was relatively high. The absence of significant uranium quantities in the shoot and its relative high content in the root suggest the immobility of this metal from Azolla root. Cadmium formed precipitates with phosphate and calcium in xylem cells of the shoot bundle and caused a two- to threefold increase in the content of phosphate in the root. Uranium in roots and cadmium in shoots were associated with calcium. All three treatments caused losses of potassium, chloride, and magnesium from Azolla roots. Accumulation of heavy metals in Azolla and their mobility from the root to the shoot can be correlated with damage caused by the loss of essential nutrients.     

Cd - tolerance of maize, rye and wheat seedlings

The effect of cadmium on growth parameters of seedlings of maize, rye and wheat as well as the role of phytochelatins in Cd detoxication in these species were studied. Cadmium was found to inhibit root growth and decrease fresh weight and water content in roots and shoots of the studied plants. Although a considerably lower Cd accumulation was shown in maize seedlings than in other species, they were characterized by the highest sensitivity to cadmium. Among γ-Glu-Cys peptides synthetized by plant species, phytochelatins — glutathione derivatives predominated. In maize they were synthetized in amounts sufficient for binding the total pool of the metal taken up, and the detoxication mechanism was localized in their roots. Larger amounts of cadmium were accumulated in roots of wheat and rye, but the quantity of the formed γ-Glu-Cys peptides seems insufficient for detoxication of the metal.     

The cytosolic O-acetylserine(thiol)lyase gene is regulated by heavy metals and can function in cadmium tolerance

Regulation of the expression of the cytosolic O-acetylserine(thiol)lyase gene (Atcys-3A) from Arabidopsis thaliana under heavy metal stress conditions has been investigated. Northern blot analysis of Atcys-3A expression shows a 7-fold induction after 18 h of cadmium treatment. Addition of 50 microm CdCl(2) to the irrigation medium of mature Arabidopsis plants induces a rapid accumulation of the mRNA throughout the leaf lamina, the root and stem cortex, and stem vascular tissues when compared with untreated plants, as observed by in situ hybridization. High pressure liquid chromatography analysis of GSH content shows a transient increase after 18 h of metal treatment. Our results are compatible with a high cysteine biosynthesis rate under heavy metal stress required for the synthesis of GSH and phytochelatins, which are involved in the plant detoxification mechanism. Arabidopsis-transformed plants overexpressing the Atcys-3A gene by up to 9-fold show increased tolerance to cadmium when grown in medium containing 250 microm CdCl(2), suggesting that increased cysteine availability is responsible for cadmium tolerance. In agreement with these results, exogenous addition of cystine can, to some extent, also favor the growth of wild-type plants in cadmium-containing medium. Cadmium accumulates to higher levels in leaves of tolerant transformed lines than in wild-type plants.     

Overexpression of glutathione reductase in Brassica juncea: Effects on cadmium accumulation and tolerance

To determine the importance of glutathione reductase (GR, EC 1.6.4.2) for heavy metal accumulation and tolerance, a bacterial GR was expressed in Indian mustard ( Brassica juncea L.), targeted to the cytosol or the plastids. GR activity in the cytosolic transgenics (cytGR) was about two times higher compared to wild-type plants; in the plastidic transgenics (cpGR) the activity was up to 50 times higher. When treated with 100 μ M CdSO₄, cytGR plants did not differ from wild type in cadmium tolerance or accumulation. CpGR plants, however, showed enhanced cadmium tolerance at the chloroplast level: in contrast to wild-type plants they showed no chlorosis, and their chlorophyll fluorescence parameters F_v/F_m and photochemical quenching were higher. Cadmium tolerance at the whole-plant level (plant growth) was not affected. The lower cadmium stress experienced by the cpGR chloroplasts may be the result of reduced cadmium uptake and/or translocation: cadmium levels in shoots of cpGR plants were half as high as those in wild-type shoots. These differences in cadmium tolerance and accumulation may result from increased root glutathione levels, which were up to two times higher in cpGR plants than in the wild type.     

Transport of Cadmium via Xylem and Phloem in Maturing Wheat Shoots: Comparison with the Translocation of Zinc, Strontium and Rubidium

The toxic heavy metal cadmium is taken up by plants and maycontaminate harvested parts of agricultural crops. In the experimentsreported here, cadmium was introduced together with markersfor phloem (rubidium) and xylem (strontium) transport, eitherinto intact shoots via a flap below the flag leaf node, or intodetached shoots via the cut stem. Cadmium introduced into intactplants was redistributed during maturation from the peduncleand the flag leaf lamina to the grain. In detached shoots, somecadmium was removed from the transpiration stream, as judgedfrom the comparison of shoots steam-girdled below the ear andof controls with an intact phloem in the peduncle. A minor quantityof cadmium was transported to the grain via the phloem in controlshoots while a high percentage of this element was retainedin the peduncle. The cadmium content of the grain increasedin response to the increased cadmium concentrations in the feedingsolutions (0.1 to 10 µM). The cadmium content of the grainwas slightly lower when zinc (>10 µM) was introducedat the same time as cadmium (1 µM).Copyright 1997 Annalsof Botany Company Triticum aestivumL.; cadmium; phloem transport; wheat; zinc     

Cadmium uptake and xylem loading are active processes in the hyperaccumulator Sedum alfredii

Sedum alfredii is a well known cadmium (Cd) hyperaccumulator native to China; however, the mechanism behind its hyperaccumulation of Cd is not fully understood. Through several hydroponic experiments, characteristics of Cd uptake and translocation were investigated in the hyperaccumulating ecotype (HE) of S. alfredii in comparison with its non-hyperaccumulating ecotype (NHE). The results showed that at Cd level of 10 microM measured Cd uptake in HE was 3-4 times higher than the implied Cd uptake calculated from transpiration rate. Furthermore, inhibition of transpiration rate in the HE has no essential effect on Cd accumulation in shoots of the plants. Low temperature treatment (4 degrees C) significantly inhibited Cd uptake and reduced upward translocation of Cd to shoots for 9 times in HE plants, whereas no such effect was observed in NHE. Cadmium concentration was 3-4-fold higher in xylem sap of HE, as compared with that in external uptake solution, whereas opposite results were obtained for NHE. Cadmium concentration in xylem sap of HE was significantly reduced by the addition of metabolic inhibitors, carbonyl cyanide m-chlorophenylhydrazone (CCCP) and 2,4-dinitrophenol (DNP), in the uptake solutions, whereas no such effect was noted in NHE. These results suggest that Cd uptake and translocation is an active process in plants of HE S. alfredii, symplastic pathway rather than apoplastic bypass contributes greatly to root uptake, xylem loading and translocation of Cd to the shoots of HE, in comparison with the NHE plants.     

Uptake and Physiological Effects of Cadmium in Sugar Beet (Beta vulgaris) Related to Mineral Provision

Sugar beet seedlings (Beta vulgaris L. cv. Monohill) were grownfor 14 d on a nutrient solution based on the nutrient proportionsin healthy plants. Nutrients were supplied either once at relativelyhigh concentrations, or in small amounts with a daily incrementalincrease of 0?15 or 0?20 in accordance with an exponential growthrate. Cadmium (0, 0?6, 2?3, 50 or 20?0 µmol) was introducedeither by a single addition or in daily increments of 0?15 or0?20. Cadmium uptake, expressed as a percentage of total Cd²⁺supplied, decreased with increasing total C^d2+ content and withdecreasing availability of nutrients. With a daily supply ofcadmium, net uptake, transport and content per unit of dry weightin roots and shoots were related to the total Cd²⁺ supplied.Cadmium caused growth retardation, increased root/whole-plantratio, and decreased root-tip respiration and photosynthesis.At high initial nutrient concentrations, Cd²⁺ decreased thecontents of sucrose, glucose, fructose, and starch per unitof dry weight. The opposite was found if nutrients were addeddaily. In the latter case, the dry weight/fresh weight ratioalso increased. The effects of cadmium were related to [Cd²⁺]in proportion both to the root absorption area and to the nutrientconcentration. Key words: Sugar beet, mineral provision, cadmium uptake, sugar formation, growth     

Cadmium uptake,localization and stress-induced morphogenic response in the fern Pteris vittata

Cadmium uptake, tissue localization and structural changes induced at cellular level are essential to understand Cd tolerance in plants. In this study we have exposed plants of Pteris vittata to different concentrations of CdCl₂ (0, 30, 60, 100 μM) to evaluate the tolerance of the fern to cadmium. Cadmium content determination and its histochemical localization showed that P. vittata not only takes up, but also transports and accumulates cadmium in the aboveground tissues, delocalizing it mainly in the less bioactive tissues of the frond, the trichomes and the scales. Cadmium tolerance in P. vittata was strictly related to morphogenic response induced by the metal itself in the root system. Adaptive response regarded changes of the root apex size, the developmental pattern of root hairs, the differentiation of xylem elements and endodermal suberin lamellae. All the considered parameters suggest that, in our experimental conditions, 60 μM of Cd may represent the highest concentration that P. vittata can tolerate; indeed this Cd level even improves the absorbance features of the root and allows good transport and accumulation of the metal in the fronds. The results of this study can provide useful information for phytoremediation strategies of soils contaminated by Cd, exploiting the established ability of P. vittata to transport, delocalize in the aboveground biomass and accumulate polluting metals.     

Uptake and transport of cadmium by perennial ryegrass from flowing solution culture with a constant concentration of cadmium

Summary Perennial ryegrass was sown in flowing solution culture at 7, 6, 5 and 4 weeks before the addition of cadmium to the nutrient solution. The concentration of cadmium in solution was held constant at 0.01 ppm for the following 15 days during which period uptake by the 4 sets of plants of different ages was followed by plant analysis at 3-day intervals. During the 15-day period the total uptake per g (dry weight) root remained nearly constant. The cadmium content of the roots was much greater than that of the corresponding shoots and, although older plants contained more cadmium than younger plants, the proportion of the total content retained by roots was much the same in the 4 sets of plants,i.e. >90 per cent. It is concluded that the roots of ryegrass restrict the transport of cadmium to the shoots. The concentration in the shoots increased only slightly during the 15-day period but to a different extent amongst the 4 sets of plants. These differences reflect differences in growth rate; thus the shoots of the younger sets of plants had lower growth rates and contained correspondingly higher concentrations of cadmium.     

Hyperaccumulation of cadmium by roots, bulbs and shoots of garlic (Allium sativum L.)

The effects of cadmium chloride concentration on root, bulb and shoot growth of garlic (Allium sativum L.), and the uptake and accumulation of Cd2+ by garlic roots, bulbs and shoots were investigated. The range of cadmium chloride (CdCl2 x 2.5H2O) concentrations was 10(-6) - 10(-2) M. Cadmium stimulated root length at lower concentrations (10(-6) - 10(-5) M) significantly (P < 0.005) during the entire treatment period. The seedlings exposed to 10(-3) - 10(-2) M Cd exhibited substantial growth reduction (P < 0.005), but did not develop chlorosis. Garlic has considerable ability to remove Cd from solutions and accumulate it. The Cd content in roots of garlic increased with increasing solution concentration of Cd2+. The roots in plants exposed to 10(-2) M Cd accumulated a large amount of Cd. approximately 1,826 times the control. The Cd contents in roots of plants treated with 10(-3), 10(-4), 10(-5) and 10(-6) M Cd were approximately 114, 59, 24 and 4 times the control, respectively. However, the plants transported only a small amount of Cd to their bulbs and shoots and concentrations in these tissues were low.     

Growth Inhibition Occurs Independently of Cell Mortality in Tomato （Solanum lycopersicum） Exposed to High Cadmium Concentrations

In order to analyze the adaptation potential of tomato shoots to a sudden increase in Cd concentration, tomato plants (Solanum lycopersicum L. var. Ailsa Craig) were exposed under controlled environmental conditions to a high dose of this heavy metal (250 μM CdCl2>) in nutrient solution for 7 and 14 d. Both root and shoot growth was completely inhibited but all plants remained alive until the end of the treatment. Cell viability remained unaffected but the activity of the mitochondrial alternative pathway was stimulated by Cd stress at the expense of the cytochrome pathway. Cadmium concentration was higher in roots than in shoots and a decrease In the rate of net Cd translocation was noticed during the second week of stress. Cadmium decreased both leaf conductance (g1>) and chlorophyll concentration. However, the effect on net CO2 assimilation remained limited and soluble sugars accumulated in leaves. Photochemical efficiency of PSll (FvlFm) was not affected despite a decrease in the number of reaction centers and an inhibition of electron transfer to acceptors of PSII. It is concluded that tomato shoot may sustain short term exposure to high doses of cadmium despite growth inhibition. This property implies several physiological strategies linked to both avoidance and tolerance mechanisms.     

Maize plant growth and accumulation of photosynthetic pigments at short- and long-term exposure to cadmium

A wide range of cadmium concentrations (from 4 to 200 μM for seedlings and up to 2 mM for germinating kernels) was used to assess Cd toxic effects on maize (Zea mays L.) plants at the different developmental stages: germinating kernels, seedlings (4–9 days), and juvenile plants (34 days). Cd accumulation in plant organs was followed, and its lethal concentration was elucidated. In maize, cadmium was accumulated predominantly in roots; in shoots it was mainly accumulated in the lower leaves, and the higher was leaf position the lower was Cd content in it. At high concentrations (80 and 200 μM), kernels became the substantial cadmium depot. Germinating kernels manifested the lowest sensitivity to cadmium; seedlings were more sensitive; the inhibition of juvenile plant growth attained 90% and more. In the tested range of concentrations, cadmium suppressed shoot mass accumulation harder than that of roots. In 34-day-old plants, water content in shoots was stronger reduced than in roots. Plant death was also manifested earlier in shoots. It was concluded that maize plant sensitivity to cadmium increases with plant growing and that, under conditions of normal mineral nutrition, cadmium inhibits shoot growth more severe than root growth.     

Glutamine synthetase and glutamate dehydrogenase in cadmium-stressed triticale seedlings

The studies were performed on young triticale seedlings grown on a mineral medium containing 5 mM NO ₃ ⁻ as the nitrogen source, with the addition of 0.5 mM CdCl₂. It was determined that cadmium ions accumulated mainly in the plant roots. Decreases in nitrate concentrations both in the roots and shoots of seedlings, as well as decreases in soluble protein contents with simultaneous increases in endopeptidase activity were also observed. Both in roots and shoots significant decreases in glutamic acid were noted. Toxic cadmium ion accumulation in seedlings significantly modified activity of primary nitrogen assimilating enzymes, i.e. glutamine synthetase (GS, EC 6.3.1.2) and glutamate dehydrogenase (GDH, EC 1.4.1.2). There was a significant decrease in GS activity both in roots and in shoots of the stressed plants, in comparison to plants grown without cadmium. In shoots of the control plants and plants subjected to stress two GS isoforms were discovered: cytoplasmatic (GS₁) and chloroplastic (GS₂). Substantial decreases in total glutamine synthetase activity in green parts of seedlings, occurring under stress conditions, result from dramatic decrease in GS₂ activity (by 60 % in relation to the control plants); despite simultaneous increases in the cytoplasmatic isoform (GS₁) activity by approx. 96 %. Cadmium ions accumulating in roots and shoots of seedlings not only increased GDH activity, but also modified its coenzymatic specificity.     

Die Reaktion anfälliger und resistenter Gerstensorten auf pilzliche Krankheitserreger

Response to fungus pathogen in susceptible and resistant barley cultivars IV. Water- and dry matter content
The changes in dry matter- and water content dynamics in the root and shoots of barley infected with the fungus Erysiphe graminis f. sp. hordei Marchal were studied in variously receptive cultivars. Cultivation of plants in solid (perlite) or liquid medium was compared.
The response of susceptible barley to mildew infection is characterized at First by an increase in water content and slightly in dry matter of shoots accompanied with an unsignificant decrease in root growth. However, as the fructification progressed, barley growth is reduced in all investigated parameters. The infected resistant barley indicates unsignificantly increased values in water content of shoots, only.
In the susceptible host the growth of roots in relation to shoots is markedly reduced after infection.
The percentage of water content of shoots is slightly increased in both cultivars during the first phases of infection. Then, in susceptible barley it declines, compared with the control, from the stage of full developed fructification. In the resistant barley it doesn't change more expressively. In roots of infected plants the increased hydratation is found during the whole observation period (in the resistant barley only with plants growing in liquid medium).     

Role of calcium in AMF-mediated alleviation of the adverse impacts of cadmium stress in Bassia indica [Wight] A.J. Scott

The aim of this study was to evaluate cadmium stress induced changes in the growth, lipid peroxidation and antioxidant activity of Bassia indica associated with arbuscular mycorrhizal fungi (AMF) and their amelioration by calcium application. Cadmium stress can cause alterations in the physiological and biochemical processes in plants. A calcium application combined with an AMF treatment resulted in the reduction of lipid peroxidation and the production of hydrogen peroxide, thereby mediating the mitigation of cadmium induced oxidative stress. The activity of antioxidant enzymes increased with cadmium application, whereas AMF inoculation combined with a calcium application further enhanced their activity. An increase in the content of non-enzymatic antioxidants such as ascorbate, reduced glutathione (GSH), oxidized glutathione (GSSG) and S-nitrosoglutathione (GSNO) in AMF-inoculated and calcium-treated plants further suggests their role in strengthening the antioxidant defense system that results in maintained growth. The application of calcium combined with the AMF treatment caused a significant reduction in lipid peroxidation and in the production of hydrogen peroxide, thereby mediating the mitigation of the cadmium induced oxidative stress. Increased proline accumulation was clearly evident in stressed plants, and the calcium application as well as the AMF inoculation further induced proline synthesis, thereby providing efficient protection against cadmium stress by increasing the maintenance of the systemic resistance criteria.     

Effect of associative bacteria on element composition of barley seedlings grown in solution culture at toxic cadmium concentrations

The response of barley seedlings to inoculation with associative rhizobacteria Azospirillum lipoferum 137, Arthrobacter mysorens 7, Agrobacterium radiobacter 10 and Flavobacterium sp. L30 was studied in hydroponic and quartz sand cultures in the presence of 50 microM CdCl2. Cadmium caused severe inhibition in the growth and uptake of nutrient elements by the plants. Inoculation with the bacteria slightly stimulated root length and biomass of hydroponically grown Cd-treated seedlings. The bacteria increased the content of nutrients such as P, Mg, Ca, Fe, Mn and Na in roots and or shoots of the plants grown in the absence of Cd. Positive changes in the element composition caused by the bacteria were less pronounced in Cd-treated plants, whereas the total amount of nutrients taken by the inoculated plants was generally increased significantly. The content of Cd in the inoculated plants was unchanged, except increased in roots upon addition of A. lipoferum 137. Inoculation did not affect the activity of peroxidase, alpha-mannosidase, phosphodiesterae, alpha-galactosidase, and concentration of sulfhydryl compounds used as biochemical markers of stress in plant roots. The results showed that associative bacteria were capable of decreasing partially the toxicity of Cd for the barley plants through the improvement in uptake of nutrient elements.     

The resistance of plants Setaria veridis (L.) Beauv. to the influence of cadmium

It was shown that cadmium causes a slowdown of green foxtail Setaria veridis (L.) Beauv. shoots; however it had no effect on root growth or accumulation of underground and above-ground biomass. In the analysis of the effect of cadmium on the water regime and photosynthesis of plants, it was found that it had a negative effect on the stomatal apparatus, which led to a decrease in the transpiration rate and stomatal conductance. It was noted that the water content of tissues, as well as the rate of photosynthesis in the presence of cadmium, remained at the level of those in control plants. A high resistance of green foxtail to the effects of cadmium was established, which is provided with different adaptive mechanisms and anatomical and physiological characteristics associated with its affiliation to the group of C₄-plants.     

镉对一株深色有隔内生真菌生长、矿质营养与草酸分泌的影响

【背景】深色有隔内生真菌(dark septate endophyte,DSE)广泛定殖于镉(Cd)污染生境的植物根系,具有增强植物镉耐性的重要生态功能,但人们关于DSE对镉胁迫的生理响应的了解有限。【目的】研究一株DSE嗜鱼外瓶霉(Exophiala pisciphila)对镉胁迫的矿质营养与低分子量有机酸分泌的响应。【方法】采用液体培养法,研究不同浓度(0、25、50、100、200、400 mg/L)镉胁迫对DSE菌丝生长、矿质元素(氮、磷、钾、硫、镁、铁、钙)与镉含量、草酸分泌的影响。【结果】随着镉胁迫浓度增加,菌丝生物量显著下降,降幅为22.8%−90.6%,菌丝的氮、钾和铁含量分别减少26.0%−52.8%、53.8%−92.9%和12.8%−34.3%,而磷、镁和钙含量分别增加15.4%−111.4%、20.4%−31.4%和35.1%−62.5%,硫含量在100 mg/L镉胁迫时增加25.1%。镉胁迫还导致培养液pH值下降,草酸浓度及单位菌丝草酸分泌量显著增加。相关分析发现,菌丝镉含量与硫呈显著负相关(P<0.05),与菌丝钾含量呈极显著负相关(P<0.01),与草酸分泌量呈极显著正相关(P<0.01)。【结论】镉胁迫显著抑制DSE的生长,改变矿质元素的吸收,促进草酸分泌。     

土壤中镉、铅、锌及其相互作用对作物的影响

通过作物盆栽模拟试验(砂壤质褐土、pH值8.2)揭示：土壤中分别施入镉(CdCl2)、铅[Pb(CH3COO)2]或锌(ZnSO4)其影响表现为,植物各器官镉的含量超过对照植物的数倍至500倍。土壤镉浓度<5ppm和<10ppm分别造成某些蔬菜和水稻的污染。铅主要积累在植物根部,土壤铅污染对作物的影响较小。锌主要积累在植物叶片和根部,对水稻产生生长抑制的土壤锌浓度临界值不大于200ppm,此浓度对旱作无影响。土壤中同时施入镉和铅,植物对镉的吸收增加。而土壤中镉的增加却减少了植物体内铅的含量。土壤中由于镉、锌或铅、锌相互作用的结果,水稻对它们的吸收都有增加。在旱地土壤锌浓度的增高,降低了植物对镉、铅的吸收。镉、铅、锌同时施入土壤由于相互作用的结果,除锌之外,植物对镉、铅的吸收有明显下降。评价土壤重金属污染,不仅要看它们的含量及其存在形态,而且要分析它们之间的相互作用(促进或拮抗)特点。     

Phenols and phenol oxidases are involved in cadmium accumulation in the water plants Nymphoides peltata (Menyanthaceae) and Nymphaeae (Nymphaeaceae)

This comparative study investigates the mechanism of cadmium accumulation in the semiaquatic plant Nymphoides peltata (Menyanthaceae) and the aquatic plant Nymphaea (Nymphaeaceae). It was conducted as part of an ongoing study of the use of water plants for phytoremediation. Epidermal structures, known as hydropotes, are located on the abaxial epidermis of the leaf laminae of Nymphoides peltata and are shown to contain phenols, peroxidase and polyphenol oxidase activities. When plants are subjected to 50 mg/l of cadmium in the growth medium, these hydropotes accumulate cadmium. Cadmium-induced increases in phenols, peroxidase and polyphenol oxidase activities were determined in plant extracts. Cadmium binding by polymerized phenols was demonstrated in vivo. In comparison with Nymphaeae epidermal glands, N. peltata hydropotes are larger, open, and create bigger crystal, the latter principally composed of calcium and, proportionally, less cadmium. Although both plants showed similar levels of cadmium accumulation, N. peltata was sensitive while Nymphaeae was resistant to this cadmium level. It is suggested that in these water plants the main mechanism for cadmium accumulation is based on the trapping of cadmium crystals by polymerized phenols in specialized epidermal structures and this is due to peroxidase and polyphenol oxidase activities. Nymphaeae, with greater peroxidase activity and more polyphenols, is more resistant to this heavy metal than N. peltata.