The role of Ca ions in changes induced by excess Cu2+ in bean plants. Growth parameters

The effect of Ca on Cu toxicity in runner bean plants (Phaseolus coccineus L. cv. Piěkny Jaś) grown hydroponically in nutrient solution was studied. The toxic effect of excess Cu on plants depends on their age and Ca content in the medium. Copper applied in excess to the plants at the early phase of leaf development strongly limits the uptake of Ca ions from the nutrient solution, particularly their translocation to leaves. Increased Ca content limits the inhibitory effect of Cu on leaf growth and decreases the content of chloroplast pigments to the level approximate to that of control. At this growth stage the effect of excess Cu is at least partially connected with limited Ca transport to leaves. At the intermediate leaf phase Cu-treated plants react slightly to changed Ca content. At the end of the primary leaf development increased Ca concentration in the medium intensifies senescence processes induced by excess Cu. The changes are partially connected with intensified water deficit. Increased Ca content in the nutrient solution limits Cu accumulation in the individual organs of Cu-treated plants. However, Cu accumulation in leaves is not decreased at a high level of Ca. Copper generally decreases Ca content in the youngest plants, whereas in the oldest ones only in the case of a low level of Ca in the nutrient solution.     

Thiols of Cu-treated maize plants inoculated with the arbuscular-mycorrhizal fungus Glomus intraradices

Mycorrhizal colonization of roots, fresh weight, content of cysteine, γ-glutamylcysteine (γEC). glutathione (GSH), thiol groups in Cu-binding peptides (CuBP), and the uptake of Cu were measured in roots and shoots of maize ( Zea mays L., cv. Honeycomb F-1) grown in quartz sand, with Cu at 0, 4.5, 9, 15 and 30 μg g⁻¹ added with or without inoculum of the arbuscular-mycorrhizal fungus (AMF) Glomus intraradices . In control plants (no Cu added) AMF significantly reduced shoot growth, but did not affect root growth. At an external Cu supply of 9 μg (g quartz sand)⁻¹ or higher, both mycorrhizal colonization and growth of roots and shoots of mycorrhizal and non-mycorrhizal plants were significantly reduced.
With up to 9 μg Cu g⁻¹, mycorrhizal colonization increased the content of cysteine, γEC and GSH in the roots. However, the amount of thiols in CuBPs was not increased by mycorrhizal colonization in Cu-treated plants and no differences in Cu uptake were detected between non-mycorrhizal and mycorrhizal plants. A CuBP-complex with a relative molecular mass of 7300 and a SH:Cu ratio of 1.77:1 was separated on a Sephadex G-50 column from both non-inoculated and inoculated roots of Cu-treated plants. HPLC chromatography of the CuBPs of both non-inoculated and inoculated roots resulted in a similar peak pattern, indicating that no additional CuBPs were formed by the fungus. In conclusion, our results do not support the idea that AMF protects maize from Cu-toxicity.     

Physiological and ultrastructural changes in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> as affected by changed GSH level and Cu excess

We investigated the responses of wild-type Arabidopsis thaliana plants to the excess of Cu under conditions of the changed intracellular level of reduced glutathione (GSH) after application of buthionine sulfoximine (BSO) or exogenous GSH to the nutrient solution. BSO (500 μM) decreased and exogenous GSH (500 μM) increased GSH level, while increasing Cu concentration (from 5 to 50 μM) resulted in a decreased GSH content in the roots, but in its increased content in the shoots. BSO did not affect plant growth in contrast to exogenous GSH and Cu, which significantly reduced plant fresh weight. Both Cu and BSO or GSH induced changes in the root structure and leaf chloroplasts ultrastructure. Cu did not induce phytochelatin accumulation. Application of BSO or exogenous GSH did not significantly affect either the GSH level in the Cu-treated plants (except for 50/50 and 50/500 μM/μM Cu/GSH treatments increasing intracellular GSH content in the roots) or Cu toxicity to plants. These results suggest that GSH is not directly involved in Cu detoxification and tolerance in A. thaliana, yet it influences the proper anatomical structure of plants.     

Leaf endophyte Neotyphodium coenophialum modifies mineral uptake in tall fescue

Neotyphodium coenophialum (Morgan-Jones and Gams) Glenn, Bacon and Hanlin, a fungal endophyte found primarily in shoots of tall fescue (Festuca arundinacea Shreb.), can modify rhizosphere activity in response to phosphorus (P) deficiency. In a controlled environment experiment, two cloned tall fescue genotypes (DN2 and DN4) free (E-) and infected (E+) with their naturally occurring endophyte strains were grown in nutrient solutions at low P (3.1 ppm) or high P (31 ppm) concentrations for 21 d. Endophyte infection increased root dry matter (DM) of DN4 by 21% but did not affect root DM of DN2. Under P deficiency, shoot and total DM were not affected by endophyte but relative growth rate was greater in E+ than E- plants. In high P nutrient solution, E+ plants produced 13% less (DN2) or 29% more (DN4) shoot DM than E- plants. Endophyte affected mineral concentrations in roots more than in shoots. Regardless of P concentration in nutrient solution, E+ DN2 accumulated more P, Ca, Zn and Cu but less K in roots than E- plants. When grown in high P nutrient solution, concentrations of Fe and B in roots of E+ DN2 plants were reduced compared with those of E- plants. Concentrations of P, Ca and Cu in roots of DN4 were less, but K was greater in E+ than E- plants. In shoots, E+ DN2 had greater concentrations of Fe and Cu than E- DN2, regardless of P concentration in nutrient solution. Genotype DN4 responded to endophyte infection by reducing B concentration in shoots. Nutrient uptake rates were affected by endophyte infection in plants grown in low P nutrient solution. A greater uptake rate of most nutrients and their transport to shoots was observed in DN2, but responses of DN4 were not consistent. Results suggest that endophyte may elicit different modes of tall fescue adaptation to P deficiency. This revised version was published online in June 2006 with corrections to the Cover Date.     

Application of chelator-buffered nutrient solution technique in studies on zinc nutrition in rice plant (Oryza sativa L.)

It has been difficult to impose different degrees of Zn deficiency on Poaceae species in nutrient solution because most chelators which would control Zn to low activities also bind Fe³⁺ so strongly that Poaceae species cannot obtain adequate Fe. Recently, a method has been developed to provide buffered Fe²⁺ at levels adequate for rice using Ferrozine (FZ), and use of other chelators to buffer the other micronutrient cations. The use of Fe²⁺ buffered with FZ in nutrient solutions in which Zn is buffered with HEDTA or DTPA was evaluated for study of Zn deficiency in rice compared to a conventional nutrient solution technique. The results showed that growth of rice plants in FZ+HEDTA-buffered nutrient solution was similar to that in the conventional nutrient solution. Severe zinc deficiency symptoms were observed in 28-day-old rice seedlings cultured with HEDTA-buffered nutrient solution at Zn²⁺ activities < 10^-10.6 M. With increasing free Zn²⁺ activities, concentrations of Zn, Fe, Cu, and Mn in shoots and roots were quite similar for the FZ+HEDTA-buffered nutrient solution and the conventional nutrient solution techniques. The percentages of water soluble Zn, Fe, Cu and Mn in shoots with HEDTA-buffered nutrient solution were also similar to those with the conventional solution. However, with DTPA-buffered nutrient solution, the rice seedlings suffered severe Fe deficiency; adding more FeFZ₃ corrected the Fe-chlorosis but shifted microelement buffering. Further, much higher total Zn concentrations are required to provide adequate Zn²⁺ in DTPA-buffered solutions, and the contents of Mn and Cu in shoots and roots cultured with DTPA-buffered solutions were much higher than those with the conventional or HEDTA-buffered solutions. In conclusion, DTPA-buffered nutrient solutions are not suitable but the FZ/HEDTA-buffered nutrient solution technique can be used to evaluate genotypic differences in zinc efficiency in rice.     

Mobilization of Cu and Zn by root exudates of dicotyledonous plants in resin-buffered solutions and in soil

It has been frequently suggested that root exudates play a role in trace metal mobilization and uptake by plants, but there is little in vivo evidence. We studied root exudation of dicotyledonous plants in relation to mobilization and uptake of Cu and Zn in nutrient solutions and in a calcareous soil at varying Cu and Zn supply. Spinach (Spinacia oleracea L.) and tomato (Lycopersicon esculentum L.) were grown on resin-buffered nutrient solutions at varying free ion activities of Cu (pCu 13.0–10.4) and Zn (pZn 10.1–6.6). The Cu and Zn concentrations in the nutrient solution increased with time, except in plant-free controls, indicating that the plant roots released organic ligands that mobilized Cu and Zn from the resin. At same pCu, soluble Cu increased more at low Zn supply, as long as Zn deficiency effects on growth were small. Zinc deficiency was observed in most treatment solutions with pZn ≥ 9.3, but not in nutrient solutions of a smaller volume/plant ratio in which higher Zn concentrations were observed at same pZn. Root exudates of Zn-deficient plants showed higher specific UV absorbance (SUVA, an indicator of aromaticity and metal affinity) than those of non-deficient plants. Measurement of the metal diffusion flux with the DGT technique showed that the Cu and Zn complexes in the nutrient solutions were highly labile. Diffusive transport (through the unstirred layer surrounding the roots) of the free ion only could not explain the observed plant uptake of Cu and of Zn at low Zn²⁺ activity. The Cu and Zn uptake by the plants was well explained if it was assumed that the complexes with root exudates contributed 0.4% (Cu) or 20% (Zn) relative to the free ion. In the soil experiment, metal concentrations and organic C concentrations were larger in the solution of planted soils than in unplanted controls. The SUVA of the soil solution after plant growth was higher for unamended soils, on which the plants were Zn-deficient, than for Zn-amended soils. In conclusion, root exudates of dicotyledonous plants are able to mobilize Cu and Zn, and plants appear to respond to Zn deficiency by exuding root exudates with higher metal affinity.     

Thiols in cadmium- and copper-treated maize (Zea mays L.)

Maize plants (Zea mays L. cv. Honeycomb F-1) were grown on quartz sand containing amounts of Cd or Cu which resulted in comparable internal contents in the roots. Fresh and dry weights and the content of Cd or Cu were measured in roots and shoots after eight weeks. In addition, cysteine, γ-glutamylcysteine (γEC), glutathione (GSH) and the thiols in heavy-metal-binding peptides (HMBPs) were determined in the roots. At low internal contents, Cd and Cu inhibited root growth to the same extent. Inhibition by Cu was enhanced, however, at high internal contents, indicating that Cu was more toxic than Cd. Separation of extracts from roots of Cd- and Cutreated plants on a Sephadex G-50 column resulted in HMBP complexes with relative molecular masses (M_rs) of 6200 and 7300, respectively. Separation of these HMBP-complexes using HPLC resulted in a distinct pattern of thiol compounds for each heavy metal. The accumulation of HMBPs was linearly dependent on the content of Cd at all values examined. In Cu-treated roots, HMBP accumulation was linearly dependent on the internal Cu content only up to 7.1 μmol·g^?1 dry weight. At internal contents which caused an enhanced inhibition of root growth, no further significant increase in the HMBP content was detected. At these internal Cu contents an increased transport of Cu to the shoot was measured. This result indicates that HMBPs are involved in reducing heavy-metal transport from roots to shoots.     

Effects of Cadmium on Antioxidant Enzyme Activities in Sugar Cane

Sugar cane (Saccharum officinarum L. cv. Copersucar SP80-3280) seedlings were grown in nutrient solution with varying concentrations (0, 2 and 5 mM) of cadmium chloride for 96 h. Leaves were analysed for catalase (CAT), glutathione reductase (GR) and superoxide dismutase (SOD) activities. Although a clear effect of CdCl₂ on plant growth was observed, the activity of SOD was not altered significantly. However, the CAT activity decreased as the concentration of CdCl₂ increased. GR exhibits a significant increase in activity at 2 and 5 mM CdCl₂. CAT and SOD isoenzymes were further characterised by analysis in non-denaturing PAGE. Activity staining for SOD revealed up to seven isoenzymes in untreated control and 2 mM CdCl₂ treated plants, corresponding to Cu/Zn-SOD isoenzymes. At 5 mM CdCl₂, only six Cu/Zn-SOD isoenzymes were observed. No Fe-SOD and Mn-SOD isoenzymes were detected. For CAT, one band of activity was observed.     

铜、镉胁迫下外源NO介导的番茄解毒途径

一氧化氮(NO)作为信号分子,在抵御重金属胁迫中起重要作用,但对不同离子胁迫下的解毒机制尚缺乏研究.本研究采用营养液培养法,研究了铜(Cu)、镉(Cd)单一或复合胁迫下,番茄幼苗对Cu、Cd的吸收转运特性及对外源NO的响应机制.结果表明: 50 μmol·L^-1的Cu²⁺、Cd²⁺均显著抑制番茄植株的生长,其中Cd胁迫对生长的抑制效应远高于Cu胁迫.Cu、Cd单一或复合胁迫均使番茄根系Cu、Cd含量显著升高,但根系对Cu、Cd吸收存在严格选择性.根细胞对必需元素Cu表现出“奢侈吸收”的现象,而对毒性较强的Cd则吸收相对较少,胞内Cd浓度仅为Cu的1/10左右.外源NO处理可不同程度地缓解Cu、Cd胁迫,其中缓解Cd胁迫的效能更强.番茄对被动进入细胞的Cu、Cd具有相似的解毒机制:一方面,Cu、Cd胁迫诱导细胞质中产生谷胱甘肽(GSH)、植物螯合肽(PCs)和金属硫蛋白(MTs),络合过多的Cu、Cd离子,降低其生物毒性;另一方面,过多的Cu、Cd离子或螯合物被转运至液泡区隔化.外源NO通过调控GSH-GSSG(氧化型谷胱甘肽)氧化还原状态及GSH-PCs代谢方向的改变,促进Cu、Cd离子转运至液泡区隔化来缓解胁迫抑制;NO还可诱导植株叶片或根系表达更多的金属硫蛋白、GSH和PCs,而且上述响应普遍存在叠加效应.这可能是NO介导番茄对Cu、Cd胁迫的另一主要解毒途径.     

Cadmium and copper interactions on the accumulation and distribution of Cd and Cu in birch (Betula pendula Roth) seedlings

The effect of different external cadmium (Cd) and copper (Cu) regimes on the concentration of Cd and Cu in roots and shoots of birch (Betula pendula Roth.) seedlings was investigated. The seedlings were grown for 12 days in a weak nutrient solution (containing all essential nutrient elements including 0.025 µM Cu) at pH 4.2 with combinations of additional 0–2 µM CdCl₂ and 0–2 µM CuCl₂. Root and shoot concentrations of Cu were decreased by Cd in all treatments which included 0.1–2 µM of additional Cu in the treatment solution. When no extra Cu was added, only the shoot concentration of Cu was decreased by Cd whereas the root concentration was not affected. The shoot concentration of Cd was decreased by 0.5 and 2 µM of additional Cu in the treatment solution. The root concentration of Cd was decreased by Cu only when the concentration of additional Cu in the treatment solution was equal to or exceeded the concentration of Cd.     

Effects of Hydroponic Solution EC,Substrates, PPF and Nutrient Scheduling on Growth and Photosynthetic Competence During Acclimatization of Micropropagated <Emphasis Type="Italic">Spathiphyllum</Emphasis> plantlets

In vitro regenerated shoots of Spathiphyllum from bioreactor were hydroponically cultured for 30 days. The response of plant growth and photosynthesis to different substrates, photosynthetic photon flux (PPF), nutrient scheduling and electrical conductivity (EC) of hydroponic solution were studied. The best plant growth response was observed in perlite based substrates with moderate PFF (70–100μmol m⁻² s⁻¹). Highest fresh weight, dry weight, shoot length, root length, root number and photosynthetic characteristics (chlorophyll, carotenoids and Fv/Fm) was observed in continuous immersion system. Plant growth responses, photosynthetic rate, stomatal conductance and transpiration rate were also found to be affected by EC levels. The optimum EC of a balanced nutrient solution was recorded as 1.2 dS m⁻¹. Photosynthetic activity was also characterized in terms of photochemical efficiency using measurements of chlorophyll fluorescence. Fv/Fm (it is a measure of the intrinsic or maximum efficiency of PSII i.e. the quantum efficiency if all PSII centers were open) also decreased significantly in plants grown under higher EC level; a decrease in this parameter indicates down regulation of photosynthesis or photoinhibition. Antioxidant defense enzymes such as catalase (CAT), ascorbate peroxidase (APX), peroxidase (POD), glutathione reductase (GR) and monodehydroascorbate reductase (MDHAR) significantly elevated in the leaves and roots of plantlets at higher EC levels. This increase could reflect a defense response to the cellular damage provoked by higher EC levels in the nutrient solution.     

Lolium multiflorum uptake of iron supplied as different synthetic chelates

The plant availability of Fe from synthetic chelates has not been examined extensively for plants having the second strategy in iron uptake. Since these plants also excrete chelating agents, competition between natural and synthetic ligands is expected. This research was conducted to study the efficiency of different iron-chelates (Fe-EDTA, Fe-DTPA, Fe-EDDHA and a commercial product, Rexene) inLolium multiflorum iron nutrition. Plants were grown in a greenhouse with hydroponic culture using a buffered nutrient solution at pH 8. Initial iron concentration in the nutrient solution was near 0.5 mgl^–1 and solutions were replaced weekly. In an other Fe-EDTA treatment the same amount of chelate was supplied by four additions during each week.Changes of iron concentration in the nutrient solution, harvestable yield, Fe, Mn, Cu and Zn content in plant tissue and chlorophylllevels in leaves are discussed as parameters to evaluate chelate efficacy. Fe-EDDHA, without inorganic iron in the medium was not as effective as the commercial product Rexene, containing Fe-EDDHA and some extra weakly complex iron, which gave the highest yields. Fe-EDTA applied once a week with fresh nutrient solution was less effective than a four part addition as seen from Chl₁/[Fe] ratios.     

Effect of iron plaque outside roots on nutrient uptake by rice (Oryza sativa L.). Zinc uptake by Fe-deficient rice

This solution culture study examined the effect of the deposition of iron plaque on zinc uptake by Fe-deficient rice plants. Different amounts of iron plaque were induced by adding Fe(OH)₃ at 0, 10, 20, 30, and 50 mg Fe/L in the nutrient solution. After 24 h of growth, the amount of iron plaque was correlated positively with the Fe(OH)₃ addition to the nutrient solution. Increasing iron plaque up to 12.1 g/kg root dry weight increased zinc concentration in shoots by 42% compared to that at 0.16 g/kg root dry weight. Increasing the amount of iron plaque further decreased zinc concentration. When the amounts of iron plaque reached 24.9 g/kg root dry weight, zinc concentration in shoots was lower than that in shoots without iron plaque, implying that the plaque became a barrier for zinc uptake. While rice plants were pre-cultured in –Fe and +Fe nutrient solution in order to produce the Fe-deficient and Fe-sufficient plants and then Fe(OH)₃ was added at 20, 30, and 50 mg Fe/L in nutrient solution, zinc concentrations in shoots of Fe-deficient plants were 54, 48, and 43 mg/kg, respectively, in contrast to 32, 35, and 40 mg/kg zinc in shoots of Fe-sufficient rice plants. Furthermore, Fe(OH)₃ addition at 20 mg Fe/L and increasing zinc concentration from 0.065 to 0.65 mg Zn/L in nutrient solution increased zinc uptake more in Fe-deficient plants than in Fe-sufficient plant. The results suggested that root exudates of Fe-deficient plants, especially phytosiderophores, could enhance zinc uptake by rice plants with iron plaque up to a particular amount of Fe.     

Copper-induced changes in the growth, oxidative metabolism, and saponin production in suspension culture roots of Panax ginseng in bioreactors

Roots of Panax ginseng exposed to various concentrations of Cu (0.0, 5, 10.0, 25.0, and 50.0 μM) accumulated high amounts of Cu in a concentration-dependent and duration-dependent manner. Roots treated with 50 μM Cu resulted in 52% and 89% growth inhibition after 20 and 40 days, respectively. Saponin synthesis was stimulated at a Cu concentration between 5 and 25 μM but decreased at 50 μM Cu. Malondialdehyde content (MDA), lipoxygenase activity (LOX), superoxide ion (O₂ ^•−) accumulation, and H₂O₂ content at 5 and 10 μM Cu-treated roots were not increased but strongly increased at 50 μM Cu resulting in the oxidation of ascorbate (ASC) and glutathione (GSH) to dehydroascorbate (DHA) and glutathione disulfide (GSSG), respectively indicating a clear oxidative stress. Seven well-resolved bands of superoxide dismutase (SOD) were detected in the gel and an increase in SOD activity seemed to be mainly due to the induction of Fe-SOD 3. Five to 10 μM Cu slightly induced activity of ascorbate peroxidase (APX) and dehydroascorbate reductase (DHAR), guaiacol peroxidase (G-POD) but inhibited monodehydroascorbate reductase (MDHAR) and glutathione reductase (GR) enzyme activities. No changes in catalase (CAT) activity and in activity gel were found up to 25 μM Cu, but both G-POD and CAT activities were inhibited at 50 μM Cu. Glutathione metabolism enzymes such as γ-glutamylcysteine synthetase (γ-GCS), glutathione-S-transferase (GST), and glutathione peroxidase activities (GPx) were activated at 5 and 10 μM Cu but were strongly inhibited at 50 μM Cu due to the Cu accumulation in root tissues. The strong depletion of GSH at 50 μM Cu was associated to the strong induction of γ-glutamyltranspeptidase (γ-GGT) activity. These results indicate that plant could grow under Cu stress (5–25 μM) by modulating the antioxidant defense mechanism for combating Cu induced oxidative stress.     

The use of aeroponics to investigate antioxidant activity in the roots of <Emphasis Type="Italic">Xerophyta viscosa</Emphasis>

In order to ultimately understand the whole plant mechanism of attaining desiccation tolerance, we undertook to investigate the root tissues of the resurrection plant Xerophyta viscosa, as previous work has only been conducted on the leaf tissues of resurrection plants. An aeroponic plant growth system was designed and optimised to observe the root’s response to desiccation without the restrictions of a soil medium, allowing easy access to roots. Successful culture of both X.viscosa and the control, Zea mays, was achieved and dehydration stress was implemented through reduction of nutrient solution spraying of the roots. After drying to the air dry state (achieved after 7 days for roots and 10 days for shoots), rehydration was achieved by resumption of root spraying. X.viscosa plants survived desiccation and recovered but Z. mays did not. The activity of the antioxidant enzymes superoxide dismutase, catalase, ascorbate peroxidase and glutathione reductase and quantities of ascorbate and glutathione were determined during root desiccation. There was an initial decline in activity in all enzymes upon drying to 80% RWC, but activity thereafter remained constant, at rates indicative of potential metabolic activity, to the air-dry state. This data suggests that these enzymes are not denatured by desiccation of the root tissue. Ascorbate and glutathione content remained constant at concentrations of 70 and 100 μM, respectively during drying. Thus root tissues appear to retain antioxidant potential during drying, for use in recovery upon rehydration, as has been reported for leaf tissues of this and other resurrection plants.     

The Effect of Copper Toxicity on the Growth and Root Morphology of Rhodes Grass (Chloris gayana Knuth.) in Resin Buffered Solution Culture

A solution culture experiment was conducted to examine the effect of Cu toxicity on Rhodes grass (Chloris gayana Knuth.), a pasture species used in mine-site rehabilitation. The experiment used dilute, solution culture to achieve external nutrient concentrations, which were representative of the soil solution, and an ion exchange resin to maintain stable concentrations of Cu in solution. Copper toxicity was damaging to plant roots, with symptoms ranging from disruption of the root cuticle and reduced root hair proliferation, to severe deformation of root structure. A reduction in root growth was observed at an external Cu concentration of < 1 μM, with damage evident from an external concentration of 0.2 μM. Critical to the success of this experiment, in quantitatively examining the relationship between external Cu concentration and plant response, was the use of ion exchange resin to buffer the concentration of Cu in solution. After some initial difficulty with pH control, stable concentrations of Cu in solution were maintained for the major period of plant growth. The development of this technique will facilitate future investigations of the effect of heavy metals on plants.     

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.     

Adaptive Copper Tolerance in <Emphasis Type="Italic">Elsholtzia haichowensis</Emphasis> Involves Production of Cu-induced Thiol Peptides

Copper (Cu) accumulation and tolerance mechanisms in Elsholtzia haichowensis, an indicator plant of Cu mines, were investigated under hydroponics supplied with different concentrations (0.32, 50.0, 100.0 and 200.0 μM) of Cu for 8 days. Cu at 100 and 200 μM significantly decreased the root dry weight, but had no significant effect on shoot dry weight. The plants grown in the presence of 200 μM Cu accumulated 288 and 7626 μg g⁻¹ DW total Cu in the shoots and roots, respectively. A greater proportion of accumulated Cu was water-soluble accounting for 42–93% of the total Cu content in the shoots. The concentrations of reduced glutathione (GSH) and protein thiols were significantly enhanced under excess Cu supply. However, the concentrations of these compounds, particularly protein thiols, were much higher in the leaves than that in the roots. Three UV-absorbing peaks could be eluted out through gel filtration chromatography on Sephadex G-50. A large amount of Cu was detected in the UV-absorbing peaks in 40–50 and 70–90 ml elution fractions of the root extract, and in 40–50 and 120–140 ml elution fractions of the leaf extract. The results suggested that the adaptive Cu tolerance mechanism in E. haichowensis might involve the active participation of protein thiols which had a more important role in the leaves than in the roots.     

The Activity of the Antioxidative System in Cadmium-Treated Arabidopsis thaliana

Changes in the content of reactive oxygen species (ROS) and activity of the antioxidant system were measured in leaves of Arabidopsis thaliana (L.) Heynh exposed to Cd²⁺. Mature plants growing in the nutrient solution were treated with Cd²⁺ at different concentrations (0, 5, 25, 50, 100 μM). An increase of content in leaves was observed at 5, 25 and 50 μM Cd²⁺. A strong accumulation of H₂O₂ was found only at the lowest Cd²⁺ concentration. The content of OH^*. was high at 50 and 100 μM Cd²⁺. Superoxide dismutase (SOD) activity was always higher in Cd²⁺-treated plants than in control. Catalase (CAT) activity decreased with increasing Cd²⁺ concentration in the nutrient solution. Guaiacol peroxidase (POX) activity was particularly high at the lowest and highest Cd²⁺ concentrations and ascorbate peroxidase (APX) activity additionally at 50 μM Cd²⁺. Enhanced activity of monodehydroascorbate reductase (MDHAR) and strong reduction in ascorbate (AA) content were observed at 25 μM Cd²⁺. Glutathione reductase (GR) activity was always higher than in control but decreased as Cd²⁺ concentration increased. However, it was accompanied by gradual content increase of SH-groups. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dynamics of zinc uptake and accumulation in the hyperaccumulating and non-hyperaccumulating ecotypes of Sedum alfredii Hance

Sedum alfredii Hance has been identified as a Zn-hyperaccumulating plant species native to China. The characteristics of Zn uptake and accumulation in the hyperaccumulating ecotype (HE) and non-hyperaccumulating ecotype (NHE) of S. alfredii were investigated under nutrient solution and soil culture conditions. The growth of HE was normal up to 1000 μM Zn in nutrient solution, and 1600 mg Zn kg⁻¹ soil in a Zn-amended soil. Growth of the NHE was inhibited at Zn levels ≥250 μM in nutrient solution. Zinc concentrations in the leaves and stems increased with increasing Zn supply levels, peaking at 500 and 250 μM Zn in nutrient solution for the HE and the NHE, respectively, and then gradually decreased or leveled off with further increase in solution Zn. Minimal increases in root Zn were noted at Zn levels up to 50 μM; root Zn sharply increased at higher Zn supply. The maximum Zn concentration in the shoots of the HE reached 20,000 and 29,000 mg kg⁻¹ in the nutrient solution and soil experiments, respectively, approximately 20 times greater than those of the NHE. Root Zn concentrations were higher in the NHE than in the HE when plants were grown at Zn levels ≥50 μM. The time-course of Zn uptake and accumulation exhibited a hyperbolic saturation curve: a rapid linear increase during the first 6 days in the long-term and 60 min in the short-term studies; followed by a slower increase or leveling off with time. More than 80% of Zn accumulated in the shoots of the HE at half time (day 16) of the long-term uptake in 500 μM Zn, and also at half time (120 min) of the short-term uptake in 10 μM ⁶⁵Zn²⁺. These results indicate that Zn uptake and accumulation in the shoots of S. alfredii exhibited a down-regulation by internal Zn accumulated in roots or leaves under both nutrient solution and soil conditions. An altered Zn transport system and increased metal sequestration capacity in the shoot tissues, especially in the stems, may be the factors that allow increased Zn accumulation in the hyperaccumulating ecotype of S. alfredii. Section Editor: F. J. Zhao