Effect of calcium on the absorption and translocation of heavy metals in excised barley roots: Multi-compartment transport box experiment

Summary The effect of Ca on the absorption and translocation of Mn, Zn and Cd in excised barley roots was studied using a multi-compartment transport box technique. A radioisotope (⁵⁴Mn,⁶⁵Zn or^115mCd)-labelled test solution was supplied to the apexes of excised roots and the distribution pattern in the roots was examined in the absence or presence of Ca. Results obtained were as follows. Addition of Ca to the test solution reduced the absorption of Mn and inhibited drastically its translocation in excised roots. With increasing concentrations of Ca in test solutions, its inhibitory effects on the absorption and translocation of Mn became severe. Similar results were observed for the absorption and translocation of Zn. Ca in the test solution decreased the absorption and inhibited drastically the translocation of Zn; as in the case of Mn, higher concentrations of Ca had severe effects on these functions. It was also evident that the addition of Ca to the test solution reduced the absorption of Cd at all levels of Cd concentration (1, 10, and 100 μM). Cd absorption decreased with increasing concentrations of Ca in the test solution. However, Ca accelerated the translocation of Cd in excised roots supplied with test solutions containing up to 10μM Cd. At 100μM Cd, addition of Ca caused a negligibly small acceleration of Cd translocation. The accelerating effect of Ca on Cd translocation, especially “xylem exudation”, decreased markedly with the addition of 2,4-dinitrophenol, but not with the addition of chloramphenicol or p-chloromercuribenzene sulphonic acid. When barley plants were supplied with only CaSO₄ during the entire growing period, that is, plants were not supplied with nutrient solution on the last day of this period, Ca had no accelerating effect on Cd translocation in excised roots.     

Effect of rhizosphere and plant-related factors on the cadmium uptake by maize (Zea mays L.)

The characteristics of 12- and 24-day-old maize plants (Zea mays L. cv MB862) related to Cd absorption were investigated with respect to the influence of Cd concentration in the plant organs, to plant age, absorption time and competition with micronutrients. Despite high Cd concentrations in the nutrient solution, hydroponically cultivated maize did not seem to be affected by Cd toxicity, except for the highest Cd level (100 μmol L⁻¹). There was on average five times more Cd in roots than in shoots and the Cd root to shoot ratio increased with increasing Cd concentration in the nutrient solution. No significant differences were observed between influx measured for 2 h in the middle of the day light period and for a full day period. Plants with different internal Cd concentrations showed similar root absorption characteristics of this metal. The root Cd influxes were three times higher in solutions with low micronutrient contents than in the solutions with higher micronutrient contents, and almost three times higher in 12-day-old roots than in 24-day-old roots. The root Cd influx was linearly related to its concentration in the solution, showing no saturable component. Our results suggest a non-specific and unregulated transport of Cd into the maize root symplast. They also indicate a regulation of the Cd translocation from root to shoot, as well as dependence of parameters of Cd root absorption on plant and rhizosphere conditions which should be taken into account for Cd uptake modelling.     

水稻土施硅对土壤-水稻系统中镉的降低效果

水稻中镉的积累造成人类健康的风险,增加水稻硅素能减轻镉中毒症状,降低稻米镉积累,但是硅对重金属的作用机理尚不清楚。主要研究了在中度和高度镉污染的土壤中,通过施用固态和液态的富硅物质对土壤-水稻系统中镉的吸收和转运的影响,探明决定镉和硅在根与芽的质外体和共质体中的作用机理。试验结果表明:(1)在中度和高度污染的土壤中,镉在土壤-作物系统中的转移和积累情况是不同的,可以通过富硅物质中的单硅酸与镉离子的相互作用,增加镉在硅物质表面的吸附来减少镉在土壤中的流动;(2)富硅物质可以降低水稻根和芽中镉的积累,在高度镉污染的情况下,施用硅可以使镉大量积累在水稻根及其共质体中,并降低根及其共质体中镉的转换和积累;(3)新鲜土壤中水萃取态的单硅酸含量与镉在土壤-作物系统中的流动性、转运以及积累等主要参数密切相关。     

UPTAKE OF CADMIUM BY FRESHWATER GREEN ALGAE: EFFECTS OF PH AND AQUATIC HUMIC SUBSTANCES1

The effects of humic substances and low pH on short‐term Cd uptake by Pseudokirchneriella subcapitata (Korshikov) Hindak and Chlamydomonas reinhardtii Dang were investigated under defined exposure conditions. The uptake experiments were run in the presence of either a synthetic organic ligand (nitrilotriacetate) or natural organic ligands (Suwannee River fulvic or humic acid). An ion‐exchange method was used to measure the free Cd²⁺ concentrations in the exposure solutions. At pH 5, measured free Cd²⁺ concentrations agreed with estimations made using the geochemical equilibrium model WHAM, but at pH 7 the model overestimated complexation by both Suwannee River fulvic and humic acids compared with the ion‐exchange measurements. Consistent with the metal internalization step being rate limiting for overall short‐term uptake, intracellular Cd uptake was linear for exposure times less than 20 min at pH 5 or pH 7 for both algal species. After taking into account complexation of Cd in solution, Suwannee River humic substances had no additional effects on cadmium uptake at pH 7, as would be predicted by the free ion model. This absence of effects other than complexation persisted at pH 5, where the tendency of humic substances to adsorb to the algal cell surface is favored. Changes in pH strongly influenced Cd uptake, with the intracellular flux of Cd being at least 20 times lower at pH 5 than at pH 7 for P. subcapitata. Our results support models such as the free ion model or the biotic ligand model, in which humic substances act indirectly on Cd uptake by reducing the bioavailability of Cd by complexation in solution.     

The toxicity of cadmium to barley plants as affected by complex formation with humic acid

An ‘alternating solution’ culture method was used to study the effects of chloride ions and humic acid (HA) on the uptake of cadmium by barley plants. The plants were transferred periodically between a nutrient solution and a test solution containing one of four levels of HA (0, 190, 569 or 1710 μg cm⁻³) and one of five levels of Cd (0, 0.5, 1.0, 2.5 or 5.0 μg cm⁻³) in either a 0.006M NaNO₃ or 0.006M NaCl medium. Harvest and analysis of shoots and roots was after nineteen days. The distribution of Cd in the test solutions between Cd²⁺, CdCl⁺ and HA-Cd was determined in a separate experiment by dialysis equilibrium. In the nitrate test solutions Cd uptake was clearly controlled by Cd²⁺ concentration and was therefore reduced by HA complex formation. In the absence of HA, chloride suppressed Cd uptake indicating that Cd²⁺ was the preferred species. However complex formation with Cl⁻ enhanced uptake when HA was present because of an increase in the concentration of inorganic Cd species relative to the nitrate system. The ratio root-Cd/shoot-Cd remained at about 10 across a wide range of shoot-Cd concentrations, from about 3 μg g⁻¹ (sub-toxic) up to 85 μg g⁻¹ (80% yield reduction). The ability of the barley plants to accumulate ‘non-toxic’ Cd in their roots was thus very limited. Humic acid also had no effect on Cd translocation within the plant and the root/shoot weight ratio did not vary with any treatment. At shoot-Cd concentrations in excess of 50 μg g⁻¹, K, Ca, Cu and Zn uptake was reduced, probably the result of root damage rather than a specific ion antagonism. The highest concentration of HA also lowered Fe and Zn uptake and there was a toxic effect with increasing HA concentration at Cd=0. However the lowest HA level, comparable with concentrations found in mineral soil solutions, only reduced yield (in the absence of Cd) by <5% while lowering Cd uptake across the range of Cd concentrations by 66%–25%.     

Humic acid and iron uptake by plants

Summary The behaviour of ferric EDTA and ferric citrate in nutrient solution and their interaction with humic acid was investigated at various hydrogen ion concentrations using the technique of membrane ultrafiltration to separate small iron species from high molecular weight products of hydrolysis and to estimate the binding of iron by humic acid. Ferric EDTA was found to be of small molecular size at all pH values between 5.0 and 7.0 whilst ferric citrate solutions contained an increasing proportion of high molecular weight material as pH was increased from 5.0 to 7.0. Some iron present in solutions of both ferric EDTA and ferric citrate was bound by humic acid at all pH values from 5.0 to 7.0. Studies were also made of the uptake of iron by wheat roots from nutrient solutions containing either ferric EDTA or ferric citrate and of the effect of humic acid on uptake. More iron was absorbed from ferric EDTA than from ferric citrate at all pH values. Increasing pH between 5.0 and 7.0 resulted in a progressive decrease in the uptake of iron in both cases. The presence of humic acid depressed iron absorption from both solutions at all pH values.     

Coordination and speciation of cadmium in corn seedlings and its effects on macro- and micronutrients uptake

The effect of cadmium (Cd) on both the absorption of important nutrients and the synthesis of low molecular weight thiols (LMWTs) was investigated in corn plants. The inductively coupled plasma-optical emission spectroscopy results demonstrated that the concentration of Cd in tissues (mainly in roots) increased as the concentration in the medium increased. In addition, the concentration of phosphorus increased in roots of Cd treated plants but remained at normal concentration in shoots. On the other hand, the uptake of sulfur (S) followed a similar trend as the Cd uptake. The concentration of S and the production of LMWT were found to increase significantly upon exposure to Cd. The results of the X-ray absorption spectroscopy analyses indicated that Cd within tissues was bound to S ligands with interatomic distances of 2.51–2.52 Å. These results confirm a strong linkage between S uptake and the production of LMWT upon exposure to Cd.     

Influence of pH on Cd and Cu uptake, distribution and their effect on nitrate reductase activity in cucumber (Cucumis sativus L.) seedling roots

Influence of different pH solutions (5.0 and 7.0) on Cu²⁺ and Cd²⁺ absorption and distribution in root cells as well as effects of these metals on nitrate reductase activity (NR) in roots of cucumber seedlings were estimated. The absorption of Cu and Cd by roots measured as metal depletion in uptake solution was similar, both metal absorption was independent of the pH of solution. However, after rinsing of roots in distilled water (30 minutes), more Cu than Cd was found in protoplasts of root cells. More Cu was measured in all cell fractions when Cu was uptaken from pH 5.0 than from 7.0. The nitrate reductase activity after one hour of metal treatments was drastically decreased by Cu. The strongest reduction of enzyme activity was observed in roots treated with Cu in buffer with pH 5.0. Influence of Cd on the enzyme activity was weaker and was independent of the pH of solution. Lower concentration of Cd in solution (20 μM) increased NR activity. The data obtained prove the higher mobility of Cu than Cd into the cells of root. The mobility of Cu depends on pH of solution. Cu ions, but not Cd, influenced membrane permeability (K leakage). Cu acted more drasticly than Cd on NR activity.     

EGTA对Cd胁迫下蓖麻Cd积累和营养元素吸收的影响

以‘淄蓖麻5号’蓖麻品种为材料,通过盆栽试验研究了重度Cd土壤污染（100 mg·kg^-1）条件下,不同浓度（0、0.5、1.0、2.0 mmol·kg^-1）外源螯合剂——乙二醇双(2-氨基乙基醚)四乙酸(EGTA)对蓖麻植株生长、Cd积累和营养元素吸收的影响,探讨外源螯合剂调控Cd污染土壤上植物生长和修复效应。结果显示：（1）在Cd胁迫下,土壤中外源添加0.5~2.0 mmol·kg^-1EGTA使蓖麻根系鲜、干重比不添加EGTA对照不同程度降低,但植株总干重没有受到显著影响。（2）外源EGTA能有效促进Cd从蓖麻根部向地上部的转移,2.0 mmol·kg^-1的EGTA处理使蓖麻叶片Cd 含量显著增加了41.34倍;与不添加EGTA对照相比,外源EGTA处理蓖麻叶片中Cd积累量随添加EGTA的浓度增加而显著大幅度增加14.0~45.6倍,占相应植株总积累量的36.89%~58.63%,而茎中Cd积累量增加幅度较小,根中Cd积累量则显著降低。（3）Cd胁迫条件下,外源EGTA对蓖麻各器官矿质元素含量的影响不一,EGTA促进K向蓖麻地上部的转运,同时抑制Mg向植株地上部转运;随土壤添加的EGTA浓度提高,蓖麻植株对Ca吸收表现为低促高抑,叶片Zn含量和植株Cu含量逐渐增加,叶片和根系Fe含量及植株各器官Mn含量显著增加。与无Cd胁迫对照相比,EGTA在提高植株Cd积累的同时,降低了根系对K的吸收。研究表明,Cd胁迫显著抑制了蓖麻植株的生长,适宜浓度的外源EGTA对Cd的这种抑制有显著的缓解作用;外源EGTA改变了Cd在蓖麻根、茎、叶中的积累分布情况,提高了Cd从根系向地上部,尤其是向叶片的转移能力,从而强化了蓖麻对Cd污染土壤的修复效率;在采用EGTA强化植物修复Cd污染土壤时,应适量增施K肥以保证植株的正常生理代谢。     

Role of iron plaque in Cd uptake by and translocation within rice (Oryza sativa L.) seedlings grown in solution culture

A hydroponics culture experiment was conducted to investigate the effect of iron plaque on Cd uptake by and translocation within rice seedlings grown under controlled growth chamber conditions. Rice seedlings were pre-cultivated for 43 days and then transferred to nutrient solution containing six levels of Fe (0, 10, 30, 50, 80 and 100 mg L⁻¹) for 6 days to induce different amounts of iron plaque on the root surfaces. Seedlings were then exposed to solution containing three levels of Cd (0, 0.1 and 1.0 mg L⁻¹) for 4 days. In order to differentiate the uptake capability of Cd by roots with or without iron plaque, root tips (white root part without iron plaque) and middle root parts (with iron plaque) of pre-cultivated seedlings treated with 0, 30 and 50 mg L⁻¹ Fe were exposed to ¹⁰⁹Cd for 24 h. Reddish iron plaque gradually became visible on the surface of rice roots but the visual symptoms of the iron plaque on the roots differed among treatments. In general, the reddish color of the iron plaque became darker with increasing Fe supply, and the iron plaque was more homogeneously distributed all along the roots. The Fe concentrations increased significantly with increasing Fe supply regardless of Cd additions. The Cd concentrations in dithionite–citrate–bicarbonate (DCB)-extracts and in shoots and roots were significantly affected by Cd and Fe supply in the nutrient solution. The Cd concentrations increased significantly with increasing Cd supply in the solution and were undetectable when no Cd was added. The Cd concentrations in DCB-extracts with Fe supplied tended to be higher than that at Fe₀ at Cd_0.1, and at Cd_1.0, DCB-Cd with Fe supplied was significantly lower. Cd concentrations in roots and shoots decreased with increasing Fe supply at both Cd additions. The proportion of Cd in DCB-extracts was significantly lower than in roots or shoots. Compared to the control seedlings without Fe supply, the radioactivity of ¹⁰⁹Cd in shoots of seedlings treated with Fe decreased when root tips were exposed to ¹⁰⁹Cd and did not change significantly when middle parts of roots were exposed. Our results suggest that root tissue rather than iron plaque on the root surface is a barrier to Cd uptake and translocation within rice plants, and the uptake and translocation of Cd appear to be related to Fe nutritional levels in the plants.     

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.     

Effects of amendments on copper, cadmium, and lead phytoextraction by Lolium perenne from multiple-metal contaminated solution

Chemical amendments can increase metal uptake by plant roots and translocation to shoots, however their effectiveness can be influenced by the presence of other amendments and metal ions in a multiple-metal environment. A range of amendments and combinations were tested to explore their effect on phytoextraction of Cu, Cd, and Pb by perennial ryegrass (Lolium perenne) from solutions containing one or more of these metals. The amendments studied included EDDS (an aminopolycarboxylic acid), histidine (an amino acid), citric acid (an organic acid), rhamnolipid (a biosurfactant) and sulfate (an inorganic ligand). For all amendment treatments, the presence of multiple metals in solution reduced shoot concentrations of Cd and Cu, while Pb levels in shoots were generally enhanced by the presence of Cu. Although slightly toxic to the plants, EDDS (1 mM) was the most effective individual amendment for enhancing shoot metal uptake and translocation from solution without significantly reducing biomass yield. The combination Rhm+Cit+EDDS resulted in the highest shoot metal concentrations of all the treatments but also caused severe phytotoxicity. Amendment combinations Rhm+His and Sulf+Cit were less toxic for plant growth while moderately enhancing metal mass accumulation in shoots and thus could be considered as alternative treatments for enhanced phytoextraction.     

Cd uptake by intact wheat plants

Abstract. An investigation of the uptake of Cd by intact wheat plants has been carried out. The accumulation of Cd in the roots as a function of time and external Cd concentration was determined. Since the transport of Cd to the grains and shoots was found to be small, only uptake into the root was examined further. An appreciable fraction of the Cd absorbed by the roots can be desorbed and consequently constitutes the freely diffusible and exchangeable fraction.
The effect of temperature and of metabolic inhibitors on the absorption provides evidence that another Cd fraction is taken up by metabolically mediated processes. The absorption of this Cd fraction was found to be inhibited by Cu and Zn. The inhibitory effect of Cu and Zn on Cd absorption was comparable.     

Foliar uptake and translocation of rubidium in bean plants as affected by root absorbed growth regulators

Summary The absorption and subsequent transport of foliar applied Rb⁸⁶ labeled Rb Cl (10 mM) was studied on bean plants (Phaseolus vulgaris, L. cv. Black Seeded Blue Lake) exposed to physiologically tolerable levels of certain plant growth substances in the solution culture root media. Gibberellin A₃ (10^-5 M) increased Rb uptake but did not affect total translocation from the treated leaf. Translocation was directed to the upper vegetative parts and markedly reduced to the roots. Foliar influx of Rb and transport to the roots were greatly enhanced by 1-naphthaleneacetic acid (10^-6 M) but mobilization of Rb into the leaves and upper stem was reduced. 2-Chloroethyltrimethylammonium chloride (10^-3 M) and N,N-dimethylaminosuccinamic acid (3×10^-4 M) decreased the mobility of Rb to the upper stem, increased it to the roots, and had no effect on initial uptake. Rb absorption was depressed by 2,4-dichlorobenzyltributylphosphonium chloride (10^-5 M) with no effect on subsequent translocation. Both uptake and mobility were strikingly inhibited by N⁶-benzyladenine (10^-6 M).These results suggest that absorption and the subsequent transport of foliar absorbed Rb are independent processes and that the distribution or mobilization of Rb in the various plant organs was not always a function of the chemically modified growth rate of the corresponding organ.Report No. COO-888-50 in cooperation with the Division of Biology and Medicine of the United States Atomic Energy Commission, Contract No. AT (11-1)-888. Journal Article No. 3643 of the Michigan Agricultural Experiment Station.     

黑麦草生长过程中有机酸对镉毒性的影响

研究了低分子量有机酸草酸、柠檬酸、乙酸及高分子量有机酸胡敏酸对黑麦草(Lolium Loinn)生长过程中Cd毒性的影响.结果表明,随着低分子量有机酸浓度增加,Cd毒性有所增强,致使黑麦草中的叶绿素含量降低及黑麦草的生物量降低,递降顺序是草酸＜乙酸＜柠檬酸.而施入胡敏酸后,Cd毒性逐渐减弱,黑麦草中的叶绿素含量及黑麦草生物量逐渐增加.对低分子量有机酸而言,无论迁移到黑麦草茎叶中,还是迁移到黑麦草根系中的Cd,随着施入的有机酸浓度增加,增加顺序为柠檬酸＞乙酸＞草酸.对胡敏酸而言,迁移到黑麦草茎叶和根系中的Cd,随着施入的胡敏酸浓度增加,Cd含量减少,说明其具有降低Cd毒性的作用.另外,根系中Cd含量明显高于茎叶中Cd含量,由此得知,黑麦草根系对Cd有较强的富集作用,并阻止Cd向茎叶中迁移.     

Effect of neutralization and addition of urea,sucrose, and various glycols on phosphorus absorption and leaf damage from foliar-applied phosphate

Summary Inclusion of sucrose in the solution applied to soybean (Glycine max L. merr.) leaves much reduced the severity of the damage to the leaves from application of urea and, to a lesser extent, from application of phosphorus (P) as orthophosphoric acid. Sucrose had no evident effect on P absorption. Damage to the leaves from joint application of orthophosphoric acid and urea exceeded the sum of the damage caused by the substances individually. Urea did not seem to influence P absorption, but the effect, if any, was not readily determined because nearly all values for P absorption exceeded 90%.Neutralization of orthophosphoric acid with nitrogen-containing organic bases, including choline, guanidine, and guanyl urea, did not prove useful as a technique for increasing the quantity of orthophosphate that could be applied without damage to the leaves.Absorption and translocation of orthophosphate by corn (Zea mays L.) and soybean leaves were not influenced by the pH of the solution within the range from 2 to 10. Absorption of tripolyphosphate by corn leaves decreased with an increase in pH of the solution applied, but translocation of the absorbed P was not influenced by pH. With soybeans, absorption of tripolyphosphate decreased with an increase in pH of the solution. Translocation of P applied to soybean leaves as tripolyphosphate was less than 5% of the amount absorbed within the first 24 hr and decreased with an increase in pH after 10 days.     

Genotypic variation in safflower (Carthamus spp.) cadmium accumulation and tolerance affected by temperature and cadmium levels

Soil pollution is a world-wide problem, with heavy metals being a major part of the concern. To investigate the effect of temperature on cadmium (Cd) uptake and translocation, as well as Cd tolerance in wild and cultivated species of safflower, a hydroponic experiment was conducted under controlled conditions. The responses of four wild genotypes (Isfahan, Arak, Azari, and Shiraz) and four cultivated genotypes (AC-Sterling, 2811, Saffire, and C111) of safflower to nine levels of CdCl₂ (0, 0.5, 1, 5, 10, 20, 50, 100, and 500 μM) in solution were examined under two temperatures (18 and 23 °C). Cadmium sensitivity was determined using the Weibull model on the total dry weight of the plants. Cadmium uptake and translocation were analyzed on 1 μM Cd treated plants. Results revealed that safflower genotypes differed in terms of uptake, translocation, and tolerance to Cd, with AC-Sterling and Arak indicating the most and the least tolerance to Cd, respectively. Relative Cd uptake and Cd concentration in roots and shoots increased with an increase in temperature in all genotypes, with the exception of AC-Sterling. Net accumulation of Cd via root increased with an increase in temperature for the wild Azari and the cultivated 2811, Saffire, and C111, though it decreased for the rest of genotypes. Cadmium translocation to shoots significantly increased with increased temperature in all genotypes. Cadmium translocation from roots to shoots in cultivated genotypes was significantly greater than in wild genotypes. Root Cd concentration in wild genotypes was significantly greater than in cultivated genotypes. It seems that wild and cultivated species of safflower differ in their response to Cd. Furthermore, temperature may affect the plant's tolerance to Cd, probably through accompanying changes in Cd uptake and translocation from root to shoot.     

Effects of pH and nitrogen on cadmium uptake in potato

This study investigated the effects of pH and nitrogen form and concentration on cadmium (Cd) uptake by potato (Solanum tuberosum L.) grown in hydroponic culture. Potato plants grown in a pH-buffered nutrient solution for 10 d were exposed for 24 h to 25 nM CdCl₂ labelled with ¹⁰⁹Cd. Plants showed a significantly higher Cd uptake and accumulation at pH 6.5 than at pH 4.5 and 5.5. Nitrogen supplied as nitrate (NO₃ ^?) generally resulted in a higher Cd uptake and accumulation than N supplied as ammonium (NH₄ ⁺). This effect was most pronounced at pH 6.5. The N concentration increasing from 6.5 to 26 mM resulted in a decreased Cd influx when either NO₃ ^? or NH₄ ⁺ was used. Cd translocation to the shoot was increased when NO₃ ^? was used as the sole N source. In conclusion, pH had a strong influence on Cd uptake by roots and N form is especially important for Cd translocation within the potato plant.     

Role of roots in differences in seed cadmium concentration among soybean cultivars—proof by grafting experiment

Soybean cultivars show significant differences in cadmium (Cd) concentrations in seeds, due primarily to genetics, not environmental factors. We previously suggested that low-Cd cultivars accumulate Cd in their roots and thus prevent its translocation to the rest of the plant. Through grafting experiments, we drew the following conclusions about Cd absorption and translocation: (1) The amount of Cd accumulated in shoots is determined by the Cd accumulation capacity of roots: cultivars with a small capacity to accumulate Cd in roots translocate more Cd and accumulate it in shoots; (2) The Cd concentration in shoots is determined by the Cd accumulation capacity of roots and the shoot productive ability of the scion cultivar; (3) The Cd tolerance of shoots differs among cultivars. Enrei, with a high-Cd accumulation capacity of roots, had a low Cd tolerance of shoots compared with Suzuyutaka and Hatayutaka, with a low Cd accumulation capacity of roots; (4) Cultivars differ in their distribution of Cd to seed; (5) These results show that seed Cd concentration is influenced by the differences among cultivars in ease of translocation of Cd to seed and in Cd accumulation capacity of roots.     

Growing,physiological responses and Cd uptake of Corn (Zea mays L.) under different Cd supply

The effects of Cd on the growth and Cd uptaking in corn (Zea mays L.) were explored under different Cd stress. The results showed that no reduction in shoot and root dry matter yields were noted when the plants were grown at Cd supply levels ≤100 μmol l^?1 nutrient solution. The Cd concentration in the shoots and roots of corn increased sharply with increasing external Cd supply levels, peaked at 50 μmol l^?1, and then decreased slowly with further increasing Cd levels due to high Cd toxic effects on root growth. The concentrations of chlorophyll a, chlorophyll b and chlorophyll a + b in the leaf of corn decreased slowly with increasing external Cd supply levels. Proline concentrations of corn increased when the plants were grown under the external Cd influence. The lower concentration of Cd treatments did not influenced the growth of corn significantly, and increased the uptake of Cd, the higher levels of Cd supply caused significantly physiological resposes and decreased the Cd uptaking.