农作物对Cd毒害的耐性机理探讨

对生长在Ｃｄ污染条件下的８种作物体内Ｃｄ的存在形态分析表明,作物的耐Ｃｄ性与Ｃｄ的形态分布密切相关,在耐性作物体内,蛋白质（多肽）结合Ｃｄ量的比例低于非耐性作物;有机酸盐和一代磷酸盐态Ｃｄ的比例增加;分离得到Ｃｄ诱导蛋白?其中束缚了一定量的Ｃｄ,限制了Ｃｄ以自由态存在,耐性较低的作物本内,大分子量的蛋白质中富Ｃｄ量较高。     

镉与豆磺隆复合胁迫下小麦根－土界面镉形态的变化

通过根际箱试验,研究了Cd与豆磺隆复合胁迫下小麦根 土界面Cd形态变化的空间和时间效应.在空间上将根－土界面(0～5 mm)细化到1 mm,在时间上将取样时间分为14、21、28、35和42 d,并将小麦体吸收的Cd与根 土界面各形态Cd作相关分析,从而得出影响小麦体生长的Cd形态.结果表明,在小麦不同的生长时间内,可交换态Cd表现出的空间效应明显不同.在小麦生长的第14天,根－土界面可交换态Cd大体上由根中心区(6.186 mg·kg^-1)向根外区(6.482 mg·kg^-1)逐渐增加;从小麦生长第21天到42天,根-土界面可交换态Cd呈现出由根中心区到某一层升高,之后又由该层到土体下降的趋势.根-土界面各层碳酸盐和铁锰结合态Cd向可交换态Cd转化的趋势由根中心区向根外区逐渐减弱,而向残留态Cd转化的趋势逐渐加强,有机结合态Cd浓度变化在近根区较大.碳酸盐结合态Cd、铁锰结合态Cd、有机结合态Cd浓度随时间而逐渐下降;残留态Cd浓度则表现出明显的上升趋势.相关分析表明,近根层的可交换态Cd和有机结合态Cd是小麦能直接利用的两种Cd形态.豆磺隆对可交换态Cd含量变化以及碳酸盐和铁锰结合态Cd的转化有明显影响.     

Tolerance of Ricinus communis L. to Cd and screening of high Cd accumulation varieties for remediation of Cd contaminated soils

Response of castor (Ricinus communis L.) to cadmium (Cd) was assessed by a seed-suspending seedbed approach. Length of total radicle was the most sensitive indicator of Cd tolerance among the tested germination and growth characters. The ED₅₀ value for Cd was 11.87 mg L^?1, indicating high Cd tolerance in castor. A pot experiment was conducted by growing 46 varieties of castor under CK (without Cd) and Cd1 (10 mg kg^?1 of Cd) and Cd2 (50 mg kg^?1 of Cd) treatments to investigate genotype variations in growth response and Cd accumulation of castor under different Cd exposures. Castor possessed high Cd accumulation ability; average shoot and root Cd concentrations of the 46 tested varieties were 21.83 and 185.43 mg kg^?1, and 174.99 and 1181.96 mg kg^?1 under Cd1 and Cd2, respectively. Great variation in Cd accumulation was observed among varieties, and Cd concentration of castor was genotype dependent. The correlation between biomass and Cd accumulation was significantly positive, while no significant correlation was observed between Cd concentration and Cd accumulation, which indicated that biomass performance is the dominant factor in determining Cd accumulation ability.     

The amount of cadmium associated with Cd-binding protein in roots of Agrostis gigantea,Maize and tomato

Roots retained a major portion of the Cd in seedlings exposed to 0.5–6 μM Cd in nutrient solutions. The Cd-binding (CdBP) protein of tomato did not account for the early retention of Cd by roots, since the protein only appeared at 7 days. The percentage of root Cd in CdBP increased over 7 days to 11–34% in Agrostis gigantea clone 4 and to 28–71% in maize. Cd toxicity occurred in both species. Clone 6 of A. gigantea sequestered 21–68% of the root Cd in CdBP protein after 1 day of excess Cd and maintained a high percentage through to day 7. No Cd toxicity was manifested. Only the specific response pattern observed in plants of clone 6, the rapid, early and sustained production of CdBP, was consistent with a detoxification role for CdBP.     

Effect of supplemental magnesium on the kidney levels of cadmium, zinc, and copper of mice exposed to toxic levels of cadmium

In this report, we present the results of our investigations on the effect of Mg pretreatment on Cd and bioelements (Cu and Zn) contents in kidney of mice exposed to acute and subacute Cd intoxication. Acute intoxication was performed on male Swiss mice given a single oral dose of 20 mg Cd/kg body weight and mice given the same dose of Cd but pretreated with 40 mg Mg/kg body weight. For subacute intoxication one group of mice was given 10 mg Cd/kg body weight every day, for 2 wk, and the other one received the same dose of Cd after oral Mg intake of 20 mg/kg body weight. Cd, Cu, and Zn content was determined in kidney by atomic absorption spectrophotometry. In acute Cd intoxication, Mg pretreatment resulted in significant decrease of Cd in kidney after 4 and 6 h, compared with animals given only Cd. Under the condition of subacute Cd intoxication, Mg supplementation reduced Cd kidney content after 2 wk for about 30%, compared with animals treated with Cd only. The effect of Mg on Cu and Zn kidney content was also beneficial.     

染色体着丝点结构变化与习惯性流产的关系

为探讨染色体Cd结构变化与习惯性流产关系,采用Cd-NOR同步银染技术,对38例习惯性流产患者和42例正常人Cd结构变异、Cd结构消失、Cd结构最大横径和Cd-NOR融合进行测量和比较分析。发现习惯性流产患者的Cd结构变异和Cd结构消失的频率明显高于正常人,Cd结构最大横径明显小于正常人。Cd结构消失和Cd结构变异频率的增高以及Cd结构最大横径变小可能是影响习惯性流产的相关因素。 Abstract:To study the correlation between chromosome centromeric dots and habitual abortions,Cd variation,Cd loss,maximum diameter of Cd and Cd-NOR of 38 habitual abortion patients and 42 healthy persons were measured,compared and analysed with Cd-banding technique.It was found that the frequencies of Cd variation and Cd loss were obviously higher and maximum diameter of Cd was smaller in habitual abortion patients than those in healthy persons.The increase of frequencies of Cd variation and Cd loss and the decrease of maximum diameter of Cd might be the causes affecting habitual abortions.     

有机物料对土壤镉形态及其生物有效性的影响

采用盆栽试验,研究了淹水种稻条件下添加猪粪和泥炭对红壤和潮土中内源和外源Cd形态及其生物有效性的影响。结果表明,土壤中内源Cd在各形态之间的分布比较均匀;添加外源Cd时Cd主要分布于交换态,从分蘖期到成熟期,内源Cd交换态普遍升高,添加外源Cd时交换态普遍降低。有机物料对内源Cd交换态的影响不显著,但当添加外源Cd时则对交换态有显著影响,在不添加外源Cd的条件下,有机物料普遍促进水稻根系对Cd的吸收。在添加外源Cd的条件下,有机物料普遍抑制水稻根系对Cd的吸收,猪粪的抑制效果强于泥炭,水稻根系对Cd与Fe的累积呈显著抑制作用。     

Cd accumulation in roots and shoots of durum wheat: the roles of transpiration rate and apoplastic bypass

Cadmium is readily taken up from soils by plants, depending on soil chemistry, and variably among species and cultivars; altered transpiration and xylem transport and/or translocation in the phloem could cause this variation in Cd accumulation, some degree of which is heritable. Using Triticum turgidum var. durum cvs Kyle and Arcola (high and low grain Cd accumulating, respectively), the objectives of this study were to determine if low-concentration Cd exposure alters transpiration, to relate transpiration to accumulation of Cd in roots and shoots at several life stages, and to evaluate the role of apoplastic bypass in the accumulation of Cd in shoots. The low abundance isotope (106)Cd was used to probe Cd translocation in plants which had been exposed to elemental Cd or were Cd-na?ve; apoplastic bypass was monitored using the fluorescent dye PTS (8-hydroxy-1,3,6-pyrenetrisulphonate). Differential accumulation of Cd by 'Kyle' and 'Arcola' could be partially attributed to the effect of Cd on transpiration, as exposure to low concentrations of Cd increased mass flow and concomitant Cd accumulation in 'Kyle'. Distinct from this, exposure of 'Arcola' to low concentrations of Cd reduced translocation of Cd from roots to shoots relative to root accumulation of Cd. It is possible, but not tested here, that sequestration mechanisms (such as phytochelatin production, as demonstrated by others) are the genetically controlled difference between these two cultivars that results in differential Cd accumulation. These results also suggest that apoplastic bypass was not a major pathway of Cd transport from the root to the shoot in these plants, and that most of the shoot Cd resulted from uptake into the stele of the root via the symplastic pathway.     

Influence of prior Cd(2+) exposure on the uptake of Cd(2+) and other elements in the phytochelatin-deficient mutant, cad1-3, of Arabidopsis thaliana

In order to test the potential effect of prior exposure to different Cd concentrations on Cd uptake and accumulation, plants of Arabidopsis thaliana, including a phytochelatin-deficient mutant, cad1-3, and the wild type, were compared. For Cd uptake experiments, plants were grown for 1 week in nutrient solution containing different Cd concentrations (0, 0.05, 0.1, 0.25, 0.5, and 1.0 microM Cd(NO(3))(2)). Thereafter they were subjected to 0.5 microM Cd labelled with (109)Cd for 2 h. Uptake experiments with (109)Cd showed that the phytochelatin-deficient mutant cad1-3, accumulated less Cd than the wild type. Both a lower proportion and lower total amount of absorbed Cd were translocated to the shoot in cad1-3 plants compared to wild-type plants. Cadmium exposure also influenced the amounts of nutrients found, whereby after exposure to high Cd concentrations (0.5, 1.0 microM) during growth, cad1-3 roots contained less Fe, K, Mg, P, and S compared to roots of the wild type. In cad1-3 these elements decreased with increasing Cd concentration. The total Cd content in roots and shoots increased significantly with increasing Cd concentration during growth, although the increase was much less in cad1-3 plants. In time-dependent experiments of Cd uptake carried out between 15 and 120 min on plants not previously exposed to Cd, no significant difference in Cd accumulation between the mutant and wild type were found, although a smaller amount of Cd was translocated to the shoot in cad1-3 plants. The possibility that the differences in Cd accumulation in mutant and wild-type lines may be due to the cytosolic Cd regulation, which is inhibited by the complexation of Cd by phytochelatins, is discussed.     

The influence of zinc on apical uptake of cadmium in the gills and cadmium influx to the circulatory system in zebrafish (Danio rerio)

Zn (0-16 microM) effects on apical Cd uptake from the water into the branchial epithelium and influx of Cd from the water to the circulatory system in zebrafish (Danio rerio) were studied in three experiments. Apical Cd uptake was decreased by Zn in all three experiments. In fish exposed to 1-600 nM Cd (experiment 1), apical Cd uptake showed saturation kinetics at 2 and 4 microM Zn, and a competitive interaction was indicated. At 16 microMZn, Cd uptake increased linearly. Cadmium influx did not show saturation kinetics, but was inhibited by 16 microM Zn at low Cd exposure concentrations. In fish exposed to 0.1-600 nM Cd (experiment 2), Cd uptake was inhibited by 16 microM Zn, whereas at 30 nM Cd uptake was inhibited by 2 microM Zn. Similarly, 2 microM Zn did not influence Cd uptake in fish exposed to 0.1-2 nM Cd (experiment 3), whereas 2 microM Zn inhibited uptake at 8-30 nM Cd. Zinc also inhibited Cd influx at higher Cd concentrations. However, at lower Cd exposures, a Zn-induced increased influx was indicated. Zinc influences the Cd uptake and influx processes at several sites in the branchial epithelial cells, indicating that influx of Zn2+ and Cd2+ occurs through common pathways.     

Cadmium-resistant mutant of Bacillus subtilis 168 with reduced cadmium transport.

Cd2+ and Mn2+ accumulation was studied with wild-type Bacillus subtilis 168 and a Cd2+-resistant mutant. After 5 min of incubation in the presence of 0.1 microM 109Cd2+ or 54Mn2+, both strains accumulated comparable amounts of 54Mn2+, while the sensitive cells accumulated three times more 109Cd2+ than the Cd2+-resistant cells did. Both 54Mn2+ and 109Cd2+ uptake, which apparently occur by the same transport system, demonstrated cation specificity; 20 microM Mn2+ or Cd2+ (but not Zn2+) inhibited the uptake of 0.1 microM 109Cd2+ or 54Mn2+. 54Mn2+ and 109Cd2+ uptake was energy dependent and temperature sensitive, but 109Cd2+ uptake in the Cd2+-resistant strain was only partially inhibited by an uncoupler or by a decrease in temperature. 109Cd2+ uptake in the sensitive strain followed Michaelis-Menten kinetics with a Km of 1.8 microM Cd2+ and a Vmax of 1.5 mumol/min X g (dry weight); 109Cd2+ uptake in the Cd2+-resistant strain was not saturable. The apparent Km value for the saturable component of 109Cd2+ uptake by the Cd2+-resistant strain was very similar to that of the sensitive strain, but the Vmax was 25 times lower than the Vmax for the sensitive strain. The Km and Vmax for 54Mn2+ uptake by both strains were very similar. Cd2+ inhibition of 54Mn2+ uptake had an apparent Ki of 3.4 and 21.5 microM Cd2+ for the sensitive and Cd2+-resistant strains, respectively. Mn2+ had an apparent Ki of 1.2 microM Mn2+ for inhibition of 109Cd2+ uptake by the sensitive strain, but the Cd2+-resistant strain had no defined Ki value for inhibition of Cd2+ uptake by Mn2+.     

Cadmium distribution in maize inbred lines: Effects of pH and level of Cd supply

In order to investigate the physiological basis of the differential Cd distribution and the degree of variation of this Cd distribution among maize inbred lines, six inbreds designated earlier as ‘shoot Cd excluders’ (B73, H99, and H96) and ‘non-shoot Cd excluders’ (B37, H98, and N28) were grown in nutrient solution culture at different external Cd levels or at different pH. The characterization of the inbreds according to their shoot/root partitioning of Cd was consistent, independent of pH or level of Cd supply. The Cd concentrations in the plants were highest at the highest pH of the solution cultures. Generally, there was a positive correlation between the Cd concentrations in shoots and xylem exudates. It was shown that the Cd concentration in the roots is particularly important in the Cd distribution process. Above a ‘critical’ internal Cd concentration in the roots, specific for each inbred, the ability to retain Cd is strongly diminished. It is concluded that structural and/or physiological characteristics of the roots are involved in Cd partitioning.     

Transport of cadmium across the apical membrane of epithelial cell lines

Cadmium (Cd) uptake and secretion across the apical membrane of epithelial cells was studied using LLC-PK1 cells cultured on Petri dishes and permeable membranes, respectively. Cd accumulation in cells from the apical medium was decreased by low temperature and metabolic inhibitors. A saturable tendency was observed between initial Cd accumulation and increased concentrations of Cd in the apical medium at 37 degrees C, but not at 4 degrees C. Co-incubation with ZnCl2 or CuCl2 competitively decreased Cd accumulation at 37 degrees C. A decrease in the pH of the apical medium markedly decreased Cd accumulation. Pretreatment of cells with an inorganic anion-exchange inhibitor significantly decreased Cd uptake at pH 7.4 in the presence of bicarbonate, but only marginally in its absence. A decrease in the pH of the apical medium increased the secretory (basolateral-to-apical) transport of Cd, with a concomitant decrease in the cellular accumulation of Cd. Co-incubation with Cd and tetraethylammonium, a typical substrate of the organic cation transporter, decreased Cd transport, with a concomitant increase in cellular Cd accumulation. The uptake and secretion of Cd across the apical membrane appear to be partly mediated via an inorganic anion exchanger and a H+ antiport of the organic cation transport system, respectively. Therefore, a decrease in pH of the apical medium markedly decreases Cd accumulation, possibly as a result of not only the decrease in Cd uptake via an inorganic anion exchanger, but also the increase in Cd secretion via the Cd2+/H+ antiport. Further evidence of the antiport was obtained from experiments using brush border membrane vesicles isolated from rat kidney and small intestine. In addition, passive diffusion of Cd appears to be decreased by low temperature and a decrease in pH.     

Effects of Cd on Uptake of P in Potato Grown in Sierozems

The effects of Cd on the bioaccumulation of P in soil-plant system have aroused wide interest and been widely explored. Sierozem has been contaminated by Cd in many areas in Northwest China. To investigate the effects of Cd on the uptake and translocation of P in plants in sierozem, pot experiments were carried out by cultivating potato (Solanum tuberosum L.) under Cd treatment. The fractions of Cd in the soil were examined by soil extraction; available P in the soil was determined; Cd and P accumulation in the plants was also determined. The result of the soil extraction shows that the acid-soluble Cd fraction gradually became the main fraction with the increasing Cd concentrations in the soil. This suggests that the change in the main fraction of Cd may promote the uptake of Cd in plants because acid-soluble Cd fraction may be utilized easily by plants. Given increasing Cd concentrations in the soil, Cd concentrations increased in each part of potato plants, whereas the soil available P and plant P contents were decreased. These results indicate that increasing Cd concentrations in sierozems exerts negative effects on the uptake and translocation of P in plants.     

Screening of marine microalgae for bioremediation of cadmium-polluted seawater

Twenty four strains out of 191 marine microalgal strains exhibited cadmium (Cd) resistance. They were tested for their Cd removal ability in growth media containing 50 μM Cd. Six strains out of 19 green algae and one out of five cyanobacteria removed more than 10% of total Cd from the medium. The marine green alga Chlorella sp. NKG16014 showed the highest removal of Cd 48.7% of total. Cd removal by NKG16014 was further quantitatively evaluated by measuring the amount of cell adsorption and intracellular accumulation. After 12 days incubation, 67% of the removed Cd was accumulated intracellularly and 25% of the Cd removed was adsorbed on the algal cell surface. The maximum Cd adsorption (q_max) was estimated to be 37.0 mg Cd (g dry cells)⁻¹ using the Langmuir sorption model. The Cd removal by freeze-dried NKG16014 cells was also determined. Cd was more quickly adsorbed by dried cells than that by living cells, with a q_max of 91.0 mg Cd (g dry cells)⁻¹.     

矿区分离丛枝菌根真菌对万寿菊吸Cd潜力影响

盆栽试验研究土壤不同施Cd水平(0、5、20、50μg/g)下,接种矿区污染土壤中丛枝菌根真菌对万寿菊根系侵染率、植株生物量及Cd吸收与分配的影响。结果表明:接种丛枝菌根真菌显著提高Cd胁迫下万寿菊的根系侵染率和植株生物量;随着施Cd水平提高,各处理植株Cd浓度显著增加。各施Cd水平下万寿菊地上部Cd吸收量远远高于根系Cd吸收量,在土壤施Cd量达到50μg/g时,接种处理地上部Cd吸收量是根系的3.48倍,对照处理地上部Cd吸收量是根系的1.67倍;同一施Cd水平下接种处理植株Cd吸收量要显著高于对照。总体上,试验条件下污染土壤中分离的丛枝菌根真菌促进了万寿菊对土壤中Cd的吸收,并在一定程度上增加Cd向地上部分的运转,表现出植物提取的应用潜力。     

蒌蒿对镉的富集特征及亚细胞分布特点

以镉(Cd)富集植物蒌蒿(Artemisia selengensis)为试材, 采用超声波细胞破碎处理和超速离心的方法, 对蒌蒿根和叶中亚细胞水平的Cd分布状况进行研究, 同时测定Cd在蒌蒿不同器官中的富集效果。结果表明, 在30 mg·kg^–1Cd胁迫下, 蒌蒿叶片中Cd的富集浓度是根和茎中的2–3倍, 但因叶片所占植株的生物量比例较小, 其对Cd的积累量远小于茎和根; Cd在蒌蒿叶片细胞壁、胞液和细胞器中含量比为16:5:1。细胞壁固定是叶片对Cd的主要防御机制。随着Cd处理浓度的增加, 细胞壁和胞液中的Cd含量大幅上升, 但细胞器中Cd含量仍维持在较低水平。长时间和高浓度的Cd胁迫可使细胞壁解毒机制失活并诱导细胞器中的Cd含量增加, 导致植株死亡。根中液泡的Cd贮存量较大, 解毒效果显著。     

Characterization of Cd translocation and identification of the Cd form in xylem sap of the Cd-hyperaccumulator Arabidopsis halleri

Arabidopsis halleri is a Cd hyperaccumulator; however, the mechanismsinvolved in the root to shoot translocation of Cd are not wellunderstood. In this study, we characterized Cd transfer fromthe root medium to xylem in this species. Arabidopsis halleriaccumulated 1,500 mg kg^–1 Cd in the shoot without growthinhibition. A time-course experiment showed that the releaseof Cd into the xylem was very rapid; by 2 h exposure to Cd,Cd concentration in the xylem sap was 5-fold higher than thatin the external solution. The concentration of Cd in the xylemsap increased linearly with increasing Cd concentration in theexternal solution. Cd transfer to the xylem was completely inhibitedby the metabolic inhibitor carbonyl cyanide 3-chlorophenylhydrazone(CCCP). Cd concentration in the xylem sap was decreased by increasingthe concentration of external Zn, but enhanced by Fe deficiencytreatment. Analysis with ¹¹³Cd-nuclear magnetic resonance (NMR)showed that the chemical shift of ¹¹³Cd in the xylem sap wasthe same as that of Cd(NO₃)₂. Metal speciation with Geochem-PCalso showed that Cd occurred mainly in the free ionic form inthe xylem sap. These results suggest that Cd transfer from theroot medium to the xylem in A. halleri is an energy-dependentprocess that is partly shared with Zn and/or Fe transport. Furthermore,Cd is translocated from roots to shoots in inorganic forms.     

镉在互花米草中积累、转运及亚细胞的分布

研究了在不同Cd浓度(0、5、100、200μg·g-1)处理下,互花米草花序、叶、茎、根茎、须根中Cd含量、积累量、转运特征,及Cd在互花米草体内的亚细胞分布。结果表明,Cd在互花米草不同器官中的积累能力存在较大差异。茎、根茎、须根中Cd含量及积累量随处理浓度的增加而升高,其中须根中Cd含量及积累量均高于其他器官。Cd处理浓度为100gμ·g-1时,花序和叶中Cd含量达到最大值,分别为8.65和7.82μg·g-1。在Cd处理浓度为200μg·g-1时,须根中Cd含量可高达390.00μg·g-1,积累量达3200μg·株-1。Cd在互花米草体内转运能力极低,绝大部分Cd积累在地下部位。Cd在互花米草亚细胞中的分布规律为细胞壁>胞液>细胞器。随着Cd处理浓度的增加,Cd在细胞壁中的分配比例增大,胞液中Cd分布比例则相应减小,细胞壁和胞液相互协调,增强互花米草对重金属Cd的耐性。     

镉在土壤-蔬菜-昆虫食物链的传递特征

通过温室盆栽试验,以两种蔬菜(小白菜和苋菜)和一种昆虫(斜纹夜蛾)幼虫为对象,研究了重金属镉(Cd)在土壤-蔬菜-昆虫食物链的传递特征以及两种蔬菜中Cd化学形态分布特征.结果表明： 随着土壤Cd处理浓度的升高,两种蔬菜生物量均显著下降(P<0.05),而其各器官中的Cd含量均显著上升(P<0.05),两种蔬菜各器官Cd含量大小顺序为苋菜茎>根>叶,小白菜茎>叶>根;食用小白菜和苋菜的斜纹夜蛾幼虫体内Cd含量随着土壤Cd处理含量的升高而升高,最高分别为36.7和46.3 mg·kg^-1,但粪便中Cd含量分别高达190.0和229.8 mg·kg^-1,表明斜纹夜蛾幼虫食入的Cd大部分通过粪便排泄出体外.小白菜和苋菜各器官Cd化学形态均以氯化钠提取态为主(>70%),其次为无机态和有机水溶态Cd(乙醇提取态和去离子水提取态),而不溶性Cd磷酸盐(醋酸提取态)、草酸盐结合态Cd(盐酸提取态)和残渣态均极低,这有利于重金属Cd在食物链中传递.斜纹夜蛾幼虫通过粪便排泄大量Cd以缓解Cd对自身的毒害,可有效限制Cd向下一营养级传递.小白菜和苋菜对Cd的富集性均较高,不宜在Cd高污染土壤种植.