Cadmium biosorption by a cadmium resistant strain of Bacillus thuringiensis: regulation and optimization of cell surface affinity for metal cations

A marine bacterial strain putatively identified asBacillus thuringiensis strain DM55, showed multiple heavy metal resistance and biosorption phenotypes. Electron microscopic studies revealed that DM55 cells are encased in anionic cell wall polymers that can immobilize discrete aggregates of cations. Factors affecting cell surface affinity for metal cations, monitored by means of Cd²⁺ binding capability, are investigated. The mechanisms of cadmium resistance and Cd²⁺ biosorption by the bacterium appeared to be inducible and coincident. Medium components affecting metal removal under cadmium-stressed growth conditions were explored based on the application of two sequential multi-factorial statistical designs. Concentrations of potassium phosphates and peptone were the most significant variables. Optimized culture conditions allowed DM55 cells grown in the presence of 0.25 mM CdCl₂ to remove about 79% of the metal ions within 24 h with a specific biosorption capacity of 21.57 mg g^–1 of biomass. Both fresh and dry cells of DM55 prepared under cadmium-free optimal nutrient condition were also able to biosorb Cd²⁺. In addition to the concentration of phosphate in the medium, KinA, a major phosphate provider in the phosphorelay of Bacillus cells, was also demonstrated to regulate the magnitude of cell surface affinity for cadmium ions.     

Hormonal Control of Tumor Formation in Radish

The role of phytohormones in genetic tumor formation on radish crop-roots was investigated using the collection of inbred Raphanus sativus lines as a model system. The genetic analysis showed that the trait <<tumor formation>> was recessive and monogenic in some crossings. The spectrum of main phytohormones in tumor and non-tumor radish lines has shown that at the initiation of tumor formation (30 days old plants) the amounts of main cytokinins in the lower part of plants from the tumor line were dramatically increased. The transformation of the non-tumor line by the ipt gene of Agrobacterium tumefaciens resulted in tumor formation in plants of the T₁ progeny. We propose that increasing the cytokinin/auxin ratio may lead to tumor formation on radish crop roots.     

Interactions between Cadmium and Nickel in Phytochelatin Biosynthesis and the Detoxification of the Two Metals in Suspension-Cultured Tobacco Cells

We examined the effects of simultaneous treatments with Cd and Ni on the phytochelatin (PC) biosynthesis in suspension-cultured tobacco (Nicotiana tobacum cv. Bright Yellow-2) cells. The induction of PC biosynthesis in response to Cd was not affected by the coexistence of Ni. Cd and Ni formed complexes with different compounds in cells.     

Responses of elongation growth rate,turgor pressure and cell wall extensibility of stem cells of Impatiens balsamina to lead,cadmium and zinc

Elongation growth rate of stem cells of Impatiens balsamina was inhibited by the heavy metals Pb²⁺, Cd²⁺ and Zn²⁺ due to their suppression on cell wall extensibility. Effective turgor was also inhibited by Pb²⁺ and Cd²⁺ but it played a secondary role in reducing the stem cell elongation growth rate. The major rate-limiting factor for cell elongation growth was the cell wall extensibility. Furthermore, Cd²⁺ was found to be more toxic than Pb²⁺, while Pb²⁺ was more toxic than Zn²⁺.     

Influence of Triadimefon on the Metabolism of NaCl Stressed Radish

The effect of triadimefon (TDM) on various biochemical parameters was studied in NaCl stressed radish (Raphanus sativus L.). Stress imposed by 80 mM NaCl decreased the protein content and proline oxidase activity, and increased the proline and glycine betaine contents, and protease, -glutamyl kinase and ATPase activities. The TDM treatment alleviated the stress by increasing protein, and glycine betaine contents, and by decreasing proline accumulation, and proline oxidase and ATPase activities.     

Changes in cell-wall polysaccharide composition of developingNitella internodes

Changes in the uronide, neutral-polysacharide, and cellulose composition of the cell wall ofNitella axillaris Braun were followed throughout development of the internodes and correlated with changes in growth rate. As the cells increased in length from 4 to 80 mm during development, the relative growth rate decreased. Cell wall thickness, as measured by wall density, increased in direct proportion to diameter, indicating that cell-wall stress did not change during elogation. Cell-wall analyses were adapted to allow determination of the composition of the wall of single cells. The total amounts of uronides, neutral sugars and cellulose all increased during development. However, as the growth rate decreased, the relative proportions of uronides and neutral sugars, expressed as percent of the dry weight of the wall, decreased, while the proportion of cellulose increased. The neutral sugars liberated upon hydrolysis ofNitella walls are qualitatively similar to those found in hydrolysates of higher plant cell walls: glucose, xylose, mannose, galactose, arabinose fucose and rhamnose. Only the percentage of galactose was found to increase in walls of mature cells, while the percentage of all other sugars decreased. The rate of apposition (g of wall material deposited per unit wall surface area per hour) of neutral polysaccharides decreased rapidly with decreasing growth rate during the early stages of development. The rate of apposition of uronides decreased more steadily throughout development, while that of cellulose, after an early decline, remained constant until dropping off at the end of the elongation period. These correlations between decreasing growth rate and decreasing rate of apposition of neutral sugars and uronides indicate that synthesis of these cell-wall components could be involved in the regulation of the rate of cell elongation inNitella.     

Protective Role of Thidiazuron Treatment on Cucumber Seedlings Exposed to Heavy Metals and Chilling

The action of thidiazuron, a synthetic growth regulator, was studied on 7-day-old cucumber seedlings (Cucumis sativus L., cv. Monastyrskii) exposed to chilling and sublethal concentrations of lead and copper ions. The extent of injury was assessed from the electrolyte leakage from cotyledonary leaves into distilled water. Separate application of each stress factor induced an increase in membrane permeability; however, their combined application caused a weaker response. A preliminary treatment of seedlings with thidiazuron fully or partly prevented the stress-induced stimulation of electrolyte leakage from cotyledon segments. It is concluded that thidiazuron elevates plant resistance to adverse environments.     

细胞壁在植物重金属耐性中的作用

植物细胞壁主要是由多糖、蛋白质和木质素等组成的一个复合体,广泛参与植物生长发育及对各种逆境胁迫的响应,是重金属离子进入细胞质的第一道屏障。本文主要综述了植物细胞壁主要成分,包括细胞壁多糖、细胞壁蛋白质和木质素,在响应重金属胁迫反应中的作用及其参与重金属耐性的机制,以期能对植物细胞壁在重金属耐性中的作用有更深入的了解。     

Cadmium Toxicity: The effect on Macro- and Micro-Nutrient Contents in Soybean Seedlings

The effect of Cd (10, 100, and 200 M) on tissue contents of macronutrients (N, P, K, Ca, Mg) and micronutrients (Fe, Zn, Cu, Mn) was investigated in hydroponically grown soybean (Glycine max) seedlings. Concentration changes of analysed elements observed against increasing Cd accumulation indicated that acute Cd-phytotoxic effect monitored through chlorophyll content was not a consequence of nutrient deficiency.     

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.     

Water Stress Induced Changes in Anatomy of Tomato Leaf Epidermes

Anatomical changes of leaf epidermes of tomato plants (Lycopersicon esculentum Mill. cv. INCA 9) submitted to water stress in the preflowering stage were studied. 20 d after germination, plants were subjected to three treatments: 1) 100 % of evapotranspired water was applied every day, 2) from 100 up to 10 % of evapotranspired water was applied every day, and 3) water supply was completely suppressed. Trichome density was similar in apical, middle and basal zones, and adaxial and abaxial leaf surfaces. Stomatal density and length, and epidermal cell length and width had similar values on the same leaf surface, but the values were higher on the abaxial than on the adaxial leaf surface. The water deficit had little effect on number of trichomes, length and width of epidermal cells and length of stomata, and decreased the stomatal density especially on adaxial surface.     

Changes in the cell wall of Clostridium species following passage in animals

Morphological changes in clostridial isolates after animal passage with other flora in mixed infections were studied by utilizing a subcutaneous abscess model in mice. We used 26 isolates of 7 clostridial species, and one isolate each of Bacteroides fragilis and Klebsiella pneumoniae. Abscesses were induced by all 7 Clostridium perfringens and 3 Clostridium butyricum isolates and by some of the other isolates. A thick granular wall prior to animal inoculation was shown only in C. perfringens, C. butyricum, and C. difficile. This structure was observed in other clostridia only following their animal passage alone or when co-inoculated with K. pneumoniae or B. fragilis.     

Changes in the Leaf Polypeptide Patterns of Barley Plants Exposed to Soil Flooding

Exposure of barley plants (Hordeum vulgare L.) to soil flooding for 72 – 120 h led to decrease in the content of the both subunits of ribulose-1,5-bisphosphate carboxylase/oxygenase. The effect was more pronounced on the small subunit. Further, the changes in protein pattern were observed, mainly proteins with molecular masses 30 – 85 kD were down-regulated. This revised version was published online in July 2006 with corrections to the Cover Date.     

NaCl-Induced Changes in Putrescine Content and Diamine Oxidase Activity in Roots of Rice Seedlings

The effects of NaCl on putrescine (Put) content and diamine oxidase (DAO) activity in roots of rice seedlings were examined. NaCl treatment lowered the content of Put and increased the activity of DAO in roots. Our current results indicate that Cl^– is not required for NaCl-induced decline in Put content and increase in DAO activity in roots. Put content in roots of rice seedlings exposed to NaCl is possibly regulated by DAO activity.     

Nitrogen Deprivation Induces Changes in the Leaf Elongation Zone of Maize Seedlings

The influence of nitrogen deprivation on leaf development and the biomechanics of leaf growth were studied using maize (Zea mays L.) seedlings grown under low irradiance. Although the nitrogen deprivation had no significant effect on photosynthesis, the leaf length, the leaf area, and the total assimilation area of plants decreased. The mature size of the epidermal cells was not altered, while the cells of nitrogen-deprived plants reached their final length closer to the leaf base than the epidermal cells of control plants. Decreases in the length of the growing zone (from 50 to 30 mm) and in the maximum value of relative elemental growth rate (from 0.08 to 0.06 mm mm^–1 h^–1) were observed in the nitrogen deprived plants. The maximal value of growth velocity in the control treatment was higher along the elongation zone, except for the basal 20 mm, where there was no significant difference between the control and the N-deprived plants. The net deposition rates of water and dry matter were also affected by nitrogen deprivation: the values of these features decreased and the spatial position of the maximum of the deposition rates shifted towards the leaf base.     

巨桉不同状态叶片浸提液对萝卜幼苗形态和抗性生理特性的影响

以珍珠岩作为基质,选择4年生巨桉(Eucalyptus grandis)嫩叶(T1)、老叶(T2)、表层凋落叶(T3)、腐解凋落叶(T4)4种状态的叶片,每种状态叶片设置3个浸提液浓度水平[分别称取风干叶片30g、15g和7.5g加入900mL蒸馏水进行浸提,以蒸馏水为对照(CK)],采用水培法研究了不同状态叶片浸提液对萝卜(Raphanus sativus)幼苗形态生长和抗性生理特性的影响。结果显示:(1)巨桉不同状态叶片浸提液显著抑制了萝卜幼苗的根长,其中嫩叶的抑制作用最强,腐解凋落叶抑制作用最弱。(2)各状态叶片浸提液处理后萝卜幼苗中过氧化氢酶(CAT)和过氧化物酶(POD)的活性均呈现升高趋势,嫩叶各浓度处理以及其他状态叶片的高浓度处理下超氧化物歧化酶(SOD)活性升高,而其余浓度处理的SOD活性降低。(3)各状态叶片浸提液处理萝卜幼苗的丙二醛(MDA)含量在低浓度处理时低于CK,其余处理下则高于CK。(4)嫩叶各浓度处理萝卜幼苗的可溶性糖(SS)含量显著高于CK,且随着老叶和表层凋落叶浸提液浓度的升高,幼苗SS含量先升后降,腐解凋落叶各浓度处理下则呈渐增的趋势;而可溶性蛋白(SP)含量则随浸提液浓度的增加而升高,且T2和T3两种状态叶片的各浓度处理与CK差异显著。研究表明,巨桉不同状态叶片浸提液对萝卜幼苗生长和抗性生理产生了强烈的抑制作用,其中以嫩叶最强,老叶和表层凋落叶次之,腐解凋落叶最弱。     

Stress Responses of Zea mays to Cadmium and Mercury

A hydroponic experiment was carried out to characterize the oxidative stress responses of maize seedlings (Zea mays L. cv. Dekalb DK604) to cadmium (Cd) and mercury (Hg). Plants were grown hydroponically for 7 days in a nutrient solution supplemented with several concentrations of Cd and Hg: 0.0 (control), 6 or 30 μM. Growth was inhibited by both metals. The effect was more severe in plants exposed to Hg. Oxidative stress was caused by the exposure to the metals, as quantified by malondialdehyde and carbonyl accumulation, by-products of lipid peroxidation and protein oxidation, respectively. The activity of ascorbate peroxidase (APX) and superoxide dismutase (SOD), enzymes involved in the scavenging of reactive oxygen species, were measured upon metal treatment. We found an activation of a cytosolic APX isoform, as identified by using a specific polyclonal antiserum. However, there were negligible changes in SOD activity. Analysis of thiol-peptides revealed that at 6 μM Cd a remarkable increase in root reduced glutathione (GSH) content occurred, and little effect on the relative content of oxidised glutathione (GSSG) was observed. However, at 30 μM Cd and in plants exposed to 6 and 30 μM of Hg, GSH root content either remained stable or decreased significantly, while the proportion of GSSG increased. Moreover, only Cd was able to induce accumulation of phytochelatins at both assayed concentrations. Apparently, Hg was more toxic than Cd, as inferred from the magnitude of the changes found in the physiological parameters tested.     

Calcium Ameliorates Effects of Lead in Protonema of Funaria hygrometrica Hedw.

Two-days-old in vitro grown protonemata of Funaria hygrometrica Hedw. were treated with a mixture PbCl₂ (4 M Pb²⁺) and CaCl₂ (16 M Ca²⁺) (Ca+Pb) for 48 h. The results were compared with the control: distilled water (H₂O) and the solution of PbCl₂ (4 M Pb²⁺) (Pb). Protonemata treated with Ca+Pb were longer and contained more cells than those treated with Pb. Moreover, a lower number of cells showed apical cell deformations typical for lead toxicity: swollen tips and wall thickenings at the apex. If deformations were present they were not as extended as in Pb. In comparison with the control, however, protonemata treated with Ca+Pb were shorter, contained a lower number of cells and some apical cells in this material were altered. It can be concluded that the presence of calcium partially neutralised toxic effects of lead in Funaria hygrometrica protonemata cells.     

Effect of Increasing Concentrations of Lead and Cadmium on Cucumber Seedlings

The effect of lead and cadmium on biomass accumulation of cucumber seedlings (Cucumis sativus L.) as well as the contents of abscisic acid (ABA), free proline and soluble proteins in leaves were studied. Seedlings were subjected to lead nitrate or cadmium bromide in low concentrations (1 – 5 µM) for 1, 4 or 7 d, and then to the action of the same substances in high concentrations (500 – 1000 µM). The pretreatments of the seedlings with heavy metals in low concentrations enabled them to tolerate the subsequent high concentrations of cadmium and lead without injury. The plant responses to heavy metal treatment were accompanied by the accumulation of ABA, free proline and soluble proteins in leaf tissues.     

The Role of Abscisic Acid in Acclimation of Plants Cultivated in vitro to ex vitro Conditions

The content of endogenous free abscisic acid (ABA) in the shoots of in vitro cultivated tobacco (Nicotiana tabacum L. cv. White Burley) and its changes during ex vitro acclimation of these plants to the greenhouse or growth chamber were estimated. The content of free ABA significantly increased at the 1^st and/or 2^nd day after plant transfer from in vitro to ex vitro. The ABA content of plants covered with transparent foil to maintain higher relative humidity (RH), did not significantly differ from ABA content of plants cultivated under ambient RH. Transfer to fresh medium also transiently increased the content of endogenous ABA. The ABA content in plants, which had been acclimated for 1 week to ex vitro conditions, decreased to the content found in the in vitro plants. Acclimation to ex vitro conditions affected the stomata on adaxial and abaxial sides differently: stomata on the adaxial side were less open than those on the abaxial one. The exogenous application of 5 μM ABA increased transiently its endogenous concentration in shoots of in vitro plants more than ten fold, but after 1 week the concentration in the shoots decreased. This revised version was published online in July 2006 with corrections to the Cover Date.