Interaction of Pb and Cd with gum kondagogu (Cochlospermum gossypium): A natural carbohydrate polymer with biosorbent properties

Gum kondagogu (Cochlospermum gossypium), an exudates tree gum from India was explored for its potential to decontaminate toxic metals (Pb²⁺ and Cd²⁺). Optimum biosorption of metals were determined by investigating the contact time, pH, initial concentration of metal ions and biosorbent dose at 25 ± 2 °C. The maximum metal biosorption capacity for gum kondagogu was observed for Pb²⁺ (48.52 mg g⁻¹) and Cd²⁺ (47.48 mg g⁻¹) as calculated by Langmuir isotherm model. Kinetic studies showed that the biosorption rates could be described by pseudo-second-order expression. The metal interactions with biopolymer were assessed by FT-IR, SEM–EDXA and XPS analysis. Results based on these techniques suggest that mechanism of metal binding by the biopolymer involves micro-precipitation, ion-exchange and metal complexation.     

不同苗龄伊贝母根系分泌物GC-MS分析

以不同苗龄伊贝母幼苗为试验材料,采用连续收集法收集伊贝母不同苗龄根系分泌物,并采用气相色谱质谱联用技术(GC-MS)分析了根系分泌物的组分和含量.结果表明:一、二、三、四年苗龄伊贝母幼苗根系分泌物化合物在含量上存在较大差异,醛酮类化合物含量最多,分别为57.90%、74.15%、59.66%、59.32%.脲类、苯酚类、醇类含量较小,均在0.5%以下.但不同苗龄根系分泌物在种类和组成上相似,连续捕获系统获得的根系分泌物种类丰富,主要为有机物,包括烷烃类、酯类、醚类、烯烃类、苯酚类等有机物质.     

石油污染土壤中菲、蒽和正十六烷的微生物降解

在模拟自然条件下,考察了芳香烃(菲、蒽)和脂肪烃(正十六烷)单独存在以及共存于土壤中时,土著微生物对它们降解的影响。结果表明,土著微生物对它们的降解均符合一级反应动力学。菲、蒽或正十六烷单独存在于土壤中时,其微生物降解速率常数分别为0.0226、0.0283和0.0096 d^-1。菲和正十六烷共存时,正十六烷能够作为土著微生物降解菲的共代谢底物,促进菲的降解,使菲的半衰期比其单独存在于土壤中缩短44%;同时,正十六烷的加氧酶被菲诱导,使其活性提高而增强对正十六烷的降解作用,其微生物降解半衰期比其单独存在于土壤中缩短49%。菲和蒽共存促进了土著微生物对菲的降解,却抑制了对蒽的降解。     

Relationships between cell membrane stability, exudate content and infectivity of Bradyrhizobium japonicum strain 639 to boron starved soybean plants

The influence of boron starvation on the root exudates content in soybean seedlings (Glycine max. L. Merr.) and the effect of exudates pretreatment on the pre-infection processes in symbiotic system Br. japonicum strain 636 and soybean were investigated. Root cell membrane stability of boron starved soybean plants (-B) decreased compared to the control. The concentrations of all analyzed metabolites (reducing sugars, free amino acids, organic acids, soluble phenols and total flavonoids) from root exudates of -B plants were lower than the control concentrations. Analysis of polyphenols after HPLC chromatography of root exudates showed significant difference of peak numbers between chromatograms of exudates obtained from boron starved and from control plants. Bacterial culture treatment with root exudates from -B plants showed decreased growth, chemotaxis and attachment ability toward the host root compared to the control exudate treatments. These changes were accompanied by decreased nodulation and acetylene reduction activity of boron starved soybean plants.     

Specialized 'dauciform' roots of Cyperaceae are structurally distinct, but functionally analogous with 'cluster' roots

When grown in nutrient solutions of extremely low [P] (相似文献   

Three ent-trachylobane diterpenes from the leaf exudates of Psiadia punctulata

Three ent-trachylobane diterpenes have been isolated from the leaf exudates of Psiadia punctulata and characterised as 6α,17,19-ent-trachylobantriol; 2α,18,19-ent-trachylobantriol; and 2β,6α,18,19-ent-trachylobantetraol. The structures were determined on the basis of spectroscopic evidence.     

Banana Rhizodeposition: Characterization of Root Border Cell Production and Effects on Chemotaxis and Motility of the Parasitic Nematode Radopholus similis

Rhizodeposition was collected from root tips of banana (Musa acuminata). Two varieties, Grande naine and Yangambi km5, susceptible and resistant towards the burrowing nematode Radopholus similis, respectively, were examined for root border cell production under in vitro and in soil growing conditions. Two types of cells were observed in rhizodeposition: spherical cells containing large amyloplasts, called statocytes (8% of total), and long ellipsoidal border cells (92%). Border cell production was high, related to root length and not different between the two cultivars. Rhizodeposition from plants grown in soil contained similar amounts of border cells, but viability was lower than in in vitro grown plants. Chemotaxis and motility assays were performed to test the effects of banana roots, roots without rhizodeposition, rhizodeposition, exudates and border cells on the behaviour of R. similis. Roots of both the susceptible and resistant variety attracted R. similis, but only in the presence of rhizodeposition. Isolated rhizodeposition of Yangambi km5 also attracted nematodes. Border cells and exudates did not affect nematode chemotaxis. Roots of both varieties induced quiescence in R. similis in the chemotaxis assay. Thirty to fifty percent of the nematodes became temporary quiescent in the motility assay with rhizodeposition and exudates. The effect lasted for 24 h for Grande naine and up to 3 days for Yangambi km5. Rhizodeposition collected from plants grown in soil affected neither R. similis chemotaxis nor motility. Overall, there were no indications that rhizodeposition is involved in preformed resistance against R. similis in Yangambi km5.     

Effects of pH,Ca and Al on the exudation from clover seedlings of compounds that induce the expression of nodulation genes inRhizobium trifolii

The expression of nodulation genes inR. trifolii is induced by flavone compounds present in clover root exudates. In the present experiments a bioassay with an indicator strain ofR. trifolii, which contained thelacZ gene fromEscherichia coli fused to theR. trifolii nodA gene, was used to measure the level ofnod gene expression inR. trifolii. Compounds that stimulatednodA gene expression were shown to be present in exudates of white clover (Trifolium repens L.) and nine cultivars of subterranan clover (T. subterraneum L.) seedling sgrown at a range of pH between pH 3.0 and pH 8.0. Thenod gene-induction activity of exudates was, however, reduced when seedlings of all clover species were grown at pH>7.0 and at pH<4.0 and pH<5.0 for white clover and subterranean clover respectively. No major differences were apparent in the activity of exudates from seedlings of the various cultivars of subterranean clover.Nod gene-induction activity of exudates was shown to increase markedly with seedling age. The presence of Ca at concentrations up to 10 mM in seedling culture solutions also resulted in marked increases in thenod gene-induction activity of seedling exudates. Increases in activity due to the presence of Ca were most apparent at low pH where between 5 and 10-fold increases were observed for white clover and subterranean clover respectively. Conversely, the presence of Al at concentrations up to 60 M in seedling culture solutions had no effect on thenod gene-induction activity of seedling exudates.The observations that both low pH and Ca concentrations affected thenod gene-induction activity of seedling exudates suggested that the net presence of stimulatory flavones in root exudates was an important contributing factor to the acid-sensitive step in nodule formation.     

Effect of a phosphate solubilizing bacteria on maize growth and root exudation over four levels of labile phosphorus

The influence of inoculation with phosphate-solubilizing bacteria (Enterobacter agglomerans) on maize growth, P uptake and root exudation was studied. Plants were grown in an axenic culture device where P was supplied as soluble phosphate at different contents (0, 5, 15 or 25 ppm) in the nutrient solution and as insoluble rock phosphate added to the culture sand. Experimental device was successfully used to obtain axenic root systems or good establishment of the inoculated strain in the rhizosphere of maize (10⁹ bact. g⁻¹ dry rhizospheric material). Plant growth was promoted by inoculation only for 5 or 15 ppm of soluble P in the nutrient medium without any significant effect on P uptake by the plant, suggesting that the quantities of P released by bacterial rhizospheric activity were very small. Amounts of organic compounds (total C and water-soluble C) exuded were relatively low (3.0 to 6.4% of the total plant biomass) and were reduced by bacterial inoculation when plant growth was largely promoted. Carbon balance modification and plant growth hormone production by the inoculated strain were suspected and discussed.     

Metal speciation in xylem and phloem exudates

Summary Two computer programs based on simultaneous chemical equilibria were compared for calculation of chemical species in xylem exudates. The first program, CHELATE, was developed to calculate the chemical species in xylem exudates while GEOCHEM was developed to calculate the speciation of natural aquatic systems. The output of the two programs should be similar since they are based on similar calculations. Data input to the programs consisted of concentration data for Ca, Cu, Fe, Mg, Mn, Zn, NH₄, PO₄, pH and 28 organic ligands reported for xylem exudates from soybean (Glycine max (L.) Merr.) and tomato (Lycopersicon esculentum Mill.) plants grown in nutrient solution¹⁷. The organic ligands included amino acids and low molecular weight organic acids (e.g., citric and malic). With the exception of Fe, there were large differences between CHELATE and GEOCHEM in the calculated speciation of nearly all metals in the xylem exudates. In general, there was better agreement between the programs for the speciation of alkaline earth metals than for transition metals. Discrepancies between the two programs were attributed to differences in 1) species considered and 2) stability constants. GEOCHEM considered a greater number of possible complexes. In addition, stability constants for some complexes differed by as much as 10 fold between the two programs. When the data base for GEOCHEM and CHELATE were the same, the output from CHELATE and GEOCHEM was almost identical. Thus, computations performed by the two programs are equally valid, but it is essential that the data base used in chemical models be verified before interpreting the output. Average concentration data for Al, Au, Ca, Cu, Fe, K, La, Mg, Mn, Na, Rb, Zn, Cl, MoO₄, PO₄, SO₄, HVO₄, pH and 18 organic ligands in phloem exudates from Yucca (Yucca flaccida Haw.) were complied from available literature and analyzed by GEOCHEM. Amino acids were the predominant organic ligand analyzed. Calculations revealed that alkali metals existed almost totally as the free ionic species (≥99%) whereas alkaline earth metals were transported as complexes with organic acids (oxalic, malic, and asparagine). Aluminum and Fe were present as hydroxyl species while <1% of micronutrients were transported as the free ion. Major micronutrient species were Cu-glutamine, Mn-asparagine and Zn-alanine. Information on calculated species present in phloem exudates could be useful to guide studies for isolation of metal-ligand complexes in phloem exudates.