No abstract

The absorption characteristics of Cd2' by 10-to 12-day-old soybean plants (Glycine max cv Williams) were investigated with respect to influence of Cd concentration on adsorption to root surfaces, root absorption, transport kinetics and interaction with the nutrient cations Cu2+, Fe2 , Mn2 , and Zn2 . The fraction of nonexchangeable Cd bound to roots remained relatively constant at 20 to 25% of the absorbed fraction at solution concentration of 0.0025 to 0.5 micromolar, and increased to 45% at solution concentration in excess of 0.5 micromolar. The exchangeable fraction represented 1.4 to 32% of the absorbed fraction, and was concentration dependent. Using dinitrophenol as a metabolic inhibitor, the 'metabolically absorbed' frction was shown to represent 75 to 80% of the absorbed fraction at concentration less than 0.5 micromolar, and decreased to 55% at 5 micromolar. At comparatively low Cd concentrations, 0.0025 to micromolar 0. Cadmium Uptake. Evaluation of the absorption behavior of Cd was performed using 10-to 12-d-old plants. Prior to use, plants were transferred from nutrient solutions to 0.5 mM CaCl2 solutions (pH 5.8) for 12 h to allow for desorption of possible interfering ions from root surfaces. Individual plants were then transferred to fresh 0.5 mm CaCl22 and various concentrations of CdCl2. CaCl2 was employed in all uptake and absorption solutions to provide sufficient Ca2`to maintain membrane permeability (20,22). For absorption periods of 60 min or less, 500 ml volumes were employed; for absorption periods of over 60 min, 1-L volumes were employed to limit reduction of total Cd levels in solution to less than 10% during the experiment.Solutions containing CdCl2 levels from 0.0025 to 5.0 liM were traced with carrier-free`°CdCI2, and adjusted to pH 5.8 with KOH. Following the absorption period, shoots were removed and roots were transferred to 0.5 mm CaCl2 solutions containing unlabeled CdCl2 at concentrations 20-fold higher than treatment concentrations. Roots were routinely desorbed using three changes of solution for a total of 2 h; in preliminary studies, desorbed '"Cd was measured in efflux solutions at 30-min intervals following 5-min wash in 0.5 mM CaC12.

A method is proposed for analysis of total nitrogen in plant tissues enabling predigestion (to reduce nitrate to ammonium) and digestion to be performed in a Folin‐Wu tube. Following digestion, a sensitive colorimetric assay for ammonium is used to quantitate N‐content in an aliquot of the digest. The proposed method has several advantages: 1) up to 110 tissue samples can be predigested and digested in one batch; 2) small tissue samples (5 to 100 mg) can be accommodated; 3) the colorimetric assay for ammonia is very sensitive; 4) tissues can be predigested to recover all nitrate in the samples; and 5) aliquot size from the diluted digest can be varied to effectively detect as little as 1 µg of N.

Soils amended with [14C]hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine (RDX) were sampled over 60 d and subjected to exhaustive Soxhlet extraction followed by HPLC analysis. RDX was the only radiolabeled compound observed in soil extracts. Emission of volatile organics and 14CO2 from soil accounted for only 0.31% of the amended radiolabel. Mass balance for RDX‐amended soil was better than 84% throughout the two‐month study. The analytical method developed for plants involved acid hydrolysis, solvent extraction, fractionation on Florisil® adsorbent and separation by HPLC. The described methodology allowed for RDX recovery of 86 ± 3% from fortified bush bean leaf tissue. Further experiments were conducted with bush bean plants maintained on RDX‐containing hydroponic solutions. Hydroponic plants did not emit detectable amounts of 14CO2 or radiolabeled volatile organics. Analysis of the plant tissue indicated bioaccumulation of RDX in the aerial tissues of hydroponic plants exposed for either 1 or 7 d. Metabolism of RDX to polar metabolites was observed in plants exposed for 7 d.

The findings of this report are not to be construed as official Department of the Army positions unless so designated by other authorized documents DISClAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor Battelle Memorial Institute, nor any of their employees, makes .tny wMr.Jnty, expressed or implied, or assumes .tny legal liability or responsibility for the accur.tcy, completeness, or usefulness of .1ny information, apparatus, product, or process disclosed, or represents th.tt its use would not infringe printely owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government of any agency thereof, or Battelle Memorial Institute. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

No abstract

The xylem exudates of soybean (Glycine max cv Williams), provided with fixed N, were characterized as to their organic constituents and in vivo and in vitro complexation of plutonium, iron, cadmium, and nickel. Ion exchange fractionation of whole exudates into their compound classes (organic acid, neutral, amino acid, and polyphosphate), followed by thinlayer electrophoresis, permitted evaluation of the types of ligands which stabilize each element. The polyvalent elements plutonium(IV) and iron(III) are found primarily as organic acid complexes, while the divalent elements nickel(II) and cadmium(II) are associated primarily with components of the amino acid/peptide fraction. For plutonium and cadmium, it was not possible to fully duplicate complexes formed in vivo by back reaction with whole exudates or individual class fractions, indicating the possible importance of plant induction processes, reaction kinetics, and/or the formation of mixed ligand complexes. The number and distribution of specific iron-and nickel-containing complexes varies with plant age and appears to be related to the relative concentration of organic acids and amino acids/peptides being produced and transported in the xylem as the plant matures.complexed forms in xylem exudates (1, 12), as do Mn and Zn in phloem exudates (15). Recently, xylem exudates have received increased attention in studies on the role of organic complexation in chemical stabilization and subsequent availability to animals of potentially toxic elements (3,19). The importance of complexation in plant transport process became known with the work of Tiffin (13) on Fe complexes in exudates. However, more recent studies have addressed the behavior of pollutant elements, such as Pu, Ni, and Cd, in plant exudates (4, 6, 10), and the composition and role of xylem exudate constituents in cation complexation (17)(18)(19). These studies have shown that a wide range of cations, even the most insoluble polyvalent element species such as Pu and Fe, are soluble and mobile in plant transport fluids, primarily as organically complexed species. Also, many nutrient and nonnutrient cations extracted from plant tissues (leaves, roots, and seeds) are soluble and associated with organic ligands of varying mol w (2, 5-7, 9, 10-12, 14, 16). This cation mobility and solubility would suggest that plant-produced organic ligands are important in the transfer of potentially toxic elements from plants to consuming animals.The objectives of this study were to characterize the major organic constituents of soybean xylem exudates, and to evaluate the in vivo and in vitro interactions and complexation of plutonium, iron, nickel, and cadmium with these constituents.

The use of plants to monitor heavy metal pollution in the terrestrial environment must be based on a cognizance of the complicated, integrated effects of pollutant source and soil-plant variables. To be detectable in plants, pollutant sources must significantly increase the plant available metal concentration in soil. The major factor governing metal availability to plants in soils is the solubility of the metal associated with the solid phase, since in order for root uptake to occur, a soluble species must exist adjacent to the root membrane for some rinlte period. The rate of release and form of this soluble species will have a strong influence on the rate and extent of uptake and, perhaps, mobility and toxicity in the plant and consuming animals. The factors influencing solubility and form of available metal species in soil vary widely geographically and include the concentration and chemical form of the element entering soil, soil properties (endogenous metal concentration, mineralogy, particle size distribution), and soil processes (e.g., mineral weathering, microbial activity), as these influence the kinetics of sorption reactions, metal concentration in solution and the form of soluble and insoluble chemical species.The plant root represents the first barrier to the selective accumulation of ions present in soil solution. Uptake and kinetic data for nutrient ions and chemically related nonnutrient analogs suggest that metabolic processes associated with root absorption of nutrients regulate both the affinity and rate of absorption of specific nonnutrient ions. Detailed kinetic studies of Ni, Cd, and Tl uptake by intact plants demonstrate multiphasic root absorption processes over a broad concentration range, and the use of transport mechanisms in place for the nutrient ions Cu, Zn, and K. Advantages and limitations of higher plants as indicators of increased levels of metal pollution are discussed in terms of these soil and plant phenomena.The principal objectives of this review are to briefly describe the soil and plant factors influencing trace metal uptake by plants, and, with this information as a basis, illustrate some of the parameters which must be considered in using higher plants as indicators of increased levels of metals in the terrestrial environment.In order to utilize plants as monitors of metal pollution in the field, it is necessary to distinguish between uptake arising from natural metal sources and from pollutant sources. Metals from both natural and pollutant sources have the potential for being assimilated by the plant through foliar or root absorption processes. The importance of foliar absorption processes for several heavy elements has been discussed elsewhere (1, 2). Separation of the sources of metals taken up by roots is complicated by the mediating effect of soil properties and soil and plant processes. These effects may be illus-* Battelle, Pacific Northwest Laboratories, Richland, Washington, 99352. trated by examination of the concentration of metals in soil relative to po...