[en] The mechanisms underlying heavy metal accumulation, toxicity and tolerance in higher plants are poorly understood. Since subcellular processes are undoubtedly involved in all these phenomena, it is of interest to study the extent of, subcellular site of and nature of intracellularly accumulated cadmium in higher plants. Whole plants supplied ¹⁰⁹CdCl₂ or ¹¹²CdSO₄ accumulated Cd into roots and aerial tissues. Preparation of protoplasts from aerial tissue followed by subcellular fractionation of the protoplasts to obtain intact vacuoles, chloroplasts and cytosol revealed the presence of Cd in the cytosol but not in vacuoles or chloroplasts. Particulate materials containing other cell components were also labeled. Of the ¹⁰⁹Cd supplied to plants, 2 to 10% was recovered in both cytosol preparations and in particulate materials. Cytosol contained proteinaceous--Cd complexes, free metal and low molecular weight Cd complexes. Labeling of protoplasts gave similar results. No evidence was obtained for the production of volatile Cd complexes in tobacco

[en] The resonance-like excitation function that is observed in (π⁺, π^-)-reactions near 50 MeV in all investigated nuclei, has not been explained by conventional reaction mechanisms. We demonstrate that the world data base is reproduced with few parameters assuming a narrow resonance in the πN N-subsystem with mass 2065 MeV, J^P=0^- and isospin even. (author). 15 refs, 5 figs

[en] Three experimental activities related to the question of short-range correlations (SRCs) in nuclei are reported. The shell-model occupancy of 3s protons in ²⁰⁸Pb has been determined by the CERES method to be (77 ± 9)%. The depletion exceeds that predicted from long-range correlations alone, but is weaker than predicted from some models accounting for SRCs. More direct evidence for SRCs is expected from (γ,2N) experiments with 100 ≤ E_γ ≤ 500 MeV performed at MAMI-B. As a very promising first result we are able to present ⁶Li(γ,pn) cross sections whose energy dependence for transitions from the 1p and 1s shells, respectively, differ remarkably. Finally, in studying pionic double-charge-exchange reactions which are known to depend on nucleon-nucleon correlations in nuclei, we discovered a candidate for a narrow πNN resonance called d' with I(J^P) = 0(0^-) at 2.06 GeV. The various experiments pursued in the hunt for this dibaryon state are described. (author)

[en] The mechanisms underlying heavy metal accumulation, toxicity, and tolerance in higher plants are poorly understood. Since subcellular processes are undoubtedly involved in all these phenomena, it is of interest to study the extent, subcellular site and nature of intracellularly accumulated cadmium in higher plants. Whole plants supplied ¹⁰⁹CdCl₂ or ¹¹²CdSO₄ accumulated Cd into roots and aerial tissues. Preparation of protoplasts from aerial tissues followed by subcellular fractionation of the protoplasts to obtain intact vacuoles, chloroplasts and cytosol revealed the presence of Cd in the cytosol but not in vacuoles or chloroplasts. No evidence was obtained for the production of volatile Cd complexes in tobacco

[en] The paper addresses the question of which open problems might be attacked with the NIKHEF (e,e'p) facility now being in operation. To this aim after a brief status summary of proton removal experiments, i.e. (p,2p), (e,e'p) and (d,³He) reactions, the uncertainties in our treatment of the reaction mechanisms are recorded. Then a list of open nuclear structure problems is presented which are within reach of present facilities. (Auth.)

[en] Vacuolar-extravacuolar compartmentation studies were performed to determine if the vacuole serves as an accumulation site for Cd, Zn, and Ni, after growth of Datura cultured cells in trace and high levels of these metals. After 3 to 4 days growth with 0.12 μM Cd or 0.02 μM Ni (radiolabeled) no evidence was obtained for vacuolar accumulation of these metals. In contrast, growth with 30 or 45 μM Cd, 11 μM Ni (with or without trace radiolabel), or 300 and 500 μM Zn resulted in isolated vacuoles which were enriched in metal. Compartmentation after exposure to low levels of Zn and also Cu is being investigated as is the subcellular site(s) of Cd-binding peptide formed during growth in high Cd. The hypothesis that Zn is accumulated as vacuolar organic acid salts is being tested directly because no evidence was found for formation of substantial ligand of Cd-peptide in response to Zn exposure

[en] Comparison of amino acid composition and sequence of tobacco Cd-binding peptide from leaves of plants grown in 3 or 90μM Cd and cultured cells (90μM Cd) with that of rat liver metallothionein (MT) demonstrate the unrelatedness of these molecules. Differences in structure are further shown by the lack of cross reactivity between the Cd-peptide and antibodies raised against MT. Studies of the effects of pII and salt (GuHCl) on Cd binding indicate that MT binds the metal with a higher affinity than does tobacco Cd-peptide (50% dissociation at pH 3.5 and 5.0, respectively). Suspension-cultured tobacco cells were grown in the presence of ³⁵S and 90μM Cd, 90μM Cd+150μM Zn or 150μM Zn and labeled ligand (³⁵S) was only formed when Cd was present. Efforts to demonstrate Zn binding to ligand of Cd-peptide in vitro were unsuccessful. Studies of Cu inducibility and binding to ligand are in progress. MT is inducible by Cu, Zn, Cd and other heavy metal and a number of the proposed functions of this protein in animals involve Cu and Zn binding. The question of Zn and Cu binding to plant Cd-peptides is crucial to understanding the function(s) of these Cd-inducible, Cd-accumulating forms

[en] Cadmium complexes with apparent molecular weights of 10,000 were observed in aqueous extracts of Cd-treated cabbage (Brassica capitata L., cv. red danish) and tobacco (hybrid of Nicotiana glauca and N. langsdorffii) plants. The amount of complex (as Cd) recovered was found to be dependent on the concentration of the metal in the growth medium and the total time of exposure of plants to the metal. Induction of the complex at moderate levels of ¹¹²Cd exposure was monitored after labeling the complex with ¹⁰⁹Cd in vitro. The constitutive nature of the ligand of the complex in cabbage and tobacco leaves was suggested when control plant extracts were exposed to ¹⁰⁹Cd. Such extracts contained ¹⁰⁹Cd, which eluted froom Sephadex G-50 in the region of Cd complex. Simultaneous labeling with ¹¹²Cd and ³⁵S or ³²P indicated that the complex contained sulfur but probably not phosphorus. The amount of ³⁵S which eluted coincident with ¹¹²Cd complex increased during complex induction. No evidence was found for the presence of 10,000 molecular weight Cd complex in stem exudates (vascular sap) of Cd-treated plants. The results obtained are consistent with the presence in these tissues of a ligand which is both inducible and consitutive and binds Cd in mercaptide bonds. All of these properties and oters reported earlier, are characteristic of Cd-metallothionein formed in animals

[en] Pion-nucleon scattering and charge-exchange experiments aim at a determination of the pion-nucleon coupling constant, the sigma term of chiral symmetry breaking in non-perturbative QCD and the possible isospin breaking of strong interactions. A review of the present situation shows that the accuracy of the results is still limited by the existing data base despite 20 years of experimental efforts at meson factories. The present new generation of experiments at PSI and TRIUMF, using novel instrumentation, promises considerable progress. (author)

[en] Ca-oxalate crystal containing cells from detached glandular heads of trichomes from Nicotiana tabacum, TI 1068, are capable of converting [1-¹⁴C] ascorbic acid (AA) and [1-¹⁴C] glyoxylic acid (GA) to oxalate. AA was found to be a better precursor for oxalate formation than GA. In detached glandular heads, 3.6x more label was converted to oxalate from AA than from GA, in the epidermis the factor was 3x while that with petiole tissue was 7x. Oxalate formation from AA, in detached glandular heads, was only partially inhibited in the dark and in the presence of metabolic inhibitors, suggesting that a nonenzymatic component might be involved. Oxalate formation from GA increased in the presence of metabolic inhibitors. During treatment of detached glandular heads with 2 mM Ca-acetate for 2 days, oxalate formation from AA was stimulated 3 fold, while the presence of 2mM Ca-acetate had no effect on the oxalate formation from GA. These results suggest that Ca²⁺ stimulates the formation of Ca-oxalate crystals in glandular head cells, and that AA can serve as a precursor for oxalate production