Release of iron from ferritin by semiquinone, anthracycline, bipyridyl, and nitroaromatic radicals

The cytotoxicity of many xenobiotics is related to their ability to undergo redox reactions and iron dependent free radical reactions. We have measured the ability of a number of redox active compounds to release iron from the cellular iron storage protein, ferritin. Compounds were reduced to their corresponding radicals with xanthine oxidase/hypoxanthine under N₂ and the release of Fe²⁺ was monitored by complexation with ferrozine. Ferritin iron was released by a number of bipyridyl radicals including those derived from diquat and paraquat, the anthracycline radicals of adriamycin, daunorubicin and epirubicin, the semiquinones of anthraquinone-2-sulphonate, 1,5 and 2,6-dihydroxyanthraquinone, 1-hydroxyanthraquinone, purpurin, and plumbagin, and the nitroaromatic radicals of nitrofurantoin and metronidazole. In each case, iron release was more efficient than with an equivalent flux of superoxide. Introduction of air decreased the rate of iron release, presumably because the organic radicals reacted with O₂ to form superoxide. In air, iron release was inhibited by superoxide dismutase. Semiquinones of menadione, benzoquinone, duroquinone, anthraquinone 1,5 and 2,6-disulphonate, 1,4 naphthoquinone-2-sulphonate and naphthoquinone, when formed under N₂, were unable to release ferrin iron. In air, these systems gave low rates of superoxide dismutase-inhibitible iron release. Of the compounds investigated, those with a single electron reduction potential less than that of ferritin were able to release ferritin iron.     

The influence of creosote compounds on the aerobic degradation of toluene

The inhibiting effect of 14 typical creosote compounds on the aerobic degradation of toluene was studied in batch experiments. Four NSO-compounds (pyrrole, 1-methylpyrrole, thiophene, and benzofuran) strongly inhibited the degradation of toluene. When the NSO-compounds were present together with toluene, little or no degradation of toluene was observed during 16 days of incubation, compared with a total removal of toluene within 4 days when the four compounds were absent. Indole (an N-compound) and three phenolic compounds (phenol, o-cresol, and 2,4-dimethylphenol) also inhibited the degradation of toluene, though the effect was much weaker that of the four NSO-compounds. O-xylene, p-xylene, naphthalene and 1-methylnaphthalene seemed to stimulate the degradation even though the influence was very weak. No effects of benzothiophene (an S-compound) and quinoline (an N-compound) were observed. Benzofuran (an O-compound) was identified as the compound that most inhibited the degradation of toluene. An effect could be detected even at low concentrations (40 g/l).Abbreviations bf benzofuran - bt benzothiophene - dmp 2,4-dimethylphenol - GC gas chromatograph - ind indole - mnap 1-methylnaphthalene - MAH monoaromatic hydrocarbons - mpyr 1-methylpyrrole - nap naphthalene - o-cre o-cresol - o-xyl o-xylene - phe phenol - pyr pyrrole - p-xyl p-xylene - tol toluene - thi thiophene - qui quinoline     

Iron toxicity and other chemical soil constraints to rice in highland swamps of Burundi

Iron toxicity is suspected to be a major nutritional disorder in rice cropping systems established on flooded organic soils that contain reductible iron. A pot trial was carried out to assess Fe toxicity to rice in flooded Burundi highland swamp soils with a wide range of organic carbon contents. Soil and leaf analyses were performed and total grain weight was determined. Clear Fe toxicity was diagnosed, based on leaf Fe content at panicle differentiation. Leaf Fe contents higher than 250 g g^–1 dry matter induced lower Mg (and probably Mn) uptake, and a 50% total grain weight reduction. These features were associated with exchangeable Fe equivalent fractions higher than 86%. Besides, several non-Fe toxic soils exhibited an Mg-Mn imbalance.     

Effect of nitrogen supply on frost resistance, nitrogen metabolism and carbohydrate content in white clover (Trifolium repens)

Effects of mineral nitrogen (2, 4, 6 and 8 m M NH₄NO₃) and nodulation with Rhizobium on frost hardiness in seedlings of white clover ( Trifolium repens ) have been studied. Seedlings of a population from Bodø (67°N lat.) were grown in Leonard jars under controlled conditions in a phytotron. For induction of frost hardening, plants were first exposed to 12 h photoperiod conditions for 2 weeks at 18°C, then for 2 weeks at 6°C and finally for 2 weeks at 0.5°C. Frost hardiness after treatments at 6 and 0.5°C was significantly enhanced by increasing nitrogen supply and was positively correlated with total nitrogen content of the stolons. Frost hardiness of nodulated plants correlated to the tissue nitrogen concentration. Content of soluble proteins in stolons decreased during hardening at 6°C but did not change during treatment at 0.5°C. There were minor changes in total amount of free amino acids during hardening. Both absolute and relative amounts of proline and arginine increased, and those of asparagine decreased during hardening. Absolute amounts of all free amino acids increased with increasing nitrogen supply, but the changes during hardening were similar in all treatments. There was a significant increase in the content of soluble carbohydrates during hardening. However, this increase was inversely related to nitrogen supply.     

Accumulation of calcium, potassium and magnesium in apple fruits under various conditions of humidity

In each of two experiments done under controlled conditions, starting at bloom, 4 humidity treatments were applied to potted trees of apple ( Malus pumila Mill. cv. Cox's Orange Pippin), i. e. in experiment 1: (1) high humidity throughout, (2) low humidity throughout, (3) low humidity for 7 weeks followed by high humidity for 6-7 weeks, and (4) the reverse (first high and then low humidity); in experiment 2: (1) day/night humidity high/high, (2) low/low, (3) low/high, and (4) high/low.
In both experiments high humidity favoured shoot growth appreciably. Change from low to high humidity after 7 weeks resulted in some growth stimulation but in the reverse situation growth was markedly reduced. Shoot growth responded little to different night humidities. In the two experiments fruit growth was little affected by treatments. In experiment 2 irrespective of night humidity, water consumption was higher at low than at high day humidity. In the high/low humidity regime water use during the night was high and leaf water potential low, relatively; during the day water potential was little affected by treatments.
At any time leaf Ca and Mg were clearly highest at low day humidity; night humidity had no effect. Leaf K did not respond to treatments. Fruit Ca at high humidity throughout was lower than at low humidity throughout. Increasing humidity later in the season was ineffective but a decrease at that time tended to reduce fruit Ca slightly. The clearly lowest Ca values occurred in the high/low day/night treatment. Fruit K and Mg were not or hardly affected by treatments.
The findings are discussed in terms of humidity effects on transpiration, shoot and fruit growth, and xylem mineral concentration and ion exchange translocation along the xylem walls.     

Bio-availability of phosphorus in sediments of the western Dutch Wadden Sea

The purpose of this study was to make a prognosis of the effects of extended purification of terrestrial waste water, reaching the Wadden Sea by the River Rhine and Lake IJssel, on the phosphate concentration in the western Wadden Sea.The quantities of different phosphorus fractions in intertidal and subtidal sediments of the Marsdiep tidal basin (western Dutch Wadden Sea) were measured. Different methods are applied to determine the amount of phosphorus that can be released from these sediments. The direct bioavailability is determined by inoculating sediment suspensions with a natural mixture of precultured micro-organisms from the sampling area. A second approach is the measurement of the phosphate release under different redox conditions. Sequential extraction of sediment samples with different solvents is also applied. Under the present conditions and compared to the nutrient loads from fresh water (Lake IJssel) and from the North Sea, the phosphorus stored in the sediments of the western Dutch Wadden Sea plays a minor role in the total supply to micro-algae and bacteria. The bulk of the biologically available phosphorus in the sediments originates from the metal-associated fraction. Releasable phosphate may contribute to the local annual primary production to an extent of ca 45 to ca 150 g C m^–2 a^–1. The total amount of phosphorus in the sediment (mainly calcite associated) is twice to 6 times the biologically available amount.     

Direct resolution of enantiomers of basic imidazol-2-yl-substituted alcohols by gas chromatography on chirasil-val

The direct resolution of enantiomers of a series of imidazol-2-yl-substituted alcohols has been achieved by gas chromatography on a well-deactivated fused-silica capillary column, coated with L -Chirasil-Val as the chiral stationary phase. The separation of these basic compounds is accomplished without exaggerated peak tailing. Compared to simpler alcohols the resolution factors (α) observed are extraordinarily large. While the imidazolyl substituent may contribute to the mechanism of the chiral discrimination, the crucial interaction is assumed to be through the hydroxy group, based on the observation that the resolution factors for the corresponding O-acetyl derivatives are markedly reduced. © 1993 Wiley-Liss, Inc.     

EPR Spin Trapping Study of the Decomposition of Azo Compounds in Aqueous Solutions by Ultrasound: Potential for Use as Sonodynamic Sensitizers for Cell Killing

Sonodynamic therapy, a promising new approach to cancer treatment, is based on synergistic cell killing by combination of certain drugs (sonosensitizers) and ultrasound. Although the mechanism of sonodynamic action is not understood, the role of free radicals produced from sonosensitizers by ultrasound is implicated. In this work, we studied formation of free radicals during the decomposition of several water-soluble azo compounds by 50 kHz ultrasound in aqueous solutions. Using the spin trap 3, 5-dibromo-4-nitrosobenzene sulfonate (DBNBS) tertiary carbon-centered radicals from 2, 2'-azobis (N,N'-dimethyl-eneisobutyramidine) dihydrochloride (VA-044), 2-(carbamoylazo)-isobutyronitrile (V-30), and 2, 2'-azobis (2-amidinopropane) dihydrochloride (AAPH) and CH3 radicals from 1, 1'-azobis (N,N'-dimethylformamide) (ADMF) were detected in argonsaturated solutions and the corresponding oxygen-centered radicals (alkoxyl and peroxyl) from VA-044, V-30, and AAPH were identified using the spin trap 5, 5'-dimethyl-l-pyrroline-N-oxide (DMPO) in aerated sonicated solutions. No free radicals from 4, 4'-dihydroxyazobenzene-3, 3'-dicarboxylic acid, disodium salt (DHAB) could be found in either system. While VA-044 and AAPH could also be readily decomposed by heat (42.5°C and 80°C), V-30 decomposition only occurred in the ultrasound-exposed solutions. The most likely mechanism of decomposition of azo compounds by ultrasound is their thermolysis in the heated shell of the liquid surrounding ca vita ting bubbles driven by ultrasound and/or by pyrolysis inside these bubbles. Experiments using scavengers of ·OH and ·H, which are produced by sonolysis in aqueous solutions, demonstrated that these radicals are not involved in the ultrasound-mediated radical production from the azo compounds. Due to the known cytotoxic potential of free radicals produced from azo compounds, the use of these compounds as ultrasound sensitizers appears to be a promising approach for sonodynamic cell killing.     

Drought stress of apple trees alters leaf emissions of volatile compounds

Actively growing potted apple trees ( Malus domestica [L.] Borkh. ev. Delicious) unacclimated to drought stress were subjected to drought to determine changes in emissions of leaf volatile compounds. Drought stress was imposed over a 2-week period by weighing pots every 2 or 3 days and adding water hack to an arbitrary and decreasing traction of the original pot weight. Stem water potential was -2.7. -2.0 and -0.8 MPa for the severely stressed, moderately stressed and control trees, respectively. 13 days alter watering treatments were begun. Water use the last 4 days of the experiment was about one-half for the moderately and severely stressed trees compared to that of the controls Twenty-nine volatile compounds were identified by using gas chromatography and mass spectroscopy. Emission rates of hexanal, (E)-2-hexenal, (E)-2-hexen-1-ol, 1-hexenol, hexyl acetate and (E)-2-hexenyl acetate were 5 to 310 times higher for severely stressed trees compared to those of the controls with the moderately stressed trees intermediate. The large increases in hexanal. (E)-2-hexenal and l-hexanol may be related. In enhanced lipoxygenase activity. Volatile compounds are products of metabolism and measurement of their changes after biotic or abiotic stresses will increase understanding of the relationship of changes in plant metabolism by those stresses.