Molecular and physiological analysis of Al³âº and H⁺ rhizotoxicities at moderately acidic conditions.

Al³âº and H⁺ toxicities predicted to occur at moderately acidic conditions (pH [water] = 5-5.5) in low-Ca soils were characterized by the combined approaches of computational modeling of electrostatic interactions of ions at the root plasma membrane (PM) surface and molecular/physiological analyses in Arabidopsis (Arabidopsis thaliana). Root growth inhibition in known hypersensitive mutants was correlated with computed {Al³âº} at the PM surface ({Al³âº}(PM)); inhibition was alleviated by increased Ca, which also reduced {Al³âº}(PM) and correlated with cellular Al responses based on expression analysis of genes that are markers for Al stress. The Al-inducible Al tolerance genes ALUMINUM-ACTIVATED MALATE TRANSPORTER1 and ALUMINUM SENSITIVE3 were induced by levels of {Al³âº}(PM) too low to inhibit root growth in tolerant genotypes, indicating that protective responses are triggered when {Al³âº}(PM) was below levels that can initiate injury. Modeling of the H⁺ sensitivity of the SENSITIVE TO PROTON RHIZOTOXICITY1 knockout mutant identified a Ca alleviation mechanism of H⁺ rhizotoxicity, possibly involving stabilization of the cell wall. The phosphatidate phosphohydrolase1 (pah1) pah2 double mutant showed enhanced Al susceptibility under low-P conditions, where greater levels of negatively charged phospholipids in the PM occur, which increases {Al³âº}(PM) through increased PM surface negativity compared with wild-type plants. Finally, we found that the nonalkalinizing Ca fertilizer gypsum improved the tolerance of the sensitive genotypes in moderately acidic soils. These findings fit our modeling predictions that root toxicity to Al³âº and H⁺ in moderately acidic soils involves interactions between both toxic ions in relation to Ca alleviation.

Large deuterium isotope effects and their use: a historical review.

Isotope effects are differences in the properties of the isotopes of an element resulting in different reaction rates of a corresponding compound, in equilibrium constants and in the spectra. Shortly after the discovery of stable isotopes of hydrogen, oxygen, and carbon, Jacob Bigeleisen formulated a theory of isotope effects and calculated possible maximum values. Large isotope effects of (2)H (deuterium) against (1)H (protium) were seen to possibly influence interpretations of reaction mechanisms if corresponding labelling is used. Much work was invested to ensure the safety of deuterium use in men in spite of the large isotope effect. On the other hand, large deuterium isotope effects gave rise to several practical applications. Examples are the enhancement of the stability of some technical products against oxidative and against hydrolytic degradation (oils, pharmaceuticals) as well as alterations of the detoxification metabolism of pharmaceuticals in vivo.

Effect of cation competition on cadmium uptake from solution by the earthworm Eisenia fetida.

Metal speciation alone is insufficient to predict metal accumulation in aquatic and terrestrial organisms, because competition between cations can play an important role. In the present study, the effects of competing cations (Ca2+, Mg2+, and H+) on Cd uptake by the earthworm Eisenia fetida were quantified through short-term experiments over a large Cd concentration range in aqueous exposure solutions. Free Cd2+ activity was a better predictor for Cd accumulation in the earthworms than was total Cd concentration in solution, thus supporting the free ion activity model. The presence of the other cations at environmentally pertinent concentrations inhibited Cd uptake to different degrees. A competitive equilibrium model based on the biotic ligand model was developed to quantify the effect of the cations. The model parameters are the conditional constants for binding of H+ (log K = 4.97), Ca2+ (log K = 3.00), and Mg2+ (log K = 2.64) to the biological uptake sites of E. fetida. Autovalidation of the model with experimental results showed that 48-h Cd accumulation in the earthworm could be successfully predicted with activities of free Cd2+ and the major cations (Ca2+, Mg2+, and H+) as input.

Environmentally friendly use of non-coal ashes in Sweden.

The Swedish Thermal Engineering Research Institute (Värmeforsk) initiated an applied research program "Environmentally friendly use of non-coal ashes", in 2002. The program aims at increasing knowledge on the by-products of energy production and their application. The goal of formulating technical and environmental guidelines and assessments is a major point of the program, which is supported by about forty authorities and private organisations. The programme has been divided into four areas: recycling of ashes to forests, geotechnical applications, use in landfilling, and environmental aspects and chemistry. Among all results obtained, the following progress is shown: *Evidence for the positive effects of spreading ashes on forest growth. *A proposal for environmental guidelines on the utilisation of ashes in construction. *A handbook for using non-coal fly ashes in unpaved roads. *Technical and environmental assessments of MSWI bottom ashes in road construction. *Development of the use of ashes with municipal wastewater sludge as a cover for landfills and mine tailings. *Use of ashes from bio-fuels in concrete and replacement of cement in stoop mining. *A method to classify those by-products from combustion that have mirror entries in the EWC as a hazardous or non-hazardous compound. The Ash Programme has also made it possible to increase knowledge on ashes as valuable materials, on quality assurance and on markets for recovered materials.

Marinitoga hydrogenitolerans sp. nov., a novel member of the order Thermotogales isolated from a black smoker chimney on the Mid-Atlantic Ridge.

A novel, thermophilic, anaerobic bacterium that is able to tolerate hydrogen was isolated from a deep-sea hydrothermal chimney collected at the Rainbow field on the Mid-Atlantic Ridge. Cells were rod-shaped and surrounded by a sheath-like outer structure (toga); they were weakly motile by means of a polar flagellum. They appeared singly, in pairs or in short chains. They grew at 35-65 degrees C (optimum 60 degrees C), pH 4.5-8.5 (optimum pH 6.0) and 10-65 g sea salts l(-1) (optimum 30-40 g l(-1)). The isolate was organotrophic, and able to grow on various carbohydrates or complex proteinaceous substrates. Growth was not inhibited under 100 % hydrogen or in the presence of 2 % oxygen in the gas phase. The isolate reduces sulfur, although sulfur reduction is not required for growth. The fermentation products identified on glucose were acetate, ethanol, formate, hydrogen and CO(2). The G + C content of the genomic DNA was 28 +/- 1 mol%. Phylogenetic analysis of the 16S rRNA gene placed the strain within the genus Marinitoga, order Thermotogales, in the bacterial domain. On the basis of the 16S rRNA gene sequence comparisons and physiological characteristics, the isolate is considered to represent a novel species, for which the name Marinitoga hydrogenitolerans sp. nov. is proposed. The type strain is AT1271(T) (=DSM 16785(T) = JCM 12826(T)).

C/G to A/T transversions represent the main type of mutation induced by gamma-irradiation in double-stranded M13mp10 DNA in a nitrogen-saturated solution.

To get more insight into the possible mutagenic consequences of DNA damage induced by radiation-generated H radicals (.H), a nitrogen-saturated solution of double-stranded (ds) M13mp10 DNA in phosphate buffer was irradiated with gamma-rays. Under these conditions 55% of the DNA-damaging species consists of H radicals and 45% of OH radicals (.OH). The mutations were investigated in a 144-bp mutational target sequence inserted into the lacZ alpha gene. A very specific mutation spectrum was obtained with respect to the type of mutations. Twenty out of the 28 radiation-induced mutations were C/G to A/T transversions; the remaining 8 mutations were 4 C/G to G/C transversions, 2 C/G to T/A transitions, one T/A to A/T transversion and only one -1 bp deletion. The mutations were rather randomly distributed along the 144-bp mutation target sequence with no clear mutational hot spots. When these results are compared with those we have obtained previously after irradiation of ds M13mp10 DNA under O2 (100% .OH) or N2O (90% .OH; 10% .H) (Hoebee et al., 1988, 1989), the data strongly suggest that H radicals may be responsible for the observed C/G to A/T transversions but not for -1 bp deletions.

Aluminium and hydrogen ions inhibit a mechanosensory calcium-selective cation channel.

The tension-dependent activity of mechanosensory calcium-selective cation channels in excised plasmalemmal patches from onion bulb scale epidermis is modulated by pH in the physiologically meaningful range between 4.5 and 7.2. It is rapidly lowered by lowering pH and rapidly raised by raising pH. Channel activity is effectively inhibited by low levels of aluminium ions and activity can be partially restored by washing for a few minutes. We suggest that under normal conditions the sensitivity of the mechanosensory channels to pH of the wall free space plays important roles in regulation of plant activities such as growth. We further suggest that, when levels of acid and aluminium ions in the soil solution are high, they might inhibit similar sensory channels in cells of the root tip, thus contributing critically to the acid soil syndrome.

Absorption of in vivo inert gas bubbles.

The resolution rates of gas bubbles in perfused tissue are examined using a mathematical model which is consistent with transient-state and steady-state data from large gas pocket experiments. The tissue surrounding the bubble is assumed to have an infinite number of infinitesimally small capillaries (distributed sink). The time for complete disappearance of a bubble depends on initial bubble size. blood perfusion rate of the tissue, physical characteristics of the inert gas and the fraction (1-Pa/Pg), where Pa and Pg are inert gas partial pressures in the surrounding tissue and inside the bubble, respectively. Calculated time for disappearance of a nitrogen bubble of 1 mm radius in an O2-breathing man is 100-250 min, depending on blood perfusion. Breathing of air increases the time of persistence of the bubble about 10-fold. The "transient state", when gas is dissolving in the immediate surroundings of the bubble, is most influential when there is no perfusion and the partial pressure gradient gas volume is the largest. However, our major conclusion is that the initial transient state has little effect on total lifetime of the bubble in any case.