Rice tolerance to excess Mn: Implications in the chloroplast lamellae and synthesis of a novel Mn protein

Rice (Oryza sativa L. cv. Safari) plants were grown over a 21-d period in nutrient solutions containing Mn concentrations varying between 0.125 and 32 mg·L^–1. The plant shoots and the thylakoid membranes showed similar overall Mn increases for this range of treatments, but different accumulation kinetics. It was found that the highest Mn treatment were associated to the synthesis of a new thylakoid protein with an average molecular mass of 36.5 kDa and a Mn:protein ratio of about 1. This protein exhibited superoxide dismutase activity, as well as a high content of Gln, Asp, Glu, Leu and Gly. Its EPR spectrum is characteristic of high-spin Mn(II), in a S=5/2 ground state. A comparative study of SDS polyacrylamide gel profiles of thylakoid polypeptides from the various treatments disclosed quantitative changes, as well as a new 37/36-kDa polypeptide band in the two highest Mn treatments. The photosynthetic electron transport rates coupled to PSII and PSI showed a significant increase until the 8-mg·L^–1 Mn treatment. The related superoxide production of thylakoids (monitored by EPR spectroscopy) showed minimum values from the 0.5-mg·L^–1 Mn treatment onwards, which, as shown by the thiobarbituric acid reaction was coupled to a non-significant variation of the acyl lipid peroxidation. It was concluded that Oryza sativa L. cv. safari has a high internal tolerance to Mn as it synthesises a new manganese protein that mimics superoxide dismutase functioning.     

Active uptake of aluminium,copper and manganese by the freshwater amphipod Paramelita nigroculus in acidic waters

Experiments were performed on the freshwater amphipod Paramelita nigroculus to determine the route of uptake for Al, Cu and Mn. The extent of correlation between the concentrations of Al, Cu and Mn and those of macro-cations Na, Ca and Mg was investigated in order to determine appropriate strategies of water quality management. Indeed, active uptake of toxicants can be controlled by disturbing the active pump used. After 21 days of exposure to different combined concentrations, survivors were analysed chemically by ICP-S after depuration, drying, ashing and digestion with concentrated nitric acid.The results showed significant correlations between the concentrations of major cations and the three metals under study (i.e. Al, Cu and Mn) at p < 0.05. These are Ca vs Al, Ca vs Mg, Na vs Mg, Na vs Mn, Al vs Mg, Al vs Cu, and Mg vs Mn. No other combination showed significant correlation. High r-values for Na vs Mg (r=0.7194) and for Na vs Mn (r=0.6253), as well as low concentrations of Mg and Mn, suggest interactions between the active uptake of Mn and Mg, although there may be interferences due to the use of Na pump. Additional experiments examined the type of interaction occurring when Mn and Mg were present in 1:1 mixtures in water. The Student's t test showed that observed differences in bioaccumulation of Mn, when alone and when combined, were not statistically significant at p < 0.05. These differences may be attributed to chance but not to the presence of Mg in the medium; while differences in bioaccumulation of Mg, when alone and when combined, were statistically significant at p < 0.002. These were attributed to Mn, which lowers Mg uptake by P. nigroculus.     

Divalent Mn in calcium hydroxyapatite by pulse laser deposition

Pulse laser deposition (PLD) was used to deposit Mn containing calcium hydroxyapatite (HAMn). The PLD process ensures that the composition of the target and the deposited layer is the same. In some cases additional effort should be made to preserve some volatile components, namely OH. This was ensured by water steam supply. Calcium hydroxyapatite deposited by this method has the same properties as the target in respect to lattice parameters and valence state of Mn, which ensures the fixation between hard tissue and metal implants. This fact makes PLD grown HAMn layer covering implants to be improved for practical use.     

New insights into manganese toxicity and speciation

Manganese (Mn) is known to be a neurotoxic agent for nearly 175 years now. A lot of research has therefore been carried out over the last century. From preliminary describing only symptoms of Mn-(over)exposed workers, research was preceded to more detail on toxic mechanisms of Mn. Unraveling those neurotoxic mechanisms implicated a number of studies, which were summarized partly in several reviews (e.g. Yokel RA. Neuromol Med 2009;11(4):297–310; Aschner M, et al. Toxicology Appl Pharmacol 2007;221(2):131–47; Michalke B, et al. J Environ Monit 2007;9(7):650). Since our recent review on Mn-speciation in 2007 (Michalke B, et al. J Environ Monit 2007;9(7):650), Mn-research was considerably pushed forward and several new research articles were published. The very recent years though, Mn toxicity investigating science is spreading into different fields with very detailed and complex study designs. Especially the mechanisms of Mn-induced neuronal injury on cellular and molecular level was investigated in more detail, discussing neurotransmitter and enzyme interactions, mechanisms of action on DNA level and even inclusion of genetic influences. Depicting the particular Mn-species was also a big issue to determine which molecule is transporting Mn at the cell membranes and which one is responsible for the injury of neuronal tissue. Other special foci on epidemiologic studies were becoming more and more important: These foci were directed toward environmental influences of Mn on especially Parkinson disease prevalence and the ability to carry out follow-up studies about Mn-life-span exposure. All these very far-reaching research applications may finally lead to a suitable future human Mn-biomonitoring for being able to prevent or at least detect the early onset of manganism at the right time.     

SO2-dependent cation competition and compartmentalization in Norway spruce needles

Ion contents in needles from Norway spruce trees [Picea abies (L.) Karst.] growing in Würzburg and in the SO₂-polluted Erzgebirge mountains were analysed to quantify cations which accumulate together with sulphate. In Würzburg there was a positive correlation of potassium (0.680 ± 0.300 Eq Eq^?1 SO₄^?2), magnesium (0.415 ± 0.111 Eq Eq^?1 SO₄^?2) and zinc (0.059 ± 0.006 Eq Eq^?1 SO₄^2?). In the Erzgebirge, potassium was also the stoichiometrically most important cation (0–887 ± 0–180 Eq K⁺ Eq^?1 SO₄^2?). All other correlations examined were weak or statistically non-significant. At both sites the calcium content of spruce needles did not depend on the sulphate content. The lack of a role for Ca²⁺ in neutralizing sulphate is a consequence of the presence of free oxalic acid in needles. Soluble oxalic acid precipitates Ca²⁺, which thereby becomes unavailable as a counterion for SO₄^2?. The activity coefficients of Ca²⁺ and oxalate^2?, and the solubility product of Ca-oxalate, were determined from in vivo data. It is concluded that the chronic accumulation of atmospheric sulphate in spruce needle vacuoles depletes available potassium and thereby strongly interferes with spruce growth and canopy turnover. This leads to impaired spruce vitality, even at sites where acute SO₂ disease symptoms are absent.     

A Novel Dendrite‐Free Mn2+/Zn2+ Hybrid Battery with 2.3 V Voltage Window and 11000‐Cycle Lifespan

With the increasing energy crisis and environmental pollution, rechargeable aqueous Zn‐based batteries (AZBs) are receiving unprecedented attention due to their list of merits, such as low cost, high safety, and nontoxicity. However, the limited voltage window, Zn dendrites, and relatively low specific capacity are still great challenges. In this work, a new reaction mechanism of reversible Mn²⁺ ion oxidation deposition is introduced to AZBs. The assembled Mn²⁺/Zn²⁺ hybrid battery (Mn²⁺/Zn²⁺ HB) based on a hybrid storage mechanism including Mn²⁺ ion deposition, Zn²⁺ ion insertion, and conversion reaction of MnO₂ can achieve an ultrawide voltage window (0–2.3 V) and high capacity (0.96 mAh cm^?2). Furthermore, the carbon nanotubes coated Zn anode is proved to effectively inhibit Zn dendrites and control side reaction, hence exhibiting an ultrastable cycling (33 times longer than bare Zn foil) without obvious polarization. Benefiting from the optimal Zn anode and highly reversible Mn²⁺/Zn²⁺ hybrid storage mechanism, the Mn²⁺/Zn²⁺ HB shows an excellent cycling performance over 11 000 cycles with a 100% capacity retention. To the best of the authors' knowledge, it is the highest reported cycling performance and wide voltage window for AZBs with mild electrolyte, which may inspire a great insight into designing high‐performance aqueous batteries.     

Gut retention of metals in rats

In sucklings, a high fraction of orally administered metals and radionuclides is retained in the gut. The location of elements in the gut is of interest because of their potential local health effect. The purpose of this work was to evaluate the influence of chelation therapy on gut retention and location of cadmium, mercury, and cerium in-suckling rats. Radionuclides^115mCd,²⁰³Hg, and¹⁴¹Ce were administered orally to 6-d-old rats. Chelating agent Zn-DTPA (3.64 mmol/kg) was administered to animals that received^115m Cd or¹⁴¹Ce and Na-DMPS (375 μmol/kg) to those that received²⁰³Hg, immediately and 24 h or 24 and 48 h after radionuclide administration. Radio-activity was determined in the whole body and gastrointestinal tract 6 d later. Both early and delayed chelation treatment very effectively reduced whole body retention, and this was mainly owing to reduced gut retention. Although chelation therapy reduced gut retention of administered radionuclides 3–30 times, the site of metal accumulation and retention in the intestine remained unchanged. For all 3 radionuclides, both after early and delayed therapy, the site of metal accumulation was always the lower part of small intestine—ileum.     

Chemical Partitioning of Fe,Mn, Zn and Cr in Mountain Soils of the Iberian and Pyrenean Ranges (NE Spain)

The bioavailability of heavy metals, and thus their possible harmful impact on ecosystems and humans, depends on metal partitioning. This study describes the chemical partitioning of iron, manganese, zinc and chromium, because the potential effect of soil contamination is better assessed through the knowledge of the forms in which a given metal is present rather than the use of its total concentration. In four soil types representative of mountain soils in the Iberian and Pyrenean ranges in Aragón, a total of 16 selected sites have been sampled and five subsamples were taken in each site to create a composite sample. The 4 heavy metals have been extracted by the sequential extraction procedure of Tessier et al. (1979) Tessier, A., Campbell, P. G.C. and Bisson, N. 1979. Sequential extraction procedure for the speciation of particulate trace metals. Anal. Chem., 51: 844–850. [CROSSREF][Crossref], [Web of Science ®] [Google Scholar] and analyzed by emission atomic spectrometry of solid state (ICP OES). Little Fe, Mn and Zn (< 1, 2.4–35.9, < 1–24.5 mg/kg, respectively) were retrieved from the exchangeable phase, a readily available phase for biogeochemistry cycles in the ecosystems. Chromium was not detected in the potentially bioavailable forms. The largest contents of Fe, Zn and Cr were retrieved from the residual phase with mean values of 21100, 72 and 60 mg/kg, and maximum values of 35700, 279 and 271 mg/kg, respectively. Mn was mainly bound to oxide phases with mean and maximum values of 236 and 887 mg/kg, respectively. For all metals, the highest contents are found in Leptosols on igneous rocks due to the rich and diverse mineral composition of their parent materials. The knowledge of the chemical partitioning of Fe, Mn, Zn and Cr provides information to identify the soils in which their mobile forms may be transferred to the soil-water-plant system. This information is of interest for the management of fragile mountain soils to avoid the environmental risk of cycling these metals in the environment.     

A compact RNA tertiary structure contains a buried backbone-K+ complex

The structure of a 58 nucleotide ribosomal RNA fragment buries several phosphate groups of a hairpin loop within a large tertiary core. During refinement of an X-ray crystal structure containing this RNA, a potassium ion was found to be contacted by six oxygen atoms from the buried phosphate groups; the ion is contained completely within the solvent-accessible surface of the RNA. The electrostatic potential at the ion chelation site is unusually large, and more than compensates for the substantial energetic penalties associated with partial dehydration of the ion and displacement of delocalized ions. The very large predicted binding free energy, approximately -30 kcal/mol, implies that the site must be occupied for the RNA to fold. These findings agree with previous studies of the ion-dependent folding of tertiary structure in this RNA, which concluded that a monovalent ion was bound in a partially dehydrated environment where Mg2+ could not easily compete for binding. By compensating the unfavorable free energy of buried phosphate groups with a chelated ion, the RNA is able to create a larger and more complex tertiary fold than would be possible otherwise.     

Manganese deficiency and transcriptional regulation of mitochondrial superoxide dismutase in hepatomas

The presumed involvement of the transition metals manganese and copper in the regulation of the expression of the Mn- and CuZn-containing superoxide dismutase genes has been investigated in normal and neoplastic tissues of the rat. Two hepatomas of the Morris line have been employed, the slow growing, highly differentiated 9618A and the fast growing, poorly differentiated 3924A. The data obtained indicate a control at the pretranslational level of the Mn-containing enzyme, presumably exerted by the manganese ion. The CuZn-containing superoxide dismutase is also regulated pretranslationally in the normal tissues examined and in the hepatoma 3924A. However, there is no indication for the involvement of the copper ion, which in the liver is mostly located in the cytosol bound to CuZnSOD, in such regulation. The possible role of a reduced redox state, concomitant to the manganese deficiency in hepatoma tissues, in the down regulation of Mn-containing superoxide dismutase is discussed.