Manganese phytotoxicity: new light on an old problem

Background Manganese (Mn) is an essential micronutrient that is phytotoxic under certain edaphic and climatic conditions. Multiple edaphic factors regulate Mn redox status and therefore its phytoavailability, and multiple environmental factors including light intensity and temperature interact with Mn phytotoxicity. The complexity of these interactions coupled with substantial genetic variation in Mn tolerance have hampered the recognition of Mn toxcity as an important stress in many natural and agricultural systems.Scope Conflicting theories have been advanced regarding the mechanism of Mn phytotoxicity and tolerance. One line of evidence suggests that Mn toxicity ocurs in the leaf apoplast, while another suggests that toxicity occurs by disruption of photosynthetic electron flow in chloroplasts. These conflicting results may at least in part be attributed to the light regimes employed, with studies conducted under light intensities approximating natural sunlight showing evidence of photo-oxidative stress as a mechanism of toxicity. Excessive Mn competes with the transport and metabolism of other cationic metals, causing a range of induced nutrient deficiencies. Compartmentation, exclusion and detoxification mechanisms may all be involved in tolerance to excess Mn. The strong effects of light, temperature, precipitation and other climate variables on Mn phytoavailability and phytotoxicity suggest that global climate change is likely to exacerbate Mn toxicity in the future, which has largely escaped scientific attention.Conclusions Given that Mn is terrestrially ubiquitous, it is imperative that the heightened risk of Mn toxicity to both managed and natural plant ecosystems be factored into evaluation of the potential impacts of global climate change on vegetation. Large inter- and intraspecific genetic variation in tolerance to Mn toxicity suggests that increased Mn toxicity in natural ecosystems may drive changes in community composition, but that in agroecosystems crops may be developed with greater Mn tolerance. These topics deserve greater research attention.     

'The effect of micronutrients on superoxide dismutase in senescent fibroblasts'

The specific activities of zinc/copper (Zn/Cu)-superoxide dismutase (SOD-1) and manganese (Mn)-superoxide dismutase (SOD-2) were assayed in young passage 5 fibroblasts and in serially subcultured cells that were characterized as senescent at passages 15-35. SOD-1 and SOD-2 activities did not significantly change in senescent and young cells cultured in either routine medium [minimum essential medium 1 (MEM1)], or in Zn, Cu and Mn supplemented medium (MEM2) containing normal human plasma levels of the cations. SOD-1 and SOD-2 activities, however, underwent parallel progressive significant activity increases in senescent passage 20 and 25 cells, which peaked in value in passage 30 and 35 cells subcultured in supplemented medium (MEM3) containing triple human plasma levels of the cations. Concurrently, superoxide radical generation rates underwent progressive significant increases in senescent passage 15-25 cells, which peaked in value in passage 30 and 35 cells subcultured in MEM1 or MEM2. These rates, however, were significantly lowered in senescent cells subcultured in MEM3. We infer that it was only possible to significantly stimulate SOD-1 and SOD-2 activities in senescent MEM3 cultured cells enabling them to combat oxidative stress.     

锰作用下PC12细胞的氧化应激机制研究

目的:以鼠嗜铬神经瘤细胞(PC12)为模型,筛选锰对神经细胞增殖抑制作用的时间及剂量,观察锰作用下PC12细胞的氧化应激反应与细胞形态学、生化指标改变和丝裂原活化蛋白激酶pp38(p38MAPKs)的活化表达。方法:用200,400,600,800μmol/LMnCl2的培养液,分别作用对数生长期PC12细胞1,2,3,4d后,用MTT筛选锰的细胞毒性剂量;测定200-600μmol/L MnCl2作用4d后,PC12细胞还原型谷胱甘肽和丙二醛含量;透射电镜观察细胞形态学变化;琼脂糖凝胶电泳检测MnCl2对PC12细胞基因组DNA的影响。western-blot法检测p-p38。结果:MTT实验显示200~800μmol/LMnCl2作用1,2,3,4d对PC12有显著的抑制作用,呈剂量和时间依赖趋势,600μmol/LMnCl2作用4d对PC12的抑制率可达50%以上。200-600μmol/LMnCl2作用于细胞4d后,随着浓度的升高,还原型GSH逐渐降低,MDA的含量逐渐升高;600μmol/LMnCl2作用4d电镜可见细胞凋亡,同样条件下细胞DNA碎片化。Western-blot实验显示600μmol/LMnCl2作用1,2,3,4dp-p38逐渐升高,3d时较对照组增加6.6倍(n=3,p<0.05),200,400,600μmol/L MnCl2作用4d时,磷酸化蛋白38(p-p38)也逐渐升高,400μmol/L MnCl2作用4d时较对照组升高了4.7倍(n=3,p<0.05)。结论:PC12细胞在锰作用下发生氧化应激反应,上调p-p38,诱导细胞凋亡,细胞增殖抑制。     

耐辐射球菌基因DR1709与DR2523的突变分析

摘要：【目的】检测在耐辐射球菌抵抗外来辐射和氧自由基的过程中,锰离子转运蛋白基因（DR1709和DR2523）是否发挥了作用。探讨锰离子、锰离子转运蛋白基因与耐辐射球菌辐射抗性之间的关系。【方法】分别构建这两个基因的突变体。对突变体和野生型进行紫外线照射和过氧化氢处理。对处理后的菌株存活率进行分析。【结果】DR2523被突变以后,耐辐射球菌在tryptone-glucose-yeast extract (TGY)培养液中的生长受影响很小。而DR1709突变体M1709在对数生长阶段的生长速度远低于野生型。     

燕麦/小麦间作对小麦生长和锰营养的影响

通过根系分隔的盆栽试验,研究了燕麦,小麦间作对小麦生长及其锰营养的影响。结果表明：根系不分隔处理,小麦地上部干重和植株吸锰量都高于其他两种分隔方式;而根系完全分隔处理,小麦地上部植株锰含量高于其他两种分隔方式;根系不同分隔方式对川麦28土壤DTPA-Mn含量几乎没有影响,小麦9023土壤DTPA-Mn含量则以完全分隔处理高于另外两种分隔方式。推测在该间作体系中,燕麦可能通过根系分泌物来活化土壤难溶性的锰氧化物,从而促进了小麦的生长,改善了小麦的锰营养,但因其竞争能力不如小麦而消弱了自身的生长。具体原因有待于进一步试验验证。试验还发现,种植燕麦后土壤的DTPA-Mn含量要高于种植小麦后的土壤,而且燕麦地上部植株锰含量也比小麦高,表明燕麦活化、吸收土壤锰的能力强于小麦。不同间作组合时,小麦各项研究指标无一致的规律性,说明在促进小麦生长、改善小麦锰营养的能力方面,本试验采用的3个燕麦品种之间无明显差异。     

Oxoiron(IV) porphyrin π-cation radical complexes with a chameleon behavior in cytochrome P450 model reactions

There is an intriguing, current controversy on the involvement of multiple oxidizing species in oxygen transfer reactions by cytochromes P450 and iron porphyrin complexes. The primary evidence for the multiple oxidants theory was that products and/or product distributions obtained in the catalytic oxygenations were different depending on reaction conditions such as catalysts, oxidants, and solvents. In the present work, we carried out detailed mechanistic studies on competitive olefin epoxidation, alkane hydroxylation, and C=C epoxidation versus allylic C–H hydroxylation in olefin oxygenation with in situ generated oxoiron(IV) porphyrin -cation radicals (1) under various reaction conditions. We found that the products and product distributions were markedly different depending on the reaction conditions. For example, 1 bearing different axial ligands showed different product selectivities in competitive epoxidations of cis-olefins and trans-olefins and of styrene and para-substituted styrenes. The hydroxylation of ethylbenzene by 1 afforded different products, such as 1-phenylethanol and ethylbenzoquinone, depending on the axial ligands of 1 and substrates. Moreover, the regioselectivity of C=C epoxidation versus C–H hydroxylation in the oxygenation of cyclohexene by 1 changed dramatically depending on the reaction temperatures, the electronic nature of the iron porphyrins, and substrates. These results demonstrate that 1 can exhibit diverse reactivity patterns under different reaction conditions, leading us to propose that the different products and/or product distributions observed in the catalytic oxygenation reactions by iron porphyrin models might not arise from the involvement of multiple oxidizing species but from 1 under different circumstances. This study provides strong evidence that 1 can behave like a chameleon oxidant that changes its reactivity and selectivity under the influence of environmental changes.Electronic Supplementary Material Supplementary material is available for this article at .     

A culture unit system for the study of responses of mycorrhizal and non-mycorrhizal seedling to treatments

The time-dependence of Mn accumulation was confirmed in potato foliage (Solanum tuberosum. L.cv. Norland) grown in solution culture. Older leaves grown at 0.61 mM Mn had substantially higher Mn concentrations than younger leaves and stem samples. Levels of Mn in older leaves increased steadily from 4000 µg g^–1 at one week to 8–10,000 µg g^–1 at 6 weeks, but were relatively constant in the emerging leaves. Even foliage grown at low Mn levels (0.01 mM Mn) had 4 fold gradients in Mn concentration from younger (40 µg g^–1) to older leaves (180 µg g^–1).At 0.61 mM Mn, concentrations of 3–4000 µg g^–1 in the youngest fully-developed leaves did not bring about any decline in yield, and levels of up to 5000 µg g^–1 occurred in individual potato leaves before Mn toxicity symptoms were observed. Potato foliage grown at the high Mn had similar leaf numbers, but showed an increased stem length and smaller leaves than foliage grown at 0.01 mM Mn. In particular, the leaf area of the middle and lower leaf fractions were affected by the high Mn level.The ability of rapidly growing plants to withstand high concentrations of Mn is discussed in relation to the pattern of dry matter and Mn accumulation shown by potato foliage.     

DNA Binding,Antioxidant Activity,and DNA Damage Protection of Chiral Macrocyclic Mn(III) Salen Complexes

We are reporting the synthesis, characterization, and calf thymus DNA binding studies of novel chiral macrocyclic Mn(III) salen complexes S‐1 , R‐1 , S‐2 , and R‐2 . These chiral complexes showed ability to bind with DNA, where complex S‐1 exhibits the highest DNA binding constant 1.20 × 10⁶ M^?1. All the compounds were screened for superoxide and hydroxyl radical scavenging activities; among them, complex S‐1 exhibited significant activity with IC₅₀ 1.36 and 2.37 μM, respectively. Further, comet assay was used to evaluate the DNA damage protection in white blood cells against the reactive oxygen species wherein complex S‐1 was found effective in protecting the hydroxyl radicals mediated plasmid and white blood cells DNA damage. Chirality 24:1063–1073, 2012.© 2012 Wiley Periodicals, Inc.     

土壤湿度水平和湿-干循环对硝酸钙盐积累土壤锰释放的影响

在[Ca(NO₃)²]盐处理土壤中,研究了两种湿度水平(200、400g·kg^-1)和湿干循环对土壤Mn释放的影响.结果表明,土壤水分状况影响土壤Mn的有效性,湿度大时,易还原态Mn转化为水溶态、交换态Mn;盐分对易还原态Mn的转化有一定影响,NO₃^-能缓冲土壤Eh的下降,有抑制易还原态Mn转化的作用.连续的湿干循环能使土壤2价Mn(水溶态Mn、交换态Mn)浓度降低,而Ca(NO₃)²盐能增加Mn的不溶性.这在Mn含量低的土壤上,最终将导致Mn的缺乏.     

Effects of liming on the extractability of Fe,Mn, Zn and Cu from a peat medium and the growth and micronutrient uptake of highbush blueberry plants

Summary Levels of extractable micronutrients in a peat and the growth and nutrient uptake of young highbush blueberry plants (Vaccinium corymbosum L cv. Blueray) were studied in a greenhouse experiment in response to liming and two rates of addition of Fe, Mn, Zn and Cu.Levels of extractable micronutrients showed different trends with liming depending upon the extractant used and the element being considered. Levels of 0.05M CaCl₂-extractable Fe, Mn and Zn decreased as the pH was raised whilst those of Cu first decreased and then increased again. There was a general decline in 0.1M HCl-extractable Fe, Mn and Cu with increasing pH but levels of Zn were not greatly affected. Levels of 0.005M DTPA extractable Fe, Mn Zn and Cu generally declined but those extractable with 0.04M EDTA were either unaffected or increased as the pH was raised. Levels of CaCl₂-extractable Mn and Zn were the same order of magnitude as those extractable with HCl, DTPA and EDTA. In contrast, the latter reagents extracted considerably more Fe and Cu than did CaCl₂.Dry matter yields of plants were increased as the pH was raised from 3.9 to 4.3 but then decreased markedly as the pH was raised further to 6.7. With increasing pH, concentrations of plant Fe generally increased those of Mn were decreased and those of Zn and Cu were not greatly affected except for a marked decline in plant Cu at pH 6.7.