Nanoherding : plasma-chemical synthesis and electric-charge-driven self organization of SiO2 nanodots

We report on the chemical synthesis of the arrays of silicon oxide nanodots and their self-organization on the surface via physical processes triggered by surface charges. The method based on chemically active oxygen plasma leads to the rearrangement of nanostructures and eventually to the formation of groups of nanodots. This behavior is explained in terms of the effect of electric field on the kinetics of surface processes. The direct measurements of the electric charges on the surface demonstrate that the charge correlates with the density and arrangement of nanodots within the array. Extensive numerical simulations support the proposed mechanism and prove a critical role of the electric charges in the self-organization. This simple and environment-friendly self-guided process could be used in the chemical synthesis of large arrays of nanodots on semiconducting surfaces for a variety of applications in catalysis, energy conversion and storage, photochemistry, environmental and biosensing, and several others.

低分子有机酸对辣椒生长发育及叶片活性氧代谢的影响

采用盆栽试验与室内分析相结合的方法,研究了6种低分子有机酸和一种有机酸盐对辣椒生长发育和叶片活性氧代谢的影响。结果表明:柠檬酸、乙酰丙酸和有机酸钾处理不仅可显著提高辣椒根系干质量,增加辣椒vC含量,而且提高了辣椒的产量。甲酸、柠檬酸、乙酰丙酸和有机酸钾处理使根系活力比对照分别提高83%、93.8%、96.75%和99.5%。柠檬酸、乙酰丙酸和有机酸钾处理提高了辣椒叶片的SOD和POD活性,降低了膜脂过氧化产物MDA含量,延缓了叶片衰老。但是低分子有机酸处理对CAT活性的影响较小。

水分亏缺和凋落物水浸液对云杉幼苗生长和种子萌发的影响

在人类活动导致全球变暖的前提下，由于全球气温的升高，地表水分加速向空中蒸发。从20世纪70年代至今，地球上严重干旱地区的面积几乎扩大了一倍。这一增长的一半可归因于气温升高而不是降雨量下降，因为实际上同期全球平均降水量还略有增长。干旱对陆地植物和农林生态系统产生深远影响，并已成为全球变化研究的一个重要方面。位于青藏高原东部的川西亚高山针叶林是研究气候变暖对陆地生态系统影响的重要森林类型。森林采伐迹地、人工林下和林窗环境作为目前该区人工造林和森林更新的重要生境，其截然不同的光环境对亚高山针叶林更新和森林动态有非常重要的影响。凋落物产生的化感物质可通过影响种子萌发和早期幼苗的定居而影响种群的建立和更新，而人工林和自然林物种以及更新速度的差异性也都受凋落物的影响。 云杉是川西亚高山针叶林群落的重要树种之一,在维持亚高山森林的景观格局和区域生态安全方面具有十分重要的作用，其自然更新能力及其影响机制一直是研究的热点问题。本试验以云杉种子和2年生幼苗为研究对象，从萌发、根尖形态、幼苗生长、光合作用、渗透调节和抗氧化能力等方面研究了不同光环境下水分亏缺和凋落物水浸液对云杉种子和幼苗生长的影响。旨在从更新的角度探讨亚高山针叶林自然更新的过程，其研究成果可在一定程度上为川西亚高山针叶林更新提供科学依据，同时也可为林业生产管理提供科学指导。主要研究结论如下： 水分亏缺在生长形态、光合作用、抗氧化能力、活性氧化对云杉幼苗都有显著影响。总体表现为，水分亏缺导致了云杉幼苗的高度、地径、单株总生物量降低，增加了地下部分的生长；水分亏缺显著降低了云杉叶片中相对含水量、光合色素、叶氮含量，净光合速率和最大量子产量(Fv/Fm)，提高了幼苗叶片中膜脂过氧化产物（MDA）的含量；水分亏缺提高了幼苗叶片中过氧化氢(H2O2)含量，超氧荫离子（O2-）生成速率以及脯氨酸和抗氧化系统的活性（ASA, SOD, CAT, POD, APX和GR）。从这些结果可知，植物在遭受水分亏缺导致的伤害时，其自身会形成防御策略，并通过改变形态和生理方面的特性以减轻害。但是，这种自我保护机制依然不能抵抗严重水分亏缺对植物的伤害。 模拟林下低光照条件显著增加单株植物的地上部分生长，尤其是其叶片的比叶面积（叶面积/叶干重），同时其光合色素含量和叶片相对含水量也显著增加，这些改变直接导致植株光合速率和生物量的增加。同时，与高光照水平相比，低光照幼苗的膜脂过氧化产物（MDA）和活性氧物质均较低，显示出低光照比高光照水平对植物的更低的氧化伤害。尽管低光照也导致大部分抗氧化酶活性降低，但这正显示出植物遭受低的氧化伤害，更印证了前面的结论。 凋落物水浸液影响了云杉种子的萌发和根系的生长，更在形态、光合作用、抗氧化能力、活性氧物质以及叶氮水平上显著影响了云杉幼苗，其中，以人工纯林凋落物的影响更有强烈。具体表现在，种子萌发速率和萌发种子幼根的长度表现为对照>自然林处理>人工纯林；凋落物水浸液抑制种子分生区和伸长区的生长，人工林处理更降低了根毛区的生长，使根吸水分和养分困难。对2年生幼苗的影响主要表现在叶绿素含量、光合速率以及叶氮含量的降低；膜脂过氧化产物、活性氧物质和抗氧化酶系统的显著增加。同样的，人工纯林处理对云杉幼苗的影响显著于自然林处理。 在自然生态系统中，由于全球变暖气温升高导致的水分亏缺和森林凋落物都存在森林的砍伐迹地，林窗和林下环境中。我们的研究表明，与迹地或林窗强光照比较，林下的低光照环境由于为植物的生长营造了较为湿润的微环境，因此水分亏缺在林下对云杉幼苗造成的影响微弱。这可以从植物的形态、光合速率以及生物量积累，过氧化伤害和抗氧化酶系统表现出来。另一方面，凋落物水浸液在模拟林下低光照环境对植物的伤害也微弱于强光照环境，这与强光照环境高的水分散失导致环境水分亏缺有关；而人工纯林处理对云杉幼苗的伤害比对照和自然林处理显示出强烈的抑制作用。 Under the pre-condition of global warming resulted from intensive human activities, water in the earth’s surface rapidly evaporates due to the increase of global air temperature. From 1970s up to now, the area of serious drought in the world is almost twice as ever. This increase might be due to the increasing air temperature and not decreasing rainfall because global average rainfall in the corresponding period slightly is incremental. Drought will have profound impacts on terrestrial and agriculture-forest system and has also become the important issue of global change research. The subalpine coniferous forests in the eastern Qinghai-Tibet Plateau provide a natural laboratory for the studying the effects of global warming on terrestrial ecosystems. The light environment significantly differs among cutting blanks, forest gap and understory, which is particularly important for plant regeneration and forest dynamics in the subalpine coniferous forests. Picea asperata is one of the keystone species of subalpine coniferouis forests in western China, and it is very important in preserving landscape structure and regional ecological security of subalpine forests. The natural regeneration capacities and influence mechanism of Picea asperata are always the hot topics. In the present study, the short-term effects of two light levels (100% of full sunlight and 15% of full sunlight), two watering regimes (100% of field capacity and 30% of field capacity), two litter aqueous extracts (primitive forest and plantation aqueous extracts) on the seed germination, early growth and physiological traits of Picea asperata were determined in the laboratory and natural greenhouse. The present study was undertaken so as to give a better understanding of the regeneration progress affected by water deficit, low light and litter aqueous extracts. Our results could provide insights into the effects of climate warming on community composition and regeneration behavior for the subalpine coniferous forest ecosystem processes, and provide scientific direction for the forest production and management. Water deficit had significant effects on growth, morphological, physiological and biochemical traits of Picea asperata seedlings. Water deficit resulted in the decrease in height, basal diameter, total biomass and increase in under-ground development; water deficit significantly reduced the needle relative water content, photosynthetic pigments, needle nitrogen concentration, net photosynthetic rate and the maximum potential quantum yield of photosynthesis (Fv/Fm), and increased the degree of lipid peroxidation (MDA) in Picea asperata seedlings; water deficit also increased the rate of superoxide radical (O2-) production, hydrogen peroxide (H2O2) content, free proline content and the activities of antioxidant systems (ASA, SOD, POD, CAT, APX and GR) in Picea asperata seedlings. These results indicated that some protective mechanism was formed when plants suffered from drought stress, but the protection could not counteract the harm resulting from the serious drought stress on them. Low light in the understory significantly increased seedling above-ground development, especially the species leaf area (SLA), and photosynthetic pigments and relative needle content. These changes resulted in the increase in net photosynthetic rate and total biomass. Moreover, the lower MDA content and active oxygen species (AOS) (H2O2 and O2-) in low light seedlings suggested that low light had weaker oxidative damage as compared to high light. Lower antioxidant enzymes activities in low light seedlings indicated the weaker oxidative damage on Picea asperata seedlings than high light seedlings, which was correlative with the changes in MDA and AOS. Litter aqueous extracts affected seed germination and root system of Picea asperata seedlings. Significant changes in growth, photosynthesis, antioxidant activities, active oxygen species and leaf nitrogen concentration were also found in Picea asperata seedlings, and plantation treatment showed the stronger effects on these traits than those in control and primitive forest treatment. The present results indicated that seed germination and radicle length parameters in control were superior to those in primitive forest treatment, and those of primitive forest treatment were superior to plantation treatment; litter aqueous extracts inhibited the meristematic and elongation zone, and plantation treatment caused a decrease in root hairs so as to be difficult in absorbing water and nutrient in root system. On the other hand, litter aqueous extracts significantly decreased chlorophyll content, net photosynthetic rate and leaf nitrogen concentration of Picea asperata seedlings; MDA, AOS and antioxidant system activities were significantly increased in Picea asperata seedlings. Similarly, plantation treatment had more significant effect on Picea asperata seedlings as compared to primitive forest treatment. In the nature ecosystem, water deficit resulted from elevating air temperature and litter aqueous extract may probably coexist in the cutting blank, forest gap and understory. Our present study showed that water deficit had weaker effects on low light seedlings in the understory as compared to high light seedlings in the cutting blank and forest gap. The fact was confirmed from seedlings growth, gas exchange and biomass accumulation, peroxidation and antioxidant systems. This might be due to that low light-reduced leaf and air temperatures, vapour-pressure deficit, and the oxidative stresses can aggravate the impact of drought under higher light. On the other hand, litter aqueous extracts in the low light had weaker effects on the Picea asperata seedlings than those at high light level, which might be correlative to the water evapotranspiration under high light. Moreover, plantation litter aqueous extracts showed stronger inhibition for seed germination and seedling growth than control and primitive forest treatments.

川西亚高山两种针叶树幼苗对增温和施氮的响应

人类活动引起全球大气中温室气体（CO2、CH4、NOx）浓度不断增加，致使地球表面温度在过去的100 年中已经增长了0.74 ± 0.18℃，预计到本世纪末将会增加1.1-6.4℃。此外，氮沉降也是当今社会的重要环境问题，随着经济发展的全球化, 高氮沉降也呈现出全球化趋势。全球气候变暖和氮沉降给陆地生态系统的地上、地下生物学和生物地球化学过程所带来巨大影响越来越引起人们的关注。 本文以川西亚高山针叶林的两个重要树种云杉和油松幼苗为研究对象，采用红外辐射增温（空气增温2.1℃，土壤增温2.6℃）和根部施氮（施氮量25 g N m-2yr-1）的方法，从生长形态、光合作用、抗氧化能力和矿质营养等方面研究这两种幼苗对气候变暖和氮沉降的响应。该实验为室外控制实验，包括四个处理：(1)不增温+不施氮（UU）；(2) 不增温+施氮（UF）；(3) 增温+不施氮（WU）；(4) 增温+施氮（WF）。本研究旨在从生理生化、物质代谢 、生长及形态等不同水平上研究模拟增温和施氮对两种树苗的联合效应，提高我们对全球变化下亚高山针叶林早期更新过程的理解，同时也为森林管理提供科学依据。具体研究结果如下： 单独增温处理显著提高了云杉和油松幼苗的地茎、叶重、茎重、根重以及总生物量；单独施氮处理也增加了两种幼苗的株高和总生物量。而增温和施氮联合作用对两种幼苗生长的影响并不相同，联合作用对云杉幼苗生长指标的正效应显著低于单独施氮处理，但是联合作用比单独增温或施氮更大程度的促进了油松幼苗生物量的积累。 单独增温和施氮都有利于提高云杉和油松叶片中叶绿素含量、净光合速率(A)、最大净光合速率(Amax)、表观量子效率（Φ）、最大光能转化效率（Fv/Fm）和量子产量（Y）。与对两种幼苗生长指标的影响相似，加氮和增温共同作用下油松幼苗的以上光合指标比在单独增温或施氮处理下有更大程度的提高；而联合作用下云杉幼苗叶绿素含量、净光合速率、最大净光合速率、表观量子效率、最大光能转化效率以及量子产量比单独施氮处理明显地降低。 增温和施氮都显著地降低了云杉和油松幼苗针叶组织中活性氧和丙二醛的积累。交互作用降低了云杉幼苗叶片的抗氧化酶活性、脯氨酸和ASA 的含量，却显著提高了油松幼苗SOD、POD、APX 等抗氧化酶的活性，并且对油松幼苗脯氨酸和ASA 积累的促进作用比单一因子更加明显。因此，增温和施氮共同作用下油松幼苗叶片中O2-产生速率、H2O2 及MDA 含量明显降低，而云杉叶片中只有O2-产生速率出现降低趋势。 增温和施氮都降低了云杉体内的P、Ca、Mg 元素的含量，增加了Cu、Zn、Mn 在各器官内的积累。对油松幼苗而言，增温和加氮单独作用也显著降低了Ca 含量增加了Cu、Zn、Mn 的积累，但是不同于云杉幼苗的是P、Mg 也显著增加。增温和施氮联合作用对云杉幼苗体内元素的影响与单一施氮处理或增温处理相似，不同的是比单一因子作用更为明显降低了P、Ca、Mg 含量，增加了植株中N、Cu、Zn、Mn 的含量，但是油松矿质元素含量在联合作用下并没有产生类似于云杉幼苗的双因子叠加效应。 总之，尽管单独增温或者施氮都有利于云杉和油松幼苗生长指标、光合能力以及抗氧化能力的提高。但是，增温和施氮对云杉幼苗生长生理的促进效应非但没有在交互作用下有更大的提高，反而低于单独氮处理。与此不同的是，增温和施氮联合作用比单因子作用更有利于油松幼苗生长及生理指标的提高。 With the continued increase in atmospheric concentrations of greenhouse gases (CO2、CH4、NOx), the mean global surface temperature has increased by about 0.74 ± 0.18℃ over the past century and is predicted to rise by as much as 6.4℃ during this century. Besides global warming, nitrogen deposition is another serious environmental problem caused by human activities, and high nitrogen load has become globalization as a result of global economy development. Global climate warming and nitrogen deposition have induced dramatic alternations in above - and below- ground biology and biogeochemistry process in terrestrial ecosystems, and more and more attention has been invited to those problems. This experiment mainly studies two important species Picea asperata and Pinus tabulaeformis in subalpine coniferous forest of western Sichuan, China. Infared heaters are induced to increase both air and soil temperature by 2.1℃ and 2.6 ℃, respectively. Ammonium nitrate solution (for a total equivalent to 25 g N m-2 year-1) is added to soil surface. There are four treatments in this study: (1) unwarmed unfertilized (UU); (2) unwarmed fertilized (UF); (3) warmed unfertilized (WU); (4) warmed fertilized (WF). This study is conducted to determine the influences of experimental warming and nitrogen fertilization on physiolchemistry, nutrition metabolism, growth and morphology in the two coniferous species seedlings. The current study is favorable for increasing our understanding on the early phase of regeneration behavior in subalpine coniferous forest, and it also provide scientific direction for forest management under future global changes. The results are as follows: Artificial warming alone significantly increased basal diameter, leaf mass, stem mass, root mass and total biomass for Picea asperata and Pinus tabulaeformis seedlings, and single nitrogen fertilization are also favorable for growth of the two species and stimulate plant hight and total biomass. The two species seedlings respond differently to the combination of elevated temperature and nitrogen addition. Warming combined with nitrogen fertilization weakens the positive effects of nitrogen addition for growth of Picea asperata seedlings. However, the combination of elevated temperature and nitrogen fertilization further increase biomass accumulation of Pinus tabulaeformis seedlings. Both elevated temperature alone and nitrogen fertilization alone can increase photosynthetic pigments contents, net photosynthetic rate (A), maximum net photosynthetic rate (Amax), apparent quantity yield (Φ), maximum photochemical efficiency of photosystem II (Fv/Fm) and effective quantum yield (Y). Similarly with growth parameters, the combination of warming and nitrogen addition induced more increment of these above photosynthetic parameters for Pinus tabulaeformis seedlings. However, these photosynthetic parameters of Picea asperata seedlings under the combination of warming and nitrogen addition are lower than those under nitrogen fertilization alone. The levels of active oxygen species (AOS) and malodiadehyde (MDA) in needles of the two coniferous species seedling are obviously decreased by experimental warming or additional nitrogen. Warming combined with nitrogen fertilizer reduces the activities of SOD, CAT and APX, and the contents of proline and ASA of Picea asperata seedlings, but the combination significantly increases activities of these antioxidant enzymes in needlels of Pinus tabulaeformis seedlings and further improves the accumulation of proline and ASA compared to either artificial warming or nitrogen addition. Therefore, the rate of O2 - production, the contents of H2O2 and MDA in needles of Pinus tabulaeformis seedlings are remarkably reduced by the combination of warming and nitrogen addition, but the combination only significantly decreased the rate of O2 - production of Picea asperata seedlings. Elevated temperature or nitrogen fertilization decrease the contents of P, Ca, Mg but increase Cu, Zn, Mn contents for Picea asperata seedlings. For Pinus tabulaeformis seedlings, elevated temperature alone and nitrogen fertilization alone decreased Ca, but increased P, Mg, Cu, Zn, Mn contents. The effects of the combination of warming and nitrogen addition on these element contents in needles of Picea asperata seedlings are added or multiplied the effects of warming and nitrogen addition alone, resulting in less contens of P, Ca, Mg and more contents of Cu, Zn, Mn than either elevated temperature or nitrogen fertilization. Howere, these adding or multipluing single-factor effects on contents of these elements are not observed in the case of Pinus tabulaeformis seedlings. In conclusion, growth parameters, photosynthetic capacities and antioxidant abilities of Picea tasperata and Pinus abulaeformis seedlings are improved by experimental warming or nitrogen fertilization. Interestingly, the positive effects of warming and nitrogen addition on growth and physiological performances are not multiplied by the combination of elevated temperature and nitrogen fertilization, even dempened for Picea asperata seedlings. However, for Pinus tabulaeformis seedlings, growth and physiological performances are further improved by the combination.

Reduction property and catalytic activity of Ce1-XNiXO2 mixed oxide catalysts for CH4 oxidation

Ce1-XNiXO2 oxides with X varying from 0.05 to 0.5 were prepared by different methods and characterized by XRD and TPR techniques. Ce(0.7)Mi(0.3)O(2) sample prepared by sol-gel method shows the highest reducibility and the highest catalytic activity for methane combustion. Three kinds of Ni phases co-exist in the Ce1-XNiXO2 catalysts prepared by sol-gel method: (i) aggregated NiO on the support CeO2, (ii) highly dispersed NiO with strong interaction with CeO2 and (iii) Ni atoms incorporated into CeO2 lattice. The distribution of different Ni species strongly depends on the preparation methods. The highly dispersed NiO shows the highest activity for methane combustion. The NiO aggregated on the support CeO2 shows lower catalytic activity for methane combustion, while the least catalytic activity is found for the Ni species incorporated into CeO2. Any oxygen vacancy formed in CeO2 lattice due to the incorporating of Ni atoms adsorbs and activates the molecular oxygen to form active oxygen species. So the highest catalytic activity for methane combustion on Ce0.7Ni0.3O2 catalyst is attributed not only to the highly dispersed Ni species but also to the more active oxygen species formed. (C) 2002 Elsevier Science B.V. All rights reserved.

Preparation, physico-chemical behavior and catalytic property for ammonia oxidation of perovskite like mixed oxides La2-xSrxCuO4-lambda

A series of Sr2+ doped perovskite like oxides La2-xSrxCuO4-lambda (x = 0 similar to 1) were prepared, the structure, lattice parameters, content of Cu3+, oxygen vacancies created by Sr2+ substitution and composition of these complex oxides were studied by XRD and iodic titration method. The redox ability,active oxygen species and surface image were evaluated and analyzed with TPD, TG, XPS and SEM measurements. The catalytic activity for ammonia oxidation over these oxides was tested, and the relationship among the catalytic properties, structure, nonstoichiometric oxygen,redox ability and surface behavior were correlated and some information on the mechanism of ammonia oxidation was obtained.

SOLID DEFECT STRUCTURE AND CATALYTIC ACTIVITY OF PEROVSKITE-TYPE CATALYSTS LA1-XSRXNIO3-LAMBDA AND LA1-1.333XTHXNIO3-LAMBDA

Two series of La1-xSrxNiO3-lambda and La1-1.333xThxNiO3-lambda catalysts have been prepared, and the relationships between the solid defect structure and catalytic activity for NH3 oxidation were measured. The results showed that in the range of x < 0.3, the samples possessed single perovskite-type structure, and as the content of Sr2+ decreased and that of Th4+ increased the catalytic activity increased which was paralleled with the Ni3+ concentration within the catalysts. The active oxygen species (O- or O2(2-)) were present not only on the surface but also in the bulk of the samples. The synergistic effect of transition metal ions with higher oxidation states and randomly distributed oxygen vacancies was the key factor determining catalytic activity of perovskite-type oxides. A redox mechanism for NH3 oxidation over ABO3 is proposed.

TAP studies of CO oxidation over CuMnOX and Au/CuMnOX catalysts

The mechanism of CO oxidation reactions over undoped and gold-doped CuMnOX (Hopcalite) catalysts has been examined using a temporal analysis of products (TAP) reactor Gold doping has been found to increase the activity of the mixed oxide catalyst significantly however using consecutive pulsing TAP experiments the presence of gold was not found to affect the contribution of the Langmuir-Hinshelwood mechanism Conversely gold doping was found to promote the Mars van Krevelen mechanism Using CO and O-2 multi-pulse TAP experiments the gold was found to modify the catalyst surface such that it stores much more oxygen that is active for the CO oxidation The CO multi-pulse experiments indicated that two distinct types of active oxygen species were found to be involved in the CO oxidation One type was observed in a similar amount on both doped and undoped catalysts and was associated with mixed oxide while the second type was only found on the gold-doped catalyst and was therefore clearly associated with the presence of gold on the catalyst surface The latter was found to be much less active than the oxygen inherent to the oxide but was at a concentration of approximately 10 times larger leading to the enhanced activity observed on gold doping (C) 2010 Elsevier Inc All rights reserved

GABA accumulation and the hypersensitive response in isolated mesophyll cells treated with the G protein activator mastoparan

GABA (y-amino butyric acid) is a non-protein amino acid synthesized through the a-decarboxylation of L-glutamate. This reaction is catalyzed by L-glutamate decarboxylase (EC 4.1.1.15), a cytosolic Ca2+/calmodulin-stimulated enzyme. The purpose of this study is to determine whether or not GABA accumulation is associated with the hypersensitive response of isolated Asparagus sprengeri mesophyll cells. The addition of 25 J.lM mastoparan, a G protein activator, to suspensions of isolated asparagus mesophyll cells significantly increased GABA synthesis and cell death. Cell death was assessed using Evan's blue dye and fluorescein diacetate tests for cell viability. In addition, mastoparan stimulated pH-dependent alkalinization of the external medium, and a rapid and large 02 consumption followed by a loss of photosynthetic activity. The rate of 02 consumption and the net decrease in 02 in the dark was enhanced by light. The inactive mastoparan analogue Mas17 was ineffective in stimulating GABA accumulation, medium alkalinization, 02 uptake and cell death. Accumulation of H202 in response tomastoparan was not detected, however, mastoparan caused the cell-dependent degradation of added H202. The pH dependence of mastoparan-stimulated alkalinization suggests cellular electrolyte leakage, while the consumption of 02 corresponds to the oxidative burst in which 02 at the cell surface is reduced to form various active oxygen species. The results are indicative of the "hypersensitive response" of plants to pathogen attack, namely, the death of cells in the locality of pathogen invasion. The data are compatible with a model in which mastoparan triggers G protein activity, subsequent intracellular signal transduction pathway/s, and the hypersensitive response. It is postulated that the physiological elicitation of the hypersensitive response involves G protein signal transduction. The synthesis of GABA during the hypersensitive response has not been documented previously; however the role/s of GABA synthesis in the hypersensitive response, if any, remain unclear.

Eucalyptus ESTs related to genes for oxidative stress

Oxidative stress generating active oxygen species has been proved to be one of the underlying agents causing tissue injury after the exposure of Eucalyptus (Eucalyptus spp.) plants to a wide variety of stress conditions. The objective of this study was to perform data mining to identify favorable genes and alleles associated with the enzyme systems superoxide dismutase, catalase, peroxidases, and glutathione S-transferase that are related to tolerance for environmental stresses and damage caused by pests, diseases, herbicides, and by weeds themselves. This was undertaken by using the eucalyptus expressed-sequence database (https//forests.esalq.usp.br). The alignment results between amino acid and nucleotide sequences indicated that the studied enzymes were adequately represented in the ESTs database of the FORESTs project.

Role of xanthophyll and water-water cycles in the protection of photosynthetic apparatus in Arbutus unedo and Arabidopsis thaliana

Photosynthetic organisms have sought out the delicate balance between efficient light harvesting under limited irradiance and regulated energy dissipation under excess irradiance. One of the protective mechanisms is the thermal energy dissipation through the xanthophyll cycle that may transform harmlessly the excitation energy into heat and thereby prevent the formation of damaging active oxygen species (AOS). Violaxanthin deepoxidase (VDE) converts violaxanthin (V) to antheraxanthin (A) and zeaxanthin (Z) defending the photosynthetic apparatus from excess of light. Another important biological pathway is the chloroplast water-water cycle, which is referred to the electrons from water generated in PSII reducing atmospheric O2 to water in PSI. This mechanism is active in the scavenging of AOS, when electron transport is slowed down by the over-reduction of NADPH pool. The control of the VDE gene and the variations of a set of physiological parameters, such as chlorophyll florescence and AOS content, have been investigated in response to excess of light and drought condition using Arabidopsis thaliana and Arbutus unedo.. Pigment analysis showed an unambiguous relationship between xanthophyll de-epoxidation state ((A+Z)/(V+A+Z)) and VDE mRNA amount in not-irrigated plants. Unexpectedly, gene expression is higher during the night when xanthophylls are mostly epoxidated and VDE activity is supposed to be very low than during the day. The importance of the water-water cycle in protecting the chloroplasts from light stress has been examined through Arabidopsis plant with a suppressed expression of the key enzyme of the cycle: the thylakoid-attached copper/zinc superoxide dismutase. The analysis revealed changes in transcript expression during leaf development consistent with a signalling role of AOS in plant defence responses but no difference was found any in photosynthesis efficiency or in AOS concentration after short-term exposure to excess of light. Environmental stresses such as drought may render previously optimal light levels excessive. In these circumstances the intrinsic regulations of photosynthetic electron transport like xanthophyll and water-water cycles might modify metabolism and gene expression in order to deal with increasing AOS.

Air bells of water spiders are an extended phenotype modified in response to gas composition

The water spider Argyroneta aquatica (Clerck) is the only spider that spends its whole life under water. Water spiders keep an air bubble around their body for breathing and build under-water air bells, which they use for shelter and raising offspring, digesting and consuming prey, moulting, depositing eggs and sperm, and copulating. It is unclear whether these bells are an important oxygen reservoir for breathing under water, or whether they serve mainly to create water-free space for feeding and reproduction. In this study, we manipulated the composition of the gas inside the bell of female water spiders to test whether they monitor the quality of this gas, and replenish oxygen if required. We exchanged the entire gas in the bell either with pure O(2), pure CO(2), or with ambient air as control, and monitored behavioural responses. The test spiders surfaced and replenished air more often in the CO(2) treatment than in the O(2) treatment, and they increased bell building behaviour. In addition to active oxygen regulation, they monitored and adjusted the bells by adding silk. These results show that water spiders use the air bell as an oxygen reservoir, and that it functions as an external lung, which renders it essential for living under water permanently. A. aquatica is the only animal that collects, transports, and stores air, and monitors its property for breathing, which is an adaptive response of a terrestrial animal to the colonization of an aquatic habitat. J. Exp. Zool. 307A:549-555, 2007. (c) 2007 Wiley-Liss, Inc.

Dithiothreitol triggers photooxidative stress and fragmentation of the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase in intact pea chloroplasts

In intact chloroplasts isolated from mature pea leaves (Pisum sativum L.), the large subunit (LSU) of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39) was rapidly fragmented into several products upon illumination in the presence of 1 mM dithiothreitol (DTT). Very similar effects on LSU stability could be observed when illuminated chloroplasts were poisoned with cyanide which, like DTT, inhibits important plastid antioxidant enzymes, or when a light-dependent hydroxyl radical-producing system was added to the incubation medium. Moreover, DTT-stimulated light degradation of LSU was markedly delayed in the presence of scavengers of active oxygen species (AOS). It is therefore suggested that light degradation of LSU in the presence of DTT is mainly due to inhibition of the chloroplast antioxidant defense system and the subsequent accumulation of AOS in intact organelles. When chloroplasts were isolated from nonsenescent or senescent leaves, LSU remained very stable upon incubation without DTT, indicating that the antioxidant system was still functional in the isolated chloroplasts during leaf ageing. Our data support the notion that AOS might be important for the degradation of Rubisco in vivo under oxidative stress.

INDUCTION OF DNA STRAND BREAKS AND CROSS-LINKS BY THE NEW ANTICANCER AGENT 3,6-DIAZIRIDINYL-2,5-BIS(CARBOETHOXYAMINO) -1,4-BENZOQUINONE

The DNA breakage effect of the anticancer agent 3,6-diaziridinyl-2,5-bis(carboethoxyamino)-1,4-benzoquinone (AZQ, NSC-182986) on bacteriophage PM2 DNA was investigated using agarose gel electrophoresis. AZQ caused both single-stranded and double-stranded breaks after reduction with NaBH(,4), but it was not active in the native state. At 120 (mu)M, it degraded 50% of the closed circular form I DNA into 40% form II DNA (single-stranded break) and 10% form III DNA (double-stranded break). It produced a dose-response breakage between 1 (mu)M and 320 (mu)M. The DNA breakage exhibited a marked pH dependency. At 320 (mu)M, AZQ degraded 80% and 60% of form I DNA at pH 4 and 10 respectively, but none between pH 6 to 8. The DNA breakage at physiologic pH was greatly enhanced when 10 (mu)M cupric sulfate was included in the incubation mixture. The DNA strand scission was inhibited by catalase, glutathione, KI, histidine, Tiron, and DABCO. These results suggest that the DNA breakage may be caused by active oxygen metabolites including hydroxyl free radical. The bifunctional cross-linking activity of reduced AZQ on isolated calf thymus DNA was investigated by ethidium fluorescence assay. The cross-linking activity exhibited a similar pH dependency; highest in acidic and alkaline pH, inactive under neutral conditions. Using the alkaline elution method, we found that AZQ induced DNA single-stranded breaks in Chinese hamster ovary cells treated with 50 (mu)M of AZQ for 2 hr. The single-stranded break frequencies in rad equivalents were 17 with 50 (mu)M and 140 with 100 (mu)M of AZQ. In comparison, DNA cross-links appeared in cells treated with only 1 to 25 (mu)M of AZQ for 2 hr. The cross-linking frequencies in rad equivalents were 39 and 90 for 1 and 5 (mu)M of AZQ, respectively. Both DNA-DNA and DNa-protein cross-links were induced by AZQ in CHO cells as revealed by the proteinas K digestion assay. DNA cross-links increased within the first 4 hr of incubation in drug-free medium and slightly decreased by 12 hr, and most of the cross-links disappeared after cells were allowed to recovered for 24 hr.^ By electrochemical analysis, we found that AZQ was more readily reduced at acidic pH. However, incubation of AZQ with NaBH(,4) at pH 7.8 or 10, but not at 4, produced superoxide anion. The opening of the aziridinyl rings of AZQ at pH 4 was faster in the presence of NaBH(,4) than in its absence; no ring-opening was detected at pH 7.8 regardless of the inclusion of NaBH(,4). . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI ^