Silicon decreases the arsenic level in rice grain by limiting arsenite transport

Silicon (Si) reduces arsenic (As) levels in rice shoot and grain. However, the underlying mechanisms remain unclear. In this study, we examined the effect of Si application to three rice paddy soils on the dynamics of Si, iron (Fe), phosphorus (P), and As in the soil solution, As accumulation in rice straw, flag leaf, husk, brown rice, and polished rice, and on As speciation in polished rice. Silicon application to soil increased the concentrations of Si, Fe, As, and P in the soil solution, while the redox potential was unaffected. Arsenic concentrations of straw, flag leaf, and husk were reduced by half by Si application, while As concentrations of brown and polished rice were decreased by 22%. The main As species in polished rice was arsenite, As(III), with a fraction of 70%, followed by dimethylarsinic acid (DMA) and arsenate, As(V), with 24% and 6%, respectively. Silicon application to the soil did not affect DMA or As(V) concentration of polished rice, while the As(III) concentration was reduced by 33%. These results confirm that Si reduces As(III) uptake and translocation into the shoot. Furthermore, data indicate that decrease of As concentration of polished rice is due to decreased As(III) transport into grain. Possible underlying mechanisms are discussed.     

不同措施对冷浸田土壤还原性物质含量及水稻产量的影响

研究明确不同措施对冷浸田土壤还原性物质含量及水稻产量的影响,以期为适宜改良剂的筛选和应用提供理论依据。田间试验设置优化施肥及不同措施（石灰、有机肥和秸秆）等6个处理,比较各处理对土壤氧化还原电位、还原性物质含量、水稻产量和养分吸收的影响。合理施肥可以显著地降低冷浸田土壤还原性物质总量,并提高水稻产量,增幅为26.2%。石灰和有机肥对水稻产量无显著影响;秸秆还田可显著提高土壤氧化还原电位,降低土壤还原性物质浓度,增产14.2%。石灰和秸秆混合施用不仅显著提高土壤Eh,而且降低土壤活性还原性物质和Fe2+含量,降幅分别为40.0%和49.3%,显著增产19.8%。优化施肥、石灰和秸秆的配合施用均是消减冷浸田还原性物质含量的有效措施。     

In Vitro Functional Study of Rice Adenosine 5'-Phosphosulfate Kinase

Sulfate can be activated by ATP sulfurylase and adenosine 5'-phosphosulfate kinase(APSK) in vivo. Recent studies suggested that APSK in Arabidopsis thaliana regulated the partition between APS reduction and phosphorylation and its activity can be modulated by cellular redox status. In order to study regulation of APSK in rice(Os APSK), Os APSK1 gene was cloned and its activity was analyzed. Os APSK1 C36 and C69 were found to be the conserved counterparts of C86 and C119, which involved in disulfide formation in At APSK. C36A/C69 A Os APSK1 double mutation was made by site directed mutagenesis. Os APSK1 and its mutant were prokaryotically over-expressed and purified, and then assayed for APS phosphorylation activity. Os APSK1 activity was depressed by oxidized glutathione, while the activity of its mutant was not. Further studies in the case that oxidative stress will fluctuate in vivo 3'-phosphoadenosine-5'-phosphosulfate content, and all APSK isoenzymes have similar regulation patterns are necessary to be performed.     

Sulfur speciation in well‐aerated and wetland soils in a forested catchment assessed by sulfur K‐edge X‐ray absorption near‐edge spectroscopy (XANES)

In forested catchments, retention and remobilization of S in soils and wetlands regulate soil and water acidification. The prediction of long‐term S budgets of forest ecosystems under changing environmental conditions requires a precise quantification of all relevant soil S pools, comprising S species with different remobilization potential. In this study, the S speciation in topsoil horizons of a soil toposequence with different groundwater influence and oxygen availability was assessed by synchrotron‐based X‐ray absorption near‐edge spectroscopy (XANES). Our investigation was conducted on organic (O, H) and mineral topsoil (A, AE) horizons of a Cambisol–Stagnosol–Histosol catena. We studied the influence of topography (i.e., degree of groundwater influence) and oxygen availability on the S speciation. Soil sampling and pretreatment were conducted under anoxic conditions. With increasing groundwater influence and decreasing oxygen availability in the sequence Cambisol–Stagnosol–Histosol, the C : S ratio in the humic topsoil decreased, indicating an enrichment of soil organic matter in S. Moreover, the contribution of reduced S species (inorganic and organic sulfides, thiols) increased systematically at the expense of intermediate S species (sulfoxide, sulfite, sulfone, sulfonate) and oxidized S species (ester sulfate, SO ). These results support the concept of different S‐retention processes for soils with different oxygen availability. Sulfur contents and speciation in two water‐logged Histosols subject to permanently anoxic and temporarily oxic conditions, respectively, were very different. In the anoxic Histosol, reduced S accounted for 57% to 67% of total S; in the temporarily oxic Histosol, reduced S was only 43% to 54% of total S. Again, the extent of S accumulation and the contribution of reduced S forms to total S closely reflected the degree of O₂ availability. Our study shows that XANES is a powerful tool to elucidate key patterns of the biogeochemical S cycling in oxic and anoxic soil environments. In contrast to traditional wet‐chemical methods, it particularly allows to distinguish organic S compounds in much more detail. It can be used to elucidate microbial S‐metabolism pathways in soils with different oxygen availability by combining soil inventories and repeated analyses of a sample in different stages of field or laboratory incubation experiments under controlled boundary conditions and also to study (sub)microspatial patterns of S speciation in aggregated soils.     

硒对甜樱桃叶片褪黑素和谷胱甘肽氧化还原循环的影响

【目的】研究不同价态和浓度硒对甜樱桃叶片褪黑素含量以及谷胱甘肽(GSH)氧化还原循环的影响,为探究外源硒、内源褪黑素和GSH氧化还原循环间的关系提供参考。【方法】2015年在四川广元进行田间试验,以两年生甜樱桃‘红蜜’和‘布鲁克斯’为试验材料,试验包括清水处理(CK)、单施Se~(6+)(来源于Na_2SeO_4)、单施Se~(4+)(来源于Na_2SeO_3)、Se~(6+)+褪黑素和Se~(4+)+褪黑素5个处理,30 d后采取叶片,测量叶片硒含量和褪黑素的含量。2016年以重庆綦江两年生甜樱桃‘布鲁克斯’叶片为试验材料进行离体试验,将甜樱桃离体叶片放置在2 mg·L~(-1) Se~(6+)处理0、1、2、3和4 d,以清水处理为对照,每天上午10:00采取叶片;将离体叶片分别置于0、0.5、1.0、2.0、4.0 mg·L~(-1) Se~(6+)溶液24 h后采取叶片,离体试验分别测量叶片硒和褪黑素的含量以及GSH氧化还原循环的物质和酶活性。【结果】田间试验中,2.0 mg·L~(-1) Se~(4+)和Se~(6+)处理显著降低了‘红蜜’和‘布鲁克斯’甜樱桃叶片褪黑素含量,且两种甜樱桃叶片褪黑素含量在Se~(6+)+褪黑素和Se~(4+)+褪黑素处理下分别比单施Se~(6+)和单施Se~(4+)处理高。离体试验中,硒处理第1天‘布鲁克斯’离体叶片褪黑素含量高于对照,之后低于对照且随着时间延长而逐渐降低。硒处理第1天迅速降低了GSH氧化还原循环的物质和酶活性,即GSH、氧化性谷胱甘肽(GSSG)、GSH+GSSG和GSH/GSSG比值低于对照,谷胱甘肽过氧化物酶(GPX)和谷胱甘肽还原酶(GR)活性也低于对照,之后随着时间的延长,GSH氧化循环效率升高并超过对照。在不同浓度Se~(6+)处理24 h下,Se~(6+)处理增加了叶片褪黑素的含量,且随着浓度的增加而增加,GSH氧化循环效率则呈下降的趋势。【结论】外源硒处理提高了甜樱桃叶片硒含量,且六价硒的效果显著高于四价硒。外源硒处理影响甜樱桃褪黑素的含量和GSH氧化还原循环。     

土地管理方式对盐化水稻土生物地球化学机能的影响

Most lowlands in Northeast Thailand （Isaan region） are cultivated with rice and large areas are affected by salinity, which drastically limits rice production. A field experiment was conducted during the 2003 rainy season to explore the interactions between salinity and land management in two fields representative of two farming practices： an intensively managed plot with organic inputs and efficient water management, and one without organic matter addition. Field measurements, including pH, Eh, electrical conductivity （EC）, and soil solution chemistry, were performed at three depths, with a particular focus on Fe dynamics, inside and outside saline patches.
High reducing conditions appeared after flooding particularly in plots receiving organic matter and reduction processes leading to oxide reduction and to the release of Fe and, to a lesser extend, Mn to the soil solution. Oxide reduction led to the consumption of H^＋ and the more the Fe reduction was, the higher the pH was, up to 6.5. Formation of hydroxy-green rust were likely to be at the origin of the pH stabilization. In the absence of organic amendments, high salinity prevented the establishment of the reduction processes and pH value remained around 4. Even under high reduction conditions, the Fe concentrations in the soil solution were below commonly observed toxic values and the amended plot had better rice production yield.     

Redox potential: An intrinsic parameter of the rumen environment

The ruminal ecosystem is a fermentative milieu which is interesting to discuss in terms of its redox status as a reflection of an intense bacterial activity. The objective of this systematic literature review is to quantitatively analyze data collected on redox potential (Eh) in the rumen and to explore relationship between ruminal Eh, nature of the diet fed to ruminants, and ruminal fermentation parameters. Data obtained from 15 studies comprising 24 different diets was used in the analysis. Studies included in the data file were selected based on the criteria of: (i) the nature of the reference electrode was specified, (ii) the ruminal Eh was recorded simultaneously to pH, (iii) animal body weight (BW) and dry matter intake (DMI) were reported and (iv) the composition of the diet was precisely described. Results showed a high variability in ruminal Eh values. However, all recorded values are markedly negative reflecting the absence of oxygen and the strong reducing power of the rumen environment. The main factors contributing to the variation were the method of Eh measurement and the nature of the diet fed to ruminants. Redox potential was positively correlated with DMI and proportion of concentrate in the diet, and tended to be positively correlated with soluble carbohydrates content. In contrast, it was negatively correlated with neutral detergent fibre from forages. The hierarchical ascendant classification discriminated two groups of diets leading to significant change in ruminal Eh level. Ruminal Eh was negatively correlated with pH, total volatile fatty acids produced and proportion of acetate, and positively correlated with proportion of propionate. This review revealed Eh to be dependent on the diet composition and DMI, at least within the range of diets included in the database.     

水分胁迫对梨树叶片质膜氧化还原系统的影响

对水分胁迫下早酥梨和杜梨两种梨树叶片的质膜氧化还原系统进行了研究.结果表明,水分胁迫使梨幼树叶片质膜ATPase活性提高,质膜NADH(还原性辅酶Ⅰ)和NADPH(还原性辅酶Ⅱ)的氧化速率及Fe(CN)6 (3-)和EDTA-Fe 3+ 的还原速率降低,GSH(谷胱甘肽)和Vc(抗坏血酸)的氧化速率明显增加,表明除了NADH 和NADPH外,GSH和Vc也可以作为早酥梨幼树叶片质膜氧化还原系统的电子供体.进一步而言 ,在水分胁迫条件下,GSH和Vc可能是代替NADH和NADPH的质膜氧化还原系统的电子供体.     

控制灌溉稻田部分土壤环境因子变化规律

根据现场试验资料,分析了控制灌溉条件下稻田的土壤温度、氧化还原电位、土壤中有机质及铵态氮含量的变化规律及其对水稻生长、稻田环境的影响.结果表明,气温变化对控灌稻田土壤温度的影响较淹灌更加明显,控灌稻田土壤昼夜温差大,有利于改善稻田生态环境和水稻产量的形成;水分调控提高了稻田土壤的Eh水平,控灌稻田5 cm和20 cm土层土壤Eh均极显著高于淹灌稻田(p<0,01),10 cm土层差异不显著,土壤Eh升高减少了土壤中还原性有毒物质含量,增强了水稻根系活性;水分调控加速了土壤中有机质的分解,增加了土壤中的有效养分,有利于水稻的正常生长和发育;控制灌溉条件下土壤中氮素形态发生变化,铵态氮含量降低.     

1,3,4(2H)‐Isoquinolinetriones: evaluation of amino‐substituted derivatives as redox mediator herbicides

Amino‐substituted derivatives of 2‐ethyl‐1,3,4(2H)‐isoquinolinetrione have been prepared with the aim of enhancing their hydrolytic stabilities relative to other isoquinolinetriones, and hence potentially improving their herbicidal effects. 5‐Amino‐2‐ethyl‐1,3,4(2H)‐isoquinolinetrione has been shown to be 12 and 8 times more stable towards hydrolysis than the isomeric 7‐ and 8‐amino derivatives, respectively, and 120 times more stable than 2‐ethyl‐1,3,4(2H)‐isoquinolinetrione itself. Pulse radiolysis studies have shown 5‐amino‐2‐ethyl‐1,3,4(2H)‐isoquinolinetrione to have free‐radical properties which could enhance the generation of superoxide radicals in plants. The compound is a potent stimulator of the light‐dependent consumption of oxygen at photosystem I in isolated chloroplasts and also shows high activity in isolated leaf discs. Evidence is presented which indicates that the rate of foliar uptake is a major factor affecting herbicidal activity for this compound. © 2000 Society of Chemical Industry