Cytotoxicity of PM(2.5) and PM(2.5--10) ambient air pollutants assessed by the MTT and the Comet assays

Ambient air particulate matters are classified into two distinct modes in size distribution, namely the coarse and fine particles. Correlation between high particulate concentration and adverse effects on human populations has long been recognized, however, the toxicology of these adverse effects has not been clarified. In the current report, the cytotoxic effects of the solvent-extractable organic compounds (SEOC) from fine particles smaller than 2.5 microm (PM(2.5)) and from coarse particles between 2.5-10 microm (PM(2.5-10)) were studied. Nine 24h consecutive monthly samples were tested to determine the correlation between cytotoxicity and total SEOC in two size fractions of particulate air pollution. Cytotoxicity of SEOC was measured by two micro-scale mammalian cells-based bioassays: the MTT cell proliferation assay, and the Comet assay for the detection of DNA damage. A well-defined mammalian cell line - Rat 6 rodent fibroblast was employed in the study. The SEOC extracts of air particulate matters were sub divided into two equal parts. One part was dissolved in DMSO, the other in KOH/hexane and then conjugated with bovine serum albumin to produce a lipid-soluble fraction for testing. The DMSO fraction would contain mainly the polycyclic aromatic hydrocarbons (PAH), alkanes and alkanols, while the lipid-soluble fraction would be enriched with fatty acids. The results from MTT assay showed that cytotoxicity of the PM(2.5) was much more severe than the PM(2.5-10), suggesting that toxic SEOC were confined to the fine particles. By and large, the DMSO solubles were much more toxic than the lipid solubles. The degree of cytotoxicity of the DMSO soluble samples is positively correlated to the amount of particulates present in the ambient air. For the PM(2.5), the winter samples were significantly more toxic than the summer samples in terms of cell killing, which seemed to be a direct reflection of the total loading of organic matter in the samples. Results from Comet assays showed that SEOC samples of PM(2.5) derived from winter months induced DNA damage at dosages resulting in no obvious cell killing in the MTT assay. Thus, long-term exposure to non-killing dosage of air pollutants may lead to the accumulation of DNA lesions, which may be one of the mechanisms responsible for the chronic adverse health effects of particulate air pollution.     

Particle-induced oxidative damage is ameliorated by pulmonary antioxidants

This investigation focuses on the application of an in vitro assay in elucidating the role of lung lining fluid antioxidants in the protection against inhaled particles, and to investigate the source of bioreactivity in urban PM10 collections from South Wales. The Plasmid Assay is an in vitro method of assessing and comparing the oxidative bioreactivity of inhalable particles. This method has provided the basis of limited toxicological studies into various inhaled xenobiotics including asbestos, and more recently PM10. Carbon Black M120 and Diesel Exhaust Particles (DEP) were tested as PM10 surrogates, DEP displaying the greatest oxidative bioreactivity. Both urban PM2.5 (fine fraction) and PM2.5-10 (coarse fraction) (Cardiff, S. Wales, UK) caused significant damage, the coarse fraction displaying higher oxidative capacity. The soluble components were found to be responsible for most of the bioreactivity in both PM sizes. Low molecular components of fresh lung lavage were found to offer most antioxidant protection, and surrogate Epithelial Lining Fluid (sELF) showed significant amelioration of DNA damage by the coarse fraction but less effect against the fine. Overall, the coarse, soluble fraction of PM10 is a great source of oxidative bioreactivity, but natural pulmonary low molecular weight antioxidants can significantly ameliorate its effects.     

Analysis and tracing of polycyclic aromatic hydrocarbons and mutagenicity of airborne particulates from the Taipei area

In a 3-year study, we determined the mutagenicity and polycyclic aromatic hydrocarbons (PAHs) of airborne particulates collected during December 1987-September 1988 (216 samples), October 1988-January 1989 (81 samples), and October 1989-April 1990 (52 samples) from 9 locations in the Taipei area. We found that dichloromethane extracts of all the samples were mutagenic to Salmonella typhimurium in the Ames test. Moreover, the mutagenicity was much higher in the presence of rat liver microsomal fraction (S9 mixture) than that observed in its absence, which indicates that airborne particulates contained both direct and indirect mutagens. The average mutagenicity of the samples collected in the 3-year period was 137, 127, and 118 histidine revertants/10 m3 air, respectively. On the other hand, we found that dichloromethane extracts of each airborne particulate sample contained 14 PAHs with wide variations in concentration and relative distribution. The levels of Pha, Flu, Pyr, and Ben were much higher than the PAHs with higher ring numbers such as BaP, BeP, Pr, IP, and DbA. The average PAH content was 8.0, 5.0, and 7.8 ng/m3 air for airborne particulates collected during December 1986-September 1987, October 1988-January 1989, and October 1989-April 1990, respectively. Among the 9 stations, Fu Hsing Elementary School and Chung Hsing University (Taipei campus), which are, respectively, located in the downtown area and a heavy traffic zone, had significantly higher levels of mutagenicity and PAHs than did the other stations. Moreover, comparative analysis of PAH levels of airborne particulates over the 3-year period revealed an interesting season-dependent change of PAH content in airborne particulates from the Taipei area. The concentrations of individual and total PAHs were consistently lower in the summer than those in the winter. A similar pattern of seasonal change was also observed in the mutagenicity of airborne particulate samples examined. It is worth mentioning that neither PAH level nor mutagenicity of airborne particulates showed significant yearly change over the 3-year period of study. As part of an effort to identify pollution sources, we examined the mutagenicity and PAH compounds of air particulates collected from the burning of garbage (14 samples) and motor-vehicle exhaust in the Hsin Hai Tunnel (17 samples), Taipei. The results showed that garbage burning gave rise to air particulates containing several hundred times higher levels of PAHs and about 20 times stronger mutagenicity, while the motor-vehicle exhaust contained about ten times higher PAH content and mutagenicity as compared with those of airborne particulates of the Taipei city.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effect of grazing on plant patterns in arid ecosystems of Patagonian Monte

Our objective was to assess the relationship between the spatial patterning of perennial grasses (total, grazed, and non‐grazed) and shrub patches in rangelands under different grazing pressures of the Patagonian Monte. We selected three grazed paddocks with the usual stocking rate for the area, where previous studies showed that a piosphere formation is common. At each paddock, we analysed the grain of heterogeneity at sites located at two distances from the single watering point (near, far), using high‐resolution aerial photographs. At these sites, we also assessed in the field the density, size, cover, and spatial patterning of grazed and non‐grazed perennial grasses and shrub patches. The grain of heterogeneity of shrub patches was coarser in sites near the watering point than in those distant from it, as a consequence of the increase in size of both, bare soil and shrub patches. Field sampling showed that a coarse grain of heterogeneity relative to fine‐grained sites resulted from changes in species composition, increased bare soil areas and reduced perennial grass cover. In coarse‐grained sites, lower perennial grass cover resulted from lower density and/or smaller size of grass bunches than in fine‐grained sites. We did not find significant differences among sites in the proportion of perennial grazed grasses. Since the density and cover of perennial grasses was higher in fine‐ than in coarse‐grained sites, we suggested that fine‐grained sites are more important as feeding stations than coarse‐grained sites. The consequences of this differential use could lead to degradation of fine‐grained sites and to higher homogeneity in spatial plant structure and floristic composition within paddocks with respect to the condition observed at present, increasing the size of the highly degraded zone within the piosphere. At the patch level, we found that at about one third of the sampled transects, both total and non‐grazed perennial grasses were spatially aggregated with shrub patches. However, in most transects grazed perennial grasses were indifferently distributed in relation with shrub patches, showing that grazers display high selectivity of foraging sites at macro level (i.e. high and low grazing pressure sites at the paddock level), but random occupancy of vegetation units (randomness in the distribution of grazed perennial grasses at the patch level). The intensity of the positive association between non‐grazed grasses and shrub patches was higher in fine‐grained than in coarse‐grained sites and may be attributed to higher protection against herbivores associated to denser shrub patches in fine‐ relative to coarse‐grained sites. We concluded that a feedback exists between the spatial distribution of species preferred by grazers and the spatial patterning of use of these species.     

模拟酸雨及其酸化土壤对小麦幼苗体内可溶性糖和含氮量的影响

以小麦为试材,采用盆栽方法研究了模拟酸雨及其酸化土壤对小麦幼苗体内可溶性糖和含N量的影响.结果表明,pH值为5.6、4.5、3.5、3.0和2.5的系列模拟酸雨引起了土壤酸化和盐基流失.当模拟酸雨的pH值由5.6下降到2.5时,被淋溶土壤的pH值由.0下降到3.41,土壤中交换性盐基总量从56.5下降到41.1mmol·kg^-1.将小麦幼苗栽培在该系列酸化土壤上,并分别用5种不同pH值的模拟酸雨喷淋地上器官,导致小麦幼苗体内的可溶性糖含量、含N量迅速下降,某些生理活动降低.其中,模拟酸雨喷淋对小麦幼苗茎叶可溶性糖含量、含N量、叶绿素含量以及光合速率的影响大于酸化土壤对其产生的影响.而酸化土壤对小麦幼苗根系中可溶性糖含量、含N量、硝酸还原酶(NR)和谷氨酸合成酶(GOGAT)活性的影响大于模拟酸雨喷淋的影响.pH≤3.0的高强度酸雨以及由其产生的酸化土壤(T₄、T₅土壤)对小麦幼苗的碳素代谢和氮素代谢具有明显的抑制作用.     

沙地樟子松幼苗干旱致死过程中非结构性碳水化合物的变化

以2年生沙地樟子松幼苗为对象,通过持续自然干旱处理,研究当土壤含水量下降到田间持水量的60%、40%、30%、20%和15%时幼苗叶片水势及不同器官(一年生叶、当年生叶、茎、粗根和细根)的可溶性糖、淀粉和非结构性碳水化合物(NSC)的含量,分析沙地樟子松幼苗在干旱致死过程中各器官NSC的分配规律及其适应机制.结果表明: 土壤含水量从田间持水量的40%下降到15%,幼苗叶片凌晨及正午水势无显著变化.当土壤含水量从田间持水量的60%下降到30%,各器官可溶性糖、淀粉、NSC含量和可溶性糖/淀粉先下降后上升.从30%下降到20%,当年生叶、一年生叶、茎和细根可溶性糖、淀粉和NSC含量降低,而粗根可溶性糖含量增加,淀粉和NSC含量减少.从20%下降到15%,当年生叶、一年生叶和茎可溶性糖、淀粉和NSC含量降低,粗根可溶性糖和NSC含量下降,淀粉含量上升,细根可溶性糖含量减少,淀粉和NSC含量增加.沙地樟子松幼苗通过不断调整各器官NSC及其组分含量变化以适应不同干旱环境,土壤含水量下降到田间持水量的30%后,幼苗可溶性糖和NSC含量总体呈下降趋势,淀粉在粗根和细根中积累,幼苗可能因碳耗竭而死亡.     

蒙古莸幼苗干旱致死过程中非结构性碳水化合物的变化

以一年生蒙古莸幼苗为对象,设置适宜水分、慢速干旱致死和快速干旱致死3个处理,研究不同干旱强度致死下蒙古莸幼苗各器官中非结构性碳水化合物(NSC,包括可溶性糖和淀粉)的含量变化及其分配规律.结果表明:慢速干旱致死胁迫下各器官可溶性糖含量与适宜水分组无显著差异.随时间的推移,茎可溶性糖含量先增加后减少,淀粉和NSC含量增加;粗根可溶性糖含量减少,淀粉和NSC含量增加;叶可溶性糖含量增加,淀粉和NSC含量减少.致死时(80 d),叶、茎、粗根和细根的NSC含量分别为6.2%、7.8%、8.3%和7.4%.快速干旱致死胁迫下,各器官可溶性糖含量均高于适宜水分处理组,而淀粉和NSC含量均低于适宜水分组.随时间的推移,根可溶性糖含量下降,淀粉和NSC含量上升;茎可溶性糖、淀粉和NSC含量均上升;叶可溶性糖含量上升,淀粉和NSC含量下降.致死时(30 d),叶、茎、粗根和细根的NSC含量分别为5.9%、6.6%、8.9%和7.7%.应对不同的干旱致死情况,蒙古莸幼苗各器官间非结构性碳水化合物呈现出不同的动态变化.在慢速干旱致死胁迫下,NSC优先为维持各器官生理代谢活动提供能量;而在快速干旱致死下,NSC主要以可溶性糖形式维持植物代谢,调节渗透势,促进吸水,应对急剧的干旱胁迫.     

Root Growth of the Annual Tillering Grass Panicum miliaceum in Heterogeneous Nutrient Environments (in English)

To study growth responses of the roots of Panicum miliaceum L. to heterogeneous supply of nutrients. The authors analyzed the effects of the nutrient levels in both original patches (O) and destination patches (D) on the root growth of P. miliaceum when its roots were allowed to extend from original patch into destination patch. When the nutrient levels in the original patches were low, coarse root biomass ratio (coarse root biomass in the D/total coarse root biomass), coarse root length ratio (coarse root length in the D/total coarse root length), coarse root surface area ratio (coarse root surface area in the D/total coarse root surface area) and fine root length ratio (fine root length in the D/total fine root length) were greater in the destination patches with lower nutrient levels than in the destination patches with higher nutrient levels, while fine root length, fine root length density, fine root surface index, and fine root surface area density were smaller in the former than in the latter. When the nutrient levels in the original patches were high, fine root length, fine root length density, fine root surface area index and fine root surface density were greater in the destination patches with lower nutrient levels than in the destination patches with higher nutrient levels, coarse roots did not respond to the nutrient levels in the destination patches significantly. When the roots extended from the original patches with the same nutrient level into the destination patches with contrasting nutrient levels, fine root biomass and its percentage allocation did not respond to the nutrient levels in the destination patches significantly, whereas both root length and root surface area did. This indicates that the fine roots of P. miliaceum responded to difference in nutrient supply by plasticity in their length and surface area, rather than in their root biomass.     

异质养分环境中一年生分蘖草本黍根系的生长特征

为揭示黍（Panicum miliaceum L.)根系对异质养分环境的生长反应,作研究了黍根系从起始斑块向目标斑块水平生长时,时始斑块和目标斑块养分水平根生长的影响,就低养分起始珏块而言,粗根生物量,粗根长度,粗根表面积和细极长度在高养分目标斑块中的分配比例均小于其在低养分目标斑块中的分配比例,而细根长度及其密度,细根表面积指及其密度的变化恰好相反,就高养分起始斑块而言,高养分目标斑块的细根长度,细根长度密度,细根表面积指数和细根表面积密均不于低养分目标斑块,而粗根对目标斑块中养分状的反应不明显。当黍根系从桢的起始斑块进入不同的目标斑块后,目标斑块的养分状况对细根生物量及其分配无影响,而显影响细根长度和表现积,这指示细根是通过长度和表面积可塑性而不是生物量变化响应目标斑块中的养分差异。     

Does soil acidity reduce subsoil rooting in Norway spruce (Picea abies)?

Increasing evidence suggests that forest soils in central and northern Europe as well as in North America have been significantly acidified by acid deposition during the last decades. The present investigation was undertaken to examine the effect of soil acidity on rooting patterns of 40-year-old Norway spruce trees by comparing fine and coarse roots among four stands which differed in soil acidity and Mg (and Ca) nutrition. The coarse root systems of four to five 40-year-old Norway spruce trees per stand were manually excavated. The sum of cross sectional area (CSA) at 60 cm soil depth and below of all vertical coarse roots, as a measure of vertical rooting intensity, was strongly reduced with increasing subsoil acidity of the stands. This pattern was confirmed when 5 additional acidic sites were included in the analysis. Fine root biomass in the mineral soil estimated by repeated soil coring was strongly reduced in the heavily acidified stands, but increased in the humic layer. Using ingrowth cores and a screen technique, we showed that the higher root biomass in the humic layer of the more acidic stands was a result of higher root production. Thus, reduced fine root biomass and coarse root CSA in deeper soil layers coincided with increased root growth in the humic layer. Root mineral analysis showed Ca/Al ratios decreased with decreasing base saturation in the deeper mineral soil (20–40 cm). In the top mineral soil, only minor differences were observed among stands. In general, low Ca/Al ratios coincided with low fine root biomass. Calcium/aluminum ratios determined in cortical cell walls using X-ray microanalysis showed a similar pattern as Ca/Al ratios based on analysis of whole fine roots, although the amplitude of changes among the stands was much greater. Aluminum concentrations and Ca/Al ratios in cortical cell walls were at levels found to inhibit root growth of spruce seedlings in laboratory experiments. The data support the idea that Al (or Ca/Al ratios) and acid deposition-induced Mg (and possibly Ca) deficiency are important factors influencing root growth and distribution in acidic forest soils. Changes in carbon partitioning within the root system may contribute to a reduction in deep root growth.     

长沙城市斑块湿地资源的时空演变

利用GIS技术,对长沙市1955、1972和1990年地形图湿地数据及2007年长沙市湿地资源普查数据进行提取和分析,选取最具代表性的斑块湿地作为研究对象,从时间与空间、动态与静态、规模与填埋等视角,研究50年来城市斑块湿地生态系统各层次要素的时空演变过程和变化规律.结果表明:(1)时间层次上,长沙城市斑块湿地总面积呈现先增后减、总体增加的态势;斑块湿地面积变化幅度不断加大,速率逐步加快;(2)规模层次上,面积在32 hm2规模以下的斑块湿地呈增加态势,32 hm2规模以上斑块湿地呈减少态势;(3)动态空间层次上,被填埋斑块湿地的比例在建成区和郊区呈相反的演变结果;(4)静态空间层次上,斑块湿地密度在建成区范围和郊区范围演变结果相背.研究显示,伴随着城市化进程,不同时间尺度、不同规模尺度、不同空间属性、不同空间状态的城市斑块湿地常常呈现差异很大、甚至是截然相反的演变结果;无论是动态空间还是静态空间,建成区与郊区的空间分界线往往是城市斑块湿地演变态势的分水岭.     

Gel formation by fibrin oligomers without addition of monomers

Soluble fibrin oligomers were formed by reacting fibrinogen with thrombin under fine clotting conditions where the action of thrombin is the rate-determining step for polymerization, and by inhibiting the reaction shortly before gelation. Oligomeric fibrin was separated from unreacted fibrinogen and small oligomers by gel permeation chromatography. Electron microscopy revealed that the largest soluble fibrin oligomers resemble the protofibrils present in fine clots, but are somewhat shorter and entirely lack the twisted, trifunctional junctions that contribute to the elastic properties of fine clots. When thrombin was added to the soluble fibrin oligomers, polymerization resumed and clots were formed at a more rapid rate than from fibrinogen at the same concentration and resulted in a less-opaque clot under coarse clotting conditions. The results confirm a prediction of a theory for the polymerization of fibrin and provide additional evidence that the final state of a coarse fibrin clot depends on the mobility of protofibrils during its formation.     

Mutagenicity and polycyclic aromatic hydrocarbons analysis of airborne particulate matters from Taipei City

The mutagenic activity of dichloromethane extracts of 147 air particulate samples collected from 8 stations during December 1986-June 1987 in Taipei city was consistently higher in S. typhimurium strain TA 98 than in strain TA 100 in the presence of S9 mixture. Among the 8 stations, Nan Kang Police Station, Fu Hsing Elementary School, and Chung Hsing University which were located in the industrial district, downtown area, and heavy traffic zone, respectively, had significantly higher levels of PAHs than the other stations. In contrast, the levels of PAHs were much lower in the suburban station, near Pei Tou Elementary School. However, PAH contents of the air particulate samples collected from these stations did not show good correlation with their mutagenicity. The air particulates collected at some stations on Sunday when the traffic changed from heavy to light showed lower mutagenicity and PAH contents as compared with the other weekdays at the same stations. On the contrary, the samples collected at Pei Tou station in a suburban area where the traffic changed from light to heavy on Sunday showed higher mutagenicity and PAH contents. The monthly average of PAHs of air particulate samples collected over a 7-month period from 8 stations in Taipei city was lower than the average in 1980. Moreover, when compared with other countries, such as U.S.A., the Netherlands, West Germany, Italy, Norway, and Japan, the levels of PAHs and mutagenicity of air particulate matters in Taipei city were similar or slightly lower. The mutagenicity and contents of PAHs of air particulates collected from burnt ABS were significantly higher than those of burnt PVC. One sample PT-6-3 was collected while a nearby garbage collection area was on fire. The mutagenicity of that sample increased 3 to 16 fold and contained an 11 to 33 times higher content of the six PAHs (BaP, BeP, BbF, BaA, Chr, and DbA) as compared with the other samples collected at the same location at a different time. The higher mutagenicity and PAH contents of that sample might be due to the pollution of the air from combustion of the garbage containing products made of ABS.     

Involvement of nitro-compounds in the mutagenicity of urban Pm2.5 and Pm10 in Turin

Fine particles can be active carriers of toxic compounds into the alveoli of the lungs. Among these compounds are numerous mutagens and carcinogens. The direct mutagenicity per unit mass of fine particulate matter (PM) is significantly higher than that of coarse particles, especially in urban areas. In this study, the mutagenic properties of urban PM2.5 and PM10 were evaluated, and the role of nitro-compounds was estimated. PM2.5 and PM10 samplings, and measurements of NOx and some PAHs were performed daily in 2007 in Turin, following a consolidated in vitro test - the Salmonella mutagenicity assay - conducted with organic extracts of PM2.5 and PM10. The mutagenic properties were assessed for each month of sampling with Salmonella typhimurium strain TA98 and TA98-derived strains: a nitroreductase-deficient mutant strain (TA98NR) and an additional nitroreductase-producing plasmid strain (YG1021). The annual measured mean levels of PM2.5 and PM10 were 34±20 and 48±18μg/m(3). The PM2.5/PM10 ratio ranged from 0.36 to 0.89. The Salmonella assay showed higher mutagenicity in autumn/winter (20±15 TA98NR; 54±39 TA98; 173±161 YG1021 net revertants/m(3)) compared with spring/summer (2±2 TA98NR; 7±8 TA98; 24±27 YG1021 net revertants/m(3)) (p<0.01). There are also statistically significant seasonal differences in the gravimetric analysis data. The number of TA98 net revertants per μg of PM2.5 is 6.5 times greater than per μg PM10. Moreover, the bioassay results showed an amplified response in the YG1021 strain and a reduced response in the TA98NR strain. The net revertant ratio TA98NR/YG1021 is 11±4 for organic extracts of PM2.5 and 13±6 for extracts of PM10 (p<0.01). There is a significant correlation between the NOx and PAH concentrations. These findings illustrate the relevant role of nitro compounds, and they underline the priority in improving preventive measures to reduce air pollution by nitrated molecules.     

大气CO2浓度升高对红桦幼苗根系的影响

应用封闭式生长室系统,研究了CO2浓度升高对红桦(Betula albosinensis)幼苗的根/冠、粗根和细根的干质量、非结构性碳水化合物类含量、碳含量和碳/氮、氮和磷的含量及氮磷吸收量的影响。结果表明:CO2浓度升高使红桦幼苗粗根和细根的干质量增加,同时根/冠值显著升高,表明CO2浓度升高使红桦幼苗生物量向根系的分配增加;与对照相比,粗根的还原糖、蔗糖和总可溶性糖含量显著增加,而在细根中没有显著变化;粗根、细根的淀粉和总的非结构性碳水化合物含量显著增加;CO2浓度升高下粗根和细根的碳含量有升高的趋势但未达到显著水平,同时氮含量降低,碳/氮值升高;氮的吸收量在粗根和细根中均无显著变化。上述结果表明,CO2浓度升高下红桦幼苗根系氮含量下降是由非结构性碳水化合物(主要是淀粉)含量升高和(或)根系生物量增加产生的稀释效应引起的。     

去叶对水曲柳苗木根系非结构性碳水化合物分配的影响

全球气候变化有促进食叶害虫爆发的趋势.叶片被食会导致光合产物的生产降低,进一步影响非结构性碳水化合物(NSC)在树木体内的储存和分配.本研究以水曲柳2年生苗木根系为研究对象,通过40%去叶处理,于6-10月对根系取样,研究地上碳(C)供应不足条件下主根、粗根和1～5级细根NSC及其组分的分配格局.结果表明: 对照和去叶处理根系NSC浓度及其组分浓度均具有明显的季节动态;与对照相比,去叶处理苗木主根和粗根NSC浓度分别降低3.8%和30.7%,而1～5级细根NSC浓度增加1.2%～23.5%,这主要受淀粉浓度变化的影响;去叶处理苗木主根和粗根可溶性糖浓度增加7.1%和62.3%,而1～5级根可溶性糖浓度显著降低2.7%～42.8%;去叶对苗木根系可溶性糖和淀粉浓度的不同影响,导致二者的比值在主根和粗根中增加,而在1～5级细根中降低.去叶引起光合产物的生产减少,导致水曲柳苗木主根和粗根中淀粉活化后流向细根并以淀粉的形式储存,这可能有利于提高细根对冬季低温胁迫的抵抗力.     

Nickel carcinogenesis: epigenetics and hypoxia signaling

Both water soluble and insoluble nickel compounds have been implicated in the etiology of human lung and nasal cancers. Water insoluble nickel compounds have been shown to enter cells by phagocytosis and are contained in cytoplasmic vacuoles, which are acidified thus accelerating the dissolution of soluble nickel from the particles. Using Newport Green, a dye that fluoresces when ionic nickel is bound, we have shown that following exposure (48-72 h) of human lung (A549) cells to NiS particles, most of the nickel is contained in the nucleus, while cells exposed to soluble NiCl2 exhibit most of the ions localized in the cytoplasm. This effect is consistent with previously published reports showing that short-term exposure of cells to crystalline nickel particles (1-3 days) is able to epigenetically silence target genes placed near heterochromatin, while similar short-term exposure to soluble nickel compounds are not able to induce silencing of genes placed near heterochromatin. However, a 3 week exposure of cells to soluble NiCl2 is also able to induce gene silencing. A similar effect was found in yeast cells where nickel was able to silence the URA-3 gene placed near (1.3 kb) a telomere silencing element, but not when the gene was placed farther away from the silencing element (2.0 kb). In addition to epigenetic effects, nickel compounds activate hypoxia signaling pathways. The mechanism of this effect involves the ability of either soluble or insoluble nickel compounds to block iron uptake leading to cellular iron depletion, directly affect iron containing enzymes, or both. This results in the inhibition of a variety of iron-dependent enzymes, such as aconitase and the HIF proline hydroxylases (PHD1-3). The inhibition of the HIF proline hydroxylases stabilizes the HIF protein and activates hypoxic signaling. Additional studies have shown that nickel and hypoxia decrease histone acetylation and increase the methylation of H3 lysine 9. These events are involved in gene silencing and hypoxia can also cause these effects in human cells. It is hypothesised that the state of hypoxia either by low oxygen tension or as a result of agents that signal hypoxia under normal oxygen tension (iron chelation, nickel and cobalt) results in low levels of acetyl CoA, which is a substrate for histone and other protein acetylation. This effect may in part be responsible for the gene silencing following nickel exposure and during hypoxia.     

Cytotoxicity of salicylaldehyde benzoylhydrazone analogs and their transition metal complexes: quantitative structure-activity relationships

A series of salicylaldehyde benzoylhydrazone derivatives, their copper(II) complexes and a range of transition metal complexes of the unsubstituted ligand has been synthesized and evaluated for cytotoxicity against a human adenocarcinoma cell line. A QSAR analysis revealed ligand cytotoxicity is strongly correlated with electronic and transport factors and can be modeled by treating each 'half' of the molecule as an isolated unit. Activity increases when substituents in the benzoyl ring were electron withdrawing whereas, for the salicylaldehyde ring, electron donation was required. The cytotoxicity of the Cu(II) complexes was greater than, and paralleled the ligands. Activity for the transition metal complexes of the unsubstituted ligand mirrored charge density on the metal.     

水曲柳和落叶松人工林根系分解与养分释放

采用埋袋法对水曲柳和落叶松粗根(5～10 mm)、中根(2～5 mm)、细根(＜2 mm)的分解速率及其养分释放进行了为期2年的研究.结果表明,水曲柳粗根、中根和细根年分解系数分别为0.3649、0.4381和0.2720,落叶松依次分别为0.1967、0.1955和0.2464.通过养分分析发现,根系分解过程释放大量C和养分.分解150 d后,两树种所有级别根系的可溶性糖释放均超过90%.水曲柳粗根和中根K的释放均在40%左右,细根K的释放为71%,落叶松所有级别的根系K的释放均在95%以上.在根系分解第2年,两树种粗根和中根N的释放在50%左右波动,P在40%左右波动,两树种细根N和P的释放均达到60%.因此,根系分解在C和养分循环中起重要作用,如果将其忽略,土壤有机质和养分元素的循环将会被严重低估.