豌豆根瘤菌ohrB基因的抗氧化和共生固氮表型

采用基因敲除构建豌豆根瘤菌ohr B基因突变株,研究突变株的抗氧化和共生固氮表型。结果表明:ohr B基因不影响菌株在自生培养条件下的生长能力,但对氢过氧化枯烯(cumene hydroperoxyde,Cu OOH)、过氧化氢(H2O2)、次氯酸钠(Na Cl O)等氧化物敏感,且在Cu OOH胁迫下,相比野生型菌株,突变株的存活率显著下降。荧光定量RT-PCR结果显示,豌豆根瘤菌ohr B基因表达不受H2O2诱导,且ohr B基因的缺失对其他抗氧化基因的表达没有影响。共生实验表明,ohr B基因对根瘤菌共生固氮能力及根际定殖能力没有影响,但在7 d瘤龄的豌豆根瘤类菌体中表达水平显著提高,并对根瘤菌结瘤能力有影响。ohr B基因虽对豌豆根瘤菌的自生生长、共生固氮、根圈定殖没有影响,但在抗氧化及竞争结瘤中发挥重要作用。     

施氮后蚯蚓对植物吸氮及微生物固氮的影响

为探讨尿素施用后蚯蚓对植物吸氮量及微生物固氮量的影响,通过盆栽试验,以威廉腔环蚓(Metaphire guillelmi)为试验材料,对比有、无蚯蚓作用下15N标记的尿素施入后植物氮素含量的差异及土壤微生物量的变化过程。结果表明:培养结束后对植物进行取样测定,发现不同处理间植株氮含量并无显著差异,但接种蚯蚓的处理增加了植株生物量,进而导致蚯蚓作用下的植株总吸氮量提高了约30.8%。从分配比例上看,接种蚯蚓显著增加了植物吸收土壤氮的比例,却显著降低了植物吸收肥料氮的比例。在整个试验过程中,两处理的全氮(TN)含量均无显著变化,但土壤中来源于肥料的氮却随着培养的进行逐渐降低,且接种蚯蚓使其下降速度更快。微生物生物量氮(M BN)先下降后上升,且接种蚯蚓处理的MBN含量在试验初期(第5d)与试验末期(第30d)较高,但MBN中固定的肥料氮含量始终低于不接种蚯蚓的对照处理。试验过程中,土壤可溶性有机氮(D ON)的含量先下降后上升,与MBN变化趋势一致。与对照处理相比,接种蚯蚓处理的铵态氮(N H4+-N)含量降低,硝态氮(N O-3-N)含量则差异不显著。综上,蚯蚓可通过调节微生物生物量形成氮素缓冲库,从而促进植株对土壤氮而非尿素氮的吸收。     

Biological nitrogen fixation in Lake Erie

Biological nitrogen fixation, as determined by acetylene reduction, occurs in Lake Erie. Fixation potential by blue-green algae in situ in water and by bacteria in collected sediments was demonstrated. Nitrogen-fixing activity occurred from June through November suggesting that it is significant over the extremes of seasonal variation in light, temperature, and nutrients.     

StP5CS基因过表达增强高温胁迫下菜用大豆结瘤固氮的能力

高温胁迫严重影响菜用大豆的结瘤固氮过程,增强高温胁迫下菜用大豆结瘤固氮的能力对提高菜用大豆产量具有重要意义。采用蛭石栽培的方法,以转StP5CS基因菜用大豆(T6)为试验材料,研究在35℃高温胁迫下StP5CS基因过表达对菜用大豆结瘤固氮的影响。结果显示:转基因株系的株高、干鲜重及根瘤数目、根瘤干鲜重、单株荚数、粒数、种子重均显著高于非转基因株系(WT);转基因株系根瘤中脯氨酸、豆血红蛋白含量及谷氨酰胺合成酶活性均显著高于WT;经qRT-PCR分析,5个结瘤固氮关键基因(GmENOD40-1,GmENOD40-2,GmGS1β1,GmGS1β2及GmLba)在转基因株系中的相对表达量均显著高于WT。结果表明,高温胁迫下StP5CS基因过表达,促进了脯氨酸的积累,显著增强了菜用大豆的耐热性和结瘤固氮能力,进而提高了菜用大豆的产量。     

Ecosystem feedbacks and nitrogen fixation in boreal forests

Biological feedback mechanisms regulate fundamental ecosystem processes and potentially regulate ecosystem productivity. To date, no studies have documented the down-regulation of terrestrial nitrogen (N) fixation via an ecosystem-level feedback mechanism. Herein, we demonstrate such a feedback in boreal forests. Rapid cycling of N in early secondary succession forests yielded greater throughfall N deposition, which in turn decreased N fixation by cyanobacterial associates in feather moss carpets that reside on the forest floor. The forest canopy exerts a tight control on biotic N input at a period of high productivity.     

StNHX1基因过表达对盐胁迫下菜用大豆结瘤固氮的影响

盐胁迫严重影响菜用大豆结瘤固氮过程,提高盐胁迫下菜用大豆结瘤固氮效率对提高菜用大豆产量具有重要意义。采用砂培方法,以转StNHX1基因菜用大豆(T4)为试验材料,研究了在50mmol NaCl胁迫下StNHX1基因过表达对菜用大豆结瘤固氮的影响。结果显示:转基因株系种子粒数、种子重量及根瘤数目均显著高于非转基因株系(WT);转基因株系根瘤中Na+含量显著低于WT,K+及脯氨酸含量均显著高于WT。转基因株系的全氮、豆血红蛋白含量及谷氨酰胺合成酶活性均显著高于WT。经qRT-PCR分析,5个结瘤固氮关键基因(GmENOD40a、GmENOD40b、GmLba、GmGS1β1和GmGS1β2)在转基因株系中的相对表达量均显著高于WT。以上结果表明,盐胁迫下,过表达StNHX1基因显著增强了菜用大豆的结瘤固氮能力,进而提高了菜用大豆的产量。     

氮素与豆科作物固氮关系研究进展

氮素与根瘤固氮结合可达高产,两者矛盾对根瘤固氮产生不利影响。氮素影响根瘤固氮作用机制仍不明确。文章在现有研究成果基础上,总结氮素与大豆根瘤固氮关系研究发展进程;综述不同氮素形态和氮素浓度对根瘤形成和生长、根瘤固氮酶活性影响及相关机制研究动态;阐述氮素抑制根瘤固氮碳水化合物争夺、抑制根瘤氧供给、硝酸盐毒害、反馈调节及其他可能抑制机制;提出氮素抑制结瘤氮浓度界限模糊化,不同氮素形式、豆科种类氮素抑制机制差异化及详细抑制机制不明确等问题。     

Quantitative imaging of nitrogen fixation by individual bacteria within animal cells

Biological nitrogen fixation, the conversion of atmospheric nitrogen to ammonia for biosynthesis, is exclusively performed by a few bacteria and archaea. Despite the essential importance of biological nitrogen fixation, it has been impossible to quantify the incorporation of nitrogen by individual bacteria or to map the fate of fixed nitrogen in host cells. In this study, with multi-isotope imaging mass spectrometry we directly imaged and measured nitrogen fixation by individual bacteria within eukaryotic host cells and demonstrated that fixed nitrogen is used for host metabolism. This approach introduces a powerful way to study microbes and global nutrient cycles.     

MCHK＿7135基因在华癸中慢生根瘤菌共生固氮中的功能

为研究MCHK＿7135基因在根瘤菌与宿主植物共生固氮中的功能,用同源重组的方法构建了MCHK＿7135基因的突变体及回补菌株,对突变菌株和回补菌株在人工培养条件以及与宿主植物紫云英共生下的各项表型进行了考察,结果显示：与野生型菌株相比,突变菌株对氧胁迫的敏感性增强;接种突变株的紫云英长势矮小,侵染线及根瘤原基数目减少,根瘤数量少,固氮酶活性低,而向突变菌株导入完整MCHK＿7135基因后,各项共生表型得到不同程度恢复。研究结果表明,华癸中慢生根瘤菌的过氧化物还原酶基因MCHK＿7135基因在根瘤菌与宿主植物共生固氮的过程中具有重要功能。     

Translocation and rearrangement of myeloperoxidase gene in acute promyelocytic leukemia

Acute promyelocytic leukemia (subtype M3) is characterized by malignant promyelocytes exhibiting an abundance of abnormally large or aberrant primary granules. Myeloperoxidase (MPO) activity of these azurophilic granules, as assessed by cytochemical staining, is unusually intense. In addition, M3 is universally associated with a chromosomal translocation, t(15;17)(q22;q11.2). In this report, the MPO gene was localized to human chromosome 17 (q12-q21), the region of the breakpoint on chromosome 17 in the t(15;17), by somatic cell hybrid analysis and in situ chromosomal hybridization. By means of MPO complementary DNA clones for in situ hybridization and Southern blot analysis, the effect of this specific translocation on the MPO gene was examined. In all cases of M3 examined, MPO is translocated to chromosome 15. Genomic blot analyses indicate rearrangement of MPO in leukemia cells of two of four cases examined. These findings suggest that MPO may be pivotal in the pathogenesis of acute promyelocytic leukemia.     

接种根瘤菌对豆科绿肥的固氮效果研究

对豆科绿肥接种根瘤菌能显著提高豆科绿肥的固氮作用,提高土壤的肥力水平,增加土壤微生物,增加豆科绿肥的年固氮量,提高豆科绿肥与禾本科牧草的鲜草产量和品质,从而提高豆科绿肥的利用率。     

Optimized nitrogen application methods to improve nitrogen use efficiency and nodule nitrogen fixation in a maize-soybean relay intercropping system

In China, the abuse of chemical nitrogen(N) fertilizer results in decreasing N use efficiency(NUE), wasting resources and causing serious environmental problems. Cereal-legume intercropping is widely used to enhance crop yield and improve resource use efficiency, especially in Southwest China. To optimize N utilization and increase grain yield, we conducted a two-year field experiment with single-factor randomized block designs of a maize-soybean intercropping system(IMS). Three N rates, NN(no nitrogen application), LN(lower N application: 270 kg N ha–1), and CN(conventional N application: 330 kg N ha–1), and three topdressing distances of LN(LND), e.g., 15 cm(LND1), 30 cm(LND2) and 45 cm(LND3) from maize rows were evaluated. At the beginning seed stage(R5), the leghemoglobin content and nitrogenase activity of LND3 were 1.86 mg plant–1 and 0.14 m L h–1 plant–1, and those of LND1 and LND2 were increased by 31.4 and 24.5%, 6.4 and 32.9% compared with LND3, respectively. The ureide content and N accumulation of soybean organs in LND1 and LND2 were higher than those of LND3. The N uptake, NUE and N agronomy efficiency(NAE) of IMS under CN were 308.3 kg ha–1, 28.5%, and 5.7 kg grain kg–1 N, respectively; however, those of LN were significantly increased by 12.4, 72.5, and 51.6% compared with CN, respectively. The total yield in LND1 and LND2 was increased by 12.3 and 8.3% compared with CN, respectively. Those results suggested that LN with distances of 15–30 cm from the topdressing strip to the maize row was optimal in maize-soybean intercropping. Lower N input with an optimized fertilization location for IMS increased N fixation and N use efficiency without decreasing grain yield.     

Oligotrophy and nitrogen fixation during eastern mediterranean sapropel events

Nitrogen isotopic measurements in fossil chlorophyll from late Pleistocene organic-rich sediments (sapropels) in the eastern Mediterranean Sea provide geochemical evidence for stratified, nutrient-depleted surface water and extensive nitrogen fixation. This evidence is reconciled with previous indications of high productivity by invoking a model of sapropel formation in which increased river discharge facilitates development of a specialized phytoplankton population whose annual mass sinking provides the organic flux to generate sapropels. This interpretation is consistent with the widespread occurrence of mat-forming diatoms that thrive in stratified water and can harbor diazotrophic bacterial symbionts, but does not support eutrophication of surface waters by enhanced river runoff or a circulation reversal.     

Suppression of nitrogen fixation by blue-green algae in a eutrophic lake with trace additions of copper

Nitrogen fixation by blue-green algae in highly eutrophic Clear Lake, California, was severely inhibited by trace amounts of copper. The chelation capacity of the lake is probably saturated by indigenous copper. Additions were only 1/200 of those normally used in algal control. Since nitrogen fixation provides half of the lake's annual nitrogen budget, economical eutrophication control appears possible.     

Role of symbiotic nitrogen fixation in increasing photosynthetic productivity of soybean

The relation between symbiotic and photosynthetic activities of soybean variety Garmoniya crops is shown. The positive effect of sodium humate, root nodule strains, and molybdenum and ammophos salts on the accumulation of the mass of nodules and their activity, formation of the accumulation surface of plants and length of its functioning is established. The close correlation between the accumulation of the mass of nodules and nitrogen content in leaves and vegetative mass of plants is determined. Activation of symbiotic activity of crops increases soybean seed productivity by 10.8–24.7%.