聚乙二醇（PEG）浸种对茎瘤芥老化种子活力及其幼苗生长的影响

茎瘤芥品种‘永安小叶’老化种子经聚乙二醇（PEG）浸种后,其种子活力和幼苗生长与PEG浓度有一定的相关性,不同浓度PEG浸种后的茎瘤芥种子膜透性均降低,种子发芽率、发芽势、发芽指数和活力指数增大,幼苗根干重、茎干重和根长也均增大,幼苗叶片中丙二醛（MDA）含量降低。幼苗生长与种子活力的变化趋势一致,PEG浓度小于30%时呈增大趋势,大于30%时呈减小趋势,但均大于不做PEG处理的;幼苗叶片中MDA含量与种子膜透性变化趋势一致,PEG浓度小于25%时,呈降低趋势,大于25%时则呈升高趋势,但这些指标均低于不做PEG处理的。     

入侵植物牛膝菊种子萌发对PEG模拟干旱胁迫的响应

采用浓度分别为5%、10%、15%、20%和25%的PEG-6000溶液模拟干旱条件,测定不同干旱胁迫条件下牛膝菊的种子萌发时间、萌发率、日相对萌发率、发芽势、发芽指数、活力指数及幼苗的初生根与胚芽的长度等指标,研究了干旱胁迫对牛膝菊种子萌发及幼苗生长的影响,探讨了经PEG浸种预处理后种子的萌发恢复能力。结果表明:随着水分胁迫的加重,牛膝菊种子萌发和幼苗生长受到抑制程度增加,牛膝菊种子的日相对萌发率、发芽率、发芽势和发芽指数、活力指数及幼苗的初生根长和胚芽长均呈下降趋势;与对照组相比,牛膝菊种子首次萌发时间延迟越长,当PEG浓度为20%、25%时牛膝菊种子未见萌发;本研究建立了水分胁迫PEG浓度与种子萌发率的线性回归方程,得出牛膝菊种子萌发的PEG浓度临界值为12.9%;经PEG浓度为20%、25%处理的种子在适宜条件下可以恢复萌发,浸种时间相同条件下,20%PEG浓度对牛膝菊种子伤害较小,其恢复性较强,25%PEG浓度对牛膝菊种子伤害较大,其恢复性较弱。     

Flor-essence对小麦种子萌发和幼苗生长的影响

研究不同浓度Flor-essence对小麦种子萌发及幼苗生长的影响,以开拓其在植物生长调节剂领域的新应用。通过室内水培试验,分别设定50、100、150、200和250 mg/L 5组不同浓度的Flor-essence溶液处理,测定小麦种子发芽和植株生长的相关指标,同时选取清水(0 mg/L Flor-essence)和0.015 mg/L的油菜素内酯(BR)作对照。结果显示,与对照相比,不同浓度Floressence浸种均促进了小麦种子的萌发和生长,小麦的发芽势、发芽率、发芽指数、根长、株高、鲜重、干重、叶绿素含量和根冠比均有不同程度提高。不同浓度处理中,以200和250 mg/L处理的幼苗发芽情况最好;以150 mg/L处理的株高最高;以200 mg/L处理的根长最长、根冠比最大;以250 mg/L处理的鲜重、干重和叶绿素含量最高。利用Flor-essence浸种可促进小麦种子萌发和幼苗生长,且浓度为150-250 mg/L Flor-essence更能够在不同程度上促进小麦苗期的生长。     

外源H2O2对盐胁迫下小白菜种子萌发和幼苗生理特性的影响

以小白菜"甜脆青"为试材,研究不同浓度（5、10、25、50和100 mmol/L）过氧化氢（H₂O₂）浸种处理对100 mmol/L NaCl胁迫下小白菜（Brassica chinensis L.）种子萌发、幼苗生长及生理特性的影响。结果表明：100 mmol/L NaCl胁迫明显抑制小白菜种子的萌发状况和幼苗生长,发芽势、发芽指数、活力指数及幼苗根和芽长度和鲜重均明显降低,根和芽中CAT的活性及K⁺含量明显受到抑制,渗透调节物质、活性氧和MDA含量显著增加。不同浓度H₂O₂浸种处理提高了NaCl胁迫下小白菜种子发芽势、发芽指数和活力指数,促进小白菜根和芽的生长,增强了NaCl胁迫下根和芽中SOD、CAT和APX的活性及K⁺含量,降低O₂^-·产生速率及H₂O₂和MDA含量,进一步促进脯氨酸和可溶性糖含量的增加,降低体内Na⁺含量。其中以10 mmol/L H₂O₂处理缓解盐胁迫效果最好,明显缓解NaCl胁迫对小白菜种子萌发和幼苗生长的抑制。     

磁化水浸种对苦瓜种子萌发及对其幼苗生理指标的影响

目的：研究磁化水对苦瓜种子萌发的影响。方法：用不同强度的磁化水浸种处理苦瓜种子,测定其以下几个生理指标：种子的发芽率、发芽指数、活力指数和幼苗中的酯酶以及抗坏血酸的含量。实验结果显示：磁化水能够提高苦瓜种子的发芽率、发芽指数、活力指数,同时也能提高苦瓜幼苗的酯酶活性,但对抗坏血酸含量影响不大。结论：一定强度的磁化水能提高苦瓜种子的萌发能力,并使幼苗生长整齐一致。     

田菁茎瘤固氮根瘤菌对小麦叶组织的促生作用研究

利用GFP标记的田菁茎瘤固氮根瘤菌(Azorhizobium caulinodans ORS 571)侵染露白24h的小麦种子,分别在侵染后0、6、12、24、48、72和96h采样,利用实时荧光定量PCR方法检测小麦体内6条与促生作用相关miRNAs(miR156、miR159、miR160、miR167、miR168和miR403)的表达模式,检测其中3条miRNAs(miR159、miR167和miR168)的靶基因表达模式;以接菌8d的小麦样品做切片,利用激光共聚焦显微镜检测小麦叶部田菁茎瘤固氮根瘤菌的分布,并测定小麦的生理指标。结果显示:(1)田菁茎瘤固氮根瘤菌侵染小麦后能够在叶片边缘部位定殖。(2)小麦叶片中与促生作用相关的6条miRNAs出现了不同程度变化,在12~24h到达其峰值,随后逐渐下降,其中miR159在峰值时的表达量为初始表达量的2.88倍。(3)3条miRNAs的靶基因表达模式与相应miRNA表达模式相对应,但并不严格。(4)生理指标测定结果显示,接种田菁茎瘤固氮根瘤菌对小麦叶片产生明显的促生作用,其中叶鲜重在96h的变化与对照差异极显著。研究表明,接种的田菁茎瘤固氮根瘤菌能够到达小麦叶组织,对小麦叶片的生长产生明显的促生作用,其中miRNAs在促生过程中发挥重要作用。     

磁化水浸种对苦瓜种子萌发及对其幼苗生理指标的影响

目的 :研究磁化水对苦瓜种子萌发的影响。方法 :用不同强度的磁化水浸种处理苦瓜种子 ,测定其以下几个生理指标 :种子的发芽率、发芽指数、活力指数和幼苗中的酯酶以及抗坏血酸的含量。实验结果显示 :磁化水能够提高苦瓜种子的发芽率、发芽指数、活力指数 ,同时也能提高苦瓜幼苗的酯酶活性 ,但对抗坏血酸含量影响不大。结论 :一定强度的磁化水能提高苦瓜种子的萌发能力 ,并使幼苗生长整齐一致。     

不同浓度亚硒酸钠溶液对水杉种子萌发的影响

硒元素是植物生长所需的微量元素。在水杉母树主要生长所在地恩施境内形成立体的硒资源环境,而该区的水杉群落天然更新困难,林下鲜见更新幼苗或幼树。因此,结合硒资源,研究硒元素与水杉种子萌发的相互关系对水杉的天然更新繁育具有重要意义。为了揭示硒元素对水杉种子发芽的影响,该研究通过测定不同环境条件(温度:20、25、30 ℃; 光照:12 h光照/12 h黑暗、24 h全黑暗; 是否浸种)下原生水杉种子的萌发率,筛选出最适萌发条件,并在此条件下采用不同浓度(0、0.25、0.5、1.0、2.0、4.0、8.0、16.0 mg·L^-1)的亚硒酸钠对水杉种子进行处理,观察其萌发的变化。结果表明:当使用浓度为0.25 mg·L^-1的亚硒酸钠溶液处理水杉种子时,种子的发芽率、发芽势和发芽指数都为最高,分别为34.0%、29.0%、13.9; 当亚硒酸钠浓度大于0.25 mg·L^-1时,水杉种子的发芽率、发芽势和发芽指数开始随着浓度的增加而降低,在亚硒酸钠浓度为16.0 mg·L^-1时,三个指标都达到最低值,分别为0.5%、0%、0.025。由此可知,低浓度(0～0.25 mg·L^-1)的亚硒酸钠处理对水杉种子的萌发有一定的促进作用,而高浓度(>0.25 mg·L^-1)的亚硒酸钠处理对水杉种子的萌发则有一定的抑制作用。     

亚精胺浸种对渗透胁迫下白三叶种子萌发及淀粉代谢的影响

以‘拉丁诺’白三叶为材料,用0、10%、15%、20%（W/V）的聚乙二醇（PEG-6000）溶液模拟干旱条件,研究亚精胺（Spd）浸种对渗透胁迫下白三叶种子萌发和淀粉代谢的影响。结果表明,在PEG渗透胁迫下,白三叶种子的发芽率、发芽势、发芽指数、胚芽及胚根鲜重和胚根长度均显著（P<0.05）降低,淀粉水解为糖类的速率减慢;与蒸馏水浸种相比,0.05mmol·L^-1Spd浸种处理显著（P<0.05）提高了在渗透胁迫条件下种子的发芽率、发芽势、发芽指数、胚芽及胚根鲜重、干重和胚根长度,同时大幅提高了α-淀粉酶、β-淀粉酶及（α+β）-淀粉酶总活性,降低了淀粉含量,增加了还原糖和葡萄糖含量。说明Spd浸种提高了白三叶种子在渗透胁迫下的萌发能力和幼苗生长的环境适应性,这可能与增强种子体内淀粉酶活性,加速淀粉水解为还原糖和葡萄糖,为种子萌发和幼苗早期生长及时提供充足能量有关。     

香附浸提液对小麦种子的萌发及幼苗生长的影响

为了了解香附有效成分对小麦种子萌发和幼苗生长的影响,采用室内培养皿培养法,分析不同浓度的香附浸提液浸种后对小麦种子发芽率、发芽指数、活力指数及幼苗高度、根长、根数、整株鲜重及干重等指标的影响。结果表明,香附浸提液对小麦种子的萌发及幼苗的生长有明显抑制作用,抑制作用随着香附浸提液浓度的增加,抑制效果增强,与浸泡蒸馏水的对照相比,香附浸提液浸种处理显著降低了小麦的种子发芽率、发芽指数、种子活力、苗高、根长、植株鲜重和干重。     

Response of common bean lines to inoculation: comparison between the <Emphasis Type="Italic">Rhizobium tropici</Emphasis> CIAT899 and the native <Emphasis Type="Italic">Rhizobium etli</Emphasis> 12a3 and their persistence in Tunisian soils

Since Phaseolus vulgaris (L) is poorly nodulated in all regions of Tunisia where this crop is grown, the response of common-bean lines CocoT and Flamingo to inoculation with reference Rhizobium tropici CIAT 899 or native rhizobia, namely Sinorhizobium fredii 1a6, Rhizobium etli 12a3, and Rhizobium gallicum 8a3, was studied in a field station. Since R. etli 12a3 was found to be the most effective native rhizobium, it was subsequently compared with R. tropici CIAT 899 in a broader study in two stations over 3 years. A significant interaction between bean and rhizobia was observed for nodule number, shoot dry weight, grain yield, and contents of nitrogen and chlorophyll. The native rhizobia was more efficient than CIAT899 for Flamingo, though not for CocoT. The Enzyme-linked immunosorbent assay technique was used with polyclonal antibody to assess the occupancy in nodule and persistence in soil of the inoculated rhizobia. For both stations the nodule occupancy was 100% during the first year for each rhizobium, but during the next 2 years, between 7 and 15% of nodules were formed by the rhizobia inoculated in the neighboring plot. It is concluded that the first-year inoculation is sufficient to maintain an adequate rate of nodulation during three growth cycles, and that the native R etli can be recommended for the common-bean inoculation in similar soils of Tunisia.     

Cassava as a Cheap Source of Carbon for Rhizobial Inoculant Production using an Amylase-producing Fungus and a Glycerol-producing Yeast

Summary The aim of this research was to develop methods to use low-cost carbon compounds for rhizobial inoculant production. Five raw starch materials; steamed cassava, sticky rice, fresh corn, dry corn and sorghum were tested for sugar production by an amylase-producing fungus. Streamed cassava produced the highest amount of reducing sugar after fermentation. Bradyrhizobium japonicum USDA110, Azorhizobium caulinodans IRBG23, Rhizobium phaseoli TAL1383, Sinorhizobium fredii HH103, and Mesorhizobium ciceri USDA2429 were tested on minimal medium supplemented with reducing sugar obtained from cassava fermentation. All strains, except B. japonicum USDA110, could grow in medium containing cassava sugar derived from 100 g steamed cassava per litre, and the growth rates for these strains were similar to those in medium containing 0.5 (w/v) mannitol. The sugar derived from steamed cassava was further used for production of glycerol using yeast. After 1 day of yeast fermentation, the culture containing glycerol and heat-killed yeast cells, was used to formulate media for culturing bradyrhizobia. A formulation medium, FM4, with a glycerol concentration of 0.6 g/l and yeast cells (OD₆₀₀ = 0.1) supported growth of B. japonicum USDA110 up to 3.61 × 10⁹ c.f.u./ml in 7 days. These results demonstrate that steamed cassava could be used to provide cheap and effective carbon sources for rhizobial inoculant production.     

Effect ofAgrobacterium radiobacter and its polysaccharide on emergence and damping-off of tomato plants

Agrobacterium radiobacter B6 and agrobacteran (an exopolysaccharide of the succinoglycan group) stimulated seed germination and tomato plant emergence. The germination was most stimulated by dipping the seeds in 0.1 % agrobacteran for 30 min whereas plant emergence in garden soil was best with 0.4 % agrobacteran at 10–20°C. Treatment of the plants withA.radiobacter cells and agrobacteran solution at 30–35°C. had a lower effect.A.radiobacter cells applied on seed surface protected the plants against damping off in garden soil artificially inoculated with the fungiRhizoctonia solani andPythium ultimum; in soils contaminated withFusarium solani 0.1 to 0.2% agrobacteran had a higher protective effect than the bacterization. The difference can be attributed to the varying density ofA.radiobacter population in plant rhizosphere in the presence of different plantpathogenic fungi, different interactions of microorganisms in the rhizosphere and different mode of penetration of the pathogens into plant roots.     

Comparative genomic and protein sequence analyses of the chemotaxis system of Azorhizobium caulinodans北大核心CSCD

［Objective］ Azorhizobium caulinodans ORS571 can fix nitrogen not only as a free-living organism and an associative-symbiotic bacterium by colonizing the root surface of non-leguminous plants, but also as a symbiotic bacterium by interacting with leguminous plant Sesbania rostrata.Due to its ability to grow and fix nitrogen under three conditions, A.caulinodans uses sophisticated chemotaxis signal transduction systems to transform environmental cues into corresponding behavioral responses.Chemotaxis appears crucial for the growth of A.caulinodansin complicated environment and the construction of associative relationship with the plant.However, little is known about the chemotactic pathway of A.caulinodans.Thus, our study aimed to compare the chemotaxis-like genes of A.caulinodans with those of well-studied species.［Methods］ NCBI protein BLAST was used for searching sequence similarity with default parameter values against the genomes of A.caulinodans.HMMER3, based on Pfam database, was used for comparative analyses of methyl-accepting chemotaxis protein （MCP）.［Results］ There was a major chemotaxis cluster in A.caulinodans and the CheR methylated MCPs independently of pentapeptide motif.There were 43 MCP homologs containing diverse signal-sensing architectures in A.caulinodans.In addition,cytoplasmic domains of these MCPs were all composed of 38 heptad repeats.［Conclusion］ Despite the extremely high homology presented between the chemotactic system of A.caulinodans and those of well-studied species, A.caulinodans shows its own unique characteristics.The classification of these chemotactic pathways by comparative genomics enables us to better understand how A.caulinodansresponds to changes in environment via exquisite signal transductions in chemotaxis system.     

Accumulation of ppGpp in symbiotic and free-living nitrogen-fixing bacteria following amino acid starvation

Following amino acid or ammonium starvation, ppGpp is accumulated by Rhizobium meliloti strain 1021 but not by R. meliloti strain 41 or Rhizobium tropici. Azorhizobium caulinodans ORS571 produced ppGpp following amino acid deprivation; however, the free-living nitrogen-fixing bacteria Azotobacter vinelandii and Azomonas agilis did not produce ppGpp. Western blot analysis using anti-RelA antibody demonstrated that R. meliloti strain 1021, Azotobacter vinelandii and Azorhizobium caulinodans cross-reacted under conditions that detected RelA in Escherichia coli CF1648. Cross-reaction was not observed in R. meliloti strain 41, R. tropici, or Azomonas agilis. All strains that accumulated ppGpp also produced high intracellular levels of ATP. Received: 28 August 1998 / Accepted: 11 November 1998     

盐磷胁迫对木麻黄和台湾相思种子萌发及幼苗生长的影响

恶劣环境下,人工海防林因面临养分胁迫而经营困难。为探讨盐、磷胁迫对主要海防林树种木麻黄和台湾相思种子萌发及生长的影响,该研究分别用不同浓度的NaCl(盐)和KH₂PO₄(磷)溶液处理种子和浇灌幼苗,测定种子萌发和幼苗生长指标。结果表明：(1)高盐胁迫显著抑制种子萌发,对幼苗生长有一定影响,但两种植物影响程度不同;台湾相思种子萌发耐盐性高于木麻黄,前者相对盐害率最大值为23.03%,后者为89.15%;随着盐浓度增加,木麻黄和台湾相思种子的发芽率、发芽势、发芽指数和活力指数均降低,对应最大值分别为38.70%、34.67%、18.70、0.055和76.67%、62.22%、48.46、6.11。(2)两种植物的株高和根长随盐浓度增加而降低,木麻黄和台湾相思株高分别为12.29～6.01 mm和48.27～17.33 mm,根长分别为8.57～1.45 mm和33.41～5.88 mm;台湾相思根、茎、叶生物量及根冠比均随盐浓度的增加逐渐减小,木麻黄各处理差异较小。(3)台湾相思的种子和幼苗较木麻黄更耐低磷环境,二者最适磷浓度存在差异;木麻黄种...     

Phage susceptibility and plasmid profile analysis of Sinorhizobium fredii

This is the first report identifying bacteriophages and documenting megaplasmids of Sinorhizobium fredii. Plasmid DNA content and bacteriophage typing of eighteen strains of S. fredii were determined. S. fredii strains fell into ten plasmid profile groups containing 1 to 6 plasmids, some evidently larger than 1000 MDa. Twenty-three S. fredii lytic phages were isolated from soil, and they lysed six different S. fredii strains. The host range and plaque morphology of these phages were studied. Susceptibility to S. fredii phages was examined for S. meliloti; Rhizobium leguminosarum bvs. viceae, trifolii and Phaseoli; R. loti; Bradyrhizobium japonicum; B. elkanii and Bradyrhizobium sp. (Arachis). Several phages that originally lysed S. fredii strain USDA 206 also lysed strains of all three S. fredii serogroups described originally by Sadowsky et al. Phages that infected S. fredii strains USDA 191 and USDA 257 were highly specific and lysed only serogroup 193 strains. S. meliloti strains L5-30 and USDA 1005 were lysed by three of the phages that lysed S. fredii strain USDA 217. No other Rhizobium or Bradyrhizobium strain tested was susceptible to lysis by any of the S. fredii phages. The present investigation indicates that phage susceptibility in conjunction with plasmid profile analysis may provide a rapid method for identification and characterization of strains of S. fredii.     

芒和荻种子对复合盐碱胁迫的生理响应

土壤盐碱化在世界范围内普遍存在,日益严峻的盐碱化形势严重威胁着植物的生长发育。芒(Miscanthus sinensis)和荻(Miscanthus sacchariflora)作为能源植物具有良好的经济效益和生态效益,并且在城市园林中已得到广泛应用。该研究以引种自辽宁省本溪阿家岭的芒和哈尔滨市太阳岛的荻为对象,模拟我国东北大庆盐碱地的低(浓度1、2)、中(浓度3)、高(浓度4、5)浓度土壤环境,分别对芒和荻的种子进行复合盐碱胁迫处理,对芒和荻的种子萌发情况进行研究。结果表明：(1)复合盐碱胁迫处理下,芒种子的发芽率随着复合盐碱浓度的升高而降低,发芽势、活力指数、发芽指数、胚根长度、胚芽长度、胚根鲜重、胚芽鲜重和耐盐碱指数均先升高后降低;荻种子的发芽率、发芽势、活力指数、发芽指数、胚根长度、胚芽长度、胚根鲜重、胚芽鲜重和耐盐碱指数均随着复合盐碱浓度的升高而降低。(2)芒和荻的种子能够抵抗低、中浓度的复合盐碱胁迫处理,当高浓度的复合盐碱胁迫处理时,各项指标均下降明显,且芒种子的各项指标均优于荻种子,说明芒种子比荻种子更耐盐碱。该研究结果基本界定芒荻种子的复合盐碱耐受范围,为今后芒荻类能源植物的耐盐碱性筛选和在园林中的应用提供了理论依据。     

茎瘤固氮根瘤菌环二鸟苷酸代谢相关基因的功能鉴定

【目的】考察茎瘤固氮根瘤菌ORS571中c-di-GMP合成酶AZC-2412的编码基因缺失的突变表型,初步探究其功能机理。【方法】本实验构建基于cre-loxp重组酶系统的根瘤菌基因敲除系统,以及采用三亲接合技术构建突变株。测定野生型和突变株的生长速率、趋化能力、胞外多糖产量、生物膜形成等表型。【结果】突变株与野生型生长速率几乎相同。与野生型相比突变株由于细胞内c-di-GMP水平降低,胞外多糖、生物膜产量等均有所下降。【结论】实验表明,环二鸟苷酸合成酶AZC-2412缺失,使得c-di-GMP水平降低,对胞外多糖生成、细菌的运动能力、生物膜的形成、细胞絮凝、与植物的互作等均有调控作用。