Diversity and symbiotic effectiveness of rhizobia isolated from field-grown soybean nodules in Paraguay

Soybean was introduced in Paraguay in the 1920s and commercial crops have been grown since the 1970s. Root nodulation occurs at the majority of the producing sites, although inoculation has been practiced in only 15-20% of the cropping areas. The diversity and symbiotic effectiveness of soybean rhizobia was studied using 78 isolates obtained from root nodules of field-grown plants at 16 sites located in the two main producing states. The rhizobial isolates were characterized in relation to several parameters in vitro (colony morphology, tolerance to high temperature and salinity, intrinsic resistance to antibiotics, synthesis of indole acetic acid, profiles of proteins and lipopolysaccharides) and in vivo (nodulation, plant growth and total N accumulated in shoots). Fifty-eight isolates had slow growth rates and alkaline reaction in medium containing mannitol as the carbon source, whereas 20 had fast growth rates and an acid reaction. Most isolates did not tolerate acidity (pH 4.5) or high temperature (40°C). Very few isolates shared similar protein and lipopolysaccharide profiles; therefore a high level of diversity was detected, with most of the isolates representing unique strains. Some of the isolates with an outstanding symbiotic performance were identified, and will now be tested under field conditions in a search for efficient and competitive strains for use in commercial inoculants in Paraguay.     

四川高效大豆根瘤菌的筛选及初步应用研究

采用无氮水培、盆栽、田间区组试验,从采集自四川33个市县35个采样点分离获得的70个大豆根瘤菌株中,筛选与四川主栽大豆品种 贡选1号 匹配性最佳的根瘤菌。对第一批分离自21个市县23个采样点的52个菌株进行无氮水培实验,其结瘤能力和共生固氮能力表明,S8、S22、S36、S46、S55、S65菌株与贡选1号共生匹配性好。用6个菌株进行的盆栽试验结果表明,S36、S8菌株与 贡选1号 匹配性较佳。将第二批分离自四川另外12个市县的12个采样点的18个菌株进行第二次水培实验,以S8、S36和CK分别作为阳性和阴性对照,结果表明接种S151、S152、S150、S149菌株的植株鲜重和干重均极显著高于CK,且高于阳性对照（S8、S36）。结合盆栽和第二次水培实验结果选择S152、S151、S150、S149、S8进行田间试验,以不接种为对照,结果显示,接种S152、S150菌株的大豆产量分别比CK显著增加33.5%和18.5%,且显著高于其它三个供试菌株S151、S149和S8接种处理。为此筛选出与四川主栽大豆品种贡选1号共生匹配性最佳的菌株是S152、S150。     

Genotypic diversity and symbiotic effectiveness of rhizobia isolated from root nodules of Phaseolus vulgaris L. grown in Tunisian soils

 One hundred and sixty isolates of rhizobia were sampled from the root nodules of common bean (Phaseolus vulgaris L.) cultivated in Tunisian soil samples originating from three geographically distinct fields. Plasmid profiling was used as a primary method to rapidly screen the isolates, and then 38 plasmid types were recorded among the 160 isolates. A sample representing the majority of plasmid types was chosen for further characterization by restriction fragment length polymorphism (RFLP) analysis of genomic DNA using chromosomal and symbiotic gene probes, and by their ability to nodulate a potential alternative host, Leucaena leucocephala. One third of the isolates showed a high similarity to Rhizobium gallicum isolated from common bean in France, another third showed the same characteristics as the R. etli-R. leguminosarum group, while the remaining isolates could not be related to any of the five species nodulating bean. When reexamined for nodulation, some of these isolates, showing similarities to R. tropici and Agrobacterium with respect to colony morphology and growth in different media, failed to nodulate their original host. The R. gallicum-like isolates, R. etli-like isolates, and R. leguminosarum-like isolates were recovered from regions where bean is frequently grown, while in fields which had not been cultivated with beans for at least the 10 previous years, solely unrecognized taxa of ineffective isolates were recovered. We detected variations in the symbiotic regions, but certain pSym RFLP patterns for nifH were conserved between Tunisian, French, and Austrian populations of bean rhizobia. Evaluation of symbiotic effectiveness showed that R. gallicum-like isolates and R. etli-like isolates were effective, whereas some R. leguminosarum-like isolates were ineffective. Furthermore, effective isolates were also found among the unrecognized taxa. Received: 10 March 1998     

Symbiotic efficiency and compatibility of native rhizobia in northern Thailand with different soybean cultivars

Symbiotic efficiency and compatibility of 81 isolates of native bradyrhizobia from irrigated areas in northern Thailand with four soybean cultivars and one cowpea cultivar were evaluated under laboratory conditions. Effectiveness and / or compatibility of the tested isolates were compared with those of a standard strain (Bradyrhizobium japonicum CB 1809) by using plants grown on plastic seed bags. Effectiveness of the isolates was also estimated using uninoculated control plants grown in a nitrogen-free solution. Nodulation of a wide range of host plants by the majority of the tested isolates was observed, which agreed well with the results of our previous field experiment (Shutsrirung et al. 2002: Soil Sci. Plant Nutr., 48, 491–499). Up to 75% of the tested isolates induced a higher growth efficiency than that of the uninoculated control in association with one of the tested cultivars, Black soybean. Comparision with uninoculated control plants, enable to estimate the proportion of the tested isolates leading to effective growth promotion (E + e) of each cultivar, namely, Black soybean (local Thai cultivar), 75%; Cowpea, 82%; SJ5 (commercial Thai cultivar), 33%; Bragg (US cultivar), 33%; and Improved Pelican (US cultivar), 9%. These results indicated that although isolates with a high infectiveness with both “Asian-type” and “US-type” soybeans could be found, a high frequency of isolates leading to inefficient nodules was observed in the US cultivar, suggesting the presence of genetic differences in the soybean cultivars that express high-preference (efficient nodules) or low-preference (inefficient nodules) for a certain group of tested isolates. Based on the results of this laboratory experiment together with our previous field experiment, native rhizobial populations in the irrigated area of northern Thailand could be separated into three groups; Group 1: rhizobium strains showing a high effectiveness with only Asian cultivars, Group 2: strains showing a high effectiveness with only US origin cultivars, and Group 3: strains showing a high effectiveness with both Asian and US origin cultivars. The majority of the native rhizobial populations belonged to Group 1. The isolates in Group 3 may display a high potential for manipulating useful rhizobial inoculant.     

Distribution and biodiversity of soybean rhizobia in the soils of Shennongjia forest reserve,China

Soil samples were collected at an altitude of 500, 1,060, 1,500, 1,950, 2,400 and 3,100 m, respectively, from Shennongjia, a forest reserve in Hubei province (central China). Their corresponding pHs were 5.50, 4.91, 5.64, 5.28, 5.49 and 4.60. By using a plant trap method, a total of 25 soybean rhizobia were isolated from the soil above an altitude of 1,500 m and all identified to be Sinorhizobium fredii. Their genetic biodiversity was characterized by 16S–23S rDNA internally transcribed spacer (ITS) region polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and random amplification DNA (RAPD) analysis. All the tested strains produced a 2.1 kb 16S–23S rDNA ITS fragment. After digestion with three restriction endonucleases (HaeIII, MspI and CfoI), respectively, great variations in 16S–23S rDNA ITS PCR-RFLP patterns were observed. The tested strains could be differentiated into 11 ITS genotypes. The genotypes of rhizobia were not related to geographical location. Twelve primers were applied to RAPD analysis and a dendrogram was obtained, showing that all the strains (including reference strain S. fredii USDA205) were divided into two diverging groups. Moreover, each group could be further divided into two subgroups. Both RAPD and 16S–23S rDNA ITS PCR-RFLP analysis indicated that a high degree of genetic diversity existed among S. fredii strains isolated from Shennongjia virgin soils. Since Shennongjia is an unexploited forest region in central China and the gene centre of soybean is located in China, the symbiotic genes harboured by these strains may be of great importance and the rich diversity of these strains might contribute to the adaptation of soybean to an alpine environment.     

Composition of amino acids,organic acids,and sugars in the peribacteroid space of soybean root nodules

In leguminous root nodules, bacteroids are differentiated from rhizobia and are surrounded by a peribacteroid membrane (PBM) forming an intracellular structure designated as symbiosome. Through the peribacteroid space (PBS) between the PBM and bacteroids, metabolic substances and signal compounds are exchanged between two symbionts. In this study, organic compounds with low molecular weight in the PBS were collected from isolated symbiosomes of soybean (Glycine max L.) root nodules, and their composition was analyzed and compared with that of the organic compounds in whole root nodules and bacteroids. Major differences were detected in the molar percentages of amino and organic acids, and sugars, to the total low molecular weight organic compounds among whole root nodules, PBS, and bacteroids. The PBS composition was characterized by abundant sugars and poor amino acids. Also the composition of the amino acids, organic acids, and sugars in the PBS was clearly different from that in whole root nodules and bacteroids. The PBS sugar composition was characterized by the predominance of inositols, especially myo-inositol at the 5th and 7th weeks of the host plant growth stages. Changes in the myo- and D-chiro- inositol balance at the host plant growth stages occurred and a syntony was observed between the PBS and bacteroids. The localization of myo-inositol in the PBS accounted for almost 70% of the total myo-inositol in root nodules. A small difference in the PBS composition between two soybean cultivars was recorded but it varied with the growth stages. It was tentatively concluded that the PBS sugar composition affected the bacteroidal sugar composition in soybean plants, and that inositol utilization in the bacteroids could be a factor controlling the bacteroidal function level which varied with the host plant growth stages.     

不同茬口土壤和大豆品种对根瘤菌遗传多样性的影响

土壤和大豆品种是影响根瘤菌遗传多样性的主要因素。本研究通过土壤捕捉试验,分别从冬小麦茬口和玉米茬口土壤中种植的4个大豆品种根瘤中分离得到149株快生根瘤菌和49株慢生根瘤菌。对这些菌株进行16S rDNA限制性酶切分析(ARDRA)、16S-23S基因间隔(IGS)以及共生基因(nod C)的限制性片段长度多态性分析(RFLP),考察土壤茬口和大豆品种对大豆根瘤菌遗传多样性的影响。ARDRA分析结果表明,快生根瘤菌全部属于中华根瘤菌属(Sinorhizobium),慢生根瘤菌全部属于慢生根瘤菌属(Bradyrhizobium)。IGS酶切分型将所有菌株分为3种图谱类型,其中型Ⅰ与辽宁慢生根瘤菌(B.liaoningense)的模式菌株酶切图谱类型完全一致,型Ⅱ和型Ⅲ与费氏中华根瘤菌(S.fredii)的模式菌株酶切图谱类型完全一致。综合以上结果,本研究分离到的菌株分属于以上2个种。在两种茬口土壤中快生根瘤菌费氏中华根瘤菌均为优势种群,在冬小麦茬口土壤中的比例(平均95.18%)远高于玉米茬口土壤(平均53.78%)。‘冀豆12’大豆品种的费氏中华根瘤菌在两种茬口土壤中所占比重均高于其他品种。对菌株的IGS基因型与宿主大豆品种的相关性分析表明,大豆品种与根瘤菌IGS基因型之间具有一定相关性。nod C-RFLP酶切分型结果表明,土壤茬口和大豆品种对菌株的共生基因无明显影响。本研究表明根瘤菌、土壤茬口和大豆品种间存在一定的相关性。土壤茬口对根瘤菌的种群结构影响较大,大豆品种对根瘤菌的基因型具有一定的选择性。     

Natural abundance of 15N in root nodules of soybean,lupin, subterranean clover and lucerne

The total nitrogen of root nodules of yellow lupins (Lupinus luteus) and soybeans (Glycine max), when grown with N₂ of air as the sole source of nitrogen, became progressively enriched with ¹⁵N relative to other parts of the plants. Nodules of subterranean clover (Trifolium subterraneum) and lucerne (Medicago sativa) were not enriched with ¹⁵N. Analysis of the distributions of ¹⁵N amongst nodule fractions showed highest specific enrichment in coarse plant cell fragments and bacteroids in soybean and in lupins the soluble protein was also highly enriched. In terms of the total μg of ¹⁵N excess, the bacteroids contained most in soybean nodules and the soluble protein contained most in lupin nodules.     

Salt tolerance of Casuarina equisetifolia and Frankia Ceq1 strain isolated from the root nodules of C. equisetifolia

Effects of NaCl on the seed germination and growth of Casuarina equisetifolia seedlings and multiplication of the Frankia Ceq1 strain isolated from the root nodules of C. equisetifolia were examined. The germination rate of the seeds markedly decreased as the NaCl concentration increased and germination did not occur at 300 mM NaCl. The fresh weight of both shoots and roots of the seedlings treated with NaCl for 6 weeks apparently decreased as the NaCl concentration increased. However, root nodules were formed by inoculation with the Frankia Ceq1 strain in some seedlings treated with 300 mM NaCl and the viability of the seedlings at 500 mM NaCl was almost the same as that of the seedlings not subjected to the NaCl treatment. The Na⁺ concentration in the shoots sharply increased with the elevation of the NaCl concentration in the ambient solution, but the level was approximately 300 mM even in the seedlings treated with 500 mM NaCl for 6 weeks. On the other hand, the increase of the Na⁺ concentration in the roots by the NaCl treatment was much smaller than that in the shoots and the level was less than 150 mM. The growth of the free-living Frankia Ceq1 strain was approximately linearly suppressed as the NaCl concentration in the medium increased and the hyphae became somewhat thicker and shorter or disintegrated in the medium containing NaCl at a concentration above 150 mM. The Na⁺ concentration in the cells increased as the NaCl concentration in the medium increased, but the level was maintained at less than 30 mM even in the medium containing 500 mM NaCl. The cells whose growth was suppressed by the NaCI treatment grew actively again at almost the same rate as the control cells (not subjected to the NaCl treatment) when they were transferred to NaCl-free medium. These results strongly suggested that both C. equisetifolia seedlings and Frankia Ceq1 strain are highly tolerant to salt and this symbiotic system is useful for the recovery of the vegetation in areas with severe salt accumulation.     

Salt tolerance of Elaeagnus macrophylla and Frankia Ema1 strain isolated from the root nodules of E. macrophylla

Effects of NaCl on the seed germination and growth of Elaeagnus macrophylla seedlings and multiplication of Frankia Ema1 strain isolated from the root nodules of E. macrophylla were examined. The germination rate of seeds was not reduced by N aCI at 50 mM, but was reduced with further increase of the concentration, and germination did not occur at 200 mM NaCl. Root nodules were formed in the seedlings treated with 100 mM NaCl. The fresh and dry weight of the seedlings slightly decreased by the increase of the concentration of NaCl and the rate of decrease was 10–20% at NaCl concentrations higher than 100 mM. However, Na+ concentrations in the shoot increased up to 300 mM by treatment with N aCI at a concentration above 50 mM for 30 d and in some plants the lower leaves fell. The growth of free-living Frankia was markedly suppressed and the hyphae became thick and short in the solution at 100 mM NaCl. This trend was more obvious at 200 mM NaCl. Na⁺ concentration in the cells in the medium with 200 mM NaCl was lower than 20 mM and the cells underwent multiplication again when they were transferred to the medium which did not contain N aCl. These results indicate that the salt tolerance of E. macrophylla seedlings was not very high and the threshold for NaCl ranged between 50 and 100 mM, whereas Frankia Ema1 strain was able to survive in a much higher salt environment.     

Polyphasic characteristics of bradyrhizobia isolated from nodules of peanut (Arachis hypogaea) in China

Peanuts (Arachis hypogaea L.) were introduced to China about 500 years ago. However, the diversity of Rhizobial strains in China that can nodulate peanut was poorly understand. Diversity and phylogeny of 50 slow-growing strains, isolated from root nodules of peanut in different geographical regions of China, were studied using polyphasic techniques. All stains were clustered by phenotypic tests into two distinct groups: Group I: 16S rRNA RFLP genotype 3, and Group II, which divided into 16S rRNA RFLP genotypes 1 and 2. Genotype 1 shares the same genotype with USDA110, USDA122 and USDA127 of Bradyrhizobium japonicum, and genotype 2 solely consisted of extra-slow growing bradyrhizobia isolated from Hongan, China. Results of 16S rRNA sequencing revealed that peanut bradyrhizobia were phylogenetically related to B. japonicum and their sequence divergence was less than 1.1%. Based upon the size of the internally transcribed spacer (ITS) between the16S and 23S RNA genes, strains were classified into ITS-I, ITS-II and ITS-III genotypes. Strains could be further divided into sub-clusters IA, IB, IIa, IIb and IIc five sub-clusters through ITS PCR-RFLP and repetitive extragenic palindromic PCR (REP-PCR) analysis. Host specificity test revealed that all peanut bradyrhizobia tested nodulated Phaseolus vulgaris and strains of clusters IIb and IIc nodulated Glycine soja efficiently. Bradyrhizobia isolated from peanut were related, but still exhibited phylogenetical divergence with B. japonicum.     

Composition and field distribution of the population of Rhizobium meliloti in root nodules of uninoculated field-grown alfalfa

Only four antibiotics (kanamycin, spectinomycin, ampicillin and novobiocin) of ten tested were capable of discriminating between root nodule isolates of Rhizobium meliloti obtained from uninoculated field-grown alfalfa (Medicago sativa L.). The 300 isolates in the collection were subdivided into seven groups based on their intrinsic antibiotic resistance characteristics with 204 and 55 isolates placed into two groups, C and F, respectively. Isolates from group C dominated the root nodule population on plants in eight of the nine quadrats analyzed. Furthermore they were one of the two dominant groups found in nodules formed on plants grown in a plant infection-soil dilution experiment and challenged with a composite soil sample from the field site. Antiserum raised to a group C isolate (No. 31) cross-agglutinated with 46 of 55 group C isolates to a titer identical with that of the parent antigen. There were no cross-reactions between isolates from any of the other six groups. Only 9 of 34 isolates from group F cross-agglutinated with antiserum raised to a group F isolate (No. 17). Thirty-three of 35 cross-agglutinating field isolates from group C had the same sodium dodecyl sulphate-polyacrylamide-gel electrophoretic protein-profile pattern as isolate No. 31 whereas non-agglutinating isolates from the same group had distinctly different protein profile patterns. The data suggest that intrinsic antibiotic resistance characteristics can be a useful complementary tool to be used in conjunction with other methods to identify and discriminate isolates of R. meliloti. It should not be used on its own as a strain identification method.     

四川地区玉米/大豆带状套作对大豆形态、叶绿素荧光特征及系统产量的影响

玉米/大豆带状套作可以充分利用光环境,提高单位土地面积物质产出。为探明玉米/大豆带状复合种植模式下不同空间配置对大豆冠层光环境、形态、产量及系统效益的影响,进而为大豆高产优质栽培提供依据,本研究选用半紧凑型（‘川单418’）和紧凑型（‘荣玉1210’）玉米品种与大豆带状套作,固定带宽为200 cm,玉米采用宽窄行种植,玉米窄行距设置3个处理：20 cm、40 cm、60 cm;并以单作大豆（SS）作为对照。分析透光率、形态、光合色素、荧光参数、生物量和系统产量的变化规律。结果表明：套作大豆冠层透光率、红光/远红光（R/FR）比值随玉米窄行距的增大而逐渐降低;套作下大豆茎粗、节数、茎干重和全叶干重均随玉米窄行距增大呈降低趋势,最大值出现在玉米窄行距20 cm处理下;与单作大豆相比,两个玉米品种下大豆茎粗、节数、茎干重和全叶干重均显著降低,而第2节间长和主茎长显著升高。套作下大豆叶片光合色素含量随玉米窄行距的增大而逐渐降低,各行距处理及不同玉米品种下套作的叶片光合色素含量均低于单作大豆。大豆叶片荧光参数F_v/F_m、NPQ、F_q''F_m''和F_q''/F_v''随玉米窄行距的增大均呈先增大后减小的趋势,而F_o变化趋势与之相反。玉米收获后,大豆光环境得到改善并迅速恢复生长,套作大豆形态生理指标与单作差异减小,但由于前期玉米的遮荫,各套作处理间大豆产量差异仍显著。通过系统效益分析,在玉米窄行距40 cm处理下,套作系统综合产量最高,两玉米品种下玉米、大豆产量平均分别为8 559.52 kg·hm^-2、1 717.60 kg·hm^-2,土地当量比平均达1.57。本试验中大豆与两个株型玉米套作,大豆形态生理指标差异影响不显著。因此,选择紧凑或半紧凑玉米品种,适度缩小玉米窄行距可以显著改善带状套作大豆的生长环境,提高其生物量和产量。     

Identification of Ensifer strains isolated from root nodules of Medicago hispida grown in association with Zea mays in the Quechua region of the Peruvian Andes

Peasants of the Quechua region of the Peruvian Andes use chacras to grow maize (Zea mays) in innate association with bur clover (Medicago hispida). From a total of 25 bacterial strains isolated from root nodules of bur clover grown in soils from chacras in Allpas (Acobamba, Peru) 7 clustered into 6 Repetitive extragenic palindromic-polymerase chain reactions (REP–PCR) groups. The nearly complete 16S rRNA gene sequence from the representative strains AP1, AP15, AP28, AP29, AP37, and AP70 showed they were closely related to members of the genus Ensifer of the Alphaproteobacteria. Sequencing of the housekeeping atpD, glnII, and recA and the symbiotic nodC genes from each of the six strains revealed they all were similar to those of strains included in Ensifer medicae. The remaining 18 strains were distributed into 8 REP–PCR groups and analyses of the 16S rRNA gene sequences showed that the isolates belong to several phylogenetic groups, being closely related to species of genera Kaistia, Pseudomonas, Achromobacter, Stenotrophomonas, Xanthomonas, Sphyngopyxis, Duganella, and Rheinheimera.     

四川省化肥面源污染环境风险评估及趋势模拟

系统评估农业化肥过量施用对生态环境的潜在风险危害,可为制定下一阶段农业面源污染防治工作提供决策参考。本文基于2000—2015年化肥施用量和耕地面积等数据,采用化肥施用环境风险评价模型,探讨了四川省化肥施用及环境风险的时空变化特征;通过设置延续现状和政策干预两种情景,模拟了四川省2016—2018年执行化肥施用零增长行动期间的化肥施用环境风险变化趋势。结果表明:四川省化肥施用总量在2000—2015年间整体呈增加态势,2015年四川省化肥施用强度为376.63 kg?hm~(-2),超过了中国生态市建设的化肥施用强度250 kg?hm~(-2)的生态标准。四川省2015年化肥施用的环境总风险指数为0.69,处于中等风险程度;氮、磷、钾肥施用的环境风险指数分别为0.69、0.72和0.46。钾肥施用的环境风险处于安全状态;氮肥和磷肥的环境风险区域集中在成都平原经济区、川南经济区和川东北经济区,呈现中等风险程度并有成片聚集特征。延续现状情景下,四川各地区化肥施用环境总风险指数处于0.48~0.69,存在不同程度增加。与延续现状情景相比,四川在完成化肥施用零增长行动的任务规划前提下,2016—2018年政策干预情景的化肥施用环境总风险呈现下降趋势。以关键时间点2018年来看,川东北经济区化肥施用环境总风险下降最明显,较2015年执行化肥零增长时下降4.24%。但四川省多数地区仍存在不同程度的化肥施用环境污染风险,当地生态环境具有明显压力。建议省级部门加强对成都平原经济区和川东北经济区的化肥面源污染监测,根据各地区差异特征制定不同施肥方案,协调粮食增产和生态保护间的关系。     

Phylogenetic positions of Mn<Superscript>2+</Superscript>-oxidizing bacteria and fungi isolated from Mn nodules in rice field subsoils

We isolated manganous ion (Mn²⁺) oxidizing bacteria and fungi from Mn nodules collected from two Japanese rice fields. The phylogenetic position of the Mn-oxidizing bacteria and fungi was determined based on their 16S rDNA and 18S rDNA sequences, respectively. Among 39 bacterial and 25 fungal isolates, Burkholderia and Acremonium strains were the most common and dominant Mn²⁺-oxidizing bacteria and fungi, respectively. Majority of the Mn-oxidizing bacteria and fungi isolated from the Mn nodules belonged to the genera that had been isolated earlier from various environments. Manganese oxide depositions on Mn²⁺-containing agar media by these microorganisms proceeded after their colony developments, indicating that the energy produced from Mn²⁺ oxidation is poorly used for microbial growth.     

大豆响应低磷胁迫的XTH基因鉴定及XTH38调节根系生长研究

  【目的】  鉴定大豆木葡聚糖内糖基转移酶/水解酶 (xyloglucan endotransglycosylases/hydrolases, XTHs) 基因家族,分析其表达模式和对低磷养分胁迫的响应,初步明确大豆XTH38调节根系生长的功能。  【方法】  供试大豆品种为粤春03-3 (YC03-3),拟南芥野生型为哥伦比亚 (Columbia-0,Col-0) 生态型。通过生物信息学方法,鉴定了大豆XTH基因家族成员,并对大豆的XTH家族成员进行进化分析。采用水培方法,设定高磷对照(HP,KH₂PO₄ 500 μmol/L)和低磷处理(LP,KH₂PO₄ 25 μmol/L)营养液培养,将大豆幼苗处理14天后,取大豆幼苗的根和叶,使用定量PCR分析幼苗中5个GmXTHs的表达;将在1/2 MS固体培养基上发芽2天的超表达GmXTH38株系和Col-0分别接种到HP、LP、低铁 (LFe,Fe 0 μmol/L)、中铁(MFe,Fe 50 μmol/L)和高铁 (HFe,Fe 500 μmol/L)固体培养基上,7天后测定GmXTH38株系的侧根长度和密度。  【结果】  通过生物信息学分析,确定了大豆XTH基因家族共有61个成员,分为3个不同亚组,其中GmXTH38与AtXTH9、AtXTH23位于同一亚组。定量PCR分析结果表明,GmXTH基因家族成员在大豆器官或组织的表达模式不同,其中GmXTH28、GmXTH38、GmXTH41和GmXTH52受LP诱导表达,特别是GmXTH38在大豆根和叶中的表达均受LP诱导。与大豆一致,LP条件下GmXTH38启动子在拟南芥幼苗根、叶的活动强于HP处理。在高磷和中铁(植物正常生长养分需求量)条件下,拟南芥异源超表达GmXTH38抑制拟南芥主根生长、侧根数目和侧根密度。在LP、LFe和HFe胁迫下,与Col-0相比,超表达GmXTH38拟南芥材料主根变短、侧根数和侧根密度减少;超表达GmXTH38导致Col-0侧根形成对LP的敏感性增加;超表达GmXTH38导致Col-0侧根密度在LFe或HFe胁迫条件下下降程度更明显,超表达GmXTH38增加拟南芥主根生长对LFe或HFe的敏感性。  【结论】  大豆基因组存在61个XTH成员,分别为GmXTH1~GmXTH61。GmXTH38在大豆根叶均受LP诱导。超表达GmXTH38 在正常养分条件下抑制拟南芥主根生长和侧根数目;超表达GmXTH38改变拟南芥根系在磷铁养分胁迫条件下的生长。     

Diversity of rhizobia isolated from an agricultural soil in Argentina based on carbon utilization and effects of herbicides on growth

Seventy-six rhizobial isolates belonging to four different genera were obtained from the root nodules of several legumes (Vicia sativa, Vicia faba, Medicago sativa, Melilotus sp., Glycine max and Lotus corniculatus). The action of five commonly used herbicides [2,4-dichlorophenoxyacetic acid (2,4-D), glyphosate (GF), dicamba, atrazine and metsulfuron-methyl] on the growth of rhizobial strains was assessed. Subsequently, GF and 2,4-D were tested in a minimum broth as C and energy sources for 20 tolerant strains. The ability of these strains to metabolize different carbon sources was studied in order to detect further differences among them. Tolerance of the bacteria to agrochemicals varied; 2,4-D and GF in solid medium inhibited and diminished growth, respectively, in slow-growing rhizobial strains. Among slow-growing strains we detected Bradyrhizobium sp. SJ140 that grew well in broth + GF as the sole C and energy source. No strain was found which could use 2,4-D as sole C source. The 20 strains studied exhibited different patterns of C sources utilization. Cluster analysis revealed three groups, corresponding to four genera of rhizobia: Rhizobium (group I), Sinorhizobium (group II) and Mesorhizobium–Bradyrhizobium (group III). On the basis of the results obtained on responses to herbicides and C sources utilization by the isolates investigated, it was possible to differentiate them at the level of strains. These results evidenced a considerable diversity in rhizobial populations that had not been previously described for Argentinean soils, and suggested a physiological potential to use natural and xenobiotic C sources.