磁场对大豆共生固氮的效应

恒定磁场处理慢生大豆根瘤菌“005”和接种后的大豆植株,发现磁场可以提高根瘤的固氮活性。在一定的磁场强度(70—100mT)下,固氮活性平均可以提高4—5倍,植株的结瘤数和根瘤重量平均提高2—3倍。从这样的根瘤中所分离出的根瘤菌,由慢生型转变成快生型,在100植株中有17株的根瘤分离出快生菌。生长世代时间和培养溶液中的pH值与慢生型不同,而与快生型相同。     

Spontaneous luminescence from soybean Rhizobium bacteroids

Abstract: A remarkable spontaneous photon emission was observed in isolated bacteroids of three strains of soybean rhizobia from different genera, but not for the same rhizobia when cultured in liquid medium. The photon emission is oxygen-dependent and can be inhibited by desferal or dipyridyl (both good iron-chelating agents), superoxide dismutase or β-carotene. It is enhanced by catalase. The emission spectrum indicates that singlet oxygen is partly responsible for the luminescence.     

The effects of soybean cultivar,rhizobium strain and nitrate on plant growth,nodule mass and acetylene reduction rate

Summary The effects of twelve strains ofBradyrhizobium japonicum and ten cultivars of soybean (Glycine max (L.) Merr.) on plant and nodule weights, and acetylene reduction rates (33 to 41 days) were measured in the presence and absence of 6mM nitrate. No interactions between strains and cultivars were observed. Strain by nitrate interactions were found for plant and nodule weights, and acetylene reduction rates per gram of nodule. Cultivar by nitrate interactions were found for nodule weights, acetylene reduction rates per plant and per gram of nodule. Blackhawk with all strains, and all cultivars with strains 110 and CB 1809, seemed to be able to grow as well in the absence of nitrate (utilizing nodule fixation) as in its presence. The problems of identifying strains and cultivars with especially good nitrogen fixing ability in the presence of nitrate are discussed.     

A pellet method to demonstrate nitrogen fixation by free-living rhizobia

Summary A method is described to demonstrate nitrogen fixation by free-living Rhizobium cells. After aerobic growth in a nutrient solution, the bacteria are centrifuged. Acetylene reduction by the rhizobial cells in the pellet can be measured within a few days. Hydrogen gas frequently stimulates acetylene reduction.     

Nodulins and nodulin genes of Glycine max

Summary Nodulins are organ-specific plant proteins induced during symbiotic nitrogen fixation. Nodulins play both metabolic and structural roles within infected and uninfected nodule cells. In soybean, several nodulin genes, coding for abundant nodulins, have been identified and isolated. Structural analysis of some of these genes has revealed their possible mode of regulation and the subcellar location of the protein product. Studies of ineffective symbiosis based on cultivar-strain genotype differences suggested that both partners influence the expression of nodulin genes. Concomitant with nodule organogenesis, the Rhizobium undergoes substantial differentiation leading to the accumulation of nodule-specific bacterial proteins, bacteroidins. The major structural alteration occuring in the infected cell is the formation of a membrane enclosing the bacteroid (peribacteroid membrane). A number of nodulins are specifically targetted to this membrane during endosymbiosis. The induction of nodulins and bacteroidins leads to the formation of an effective nodule. Nodulin genes can be induced in vitro by factors derived from nodules suggesting that trans-activators may be involved in derepression of the host genes necessary for Rhizobium-legume symbiosis.     

Symbiovars in rhizobia reflect bacterial adaptation to legumes

Legume specificity is encoded in rhizobial genetic elements that may be transferred among species and genera. Dissemination (by lateral transfer) of gene assemblies dictating host range accounts for the existence of the same biological variant (biovar) in distinct microbiological species. Different alternative biovars may exist in a single species expanding their adaptation to different niches (legume nodules). A review of all reported biovars is presented. Instead of the term biovar, symbiotic variant (symbiovar) is proposed as a parallel term to pathovar in pathogenic bacteria. Symbiovars should be determined based on the symbiotic capabilities in plant hosts, distinguished by the differences in host range and supported by symbiotic gene sequence information.     

The uptake and hydrolysis of disaccharides by fast-and slow-growing species of Rhizobium

Slow growing strains of rhizobia appear to lack both uptake systems and catabolic enzymes for disaccharides. In the fast-growing strains of rhizobia there are uptake mechanisms and catabolic enzymes for disaccharide metabolism. In Rhizobium leguminosarum WU 163 and WU235 and R. trifolii WU290, sucrose and maltose uptake appears to be constitutive whereas in R. meliloti WU60 and in cowpea Rhizobium NGR234 uptake of these disaccharides is inducible. There is evidence that there are at least two distinct disaccharide uptake systems in fast-growing rhizobia, one transporting sucrose, maltose and trehalose and the other, lactose. Disaccharide uptake is via an active process since uptake is inhibited by azide, dinitrophenol and carbonyl cyanide m-chlorophenylhydrazone but not by arsenate. Bacteroids of R. leguminosarum WU235 and R. lupini WU8 are unable to accumulate disaccharides.     

Nitric oxide in legume-rhizobium symbiosis

Nitric oxide (NO) is a gaseous signaling molecule with a broad spectrum of regulatory functions in plant growth and development. NO has been found to be involved in various pathogenic or symbiotic plant-microbe interactions. During the last decade, increasing evidence of the occurrence of NO during legume-rhizobium symbioses has been reported, from early steps of plant-bacteria interaction, to the nitrogen-fixing step in mature nodules. This review focuses on recent advances on NO production and function in nitrogen-fixing symbiosis. First, the potential plant and bacterial sources of NO, including NO synthase-like, nitrate reductase or electron transfer chains of both partners, are presented. Then responses of plant and bacterial cells to the presence of NO are presented in the context of the N₂-fixing symbiosis. Finally, the roles of NO as either a regulatory signal of development, or a toxic compound with inhibitory effects on nitrogen fixation, or an intermediate involved in energy metabolism, during symbiosis establishment and nodule functioning are discussed.     

Efficiencies and inefficiencies in the legume/Rhizobium symbiosis—A review

Summary Studies of the C and N economy of a range of temperate and tropical legume/Rhizobium symbioses indicate considerable variation (up to three-fold) in the cost of N₂ fixation. Comparisons between and within symbioses indicate that the proportion of net photosynthate utilized in nodule functioning varies almost ten-fold from as low as 3% to as high as 25%. Factors possibly responsible for variation in efficiency of C use in nodules and in the proportioning of translocated photosynthetic products to nodules are discussed.     

大豆基因工程根瘤菌田间结瘤和共生固氮效应

利用三亲本接合转移方法,将快生型大豆根病菌B_(52)的基因文库克隆转移到受体菌慢生型大豆根瘤菌2210中,获得4株大豆基因工程根瘤菌(32.43、B—2—6、B—3—8)。田间接种试验表明:在大豆分枝期(V2),43和32结瘤效分别比不接种对照增加117.9％和100.4％;在初花期(R_1),32和B—2—6结瘤数分别比对照增加122.5％和91.6％,根瘤固氮酶活性增加233.3％和195.6％;在结荚始期(R3),B—2—6和32结瘤数比对照增加78.5％和70.1％,根瘤固氟酶活性43和B—2—6分别比对照增加53.4％和49.3％。产量统计表明:32、B—2—6和43比对照分别增产16.8％、14.3％和12.2％,亩增收大豆分别为28.2、24.1和20.6公斤。以上三个菌株均比受体菌株2210增产率高。     

Effect of two granular nematicides on growth and nodulation ofArachis hypogea L.

Summary The effect of two granular nematicidesviz. oxamyl and fenamiphos, on the nodulation and growth of Rhizobium inoculatedArachis hypogaea L. was studied in glasshouse and field trials. In the glasshouse trial at the suggested rates of application shoot fresh weight was significantly reduced by oxamyl whilst root fresh weight was similarly affected by fenamiphos. In the field trial vegetative growth and plant emergence were significantly reduced by both nematicides. Nodulation at the higher rates of application was increased by both oxamyl and fenamiphos whilst oxamyl caused a significant increase in pod number at the highest rate of application.     

Nodulation studies on legumes exotic to Australia: Hedysarum coronarium

Abstract Symbiotic experiments in glasshouse, controlled environment cabinet, and field were conducted with four lines of sulla ( Hedysarum coronarium ) and 15 strains of Rhizobium spp. This plant is highly Rhizobium -specific and appropriate strains are most unlikely to occur naturally in Australia. Under several sets of experimental conditions, H. coronarium nodulated abundantly and effectively with homologous rhizobia introduced from Spain and Italy. The optimum temperature for nitrogen fixation was relatively low (approx. 21°C) but significant interactions between line of host, strain of rhizobia, and growth temperature were frequent. The rhizobia were persistent in soil.     

A comparison of nitrogen-fixing ability of peanut,cowpea and siratro plants nodulated by different strains of Rhizobium

Summary Acetylene reduction activity and nitrogen accumulation in the plant top per unit nodule mass were compared among peanut, cowpea and siratro plants nodulated by six different strains of Rhizobium. Peanut was found to have several fold higher values than cowpea and siratro for both parameters for all strains of Rhizobium which nodulated it effectively, but the bacteroid content of the peanut nodules was similar to those of cowpea and siratro.     

Specific and general effectiveness ofRhizobium trifolii populations from different agricultural locations

Summary The effectiveness ofRhizobium trifolii isolates from five locations in southern Britain representing contrasting soil types has been examined with five white clover varieties. The average effectiveness of Rhizobium isolates varied considerably as did the average productivity of plant varieties. The largest differences were, however, associated with Rhizobium population × plant variety interactions. These were often large enough to reverse relative yield differences between white clover varieties. The implications of these results for improving clover productivity in nitrogen fixation are discussed.     

Gas exchange characteristics and dry matter accumulation of soybean treated with Nod factors

The effect of Nod factors on gas exchange characteristics and growth of soybean plants was studied. Soybean responded positively to some concentrations of Nod factors. Photosynthesis was increased up to 13% over the control, and this was accompanied by increases in stomatal conductance; plant dry weight was also increased. Near-fully expanded leaves responded more strongly to Nod factors than fully expanded leaves. Only Nod factor NodBj-V (C18:1, MeFuc) had significant effects on soybean. The finding suggests that Nod factors can affect photosynthesis, possibly indirectly, by stimulating sink strength.     

The genetic locus controlling supernodulation in soybean (Glycine max L.) co-segregates tightly with a cloned molecular marker.

Summary The genetic locus (nts) controlling nitrate-tolerant nodulation, supernodulation, and diminished autoregulation of nodulation of soybean (Glycine max (L.) Merill) was mapped tightly to the pA-132 molecular marker using a restriction fragment length polymorphism (RFLP) detected by subclone pUTG-132a. The nts (nitrate-tolerant symbiotic) locus of soybean was previously detected after its inactivation by chemical mutagenesis. Mutant plant lines were characterized by abundant nodulation (supernodulation) and tolerance to the inhibitory effects of nitrate on nodule cell proliferation and nitrogen fixation. The large number of RFLPs between G. max line nts382 (homozygous for the recessive nts allele) and the more primitive soybean G. soja (P1468.397) allowed the detection of co-segregation of several diagnostic markers with the supernodulation locus in F₂ families. We located the nts locus on the tentative RFLP linkage group E about 10 cM distal to pA-36 and directly next to marker pA-132. This very close linkage of the molecular marker and the nts locus may allow the application of this clone as a diagnostic probe in breeding programs as well as an entry point for the isolation of the nts gene.