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1.
The root exudates of alfalfa ( Medicago sativa) and mungbean ( Vigna radiata) induced the Tsr (thick and short roots) factor production in Rhizobium meliloti. The factor caused a 30–40% reduction of root length in alfalfa seedlings. Pea root exudate had no Tsr induction activity.
The flavonoid naringenin could replace the roots in inducing Tsr production. Naringenin-induced Tsr factor caused 70% shortening
of main roots. The Tsr inducing property of naringenin was specific since quercetin and syringaldehyde had no such effect. 相似文献
2.
Rhizospheric application of nod regulators influenced the nodulation status, nodule efficiency and partitioning of assimilated CO 2 in Pisum sativum-Rhizobium leguminosarum symbiosis. Depending upon the plant growth stage, naringenin and flavone enhanced nodule number (22.8–87.6%), nodule weight (19.2–35.2%) and nitrogenase activity (17.8–108.6%). Syringaldehyde had negative effect on various parameters of symbiosis. Proportion of 14C-assimilates was higher in nodules of plants from naringenin and flavone treatments as compared to the control or syringaldehyde treatments. The enhanced nodule efficiency in naringenin and flavone treatments was reflected in the increased N content (12.7–50.4%) and biomass (4.3–35.1%) of plants. 相似文献
3.
A study was conducted to determine whether colonization of legume roots and nodulation by Rhizobium meliloti and Bradyrhizobium japonicum could be enhanced by using inocula containing microorganisms that produce antibiotics suppressing soil or rhizosphere inhabitants
but not the root-nodule bacteria. An antibiotic-producing strain of Pseudomonas and one of Bacillus were isolated, and mutants
of R. meliloti and B. japonicum sp. resistant to the antibiotics were used. The colonization of the alfalfa rhizosphere and nodulation by R. meliloti were enhanced by inoculation of soil with Pseudomonas sp. in soil initially containing 2.7×10 5
R. meliloti per g. The colonization of soybean roots by B. japonicum was enhanced by inoculating soil with three cell densities of Bacillus sp., and nodulation was stimulated by Bacillus sp. added at two cell densities. In some tests, the dry weights of soybeans and seed yield increased as a result of these
treatments, and co-inoculation with Bacillus also increased pod formation. Inoculation of seeds with Bacillus sp. and the root-nodule bacterium enhanced nodulation of soybeans and alfalfa, but colonization by B. japonicum and R. meliloti was stimulated only during the early period of plant growth.
Studies were also conducted with Streptomyces griseus and isolates of R. meliloti and B. japonicum resistant to products of the actinomycete. Nodulation of alfalfa by R. meliloti was little or not affected by the actinomycete alone; however, both nodulation and colonization were enhanced if the soil
was initially amended with chitin and S. griseus was also added. Chitin itself did not affect R. meliloti. Treatments of seeds with chitin or S. griseus alone did not enhance colonization of alfalfa roots by R. meliloti or soybean roots by B. japonicum, but the early colonization of the roots by both bacterial species was promoted if the seeds received both chitin and S. griseus; this treatment also increased nodulation and dry weights of alfalfa and soybeans and the N content of alfalfa. It is suggested
that co-inoculation of legumes with antibiotic-producing microorganisms and root-nodule bacteria resistant to those antibiotics
is a promising means of promoting nodulation and possibly nitrogen fixation. 相似文献
4.
Several carbon metabolism enzymes were measured in cultured cells and bacteroids of Rhizobium meliloti 102F51 and in alfalfa root nodule cytosol. The enzyme activity levels of the pentose phosphate pathway were much higher than those of the Embden-Meyerhof-Parnas or Entner-Doudoroff pathways in extracts of cultured cells. The pattern of enzyme activities in the bacteroids was different from that of cultured cells. 相似文献
5.
The pathway by which glutamate is degraded as a carbon source has not previously been elucidated, but enzymatic analysis of
Rhizobium meliloti CMF1 indicated that both glutamate dehydrogenase (GDH) and gamma-aminobutyrate (GABA) bypass activities were present in free
living cells. However, when similar studies were performed on R. meliloti CMF1 bacteroids, isolated from alfalfa nodules, only GABA bypass activities were detectable. Both GDH and GABA bypass activities
were influenced by the carbon source provided, with maximum activities being detected when glutamate was present as sole carbon
and nitrogen source. Addition of a second carbon source, such as succinate, to the growth medium did not influence GDH activity
but substantially decreased levels of the first enzyme of the GABA bypass, glutamate decarboxylase (GDC). Cyclic adenosine
3′5′-monophosphate (cAMP) failed to increase GDC activities in R. meliloti CMF1 cells grown in the presence of an additional carbon source. It is proposed that the GABA bypass is a major mechanism
of glutamate carbon degradation in R. meliloti CMF1, a system whose enzymatic activities are influenced by the nature of the carbon source present in the growth environment. 相似文献
6.
Rhizobium meliloti-alfalfa ( Medicago sativa) symbiosis was influenced by the rhizospheric application of naringenin which increased nodule number, nodule weight (2-to 8-fold) and nitrogenase activity. Plant blomass and total nitrogen content also increased by 60 to 72%. The enhancing effects of naringenin were more pronounced if it was applied at the early vegetative stage of plant growth or at the time of sowing. 相似文献
7.
Adsorption of Rhizobium meliloti L5-30 in low numbers to alfalfa ( Medicago sativa L.) roots was dependent on the presence of divalent cations, and required neutral pH. Adsorption was proportional to Ca and/or Mg concentrations up to 1.5 m M. Ca was not substituted by Sr, Ba or Mn. Adsorption was abolished and viability decreased at pH6. When lowering pH, higher Ca concentrations were required to attain similar adsorption levels, indicating a marked interactive effect between Ca and H ions. Pretreatment of the roots with Ca and low pH did not affect subsequent adsorption of the bacteria. However, Ca pretreatment of R. meliloti sustained further adsorption at low Ca levels and low pH substantially affected their ability to adsorb. Low pH appears to affect the stability of binding causing desorption of the previously bound bacteria. The presence of saturating concentrations of heterologous R. leguminosarum bv. trifolii A118, did not prevent the expression of divalent cations and pH requirements, as well as their interaction. Our results suggest that rhizobial binding to the root surface already shows the Ca and pH dependence of alfalfa nodulation, which was generally associated to some event prior to rhizobial penetration of root hairs. 相似文献
8.
Summary The enzymes involved in ammonia assimilation by Rhizobium meliloti 4l and their role in the regulation of nitrogen metabolism were studied. Glutamine synthetase (GS) and glutamate synthase (GOGAT) were present at relatively high levels in cells grown in media containing either low or high concentrations of ammonia. NADP-linked glutamate dehydrogenase could not be detected.GOGAT and GS mutants were isolated and characterised. A mutant lacking GOGAT activity did not grow even on high concentrations of ammonia, it was a glutamate auxotroph and was effective in symbiotic nitrogen fixation. The GS and assimilatory nitrate reductase activities of this mutant were not repressible by ammonia but still repressible by casamino acids. A mutant with low GS activity required glutamine for optimal growth. It was ineffective and its nitrate reductase was not inducible.These findings indicate that ammonia is assimilated via the GS/GOGAT pathway in free-living R. meliloti and bacterial GOGAT is not important in symbiosis. Furthermore, GS is suggested to be a controlling element in the nitrogen metabolism of R. meliloti. 相似文献
9.
The genome of the nitrogen-fixing soil bacterium Sinorhizobium meliloti does not possess genes for bioremediation of aromatic pollutants. It has the well-known ability to interact specifically with the leguminous alfalfa plant, Medicago sativa. Our previous work has shown enhanced degradation of the nitroaromatic compound 2,4-dinitrotoluene (DNT) when a plasmid containing degradative genes was introduced in it. In this study we report molecular evidence of the transfer of a polychlorinated biphenyl (PCB)-biodegradative plasmid pE43 to S. meliloti strain USDA 1936. Several standard analytical tests and plant growth chamber studies were conducted to test the ability of S. meliloti to degrade 2′,3,4-PCB congener. Alfalfa plant alone was able to degrade 30% of PCBs compared with control. No enhanced dechlorination was noted when alfalfa plant was grown with wild-type S. meliloti, and when alfalfa plant was grown with the S. meliloti electrotransformants (genetically modified) dechlorination of PCBs was more than twice that when alfalfa plant was grown with wild-type S. meliloti. When alfalfa plant was grown with uncharacterized mixed culture (containing nodule formers), almost equally significant PCB degradation was observed. The significance of this work is that the naturally occurring nitrogen-fixing soil bacterium S. meliloti (genetically modified) has the ability to enhance fertility of soil in association with the leguminous alfalfa plant while simultaneously enhancing bioremediation of PCB-contaminated soils. Enhanced bioremediation of PCB and robust alfalfa plant growth was also noted when uncharacterized mixed cultures containing alfalfa plant nodule formers were used. 相似文献
10.
The efficiency of two Rhizobium meliloti mutants for nodulation and nitrogen fixation (acetylene reduction) under three concentrations of p-coumaric and ferulic acids, was evaluated using a sand-culture medium. The effect of the test concentrations of both acids
on the growth of alfalfa was also determined. The results revealed that the test mutants showed considerable resistance to
the higher concentration of the test phytotoxins in terms of nodulation and nitrogen fixation, whereas seedling growth was
inhibited by increased phytotoxin concentrations.
The possible advantages of mutants resistance to the phytotoxins under field conditions are briefly discussed. 相似文献
11.
Alfalfa ( Medicago sativa L.) growth and nodulation in acid soil is reduced because the plant and its bacterial symbiont Rhizobium meliloti cannot tolerate acid, aluminum-rich soil. A study was conducted to determine if a relatively acid-tolerant alfalfa germplasm combined with a relatively acid-tolerant R. meliloti strain could overcome these limitations. In a light room study, an acid-tolerant alfalfa germplasm inoculated with a more acid-tolerant R. meliloti strain produced greater top growth, nodule number and weight, and acetylene reduction values in an unlimed soil (pH 4.6) than the same germplasm inoculated with a relatively acid-sensitive R. meliloti strain or an acid-sensitive germplasm inoculated with either a relatively acid-tolerant or acid-sensitive R. meliloti strain. 相似文献
13.
Summary Different nodulation capacities were found among nine different varieties of alfalfa, cultivated in the Central region of Mexico, by Rhizobium meliloti 2011. A correlation between nodulation capacity and foliar dry weight was observed, which points to a genotype dependance on these parameters. A correlation between the nodulation capacity and the R. meliloti nod-gene inducing activity of the root exudates from the different varieties, as measured by -galactosidase induction in a test system consisting of a R. meliloti nodC-lacZ strain incubated with each root exudate, was established. When the root exudate from the best nodulating variety was added to the four poorest nodulating varieties, an increase in nodule formation was observed. We conclude that root exuded nod-gene inducing signals are a symbiotically-limiting component in natural populations of the poorest nodulating varieties of alfalfa. 相似文献
14.
Using a plate induction assay, we demonstrate that alfalfa exudes inducer of Rhizobium meliloti nodulation genes. The inducer is exuded from the infectible zone of the root, accumulates to at least 1 micromolar, and is not affected by 10 millimolar nitrate. No zones of inhibition are observed. A nodulation minus mutant line of alfalfa, MN-1008, exudes normal levels of inducer. R. meliloti grown in rich medium requires ten-fold higher concentrations of luteolin to achieve half-maximal induction as compared to cells grown in a minimal medium. Flavonoids other than luteolin are found to have activity in R. meliloti nodulation gene induction assays. The compounds apigenin and eriodictyol have activities two-fifths and one-seventh that of luteolin, respectively. Several of the flavonoids tested (morin = naringenin > kaempferol = chrysin > quercetin = fisetin = hesperitin) demonstrate antagonistic activity toward induction by luteolin. The most effective antagonist is the coumarin, umbelliferone. 相似文献
15.
A strain of Rhizobium meliloti has been shown to be capable of growth in the presence of methionine sulphoximine concentrations at least two orders of magnitude
higher than that required for the complete inhibition of glutamine synthetase activity. Neither the specific growth rate,
nor the nutritional requirements of the organism were affected by methionine sulphoximine in the medium. Rhizobium meliloti appeared to assimilate ammonia via the glutamate dehydrogenase pathway during growth in the presence of methionine sulphoximine. This suggests that Rhizobium meliloti may have some regulatory mechanism controlling ammonia assimilation that is not present in other enterobacteria possessing
similar enzymatic machinery 相似文献
18.
Isoflavonoid (+)-pisatin, the main phytoalexin of pea ( Pisum sativum), was tested for its inducer and suppressor activity in respect of the nodABCIJ operon of Rhizobium leguminosarum bv. viciœ, a pea symbiont, in the presence of a flavonoid receptor-coding gene nodD of this biovar. No nod gene-inducing activity of pisatin could be detected up to 100 μmol/L concentration. The suppressor activity as determined
against 0.1 μmol/L naringenin was expressed only above 10 μmol/L pisatin, i.e. at a concentration higher by a one order of magnitude, than with the potent flavonoid suppressor rhamnetin and by two orders
above the isoflavonoid, suppressor daidzein. Analogously, only a weak suppression was observed with NodD1 of R. meliloti, the alfalfa symbiont. The results do not support the notion about the role of plant defence substances in the control of
rhizobial symbiosis. 相似文献
20.
Co-inoculation with antibiotic-producing bacteria and rhizobia resistant to those antibiotics has been proposed as a means of promoting colonization and nodulation of legumes by root-nodule bacteria. A study was conducted to establish some of the factors affecting co-inoculation with antibiotic-producing strains of Bacillus and Streptomyces griseus. The stimulation of Rhizobium meliloti and yield and N uptake by alfalfa was enhanced with increasing inoculum size of Bacillus sp. S. griseus and chitin added to soil increased nodulation of soybeans by Bradyrhizobium japonicum and increased nodulation, yield, and number of pods on a second crop grown in the same soil. Bacillus sp. persisted in soil in sufficient numbers for at least 51 days to increase colonization of soybean roots by B. japonicum. The populations of S. griseus, Bacillus sp., and antibiotic-resistant isolates of R. meliloti and B. japonicum fell after their addition to seeds. Nevertheless, a benefical effect by the antibiotic-producing bacteria was evident on R. meliloti colonization of the rhizosphere, nodulation, and yield of alfalfa grown from seeds stored 94 days and on B. japonicum colonization, nodule number, yield, and seed weight of soybeans grown from seeds stored 90 days. Because non-antibiotic-producing derivatives of Bacillus sp. and S. griseus did not promote colonization or nodulation of alfalfa roots by R. meliloti, the benefit of this co-inoculation is a result of antibiotic formation. 相似文献
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