Ultrastructure of root nodules formed by ineffective strains of Rhizobium meliloti

1974 ◽  
Vol 20 (5) ◽  
pp. 755-758 ◽  
Author(s):  
C. R. MacKenzie ◽  
D. C. Jordan
Keyword(s):  
Rhizobium Meliloti ◽  
Root Nodules ◽  
Plant Cells ◽  
Host Cells ◽  
Nodule Development ◽  
Nodule Formation ◽  
Starch Granules ◽  
Naturally Occurring ◽  
Intimate Association ◽  
Rough Er

In three ineffective associations between Medicago sativa (alfalfa) and Rhizobium meliloti the initial stages of nodule formation, resulting in the release of the bacteria into the host cells, were found to follow the normal pattern of nodule development. In nodule tissue formed by two laboratory-produced ineffective mutants, a rapid disintegration of the invading bacteria was observed to occur shortly after the release of the bacteria into the plant cells. The disintegrating bacteria were in intimate association with large amounts of rough endoplasmic reticulum (ER). An increase in the number of mitochondria occurred at this stage as well and the peripheries of the plant cells were often lined with starch granules. Only occasionally was the stage of enclosing-membrane formation reached. In the third ineffective association, a naturally occurring one, the bacteria were transformed into the nitrogen-fixing or bacteroidal forms and were surrounded by enclosing membranes. Dissolution of the bacteria occurred at a slightly later stage in this association and was again accompanied by a buildup of rough ER. Evidence is presented to suggest that the plant response, as characterized by this ER buildup in these ineffective associations, was a manifestation of nitrogen starvation.

Effects of a Nod-factor-overproducing strain of Sinorhizobium meliloti on the expression of the ENOD40 gene in Melilotus alba

2002 ◽  
Vol 80 (9) ◽  
pp. 907-915 ◽  
Author(s):  
Walter F Giordano ◽  
Michelle R Lum ◽  
Ann M Hirsch
Keyword(s):  
Lateral Root ◽  
Sinorhizobium Meliloti ◽  
Cortical Cell ◽  
Host Cells ◽  
Nodule Development ◽  
Nodule Formation ◽  
Additional Increase ◽  
Nod Factor ◽  
Melilotus Alba ◽  
Different Strains

We have initiated studies on the molecular biology and genetics of white sweetclover (Melilotus alba Desr.) and its responses to inoculation with the nitrogen-fixing symbiont Sinorhizobium meliloti. Early nodulin genes such as ENOD40 serve as markers for the transition from root to nodule development even before visible stages of nodule formation are evident. Using Northern blot analysis, we found that the ENOD40 gene was expressed within 6 h after inoculation with two different strains of S. meliloti, one of which overproduces symbiotic Nod factors. Inoculation with this strain resulted in an additional increase in ENOD40 gene expression over a typical wild-type S. meliloti strain. Moreover, the increase in mRNA brought about by the Nod-factor-overproducing strain 24 h after inoculation was correlated with lateral root formation by using whole-mount in situ hybridization to localize ENOD40 transcripts in lateral root meristems and by counting lateral root initiation sites. Cortical cell divisions were not detected. We also found that nodulation occurred more rapidly on white sweetclover in response to the Nod-factor-overproducing strain, but ultimately there was no difference in nodulation efficiency in terms of nodule number or the number of roots nodulated by the two strains. Also, the two strains could effectively co-colonize the host when inoculated together, although a few host cells were occupied by both strains.Key words: ENOD40, Nod factor, Melilotus, Sinorhizobium, symbiosis.

Factors involved in the amelioration of retarded symbiosis in Tinaroo glycine

1974 ◽  
Vol 25 (4) ◽  
pp. 577 ◽  
Author(s):  
A Diatloff
Keyword(s):  
Nitrogen Fixation ◽  
Ammonium Nitrate ◽  
Root Nodules ◽  
Host Cells ◽  
Starch Accumulation ◽  
Nodule Formation ◽  
Carbon And Nitrogen ◽  
Slow Development ◽  
Structural Differences ◽  
Envelope Membranes

Root nodules formed on Tinaroo glycine (Glycine wightii) were slow to pigment and begin fixing nitrogen. Various carbon and nitrogen compounds enhanced nodule pigmentation, the greening of the plants, and the rate of nitrogen fixation at 42 days. Of these inositol, glucose, ammonium nitrate (as both foliar and root applications) and coconut milk were most effective. Riboflavin, sodium glutamate and nodule infusion had little effect. There were no structural differences between nodules enhanced respectively by glucose and ammonium nitrate. Nodules on control plants showed slow development of the bacteroids and envelope membranes, with copious starch accumulation in uninvaded host cells. It was concluded that the retarded symbiosis in formed nodules was due initially to tardy nodule formation depleting the nitrogen reserves in the seeds before nitrogen fixation began. Because of the interaction of photosynthesis and nitrogen fixation, self-regeneration of nitrogen fixation in chlorotic plants was slow without an external stimulus. It is suggested that by selecting lines of the legume with larger seeds or by incorporating nitrogen in seed pellets the problem might be overcome.

Effect of rhizobia and soil nitrate on the establishment and functioning of the soybean symbiosis in the field

1984 ◽  
Vol 35 (2) ◽  
pp. 149 ◽  
Author(s):  
DF Herridge ◽  
RJ Roughley ◽  
J Brockwell
Keyword(s):  
Soil Depth ◽  
Root Nodules ◽  
Xylem Sap ◽  
Progressive Increase ◽  
Rhizobium Japonicum ◽  
Nodule Development ◽  
Initial Increase ◽  
Nodule Formation ◽  
Mineral N ◽  
Nodule Initiation

The symbiosis of the root-nodules of Bragg soybean [Glycine max (L.) Merrill] and the relative dependence of the plants on symbiotic and soil sources of N were evaluated in an experiment conducted on a vertisol which was high in organic- and mineral-N, free of Rhizobium japonicum, and where poor nodulation was characteristic of inoculated, new sowings. Effective inoculant containing R. japonicum strain CB 1809 was sprayed into the seed bed at three rates of application (10-fold intervals). Increasing rates of inoculant led to greater numbers of rhizobia in the rhizosphere and in the soil, and to improved nodulation. Uninoculated plants did not nodulate. High soil NO-3 (30 �g N/g, top 30 cm) did not prevent prompt, abundant colonization of rhizospheres by the bacteria from the inoculant, but nodule initiation was delayed and nodule development was retarded until 42 days after sowing. There was an acceleration in nodule formation and development between 42 and 62 days which coincided with a depletion of NO-3 from the top 60 cm of the soil profile. Nodulated and unnodulated soybeans took up NO-3 at similar times and rates to a soil depth of 90 cm; only unnodulated plants utilized soil NO-3 below 90 cm. Vacuum-extracted stem (xylem) exudate was sampled from plants throughout growth and analysed for nitrogenous solutes. The proportion of ureide-N relative to total-solutes-N in xylem sap was used as an index of symbiotic N2-fixation. The initial increase in concentrations of ureides coincided with the period of accelerated nodule formation and development between 42 and 62 days. Thereafter, there was a progressive increase in ureide concentrations in nodulated plants, and the levels were related to rate of inoculation, extent of nodulation, and to the decline in concentrations of soil NO-3. Ureide concentrations in unnodulated plants remained low throughout. The quantities of NO-3-N and �-NH2- N in xylem sap were not related to nodulation. The differences between treatments in terms of whole-plant N and grain N were less than predicted from the symbiotic parameters. This indicated that soybeans compensated for symbiotic deficiencies by more efficient exploitation of soil N and/or by more efficient redistribution of vegetative N into grain N, and that nodulation and soil NO-3 were interactive and complementary in meeting the N requirements of the crop.

scholarly journals Rhizobial peptidase HrrP cleaves host-encoded signaling peptides and mediates symbiotic compatibility

2015 ◽  
Vol 112 (49) ◽  
pp. 15244-15249 ◽  
Author(s):  
Paul A. Price ◽  
Houston R. Tanner ◽  
Brett A. Dillon ◽  
Mohammed Shabab ◽  
Graham C. Walker ◽  
...  
Keyword(s):  
Sinorhizobium Meliloti ◽  
Root Nodules ◽  
Nodule Development ◽  
Range Restriction ◽  
Peptide Cleavage ◽  
Bacterial Proliferation ◽  
Naturally Occurring ◽  
Signaling Peptides ◽  
Late Stages ◽  
Host Range Restriction

Legume–rhizobium pairs are often observed that produce symbiotic root nodules but fail to fix nitrogen. Using the Sinorhizobium meliloti and Medicago truncatula symbiotic system, we previously described several naturally occurring accessory plasmids capable of disrupting the late stages of nodule development while enhancing bacterial proliferation within the nodule. We report here that host range restriction peptidase (hrrP), a gene found on one of these plasmids, is capable of conferring both these properties. hrrP encodes an M16A family metallopeptidase whose catalytic activity is required for these symbiotic effects. The ability of hrrP to suppress nitrogen fixation is conditioned upon the genotypes of both the host plant and the hrrP-expressing rhizobial strain, suggesting its involvement in symbiotic communication. Purified HrrP protein is capable of degrading a range of nodule-specific cysteine-rich (NCR) peptides encoded by M. truncatula. NCR peptides are crucial signals used by M. truncatula for inducing and maintaining rhizobial differentiation within nodules, as demonstrated in the accompanying article [Horváth B, et al. (2015) Proc Natl Acad Sci USA, 10.1073/pnas.1500777112]. The expression pattern of hrrP and its effects on rhizobial morphology are consistent with the NCR peptide cleavage model. This work points to a symbiotic dialogue involving a complex ensemble of host-derived signaling peptides and bacterial modifier enzymes capable of adjusting signal strength, sometimes with exploitative outcomes.

XV.—The Effect of Certain Factors on the Formation of Root Nodules on Pea Plants in Aseptic Culture

1949 ◽  
Vol 63 (3) ◽  
pp. 219-229 ◽  
Author(s):  
Moira P. McGonagle
Keyword(s):  
Nicotinic Acid ◽  
Root Nodules ◽  
Nodule Development ◽  
Nodule Formation ◽  
Root Cultures ◽  
Growth Substances ◽  
Aseptic Culture ◽  
Whole Plant ◽  
Rooting Medium ◽  
Whole Plants

The experiments described in the present paper were undertaken as the outcome of an investigation into the possibility of securing nodule formation on leguminous roots cultured separately from the shoots. During that investigation it soon became clear that experiments on whole plants were necessary, in order to test the effect, on the nodulation of the normal whole plant, of certain conditions under which nodulation of root cultures was being attempted. It is thought that these observations on whole plants, though ancillary to the main investigation (which is still in progress), are of sufficient interest to be published separately. The observations are concerned with the effect of the following conditions or treatments on nodule development in a particular variety of pea:—(a) Depriving the plant of light;(b) the presence of sucrose in the rooting medium;(c) the presence of nitrate in the rooting medium; and(d) the presence of certain accessory growth substances, viz. aneurin and nicotinic acid, in the rooting medium.

scholarly journals Rhizobial Synthesized Cytokinins Contribute to But Are Not Essential for the Symbiotic Interaction Between Photosynthetic Bradyrhizobia and Aeschynomene Legumes

2013 ◽  
Vol 26 (10) ◽  
pp. 1232-1238 ◽  
Author(s):  
Kateřina Podlešáková ◽  
Joel Fardoux ◽  
Delphine Patrel ◽  
Katia Bonaldi ◽  
Ondřej Novák ◽  
...  
Keyword(s):  
Root Nodules ◽  
Rna Degradation ◽  
Nodule Development ◽  
Nodule Formation ◽  
Symbiotic Interaction ◽  
Extracellular Medium ◽  
Exogenous Addition ◽  
Bradyrhizobium Sp ◽  
Derivatives Of

Cytokinins (CK) play an important role in the formation of nitrogen-fixing root nodules. It has been known for years that rhizobia secrete CK in the extracellular medium but whether they play a role in nodule formation is not known. We have examined this question using the photosynthetic Bradyrhizobium sp. strain ORS285 which is able to nodulate Aeschynomene afraspera and A. indica using a Nod-dependent or Nod-independent symbiotic process, respectively. CK profiling showed that the most abundant CK secreted by Bradyrhizobium sp. strain ORS285 are the 2MeS (2-methylthiol) derivatives of trans-zeatin and isopentenyladenine. In their pure form, these CK can activate legume CK receptors in vitro, and their exogenous addition induced nodule-like structures on host plants. Deletion of the miaA gene showed that transfer RNA degradation is the source of CK production in Bradyrhizobium sp. strain ORS285. In nodulation studies performed with A. indica and A. afraspera, the miaA mutant had a 1-day delay in nodulation and nitrogen fixation. Moreover, A. indica plants formed considerably smaller but more abundant nodules when inoculated with the miaA mutant. These data show that CK produced by Bradyrhizobium sp. strain ORS285 are not the key signal triggering nodule formation during the Nod-independent symbiosis but they contribute positively to nodule development in Aeschynomene plants.

scholarly journals Minimal gene set from Sinorhizobium (Ensifer) meliloti pSymA required for efficient symbiosis with Medicago

2020 ◽  
Vol 118 (2) ◽  
pp. e2018015118
Author(s):  
Barney A. Geddes ◽  
Jason V. S. Kearsley ◽  
Jiarui Huang ◽  
Maryam Zamani ◽  
Zahed Muhammed ◽  
...  
Keyword(s):  
Root Nodules ◽  
Nodule Development ◽  
Nodule Formation ◽  
Protein Coding ◽  
Bacterial Gene ◽  
Gene Set ◽  
Background Strain ◽  
Genetic Components ◽  
Sustainable Agricultural Systems ◽  
Bacterial Genes

Reduction of N2 gas to ammonia in legume root nodules is a key component of sustainable agricultural systems. Root nodules are the result of a symbiosis between leguminous plants and bacteria called rhizobia. Both symbiotic partners play active roles in establishing successful symbiosis and nitrogen fixation: while root nodule development is mostly controlled by the plant, the rhizobia induce nodule formation, invade, and perform N2 fixation once inside the plant cells. Many bacterial genes involved in the rhizobia–legume symbiosis are known, and there is much interest in engineering the symbiosis to include major nonlegume crops such as corn, wheat, and rice. We sought to identify and combine a minimal bacterial gene complement necessary and sufficient for symbiosis. We analyzed a model rhizobium, Sinorhizobium (Ensifer) meliloti, using a background strain in which the 1.35-Mb symbiotic megaplasmid pSymA was removed. Three regions representing 162 kb of pSymA were sufficient to recover a complete N2-fixing symbiosis with alfalfa, and a targeted assembly of this gene complement achieved high levels of symbiotic N2 fixation. The resulting gene set contained just 58 of 1,290 pSymA protein-coding genes. To generate a platform for future synthetic manipulation, the minimal symbiotic genes were reorganized into three discrete nod, nif, and fix modules. These constructs will facilitate directed studies toward expanding the symbiosis to other plant partners. They also enable forward-type approaches to identifying genetic components that may not be essential for symbiosis, but which modulate the rhizobium’s competitiveness for nodulation and the effectiveness of particular rhizobia–plant symbioses.

scholarly journals A Convenient, Soil-Free Method for the Production of Root Nodules in Soybean to Study the Effects of Exogenous Additives

2018 ◽  
Author(s):  
Swarup Roy Choudhury ◽  
Sarah M. Johns ◽  
Sona Pandey
Keyword(s):  
Nitrogen Fixation ◽  
Biological Nitrogen Fixation ◽  
Root Nodules ◽  
Growth Conditions ◽  
Nodule Development ◽  
Nodule Formation ◽  
Legume Crop ◽  
Simple Protocol ◽  
Biological Nitrogen

Legumes develop root nodules that harbour endosymbiotic bacteria, rhizobia. These rhizobia convert nitrogen to ammonia by biological nitrogen fixation. A thorough understanding of the biological nitrogen fixation in legumes and its regulation is key to develop sustainable agriculture. It is well known that plant hormones affect nodule formation; however, most studies are limited to model legumes due to their suitability for in vitro, plate-based assays. Specifically, it is almost impossible to measure the effects of exogenous hormones or other additives during nodule development in crop legumes such as soybean as they have huge root system in soil. To circumvent this issue, the present research develops suitable media and growth conditions for efficient nodule development under in vitro, soil free conditions in an important legume crop, soybean. Moreover, we also evaluate the effects of all major phytohormones during soybean nodulation under identical conditions. This versatile, inexpensive, scalable and simple protocol provides several advantages over previously established methods. It is extremely time-and resource-efficient, does not require special training or equipment, and produces highly reproducible results. The approach is expandable to other large legumes as well as for other exogenous additives.

scholarly journals Rhizobium fix genes mediate at least two communication steps in symbiotic nodule development.

1988 ◽  
Vol 106 (3) ◽  
pp. 597-607 ◽  
Author(s):  
P Putnoky ◽  
E Grosskopf ◽  
D T Ha ◽  
G B Kiss ◽  
A Kondorosi
Keyword(s):  
Rhizobium Meliloti ◽  
Host Cells ◽  
Nodule Development ◽  
Peribacteroid Membrane ◽  
Symbiotic Gene ◽  
Morphological Studies ◽  
Group I ◽  
Infection Threads ◽  
Symbiotic Nodule ◽  
Bacterial Genes

To identify bacterial genes involved in symbiotic nodule development, ineffective nodules of alfalfa (Medicago sativa) induced by 64 different Fix-mutants of Rhizobium meliloti were characterized by assaying for symbiotic gene expression and by morphological studies. The expression of leghemoglobin and nodulin-25 genes from alfalfa and of the nifHD genes from R. meliloti were monitored by hybridizing the appropriate DNA probes to RNA samples prepared from nodules. The mutants were accordingly divided into three groups. In group I none of the genes were expressed, in group II only the plant genes were expressed and in group III all three genes were transcribed. Light and electron microscopical analysis of nodules revealed that nodule development was halted at different stages in nodules induced by different group I mutants. In most cases nodules were empty lacking infection threads and bacteroids or nodules contained infection threads and a few released bacteroids. In nodules induced by a third mutant class bacteria were released into the host cells, however the formation of the peribacteroid membrane was not normal. On this basis we suggest that peribacteroid membrane formation precedes leghemoglobin and nodulin-25 induction, moreover, after induction of nodulation by the nod genes at least two communication steps between the bacteria and the host plants are necessary for the development of the mature nodule. By complementing each mutant of group I with a genomic R. meliloti library made in pLAFRl, four new fix loci were identified, indicating that several bacterial genes are involved in late nodule development.

Determinate development of nodule roots in actinomycete-induced root nodules of Myrica gale

1978 ◽  
Vol 56 (11) ◽  
pp. 1357-1364 ◽  
Author(s):  
John G. Torrey ◽  
Dale Callaham
Keyword(s):  
Root Development ◽  
Root Nodules ◽  
Cortical Cell ◽  
Gas Diffusion ◽  
Nodule Development ◽  
Nodule Formation ◽  
Low Oxygen ◽  
Cortical Cells ◽  
Continuous Growth ◽  
Myrica Gale

Young seedlings of Myrica gale L. grown in water culture were inoculated with a nodule suspension containing the effective actinomycete which induced root nodule formation. Nodule development was followed from initiation to nodule lobe formation and nodule root development using living materials and fixed nodules sectioned for light microscopy. After root hair infection and prenodule formation, three stages were observed: nodule lobe formation, a transition or arrested state, and nodule root development. The primary nodule lobe meristem originates endogenously and its formation involves pericycle, endodermis, and cortical cell derivatives. The lobe develops slowly to about 2 mm in length while the cortical cells are invaded by the actinomycete endophyte. After a period of arrest of variable duration, from a few days to several weeks, the nodule lobe meristem begins altered development, forming the elongate nodule root which undergoes slow but continuous growth to about 3- to 4-cm final length. New nodule lobe primordia are initiated endogenously at the base of existing nodules lobes, ultimately forming a cluster of nodule roots. Each nodule root, which elongates at about 0.1–1.0 mm per day, has a terminal apical meristem with reduced root cap formation and produces a modified root structure possessing an elaborate cortical intercellular space system and a reduced central cylinder. Nodule root growth is distinctive in that it shows strong negative geotropism. The endophyte is restricted to cortical cells of the nodule lobe and is totally absent from tissues of the nodule root. A probable role for nodule roots is to facilitate gas diffusion to the nitrogen-fixing endophyte site in the nodule lobe when nodules occur under conditions of low oxygen tension.

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